Study On Mechanical Characteristic Of Typical Soft Rock And Design Method Of Tunnel Under High Geo-stress Condition

With the implementation and deployment of “the Belt and Road” and “Sichuan-Tibet Railway” national strategies,the infrastructure construction stressing on western area in China.However,the serious large deformation problem in tunnel caused by high geo-stress is often encounterd during tunnel construction process in western area.The fundamental premise that solves the problem is to have a clear understanding on the mechanical properties of soft rock under high geo-stress condition,and to consider the influence of high geo-stress on its mechanical properties in tunnel design process.But,the influence of confining pressure on the mechanical properties of soft rock is often neglected in calculation or analysis process for tunnel in soft rock,moreover currently the design method for soft rock tunnel is mainly based on engineering experience and its applicability is limited.Therefore,this paper presents a research which mainly contained 4 aspects: the mechanical properties of soft rock,the elastoplastic analytical solution for surrounding rock under high geo-stress condition,the longitudinal deformation curve calculation for soft rock and the design method for soft rock tunnel in high geo-stress region.And research methods included theoretical derivation,numerical simulation,statistical analysis and data research are adopted.The main conclusions were drawn as follows:The influence of confining pressure on deformation and strength characteristics of typical soft rocks(phyllite and slate)was ascertained.The calculation for deformation and shear strength parameters of soft rock due to confining pressure was respectively proposed,baseing on triaxial compression experimental datas.Basing on mechanical characteristics of soft rock,the stress partition of surrounding rock were proposed.And the theoretical calculation for stress and displacement field of soft rock was presented in accordance with Mohr-Coulomb criterion,plastoelasticity,and finite difference method,and the proposed calculation was validated accuracy and reasonable with the results of other scholars.Moreover,the stress and displacement variation of soft rocks were found out,and the calculation of ground reaction curve(GRC)was presented.Based on FISH programming,a new numerical simulation method was proposed that could consider the mechanical characteristics of soft rock under high-geo condition.The variation of longitudinal deformation curve of surrounding rock was ascertained.Finally,a new longitudinal deformation curve(LDP)for surrounding rock was presented.The calculation for support chracteristics curve(SCC)of tunnel was proposed.Based on convergent constraint method,the support design method for soft rock tunnel under high-geo stress condition was established.Moreover,the safe evaluation method for tunnel was proposed whose evaluation indexs are ultimate bearing capacity and ulitimate deformation of tunnel.Finally,the proposed method was applied to the typical soft rock tunnel project under high-gro stress condition,which verified that the method can satisify the accuracy requirement of engineering design.