Inversion Analysis of Deep Complex In-situ Stress Field Based on Multiple Linear Regression
During the excavation process of deep-buried tunnels,the presence of extremely high in-situ stress within the rock mass may lead to fracturing,deformation,or even rock burst occurrences in the surrounding rock mass of the tunnel.In a high-altitude tunnel site,there are high self-weight stresses and tectonic stresses which exacerbate the rock burst issue.In order to ensure the stability of tunnel surrounding rock and construction safety,and clarify the characteristics of in-situ stress field in tunnel site,the inversion analysis of initial in-situ stress field of super-large buried tunnel was carried out based on the principle of multiple linear regression.The influencing factors of the stress field in the tunnel site were analysed.Combined with the drilling data of hydraulic fracturing method,the multi-factor boundary load conditions were proposed.By means of numerical analysis,the distribution of in-situ stress field in the tunnel site was deduced.The research results indicate that the in-situ stress measurements reveal a range of 15.21 to 40.82 MPa for the maximum horizontal principal stress in the tunnel site area.The measured direction of the maximum horizontal principal stress is N42° to 54°E.The stress state in the tunnel along the alignment is dominated by horizontal tectonic stress.The principal stresses increase with depth,following the pattern σH>σv>σh.A comparison between the measured and inverted values of in-situ stress indicates that the majority of measurement points exhibit close proximity,with similar trends in their variations.The results prove the rationality of the method for deducing the in-situ stress field.However,there are significant errors at some individual points,especially in the azimuth angle αH of the maximum horizontal principal stress.Constrained by the measurement principles of the hydraulic fracturing method,the accuracy of the inversion for shear stress τxy is not high.Its value has a certain impact on the calculation of the azimuth angle of the maximum horizontal principal stress.
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