Research On Seismic Response And Seismic Resistance Measure For Special Structures In Mountain Region Rock

Based on the requirement of protection and functionality,military underground projects are much different from ordinary tunnel projects both in construction arrangements and forms of gateways.In consideration of the attack by weapons,the gateway of the military project is more complicated than the gateway of a tunnel and isn't in direct line with the main chamber.On the other hand,the main chamber of this project is usually constructed in the deep rock mass of mountains and will have to cross complex geological sections in which the lithology and strata change dramatically.However the present research on the seismic response of the special structure in mountain area is not systematic and cannot meet the urgent practical needs.In order to meet the needs of seismic strengthening on special projects damaged in the 5.12 Wenchuan earthquake and seismic design of projects in future,the damages of these damaged projects were investigated in this thesis.The 3-D dynamic FEM was applied to study the seismic response characteristics of the gallery gateway and the across-fault main chamber of a special underground structure.Then the effect and the mechanism of some aseismic measures for this across-fault main chamber were explored.Main research works and results in this thesis are as follows:1.Through collecting and coordinating the national and international earthquake disaster data of underground structures,the earthquake damage forms,impact factors and failure mechanism of these structures were studied.The commonly used aseismic measures and seismic analysis methods of underground structures were presented.2.Simply introducing the dynamic finite element method for underground structures,some numerical simulation techniques were discussed in ABAQUS program including realizations of the viscous-spring artificial boundary and the initial ground stress.These techniques were proved to be valid and correct by analysis of examples as well as material parameters used for concrete damaged plasticity model.3.A 3D nonlinear finite element model was established in which the infinite foundation and the self-weight stress field were considered.Kobe wave was adopted to input at the bottom of the model considering the travelling wave effect.The seismic response and damage mechanism of gallery gateway under earthquake were researched as well as mechanical and deformation characteristics of the connection part between the gallery gateway and the main chamber.Results show that the entryway and its nearby main chamber as well as gallery gateway are weak parts to earthquake excitations.In order to provide evidence for the seismic damage evaluation of tunnel engineering,effects of vibration direction in the seismic wave and seismic intensity on the seismic response of gallery gateway were analyzed.The vibration direction of seismic wave has a great effect on the seismic response of underground structures.X direction is the most unfavorable direction,followed by XYZ direction,finally is Z direction.The main deformation between both ends of the entryway is shear deformation and the deformation degree increases with the increase of seismic intensity.The whole gateway structure almost enters the plastic state under intensity 9.4.Aiming at the seismic response of the crossing-fault tunnel with arch-straight in cross-section,a 3D nonlinear finite element model was also built so that the rule of displacements,stresses and strains with time and interspace could be studied.Then influences of the seismic intensity and the material properties of faults on the seismic response of the crossing-fault tunnel were analyzed.Results show that the deformation of main chamber concentrates on fault zone and the floor and the side wall in the fault are very incidental to be destroyed under earthquake compared with no faults.The deformation degree of main chamber,especially the main chamber in fault zone,increases with the increase of seismic intensity.The improvement of material properties will significantly decrease the shrinkage of side walls and the maximum von Mises equivalent stress in the foot.5.To secure the crossing-fault tunnel in the earthquake,three kinds of seismic measures were analyzed,namely,strengthening districts,strengthening districts with softer material and seismic joints.The tunnel with the strengthening district around the fault will distort less than the tunnel with no strengthening districts but will bear larger stress and acceleration at the same time.When the material of the strengthening district is changed from ordinary concrete to polymer-cement concrete,the acceleration peak value of the floor in fault will decrease and the transverse deformation of the tunnel in fault will become smaller.Results indicate that the distance between seismic joints and faults has a greater impact on the anti-seismic effect of seismic joints than the width of seismic joint.And seismic joints can significantly minimize the maximum value of the von Mises equivalent stress in the foot of side wall only when the distance between seismic joints and faults is small enough.In this case,however,the lining will easily occur dislocation since seismic joints decrease the longitudinal entirety of tunnels.