| Xigeda stratum is a special stratum of half rock and half soil mainly distributed in the valley of Southwest China.It has the characteristics of low strength,low bearing capacity,water sensitivity and so on.Engineering disasters such as initial support deformation cracking,arch collapse,and surface collapse during the construction of the Xigeda stratum tunnel have become common problems that hinder the safe construction of the project.At present,the instability characteristics and self bearing capacity of surrounding rock after excavation of Xigeda stratum tunnel are not clear,especially the stability state and instability region boundary of surrounding rock with different water content need to be explored.In view of the above problems,this thesis relies on the Xigeda stratum tunnel on the Chengdu-Kunming railway double line,and intends to interpret the pressure arch of the tunnel from the angle of the surrounding rock stress field by means of laboratory test,theoretical analysis and numerical simulation.The distribution form of pressure arch in the Xigeda stratum tunnel is analyzed,and the stress characteristics and development evolution law of the pressure arch with the change of water content in the Xigeda stratum tunnel are analyzed to provide a theoretical reference for the load determination and support design of the Xigeda stratum tunnel.The main contents are as follows:(1)Based on the related concepts of pressure arch,the applicability of the existing pressure arch boundary division methods in different paths around the tunnel was analyzed.The basic principle is to meet the physical meaning of pressure arch,and the judgment criteria of pressure arch boundary was determined to provide theoretical basis for the subsequent determination of pressure arch.(2)Similar materials and experimental equipment for model test of pressure arch effect of Xigeda stratum tunnel with different water content were developed.The instability form and stress change of surrounding rock during tunnel excavation were recorded.Through the analysis of the collapse process of the surrounding rock,the characteristics of the instability evolution of the surrounding rock were abtained.Combined with the stress monitoring results,the dynamic relationship between the collapse arch and the pressure arch was explored.(3)Based on the physical and mechanical properties of the surrounding rock of Xigeda stratum tunnel,the micro parameters of the surrounding rock were calibrated by the discrete element software.Through the establishment of three-dimensional numerical model,the excavation simulation of Xigeda stratum tunnel with different water content considering the construction effect was carried out.Based on the criterion of pressure arch boundary,the development law and final shape of surrounding rock pressure arch in the construction stage were obtained,so as to explore the surrounding rock pressure arch effect and its change characteristics in Xigeda stratum tunnel.(4)Based on the pressure arch effect of the surrounding rock in the Xigeda stratum tunnel,the calculation formula for the deep and shallow buried boundary of the tunnel was fitted.The load calculation theory of deep buried tunnel was analyzed,and the equivalent height of surrounding rock load of deep buried Xigeda stratum tunnel was obtained by using different calculation theories.Through the comparative analysis of the calculation results and combined with the engineering practice,the load calculation theory of the Xigeda stratum tunnel with different water content was determined. |
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