Study On Surface Deformation And Its Influencing Factors Of Parallel Differential Section Pipe Jacking Project

The limitation of urban underground space makes pipe jacking project develop from the original single pipe jacking to double-line parallel pipe jacking.With the unique advantages of pipe jacking method in underground pipeline engineering construction,parallel pipe jacking has been widely used in urban tunnel construction in China.Usually,parallel pipe jacking is used with the same section and size,but the section shape and size of the two pipes of parallel pipe jacking tunnel are also different under different functions,environments and requirements.The surface deformation around the site is also inevitable in parallel differential section pipe jacking project.When the local surface deformation exceeds a certain limit,it will affect the progress of pipe jacking engineering and the safety of surrounding environment.Therefore,the surface deformation caused by parallel differential sections pipe jacking construction has become a key issue in engineering construction.In this paper,a three-dimensional numerical model is established for the parallel differential section pipe jacking tunnel under the urban main road by using the finite element software.Combined with the field measurement results,the surface deformation and its influencing factors of the parallel differential section pipe jacking project are studied.The theoretical results can guide the design and construction of similar pipe jacking projects and reduce the influence of pipe jacking on surface and surrounding environment deformation.The main research contents are as follows:(1)Based on the disturbance of pipe jacking construction on soil,the surface deformation mechanism is studied,and the influence range of parallel pipe jacking interaction is limited.It is concluded that the influence range and degree of pipe jacking engineering with parallel different sections on surface deformation depend on the following factors : the horizontal spacing between the first pipe jacking and the later pipe jacking,the difference of section size and shape of the two pipes,the depth of pipe jacking and the construction process.(2)Based on ABAQUS finite element software,a numerical model of pipe jacking with parallel differential section is established to simulate the key working conditions of soil excavation,excavation face support,grouting and pipe jacking.Firstly,the variation law of surface vertical displacement during the first construction of left-line large rectangular pipe jacking is analyzed.Secondly,the influence of right-line small rectangular pipe jacking on surface vertical displacement and left-line large rectangular pipe jacking is studied.The results show that when the pipe jacking does not reach the analysis section,the surface is slightly uplifted but the value is small and stable,which is maintained within 10 mm.When the pipe jacking passes through the analysis section,the surface deformation will have an obvious mutation,that is,from uplift deformation to settlement deformation;After the pipe jacking is far away from the analysis section,the surface deformation at the section tends to be stable.The transverse surface deformation curve of large rectangular pipe jacking in the left line is narrow and deep “V” shape,and the influence range of transverse surface deformation is about 4 times the width of pipe jacking.During the construction of small rectangular pipe jacking on the right line,the settlement deformation is further deepened and the influence range is expanded.The lateral surface deformation curve is changed from the narrow and deep “V” shape to the gentle “V” shape at the bottom,and the peak settlement point is transferred from the large rectangular axis on the left line to the center of the two pipes.(3)The influence of section shape,section size,horizontal distance between two pipes,overburden depth and successive construction procedures on surface deformation of parallel differential section pipe jacking project is analyzed by establishing different working condition models.(4)The basic law of the deformation of the surrounding soil caused by the parallel different sections pipe jacking project is obtained by analyzing the monitoring data of the construction site.The results show that the project belongs to the shallow buried close distance construction,and the influence on the surface deformation is very significant.In the construction,it is necessary to pay close attention to the surface deformation,so as to adjust the construction parameters in time to prevent excessive surface settlement deformation.The comparison between the measured results and the numerical simulation results proves that the variation trends of the surface vertical displacement obtained by the two methods are basically consistent.