Research On The Construction Effect Of Large-diameter Vertical Double-layer Pipe Jacking In Soil-rock Combined Strat

With the development of urban underground engineering construction,pipe jacking technology has been widely used in many fields such as municipal pipeline,electric power tunnel,underground traffic tunnel and integrated pipe corridor because of its advantages of short construction period and less impact on the surrounding environment.With the acceleration of urban development,the available underground space is reduced,and the spatial arrangement of pipelines is becoming more and more diversified.For large diameter pipe jacking projects with vertical double-layer layout,the environmental effects caused by construction are still unclear.Therefore,it is of great scientific significance and engineering application value to study the construction effect of vertical double-layer large-diameter pipe jacking under complex formation conditions.Based on the relocation of a high-pressure line in Jinan City,this paper studies the environmental effects of large-diameter vertical double-layer pipe jacking construction in soil-rock composite formation.The main studies are as follows:(1)Field tests are carried out to test soil deformation,pipe-soil contact pressure and pipe joint strain during construction;(2)According to the field test results,the soil deformation law and pipe force characteristics during the construction of large-diameter vertical double-layer pipe jacking in soil-rock combination formation are analyzed;(3)MIDAS GTS finite element software was used to establish a three-dimensional nonlinear numerical model to conduct numerical calculation research on large-diameter vertical double-layer pipe jacking construction in soil-rock composite formation,and further analyze the prediction law of surface settlement and jacking force.The research shows that:(1)During the double-layer pipe jacking construction in soil-rock composite stratum,the surface settlement caused by the jacking construction in the upper layer is about 3 times that caused by the rock layer in the lower layer.The maximum lateral deformation occurs near the pipe,and the position of the deformation gradually moves upward with the increase of the distance between the inclination pipe and the pipe jacking axis.(2)For vertical double-layer pipe jacking,the Peck formula is modified according to the different depth of the lower pipe jacking embedded in the rock layer,and the modified Peck formula has good applicability in the surface settlement prediction of pipe jacking construction in soil-rock combination formation.(3)During the jacking process,the jacking force gradually increases with the increase of the jacking distance.The whole section of the soil layer is under pressure.Due to the constant adjustment of the attitude of the pipeline in the process of rock layer jacking,the pipeline is skewed,and the section of the pipe is not under uniform pressure.(4)Through the calculation and analysis of comprehensive friction resistance under grouting conditions,the revised jacking force calculation formula is obtained,which can better predict the jacking force range,and the formula has good applicability in soil-rock combination formation...