Analysis Of Direct/Inverse Problems Of Surrounding Rock And Lining Considering Gradual Load

Lining is an important part of tunnel structure.The mechanical behavior analysis of lining is a significant part of tunnel safety evaluation.After the excavation,the surrounding rock's stress or displacement will be released,and the release of its stress or displacement is not completed immediately,but gradually release with time.In addition to its own gravity and external load,the stress and deformation of the initial lining and the secondary lining are mainly caused by the "stress release" or "displacement release".It is of great practical significance and theoretical value to consider the gradual change of stress release or displacement release more reasonably.The load is the direct cause of displacement,and the stress release of the surrounding rock will also produce "release load" in the hole.In this paper,the "incomplete displacement release" of the surrounding rock excavation is simulated as the gradual release of the load.Using the parameters of release intensity and release rate,the gradual load function is constructed.Considering the different construction time of the excavation,the lining and the secondary lining,the whole process is divided into three time stages,Considering the surrounding rock and lining as elastic and viscoelastic medium,the equation of displacement recursive solution is derived by using the principle of virtual displacement,finite element method and time domain adaptive method,and the correlation conditions of the finite element recursive equation of surrounding rock and lining between each period are obtained.Thus,the coupling problem of the surrounding rock and the lining is solved.This algorithm can describe time-variation of each variable more accurately.The original space-time coupling problem is converted into a series of space problems,and the FEM is used to solve the problem.When the step size changes,the calculation accuracy can be ensured by adaptive computation.The progressive release coefficient of load and the mechanical parameters of surrounding rock are important parameters in the method proposed in this paper,but it is often difficult to get in engineering practice.In this paper,through the inverse problem analysis,the least square function is constructed according to the displacement information of the partial sample point and the displacement prediction value obtained by the finite element time domain subsection adaptive method.The differential evolution method and the L-M method are used for minimization to obtain the inverse value of the related parameters.The algorithm of positive / inverse problems proposed in this paper is verified by numerical examples.