非饱和花岗岩残积土的剪切特性与抗剪强度分析

Analysis on Shear Characteristics and Shear Strength of Unsaturated Granite Residual Soil

对不同含水率的原状和重塑花岗岩残积土开展常规三轴固结不排水试验,对比分析饱和度对原状土和重塑土剪切变形特性的影响规律,并通过测定原状土和重塑土的土水特征曲线,给出基质吸力与抗剪强度指标之间的关系,建立花岗岩残积土非饱和抗剪强度表达式。结果表明:原状和重塑花岗岩残积土的应力-应变曲线的硬化程度随着含水率和围压的增加而上升,原状土的应力-应变曲线在低含水率、低围压条件下表现为软化型,重塑土均表现为硬化型;原状土和重塑土的应力路径随含水率的变化基本相同,随着含水率降低,剪切过程中产生的孔隙水压力逐渐减小,有效应力路径逐渐向总应力路径靠拢;花岗岩残积土土水特征曲线可分为饱和、过渡、残余3个阶段,脱湿过程中原状土的残余吸力大于重塑土,过渡区范围比重塑土大,在高饱和度状态下,原状土和重塑土的含水率随基质吸力的增加变化幅度很小,达到进气值后才随着基质吸力开始明显下降,进入到残余阶段含水率的变化逐渐缓慢;基质吸力对土体内摩擦角的影响很小,黏聚力随着基质吸力的增加不断增大,吸附内摩擦角逐渐减小,基质吸力对土体抗剪强度的贡献逐渐减弱,基质吸力对原状土与重塑土有效黏聚力的影响远大于有效内摩擦角,通过基质吸力与吸力强度之间的回归关系建立的非饱和双曲模型对预测花岗岩残积土的抗剪强度具有很好的适用性。

This study carried out triaxial undrained consolidation tests on undisturbed and remolded granite residual soil with different water contents and comparatively analyzed the effect of saturation on shear deformation characteris⁃tics of undisturbed and remodeled soils.Firstly,it obtained the relationship between matric suction and shear strength index by measuring the soil-water characteristic curve and established the unsaturated shear strength expression of the granite residual soil.The results show that the degree of strain-hardening of the undisturbed and remodeled soils in⁃creases with the increase of water content and confining pressure.The stress-strain curves of the undisturbed soils are softening and the remodeled soils are hardening under low water content and confining pressure.The change pattern of stress path with water content is basically the same in undisturbed soil and remodeled soil.With the decrease of wa⁃ter content,pore water pressure gradually decreases during shearing process,and the effective stress path gradually ap⁃proaches the total stress path.The soil-water characteristic curve of granite residual soil can be divided into three stages:saturation,transition and residual.During the dehumidification process,the residual suction of undisturbed soil is larger than that of remolded soil,and the transition area is larger than that of remolded soil.In the state of high saturation,the water contents of undisturbed and remodeled soils change little with the increase of matric suction and begin to decrease significantly with matric suction reaching the air-entry value,and the water contents change slowly in the residual stage.The influence of matric suction on the internal friction angle of soil is very small;the cohesion in⁃creases with the increase of matric suction;the adsorption internal friction angle decreases gradually;and the contribu⁃tion of matric suction to the soil shear strength decreases gradually.The influence of matric suction on the effective co⁃hesion of undisturbed soil and remodeled soil is much greater than the effective internal friction angle.The unsatu⁃rated hyperbolic model established by the regression relationship between matric suction and suction strength has a good applicability for predicting the unsaturated shear strength of residual granite soil.