轻量砂抗剪强度特性三轴试验研究

Triaxial compression test on shear strength characteristics of light weight sand

为了开发利用轻量砂,在对国内外具有明确物理含义的土的破坏取值标准进行系统研究的基础上,通过三轴试验对轻量砂的抗剪强度特性进行研究。研究结果表明:土的破坏取值标准有变形标准和强度标准,二者统一于有效应力原理,都与孔压发展路径有密切关系。应力-应变曲线的软化、硬化是轻量砂剪胀和剪缩的外在表现,软化型宜采用最大有效主应力比或最大主应力差标准,二者不会导致轻量砂抗剪强度指标的显著差别,硬化型宜采用轴向应变15%标准。轻量砂的Mohr破坏包线形态是由其原生结构强度与围压共同决定的,当围压大于试样的结构屈服应力,破坏包线可以用直线表示。黏聚力和有效黏聚力随着EPS球粒掺入比的增大而减小,随着水泥掺入比和龄期增大而增大;内摩擦角和有效内摩擦角随着EPS球粒掺入比的增大而减小,随着水泥掺入比和龄期增大而增大。EPS球粒的空间置换效应与水泥的结点固化效应共同决定轻量砂的抗剪强度特性。

To make use of light weight sand,soil failure criterions of definite physical meaning were researched,then shear strength characteristics of light weight sand were studied by triaxial compression test.The results show that there are two types of soil failure criterions： deformation criterion and strength criterion,the two are unified by effective stress principle,and they have close relation with pore pressure development path.Strain softening and strain hardening are external behavior of shear dilatancy-contraction for light weight sand.Maximum effective principal stress ratio criterion or maximum principal stress difference criterion should be used for the softening condition,the two criterions are unable to lead to significant difference for shear strength parameters of light weight sand,and axial strain criterion（15%） should be used for the hardening condition.Mohr failure envelope shapes of light weight sand are decided by primary structural strength and confining pressure,when confining pressure is higher than its structural yield stress,failure envelope is a beeline.Cohesion and effective cohesion decrease with increased EPS（expanded polystyrene） mixed ratio,increase with increased cement mixed ratio and age;internal friction angle and effective internal friction angle decrease with increased EPS mixed ratio,increase with increased cement mixed ratio and age.Shear strength characteristics of light weight sand are decided by spatial substitution effect of EPS beads and node cementation effect of cement.