Study On Treatment Of Foundation By Pressure Extrusion

This paper takes the pressure extrusion method to treat the foundation as the starting point,the red clay in Hainan province is selected as the test material,the main research is compaction of unsaturated red clay by pressure extrusion and the comparsion test of saturated soil with preloading treatment and pressure extrusion combined with preloading treatment.In this study a pressure extrusion device consist of air compressor,silica gel plate,pressure gauge and so on.The test soil is screening,filling,sprinkler,coner and curing with film,the test to start when the water content that is measuring by water temperature senor is close to the optimal water content.A sqseeze hole is reserved in the filling process,in order to measurement the pressure,displacement,water content around void after stable pressure extrusion by buried earth pressure,plastic coloured bead,water temperature sensor at a precalculated position.In order to measure the displacement of soil around the hole excavate plastic colored beads one by one after unloading,measurement of soil dry density around holes by using a ring knife after unloading,different pressure extrusion diameter of different soil depths were measured by tongs,Measuring the dilatation volume of the hole and observing the form of the formed concrete by the method of forming the concrete.The finite element software Abaqus is used to simply simulate the pressure extrusion of soil,the compaction coefficient of the pressure extrusion is derived by using the theory of circular hole expansion.The test soil box is divided into two parts of the same size,the test soil is sifting and filling,then full sprinkler and maintenance to reach saturation,in order to carry out pressure extrusion combined preloading model test,in the filling process,a silica gel bag,water temperature sensor and soil pressure meter are bured in precalculated position,for the sake of conduct load preloading model test pore water pressure gauge,water temperature sensor were buried in precalculated position in the filling processing in another soil box.Measurement of pore volume after pressure extrusion through sand injection method,measurement of soil thickness with plain steel bars reinforcement,the changes in the pore water pressure,water content and total volume of two are mainly compared.The results show that the value of dry density,soil displacement and pressure around the cavity of pressure extrusion gradually decreases with the increase of center distance,and its value is maximum near the center of hole;the dilatation diameter of soil is proportional to the air pressure,and the extrusion effect decreases with the increase of depth;the average compaction coefficient is increased by 6.02%,and the average void ratio is reduced by 12.05%under the pressure of 50 Pa pressure,the performance of soil is effectively improved,the feasibility of compaction foundation by pressure extrusion method is proved.The mean volume strain is derived from the back calculation of the known value of the soil under pressure extrusion and the theory of cylindrical hole expansion,introducing the concept of the compression coefficient of the theory of circular hole expansion to derive the compaction coefficient.A finite element model is established to simulate the soil model of pressure extrusion,it's found that the stress and strain of the soil model under pressure extrusion is basically the same as the experiment.The value of pore water pressure growth and dissipation of preloading pressure relative small contrast to pressure combined loading preloading;The change of moisture content of soil under load preloading is relatively uniform,The decrease of soil moisture content under loading preloading is about 31.47%of the decrease of soil moisture content under pressure combined loading preloading;Soil settlement is basically the same between loading perloading and pressure combined loading preloading,the hole expansion under pressure extrusion further squeezed the soil and the soil around the hole decreased with the water content and reached the limit of liquid,forming a more stable hole,then filling the hole with sand or stone to further improve the soil properties.