Study On Failure Mechanism And Support Measures Of High-speed Rail Tunnel In Expansive Rock

Because of the special engineering properties,expansive rock plays an important role in production and construction.Since the 1970 s,many engineering problems of expansive rock have appeared in the area of railway,water conservancy,civil air defense,highway and architecture in China.Expansive rock is a kind of special rock,which is widely distributed in China.Due to its engineering characteristics of water swelling and dehydration shrinkage,the appropriate evaluation cannot be easily made in engineering design,and if the construction method is not flexible,the rock will bring unexpected harm to projects.Therefore,it is of great significance to understand the engineering characteristics of expansive rock mass for the appropriate design and construction of tunnel engineering.Based on the Beiputuo mountain tunnel project,combining theoretical analysis,laboratory test,numerical simulation and field monitoring,this paper discusses the engineering characteristics of the expansive rock mass,the mechanical response of tunnel excavation in expansive rock,the support failure mechanism and the feasibility of related support countermeasures.The main contents of research are as follows:(1)By carrying out the triaxial compression test of expansive rock,the mechanical properties and parameters of expansive rock in Beiputuo mountain tunnel are analyzed and determined.And the strength parameters of expansive rock are calculated by Hoek-Brown strength criterion,and the strength parameters of expansive rock considering weathering degree and joints are obtained.The laboratory tests of lateral confinement no-load expansion rate and expansion pressure are carried out to analyze the expansion law under different initial water content,and the relationship among expansion coefficient,expansion pressure and initial water content is obtained.(2)Based on the FLAC3 D finite difference method,Beiputuo mountain expansive rock tunnel is simulated by thermo-mechanical coupling module in three dimensions numerically.By analyzing the mechanical response of tunnel structure and surrounding rock in normal excavation and excavation with expansive surrounding rock,the failure mechanism and influence law of expansion effect on tunnel supporting structure are obtained.(3)The three-dimensional thermo-mechanical coupling numerical simulation of expansive rock tunnel under five initial water content conditions is carried out,the mechanical response of the key parts of the tunnel structure is analyzed,and the relationship between the initial water content of surrounding rock before tunnel excavation and its influence on tunnel structure is analyzed and fitted.(4)Three-dimensional thermo-mechanical coupling numerical simulation of the whole process of Beiputuo mountain tunnel excavation,which is damaged by rock expansion under the original design and then replaced by new support is carried out.Combined with the field monitoring and the numerical simulation results,the effectiveness of on-site replacement and reinforcement of supporting structure and the rationality of dealing with the swelling effect are explained.(5)Appropriate support of expansive rock tunnel is considered.The three-dimensional thermo-mechanical coupling numerical simulation is carried out for expansive rock tunnel with rigid support and Resistance-Limiting and Energy-Dissipathing Support.Combined with the support effect,construction benefit and other aspects,the effectiveness,advantages and disadvantages of the supports are analyzed.