Inversion Of Far-field Average In-situ Stress And Prediction Of Large Deformation Of Tunnel Surrounding Rock With High In-situ Stress

The problem of high ground stress is a difficult and hot topic for tunnel and underground engineering researchers.Especially for the soft rock tunnel,because of the characteristics of large deformation of surrounding rock caused by high ground stress,high deformation rate and long deformation duration,it brings great difficulties to the design and construction.At the same time,there are many random and uncertain factors in the distribution of in-situ stress of original rock,which leads to many uncertainties in the analysis of the stress of tunnel surrounding rock and supporting structure,as well as the deformation around the tunnel.Based on the characteristics of randomness and variability of in-situ stress and stratum parameters,this paper analyzes the uncertainty of in-situ stress,and based on this,analyzes the stress field and displacement field of surrounding rock and supporting structure;Based on the extension theory,a new classification index system for large deformation of soft rock tunnel with high geostress is proposed by introducing the elastic modulus of surrounding rock and the comprehensive coefficient considering the influence factors of tunnel wall displacement.The main research work is as follows :(1)Based on the statistical data of in-situ stress in Southwest China,including 243 groups of in-situ stress data of 8 cities,including Lhasa,Shannan,Linzhi,Litang,Yajiang,Kangding,Luding,Ya’an,etc.,through curve fitting,this paper analyzes the distribution law of in-situ stress in Southwest China: except for a few cities in Southwest China,the vertical principal stress is dominant,and the horizontal principal stress is dominant in most cities,The principal stress value increases with the increase of burial depth,and the maximum horizontal principal stress data is relatively scattered.Due to the intersection of different structures,the stress field in Southwest China is controlled by multiple faults,and is also affected by the superposition of mountain canyon topography and slope stress field.Based on the uncertainty theory and Bayesian analysis method,the uncertainty evaluation method of regression prediction model of horizontal geostress changing with vertical geostress is established.Based on the measured data,the uncertainty of the existing regression prediction model is analyzed and verified.It is found that the exponential function prediction model has higher reliability within the range of sample data,and the power function prediction model has higher reliability beyond the range of sample data;(2)Based on the field measured geostress data,the far-field geostress stochastic model and average geostress estimation model are established by the statistical simulation of local stress field and Monte Carlo random sampling theory.The influence of the number of samples on the reliability of the far-field average geostress estimation is studied by programming R language.The results show that the minimum number of samples needs to be greatly increased in order to obtain the acceptable average geostress estimation in a certain depth of the formation,when it is affected by the geological structure such as stress zoning and fault zone.In the direction of buried depth,the shallower the depth,the minimum number of samples to obtain reliable estimation will also increase greatly.(3)The uncertainty theory is introduced into the analysis of surrounding rock deformation and surrounding rock support of high geostress soft rock tunnel.By analyzing the uncertainty of influencing factors of surrounding rock deformation,the uncertainty analysis model of analytical solution of surrounding rock displacement is proposed.The sensitivity analysis of the factors affecting the tunnel deformation is carried out,and it is proposed that the elastic modulus is the most obvious factor affecting the tunnel deformation.Combined with the support characteristic curve,the analysis method of surrounding displacement changing with support stiffness is established,and the change range of support stiffness corresponding to the most unfavorable deformation is proposed.It is verified by an engineering example;The reasonable range of support stiffness under different surrounding rock grades is established.(4)Based on the extenics theory,a new classification index system for large deformation of tunnel in soft rock with high geostress is proposed by introducing the elastic modulus of surrounding rock and the comprehensive coefficient considering the influence factors of tunnel wall displacement.The engineering example shows that the improved classification index has higher prediction accuracy and can better predict the large deformation level;Based on the large deformation classification index system,the uncertainty analysis method of large deformation prediction considering the uncertainty of local original rock stress is established.Combined with the engineering example,the engineering application is carried out,which can provide effective guidance for engineering personnel.