| This paper takes the Bangda Tunnel as the research object.Tunnel site areas are of high geostress and high altitude with drastic topographic relief,complex lithology and active tectonic movement;therefore,rock burst in hard rocks and large deformation in soft rocks can easily happen in engineering construction.Based on data collection and field investigation of the in-situ geostress in the study area,this paper conducted a fitting analysis of the measured in-situ geostress data in the tunnel site and explored the relationship between regional stress-lateral pressure coefficient k and the tunnel burial depth.Based on the field survey data and indoor rock physics and mechanics experiments,the classification of surrounding rock along the tunnel was predicted by using the BQ rock classification method.The lithology parameters of the three-dimensional geological model were obtained through indoor rock physical and mechanical experiments,and the stress results of the model were repeatedly checked by the measured in-situ stress data.The three-dimensional numerical simulation of in-situ stress distribution along the tunnel was carried out by combining the principles of engineering geology and engineering analogy methods.Based on the characteristics of in-situ stress distribution in the tunnel site,tunnel rock burst,large deformation and the rationality of line layout were studied and analyzed.The main results are as follows :(1)Through fitting analysis of the data of several measurement points,it was found that the in-situ stress in the tunnel site is mainly structural stress,and the direction is NE direction;(2)Transverse and longitudinal wave velocity,Poisson’s ratio,elastic modulus and compressive strength of the main lithology of the tunnel were obtained through indoor acoustic test and rock compression experiment and the influence of groundwater and fault fractures factored in,based on BQ rock classification method,it was found that the surrounding rock class of Bangda tunnel was mainly class II 、 Ⅲ and Ⅳ;(3)Through investigation of the engineering geological background of the tunnel site,the analysis of the measured in-situ stress data and the laboratory experiments of rock physical and mechanical properties,the three-dimensional geological model of the tunnel site was established.After the verification of relevant data,the geostress distribution of Bangda tunnel is obtained: the area of extremely high geostress area accounts for 6.0%;high geostress accounts for 61.25%;medium and high geostress accounts for 16.25%;the average geostress zone accounts for16.48%,and the maximum principal stress direction in the tunnel site is NE direction.(4)Based on the numerical simulation results of geostress in the tunnel site and the analysis of the angle relationship between the direction of maximum principal stress and the direction of tunnel,it was found that the tunnel route layout is reasonable.According to the current strength and stress ratio method,the distribution of rock burst in Bangda tunnel is as follows:slight rock burst area accounts for 10.44% and medium rock burst area accounts for 7.54%;The [BQ] method is used to classify the large deformation of soft rock in the tunnel site,and the results show that the first-level large deformation accounts for 3.9%,and there is no second-level and third-level large deformation in the tunnel site. |
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