Analysis Of Mechanical Performance And Excavation Stability Of TRD Method Mixing Wall

The development of urbanization requires bigger and bigger scale of urban underground rail transit,the size of the subway station is getting bigger and bigger too.While the size of the foundation pit is constantly increasing,the construction of super large deep foundation pit requires higher level of construction technology,especially in high water level areas,the problem that how to solve the adverse effects of groundwater on safe excavation also needs to be solved urgently.The TRD method is a new water proof curtain method with the advantages of good wall quality and strong continuity in multi-stratum.Miaotou Railway Station is the first time that TRD method applied in Qingdao area as a subway station foundation pit.There are too many problem need to be solved,such as its applicability to the Qingdao formation,the influence of different technological parameters on the quality of the wall and the stability of excavation.In this paper,indoor test,numerical simulation and in-situ test are used to study these problems.The main work and innovation results are as follows:(1)Laboratory tests were carried out to study that the influence of the comprehensive moisture content cement content and curing age on the strength and impermeability of cement stabilized soil.The test results show that:the strength of cement soil is positively related to the age of curing while it decreases with the increase of comprehensive moisture content,and increases with the increase of cement content.The permeability coefficient of cement soil is negatively correlated with curing age,The permeability also increases with the increase of comprehensive moisture content,and decreases with the increase of cement content.(2)Comparative analysis between laboratory test results and field measurement results,got the reduction coefficient of the actual wall performance in the field,According to the reduction factor,the optimum technological parameters suitable for the formation of Miaotou Railway Station were selected.(3)Considered the difference of physical and mechanical properties of TRD mixing wall in different strata,the FLAC excavation model was established.Through the simulation analysis of foundation pit excavation and supporting process,the force and deformation law of TRD mixing wall in the process of foundation pit excavation is obtained.(4)Relying on the foundation pit of Miaotou station,the applicability of TRD method in soft soil stratum in Qingdao area was studied,and a new TRD method for evaluating the quality of cement soil mixing wall was proposed,which including the strength of the mixing wall,the positive and negative pressure water test in the borehole for the permeability coefficient of the mixing wall,the uniformity test with the high definition borehole television imaging and the integrity test with the drilling radar.Detection results show that the strength and impermeability of the stirred wall can meet the requirements without weak structures,the quality of the wall in the sand layer is better than that in the clay layer.The TRD method can meet the requirements of water curtain in deep foundation pit in Qingdao area.