Study On CU Shear Characteristics Of Dry-wet Cyclic Red Clay

In view of the increasingly serious wetting-drying cycle problem of laterite in Yunnan,the laterite in Yunnan is taken as the research object,and the wetting-drying cycle is taken as the control condition.The dehumidification time,humidification time,wetting-drying cycle number,initial dry density,confining pressure and other influencing factors are considered.Through the undrained(CU)triaxial shear test,the shear properties of saturated laterite were studied,and the effects of dehumidification,humidification and wetting-drying cycles on the shear properties of saturated laterite were analyzed.This achievement provides an important reference value for the in-depth study of the effects of wetting-drying cycles on the engineering characteristics of Yunnan laterite.The following research results were obtained through research.The CU shear characteristics of laterite under dehumidification:During the dehumidification process,the water content of laterite decreased with the extension of dehumidification time.The moisture content decreased at the initial stage of dehumidification is greater than that of the later stage;with the increase of initial dry density,the water loss capacity of laterite decreased,after dehumidification was completed,During the saturation process,the fine laterite of the dehumidified laterite develops,and it is easy to inhale more water to achieve saturation,but the soil softening degree is not high.During the CU shearing process,the stress-strain relationship curves of saturated laterite are strain softening,and the pore pressure-strain curves are all “S”.With the extension of dehumidification time,the consolidated drainage volume and residual strain increase,while the peak stress,peak strain,residual stress,peak pore pressure,total shear strength index and effective shear strength index decrease;with initial dry density When the increase,the peak stress,residual stress,total cohesion,and effective cohesion increase,while the consolidated displacement,peak strain,peak pore pressure,residual strain decrease,total internal friction angle,and effective internal friction angle do not change.Obviously;as the confining pressure increases,the peak stress,residual stress,peak strain,residual strain,and peak pore pressure increase.The effect of dehumidification on the shear properties of laterite is that under long-term dehumidification,the laterite loses water and hardens and shrinks,forming shrinkage cracks;under saturation,water absorption softens,but the degree of softening is not high,resulting in laterite microstructural characteristics Damaged to a certain extent,correspondingly changed the force characteristics during the shearing process.The CU shear characteristics of laterite under humidification:During the humidification process,the water content of laterite increased with the increase of humidification time.The increase of water content in the initial stage of humidification was greater than that in the later stage.With the increase of initial dry density,the water absorption capacity of laterite decreased,and the moisture content decreased.During the saturation process,the linkage between the laterite particles after the humidification is softened,and the water can be saturated by inhaling less water,and the soil softening degree is higher.During the CU shearing process,the stress-strain relationship curve of saturated laterite changes from strain softening to strain hardening,and the larger the confining pressure,the more obvious the change,and the pore pressure-strain relationship curve is “S”.With the prolonged humidification time,the consolidated drainage volume,peak stress,residual stress and peak pore pressure increase,while the peak strain,residual strain,effective shear strength index and total shear strength index decrease;with the initial dry density Increase,peak stress,residual stress,effective cohesion,total cohesion,total internal friction angle increase,while consolidation displacement,peak strain,residual strain,peak pore pressure,effective internal friction angle decrease;As the confining pressure increases,the consolidated displacement,peak stress,residual stress,peak strain,residual strain,and peak pore pressure increase.The effect of humidification on the shear properties of laterite is that the softening degree of laterite is deepened under the action of humidification,which weakens the joint force and friction between the particles,and the stability of the skeleton is damaged,which changes the shearing process.The CU shear characteristics of laterite under wetting-drying cycles:During the wetting-drying cycle,the laterite samples were repeatedly dehumidified-humidified,causing cracks in their appearance,and the appearance was severely damaged.As the number of cycles increased,the water content increased during the wetting-drying process.During the saturation process,the laterite fissures that have undergone the wetting-drying cycle develop,the microstructure damage is severe,and the faster inhaled moisture reaches saturation.During the CU shearing process,the stress-strain relationship curves of saturated laterite are strain softening,and the pore pressure-strain curves are all “S”.With the increase of the number of wetting-drying cycles,the consolidation displacement and residual strain increase,while the peak stress,peak strain,residual stress,peak pore pressure,total stress intensity index and effective stress intensity index decrease;with the increase of initial dry density Large,peak stress,residual stress,total cohesion and effective cohesion increase,while consolidated displacement,peak strain,residual strain,peak pore pressure,total internal friction angle and effective internal friction angle decrease;The increase in the consolidated displacement,peak stress,peak strain,residual stress,residual strain,and peak pore pressure increase.The effect of wetting-drying circulation on the shear properties of laterite is that the dehumidification-humidification effect will weaken the shear strength of the soil to varying degrees,and the repeated dehumidification-humidification cycle will deepen and aggravate the damage of laterite microstructure.The force characteristics during the shearing process are changed accordingly.