In-site Direct Shear Test And Excavation Stability Research On Bedding Slope Of Chengdu-Ya’an Expressway

The geological structure of the red bed zone in the western mountainous area is complex,and the regional rock mass is dominated by red bed soft rock.When engineering construction is carried out in the red bed area,the reasonable determination of rock mass mechanical parameters and the stability of bedding rock slope excavation have always been the most difficult points in engineering construction.The Chengdu-Ya’an Expressway Jinjiguan Interchange Project is located in Mingshan District,Ya’an City,Sichuan,in the red bed zone of the western Sichuan Basin.The rock mass on the left side slope of the K3+585～K3+945 section of the project is mainly red-bed mudstone,in which the lower rock is softer and the structural integrity is poor.Based on the Chengdu-Ya’an Expressway Interchange Project,this paper uses various methods such as field test,field monitoring and numerical simulation to study the mechanical parameters of red mudstone and the stability of bedding slope excavation.The main work and research results are as follows:(1)The peak shear strength parameter of the rock layer obtained from the field direct shear test is:c~*=8.4k Pa,φ~*=28°;The residual strength parameters are:c_c=5.3k Pa,φ_c=26.5°;Compared with the reported value of the geological survey,the results obtained from the field direct shear test can more truly reflect the shear strength of the bedding slope.(2)By analyzing the on-site monitoring data of the bedding slope of Luojia Mountain,it can be seen that the horizontal displacement of the measuring point on the top of the third-level slope is the largest,and the slope deformation of the entire monitoring section of the slope moving toward the excavation surface is not obvious during the construction process.Sliding section.During the monitoring period,the maximum horizontal displacement increment of the measuring orifice is 0.25mm/d,which is less than the deformation warning value,and the overall displacement of the slope is still within the controllable range.(3)Combined with the field monitoring data,the field direct shear test results and the finite element analysis method considering the unloading effect were applied to the supporting project,and the excavation process of the bedding slope was simulated.The calculation results showed that:1)Adopt The calculated results of the field direct shear test parameters can more accurately reflect the development trend of the slope displacement;2)The safety factor of the slope after excavation is 1.49,and the whole is in a safe and stable state.Timely support can effectively control the development of the slope unloading area.Improve the stability of the slope;3)The unloading area of the slope is mainly concentrated in the shallow surface of the excavated slope,and the unloading depth continues to expand with the excavation process.After the excavation is completed,the unloading depth of the slope is 5.16m;4)On the side During the slope excavation process,the displacement field presents an obvious spatial effect,the principal stress in the stress field decreases,and the direction deflects.(4)Establish a numerical model through the Plaxis2D finite element software,and use the finite element analysis method considering the unloading effect to analyze the influence of the structural surface characteristics on the stability of the bedding slope excavation.The research shows that:1)After considering the unloading effect,The stability coefficient of unloaded slope is smaller than that of unloaded slope,and the maximum horizontal displacement is larger.During the gradual excavation of the slope,the unloading area of the slope continues to expand as the number of excavation stages increases.2)When the bedding slope is excavated and unloaded,the unloading failure of the structural surface mainly occurs.Compared with the rock mass,the structure is more sensitive to the unloading effect,the unloading area is larger,and the growth rate is faster.3)The safety factor of the bedding slope changes with the inclination of the structural plane in a concave shape with high at both ends and low in the middle.The distance between the structural planes has little effect on the stability of the slope.4)The distribution of unloading area on bedding slopes is related to the inclination angle of the structural surface and the excavation slope angle.When the inclination angle of the structural surface is smaller than the excavation slope angle,the unloading area has a wide upper and narrow distribution characteristics.When digging the slope angle,the unloading area is characterized by a narrow top and a wide bottom.