膨胀变形对膨胀土边坡稳定性的影响

当采用合理的强度参数时，根据常规极限平衡或极限分析方法的计算结果，很难解释一些膨胀土边坡会在极缓的坡度下发生失稳破坏的原因。事实上，由于膨胀土遇水后会发生显著的变形，在饱和区与非饱和区交界面附近会出现很大的剪应力。因此，在膨胀土边坡的稳定分析中，需要考虑这种因素的影响。根据塑性力学的上限定理，严格地导出了考虑膨胀应力作功的功能平衡方程。根据强度储备定义的安全系数即隐含在这一方程中，它可以通过迭代方法求解。边坡稳定的上限分析在数值上是利用了单元集成法来完成的。这不仅能方便地利用应力分析的成果，而且能进行滑裂面的优化，从而找到最小的安全系数。对一个坡度为1:4的膨胀土边坡的稳定计算结果表明，膨胀变形会使边坡的安全系数显著减小。当考虑膨胀时，优化得到的破坏模式是在浅层出现一个局部的滑动，它会牵动其上部的土体也相继出现局部滑动，这正好符合膨胀土滑坡时所常见的牵引性的特征。

Effect of swelling deformation on stability of expansive soil slope

Adopting reasonable shear strength parameters, calculation results obtained from conventional limit equilibrium method and limit analysis method can not explain the reason why some expansive soil slopes failure under a fairly small dip angle. In fact, there has obvious swelling deformation when water infiltrating into the soil, so as to induce large shear stress near the border between the saturated and unsaturated regions. This effect should be considered in the stability analysis of expansive soil slope. Based on the upper bound theorem in plasticity, a new energy-work balance equation has been strictly derived including the work rate done by expansive stress. Factor of safety defined by strength reduction explicitly exists in such equation can be solved by iteration; and minimized by optimizing the slip surface. The upper bound limit analysis of the slope is numerically performed by element integration method (EIM). By means of EIM, the calculation result obtained from stress analysis can be conveniently utilized. Applying the presented method to an expansive soil slope with a gradient of 1:4, it is demonstrated that the expansive deformation brings obvious decrease to the safety factor of the slope. When considering expansive of the soil, the critical failure pattern obtained from optimization is a small range of shallow slide, which will induce the upside soil mass into another small range of shallow slide. This agrees well with the common traction characters in the failure of expansive soil slope.