常含水率下Q_(3)原状黄土的应力-应变、吸力变化及临界状态特性

Stress-strain, suction variation and critical state characteristics of Q_(3) undisturbed loess under constant water content

黄土高原地区存在恒定含水率加载的工况,为了模拟这种排水条件下土体的受力变形情况,采用GDS非饱和三轴仪对兰州不同初始吸力的Q_(3)原状黄土在常含水率条件下进行了三轴等向压缩和常规剪切试验,研究其应力—应变、吸力变化及临界状态特性。等向压缩试验结果表明:初始吸力愈大,压缩变形愈小,吸力减小程度愈大;等向应力愈大,饱和度增大程度愈大。三轴剪切试验结果表明:应力—应变曲线呈硬化型,偏应力对吸力的减小程度影响不大,主要影响饱和度的增大程度;初始吸力10~100kPa范围内,q-p临界状态线相互平行,用饱和土的临界状态线统一描述;e-lnp′临界状态线随初始吸力增大平行上移,其截距与初始吸力呈双曲线关系,饱和土的e-lnp′临界状态线斜率偏小,不同初始吸力非饱和土与饱和土的临界孔隙比之比,与临界饱和度(气体饱和度)的关系可归一。研究成果为排水条件差的黄土材料测试及工程应用提供参考。

There is a constant water content loading condition in the Loess Plateau.In order to simulate the stress and deformation of the actual soil under such drainage conditions,the GDS unsaturated triaxial instrument with controllable drainage conditions was used to conduct isotropic compression and triaxial shear tests on the Q_(3) undisturbed loess from Lanzhou,China with different initial suction under the condition of constant water content,to investigate the stress-strain,suction change and critical state characteristics of Q_(3) undisturbed loess.The results of the isotropic compression test show that the greater the initial suction is,the smaller the compression deformation is and the greater the reduction of suction is;the greater the isotropic stress is,the greater the saturation degree increases.Triaxial test results show that the stress-strain curve is hardening model,and the deviator stress has little effect on the degree of suction reduction,and mainly affects the degree of saturation increase;the initial suction range within 10~100 kPa,the q-p critical state lines are parallel straight lines to each other,which can be described uniformly by the critical state lines of saturated soil;the e-lnp′critical state line moves up parallel with the increase of the initial suction,its intercept is hyperbolic relationship with the initial suction,and the slope of the e-lnp′critical state line of saturated soil is obviously smaller.The relationship between e_(fs)/e_(f0) and S_(r)(1-S_(r))can be described by the normalization method,where e_(fs)/e_(f0) is the ratio of critical void ratio between unsaturated soil and saturated soil with different initial suction,S_(r)(1-S_(r))is the critical saturation(gas saturation).The study results would provide references for testing and engineering applications of loess materials with poor drainage conditions.