The In-Situ Test And Studies On Mechanical Mechanism Of Prefabricated Diaphragm Wall

The construction technology of prefabricated diaphragm wall is an improvement and innovation of traditional technology,which can significantly improve construction efficiency,while reducing engineering risks and environmental pollution,in line with the sustainable development concept advocated by the country.Based on the assembly insertion and excavation test of five prefabricated walls in the standard section of the foundation pit of Jinglidao Station of Tianjin Metro Line 6,this paper sorts out and analyzes the wall inclination data during the excavation of the foundation pit;Then,based on the inclinometer data and the engineering survey report,PLAXIS software was used to establish a two-dimensional finite element model that can reflect the deformation characteristics of the foundation pit,and the influence of the failure of the lateral joint on the deformation characteristics of the wall was studied;In three dimensions,the spatial deformation characteristics of prefabricated diaphragm walls and their control methods are studied.Finally,ABAQUS software is used to study the force deformation mechanism of the joint structure,and an improvement plan is proposed.The results show:(1)The prefabricated diaphragm wall adopts factory prefabrication,which can use higher-strength concrete,and the quality is easier to guarantee;and under the soil quality and excavation conditions of the foundation pit in this article,the deformation of the prefabricated diaphragm wall is stable.The amount of deformation is controllable,and its deformation pattern and law are basically the same as those of the cast-in-place diaphragm wall,so it can effectively replace the cast-in-place diaphragm wall and be used in subway engineering practice.(2)The weakening of the horizontal-joint of the prefabricated wall has a significant impact on its mechanical and deformation characteristics: the deeper the joint,the less the effect of its failure on the bending moment and lateral deformation of the wall,and the shear force distribution will not be affected significantly;when the joint is located above the bottom of the pit,its failure will result in a significant increase in the lateral displacement of the wall above the bottom of the pit,and its maximum displacement point will shift to the joint;after the joint fails,the lower wall appears "cantilevered" deformation form,only by erecting supports under the joints can the deformation of the entire wall be effectively controlled.(3)The prefabricated diaphragm wall has poor synergistic deformation ability,and the deformation of the wall can be controlled by adjusting the support position,improving the bending rigidity of the crown beam and the purlin,and increasing the width of the precast wall.Among them,the improvement of bending rigidity of the purlin can be more effective to control the deformation of the prefabricated wall.(4)When a single joint is flexed,its stress is obviously concentrated at the bottom of the beam and the steel part,the section utilization is low,and after entering the yield state,the crack width increases rapidly.Compared to the single joint,the safe bending moment and ultimate bending moment bearing capacity of double joints are significantly higher than that of single joints,and the increase in crack width after yielding is also significantly smaller,indicating that double joints has stronger bending resistance,better ductility,and higher safety,and should be used in the engineering if possible.The shear deformation at the joint is affected by the combined effect of the bending moment and the reserved splicing allowance,and the latter plays a controlling role.