Study On The Stability Of The Entrance Slope Of A Tunnel

The thesis is based on the proposed project for evaluating the slope stability of a tunnel of a special rail transit line,taking the entrance slope of a tunnel as the research object,by collecting high-resolution topographic data,formation data and engineering geological data at the entrance of the tunnel,field surveys of rock joints?part including cleavage surface?and rock mechanics tests were conducted on the slope,and the structural characteristics of the rock mass of the slope were investigated and analyzed in detail.The qualitative analysis method of stereographic projection and CSMR were used to analyze the slope rock mass stability and rock mass classification respectively,and FLAC3D numerical simulation software based on finite difference principle was used to quantitatively analyze and evaluate,and the analysis results are compared.The research results provide reference and theoretical basis for the construction of the slope project,the main research results of the paper are as follows:?1?Considering the development characteristics of the dominant structural plane of the rock mass,the slope rock mass is analyzed by the stereographic projection method,the possible sliding block formed by the combination of the dominant structural plane and the slope tendency is in a stable state under natural conditions,but it is necessary to clean up the fractured rock mass?block?with weathering fracture and unloading fracture on the slope surface.?2?The modified CSMR method can reduce the influence of human factors on the slope stability evaluation,the evaluation results show that the rock mass quality grade at the entrance of the tunnel is grade III,and the slope is in a stable state under natural conditions.?3?Through the FLAC3D software simulation analysis of slope stability sensitivity under single factor,the influence of slope angle,slope height and tunnel depth on slope stability was analyzed,the influencing factors show that:The safety factor of slope decreases with the increase of slope angle in the range of 15°⁷5°;The safety factor of slope decreases with the increase of slope height between 40m and 140m;With the increase of the depth of the tunnel portal,the greater the value of the slope safety factor,the more favorable for the stability of the slope.?4?FLAC3D was used to simulate the displacement field,stress field and shear strain increment of the rock mass at the entrance of the tunnel,the results show that the maximum displacement value of the slope colluvium at the slope toe is 1.08cm,and the maximum tensile stress value of the slope surface is 1.97×10⁵Pa,the shear stress increment is mainly distributed in the slope colluvium at the slope toe,and the maximum value of the shear strain increment is 1.525×10^-3;At the same time,the safety of the slope in the natural state is obtained the coefficient is 2.07,indicating that the slope is in a stable state under natural conditions,which is basically consistent with the evaluation results using the stereographic projection method and the CSMR method.Stability simulation analysis of the slope under excavation conditions.After unsupported excavation,the safety factor of the slope is 1.29,which is37.6%lower than the stability factor of the slope before excavation,in order to ensure the stability of the slope,corresponding protective measures should be taken during excavation to avoid accidents.As the seismic intensity increases,the safety factor of the slope decreases,and the plastic zone of the slope runs through from the upper edge to the lower edge of the colluvium,forming a shear slip surface,and the instability and failure of slip deformation occurs.The shear strain increment area and plastic area mainly occur the slope colluvium of the slope,for the safety of surrounding buildings?structures?,protective measures should be taken for the slope colluvium.