Modified Research And Application Of Expansive Soil Under The Condition Of Lateral Confined

The expansive soil has remarkable water-swelling characteristics.When its lateral expansion is restricted,the lateral swelling pressure will be produced.It has caused serious harm to retaining structure in expansive soil regions.But the existing test devices can not eliminate the initial horizontal stress due to specimen,also they can not measure the lateral swelling pressure of expansive soil under different vertical load or distinguish the lateral swelling pressure from the total pressure.Therefore,it is significance to get the relationship between the lateral swelling pressure and the vertical load of expansive soil to calculate its influence on the stability of retaining structures.In this paper,conventional oedometer and methods were modified to ensure the initial state of specimen at different vertical loads,eliminate the initial horizontal stress due to specimen and measure the lateral pressure during the test.By using the modified apparatus and method to prove the validity of the test device.The results show that the initial state of the specimen can not be guaranteed by conventional test,vertical swelling ratio is underestimated by 7%to 95%under 25kPa and 200kPa;the final lateral pressure will be smaller if the initial horizontal stress is not eliminated,it is underestimated by 43.5%and 16.1%under 0 load and constant volume.By using the modified apparatus and method,loading and stepping unloading tests of the expansive soil from Baise in Guangxi were carried out.The at-rest lateral pressure coefficient of the saturated expansive soil is measured by the compression test to extract lateral swelling pressure from total lateral pressure.The tests results by the two ways have good consistency.The vertical swelling ratio decreases with the increase of load.A power function fitting formula under the saturated state can be established.The lateral swelling pressure increases with the increase of load.A hyperbolic fitting formula is proposed to fit them.The anisotropy ratios of samples under three initial water content conditions are 0.31,0.29 and 0.25,respectively.The K0 coefficient decreases with the increase of dry density.Considering the lateral swelling pressure when expansive soil reaches its plastic limit moisture content under different loads,combined with Coulomb’s active earth pressure,the stability of the three kinds of gravity retaining walls were checked.The design calculation of vertical and uphill buffer layers were carried out.The stability of buffer layers under lateral deformation is checked.The results show that the stability coefficient of retaining wall increased with the compression of the buffer layer behind the wall.The improved test device and methods can meet the requirement of keeping the initial state unchanged and remove the initial horizontal stress caused by sample preparation.In the design of gravity retaining wall in expansive soil region,vertical swelling pressure multiplied by reduction factor can not be used to replace lateral swelling pressure,and its value increases with the increase of vertical load.It is necessary to design a buffer layer behind the wall.The stability of the retaining wall can be improved by increasing the allowable compression of the buffer layer behind the wall and changing the form of the retaining wall,such as inclined base.