Research On Seismic Response And Shock Absorption Measure For Complex Deep-buried Hydraulic Tunnel

With the rapid development of hydropower construction and the advancement of western development strategy,a series of large hydropower projects in China are built successively.Meanwhile,in order to relieve the contradiction between water supply and demand and integrate the regional resources,some large-scale,long distance water diversion projects are constructed gradually,which result in a large number of under-ground hydraulic tunnels.The constructions of hydraulic tunnel face the challenges of complicated structure form,complex stress mechanism and complicated occurrence en-vironment.Specially,under the background of earthquakes,the seismic characteristics of hydraulic tunnel have become the important contents for affecting the safety and stability of engineering structure,restricting the regional economic development,and threatening the national energy security.Therefore,researching the seismic response mechanism of hydraulic tunnel,discussing the seismic response characteristics under complex conditions and establishing the system of seismic response analysis and shock absorption measure are of great theoretical research value and social economical benefit to ensure the safety and stability of structure and enhance the earthquake fortification level.This paper focuses on several key issues related to seismic response and shock absorption measure for complex deep-buried hydraulic tunnel,including seismic response pretreatment method,combined bearing analysis model of fluid-lining-rock,seismic response under the influence of discontinuity,seismic response under the condition of high stress,aseismic and shock absorption measures.The main research contents are as follows:(1)Based on the computer programming language,the surface elevation data in topographic map are obtained,and the elements cut across by faults are reconstructed by biplane,a three-dimensional numerical modeling method considering the complex topography and geological conditions is established.The scaling method based on observed seismic wave and synthesis method based on design response spectrum are researched,and the baseline correction,filtering and direction change methods are discussed,a pretreatment method of complex seismic wave is proposed.The three-dimensional viscoelastic artificial boundary equations and numerical simulation technology are derived,and the nodal load on the artificial boundary is discussed,a complex artificial boundary condition and seismic wave input is presented.By means of numerical modeling,seismic wave and artificial boundary,a pretreatment analysis system for seismic response of underground structure is built,and a three-dimensional elastic dynamic finite element program is developed.(2)Based on the dynamic loading test results of concrete materials,the similarity principle of constitutive relation curves for concrete under static and dynamic loading is summarized.In light of the basic idea of static damage constitutive in strain space,and the definition and solution of the static tension and compression damage variables for concrete under three-dimensional stress state,the basic format of dynamic damage cons-titutive relation for concrete is derived.According to the analysis and assessment of damage state,cracking constitutive and seepage characteristic,a dynamic damage and cracking model of concrete suitable for programming is developed.Considering the coupling interaction of inner water and lining,the combined bearing of lining and surrounding rocks,a dynamic explicit finite element solving format of hydraulic tunnel is derived.A dynamic response numerical analysis model under the combined action of fluid-lining-rock is presented,and a non-linear seismic response analysis method of hydraulic tunnel is established.(3)Based on the non-associated plastic theory,a constitutive model of rock dis-continuities considering the coupling of dilatancy and plasticity is established.Starting from the basic damage mechanism,with regard to the separation of tension and shear,a new damage constitutive model based on energy theory is presented.The plastic evolution and damage evolution process are solved separately,and a mixed integration algorithm for elastoplastic damage constitutive relation of rock discontinuities is put forward.With regard to the two failure modes of tension and shear,the different stress-strain relationships of crack interface in the normal and tangential directions are introduced.Based on strain decomposition theory of cracked elements,the elastic-brittle and elastic-plastic constitutive relations are respectively adopted for crack interface and rock mass,and an equivalent elastic-plastic constitutive model for cracked rock mass is presented.According to researching the effect of macroscopical structure plane on seismic response of hydraulic tunnel,and the dynamic crack propagation process of rock mass with mesoscopic structure plane,a seismic response analysis method under complex geological conditions is established.(4)Based on the tri-axial compression test results of rock mass under different confining pressure conditions,the effect of confining pressure and brittle failure process are discussed,and the nonlinear hardening with confining pressure,linear degradation with plastic strain for intensity parameters are presented.Combining with the strain rate effect of intensity parameters under earthquake,,an elastic-brittle-plastic dynamic con?stitutive relation model for high stress rock mass is proposed.In light of the combined action mode of static and dynamic loads when high stress hydraulic tunnel is subjected to earthquake,considering the static loads of different confining pressure and axial pressure,and the dynamic loads of different peak load,loading rate and loading time,a combined action analysis model of static and dynamic loads for hydraulic tunnel is put forward.On this basis,the seismic response characteristics of hydraulic tunnel under different combinations of static and dynamic load are discussed,and a seismic response analysis method under complex stress conditions is established.(5)Based on the transverse action mechanism of surrounding rock,shock absorp-tion layer and lining in hydraulic tunnel,it is simplified to vibration system with three degree of freedom.According to the structural vibration theory,the motion equa-tion is derived,and the deformation transfer coefficient is solved.On this b'asis,the effects of stiffness ratio between shock absorption layer and surrounding rock mass,and frequency ratio between seismic wave and structural self-vibration on the aseismic and shock absorption properties of hydraulic tunnel are discussed.In view of soft-fractured rock mass,the anti-seismic enffect of grouting on hydraulic tunnel is discussed,and the influences of different grouting parameters and grouting circles on seismic response of hydraulic tunnel are analyzed.In view of intact and hard rock mass,the effect of setting shock absorption layer on hydraulic tunnel is discussed,and the influences of different damping materials and thicknesses on seismic response of hydraulic tunnel are analyzed.According to researching the mechanism of aseismic and shock absorption technology,and the effect of different aseismic and shock absorption measures,the reinforcing system of aseismic and shock absorption for complex hydraulic tunnel is established.