考虑土体结构性的库岸滑坡成因机制和力学特征分析

An Analysis of Disaster-causing Mechanism and Mechanical Characteristics of Landslides of Reservoir Bank Based on Soil Structure

滑坡的成因机制和力学特征是指导滑坡防治策略的重要依据,在当前库岸滑坡仿真模拟中存在滑带土强度弱化假设不能反映土体的结构性损伤特征及未考虑变形参数同步弱化的问题,因而揭示的滑坡成因机制和力学特征失真。提出以应力水平代替塑性剪应变表征结构性损伤程度构建新的强度折减法,基于此分析了不同类型滑坡的渐进破坏过程、应力位移特征及稳定性衰减规律,揭示不同类型滑坡的成因机制,所得主要结论有:(1)推移式滑坡中部首先发生滑移导致上部土体失去支撑随之滑移并与之一起挤压下部土体,使下部土体剪切力增大明显进而产生较大剪切变形,最终形成整体剪切破坏面;因而推移式滑坡的主滑段在中部,牵引段在滑坡上部,抗滑段在滑坡下部;(2)牵引式滑坡中下部抗剪力不足以平衡剪切力率先滑移,使临近土体失去支撑抗滑力降低随之滑移,并依次迅速引发滑坡的"多米诺骨牌"式破坏,因而牵引式滑坡的主滑段在中下部,其上土体均为牵引段,其破坏面为剪切-拉剪-张拉复合型破坏面;(3)当发生一定剪切变形后,牵引式滑坡位移增长迅速并呈不可控态势,并由稳定迅速降低至失稳状态;而推移式滑坡则在发生较大剪切变形后长时间处于欠稳定状态,破坏前有较长的缓冲时间;(4)从灾害防治角度,推移式滑坡应注重"强腰",牵引式滑坡应注重"固脚"。

The formation mechanism and mechanical characteristics of landslides are an important basis for guiding landslide prevention strategies.In the current landslide simulation,the hypothesis of soil strength weakening cannot reflect the structural damage characteristics and the weakening of deformation parameters are not considered.Thus mechanical characteristics revealed are distorted.This paper suggests using stress level instead of plastic shear strain to characterize the degree of structural damage to construct a new strength reduction method.Based on this,the progressive failure process,stress and displacement characteristics and stability attenuation laws of different types of landslides are analyzed,which reveals the cause mechanism of different types of landslides.Main conclusions are as follows.(1)The main sliding section of the push type landslide is in the middle of the slope,the pull section is in the upper part of the slope,and the anti-sliding section is in the lower part of the slope.The main sliding section is destroyed first.Then failure gradually expands to the upper and lower parts.Finally a shear failure surface is formed,on which the shear strength is fully exerted.(2)The main sliding section of the pull-type landslide is at the foot of the slope,the pull section is in the middle of the slope,and the anti-sliding section is in the upper part of the slope.After the shear sliding of the main sliding section,the tension-shear sliding occurs quickly at the pull-type section and anti-sliding section because of losing the support from the main sliding section.And the shear strength of the rock and soil mass in the upper part of the pull-type landslide is not fully exerted.(3)For the pull-type landslide and push landslide whose initial stability state is similar,the stability state of the pulltype landslide decreases rapidly after the occurrence of large shear deformation,and failure of pull-type landslides happens suddenly and uncontrollably.But the push landslide is under metastable state for a long time before failure.So there is a long buffer time for push type landslides to reinforcement treatment.(4)From the perspective of disaster prevention,the push type landslide should pay attention to“strengthening the waist”,and the pull-type landslide should pay attention to“strengthening the foot”.