河谷宽高比对高心墙坝黏土垫层剪切强度的影响

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。

Effects of width-height ratio of river valley on shear strength of clay layer in high core rockfill dams

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°.