Study On The Working Mechanism And Effect Of Direct Displacement Vacuum Preloading For Soft Soil Foundation

The vertical row vacuum preloading method is a new technology of treating and reinforcing foundation,which removes the horizontal drainage sand cushion,directly connects the drainage pipe network with the plastic drainage board,so it eliminates the vacuum load loss which caused by the filter tube,the filter membrane and horizontal drainage mat,thus improving the utilization of vacuum load.This paper takes the direct-row vacuum preloading test area in a port area in the north as the research object,the reinforcement mechanism of the foundation treatment method is studied through theoretical analysis,on-site monitoring data analysis,and numerical simulation,and the optimization design is proposed.Through the above study,the following conclusions are drawn:(1)The reinforcement mechanism of the vertical row vacuum preloading method is to use the drainage pipe network directly connected to the plastic drainage plate,which reduces the vacuum load loss,increases the effective stress of the soil,and improves the utilization of the vacuum load.(2)The degree of consolidation of foundation soil calculated from the settlement curve is 94.0%in the straight row area,slightly higher than 93.4%in the conventional area;the consolidation degree of the silt layer is high,averaging 95%,and the clay layer has a relatively low degree of consolidation,with an average of 84%.(3)The pore water pressure dissipates quickly in the early stage of vacuum preloading,and the vacuum degree decreases along the depth of the drainage plate.Within the depth of the reinforcement zone,the degree of vacuum in the soil of the direct drainage zone is slightly larger than that of the conventional zone.(4)According to the principle of equal drainage,the plastic drainage plate foundation is simplified as a two-dimensional sand-wall foundation,and the vacuum preloading method can be effectively simulated by adjusting the pore pressure at the top node of the sand-walls.(5)During the designing process of the vertical row vacuum preloading,a large vacuum load should be used as much as possible,and the design of the length of the draining plate should correspond to the required treatment depth of the building foundation.For the port area,the best effect is achieved when the distance between the drains is 1m.