Behaviours Of Hydro-mechanical And Laws Of Water And Gas Permeability During Wetting For Intact Loess

Loess with apparently water sensitivity and structural is a kind of special soil.The natural state of intact loess has good engineering properties.The moisture of soil mass increased with water table rising or rainfall infiltration.The hydromechanical coupling results in sudden reduction in strength and increasing in deformation.It thus may be cause engineering accident,such as landslides,foundation instability and so on.The models of strain-stress constitutive,water retention,water and gas permeability are used in performing consolidation analysis of unsaturated loess during wetting.Therefore,it is of great significance to experimental study the behaciours of hydro-mechanical and laws of water and gas permeability during wetting for intact loess,basing on the viewpoint of unsaturated soil mechanics.A series of tests were carried out closely around the clue mentioned above,including loading tests at constant suction,wetting tests at constant stress and gas permeability tests under different stress paths.Influences of suction,stress path and loading and wetting path on deformation,strength and yielding were investigated.The effects of net mean stress p and deviatoric stress q on water retention behaviors,water and gas permeability were analyzed.And then the elastic-plastic constitutive models were proposed,in which the effects of loading and wetting path were considered.The models to describe the behaviours of water retention curve,water and gas permeability were put forward respectively,in which the effects of stress were considered.The major work and achievements obtained in this study arc summarized as follows.A series of triaxial tests at constant suction(i.e.,first wetting and then loading,also called pre-wetting)were performed on intact loess with different suctions,including isotropic compression,conventional triaxial,constant stress ratio and pure shear(constant p)paths.Effects of stress path and suction s on behaviors of stress-strain,yielding and critical state were discussed.The tests data confirm that the critical states relationship with respect to q-p and e-p be independent of stress path.Basing on the introduction of translated principal stress ?i(= ?i +?0(s),?0(s)is called a bonding stress related to suction),the q-p critical state lines related to suction were normalized in q-p plane.The LC yielding curve was determined in s-p plane under isotropic stress condition.The shapes of the initial and subsequent yield curves on the q-p plane were near skewed ellipses no centered on the p axis under deviatoric stress condition.The yield surface equations were proposed.The plastic flow of intact loess was appropriate to a non-associated flow rule.Dilatancy law of intact loess with various suctions was proposed.A series of water immersion test in stage(i.e.,first loading and then wetting,also called post-wetting)were performed for intact loess with various void ratios at null stress and with the same void ratio at different loading conditions,including isotropic stress,conventional triaxial and constant stress ratio conditions.Effect of stress conditions on yield suction and the evolutions of wetting volumetric strain and deviator strain with the suction loss were investigated.Effects of wetting and loading path on wet-increased collapsibility,yielding and critical state were analyzed.For the characteristics of loading yielding line and wetting yielding line related to loading and wetting path at s-p and q-p planes.Tests data confirm the existence of a unique yield curves relationship with respect to s-p and q-p.Moreover,there was no unique critical state identified from conventional triaxial shear and wetting shear at q-p plane.The critical state of wetting shear was described.Shear stress level threshold value corresponding to shear failure during wetting to saturation against net mean stress was established.Relationship between wetting shear loss suction corresponding to wetting shear failure as a funtions of was proposed.Selecting the translated net mean stress p,deviatoric stress q and suction s as stress state variables,and basing on critical state of triaxial shear and wetting shear,dilatancy equation,the funcitons of yielding surface at s-p and q-p plane,and non-associated flow rule mentioned above,An elastoplastic constitutive model was proposed for intact loess,using plastic volumetric strain as the hardening parameter.This model could account for effects of wetting and loading path,and reproduce the stress-strain behaviors during loading at constant suction or wetting at constant stress.Influences of void ratio,net mean stress and deviatoric stress on water retention behaviors were investigated,using the results of water immersion tests in stage at null stress and different stress conditions.Tests data confirm that void ratio and stress had effect on degree of saturation-suction and water content-suction.Interestingly,there were all unique relationships of both degree of saturation and water content ratio(defined as water content to saturated water content ratio)versus suction ratio(defined as suction to air-occlusion suction ratio)at different stress conditions.The hydro-mechanics coupling model described wetting water retention behaviour was proposed at triaxial stress conditions,taking degree of saturation and water content as variables.Influences of void ratio,net mean stress and deviatoric stress on water permeability were investigated,basing on the results of water immersion tests in stage at null stress and different stress conditions.Void ratio,net mean stress and deviatoric stress had effect on relationships among water permeability-degree of saturation,water permeability-suction,and relative water permeability-suction respectively.Interestingly,there were all unique relationships of relative water permeability as functions of both degree of saturation and suction ratio.The hydro-mechanics coupling models of wetting water permeability were proposed for intact loess at triaxial stress conditions,taking degree of saturation and water content as variables.Gas permeability tests for intact loess with various water contents were performed at isotropic stress and constant stress ratio loading conditions.Influences of mean stress and deviatoric stress as well as water content gas permeability were analyzed.Gas permeability-degree of saturation and gas permeability-volumetric gas content little changed with stress and water content,and could be described by P-vG-M model and RPLmodel.The data were consistent with a unique relationship linking gas permeability and modified gas saturation,nearly independent of applied stresses and could be predicted by the proposed modified gas saturation power law(MAPL)model.The numbers of parameters for MAPL model were one and two less than those of the RPL model and the P-vG-M model.Gas permeability as functions of both normalized isotropic stress and stress ratio at given applied mean stress for different water contents were parallel lines.The exponential function gas permeability model was proposed taking mean stress,stress ratio and water content as variable,and was more convenient for engineering application.