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Influence of coarse-grained content in the gravelly soil on steady seepage of high earth-rock dam
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摘要: 高心墙堆石坝心墙防渗料多采用砾石土，当砾石土的粗粒含量（指质量分数，下同）超过50%时，渗透系数很可能超过规范要求，不利于坝体渗透稳定。通过对粗粒含量超标单元赋予不同的渗透系数，采用三维有限元法分析了心墙局部砾石土粗粒含量超标时对坝体渗流的影响。结果表明：心墙局部砾石土粗粒含量超标对坝体的渗流场分布和单宽渗流量影响都较小，对心墙内渗透坡降影响较大，最大渗透坡降都出现在未超标单元处。对于超标区域在中下部的情况，当超标单元粗粒含量小于55%时，渗透坡降最大增幅为36.4%；超标单元粗粒含量大于55%时，最大渗透坡降显著增大，且会超过允许坡降，不利于坝体渗透稳定。因此，在实际工程中应结合砾石土料的级配和细粒含量情况，做好下游反滤层的设计，并严格控制砾石土的施工压实度，以保证坝体安全。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.
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图 1 渗透坡降和渗流量对网格尺寸的依赖性
Figure 1. Dependence of seepage gradient and seepage discharge on the mesh size
图 3 心墙下部粗粒含量超标20%时孔压分布
Figure 3. Distribution of pore pressures in the cores having an over-standard rate of 20% at the power part
图 4 心墙下部粗粒含量超标时渗流出逸高程和单宽渗流量的变化
Figure 4. Changes in the seepage exit elevation and the seepage discharge per unit width for the cases having a coarse-grained content larger than 50% in the lower part
图 5 心墙不同区域粗粒含量超标时最大渗透坡降
Figure 5. Changes in the maximum seepage gradient in the cores having a coarse-grained content larger than 50%
图 6 心墙不同区域粗粒含量超标时心墙内未超标单元渗透坡降变幅(虚线为增幅，实线为减幅)
Figure 6. Changes in the maximum gradient range in the elements having a coarse-grained content equal to 50%
图 7 心墙不同区域粗粒含量超标时心墙内超标单元渗透坡降变幅(虚线为增幅，实线为减幅)
Figure 7. Changes in the maximum gradient range in the elements having a coarse-grained content larger than 50%
图 8 心墙不同区域粗粒含量超标时单元渗透坡降超过允许坡降体积百分比
Figure 8. Changes in the volume percentage over allowable seepage gradient in the cores having a coarse-grained content larger than 50%
表 1 坝体材料计算参数
Table 1. Calculation parameters of dam materials
材料
名称孔隙率 渗透系数/
(cm∙s−1)破坏渗透
坡降允许渗透
坡降心墙（P5=50%） 0.26 1.00×10−5 7.00 3.50 心墙（P5=55%） 0.26 2.24×10−5 6.38 3.19 心墙（P5=60%） 0.26 5.00×10−5 5.75 2.88 心墙（P5=65%） 0.26 1.12×10−4 5.13 2.56 心墙（P5=70%） 0.26 2.50×10−4 4.50 2.25 反滤 0.22 3.00×10−3 − − 过渡 0.21 3.00×10−2 − − 堆石 0.20 3.00×10−1 − − 
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