Shear Characteristics And Soil-water Characteristics Of Yunnan Red Clay Under Dry And Wet Cycles

The shear characteristic of saturated laterite,the soil-water characteristic of unsaturated laterite and the mechanism of interaction between laterite and water at drying-wetting cycle are studied in this paper,in view of increasingly serious problem of drying-wetting cycle of laterite in Yunnan area.This paper aims at helping to solve the problem of increasingly serious disaster,with the drying-wetting cycle as the control condition,the macro-micro characteristic under different influencing factors as the basis,and the theoretical analysis as the combination.The triaxial tests of saturated laterite show that,along with drying-wetting cycle number and drying-wetting cycle amplitude increase,strain-softening phenomenon of saturated laterite generally enhances,peak shear strength and its corresponding axial strain,cohesion,internal friction angle,conductivity decrease,initial deformation modulus and pore water pressure peak increase,damage of microstructure deepens:microstructure becomes looser,particles of laterite are broken,pores become more scattered.Along with initial dry density increases,peak shear strength,initial deformation modulus,cohesion,internal friction angle and conductivity of saturated laterite increase,axial strain corresponded to peak shear strength and pore water pressure decrease,damage of microstructure alleviates:microstructure is tighter,pores obviously become smaller and less.The most obvious factor on the shear characteristic of saturated laterite is initial dry density,followed by cyclic number and cyclic amplitude.Along with drainage condition of UU,CU,CD changes in turn,strain-softening phenomenon of saturated laterite generally enhances,peak shear strength and its corresponding axial strain,initial deformation modulus,conductivity increase,cohesion:cuu>ccu?ccd?0,internal friction angle:?cd>?uu?0 effective cohesion:c'uu>c'cu?c'cd?0,effective internal friction angle:?'cd??'cu>?'uu?0,pore water pressure peak:uf,uu>uf,cu>uf,cd=0,damage of microstructure alleviates:microstructure is tighter,pores become smaller.Soil-water characteristic tests of unsaturated laterite show that,with the increase of initial dry density,air intake value of laterite increases,slope of dehydration and absorbing water,residual gas content reduce,residual water content and conductivity increase,microstructure takes on the feature of tighter structure and smaller pores.With the increase of initial moisture content,air intake value of laterite reduces,slope of dehydration and conductivity increase,surface morphology of microstructure vary from granular to platy,structure outlines of laterite particles and edge of pores become fuzzier.With the increase of preconsolidation pressure,air intake value of laterite increases,slope of dehydration decreases,residual water content and conductivity increase,damage of microstructure mitigates:microstructure becomes tighter and its surface becomes smoother,arrangement of laterite particles is more regular and its structure outlines is fuzzier.With the increase of particle size,moisture content after saturating of laterite increases,air intake value reduces,slope of dehydration and absorbing water,residual gas content increase,residual water content decreases;conductivity increases first,then decreases;damage of microstructure deepens:micro-surface is rougher,arrangement of laterite particles is more irregular,pores become bigger and more uneven.Hysteresis exists in the process of drying-wetting cycle,the effect of particle size is more obvious than initial dry density.When initial dry density,preconsolidation pressure and particle size(d=0.5mm except)change,power function can be used uniformly as soil-water characteristic fitting model of Yunnan laterite;when initial moisture content changes,linear function is adopted.Interaction between saturated laterite and water at drying-wetting cycle includes the escape of water,the adsorption of laterite particles,hardening and shrinkage of laterite under the condition of dehydration and the wedging,lubricating,softening of water,expansion of laterite in the process of moistening.The deepening and intensifying of above actions at drying-wetting cycle seriously damage the microstructure of laterite,constantly alter the conductivity of laterite,ultimately change its shear characteristic.Besides relating to above actions,interaction between unsaturated laterite and water at drying-wetting cycle is also closely associated with the capillary action,the flow and diffusion of the gas,eventually embodies in relationship between matrix suction and moisture content.