Study On Strength Characteristics Of Weathered Sand Improved Unsaturated Expansive Soil

Expansive soils are widely distributed in China.Due to its characteristics of water absorption,expansion,loss of water,and shrinkage,which cause huge economic losses in actual engineering,it is necessary to improve the expansion and contraction properties of expansive soils.Since natural expansive soils are generally unsaturated,Classical mechanical strength theory of the soil has been unable to explain the strength and deformation characteristics of expansive soil under dry and wet cycles.Samples of weathered sand and expansive soil were mixed at a certain ratio,and triaxial tests of consolidated and drained unsaturated soil were conducted under different initial dry densities and matrix suction conditions.The test results of the strength characteristics of unsaturated expansive soil at a certain sand content showed that :(1)The weathering sand has an inhibitory effect on the expansion and contraction of expansive soil,and its shear strength increases first and then decreases with the increase of sand mixing rate.The peak sand mixing rate is 16%.(2)The stress-strain curves of weathered sand-improved expansive soil and remolded expansive soil both show a hyperbolic hardening model.As the net confining pressure increases,the elastic modulus of the model slows down and lags;(3)The strength of the expansive soil is greatly improved after sand improvement,and the contribution coefficient of the increase in net confining pressure to the strength is slightly larger and the contribution coefficient of the increase in dry density;(4)The improvement of the weathered sand on the strength parameters of the soil mainly contributes to the increase of the internal friction angle,but the cohesion has a coefficient reduction of about 0.6;and the change of the matrix suction has little effect on the internal friction angle;Simplify and modify Fredlund and H.Rahardj strength formulas under specific conditions;(5)Parameter calculation of Duncan-Chang model and analysis of parameters show that matrix suction is positively correlated with tangent bulk modulus.