Research On The Damage Catastrophe Rule Of Weathered Rock Slope Excavation And Anchorage Optimization Design Method

In recent years,with the rapid development of urban roads,high and steep weathered rock graben slopes have inevitably emerged,while the low structural strength of weathered rock soils is prone to decomposition,collapse and accumulation,so as the excavation depth increases,there is an urgent need to study its stability.In this paper,we analyse and study the stability of weathered rock slopes during excavation and service based on K2+300～K2+460 section of Shantou Avenue,and optimise the anchorage design for the parts prone to instability.-Based on the unsaturated theory,the evolution of the seepage field,stress field,displacement field and plastic zone of the weathered rock graben slope under heavy rainfall conditions was carried out.The following main research results were obtained:(1)A summary analysis of the hydrological and geological conditions of the weathered rock graben slopes of Shenshan Avenue was carried out based on the field exploration and indoor tests and combined with the basic engineering profile to determine the physical and mechanical research parameters.(2)The basic concept of strength reduction method in Midas GTS NX finite element software is introduced.Three excavation scenarios are designed for the excavation of weathered rock graben slopes,and two working conditions are imposed.The stress field,displacement field,plastic zone and stability evolution law during the excavation process are compared and analysed by numerical simulation of each scenario.The following results were obtained:(1)the stress of the slope at all levels during excavation decreases continuously,the stress state of the slope changes from compressive to tensile,the slope is relatively less affected by vertical stress and more affected by horizontal stress;(2)the displacement of each step gradually increases during excavation,and is accompanied by the phenomenon of surface uplift;(3)Under heavy rainfall conditions,with the passage of time,the internal water content of the slope increases,and the slope of the graben gradually tends to be less stable;(4)The plastic zone of each excavation step continues to expand and develop,and the stability is reduced.(3)According to the basic theory of dynamic loading displacement response ratio,the parameters for evaluating the dynamic loading displacement response ratio of graben slopes under excavation conditions are introduced;the excavation process of graben slopes is taken as the dynamic loading process,the dynamic change value during excavation is taken as the loading parameter,and the displacement change value triggered by the dynamic change is taken as the displacement response parameter to establish the dynamic loading displacement response ratio evaluation model of weathered rock graben slopes under excavation conditions.The response ratio evaluation model was established.At the same time,based on the damage mechanics of slope materials,the relationship between excavation and damage degree of road rift slopes was clarified;using the damage variable D as the correlation parameter,the mutual correspondence between the dynamic loading displacement response ratio η and the stability coefficient K of road rift slopes was established.Based on the numerical simulation results during the service period after the actual excavation of Shantou Avenue,and by placing a row of monitoring points at each step at an interval of 1 m in turn,the horizontal displacement and horizontal stress of each measurement point were refined,and the local stability coefficients of each monitoring point under normal and storm conditions of the slope were introduced,which were compared with the stability coefficients to achieve the effect of quantifying the location of the plastic zone.The conclusions show that:(1)the stability coefficient has a good negative correlation with the power increment displacement response ratio,according to this,for the weathered rock slopes where the upper part is overburden or the stability is worse than the lower rock and soil layer,by comparing the stability analysis of various design solutions,using the bending line excavation method of Option 2,the power increment displacement response ratio is the smallest and the stability coefficient is the largest;(2)the plastic zone is For the excavation steps where the plastic zone appears,the extreme value of the power incremental displacement response ratio of the monitoring points in each row of monitoring points is determined separately,and the critical slip surface of the slope is not a smooth curve connecting the extreme value of the power incremental displacement response ratio in each row of monitoring points.The position of the slope is connected with the smooth curve in turn,and the resulting curve is the critical slip surface of the slope.(4)The parameters to be determined for the optimum design of the main anchorage of the prestressed anchor are discussed in detail based on the principle of strip division,and an optimised design scheme is proposed.Numerical simulations are carried out between the original design support scheme and the optimised anchorage design scheme to analyse and compare the changes in stability of the two schemes.Under heavy rainfall conditions,the optimised anchorage design results in an effective stabilisation of the graben slope,with less displacement than the original support solution.Comparing the safety factors under normal and storm conditions,both solutions meet the code requirements in terms of serviceability.From an economic point of view,the economic cost of the optimised anchorage design is lower.