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Analysis of collapsing gully erosion mechanism in southeast Hubei under rainfall conditions based on ABAQUS software
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摘要: 以研究崩壁在地下水抬升与不同类型降雨联合作用下的失稳模式与渗流场特性为目标，基于野外勘查和相关物理分析获取的鄂东南崩岗区典型风化岩土体剖面各层次基本指标数据，尝试从崩壁渗流场与应力场两场耦合的角度，运用数值试验探讨单次降雨诱发下水力因素影响崩岗侵蚀的过程与机理。结果发现：长期小雨环境下，崩壁破坏方式属于崩壁中下部土层局部被淘空与砂土层上覆土体整体滑移相结合；短时强雨环境下则表现为坡面浅层（分层）流滑破坏。但无论何种降雨类型都存在一个促使崩壁砂土层被水蚀并退去后形成凹腔(龛)的降雨前期阶段，直到龛深达到一极限值，龛体积不再扩大，转为历时较短的崩壁失稳前的降雨后期阶段。强降雨入渗产生的渗流区域主要分布在崩壁浅层地表，引起浅层土体持续软化，剪应力明显增大。伴随降雨历时的延长，坡面浅土层出现暂态饱和区且湿润峰(零压面)逐渐向崩壁深处推移，地下水位线逐渐抬升并以出露泉方式对砂土层下部造成机械潜蚀。分析结果与野外观测现象较为一致。
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关键词:
- 崩岗崩壁 /
- 降雨入渗 /
- 失稳模式 /
- ABAQUS耦合分析 /
- 渗流场
Abstract: Aiming at investigating the instability mode and dynamic response of the seepage field of the collapse wall under the combined interaction of groundwater uplift and different types of rainfall duration, on the basis of mechanical index parameters of rock and soil layers of the collapsing hill obtained from in-situ observation and relevant geotechnical physical model tests, we attempt to explore the process and mechanism of hydraulic factors affecting the collapsing gully erosion under a single rainfall from the angle of coupling seepage domain and stress field of collapse wall through performing plenty of numerical experiments. The FEM analysis results indicate that the failure mode of the collapse wall in successive light rain environment belongs to the combination of local erosion of the middle and lower soil layers of collapse wall and integral-sliding failure of the soil body above the sandy soil layer, and in short-term heavy rain environment, the failure mode of the collapse wall is manifested by the (layered) flow sliding of the shallow slope surface. Whereas, no matter what type of rainfall, there must be an earlier stage (lasting for a long time) of precipitation that causes the sandy soil layer of the collapse wall to be eroded by water to form a concave cavity. Until the depth of the concave cavity reaches an ultimate value, the volume of concave cavity will no longer expand, and it will turn into a later stage of precipitation before the collapse wall is in critical failure status. The seepage areas generated by rainfall infiltration mainly occur in the shallow soil layers of the collapse wall, as a result, the shear strength properties of the shallow soil unceasingly weaken and the maximum shear stress increases obviously. With the prolongation of rainfall duration, a transient saturated zone appears in the surface soil layer of the catchment slope and the wetting peak (zero pressure surface) gradually moves towards the deep strata of the collapsing gully wall. The groundwater level line gradually rises and thus causes pipe erosion to the bottom of the sandy soil layer by (downward) outcropping springs. The analysis results are in good agreement with the field observation phenomena. -
图 1 典型崩岗侵蚀地貌(降雨刚刚停止)
Figure 1. Typical collapsing gully erosion landform after rainfall
图 2 采样点处崩壁地质纵剖面概化示意
Figure 2. Generalization of geological longitudinal profile of collapse wall at sampling points
图 6 崩壁真三维整体模型及二维有限元网格剖分
Figure 6. True three-dimensional global model and 2D FE grid partition for collapse wall
图 7 降雨不同时刻崩壁域内塑性应变区等值云图的动态演变(事件1)
Figure 7. Equivalent nephogram evolution of plastic strains zone of collapse wall for different time durations of rainfall (event 1)
图 8 降雨环境下不同时刻的总位移矢量(事件１，单位： m)
Figure 8. Vectors chart of total displacement and deformation for different time durations of rainfall (event 1, unit: m)
图 9 隐藏龛所在单元后崩壁的总位移等值云图( 事件１，单位： m)
Figure 9. Equivalent nephogram of total displacement of caved wall after hidden concave (hollowed) cavity (event 1, unit: m)
图 10 各土层监控点水平位移 U1变化规律(以向右为正)
Figure 10. Variation curves of U1 of monitoring points of soil layers versus continuous rainfall duration (event 1)
图 11 事件1降雨停止时刻崩壁流速矢量( T =164.00 h)
Figure 11. Current velocity vectors of collapse wall at rainfall stop point in event 1 ( T =164.00 h)
图 12 事件2降雨不同时刻的总位移云图(单位： m)
Figure 12. Total displacement contours for different time durations of rainfall in event 2 (unit: m)
图 13 事件2不同时刻崩壁的总位移矢量(单位： m)
Figure 13. Total displacement vectors of collapse wall for different time durations of rainfall in event 2 (unit: m)
图 14 降雨事件2雨停0.77 h后的流速矢量
Figure 14. Vectors of the current velocity of collapse wall after rainfall stop 0.77 h (event 2)
图 15 天然状态下崩壁剖面的稳定孔隙水压力分布与浸润面(单位： kPa)
Figure 15. Steady pore water pressure distribution and phreatic line of collapse wall profile under natural condition (unit: kPa)
图 16 极端降雨天气下浸润面变化(单位： kPa)
Figure 16. Changes of saturated surface during extreme rainfall process (unit: kPa)
图 17 极端降雨环境下应力等值分布云(ABAQUS默认应力以拉为正,单位： kPa)
Figure 17. Stress equivalent distribution nephogram of collapsing gully wall in extreme rainfall environment (unit: kPa)
图 18 极端强暴雨停止半小时后的塑性形变及位移
Figure 18. Plastic deformation and total displacement vectors half an hour after extreme rainstorm stopped
表 1 崩壁各岩土层初始物理力学参数
Table 1. Basic physico-mechanical parameters of soil masses of collapse wall
土层编号 土壤质地 Hs/m Kws/ $\left( {{\rm{mm\cdot h}}^{ - 1}} \right)$ cs/kPa n/% ${\omega _*}$ /%$\gamma /$ $\left( {{\rm{kN\cdot}}{{\rm{m}}^{ - 3}}} \right)$ es ${\;\rho _{\rm{d}}}/$ $\left( {{\rm{g\cdot c}}{{\rm{m}}^{ - 3}}} \right)$ ds/ $\left( {{\rm{g\cdot c}}{{\rm{m}}^{ - 3}}} \right)$ Es/MPa $\nu $ $\varphi /{\rm{^\circ }} $ ①表土层 黏壤土 7.0 54.600 18.62 47.7 23.95 16.113 0.912 1.30 2.486 9.3 0.34 25.7 ②红土层1 黏壤土 3.4 13.371 35.36 46.0 22.10 17.216 0.852 1.41 2.611 18.5 0.35 27.1 ③红土层2 砂质
黏壤土2.3 9.306 73.19 45.5 20.42 16.738 0.835 1.39 2.550 20.8 0.31 29.9 ④砂土层 砂质壤土 0 11.665 14.05 48.1 21.25 16.248 0.927 1.34 2.582 21.2 0.30 29.3 ⑤碎屑层 壤质砂土 － 24.353 40.10 49.0 24.98 18.000 0.961 1.44 2.824 55.5 0.28 36.0 注：Hs为土层底面高程；Kws为饱和渗透系数；cs为有效黏聚力；ds为土颗粒相对密度； ${\omega _*}$ 为天然含水率；$\gamma $ 为天然重度；$n$ 为孔隙率；es为孔隙比；${\rho_{\rm d}}$ 为干密度；Es为杨氏模量；$\nu $ 为泊松比；$ \varphi$ 为有效内摩擦角。
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