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doi: 10.12170/20210803001
Abstract:
With the construction of a number of high head, high flow high arch dams, the reasonable design of plunge pools has become a major technical problem in engineering design, and the dynamic water impact pressure is an important indicator of the design of high dam cushion pools, the piezometer method is a more economical method commonly used in the current hydraulic model test. In order to evaluate the sensitivity of the piezometer to measure the dynamic water impact pressure, this paper used a three-dimensional turbulent flow numerical simulation method to analyze the effect of dynamic water impact pressure measurement in a cushion pool under different ratios of the inner diameter of the pressure tap and the inner diameter of the piezometer. The results showed that the ratio of the inner diameter of the pressure tap and the inner diameter of the piezometer has a greater impact on the measurement of the dynamic water impact pressure, different from the conventional hydraulic model test requirements (the inner diameter of the pressure tap should be less than 2 mm, the inner diameter of the piezometer should be greater than 6 mm). This paper recommended that the ratio of the inner diameter of the pressure tap and the inner diameter of the piezometer should be greater than 0.7 and the inner diameter of the piezometer should be greater than 6 mm, and the core area of the impact, combined with the pulsation pressure sensor method to measure.
doi: 10.12170/20210223001
Abstract:
The flow and sediment of inland waterways are generally characterized as strong time-varying, nonlinear and randomness. The rapid and efficient measurement of the spatio-temporal data in a large range is noted as a challenging task. With the development of shipborne sensors, Internet of Things, mobile computing and other technologies, the hydrology observations based on shipborne sensors have drawn more attentions in the past several years. The research progress of shipborne integrated underwater and aquatic measurement system is introduced. The technical requirements of a shipborne observation system of waterway hydrology are thus demonstrated in details. The basic principles and characteristics of the information processing technology of flow and sediment particles are further analyzed. Literature review of intelligent multi-source image processing methods for waterway engineering is provided. Prospects of the core sensors, intelligent algorithms, real-time computing models and other key technologies are summarized. The technical analysis shows that it is generally feasible to develop an integrated mobile measurement system of hydrological elements of inland waterways based on the new generation of artificial intelligence technology and the high resolution shipborne sensors.
doi: 10.12170/20210626001
[Abstract](5) [FullText HTML](3) [PDF 964KB](0)
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Graph and complex network theory were used to construct the network topology of long-distance water delivery system. Node attack was selected since its higher destruction efficiency. Under the condition of unknown, partially known and fully known about the network topology, the attack strategies of random attack, conditional attack and deliberate attack were implemented respectively, then the invulnerability of the water delivery system under different attack strategies was evaluated. The degree, betweenness and closeness centrality were furtherly used to quantify the node importance under the condition of fully known about network topology, then the response of water delivery system invulnerability to different node importance indexes was analyzed. The results showed that deliberate attacked most efficiently while the random attack had the lowest efficiency, as information acquisition increased, the attack efficiency increased correspondingly. Node betweenness had the greatest impact on water delivery system invulnerability while node degree had the least impact. This study can provide theoretical support for the identification and protection of important facilities in long-distance water delivery system.
doi: 10.12170/20210105008
[Abstract](5) [FullText HTML](3) [PDF 802KB](1)
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Processes of hydrological cycle and distribution of water resources have being changed significantly under the driving of climate changes. To fully understand runoff evolution mechanism under changing environment has become one of the hot and difficult issues in the field of hydrological research. In this study, state-of-the-art on related studies during the past decades has been reviewed and summarized, which includes major methodologies and progresses on the mechanism of runoff evolution, i.e., identification of runoff variation characteristics, attribution analysis of runoff changes, simulation of runoff under changing environment, and response of runoff to future climate change. Further studies are then emphasized considering those issues related to runoff evolution and its driving factors, identification of impact factors on runoff changes, as well as runoff simulation and uncertainty analysis ,etc.
doi: 10.12170/20210428002
Abstract:
Climate warming, population growth and excessive economic development have exacerbated water scarcity in China. The spatio-temporal evolution of China’s human water use (341 prefectures) is explored, based on the methods of Breaks for Additive Seasonal and Trend and Spatial Autocorrelation Analysis. Results show that China’s human water usage is continuously increasing from 1965 to 2013, although a breakpoint is detected mainly after 1990. Increasing and decreasing of water use coexist after the breakpoint year, thus resulting in a deceleration of China’s human water use. The distribution of human water use has spatial agglomeration characteristics, and the agglomeration of water use is high in the east and low in the west (except Xinjiang) basically in line with Hu Huanyong boundary. The agglomeration regions of human water use and irrigation water use are relatively consistent before 1985, and regions with high water use concentrations are in Xinjiang and Yangtze River Delta. But the agglomeration regions of human water use are more similar to the agglomeration regions of industrial water use after 1995. Regions with high concentrations of industrial and urban and rural water uses are distributed in Northeastern, Northern China and Southern China, and regions with low concentrations are in Western China (largest agglomeration effect exists in rural water use). Exploring the spatio-temporal characteristics of water use in China could provide scientific basis for water resources management and the improvement of water use efficiency.
doi: 10.12170/20201209001
Abstract:
Intense rainfall always results in the air in soil slopes being closed, and it will decrease the slope stability therefore. Present researches mainly focused on the effect of closed air pressure on infiltration and on the stability safety factor of an infinite soil slope when the slope slides along a plane which locates at wetting front surface. Firstly, in this paper, based on the theory of closed air pressure and Green-Ampt model, a slope infiltration model which considers the effect both of air pressure and slope angleon infiltration was presented. Then, combining the Mohr-Coulomb failure criterion and the limit-equilibrium method, a model was established to calculate the stability safety factor (Fsa) of a infinite soil slope and the presented model is suitable for evaluating the Fsa when the slope slides along the plane located under phreatic surface since this model can consider the decreasing effect of closed air pressure on the effective stress of soil under phreatic surface. Finally, the influences of air pressure on infinite soil slope, as well as the variation of Fsa when the slope slides along different planes, were researched. The results indicate that air pressure significantly reduces the slope stability, and the smaller the c' is, the larger the ϕ' is, the smaller the slope angle is, and the shallower the sliding surface is, the more the air pressure affects Fsa. It also shows that the critical sliding surface may locate under the phreatic surface.
doi: 10.12170/20210202003
[Abstract](13) [FullText HTML](8) [PDF 1075KB](2)
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Dam body leakage of concrete dam affects the safety and durability of dam. Based on the dam body leakage remediation of Longjiang hydropower station in Yunnan Province, remediation of the dam is introduced in detail, and the remediation result is discussed. In order to find the possible leakage entrance, temperature tracing is applied for finding the range of leakage entrance, and then the specific leakage point is indicated by subaqueous extended check. Through subaqueous check, defects in concrete dam body between the layers are detected. The main entrance points of leakage passage are located at elevation 832.00 m and 816.00 m in dam block 9#, and 830.00 m and 808.00 m in dam block 10#. Therefore, subaqueous remediation is adopted for dam body, and leakage entrance is blocked from source. After remediation of dam body, leakage decreases from maximum 74.85 L/s in recent years to 6.04 L/s under normal water level. From subaqueous check of dam body before remediation, seam between layers is identified as the main way of leakage in concrete dam. The seams between layers are produced during the whole construction process. Hence, it is necessary to enhance the quality control during construction process to ensure the bond of each layer in concrete. Above all, partial leakage defect could be solved by the leakage subaqueous remediation method provided here, and the practice could be used for similar projects..
doi: 10.12170/20210628002
Abstract:
Driven by global changes and human activities, the sediment source/transport, and riverbed erosion and deposition pattern of the Yangtze River Basin are undergoing continuous adjustments, which influence both magnitude and property of fluvial sediment to the estuary. In order to explore sediment transport and correlated topographic changes of the Yangtze River Estuary within 40 years in response to variations of fluvial sediment discharge from the upstream basin, this study uses sediment grain size trend models and multi-year zonal analysis methods to predict temporal and spatial variations of morphological changes within the Yangtze Estuary, based on grain size data and topographic data from 1980 to 2020. The results show that sediments converge toward the center of the channel within the northern branch, and a deposition center forms close to the south and north channel diversion area within the southern branch, consistent with the morphological changes between 2012 to 2020 calculated from sea maps, validating the effectiveness of the grain size trend model in predicting morphological changes within the Yangtze River Estuary. The results of the multi-year zonal analysis show that: 1980—2003 was characterized by a high volume of fluvial sediment discharge, and the entire estuary area was dominated by deposition with slightly finer sediment. Fluvial sediment discharge experienced a rapid decrease from 2003 to 2012, while the estuary area was still dominated by deposition before 2009 with similar grain size. 2009—2012, however, was a transitional period when erosion and sediment coarsening started to appear out of the estuary, although limited to small areas. From 2012 to 2020, large-scale erosion and grain size coarsening occurred widely in the estuary, and a significant correlation was found between the particle size and the magnitude of erosion. Our study shows that high-resolution zonal analysis can effectively catch the local morphological change signals in the Yangtze River Estuary. In the past 40 years, the Yangtze River Estuary has changed from deposition-dominant mode to partially erosion mode, and it may face continuous coastal erosion in the future.
doi: 10.12170/20210116001
[Abstract](37) [FullText HTML](6) [PDF 1357KB](5)
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In order to explore the influence of the severe weather in the seasonal freezing area on the expansion and contraction deformation and physical and mechanical properties of the canal base expansive soil with different water contents, the expansive soil in the Altay area of northern Xinjiang was taken as the research object, and the freeze-thaw cycle test of the actual climatic conditions in northern Xinjiang was performed in the laboratory. Based on this, the volumetric deformation test, unconfined compressive strength test and scanning electron microscope (SEM) test of the expansive soil with moisture contents of 12%, 16%, and 20% were carried out, and the influence of freeze-thaw cycles on the volume deformation and mechanical properties of expansive soil was analyzed emphatically. The results show that during the freeze-thaw cycle, with the increase of water content, the volume deformation of the sample changes from "freeze shrinkage and thaw expansion" to "freeze heave and thaw shrinkage". The characteristics of the stress-strain curve are closely related to the number of freeze-thaw cycles and the moisture content. The unconfined compressive strength of the sample decreases with the increase of the moisture content and the number of freeze-thaw cycles. Among them, the first freeze-thaw cycle is the most obvious, and it stabilizes after three times. The function fitting shows that the unconfined compressive strength of the sample has an obvious natural exponential relationship with the number of freeze-thaw cycles. The greater the water content, the greater the influence of freeze-thaw cycles on the microstructure of the soil; the porosity of the soil gradually increases with the increase in the number of freeze-thaw cycles. The first freeze-thaw cycle has obvious effect, which is manifested macroscopically as the effect of freeze-thaw cycles on the degradation of soil mechnical properties.
doi: 10.12170/20200828001
[Abstract](21) [FullText HTML](57) [PDF 1216KB](6)
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Deformation is a key indicator for analyzing the characteristics and evaluating the safety of embankment. In this research, the installation method of sensing fiber equipped with an auxiliary structure was designed for the distributed monitoring of embankment’s internal two-dimensional deformation. A distributed monitoring test was conducted on a prototype embankment and the test result of its internal deformation validated the measurement accuracy and feasibility of the distributed monitoring technology as the maximum absolute error between the test result and the actual measured result of the embankment’s two-dimensional deformation was 4.3 mm; and mm-level measurement accuracy was realized not only for the internal two-dimensional deformation at certain points, but also for the whole section of the embankment, which proves the applicability and advancement of the fibre-optical distributed monitoring technology of the two-dimensional deformation inside the embankment.
doi: 10.12170/20200710001
[Abstract](29) [FullText HTML](13) [PDF 1454KB](4)
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As a new type of foundation, the suction bucket foundation has good technical and economic performances compared with traditional foundations. The key construction parameter, soil plug, and construction efficiency are analyzed through model tests of a suction bucket foundation in silty clay with different suction pressures applied. Measured suction pressure in tests with different suction pressure applying patterns are between the required value and the critical value calculated by the DNV standard. The suction pressure in suction releasing pattern is larger than that in suction maintaining pattern for suction bucket to reach the same depth. In addition, the least soil plug degree is obtained in the suction releasing pattern with a large suction pressure increment, provided penetration efficiency is assured. Theoretical analysis shows that the inside friction resistance increases with the gradient of inside pressure along depth and large friction resistance restricts the formation of soil plug. The mechanism of reduced soil plug in suction releasing pattern is explained by the excess pore water pressure results. The earth pressure results show that the normal effective stress mobilized on the bucket wall in the suction releasing pattern is larger than that in the suction maintaining pattern. Accordingly, the side friction mobilized of the former is also larger.
doi: 10.12170/20210416001
[Abstract](11) [FullText HTML](6) [PDF 1921KB](1)
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Large-scale hydraulic model tests can obtain similar phenomena closer to the prototype. We conducted experimental research on the overall large-scale landslide conditions that might occur in the near-dam reservoir area, and analyzed the generation, propagation and dissipation characteristics of surge caused by landslides in combination with a three-dimensional numerical model. The results show that the wave height and phase calculated by the numerical model are basically consistent with the experimental results. The type of surge in the reservoir area is a finite depth wave, and the wave energy is distributed along the depth of the water. The nonlinearity near the surge generation area is strong, and the wave height decays rapidly as it propagates; the superposition of surge at the dam abutment appears instantaneous surging. In the test, only weakly nonlinear oscillatory waves were observed in the near field waveform of surge waves. Under the experimental conditions, the impact kinetic energy conversion rate of the block model is about 2%~19%. The kinetic energy conversion rate of the slider is positively correlated with the relative volume and relative thickness, and negatively correlated with the Froude number. The low frequency wave is greatly affected by the topography, and the wave energy temporarily concentrates in the shallow water area of the bank slope, the spectral peak increases, and the high frequency wave composition increases with time passing. For narrow and deep valleys, surges are caused by large amount of landslides. Although the wave energy of the first wave is affected by the high and steep slope, the wave height in front of the dam is obviously reduced, but the maximum wave height in front of the dam is usually formed by reflection and superposition of surges. After the first wave arrives, there is still a risk of surges over the dam body.
doi: 10.12170/20201119001
[Abstract](386) [FullText HTML](19) [PDF 1117KB](106)
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At the end of year 2018, the total number of built reservoirs in China reached 98, 822, with a total storage capacity of 895.3 billion m3. Reservoirs are not only important parts of national flood defense system, but also are key engineering measures to optimize the allocation of water resources. However, once a dam failure incident happens, it will involve major public safety. In-depth analysis of the historical data of dam failure cases is of great significance for preventing dam failure and improving the management level of disaster prevention and mitigation. Based on the collection of 3541 dam failure cases that occurred in China from 1954 to 2018, this paper focuses on 84 dam failure cases that occurred from 2000 to 2018. Detailed statistical analysis of the dam failure cases is carried out from the perspective of spatial distribution, reservoir size, dam height, type, failure causes, and other aspects. The trend characteristics of dam failure cases since 2000 can be summarized as: (i) Over-standard flooding becomes the main cause of dam failure cases of overtopping; (ii) Dam failure cases caused by quality defects at different locations of reservoirs significantly increased; (iii) The dam failure rate in the western part of China is dramatically higher than in other regions; (iv) Improper operation and management of reservoirs has become an important reason of dam failure incidents. Based on the aforementioned analysis, suggestions for further strengthening the dam safety management are proposed including that more attention should be paid to the impact of climate change on reservoirs, the engineering construction and operation safety supervision system should be continuously optimized, the management and operation conditions in the central and western regions of China should be intrinsically improved, and engineering measures and non-engineering measurements should be taken into account simultaneously in the field of dam safety management.
doi: 10.12170/20201201003
[Abstract](30) [FullText HTML](3) [PDF 1172KB](0)
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Continuous transverse grates are commonly used in some urban or impervious areas to collect the runoff (the entrance of parking lots, under-crossing tunnels, and airport aprons), where it is hard to place conventional inlets due to lack of suitable transverse slopes or steep longitudinal slopes. Hydraulic efficiency of continuous transverse grates determines the flow rate into the underground sewer system during rainfall and is of great significance to preventing the occurrence of urban waterlogging. Eight types of continuous transverse grates commonly used in China were experimentally tested in this study with different approach flows (Q=10~80 m3/h) and a set of longitudinal slopes (SL=1~4%). A full-scale physical model simulating a 12 m long, 3 m wide road was constructed in the hydraulic lab in Hefei University of Technology for the hydraulic tests. Hydraulic efficiencies of these grates under different conditions were calculated during the tests, and their influencing factors were analyzed, including hydraulic parameters of the approaching flow (Froude number) and the geometric parameters of the grates (total area, length of the opening in flow direction, opening style and opening rate). The experimental results show that the hydraulic efficiency of different continuous transverse grates may not have a consistent relationship with the Froude number. The length of opening in flow direction may have greater influences on the efficiency than the opening area or rate. Compared to grates with rectangular openings symmetrically arranged, when the opening area and rate are the same, the grates with circular openings staggerly arranged are found to perform better for capturing runoff. Based on the Manning Equation and the orifice outflow formula, a set of empirical equations were also presented to relate the hydraulic efficiency and influencing factors. Good agreements were obtained between the predicted and measured results with relative difference of less than 15%.
doi: 10.12170/20210126002
[Abstract](21) [FullText HTML](11) [PDF 1796KB](2)
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The mechanical properties of soil under reciprocating shear are of great significance to the study of cyclic load response. By improving the reciprocating shear direct shear instrument, 4 normal stresses are set for 32 cycles of shear. The behavior of stress-strain curve and the law of hysteresis loop area and damping ratio are found out for sandstone-mudstone particle mixture. According to the distribution law of shear stiffness with normal stress and reciprocating shear frequency, an empirical calculation method for shear stiffness of sandstone-mudstone particle mixture is established. By generalizing the contact mode between particles, the micro mechanism of strength and deformation is revealed for sandstone-mudstone particle mixture. Experimental results and theoretical analysis show that the stress-strain curve gradually changes from strain softening to strain hardening as the normal stress increases. The area of the hysteresis loop gradually decreases with the increase of the number of reciprocating shears, and the damping ratio increases slowly with the increase of the number of reciprocating shears, and has nothing to do with the normal stress. The initial shear stiffness is linear with the normal stress, and the normalized shear stiffness has a logarithmic function relationship with the number of reciprocating shears. Based on this, an empirical calculation of the shear stiffness of the sand-shale mixture considering the normal stress and the number of reciprocating shears is established.
doi: 10.12170/20201101001
[Abstract](27) [FullText HTML](6) [PDF 1307KB](6)
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In order to explore and study the influence of gently-inclined soft interlayers on the rainfall seepage characteristics of open-pit high slope, taking the high slope of typical limestone mine as an example which is located in the southwest China, simultaneously based on the actual engineering geological and hydrogeological conditions in the site, a rainfall seepage model of open-pit high slopes with gently-inclined soft interlayers is established. Based on the saturated-unsaturated seepage theory, the infiltration process of rainwater during rainfall and post-rainfall periods is simulated under the condition of maximum rainfall, and the dynamic variation rule of pore water pressure about open-pit high slope with gently-inclined soft interlayers is revealed. The research results show that the soft interlayer, as an isolation layer which means low permeability, changes the shape of rainwater infiltration curve and the seepage path of rainfall. The rainwater infiltration curve presents a "V"-shaped structure, and the seepage path changes from vertical slope infiltration to seepage along the upper surface of the soft interlayer. In the two periods of rainfall and after rainfall, the pore water pressure of upper fractured weathered rock increases first and then decreases, but the pore water pressure is always negative. The upper surface of soft interlayer will produce rainwater accumulation and the pore water pressure first increases to a positive value and then decreases gradually. The time of pore pressure reduction is lagging behind the rainfall time, that is to say, the pore pressure decreases after the rain stops for a period of time. The pore water pressure at the foot of the slope always increases during the two periods of rain and after-the-rain; due to the good water resistance of the soft interlayer, the pore water pressure inside the soft interlayer and that of the limestone at the bottom of the slope do not change too much. The research results can provide a useful reference for revealing the rainfall seepage laws of slopes under similar geological conditions.
doi: 10.12170/20200827002
[Abstract](33) [FullText HTML](6) [PDF 1178KB](4)
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River clogging is a natural disaster caused by landslide which results from earthquake, rainfall and other factors. Among the many losses caused by river clogging disaster, the loss of life is the most serious loss. In this paper, according to the disaster mechanism of life loss because of river clogging, the evaluation index system including risk population, warning time, understanding degree, lake level rising speed, elevation of risk population, submerged depth and other parameters, and the quantitative evaluation method of each parameter is established. At the same time, a bayesian network model, consisting of emergency evacuation network, submerged water depth network and life loss quantitative assessment network, is established through the interaction among various factors to assess the life loss of river weir, and the case of Niulan River weir is used to verify the rationality of the assessment method.
doi: 10.12170/20210208004
[Abstract](29) [FullText HTML](6) [PDF 3188KB](5)
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The Hechangzhou river reach is a typical braided reach and one of the most violently changed reaches in the lower reaches of the Yangtze River. After the impoundment of Three Gorges Dam, the sediment outflow decreased greatly, the new features of river bed evolution showed up and the navigation conditions changed accordingly in Hechangzhou braided reach. In order to restrain the scour development in the left branch and improve the navigation conditions in the right branch channel, three underwater submerged dams in the left branch were successively built. Based on a large amount of measured data, the evolution characteristics of Hechangzhou braided reach were analyzed. Results show that the riverbed in the Liuwei reach continued to cut down in 2009, accompanied by occurrences of bank line collapse and development of central bar. The control effect of three submerged dams is significant, and the measured diversion ratio of left branch in 2019 was about 64%, 12% lower than that of the highest 76% in 2002. The riverbed in the right branch changed from slow deposition to general scour, and the navigation conditions were improved. However, the left branch has experienced a significant scour in the local reach and two bank collapse events happened, which should be paid enough attention to.
doi: 10.12170/20201208002
[Abstract](10) [FullText HTML](11) [PDF 1122KB](2)
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The utilization of surface water resources is difficult in coastal areas due to short flow path and sharp gradient of river channel. Incorporating unconventional water resources such as reclaimed water and desalinated seawater into unified urban water systems in coastal cities is an effective way to alleviate water shortage. A key point to realize the unified allocation of conventional and unconventional water resources is to scientifically determine the construction scales of unconventional water sources considering uncertainties of conventional water resources. In this paper, an optimal model for determining the construction scales of desalinated seawater and reclaimed water considering inflow uncertainties is established through a case study in Weihai City. The non-dominated sorting genetic algorithm-Ⅱ is adopted to solve the model. Three indexes (reliability, resilience and vulnerability) are used to measure the performance of the whole water supply system and further compare results with the current basic scheme. The results indicate that at the planning level of 2030, the suitable construction scales of reclaimed water and desalinated seawater in Weihai urban area are 230 thousand m3/d and 150 thousand m3/d respectively. Based on these scales, the guarantee rate of urban water supply in Weihai urban area increases from 63.8% to 95.2%, and the average annual water supply cost is 660 million yuan. The results can provide decision-making reference for regional water supply planning.
doi: 10.12170/20210422001
[Abstract](25) [FullText HTML](11) [PDF 3494KB](1)
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The Yangtze Estuary is a giant multi-channel bifurcated river-tide system, which is affected by medium-intensity tides (mainly semilunar tides) and obvious seasonal variation of riverine inflow, and its hyrodynamic-morphological conditions are very complex. In this research, the response of discharge to the dynamic characteristics of water and sediment in the maximum turbidity area (North Passage) of the Yangtze Estuary is studied. The research results show that the increasing of discharge means the increasing of hydrodynamics, which first of all has two consequences: one is the enhancement of sediment resuspension capacity, the other is the increase of transport capacity; in addition, in the maximum turbidity area of the estuary, because of the river effect, there is often an increase in estuarine circulation, and the change of discharge also means that the transport capacity from the bottom to land also changes. The measured data and mathematical model jointly show that the larger the discharge is, the greater the sediment concentration of the beach with low velocity will be, however in the main flow area, due to the triple effects of the increase of discharge, the sediment concentration in the maximum turbidity area does not increase in one direction. Sediment concentration in the maximum turbidity area reaches the maximum under the discharge of 30, 000-40, 000 m3/s. This study clarifies the sediment suspension state of the estuary under different discharge conditions, which could provide a reference for the development and utilization of soil and water resources, ecological environment protection and waterway dredging maintenance in the Yangtze Estuary.
doi: 10.12170/20210112001
[Abstract](19) [FullText HTML](6) [PDF 1605KB](4)
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Carbon fiber board (CFRP) has become an important reinforcement material because of its good tensile strength, light weight, good durability, and convenient construction. In order to give full play to the tensile properties of carbon fiber boards, a method of reinforcement with circumferential prestressed carbon fiber board in prestressed concrete cylinder pipe (PCCP) is proposed, which is characterised by short construction period, small environmental impact, non-excavation, and easy operation. By comparing the mechanical model calculation results of Lame’s formula with the finite element calculation results, it is concluded that the two results are basically in agreement. The maximum difference is only 9.3%. The cases of the same total wire broken rate with different broken distribution were calculated and studied, and it is found that the worst case is that the broken wires are at the same position. When wires break, the concrete damage index near broken wires increases from inside to outside. The reinforcement effect of PCCP with 10% of wire breakage rate was studied. When the wire breakage rate is 10%, the stress and strain of concrete and steel cylinder at the broken wires are significantly reduced under normal working water pressure, which is indicated that CFRP has a very good reinforcement effect. The higher the wire breakage rate, the better the effect of CFRP before the concrete inner wall is damaged.
doi: 10.12170/20210307003
[Abstract](12) [FullText HTML](5) [PDF 2482KB](1)
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Based on the FLUENT computational fluid dynamics software and its secondary development function, as well as the VOF (Volume of Fluid) multiphase flow model, a stratified numerical water flume that simulates the propagation of oceanic internal waves is established with the standard \begin{document}$k{\text{ - }}\varepsilon$\end{document}turbulence model. In the numerical water flume, two-layer density-stratified fluid is set up, and the flapping plate method is used as the wave maker. Different combinations of density differences and water depth ratio between the upper and lower fluid are numerically simulated under two boundary assumptions of rigid lid and free surface at the still water level, and their numerical results are compared to their theoretical ones respectively. It is found that the differences of the densities of upper and lower fluid do not significantly influence the consistency between the numerical results and theoretical ones, and that the differences of the depths of upper and lower fluid significantly influence the numerical results. When the depth of the upper fluid is low, the notable vertical velocity appears at the interface between water and air under the assumption of free surface.Under the two assumptions at the still water level, the calculated horizontal velocities both reflect the nonlinear effect when the depth of the upper fluid is low, but hardly reflect the nonlinear effect when the depth of the lower fluid is low. Considering the fact that the depth of the upper fluid is much lower than that of the lower fluid in the actual ocean circumstance, it is more reasonable to adopt the assumption of free surface at the still water level, especially when the internal solitary waves with larger amplitude are numerically simulated.
doi: 10.12170/20201208003
[Abstract](11) [FullText HTML](7) [PDF 1387KB](4)
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The flume experiments of bed load transport in the conditions of highslope shallow water flow were carried out, in order to explore the impact of flow hydraulics and bed forms on bed load transport in gravel-cobble rivers in mountainous areas. A total of 19 runs were conducted with two groups of sediment mixtures. A data set of fluid hydraulics, sediment and 3D topographic field of riverbed in each run were obtained. The analysis of interrelationships among the flow resistance, bed form and bed load transport in different flow and sediment transport stages are made, by combining the flume experimental data and the observed data from natural river in the references. Experimental results demonstrate that the riverbed resistance coefficient increases with the increase of riverbed morphological strength parameter. The form drag is strongly correlated with riverbed morphological strength parameter. In the stage of sufficient sediment replenishment, the bed load transport rate is positively correlated with skin friction, form drag, and riverbed morphological strength parameter; in the current scour stage where sediment replenishment is insufficient, the bed load transport rate decreases with the increase of riverbed morphological strength parameter.
[Abstract](16) [FullText HTML](10) [PDF 0KB](0)
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doi: 10.12170/20210225002
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doi: 10.12170/20210129003
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In this study, the FLUENT software was used to simulate the evolution characteristics of the lock-released gravity currents flow through rigid vegetation regions in stratified environments. The two-dimensional large eddy simulation (LES) was adopted, and the vegetation resistance was added using the user-defined function (UDF) to analyze the relationship between instantaneous entrainment coefficients, potential energy transition, and kinetic energy variation with environment stratification degree as well as vegetation height. The results show that the stratified environment will cause the neutral layer intrude in the later stage of the density currents, but the vegetation will inhibit this phenomenon. At the beginning of the movement, the head velocity of the gravity current in the weak stratified environment is greater than that in the strong stratified environment. After a transition point, the trend is opposite, i.e. the existence of vegetation patches will delay the appearance of this transition point, and the appearance of the transition point lags as the height of vegetation patches increases. Both stratified environment and vegetation can reduce curent entrainment with ambient fluids, but when these two factors coexist, vegetation plays a major role in decreasing the mixing of density currents. During current propagation, the potential energy is mainly used to maintain the currents flow in the early stage. After a transition point, the potential energy is then consumed by irreversible mixing. In addition, the vegetation and stratified environment will advance this transition point. Under the same stratification environment, the higher the vegetation is, the smaller the proportion of background potential energy to the total potential energy during the evolution of density currents is, indicating that the irreversible mixing of density currents and environmental fluid is less dominant in the transformation of total potential energy. Also, the stratified environment will restrain the multiple peaks of kinetic energy at some characteristic sections, but vegetation will promote this phenomenon.
doi: 10.12170/20201128001
[Abstract](15) [FullText HTML](11) [PDF 1503KB](2)
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The characteristics of fish convection field were analyzed by in-situ observation and numerical simulation. The numerical simulation model of the flow field downstream of the dam of Cuijiaying hydroproject is constructed to calculate the downstream flow field of the hydroproject under different operation conditions in the migratory season, and the distribution characteristics of water depth, velocity and other hydraulic elements are counted. Based on the observation of the downstream fish cluster distribution in the same period, the response relationship of fish cluster to the flow field is revealed through the comprehensive comparative analysis of fish cluster distribution and flow field characteristic distribution, and the response of fish cluster to the flow field is proposed. The preference curve of flow field characteristics provides support for the scientific formulation of ecological dispatching scheme of Cuijiaying hub and the construction of other similar ecological dispatching projects.
doi: 10.12170/20201118002
[Abstract](25) [FullText HTML](10) [PDF 1922KB](4)
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A rainfall model test was carried out indoors with regard to the enrichment of local coarse and giant particles at different development positions, the middle and the foot of the slope of the accumulation body in Dongxing County. By observing the changes in pore water pressure, matric suction, volume water content, and wetting front migration, the effect of coarse and large particles’ local enrichment in the middle and at the foot of the slope in the course of rainfall infiltration was analyzed. The research indicates : (1) The hollow parts caused by the enrichment of local coarse and giant particles from the middle of the slope (Group A) and the foot of the slope (Group B) led to the formation of a dominant rainwater infiltration channel during the rainfall, and the infiltration rate under the enrichment area was apparently faster than that around homogeneous soil. (2) The filtration rate on the right side of the accumulation in Group B was faster than that of Group A while the left side was slower than that of Group A. (3) With stronger overall seepage, the wetting front migration of Group B was the first to hit the bottom, 72 hours earlier than Group A. (4) The wetting front migration pattern of the accumulations in Group A showed a gentle concave infiltration in the early stage, which was wider than the concave infiltration on the right in Group B; later they showed smooth arc infiltration, while the infiltration area of the accumulations in Group B was larger. Group A was smaller. (5) The rainfall infiltration in Group A and B could divided into vertical infiltration stage and lateral infiltration stage, but there were obvious differences: in Group A, the vertical infiltration rate was faster than the lateral one, while the former was slower than the latter in Group B.
doi: 10.12170/20210207001
[Abstract](11) [FullText HTML](14) [PDF 942KB](0)
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The traditional analytic hierarchy process shows the problem of the possibility of cumbersome calculation and serious inconsistency. Aiming at that, we comprehensively consider the advantages of the optimal transfer matrix and the "three-scale method" to establish an improved analytic hierarchy process. A waterway ecological evaluation system, which consisted of 1 target, 6 criteria, and 17 indicators, was constructed with reference to the basis of existing research. Taking the Jingjiang Reach of the Yangtze River as an example, we evaluated and compared the situation of the waterway regulation works in 2011 (before regulation) and 2015 (after regulation) and concluded that the Channel Health Index (ICH) increased from “good” (in 2011 with ICH=3.432) to “excellent” (in 2015 with ICH=4.187). The ecology of the Jingjiang Channel exhibited significant improvement after the waterway regulation works. The 6 functions under the criterion level are classified into 4 types of influencing factors, according to the reasons for the increase of the health index. The relative deviations of the results calculated by the improved analytic hierarchy process and the traditional analytic hierarchy process are 0.94% (2011) and 0.40% (2015), respectively, which means that the improved analytic hierarchy process simplifies the evaluation scale of the comparison matrix and optimizes the consistency of the matrix while ensuring the accuracy of the calculation results.
doi: 10.12170/20210115002
Abstract:
The runoff characteristics in the Yongding River Basin have changed enormously since the 1970s with part of the lower reaches dry up frequently all year around. Based on the meteorological and hydrological data from two periods (1956—1991 and 2006—2018), the main influencing factors of runoff attenuation were analyzed using the M-K test and wavelet analysis. The attribution of runoff attenuation was performed using Double Mass Curve and Elastic Coefficient Method based on the Budyko hypothesis. The results illustrate: (1) during the years 1956 - 2018, rainfall in the Yongding River Basin did not vary significantly, the temperature increased significantly, the evaporation capacity decreased slightly, and the runoff decreased significantly, reaching 99.9% confidence level; (2) the rainfall and runoff for most of stations has a fluctuation period between 11 and 23 years; (3) the double mass curves for 10 hydrological stations have shifted 4 times (mid-1960s, early 1970s, mid-1980s, and the early 1990s) which are all biased towards runoff. This indicates that the runoff has declined in spite of no obvious change in the rainfall level; (4) the Yongding River Basin is a region affected by a lot of human activities. It should be noted that the absolute value of elasticity coefficient of precipitation is larger that the underlying surface parameters which in turn is larger than the evaporation capacity. Finally, the average contribution rate of human activities to runoff attenuation is about 95%.
doi: 10.12170/20201228001
Abstract:
In order to ease spudcan-footprint interactions during jack-up rigs penetrating in the vicinity of an existing seabed footprint, three new spudcan shapes, a six-hole lotus-shaped spudcan, a flat-bottomed spudcan, and a concave-shaped spudcan, were proposed and analyzed comparatively to carry out optimizing study of the spudcan structure.Firstly, large-deformation finite element (LDFE) was performed using the Coupled Eulerian-Lagrangian (CEL) method with the idealized elastic-plastic Tresca model to analyze differences between the innovative spudcan shapes and the traditional one in interaction mechanism of spudcan-soil during spudcan penetrating next to an existing footprint with an eccentricity of 0.5D, as well as the horizontal range of plastic deformation of the disturbed soil, the inclination angle of spudcan and the offset of the pile leg. Then FEM method and the method of Specification were used to evaluate the bearing capacities of different spudcan structures. Finally, the risk of puncturing was assessed during different spudcans penetrating in the layered soil. The results show that the six-hole lotus-shaped spudcan, flat-bottom spudcan, and concave-shaped spudcan can mitigate the horizontal sliding force and peak bending moment at the top of the pile leg compared with those of traditional spindle-shaped piles obviously, and which are reduced by 32.59%, 22.47%, 28.18%, and 26.32%, 12.88%, 18.02%, respectively. It can be seen that all the new spudcan structures can ease the adverse consequences of the spudcan-footprint interactions effectively. Among them, the six-hole lotus-shaped one works best, and the concave-shaped one is slightly less but simpler and easier to produce. Besides, considering impact of spudcan penetrating on the adjacent jacket platform, the six-hole lotus-shaped spudcan structure is priority due to the least horizontal range of soil disturbance. In view of the risk of puncturing when spudcans penetrating into the layered soil or discontinuously, the flat-bottomed spudcan is priority due to the least possibility of puncturing when the same stable load is applied and the spudcan is penetrated into the same depth.
doi: 10.12170/20200829002
Abstract:
Vegetation widely distributed in natural river shallows can change the local hydraulic characteristics of the river and the process of sediment transport. In order to understand the influence of vegetation on the flow characteristics of the bend, our experiment is aimed at the bend with rigid emergent vegetation on the convex bank under a specific flow rate, to explore the distribution law of water flow characteristics along the way when vegetation density and location are different. By establishing a generalized model of curved water flow, using ADV to collect and process the three-dimensional velocity data, and comparing the velocity distribution under the conditions of with and without vegetation (vegetation density respectively ρ=0%, ρ=2.2%, ρ=4.5%), qualitatively analyze the effect of vegetation on the turbulence characteristics of the curve flow under different working conditions, and determine the structure and strength of the curve circulation. The results show that the existence of vegetation on the convex bank (0-90°bend, evenly distributed in the quarter of the river width) can effectively weaken the circulation intensity of the bend, but the reduction effect on the convex bank area does not increase with the increase of vegetation density. The location of the dividing point of different flow direction water layers in the non-vegetation area changes with the change of vegetation density, and the distribution of vegetation also affects the circulation structure at different water depths in each section of the bend.
doi: 10.12170/20210129002
Abstract:
The soil parameters may obey different types of distribution. However, the lognormal distribution is generally chose in the probability analysis of pile foundations. The undrained strength of soil is taken as the random variable, and it is assumed to obey Lognormal distribution, Beta distribution and Gamma distribution respectively. Then the bearing behavior of single pile foundation under vertical and horizontal loads are simulated by stochastic finite element method, in which the different coefficient of variation and correlation distance are considered. The mean value and standard deviation of bearing capacity of single pile are analyzed. The results show that the average vertical bearing capacity of single pile is not affected by the distribution of soil strength. The average horizontal bearing capacity of single pile is largest when the lognormal distribution is adopted, while the bearing capacity is smallest when random field obeys the Beta distribution. The standard deviation of bearing capacity obtained by Beta distribution under vertical and horizontal loads is the largest. It is recommended to use Beta distribution to determine the bearing capacity of single pile foundation when the spatial distribution of soil strength is unknown.
doi: 10.12170/20210124001
Abstract:
A series of sand direct shear numerical simulation tests were performed using the discrete element method, so as to investigate the inherent relation of meso-mechanics between the particle's rotation-resistant capacity and the interaction of sands and soils in the case of rotational resistance. On this basis, the contact constitutive relation between sand particles was simulated with the rolling resistance linear model. Meanwhile, the feasibility of the sand direct shear numerical test was verified by numerically experimenting macro stress-strain characteristics, strength index and shear band deformation law that are similar to previous studies. In addition, from the meso scale, the average mechanical coordination number and the strong contact proportion in the sample was decreased with the increase of the rolling resistance coefficient. After studying the anisotropic evolution law in combination with the tensors characterized by rose diagram, deviator fabric and second invariant, it is found that the anisotropy properties of the normal contact force and the tangential contact force are increased with the increase of the rolling resistance coefficient in the shearing process. Of which, the strong contact deviator fabric is greater than the overall contact deviator fabric. Besides, the tensors of normal contact forces are greater than that of fabrics, which has a variation law consistent with the macroscopic shear strength. It evidently indicates that the rotational impedance principally improves the shear strength by increasing the magnitude of strong contact force between particles and the degree of anisotropy of the fabric. Also, the anisotropy of the normal contact force plays a pivotal role in resisting the shear strength.
doi: 10.12170/20201213001
[Abstract](30) [FullText HTML](4) [PDF 1213KB](1)
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Deformation prediction model provides an essential support for the analysis of dam structure safety. However, the existing dam deformation prediction models suffer from low precision and insufficient generalization. To solve this problem, an adaptive fuzzy neural network was introduced into the dam deformation prediction model in this study. Specifically, the particle swarm optimization (PSO) algorithm with dynamic weights was applied to optimize the parameter of fitness values in the fuzzy layer of the adaptive fuzzy neural network. Based on this, an adaptive fuzzy neural network called DPSO-ANFIS is formed, which is capable to search for the optimal fitness value. And a dam deformation prediction model based on DPSO-ANFIS was established. Experiments were conducted to verify the effectiveness of the proposed deformation prediction model. The monitoring data from the dam prototype was applied to the trained model to obtain the output values, and these values were then compared with the actual monitoring data. The engineering practice showed that the maximum deviation between the output values of the dam deformation prediction model based on DPSO-ANFIS and the measured values was 0.0516 mm; the RMSE (root mean square error) was 0.0351, and the average absolute error was 0.0320. All the values of these performance indicators were better than those of the dam deformation prediction models based on PSO-ANFIS, ANFIS, and BP neural network. As for the measure points and time, the predicted values from the dam deformation prediction model based on DPSO-ANFIS exhibited a trend much close to that of measured values. Also, the proposed deformation prediction model achieved a stable overall prediction performance. Therefore, the dam deformation prediction model based on DPSO-ANFIS achieves high accuracy, good generalization, strong stability, and excellent comprehensive performance in practical engineering applications.
doi: 10.12170/20210104001
Abstract:
In this study, the influence of calcium aluminate cement on the properties of fly ash based geopolymer was discussed. Calcium aluminate cement was used to replace fly ash, and the content was 0%, 2%, 4%, 8% and 12% respectively. SEM, XRD, FTIR and TG were used to explore the micro-mechanism of geopolymer with calcium aluminate cement; fluidity test, setting time and compressive strength test were carried out to analyze the macro-performance of geopolymer with calcium aluminate cement. The results show that when the content of calcium aluminate cement increases from 0% to 12%, the content of C-S-H gel increases from 2.16% to 8.1%, and the content of aluminium-rich gel grows from 55.22% to 74.6%. Increasing the content of calcium aluminate cement, the fluidity decreases from 22.4 cm to 21.5 cm, initial setting time decreases from 622 min to 106 min, final setting time drops from 740 min to 125 min, and the compressive strength increases from 27.7 MPa to 70.78 MPa. Therefore, adding calcium aluminate cement is beneficial to the formation of more C-S-H gel and aluminum rich gel, and C-S-H gel has greater generation rate, which reduce the working performance and improve the compressive strength of geopolymer, which enriches the method to improve the properties of geopolymer.
doi: 10.12170/20210114001
Abstract:
The research on the occurrence regularity of the drought-flood abrupt alternation in Haihe River Basin can provide scientific reference for flood control and drought relief. Based on the daily precipitation data of 159 meteorological stations in Haihe River Basin from 1961 to 2019, the Standardized Antecedent Precipitation Index (SAPI) is calculated. Based on the SAPI, according to the drought-flood grade standard and drought-flood abrupt alternation conditions, the drought-flood abrupt alternation events since 1961 are screened out, and the frequency and intensity characteristics of drought-flood abrupt alternation in Haihe River Basin are analyzed. The results show that the annual average frequency of drought-flood abrupt alternation in Haihe River Basin is 33 times, which basically increases year by year, with an average of 37 times in recent 10 years. The intensity of drought-flood abrupt alternation also showed an upward trend, and increased to above the average value after 2000; it showed a jumping increase with reaching the maximum value especially in recent 10 years. The drought-flood abrupt alternation occurred mostly in May, June and Mid September, and less in midsummer. The intensity of drought-flood abrupt alternation presents a single peak distribution, and the maximum value appears from the middle of June to the first ten days of July. The corresponding frequency of drought-flood abrupt alternation is also more in this period, which increases the risk of flood disaster. From the perspective of spatial distribution, the frequency and intensity of drought-flood abrupt alternation are high value areas in the southern part of Luanhe River system, the western part of Beisanhe river system and the central part of TuhaiMajia river. That is to say, the frequency and intensity of drought-flood abrupt alternation are high in these areas, consequently, the risk of drought-flood abrupt alternation is high. These areas may become the focus of flood control.
doi: 10.12170/20201228002
Abstract:
The destruction of the rock mass is the shear damage that mainly along the failure surface in nature, and it is mainly characterized by shear rheological damage. Based on the analysis of experimental data of weak intercalation under different shear stress levels, the variable D which can characterize the parameter damage in the rheological process was introduced, and a viscoelastic plastic nonlinear rheological model based on D, which can reflect the accelerated rheological characteristics of weak intercalation, was proposed, and a new shear rheological damage model of weak intercalation was constructed by connecting it with the Burgers model, which can fully reflect the three rheological stages. Then the rheological damage model was redeveloped with C + + language based on FLAC3D, and compared with the indoor rheological test. The results showed that: (1) the instantaneous strain of the increment value of strain under each shear stress was quite close, and both the stable strain value and the accelerated strain value are very close after the same time of stress loading. (2) When the applied shear load did not reach the yield stress, the deceleration period of the numerical simulation test was shorter than that of the indoor test, that was, it reached the stable rheological stage faster. When the applied shear load exceeded the yield stress threshold, the displacement change rate of the accelerated rheological stage was larger than that of the indoor test, and the final displacement was slightly larger than the indoor test displacement.
doi: 10.12170/20210120005
Abstract:
In order to provide technical support for river regulation planning and propose drifting water supply scheme in the lower reaches of water conservancy projects, a two-dimensional full hydrodynamic model is adopted to simulate the different condition conditions with the river regulation or not. The downstream river channel of Sanhekou Water Control Project is taken as an example, where are the beautiful scenery on both sides of the river channel and few dangerous banks of submerged reefs. The elevation of the river bed is generally about 514~526 m, and the thickness of the sand and pebble layer of the river bed is 5~10 m, which provides a guarantee for the implementation of the rafting project. Combined with the operation of the upstream water conservancy, hydraulic elements and related statistics on different cross sections were calculated under each working condition of drainage, which is beneficial to put forward the drift river regulation and water supply scheme. The results show that the two-dimensional hydrodynamic model can successfully simulate the downstream river channel of a water conservancy project with high efficiency and high accuracy under different discharge conditions, which provides effective technical support for the planning of river water entertainment facilities. For saving water resources and reducing the amount of engineering construction, the dredging width of the river channel should be 6 m. Under this working condition, the upstream water conservancy project only needs to discharge 4 m3/s. The minimum water depth of the cross-sections is 0.50 m, the minimum water surface width is 4 m, and the minimum flow velocity section is 1.02 m/s.
doi: 10.12170/20201117003
[Abstract](10) [FullText HTML](4) [PDF 962KB](0)
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Aiming at the demand for online training on reservoir dam patrol inspection, we studied serious games, put forward the architecture of reservoir dam patrol inspection training system on the internet, explored the key technologies of dam BIM modeling, inspection point and defect 3D modeling, reservoir hub scene simulation, analyzed the requirements, methods, equipment, contents for reservoir dam patrol inspection, and developed reservoir dam patrol inspection training system based on Unity3D. The reservoir dam patrol inspection training system is composed of data layer, model layer and application layer, with the functions of patrol inspection knowledge, inspection training, inspection examination and system management. The reservoir dam patrol inspection training system has solved the problems of narrow coverage, high cost and long time in the traditional training methods. It can be widely used for the training of reservoir management personnel, especially those for small and medium-sized reservoirs without monitoring facilities or with damaged monitoring facilities, to further standardize the reservoir dam patrol inspection work, improve the patrol inspection capacity of reservoir management personnel, and ensure the safe operation of reservoir dams.
doi: 10.12170/20210208002
[Abstract](10) [FullText HTML](8) [PDF 826KB](2)
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The Yangtze River Channel is the main logistics channel of the Yangtze River shipping and an important link for regional economic coordination. At present, there are many researches on the relationship between transportation infrastructure and economic growth, but few literatures take the Yangtze River waterway as the research object to explore its influence on economic growth. Drew a causal diagram to qualitatively analyze the interaction between the Yangtze River waterway and the Yangtze River Economic belt, and to clarify the mechanism of the waterway construction promoting regional economic growth. Selected the time series data from 2005 to 2009, and used the extended C-D production function model to quantitatively calculate the economic contribution of investment in the Yangtze River waterway construction to the Yangtze River Economic Belt. On the whole, the contribution of economy shows an increasing trend year by year. The economic output of the Yangtze River Economic Belt increases by 1.74 percentage points for every 1 percentage point increase in the input for the construction of the Yangtze River waterway. The results show that the construction of the Yangtze River waterway plays a significant role in supporting the Yangtze River economy. In order to better facilitate the development of the Yangtze River Economic Belt, more investment should be put into the construction of the Yangtze River waterway in the future to improve its carrying capacity, and at the same time, more attention should be paid to scientific and technological innovation and ecological protection.
doi: 10.12170/20201210003
[Abstract](14) [FullText HTML](3) [PDF 927KB](6)
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In recent years, China has made great progress in water conservancy informatization and is now gearing up to implement smart water conservancy. However, the specific goals, standards and technical routes of its intelligent application systems are still under exploration. Intelligent engineering safety monitoring is an indispensable component of intelligent water conservancy, and the boundary of its realistic goals is determined by the maturity of AI technology. In light of the status quo of AI technology and based on our experience in dam safety monitoring for several decades, in this paper the radical challenges of intelligent engineering safety monitoring were analyzed systematically, and the three cardinal ideas in intelligent scheme formulation and implementation, the realistic goals and roadmap, were put forward definitively. First, we have to decide "what should be done" and "what can be done" from the philosophical points of view, evaluate the reasonability of the scheme from the aspects of technology, economy and safety, and maintain a sincere attitude from the very beginning to the end to get it well done. Second, intelligent engineering safety monitoring should be focused on the principal contradiction between engineering risk and structural resistance, besides the demand and effective supply of information related to engineering safety, and currently its realistic goals should be directed towards identifying the existing structural distress in an explainable way, foreseeing the engineering safety risks and keeping them under control. Third, four key steps, including automated monitoring, full informatization, visualization and modelling, are essential to surpassing conventional informationization and realizjng the real intelligentization. With these concepts being well implemented, a solid foundation will be laid for the successful implementation of smart water conservancy.
doi: 10.12170/20201103002
[Abstract](82) [FullText HTML](51) [PDF 1719KB](3)
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The prediction of runoff into the reservoir has important indications for the operation of Danjiangkou Reservoir and the utilization of water resources. Based on the gray wolf optimization algorithm (GWO), construct different prediction models, carry out the study of reservoir runoff prediction in Danjiangkou, discuss the selection of network structure hyperparameters, verify the characteristics of global traversability and fast convergence of GWO. The results show that the prediction accuracy and generalization performance of the GWO-LSTM model are better than those of the GWO-BP model and the stepwise regression model. The Nash efficiency coefficient of its verification period reached 0.969 on average. The overall trend forecast is good, and the peak capture is slightly insufficient, which is suitable for prediction of monthly inflow to the Danjiangkou reservoir; The prediction results of model hyperparameters based on empirical values are not as good as GWO. Based on empirical values, the NSE of the verification period is less than 0.5, which does not reach the acceptable range, and there is a certain contingency. It is recommended to select an optimization algorithm with global optimization characteristics for hyperparameter selection; The global traversability and fast convergence characteristics of the GWO algorithm are verified, and the convergence state can be reached after 3 iterations on average.
doi: 10.12170/20210301001
[Abstract](16) [FullText HTML](15) [PDF 748KB](14)
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At present, there are some problems in reservoir dam safety monitoring, such as imperfect monitoring items, nonstandard construction and installation, insufficient operation and management capacity, etc. which lead to the failure of some safety monitoring systems to operate normally after completion, resulting in waste of construction funds and even affecting dam safety management. Based on the investigation results of the construction and operation status of the national reservoir dam safety monitoring system and the author's experience, a series of problems existing in the planning, design, review, bidding, construction, acceptance, operation management and other links of dam safety monitoring are systematically sorted out, and the reasons of the current situation of reservoir dam safety monitoring are deeply analyzed. The countermeasures and suggestions for improving reservoirs dams safety monitoring are put forward, which includes raising awareness of the importance of dam safety monitoring, strengthening safety monitoring training, studying and promulgating dam safety monitoring management measures, setting up dam safety monitoring expert database, strengthening special supervision of dam safety monitoring, introducing safety monitoring instrument detection and third-party identification during construction, etc. This paper has guiding value for promoting the improvement of reservoir dam safety monitoring level in China.
doi: 10.12170/20200519001
[Abstract](25) [FullText HTML](16) [PDF 1266KB](3)
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The health of ecosystem in the Yangtze River Economic Belt (YREB) is an important key factor to the sustainable development of China's economy and society. Based on the framework of Vigor-Organization- Resilience Contribution, an ecosystem health assessment model was built for the YREB, and the ecosystem health for each county in 2000 and 2015 was analyzed. The result showed that: (1) the ecosystem health was higher in the upstream and south of the Yangtze River (e.g.Yunnan province), while lower in downstream and north of the Yangtze River (e.g. Anhui province and Jiangsu province); (2) An overall increase of ecosystem health index was detected from 2000 to 2015. However, in the local area, especially coast regions of Yangtze River Delta Area, the ecosystem health index was decreased; (3) In 2015, the ecosystem health of the Yangtze River Economic Belt was dominated by four factors, the four-factor dominant area accounted for 41.2% of the total area, and most of them were transformed from the primary three-factor dominant area in 2000. In general, the ecosystem health of the YREB recovered during the study period, but declined in the areas with intensified human activities.
doi: 10.12170/20190322001
[Abstract](345) [FullText HTML](168) [PDF 764KB](11)
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In order to study the change of pore water pressure of concrete in the water pressure environment, the experiment of pore water pressure change of the concrete under different water pressure was carried out. Based on the test data, the transient inversion numerical simulation of pore water pressure variation of concrete under different water pressure is carried out by using the finite element software ANSYS, and the results are compared with the experimental results. The research results show that under the action of water pressure, the change characteristics of pore water pressure of concrete can be divided into three stages: the rapid increase stage, the slow increase stage and the stabilization stage. When the concrete is under the water pressure of 0.875 MPa, the pore water pressure of the concrete reaches the value equal to the applied water pressure for more than 9 h. The variation law of pore water pressure of concrete is in good agreement with the experimental data by using the finite element software ANSYS for numerical simulation.
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2021, (4): 1-1.
[Abstract](64) [FullText HTML](44) [PDF 9522KB](30)
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2021, (4): 1-2.
[Abstract](40) [FullText HTML](21) [PDF 338KB](12)
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2021, (4): 1-9.   doi: 10.12170/20201201001
[Abstract](145) [FullText HTML](40) [PDF 1617KB](52)
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The landslide of expansive soil slope has the characteristics of long-term and recurrence, so the long-term stability of canal slope after reinforcement is still worthy of attention. In a long distance water diversion project, although the replacement measure for surface soil was adopted, the water vapor exchange between the expansive soil and the external environment was not completely blocked. After two years of operation, obvious deformation occurred, and then measures of the umbrella anchor reinforcement and drainage hole layout were taken. Based on the monitoring data of the reinforced canal slope, the temporal and spatial deformation characteristics were analyzed by the HCPC method (hierarchical cluster analysis on principal component analysis). On this basis, the typical point was selected, the exponential smoothing method, the autoregressive moving average model and the multi factor nonlinear regression model were applied to analyze and predict the slope deformation. The results show that the deformation of the reinforced canal slope tended to be stable after nearly two months of adjustment, and was mainly affected by the external environment factors and fluctuated slightly at this stage. The deformation of the reinforced canal slope was inhomogenous in space, and the deformation range decreased to both sides with the original deformation body as the center. The canal slope deformation is mainly affected by time dependent effect, as well as rainfall, groundwater level and temperature. In view of the long-term repeated characteristics of expansive soil landslide, the follow-up observation should be strengthened.
2021, (4): 10-18.   doi: 10.12170/20200610001
[Abstract](162) [FullText HTML](53) [PDF 1281KB](59)
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The complex nonlinear mapping relationship between the deformation of gravity dam and various environmental quantities makes the input independent variables of the deformation prediction model have high dimension, which affects the accuracy and generalization ability of the prediction model to some extent. To solve the problems, a combined prediction model is proposed to combine principal component analysis, the cuckoo search algorithm, and the nuclear limit learning machine network. The model uses the principal component analysis method to extract the main component information of the water level, temperature, and time-dependent influencing factors related to deformation, and optimize the input of variables of the network model; furthermore, it uses the cuckoo search algorithm, which exhibits better optimization performance, so as to determine the kernel parameters and regularization coefficients of the kernel extreme learning machine network. With the measured data of a gravity dam, the deformation displacement of the dam in the direction of the dam axis and in the upstream and downstream directions is predicted, compared with those of various models, and evaluated with different quantitative indicators. The analysis results reveal that the certainty coefficients R2 of the proposed model in the two different directions are 0.943 and 0.931, respectively, which are higher than those of the traditional neural network model and the stepwise regression model. In the upstream and downstream directions, deformation predictions of different measurement points, the accuracy and generalization ability of the model are better than those of the comparison model, thus verifying the feasibility and advantages of the model.
2021, (4): 19-28.   doi: 10.12170/20200825004
[Abstract](41) [FullText HTML](8) [PDF 1503KB](9)
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In the failure process of rock specimen with double cracks, the stress field between different cracks will interact, and the rock bridge area will coalesce. In the research, the strain strength criterion was embedded into the expanded discrete element program UDEC, which was secondarily developed to simulate the propagation of tensile crack and shear crack of specimens with prefabricated double cracks. According to the results of the numerical simulation, four basic coalescence modes of rock bridges will appear in the double-crack specimen during uniaxial compression: (1) Non-coalescence mode: the wing cracks at the tips of the two prefabricated cracks gradually expand independently, but the discontinuous mode of penetration does not occur in the rock bridge area; (2) Shear coalescence mode: in the rock bridge area, the main stress field and the shear stress field are concentrated, resulting in shear cracks coalescence in the rock bridge. At this time, the shear stress plays a leading role in the shear coalescence mode; (3) Tensile coalescence mode: tensile cracks penetrate the rock bridge, and the rock bridge is highly concentrated by the principal stress field. At this time, the rock bridge penetration has the characteristics of instantaneousness, and the tensile crack penetrates the tensile coalescence mode of the rock bridge; (4) Mixed coalescence mode: under the combined action of tensile force and shear force, the rock bridge gets the mixed tensile and shear coalescence mode after the specimen reaches the highest peak strength. Through comparison with laboratory tests, it is concluded that applying the strain strength criterion to the numerical simulation analysis can more accurately describe the changes of stress and strain and the penetration of rock bridges during mesoscopic failure, and enrich the mechanism penetration of multi-crack rock specimen in mesomechanics. The research provides a reference for numerical simulation in studying the actual engineering of rock mass meso-damage.
2021, (4): 29-35.   doi: 10.12170/20200824002
[Abstract](63) [FullText HTML](15) [PDF 1095KB](14)
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Prediction of seepage water level extremum is one of the main means to monitor the safety of the earth rock dam, and dam body seepage water level is an important physical quantity to evaluate the seepage characteristics of the earth rock dam. Currently, the common sense of the extreme value prediction methods is on the prerequisite of giving correct independent variables, when such methods being applied. The most important factor affecting the seepage water level extremum is the upstream water level. When the correlation between the seepage water level extremum and the upstream water level is quite good, the predication accuracy provided by conventional models is quite high; when the correlation between the seepage water level extremum and the upstream water level is weak, the predication accuracy provided by conventional models is low. To resolve this issue, this paper proposes a method of predicting and evaluating the seepage water level extremum, which considers the measured value sequence only and neglects the independent variables. Based on the maximum Lyapunov index, a prediction model is established, and the ergodicity and stationary distribution of Markov chain are applied to evaluate this independent variable model. The example shows that the prediction effect of the prediction model based on maximum Lyapunov index is better than that of conventional methods for seepage water level extremum, which has weak correlation with independent variables, and the error assessment model based on Markov chain provides reasonable evaluation. The prediction model and evaluation method based on chaos theory and stochastic process that is proposed in this paper can form a systematic approach to the sequence prediction as well as evaluation method with high accuracy and strong practicability, covering the weak area of conventional prediction methods. It can be used to establish the prediction model for the measured value sequence with uncertain independent variables.
2021, (4): 36-45.   doi: 10.12170/20210114003
[Abstract](39) [FullText HTML](20) [PDF 1633KB](13)
Abstract:
The effect of valley width deformation during the initial impoundment stage on the subsequent working behavior and the long-term safety of an arch dam has become an increasingly important chanllenge faced by dam engineering and academia. This study aims to analyze the sensitivity of valley width deformation to the absorption curve of fractured rock mass to address the challenge of valley width reduction during impoundment of the Jinping Ⅰ arch dam in China. The methods of unsaturated seepage analysis theory and nonlinear finite element numerical analysis were applied to study the law of valley width deformation during unsaturated seepage process. The influence of valley width deformation on the displacement and stress of the dam was analyzed. The results showed that the slope on both sides of the valley deformed towards the center under the action of the unsaturated seepage field. The deformation of valley width upstream exceeded that downstream. The valley width deformation increased with an increasing elevation of the water level, and maximum valley width reduction occurred in the saturated seepage field. The distribution of displacement and stress of the dam changed little during the unsaturated seepage process. However, the maximum longitudinal displacement and the minor principal stress of the dam decreased gradually with increaseing elevation of the water level. There was a gradul increase in the major principal stress. The valley width reduction had a squeezing effect on the dam body, resulting in a decrease in the maximum longitudinal displacement, the transfer of the major principal tensile stress from the dam heel to the upstream side of the dam abutment, and the extension of the high-pressure stress zone on the downstream surface to the middle of the crown cantilever. The influence of the saturated seepage field on the displacement and stress of the dam was more obvious than that of the unsaturated seepage field. However, the valley width deformation resulting from the seepage field had a limited effect on the displacement and stress of the dam, which would not affect the overall stability of the dam.
2021, (4): 46-53.   doi: 10.12170/20200912001
[Abstract](46) [FullText HTML](20) [PDF 1725KB](12)
Abstract:
To study the influence of dip angle of rock bridge on rock mechanical behavior and crack propagation mechanism, the particle parallel bonding model in the PFC3D code was used to obtain a group of microscopic parameters, which could reflect the macroscopic mechanical properties of intact granite via the trial and error method. A numerical model of the combination of micro-void and parallel fissures ① and ② under different rock bridge angles was established, and the deformation and failure process of the sample in the triaxial compression were analyzed. Results show there was no significant effect on the ratio of the initiation strength to the peak strength; when α=0° and 75°, the crack propagation modes were similar, and wing cracks were initiated at the inner and outer tips of the fissure ① and ②, and then coalesced with the micro-void; when α=15°, 30°, and 90°, the crack propagation mode was relatively close, the wing cracks could be observed at the tips of the fissures ① and ②; when α=45°, 60°, the cracks grew in a similar manner, there were crack coalescence on the shear plane between the fissures ① and ② and the micro-void, and there were shear cracks at the outer tips of the fissures ① and ②. In this case, both the parallel fissures and the micro-void were on the shear plane; the number of shear cracks was far more numerous than that of the tensile cracks, and the micro-cracks extended from the initial damage zone.
2021, (4): 54-60.   doi: 10.12170/20200829001
[Abstract](39) [FullText HTML](16) [PDF 1175KB](15)
Abstract:
The coefficient of permeability of aquifer is an important hydrogeological parameter in foundation pit dewatering design. The calculated coefficient of permeability of the same soil layer by different calculation methods may be different, thus it is very important to select the most suitable calculation method for a certain soil layer to avoid large errors. Based on the test results of single well pumping tests in sandy cobble ground, four common methods, i.e. Dupuit-Kusargent method, Thiem method, straight-line slope method and water level recovery method are used to calculate the coefficient of permeability of aquifer. The difference between the simulated water level and the field measured value is compared, the reasons resulting in the differences are discussed, and the advantages, disadvantages and applicability of each method are pointed out. The analysis results show that the error of Dupuit-Kusargent method is the largest, that of the straight-line slope method is the second, and the errors of water level recovery method and Thiem method are small. Furthermore, the results from Dupuit-Kusargent method are greatly affected by the pumping flow rate, and its consistency is poor. The consistency of the results from other methods is good. For determination of the coefficient of permeability for sandy cobble aquifer, Thiem method should be preferred when there are more than two observation wells. The straight-line slope method can be used when there is an observation well, and the falling depth and the logarithm of time are in good agreement with the linear relationship. The water level recovery method can be used when there is no observation well. It is not recommended to use Dupuit-Kusargent method due to its large error.
2021, (4): 61-67.   doi: 10.12170/20200826002
[Abstract](18) [FullText HTML](18) [PDF 1183KB](10)
Abstract:
Gravelly soil has been mostly used as the core material of the high earth-rock dam. When the coarse-grained content of a gravelly soil (referring to the mass fraction, the same below) may exceed 50%, the coefficient of permeability of a gravelly soil is highly likely to fail to meet engineering specifications or standards. This is deleterious to the seepage stability of a dam. Three-dimensional finite element numerical simulation was conducted to study the influence of a gravelly soil having a coarse-grained content of greater than 50% on the seepage through a high earth-rock dam. The coefficient of permeability of elements having a coarse-grained content of greater than 50% is assigned a different value compared with those elements having a coarse-grained content equal to 50% in the simulation. The results show that the gravelly soil in the different parts of the core having a coarse-grained content of greater than 55% had little effect on the seepage field and the seepage discharge through the dam, but exerted a significant influence on the seepage gradient. The maximum seepage gradient occurred at the element having a coarse-grained content equal to 50%. For those cases having a coarse-grained content of less than 55% in the lower and middle parts of the core, the increase in the maximum seepage gradient was 36.4%. For those cases having a coarse-grained content of greater than 55% in the lower and middle parts of the core, the increase in the maximum gradient was even higher, and might exceed the allowable seepage gradient, with adverse effects upon dam safety. Therefore, in practice, the downstream filter should be designed based on the grading and the fine particle content of such gravelly soils. Besides, the relative density of such gravelly soil should be controlled to ensure the safety of the body of the dam.
2021, (4): 68-74.   doi: 10.12170/20200909002
[Abstract](51) [FullText HTML](18) [PDF 1138KB](7)
Abstract:
With the increasing application of geotechnical centrifuge model tests and the increasing demand of quantitative analysis, influencing factor and precise control of sample preparation on porosity and void distribution have arisen as a key issue in the development of geotechnical centrifuge modeling techniques. Sand pluviation is an important technique for preparing sand models and widely employed in geotechnical centrifuge modeling, due to the process of its reconstitution similar to the formation of natural coarse sand strata and the advantages of avoiding soil grain crushing and achieving a wide range of relative density. In order to understand the effect of control factors on the porosity of samples prepared by sand pluviation, a discrete element method based on PFC3D is established to simulate the process of sample reconstitution using sand pluviaiton. Through discrete element simulation of the effect of drop height, mesh-grain size ratio, environmental medium, the feasibility of the proposed discrete element method is properly validated with the general knowledge from physical model tests. The results show that the porosity and the drop height appear in an obvious negative correlation, and the rate of decreasing in the porosity gradually attenuates with the increase of drop height. Meanwhile, a positive correlation exists between the mesh-grain size ratio and the porosity, and the latter is found to distinctly increase with the increasing of the former. The density of environmental medium is exhibited in a significant negative correlation with the porosity and has an important influence. Consequently, the layer thickness of model surface water plays a leading role in the control of the porosity.
2021, (4): 75-84.   doi: 10.12170/20201029001
[Abstract](132) [FullText HTML](23) [PDF 1443KB](26)
Abstract:
The debris flow has the characteristics of suddenness, fast flow speed and strong destructive force. It is of great practical significance and theoretical value to study its dynamic mechanism and accurately simulate the formation process. This model was created in the framework of a Godunov-type finite volume scheme to solve the shallow water equations (SWEs). At the same time, the introduction of Graphics Processing Unit (GPU) improved computing technology greatly, and increased the computing speed. Taking the dam-breaking flume debris flow movement characteristics and the prediction of the risk range of the landslide and debris flow in Pusa Village, Guizhou Province as a simulation reference, the constructed GAST model was used to complete the simulation of the debris flow tank test and the prediction of the risk range. The results show that the numerical simulation is in good agreement with the measured results; the application of GPU acceleration technology effectively solves the large amount of calculation in the process of debris flow simulation problem; and the model runs fast and efficiently on the PC. The model is an ideal tool to study the sudden debris flow process, and can provide timely and accurate decision support for disaster prediction.
2021, (4): 85-91.   doi: 10.12170/20201106002
[Abstract](48) [FullText HTML](18) [PDF 1991KB](13)
Abstract:
The stress and deformation state of the sheet pile wharf is an important factor to evaluate its safe operation. This paper presents a new distributed optical fiber monitoring technology for stress and deformation of piles based on the model test, which has been successfully applied to the prototype test of reinforced concrete cast-in-situ piles for sheet pile wharf. The results show that this method can accurately reflect the distribution of deformation, bending moment and stress along the pile length during the whole process of harbor basin excavation. It can effectively monitor and evaluate the operation and construction conditions in time, which can provide safety guarantee and construction guidance for the continuous stable operation of the sheet pile wharf. This monitoring method can realize the real-time monitoring for pile structure in full depth and full period of construction, thereby overcoming the shortcomings of traditional point monitoring methods in terms of resolution and accuracy, which has certain engineering practical significance.
2021, (4): 92-98.   doi: 10.12170/20200728003
[Abstract](46) [FullText HTML](8) [PDF 1705KB](11)
Abstract:
The proposed Three Gorges New Channel’s super-long water conveyance corridor runs at high head, high flow, short time and long distance. The water flow is strongly non-constant. It is very important to ensure safe operation of the ship lock. Therefore, aiming at the super-long water conveyance corridor of the last stage of the high head lock, our model numerically simulates the unsteady hydrodynamic characteristics of the water flow during valve opening. With this mathematical model, the evolution rules and influencing factors of the flow and the water level of the ship lock chamber and the valve door well are studied under different water conveyance corridor lengths and different valve opening times. The results show that longer length of the water conveyance corridor of the ship lock will increase the value and period of inertial superfall, extend the drainage time, reduce the lifting speed of lock chamber water level and decrease the reduction of the valve well water level during valve opening. Increasing the valve opening rate will reduce the drainage time, increase the lifting speed of lock chamber water level and decrease the reduction of the valve well water level during valve opening, but it can’t change the value and fluctuation period of inertial superfall. These results can be used as a reference for the design of the ultra-long discharge corridor in the last-step ship lock chamber of the Three Gorges New Channel.
2021, (4): 99-106.   doi: 10.12170/20200830001
[Abstract](41) [FullText HTML](13) [PDF 933KB](8)
Abstract:
The reconstruction and extension project of the long-distance water transfer canal in Northern Xinjiang is key to water delivery efficiency and project safety. In order to solve the existing problems of expansive soil, the new and old anti-seepage geomembrane connection, easy deformation of drainage pipes, and labor force shortage, the multi-functional gapping machine, concrete surface molding machine and other integrated machines were developed, construction efficiency and project safety were enhanced, and the demanded labors were sharply reduced. The KS hot melt adhesive bonding and inner tube spinning geomembrane technology were developed by laboratory test and field demonstration, which ensured the efficient connection of new and old impermeable geomembranes. The deformation resetting device of deeply buried underground hose was developed, through which the blockage of the water body in the foundation of the canal could be unclogged quickly, thus avoiding large excavation and providing support for the long-term safe operation of the channel. A series of equipment and technologies have been demonstrated and applied in the north Xinjiang water supply project, and produced great social and economic benefits. The research results have important reference values to the reconstruction and expansion of similar channel projects.
2021, (4): 107-113.   doi: 10.12170/20201026001
[Abstract](64) [FullText HTML](24) [PDF 2809KB](7)
Abstract:
In the Jiangsu reach of the Yangtze River, one of the most common silting-promoting structures in the cave collapses is tree top-stone. As cutting trees has negative impact on greening and ecology, a kind of curtain-stone composed of floating block, cloth (or geotextile) and stone is invented. This curtain-stone can block the flow and promote the siltation, which is seldom studied. Based on the force analysis of the curtain-stone placed in the equilibrium state in the flow, the differential equations of the forces acting on the curtain-stone micro element are listed, and then the distribution curve (surface) of the curtain-stone along the water depth can be solved, and the relevant coefficients in the curve are determined from the test data. The formula can be used to determine the horizontal projection length and buoyancy of curtain-stone, and also explain the mechanical mechanism of the floating block floating on or submerged in the water, and the curtain floating on or submerged in the river bottom. A local model of the pit collapse near Zhinan village in the Yangzhong section of the Yangtze River is established. The water blocking effects of curtain-stone and tree head-stone are compared in the scour pools of the model. And the water blocking effect results are the same. The use of curtain-stone can reduce the impact on ecology.
2021, (4): 114-121.   doi: 10.12170/20200805001
[Abstract](40) [FullText HTML](49) [PDF 1682KB](18)
Abstract:
A nested morphodynamic model of the Tongzhou Bay and its surrounding sea areas is set up with ADCIRC+SWAN and Delft3D+SWAN models. All Typhoons that affected the Tongzhou Bay during 1949 to 2019 are classified into five types according to the characteristics of their tracks, and for each type a typical typhoon is selected to drive the model. The morphodynamic changes of the study area induced by the typical typhoons are simulated, and the responses of channel-sand system in Tongzhou Bay and its surrounding sea areas to storm surges are analyzed. The results show that the thickness of sediment erosion and deposition in the planning port area during a typical typhoon process is generally small, within about ±0.40 m. The erosion and sedimentation induced by the north-passing typhoon and the east-passing typhoon are relatively large. Generally, siltation usually occurs outside the entrance of the Basin 3 of the Tongzhou Bay port area, while erosion usually occurs in the Yaosha and Lengjiasha shoals. After a typhoon process, obvious siltation occurred in the outer channel of Lengjiasha in the north of the port area, and obvious erosion occurred in the original Lengjiasha shoal area. Although the amount of siltation/erosion induced by one storm process is not large enough to affect the port operation and navigation, attention should be paid to the impacts of such siltation/erosion in a long-term time scale.
2021, (4): 122-130.   doi: 10.12170/20200904002
[Abstract](120) [FullText HTML](14) [PDF 1315KB](11)
Abstract:
Understanding the changes in the regime of precipitation intensity plays an important role in flood risk mitigation and water resources management. Based on the field data of daily and hourly precipitation from 9 rainfall gauge stations in the Rouyuanchuan watershed from 1980 to 2017 and 10 rainfall gauge stations in the Heshuichuan watershed from 1981 to 2017, the changes in the regimes of annual maximum precipitation intensity of 1 h (Ih) and 1 d (Id) and graded precipitation intensity are analyzed using the MK trend test method. Results indicate that:(1) Spatial distributions of Ih and Id are found quite different, with the spatial variation coefficient (CV) of Ih greater than that of Id, and CV of Ih and Id in the Heshuichuan watershed greater than that in Rouyuanchuan. (2) CV of Id in the Rouyuanchuan watershed is found to increase significantly (α=0.05) at a rate of 0.018/10 a while that in the Heshuichuan watershed is found to decrease significantly at a rate of −0.039/10 a. (3) The extreme Id values in the Rouyuanchuan watershed are found to increase significantly at a rate of 7.68 mm/(d·10 a). (4) It is found that no significant change of graded precipitation intensity happens in the Rouyuanchuan watershed while the precipitation intensity of moderate-grade rains and heavy-grade rains in the Heshuichuan watershed show significant increases at rates of 0.61 and 1.29 mm/(d·10 a), respectively.
2021, (4): 131-137.   doi: 10.12170/20210105002
[Abstract](39) [FullText HTML](19) [PDF 1249KB](14)
Abstract:
The local scour around bridge piers is one of the main safety influence factors of sea-crossing bridges in the nearshore region. Based on the survey data of six bridge piers of Jintang Sea-Crossing Bridge in Hangzhou Bay during 2014, 2015 and 2017, the scour effects around the bridge piers under bidirectional tidal flows were systematically studied. The general scour depth and the maximum local scour depth were analyzed respectively. It is found that the general scour depth is about 3.3~3.6 m, while the average local scour depth is about 8.3 m. The local scour holes extend in both upstream and downstream directions with elliptic shapes due to bidirectional tidal flows. The longitudinal length of scour hole is approximately linear with the maximum local scour depth with a ratio of about 10~12. While the scour hole width of each bridge pier is nearly the same, about 4~5 times the pier width. In addition, there is no obvious correlation between the width of scour hole and the maximum local scour depth. The research results about scour depth prediction and scour profile characteristics can provide a reference for sea-crossing bridge foundation design, maintenance and scour protection.
2021, (4): 138-144.   doi: 10.12170/20201014001
[Abstract](48) [FullText HTML](10) [PDF 1050KB](7)
Abstract:
Due to the long-term erosion of marine engineering by sea water, water molecules containing corrosive media infiltrate into concrete, making steel bars prone to chloride corrosion, causing structural expansion and cracking, which greatly reduces the service life of marine engineering. With the acceleration of marine engineering construction, the use of cement-based conductive composite materials for chlorine removal and corrosion protection has gradually received attention. Conductive composite materials were prepared by adding conductive materials into cement-based materials. Based on the study of mechanical properties and conductive properties of materials, we explored the effects of different dosages of polymer emulsion and conductive fillers, and cement-sand ratio on the dechlorination performance of materials. The influence mechanism of conductive fillers and polymer emulsion on the performance of materials was analyzed by SEM scanning analysis, and the mechanism of dechlorination and anticorrosion of materials was explored. The results show that the chloride ion content in the material can be significantly reduced by adding suitable conductive filler and polymer emulsion after 60 V DC piezoelectric infiltration for 180 min, and the chlorine removal efficiency is 84.24% higher than that of the specimen without conductive filler. The research results provide reference for reducing steel corrosion in marine concrete and improving service life.
2013, (6): 47-53.
[Abstract](1058) [PDF 1145KB](42)
2014, (3): 70-76.
[Abstract](3377) [PDF 1143KB](261)

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Publication Period: Bimonthly （1979 initial issiue）