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Effects of width-height ratio of river valley on shear strength of clay layer in high core rockfill dams
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摘要: 掺砾黏土高心墙堆石坝需要在心墙与坝基面接触部位设置纯黏土垫层, 以探讨心墙与坝基接触面处的应力状态和黏土垫层的剪切强度。三维有限元数值分析主要考虑了河谷宽高比的影响, 经计算得到心墙与坝基接触面处的应力分布, 并按莫尔-库伦强度准则评估黏土垫层的抗剪强度。结果表明, 心墙与岸坡接触面上剪应力和正应力大小随着坝高变化明显。正应力自坝顶向下大致呈线性增大, 在接近坝底附近达到最大值; 剪应力自坝顶向下先增后减, 最大值发生在坝底向上约1/5坝高处, 当岸坡角为45°左右时其值最大。根据抗剪强度准则, 心墙底面黏土垫层不会发生剪切破坏; 岸坡面中上部强度较低, 当岸坡角达到或超过45°时, 上部黏土垫层会发生剪切破坏。与对称河谷模型相比, 实际工程模型左岸岸坡中下部黏土垫层偏安全, 中上部以及右岸抗剪强度系数相近。据此, 给出了岸坡角45°临界值, 在岸坡坡角达到或超过45°的狭窄河谷中修建高心墙堆石坝时, 建议采取工程措施防止黏土垫层在相应部位发生大剪切变形以及剪切破坏。Abstract: For the high gravel-mixed clay-cored rockfill dams, a pure clay layer is needed to be placed between the core wall and the dam foundation.This paper discusses the stress state on the core-foundation interface and the shear strengths of the clay layer.3D finite element calculations are performed, considering the effects of width-height ratio of the dam.Stress distributions on the interface are obtained and shear strengths of clay layer are evaluated based on the Mohr-Coulomb criterion.The following results are achieved from numerical analysis:the shear and normal stresses on the bank slope interface are influenced significantly; the normal stress on the slope interface increases almost linearly with the decreased height and reaches the maximum value near the bottom corner; the shear stress first increases with the decreased height and then decreases with the peak value at around 1/5 of the dam height above the bottom.The peak shear stress is the largest when the slope angle is about 45°.According to the shear strength criterion, the failure will not occur in the bottom clay layer.In the slope clay layer, the strength is lower in the upper part.Furthermore, the shear failure will occur in the upper slope clay layer for the steeper slopes with an angle close to or greater than 45°.Compared with the symmetric model, the clay layer of an actual engineering model is safer on the lower part of the left bank slope as well as the shear strength coefficient is approximate on the upper part and the right bank slope.According to the results mentioned above, the critical bank slope angle of 45° is obtained.It is advisable to take some engineering measures to prevent large shear deformation and shear failure in the corresponding parts of the clay layer when the high core wall rockfill dam is built in a narrow valley with a slope angle close to or greater than 45°.
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Key words:
- high clay-cored rockfill dam /
- width-height ratio /
- clay layer /
- interface /
- stress state /
- shear failure
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图 2 不同河谷宽高比计算方案示意(单位:m)
Figure 2. Schematic diagram of calculation schemes with different width-height ratios (unit:m)
图 3 心墙底面剪应力沿坝轴线的分布
Figure 3. Distribution of axial shear stress at bottom of core wall
图 4 心墙底面正应力沿坝轴线的分布
Figure 4. Distribution of axial normal stress at bottom of core wall
图 5 顺河向剪应力随距离的分布
Figure 5. Distribution of downstream shear stress along with thickness of core wall
图 6 顺河向正应力随距离的分布
Figure 6. Distribution of downstream normal stress along with thickness of core wall
图 7 岸坡向剪应力分量沿高程分布
Figure 7. Distribution of slope-direction shear stress along with elevation
图 8 顺河向剪应力分量沿高程分布
Figure 8. Distribution of downstream shear stress along with elevation
图 9 1 306 m高程岸坡向剪应力分量沿心墙厚度的变化
Figure 9. Distribution of slope-direction shear stress along with thickness of core wall (1 306 m)
图 10 1 306 m高程河流向剪应力分量沿心墙厚度的分布
Figure 10. Distribution of downstream shear stress along with thickness of core wall (1 306 m)
图 11 心墙岸坡中心线上总剪应力随高程的分布
Figure 11. Distribution of total shear stress along with elevation on centerline of bank slope
图 12 心墙岸坡中心线上正应力随高程的分布
Figure 12. Distribution of normal stress along with elevation on centerline of bank slope
图 13 1 306 m高程总剪应力沿心墙厚度的分布
Figure 13. Distribution of total shear stress along with thickness of core wall (1 306 m)
图 14 1 306 m高程正应力沿心墙厚度的分布
Figure 14. Distribution of normal stress along with thickness of core wall (1 306 m)
图 15 总剪应力与岸坡坡角的关系
Figure 15. Relationship between total shear stress and angle of slope
图 17 黏土料排水三轴剪强度包络
Figure 17. Drainage triaxial shear strength envelope of clay material
图 19 1 358 m高程R沿心墙厚度的分布
Figure 19. Distribution of R along with thickness of core wall (1 358 m)
表 1 有限元数值计算方案
Table 1. Computation cases for numerical analysis
计算方案 河谷宽高比 岸坡角 岸坡坡度 方案1 5.523 23.71° 1:2.277 方案2 4.431 30.00° 1:1.731 方案3 3.338 40.17° 1:1.185 方案4 2.646 50.00° 1:0.838 方案5 2.123 60.00° 1:0.577 方案6 -左岸 4.431 23.71° 1:2.277 -右岸 40.17° 1:1.185 方案7 平面应变 
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表 2 主堆石料邓肯-张E-B模型参数
Table 2. Duncan-Chang E-B model parameters of main rockfill materials
材料 K n Rf c/kPa φ0/° Δφ0/° Kb m Kur Pa/kPa ρ/(g·cm-3) 掺砾黏土心墙 631 0.17 0.63 104 42 15.6 602 0.21 1 211 100 1.89 上游堆石料 1 465 0.19 0.79 97 49 9.7 805 0.03 2 397 100 2.18 下游堆石料 1 446 0.14 0.81 98 48 8.7 776 0.09 2 385 100 2.18
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