浅层膨胀土及其纤维改良土的剪切强度特性  

Shear strength characteristics of shallow expansive soil and its fiber improved soil

作　　者：段君义 吴俊江 粟雨 吕志涛 林宇亮[2] 杨果林[2] DUAN Junyi;WU Junjiang;SU Yu;LV Zhitao;LIN Yuliang;YANG Guolin(School of Infrastructure Engineering,Nanchang University,Nanchang 330031,China;School of Civil Engineering,Central South University,Changsha 410075,China)

机构地区：[1]南昌大学工程建设学院,江西南昌330031 [2]中南大学土木工程学院,湖南长沙410075

出　　处：《浙江大学学报（工学版）》2024年第3期547-556,569,共11页Journal of Zhejiang University：Engineering Science

基　　金：国家自然科学基金资助项目(52208348,52208347);江西省自然科学基金资助项目(20232BAB204083,20224BAB214064,20224BAB214063);中国博士后基金资助项目(2023M731436);西康高铁膨胀土路基建造关键技术研究资助项目(XKGT-07-GGB2022-037)。

摘　　要：与膨胀土工程灾害密切相关的浅层膨胀土受到的围压通常较低,其力学特性有别于高围压下的情形.通过三轴剪切试验比较高、低围压下膨胀土的剪切行为及剪切强度的非线性特征,探讨聚丙烯纤维改良浅层膨胀土的剪切特性及加固机理.结果表明,浅层膨胀土剪切强度具有明显的非线性,可用幂函数表征.随着土体中水的质量分数增大和围压减小,膨胀土剪切强度非线性更加明显.采用高围压下的抗剪强度参数试验结果会导致浅层饱和膨胀土的黏聚力被高估225.7%、内摩擦角被低估42.5%.掺入纤维后膨胀土的剪切强度明显提高,提升幅度与土体中的三维纤维网状结构的形成度有关.增大纤维长度可以有效降低剪切强度衰减率,继而消弱膨胀土的应变软化效应;过长的纤维在膨胀土内容易弯曲和扭折,会导致纤维-膨胀土界面作用随着土体变形而逐渐劣化.The shallow expansive soils,closely related to the engineering disaster of expansive soils,are usually subjected to low confining pressures,and their mechanical properties are different from those under high confining pressures.Triaxial shear tests were conducted to compare the shear behavior and nonlinear characteristics of the shear strength of expansive soil under high and low cell pressures.The shear properties and reinforcement mechanism of shallow expansive soil improved by polypropylene fibers were explored.Results showed that the shear strength of shallow expansive soil exhibited significant nonlinearity,which could be represented by a power function.Moreover,it was observed that the nonlinearity of the shear strength of the expansive soil became more prominent with the increase of mass fraction of water and the decrease of cell pressure.Adopting shear strength parameters obtained from triaxial shear tests under high cell pressure led to an overestimation of the cohesion of saturated shallow expansive soil by 225.7%and an underestimation of the internal friction angle by 42.5%.The shear strength of expansive soil was significantly enhanced by adding fibers,and the degree of enhancement was related to the formation of three-dimensional fiber network within the soil.Longer fibers were more effective in reducing the attenuation rate of shear strength,which weakened the strain-softening effect of expansive soil.However,excessively long fibers may bend and twist within the soil,leading to the degradation of the fiber-expansive soil interface during soil deformation.

关 键 词：低围压 膨胀土 剪切强度 纤维网状结构 应变软化 纤维-土体界面作用 

分 类 号：TU443[建筑科学—岩土工程]