Stability Evaluation And Deformation Treatment Of Layered Tunnel Surrounding Rock Under High Geostress Based On Initial Stress Field Inversion

With the focus of transportation construction in our country shifting to the central and western regions,the southwestern region has become one of the most active areas for expressway construction.However,tunnels built in this area are usually deeply buried with developed tectonic stress,and high in-situ stress has become a common problem.Meanwhile,rock mass with layerd joints is often encountered during tunnel excavation,and the structural characteristics of layered joints affect the deformation and failure characteristics of surrounding rocks greatly.Therefore,it is particularly important to study the deformation and failure of layered tunnel surrounding rocks under high in-situ stress and its prevention measures.In view of above problems,this paper relies on Jiaoding tunnel project of Zhaole expressway in Yunnan,and uses the high in-situ stress deep-beried layered surrounding rock tunnel large deformation segment as the research object.The following research work was carried out:(1)The initial in-situ stress field of the tunnel surrounding rocks was inverted through the hydraulic fracturing test at the floor of the excavated tunnel,and it confirmed that the horizontal tectonic stress in the engineering area was dominant and the direction of maximum horizontal principal stress was consistent with the direction of the regional principal compressive stress;(2)The stability of the surrounding rock of the tunnel is graded and predicted based on the results of in-situ stress testing and the on-site monitoring and measurement data with considering the effects of layered joints of the surrounding rock.The possibility of large deformation for surrounding rock in the testing section is proposed by grading such aspects including rock hardness,initial in-situ stress level,large deformation of soft surrounding rock,and rock burst.(3)Using the discrete element numerical software 3DEC,the effects of different rock thickness and initial in-situ stress levels towards deformation of surrounding rock is compared and analyzed according to different indexes including surrounding rock displacement,characteristic point displacement curve,and plastic zone.The results show that with the increase of layer thickness,the deformation of surrounding rock and area of plastic zone gradually decrease.With the increase of initial in-situ stress,the deformation of surrounding rock and area of plastic zone gradually increase.And the displacement curve of characteristic points of layered tunnel surrounding rock shows obvious time lag as the time step increases.(4)The support plan including double-layered initial support and grouting reinforcement was proposed according to tunnel deformation control concept and treatment principles of weak surrounding rock.And its rationality was proved by comparing the monitoring data before and after the treatment.