Study On The Effective Range Of Plastic Vertical Drain Under Vacuum Preloading

Under the trend of green environment protection and energy saving,it is necessary to change the design and construction method of vacuum preloading to deal with the silt foundation,which needs more detailed study of vacuum preloading.In this paper,the effective range of single plastic vertical drain is studied deeply when vacuum preloading is used to preload the foundation.Based on the traditional consolidation equation,the analytic solution considering the change of the water flux of the plastic vertical drain was deduced,and the change rule of the effective range of the plastic vertical drain was analyzed theoretically.Then the indoor model test of different reinforcement time was designed and carried out.The development law of soil consolidation was further analyzed,and the results of theoretical analysis were validated.Finally,in view of the plastic drainage board clogging is the main influencing factors of the effective range of the change.The siltation effect of the plastic drainage board was studied from the migration of the silt particles and the change of the pore diameter of the drainage plate filter.The main conclusions of this paper are summarized as follows:(1)The consolidation equation considering the resistance of plastic vertical drain is deduced,and the degree of consolidation of different position of soil is obtained by analytic solution,and the effective range of plastic vertical drain is analyzed.That the effective range of plastic vertical drain is not always a cylindrical shape,but from a reverse cone,to the inverted table-like,and eventually become cylindrical changes in the process.(2)In the foundation treatment range,the effective depth of the vacuum preloading is not fixed level,but showing jagged.The reinforcement depth near the plastic vertical drain is larger,and the reinforcement depth between the plastic vertical drain is smaller.(3)The well resistance of the plastic vertical drain has a significant effect on its effective influence range.When the well resistance factor α is more than or equal to 0.4,the effective range of the plastic vertical drain will reach the cylindrical shape,and the effective range of the plastic vertical drain can be improved by extending the consolidation time.When the well resistance factor α> 0.4,the effective range of the plastic vertical drain can only be round table,increase the consolidation time has no effect on the change of the effective influence range.In addition,the thickness of the smear zone,the coefficient of permeability and the ratio of the diameter to the diameter have a certain influence on the effective range.(4)The result of the indoor model test shows that the vacuum degree in the soil obviously lags behind the vacuum degree of the plastic vertical drain,and there is a start time.In general,the start-up time is related to the soil depth and distance from the plastic vertical drain.At the same time,the vacuum degree of the edge of the plastic vertical drain is approximately linear attenuation along the depth.The attenuation amplitude is about 14 kPa / m.While the attenuation of the vacuum in the soil,in the vertical and radial can be approximated as an exponential decay.(5)The tests of shear strength and water content of the soil vane showed that the consolidation of the soil was centered on the plastic vertical drain,first appeared in the surface of the soil near the plastic vertical drain,then gradually to the soil surface away from the plastic vertical drain and the deep soil close to the plastic vertical drain expands and eventually extends to the deep soil layer away from the plastic vertical drain.This also confirms the theoretical analysis of the conclusion that the effective range of plastic vertical drain is not always a cylindrical,but by the inverted cone,to the inverted round table-like,and finally the trend of cylindrical change process.(6)The results of particle analysis of the soils with different consolidation time in the indoor model show that the migration of the silt particles occurs during vacuum preloading.The grains are most likely to migrate between 0.005 mm and 0.075 mm.The sand particles having a particle size of more than 0.075 mm and the clay particles having a particle size of less than 0.005 mm hardly migrate.(7)Plastic vertical drain filter mercury test showed that the plastic vertical drain filter easy to block the pore diameter of 0.01 mm ~ 0.075 mm.With the increase of vacuum time,the total pore volume of the membrane decreases,that is the membrane has clogged,and silt blockage has a serious tendency.At the same time,the degree of clogging of different pore diameters of the filter membrane is different.The pore diameter of the filter membrane is greater than 0.075 mm basically will not occur clogging.