New Solution For Elastoplastic Analysis Of Surrounding Rock Of Loess Tunnel Based On Joint Strengh

With the rise of the economy in the Midwest and the development of transportation,Loess Tunnels can be seen everywhere in the Loess Plateau in the Midwest of China.It has been a con-corn of geotechnical engineering to reasonable analysis of the plastic zone and mechanical behavior of surrounding rock stress redistribution after tunnel excavation has circles.The stress is distributed again after the loess tunnel is excavated.The stress state of the excavated free surface gradually changes from the compression shear failure state to the tensile shear failure state with the process of stress unloading.The surrounding rock is prone to tensile shear failure before the initial lining support.Loess is a special structured soil,and the tensile strength of loess is large,will inevitably have a great influence on the elastoplastic analysis of the surrounding rock of the loess.In this paper,a new solution for the elastoplastic analysis and calculation of the wall rock based on the joint strength theory is carried out.Firstly,a joint strength theory that can comprehensively consider the tensile strength and shear strength of the loess is proposed,and the form and influencing factors of the surrounding rock failure of the loess tunnel are given.Subsequently,based on the joint strength theory,a limit stress analysis was carried out,and a new elastoplastic analysis solution for the surrounding rock of the circular tunnel under axisymmetric and non-axisymmetric loads was derived,and verify the analysis of the new solution.Finally,the expression of the plastic zone of the surrounding rock of the elliptical tunnel based on the joint strength theory is determined by the complex variable function.The main conclusions are as follows:1.The stress in the plastic zone of the axisymmetric load circular tunnel based on the combined strength is less than that based on the traditional M-C theory,and the difference is obvious.The radius of the plastic zone and the displacement of the surrounding rock around the tunnel based on the combined strength of the axisymmetric load are greater than those based on the traditional M-C theory.2.The radial stress at the elastoplastic interface of the non-axisymmetric load based on combined strength is greater than the radial stress based on the traditional M-C theory,while the tangential stress is relatively small.The difference between the calculation results of the two theories is not obvious when the stress at the elastoplastic interface of the surrounding rock is compressive.But when the tensile stress occurs at the elastoplastic interface of the surrounding rock,the calculation results of the two theories are substantially different.3.The plastic zone of the non-axisymmetric load circular tunnel based on the joint strength is larger than that based on the traditional M-C theory.If the range of the plastic zone is small,the difference between the results of the two theoretical calculations is not large;but as the range of the plastic zone increases,the difference between the two also becomes obvious.4.The plastic zone of the non-axisymmetric load Oval tunnel based on joint strength is larger than that based on the traditional M-C theory.