Study On The Large Deformation Characteristics And Control Technology Of Weak Carbonaceous Shale Tunnel

With the rapid development of transportation infrastructure construction,many railways and highways are built in mountainous areas.Long,large,deep,difficult,and dangerous tunnel projects have emerged in large numbers,and large deformation disasters in weak surrounding rock tunnels induced by high ground stress are becoming more common.Especially in the area with intense tectonic activities or special rock masses,severe large deformation will hinder the construction progress,increase construction costs,and even threaten the long-term safety of the tunnel.Therefore,this article takes the large deformation disaster of a soft carbonaceous shale tunnel as engineering background and focuses on two topics: the large deformation characteristics and its control technology.Laboratory tests were employed to study the mechanical properties and damage evolution of carbonaceous shale.A constitutive model suitable for soft carbonaceous shale was constructed,and the secondary development of the model was carried out to study the large deformation characteristics.The influences yielding support and steel fiber reinforced concrete on the mechanical behavior of the large deformation tunnel were investigated.The main research contents and results are as follows:(1)The triaxial compression and acoustic emission tests were used to study the effects of confining pressure and water content on the stress-strain characteristics,failure characteristics,sequential and spatial distribution characteristics of acoustic emission activity,and frequency characteristics of acoustic emission signal of soft carbonaceous shale.The evolution of acoustic emission entropy of weak carbonaceous shale under different confining pressures and water-bearing conditions were studied,and the internal relationship between acoustic emission entropy and rock damage was analyzed.The feasibility of using acoustic emission entropy to assess rock damage evolution was demonstrated.The experimental research has laid a solid foundation for establishing the constitutive model of weak carbonaceous shale.(2)A modified creep constitutive model considering the short-term strain softening and long-term creep effects for carbonaceous shale was proposed.The derivation of the threedimensional finite-difference form of the constitutive model and the secondary development of the numerical program was realized,and the related numerical experiments were carried out on the improved constitutive model to verify the reliability of the proposed model.The proposal and development of the constitutive model provide an effective tool for studying the large deformation characteristics of the weak carbonaceous shale tunnel.(3)The statistical relationship between the horizontal displacement and the vertical displacement of the large deformation tunnel was analyzed.The lateral pressure coefficient at the tunnel site was inverted based on the statistical relationship.For the modified model,a creep parameter inversion algorithm based on Genetic Algorithm(GA),Particle Swarm Optimization(PSO)and Support Vector Machine(SVM)theory was established,and the relevant creep parameters are inverted and verified by on-site monitoring data.The deformation,stress and plastic zone distribution characteristics of surrounding rock and the internal force characteristics of shotcrete lining of soft carbonaceous shale tunnel under creep and strain softening were studied.The evaluation of the large deformation characteristics of the tunnel provides the basis for the study of the large deformation control technology.(4)Based on the principle of yielding support in the large deformation tunnel,the doublenode method beam elements and nonlinear yield spring were used to realize the yielding action.Moreover,the interface element was used to complete the sliding between surrounding rock and lining.The elastoplastic damage model of concrete with tensile and compressive behaviors was established.The effects of yielding member position and resistance on the surrounding rock deformation,damage of shotcrete lining,axial force,and the bending moment in large deformation tunnel were studied.The proper placement of yielding members and supporting resistance parameters were proposed.(5)Given the support principle of steel fiber reinforced concrete,a random distribution of steel fiber generation algorithm was proposed,and a numerical analysis model of steel fiber concrete lining for large deformation tunnels was established.The effects of steel fiber content,length and diameter on mechanical properties and damage features of steel fiber shotcrete lining were studied.Based on the surrounding rock pressure distribution characteristics of the soft carbonaceous shale large deformation tunnel,the support effect of the steel fiber shotcrete lining on the large deformation tunnel was studied.The influence of steel fibers number on the deformation of lining,damage of concrete and the steel fibers stress was also analyzed.