Study On Stability Of Secondary Excavation Of Existing Supported HighSlope

With the rapid development of economy,people’s demand for traffic is increasing,so some expressways in our country can not meet the current traffic demand,and need to be rebuilt and expanded.Highway reconstruction and expansion projects need to excavate the existing slope,while secondary excavation of high slope needs to break the original supporting structure,change the original stress state of the slope,and random excavation is prone to instability and destruction.Therefore,based on the reconstruction and expansion project of Beijing-Shanghai Expressway,the stability of secondary excavation of high slope with existing supporting structure is studied by means of field investigation,theoretical analysis and numerical simulation.The main conclusions are as follows:(1)Through field investigation and laboratory test on the slope of Beijing-Shanghai Expressway,the engineering information of K499 slope and K503 slope is mastered.Stereographic projection method is used to analyze the stability of the slope.It is found that K499 slope has good stability,while K503 slope has poor stability.It is necessary to focus on analysis in K503 slope.(2)The influence factors of slope stability are analyzed,and the relationship between each factor and safety factor is discussed.The grey relational degree method is used to determine the influence of each factor on the slope safety factor,which is in turn the pre-stressed anchor cable support>slope surface morphology>cohesion>internal friction angle>severity>slope degree>slope height.(3)The grey relational degree method is introduced into the fuzzy comprehensive evaluation,and a new slope evaluation model considering anchor cable support is established.The fitting formula of safety factor is put forward.It is found that the stability of K503 slope is as follows:supporting slope after excavation>supporting slope before excavation>supporting slope after excavation>unsupported slope before excavation>unsupported slope before excavation.(4)The calculation model of K503 slope is established by using Midas GTS software,and the reliability of the model is verified by comparison.By analyzing the slope with or without anchor rope support,it is found that the anchor rope support has a great influence on the safety factor of the slope and the deformation of the slope surface.In order to reduce the impact of the existing anchor rope support on the demolition and ensure the safety of the second excavation,the paper puts forward the following proposals:Fourth and fifth grade slope support is demolished,and then excavation support is excavated.After that,support is removed once,slope excavation once,support once.The stability of the slope is not linearly related to the excavation depth of each grade.When the excavation depth is 10 meters,the stability of the K503 slope is better.(5)Different excavation methods are used to simulate the secondary excavation process of existing supporting high slope.The results show that the proposed excavation method can reduce the adverse effects caused by the demolition of existing pre-stressed anchor cables and improve the stability of pre-excavation of the slope.The influence of pre-stressed anchor cables at different positions on the slope is different.The construction of the first grade slope has a greater impact on the stability of the slope,while the construction of the second and third grade slope has a smaller impact on the slope.