Study On CD Shear Characteristics And Duncan-Chang Model Parameters Of Dry-wet Cycle Laterite

In view of the increasingly serious drying-wetting cycle problem of Yunnan laterite,taking Yunnan laterite as the research object,taking drying-wetting cycle as the control condition,considering the influence factors such as drying-wetting cycle times,dryingwetting cycle amplitude,initial dry density and confining pressure,the CD shear characteristics of Yunnan saturated laterite under drying-wetting cycle were studied through consolidated and drained(CD)triaxial shear test,and the effects of drying-wetting cycle on shear strength characteristics,stress-strain characteristics and Duncan-Chang model parameters of saturated laterite were analyzed.The following results have been obtained through research.The CD shear characteristics of Yunnan laterite under the action of dryingwetting cycle are clarified: during the drying-wetting cycle,the laterite is dehumidified and humidified repeatedly,which makes the cracks on the soil surface develop.With the increase of cycle times,the cracks on the laterite surface develop obviously.During CD shear process,the curve of principal stress difference-axial strain relationship of red soil in drying-wetting cycle is characterized by strain hardening.With the increase of the number of drying-wetting cycles,the peak principal stress difference,cohesion and internal friction angle tend to fluctuate and decrease;With the increase of the amplitude of drying-wetting cycle,the difference of peak principal stress and cohesion show a trend of decreasing fluctuation,and the internal friction angle increases;With the increase of initial dry density,the peak principal stress difference and cohesion show a trend of fluctuation and increase,while the internal friction angle shows a trend of fluctuation and decrease.With the increase of confining pressure,the peak principal stress difference tends to fluctuate and increase.The stress-strain characteristics of drying-wetting cyclic laterite under CD test conditions are clear: the shear stress-strain and bulk strain-axial strain curves of dryingwetting cyclic laterite are all characterized by strain hardening,while the shear strain-axial strain curves show a linear increasing trend and the lateral strain-axial strain curves show a parabolic increasing trend.With the increase of the number and amplitude of drying-wetting cycles,the consolidation displacement,shear displacement and peak volume strain of red clay in drying-wetting cycles show a fluctuating trend of increasing,while the peak shear stress,peak shear strain and peak lateral strain show a fluctuating trend of decreasing.With the increase of initial dry density,the peak shear stress,peak shear strain and peak lateral strain show a fluctuation increasing trend,while the consolidation displacement,shear displacement and peak body strain show a fluctuation decreasing trend.With the increase of confining pressure,the consolidation displacement,shear displacement,peak shear stress and peak body strain show a fluctuating increasing trend,while the peak shear strain and peak lateral strain show a fluctuating decreasing trend.The essence of the influence of drying-wetting cycle on the shear characteristics of laterite is that repeated dehumidification-humidification cycles aggravate the damage of laterite microstructure and change the stress characteristics in the shear process accordingly.The characteristics of Duncan-Chang model parameters of drying-wetting cyclic laterite under CD test conditions are clarified: with the increase of the number and amplitude of drying-wetting cycles,the initial elastic modulus index,initial bulk modulus,initial bulk modulus coefficient,initial bulk modulus index,limit principal stress difference and other parameters of Duncan-Chang model tend to fluctuate and decrease;Parameters such as initial elastic modulus,initial elastic modulus coefficient,failure ratio and so on are fluctuating and increasing.With the increase of initial dry density,the parameters such as initial bulk modulus index and limit principal stress decrease in fluctuation.Parameters such as initial tangent elastic modulus,initial elastic modulus coefficient,initial elastic modulus index,initial bulk modulus,initial bulk modulus coefficient,failure ratio,etc.are fluctuating and increasing.With the increase of confining pressure,the failure ratio tends to fluctuate and decrease Parameters such as initial tangent elastic modulus,initial bulk modulus,and difference in ultimate principal stress tend to fluctuate and increase.