中等压缩性粉质黏土不排水剪切强度试验研究

为获得原状中等压缩性粉质黏土的剪切刚度和抗剪强度,开展了直剪固结快剪和固结不排水三轴剪切(CU)对比试验,分析了偏应力随整体、局部轴向应变的发展,研究了整体、局部变形测量获得抗剪强度的差异,探讨了刚度衰减特征,提出了固结快剪和CU试验抗剪强度之间的关系。结果表明:变形测量方式对粘聚力c′影响显著,与整体相比,局部粘聚力c′提高2.9~11.1 kPa,局部内摩擦角φ′低0.4°~1.7°。剪切刚度E_sec随轴向应变ε₁增加呈反“S”形衰减。应变ε₁＜0.005%时,局部测量刚度E_sec高于整体,其衰减幅度显著,但随轴向应变增加,二者刚度差值缩小。直剪试验与CU试验抗剪强度差值随着竖向应力的增加而增大,CU试验抗剪强度明显高于直剪,建立了抗剪强度参数的修正关系。

Experimental Study on Undrained Shear Strength of Medium-compressibility Silty Clay

To obtain the small strain stiffness and shear strength of medium-compressibility silty clay, consolidated-quick direct shear test and consolidated-undrained triaxial shear test (CU) were conducted. The development of deviatoric stress with overall and local axial strain was analyzed, and the differences in shear strength indexes between overall and local deformation measurements were investigated. The attenuation characteristics of secant stiffness at different strain intervals were explored. Finally, the correction relationship of shear strength between consolidated-quick shear test and CU test was put forward. Experimental results demonstrate that the method for deformation measurement influences cohesive strength significantly. Compared with overall values, local cohesive value increases by 2.9~11.1 kPa, and local internal friction angle reduces by 0.4°~1.7°. Shear stiffness E_sec periodically attenuates with the increase of axial strain, presenting reverse-S shape. At small strain (＜0.005%), local measured stiffness E_sec is higher than overall stiffness, showing significant attenuation trends. However, with the increase of axial strain, the difference between local and overall stiffness reduces. The difference in shear strength between direct shear test and CU test increases with the increase of vertical stress. Shear strength in CU test is evidently higher than that of direct shear test. The correction relationship of shear strength indexes is firstly established.