Experimental Study On Three-dimensional Swelling And Strength Characteristics Of Highlyexpansive Clay In Handan District Of China

Expansive clay has unique dilatancy,fissure and overconsolidation.Under the natural environment and external factors,swelling and shrinkage deformation,fissure development and strength degradation often occur,which bring potential harm to the buildings and slope facilities in the expansive land area.Therefore,it is of great significance to study the expansion characteristics and strength characteristics of expansive clay in order to accelerate the infrastructure construction of expansive land area and prevent the hazards of expansive clay.Highly expansive soil in Handan is taken the research object of this article.Through a series of three-dimensional swelling tests and shear strength tests,the three-dimensional swelling characteristics and strength characteristics of expansive clay are analyzed.The test provides reference for stability analysis of expansive clay slope and strength theory study of unsaturated expansive soil.Main research contents and conclusions are as follows:(1)Three-dimensional swelling pressure tests of highly expensive clay are carried out at multiple sample states of different dry densities,initial moisture contents,temperatures and composite modification methods.The variation law of threedimensional swelling pressure of expansive soil under different initial conditions and factors is analyzed.The results show that the vertical swelling pressure is larger than the horizontal swelling pressure.Three-dimensional swelling pressure exist anisotropy.And the anisotropy is more obvious when the dry density is higher.The three-dimensional swelling pressure is stabilized before 50 hours.The stabilization time postpones with the increase of dry density.The three-dimensional swelling pressure decreases linearly with the increase of initial moisture content.However it increases exponentially with the increase of dry density.It decreases gradually with the increase of dry and wet cycles.For soils with higher dry density,the three-dimensional swelling pressure decreases more significantly with the rise of the temperature.The influence of swelling pressure of the expansive clay in Handan modified sample treated by different mixed solutions is inconsistent with the change of temperature.The vertical swelling pressure of modified sample treated by different mixed solutions decrease.The modified sample treated by 0.8% polyvinyl alcohol(PVA)with 5% potassium chloride(KCl)mixture solution and 0.6% polypropylene fiber has a better effect of reducing vertical swelling pressure.(2)In order to explore the changing law of the three-dimensional swelling pressure and the reduction of the swelling pressure under different initial conditions,the threedimensional swelling pressure tests of highly expensive clay in Handan is carried out with unidirectional lateral limited microdeformation.Based on the attenuation effect of unidirectional micro-deformation swelling pressure of expansive soil under flexible revetment,the slope stability of reduction of micro-deformation swelling pressure is investigated under flexible revetment.The results show that the three-dimensional swelling pressure has the same decreasing tendency under one-dimensional microdeformation.Under the same dry density,the vertical swelling pressure of different initial moisture content have a different downward trend with the increase of unidirectional deformation rate.The smaller the initial moisture content is,the more rapid the decline.However,the downward trend of horizontal left and right swelling pressure of different initial moisture content is the same with the increase of deformation rate.With the same initial moisture content,the three-dimensional swelling pressure with different dry densities have the same downward trend with the increase of unidirectional deformation rate,and the downward trend is proportional to the dry density.The attenuation rate and reduction coefficient of the swelling pressure is inversely proportional to the deformation rate.Considering the swelling deformation of the flexible slope protection and the reduction of swelling pressure,the slope stability expression is given considering the swelling pressure to verify the influence of the swelling pressure on the slope stability.Through calculate analysis,the slope stability considering the reduction of swelling pressure is higher.The flexible slope protection is safer than the rigid slope protection.(3)In order to study the change law of the three-dimensional swelling pressure and unidirectional swelling deformation and analyse the attenuation law of swelling pressure when expansive clay meets water under the unidirectional unconfined.The results show that the three-dimensional swelling pressure gradually increase with time to the limit and then slowly decrease until it is stable.The unidirectional deformation increases gradually with time until it becomes stable.Since there is no lateral limit in horizontal left and right direction,the horizontal left and right swelling pressure is the lowest.And the swelling pressure is the largest when the initial water content is close to 21%.The higher the dry density is,the longer it takes for the swelling deformation to stabilize.In the early stage of swelling,the smaller the dry density is,the faster the swelling deformation is.The deformation is inversely proportional to the initial moisture content and positively proportional to the dry density.When there is no lateral limit in one direction,the attenuation rate of vertical swelling pressure increases linearly with the dry density,and the attenuation rate of horizontal swelling pressure decreases with the dry density.The attenuation rate of the three-dimensional swelling pressure decreases first and then increases with the increase of the initial water content.When the initial water content is close to 21%,the attenuation rate of swelling pressure reaches the lowest.(4)In order to study the change rule of the shear strength of the expansive clay under different initial conditions and factors and investigate the role of swelling pressure in the theoretical formula of shear strength of unsaturated expansive clay,the triaxial shear test and direct shear test of the expansive clay under different initial conditions(initial water content,dry density)and external factors(dry and wet cycle)are conducted.The results show that the triaxial shear stress-strain curves of the expansive clay are strain softening type.The peak strength has an exponential relationship with the dry density,but it has an inverse ratio with the initial moisture content.After the first dry-wet cycle,the shear strength of expansive clay decreases significantly.In direct shear test,the cohesive of expansive clay in Handan is proportional to the dry density.When the water content is close to the optimum,the adsorption strength and cohesion have the same law.The relationship between the adsorption strength caused by suction and the swelling pressure of unsaturated expansive clay is obtained.The swelling pressure is introduced into the theoretical formula of shear strength of unsaturated soil.The theoretical formula of the shear strength of unsaturated expanded clay in Handan is given by the swelling pressure to characterize the adsorption strength.It provides reference for calculating soil the shear strength of infrastructure construction in expansive clay area of Handan.