Study On The Mechanical Behavior Of Pipe-rock Contact Of Pipe Jacking Under The Action Of Carbonaceous Shale

Chongqing is separated by "Four Mountains and Two Rivers",the water resources are scattered,the interconnection between the water supply groups is low,and the urban water supply security and emergency response capacity are weak.In order to improve the level of water supply security in Chongqing,it is necessary to plan and construct a large-scale urban water supply tunnel of considerable size.The southwest area is dominated by soft and hard rocks and weak intercalated surrounding rocks.During the pipe jacking construction process,due to the large creep in the soft rock areas dominated by carbon shale,the surrounding rocks are constantly squeezing the over-digging space The contact area of the pipe rock continues to increase until it completely fits,which is prone to jamming.In this paper,the carbon shale of the No.2pipe section of the No.1 pressure tunnel of a certain project in Chongqing City is taken as the research object.The research method combining laboratory test,theoretical analysis and numerical simulation is used The contact mechanical behavior of the system has been studied in depth.The main research contents and results are as follows:(1)Carried out laboratory physical and mechanical tests of carbonaceous shale,obtained the physical property parameters of carbonaceous shale and strength parameters under different influencing factors.Based on the test results,the effects of the three influencing factors of joint surface inclination,water content and confining pressure on the strength of carbonaceous shale were analyzed.The change law of the strength and failure mode of carbonaceous shale with the inclination of the joint surface is revealed.The analytic hierarchy process was used to analyze the influence weights of the three influencing factors of joint angle,water content and confining pressure.(2)Triaxial compression creep tests under different joint dip angles,different water contents and different confining pressures of carbonaceous shale were carried out.A nonlinear creep model—Lubby2 creep model was introduced,and creep parameter identification was performed based on the creep test results.The parameters of creep model and joint dip angle,water content,confining pressure and other influencing factors were fitted and analyzed,and the triaxial compression creep model of carbon shale based on Lubby2 creep model considering different influencing factors was established.Through the combination of laboratory tests and numerical simulations,the influence of carbon shale joint dip angle,water content and confining pressure on its creep characteristics was discussed.(3)Based on Flac3 D finite-difference software,the interface contact surface unit was used to simulate the joint surface of the carbonaceous shale,and the results of the indoor triaxial compression test of the carbonaceous shale were compared with the simulation results to verify its applicability.Using the Fish language in Flac3 D,the Burgers linear creep model was extended to a Lubby2 nonlinear creep model considering different influencing factors,and the extended Lubby2 creep model was verified by the results of the indoor triaxial compression creep test.It laid the foundation for the establishment of a numerical model of the mechanical properties of tube-rock contact under the creep of carbonaceous shale.(4)The direct shear friction model test of carbon shale-concrete pipe joints under different normal forces and contact conditions was carried out,and the influence of normal force on friction coefficient under different contact conditions was discussed.Based on the friction coefficient model of the triangular synapse at the contact surface,the friction mechanism of carbonaceous shale is revealed from a microscopic perspective.The empirical equations of normal force and friction coefficient under dry friction condition of non-contact medium and friction condition of pure bentonite medium are deduced through fitting analysis of experimental data and theoretical model.(5)A numerical model of the mechanical properties of tube rock contact under creep of carbonaceous shale was established.Using field measured material parameters,the on-site stuck tube was replayed and analyzed,and the applicability of the numerical model was verified,revealing the mechanism of jammed tube jamming.The influencing factors such as joint angle,water content and confining pressure(buried depth)of carbonaceous shale were analyzed respectively on the contact area of the surrounding rock of the pipe joint,the average stress of the pipe rock contact area,the jacking force required for a single pipe joint and the promotion of the stuck pipe The influence law of the total jacking force required by the root canal joint provides a basis for solving the jamming problem of jacking engineering and reducing the risk of jamming.