Stability Evaluation And Process Control Of Soft Rock Slope

In the process of highway construction,it is inevitable to excavate the mountain body,especially in Sichuan and Guizhou areas.The geological conditions are complex and changeable,and the soft rock is widely distributed.Because of its softening and expansibility,the soft rock is more vulnerable to instability and destruction under the influence of excavation disturbance.Therefore,it is particularly important to study the stability of soft rock slope in highway construction in southwest mountainous areas.Based on the typical soft rock slope of a Expressway in Guizhou Province,this paper adopts the research methods of field investigation,theoretical analysis and numerical simulation(FLAC3D).Based on the unloading effect of excavation and the change of groundwater level,the slope is excavated without support and edges from the angles of displacement,stress,shear strain increment,safety factor,pore water pressure and seepage vector,respectively.The stability of excavation side support is evaluated dynamically.According to the principle of process control in slope engineering,the proper time,location and effective protection and reinforcement measures are selected to control the slope process,so as to improve the overall stability of the slope.The main research work and achievements of this paper are as follows:(1)In this paper,the main innovation and work focus is to treat the slope deformation and instability as a process of dynamic evolution with time,to simulate the whole process of slope deformation and instability from excavation to deformation,to analyze and evaluate the factors affecting the stability and stability at various stages,and to study the influence of groundwater level changes caused by excavation without support,excavation while support and rainfall on the slope stability.Dynamic evaluation of slope stability.Based on the results of dynamic stability evaluation,the process of slope failure is divided into four stages: creep deformation stage of the shallow surface of the slope;tensile crack stage of the back edge of the slope;settlement stage of the back edge of the slope,bulging stage of the foot of the slope;penetration stage of the plastic zone and formation of the sliding surface stage.In view of the different stability factors and deformation characteristics in each stage,appropriate engineering measures are adopted to simulate its control of stability and its influence on subsequent excavation,thus realizing the process control of slope.(2)Analyzing the numerical results,it is found that the excavation slope will produce unloading rebound deformation during excavation.The rebound deformation vector direction of the slope is perpendicular to the slope,pointing to the free surface,and the rebound deformation vector direction of the excavation platform is vertical upward;the unloading rebound amount of the excavation platform is larger than the unloading rebound amount of the excavation slope.The displacement vectors at the top of the slope are vertical downward,showing "settlement".The displacement vectors at the middle of the slope are roughly parallel to the slope surface,showing "shear".The displacement vectors at the lower part of the slope are "shear" at the excavated slope surface.(3)Under the condition of side-excavation and side-support,the horizontal negative displacement of excavation slope decreases,while the vertical positive displacement of excavation platform increases.This is due to the anchorage effect of anchor cables,which improves the anti-sliding force of the slope,reduces the horizontal deformation of the slope and reduces the impact on the unloading rebound deformation of the excavation platform.The maximum shear strain increment of each excavation stage is obviously reduced.Under the combined action of anchor cable frame beam and anti-slide pile,after excavating the first grade slope,the plastic area is still not connected,which shows that the supporting effect is good.(4)The rise of groundwater level will increase the water content and bulk density of rock and soil,increase pore water pressure and decrease effective stress,decrease the sliding resistance of slope,and increase the sliding force.At the same time,groundwater will react with rock and soil to produce softening effect,reduce cohesion and internal friction angle,and destroy the original mechanical equilibrium state of rock and soil of slope.Through the analysis of groundwater seepage vector diagram,it can be found that the greater the permeability coefficient of rock and soil,the faster the seepage velocity.When the groundwater level is lower than the potential sliding surface of the excavated slope,the influence of groundwater on the slope stability is small;when the groundwater level is higher than the potential sliding surface of the excavated slope,the groundwater has a greater impact on the slope stability.