平卧“支撑拱”锁固滑坡动力学机理与稳定性判据

DYNAMICAL MECHANISM AND STABILITY CRITERION OF LANDSLIDE UNDER LOCKUP OF SOIL ARCHING

滑坡在渐进性变形过程中,因滑床或滑坡侧翼位置局部未贯通部位的存在,或滑坡启动以后受前进方向“束口状”地形的约束,滑体变形受限制或运动制动,不能充分失能,从而在这些受限约束部位形成由松散岩土体组成的平卧“支撑拱”结构。“支撑拱”结构的形成,相当于滑坡变形的锁固段,它一方面阻挡拱后向下滑移的堆积物,使它在这一带压密、隆起,成为滑体中的应力集中部位;同时又通过拱圈将滑体中心的部分下滑推力传递至两侧拱座,使拱座成为应力相对更为集中的部位。一旦土体中孔隙水压力的增高,使土拱与拱座基岩接触面间的抗剪强度降低到一定程度,将导致某一个拱座失稳被突破,整个拱圈崩溃,进而引起“支撑拱”上部滑体的突然滑动。根据物理模型实验应力分析,滑体中“支捧拱”结构表现为拱顶凸向坡体上方的“最大主应力拱”,而在其上方一定高度范围内还出现拱顶凸向坡体下方的“最小主应力拱”,据此建立了“支撑拱”的计算模型。假定滑坡岩土体为刚塑性体,在考虑滑体自重力、滑面抗剪强度与滑坡两翼摩阻力的共同作用下,以及最小主应力拱引起的滑体中应力重分布的情况下,确定了“支撑拱”(最大主应力拱)上的均布荷载;根据拱的塑性极限平衡条件,建立了拱稳定性的判据;并定量分析了拱效应出现的条件、拱保持最大与?

Due to the fact that either there still exists an unbroken part on bedding-plane and/or flanks in landslide at the critical failure stage, or there appears a narrow and limited sliding path in front of sliding mass after the onset of landslide, a horizontal soil arching is developed across the narrow limits between the flanks of landslide, leading to restriction of deformation or braking of movement. In landslide, soil arch acts as a locked segment that gives direct support to soils over crown and prevents them from slipping downward, resulting in compacting and swelling of soil mass here. On the other hand, soil arch transfers the majority of vertical load above crown onto the arch abutment (double flanks in landslide) through the crown, which makes the abutment become the place of stress concentration. Once a rise of pore pressure by compaction of soils reduces shear strength on plane between arch and arch abutment to a low one so that one of the abutments fails keeping equilibrium, the crown would buckle completely giving rise to whole sliding of the landslide. The stress trajectories obtained from model test indicate that an arched region is composed of two different stress arches, i.e., the maximum principal stress arch protruding upward and the minor principal stress arch dipping downward, and the computation model is proposed accordingly. It is supposed that the soil is in a state of plastic equilibrium and Mohr-Coulomb yield criterion is satisfied, the vertical load acting on the support arch is estimated by considering forces of self-weight of soils, shearing strength on bedding-plane, resistances at flanks, and stress redistribution caused by the soil arching effect. Consequently, the stability criterion of landslide is deduced and a practical case is analyzed, from which the presented study result is proved to be effective in the quantitative evaluation of stability of this kind of landslide.