| With the acceleration of urbanization in my country,subway construction will inevitably pass through urban dense areas.The pipe jacking method has been widely promoted due to its advantages of small settlement,simple construction technology,and fast construction speed.It is used in underground passages and municipal works in excavation work.Compared with the circular jacking pipe under the same cross-sectional area,the rectangular jacking pipe is more widely used because of its higher space utilization rate.In the pipe jacking project,the jacking force is the driving force of the pipe jacking project,and it is the controlling factor of the pipe jacking project.The jacking force in pipe jacking project is mainly used to overcome the side friction resistance between the pipe joint and soil body and the face resistance at the palm surface,the face resistance is mainly related to the burial depth of the pipe joint and the nature of the stratum,which can be accurately calculated through the formula.The lateral resistance increases with the increase of the pipe jacking range.In engineering,the lateral resistance is reduced by injecting a dampening slurry between the pipe joint and the soil body.Based on this,this paper takes the pipe jacking project at the entrance of Ju Hua Station of Kunming Metro Line 4 as the basis,and calculates the lateral friction resistance and predicts the jacking force through formula derivation,experimental research,numerical simulation and field measurement data for rectangular pipe jacking project with large section in viscous strata.The main research contents and results are as follows.（1）The contact state of pipe-slurry-soil is analyzed through field research,and the contact state of pipe-slurry-soil is classified.Based on the shear friction mechanism of pipe-slurry-soil,and considering the influence of pipe jacking depth,the soil column theory and Prussian arch theory are adopted to calculate the lateral friction resistance of pipe jacking in deep and shallow burial,and then form the formula of rectangular pipe jacking force calculation.（2）The effect of different ratios of bentonite,soda ash and CMC on slurry viscosity,water precipitation rate,water loss and mud skin thickness index was investigated separately by using control variables,and it was concluded that the optimum content of bentonite in thixotropic slurry for cohesive strata was 12%-16%,the optimum content of soda ash was0.2%-0.4% and the optimum content of CMC was 0.1%-0.2%.（3）Concrete wax-free and waxed tests on the contact surface of full contact with pipe and soil and pipe-slurry-soil friction tests with different ratios of slurry were carried out,which showed that the wax coating on the concrete surface of the contact surface with the clay could effectively reduce the friction resistance,compared with the wax-free condition,the friction resistance was reduced by 46%.（4）Using the displacement control method,FLAC 3D software was used to finely simulate the rectangular pipe jacking process,and by comparing the measured jacking force data,it was concluded that the numerical simulation can better simulate the pipe jacking process,and the addition of thixotropic slurry between the pipe and soil can reduce the jacking force.（5）By comparing the proposed formula for calculating the jacking force of rectangular pipe jacking with the existing formula for calculating the jacking force,the results show that the proposed formula can effectively encompass the actual jacking force value of the project and can better predict the jacking force;by analyzing the ground settlement data above the jacking pipe measured on site,the longitudinal displacement settlement law of the pipe section is obtained.Through the analysis of the measured internal force data of the pipe section,the results show that: the outside of the pipe section is subject to greater internal force due to the greater frictional resistance;the side frictional resistance of the pipe section is constantly changing. |
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