Study On The Deformation Of Soil Based On Fault Action And Its Damage Mechanism For Tunnel Engineering

Active faults are the root cause of earthquakes.On the one hand,fault displacement will propagate in the medium and cause permanent deformation of the stratum.On the other hand,it will generate strong seismic waves and radiate to the surroundings,which will seriously affect the above-ground and underground structures near the fault area.With the rapid development of China's infrastructure,tunneling through active faults has become an inevitable fact.At present,the seismic research of tunnels based on active faults is not deep enough,and the actual seismogenic faults have not been included in the study.In order to start from the active fault,study the deformation of the stratum caused by the fault displacement and its damage mechanism to the tunnel structure,and provide a reference for the seismic fortification of the tunnel engineering based on the active fault.This paper mainly completed the following research work:(1)Comparative study of typical dislocation theory calculation methods is completed,and the applicable conditions of different methods are grasped.Based on the layered dislocation theory to calculate the co-seismic deformation caused by interrupting the layer dislocation in the horizontal layered half space,and the calculation accuracy was verified.Taking the 1976 Mw7.8 magnitude Tangshan earthquake as an example,the calculation method and the Okada method are compared and analyzed.The research results show that the influence of stratigraphic stratification can be more than 20%,which cannot be ignored in the actual calculation.(2)By introducing the concept of the asperity model on the fault plane,a calculation method of soil deformation based on the asperity source model of the active fault is established.The asperity is introduced into the source model with the seismic deformation calculation,the dislocation analog nonuniform slice based on the principle of superposition of static displacement.Take the 1989 Mw6.95 magnitude Loma earthquake as an example to verify the reasonableness of the introduction of asperity model and the advantages of co-seismic deformation in the calculation.Taking the magnitude Mw7.0 strike-slip and dip-slip earthquakes as examples,the influence of the uneven distribution of fault plane dislocation on the surface deformation is analyzed.The results show that,considering the uneven distribution of dislocations on the fault plane,the peak of surface displacement appears at the location of the asperity,and the magnitude has increased.(3)Based on the proposed method for calculating soil deformation of fault asperity,the spatial distribution laws and characteristics of ground deformation caused by active faults are studied and grasped.Based on the layered dislocation theory and the asperity source model,the co-seismic deformation of the surface,the distribution of strong rupture zones and their influencing factors were studied.Through a large number of calculation and analysis of different earthquake conditions,the relationship between the maximum surface displacement and the maximum surface dislocation and the magnitude,fault burial depth and fault dip angle are established respectively.Compared with traditional empirical formulas,it can consider more influencing factors,and provides a certain reference basis for earthquake hazard prediction in applicable stratigraphic regions.(4)Based on the results of the macro-model for dislocation evaluation of active faults,a rock-soil-tunnel coupling reaction analysis model considering the input of soil deformation was established,and the mechanism of seismic failure for cross-fault tunnel engineering were studied.Starting from the seismogenic fault,based on the coseismic deformation results obtained by the dislocation theory,the seismic dislocation load of the surrounding rock is clarified.Plastic damage constitutive,the damage mechanism of cross-fault tunnel under the action of fault is studied.The research results show that the damage degree,damage location and damage range of the tunnel structure under different types of faults are different.The fault dip angle,fault burial depth and surrounding rock strength all directly affect the damage degree of the tunnel structure.Rock tunnels with small inclination and shallow burial depth need to consider the impact of fault dislocation.(5)Based on the dislocation and ground motion evaluation models,a preliminary analysis of the tunnel response under the coupling effect of dislocation and ground motion is carried out,and the analysis scheme of tunnel structure response based on the coupling effect of dislocation and ground motion is researched and proposed.Based on the dislocation model of the cross-fault tunnel,with considering the seismic input method of viscoelastic artificial boundary and equivalent nodal force,a static-dynamic coupling model is established to carry out the seismic response of the tunnel under the joint action of dislocation and ground motion analysis.The research results show that the application of ground motion loads after the dislocation action is completed will cause the tunnel damage to increase,but the degree of impact is less than the dislocation effect.