Research On Load Action Mode Of Shield Tunnel In Complicated Geological Environment

Urban subway shield tunnels are in a complex water and soil mechanical environment.The surrounding rock is obviously affected by weathering,saturated water softening,and riverbed erosion and silting loading and unloading.In addition,there may be local weakand broken zones in the rock formation,making the surrounding rock The arching ability of rock is poor,so the applicability of the classic arch unloading theory including Terzaghi theory and Platts theory is debatable;when the local shield tunnel passes through the alternate soft and hard stratum,its load It is also difficult to calculate accurately because the engineering geology and hydrogeology conditions are too complicated.Secondly,the analysis of the transverse structure of shield tunnels often adopts homogeneous ring model,beam-elastic yellow model,etc.However,due to the characteristics of large cross-section,wide width,and thick tube segments,combined with the complexity and variability of the load caused by the particularity of the underwater environment,is the analysis model applicable? Are the parameters of the analysis model reasonable?It’s allworth it Important questions to consider carefully.my country has alarge population and rapid economic development.Urban traffic has an important impact on residents’ lives and urban development.Rail transit is an effective way to solve urban traffic congestion.Because the shield tunnel is in a complex water and soil environment,if the tunnel design is carried out according to the existing classical theory,there is a big difference between the theory and the actualsituation.Based on the Jinan Metro R2 line,this paper selects two representative sections to measure the water and soil pressures acting on the lining structure,and analyzes the size,variation and distribution characteristics of the water and soil pressures of the shield tunnel segments in different geological environments.The problems of modified idioms are analyzed,and the method of slip line field method based on the limit state theory is put forward to solve the earth pressure at the bottom of the tunnel.The specific research content is as follows:(1)The installation method of flexible earth pressure gauge,pore water pressure gauge and steel bar gauge for on-site monitoring of water and earth pressure of shield tunnel segment and internal force of segment is described in detail.It can be found through thedata obtained from the monitoring that the data obtained is relatively reasonable and reliable,which can provide certain reference andguidance for the subsequent field monitoring of the water and soil pressures and internal forces of the shield tunnel segments.According to the results of water quality analysis test and soil soluble salt content analysis test,the following conclusions can be drawn: the groundwater and soil in the test area are slightly corrosive to concrete and reinforcement.(2)The commonly used theoretical calculation methods and actual measurement results are compared and analyzed.In a composite formation with uneven soft and hard,the water and soil pressures are basically stable after the test segment is advanced for about 20 rings.For moderately consolidated soft clay or silty clay,when the thickness of the overlying soil is greater than 2.57D(D is the outer diameter of the segment),the soil arching effect has already occurred,and the Terzaghi loose earth pressure method should be used forcalculation.For tunnels with a thickness of less than 1.59 D,the full soil column method is more appropriate.The load on both sides of the shield tunnel lining structure is asymmetrical,and the load pattern of the modified idiom exaggerates the passive reaction force of the base,and the deviation between the measured value and the theoretical value is the largest at the bottom of the tunnel.The measured water pressure of section 1(H=2.57D)and section 2(H=1.59D)is basically the same as the theoretical static water pressure.The measured value of section 1 is closer to the theoretical hydrostatic pressure,but at the bottom of the tunnel compared with other positions,the deviation is slightly larger.(3)The slip line field method based on the limit state theory is proposed to solve the earth pressure at the bottom of the tunnel.The calculation method is compared with the modified inertial usage and the actual measured value.The radial earth pressure obtained by the load calculation method proposed in this paper is The overall law is more consistent with the measured earth pressure,the earth pressure on the left and right sides is larger,and the base earth pressure is smaller.The minimum error between the calculated load of section 1 and the measured value of the ring segment is only 1%,and the average error is 9.9%.The minimum error between the calculated load of section 2 and the measured value of the ring segment is only 1.2%,and the average error is 6.1%.It can be seen that the load model proposed in this paper is more in line with the actual tunnel load.(4)In this paper,FLAC3 D software is used for numerical analysis,and two different load distribution modes are adopted to establish the numerical models of section 1 and section 2 respectively.By analyzing the internal force calculation value of the model and the measured value,it is found that the average error of section 1 and section 2 is 12.6% and14.5% respectively when the distribution mode 1 is used;The average error of section 1 is 10.1% when using distribution mode 2;The average error of section 2 is 8.2%.The results of model analysis and calculation are generally less than the corresponding measured values,so it is reasonable to use load distribution mode 2 for design.