干湿循环下膨胀土现场大型剪切试验研究

Field tests on expansive soil during wetting-drying cycles using large shear apparatus

为获得干湿循环作用形成的裂隙对膨胀土抗剪强度特性的影响,采用现场大型剪切仪分别对未经历和经历干湿循环作用的膨胀土进行了剪切试验。膨胀土未经历干湿循环作用时,剪切位移较小时剪应力即可达到峰值,随后逐渐降低;试样的应力应变关系均呈现出明显的软化特征。经历干湿循环作用后的膨胀土,峰值剪应力与未经历干湿循环作用的相比明显减小,而软化特征不明显。经历干湿循环作用的膨胀土抗剪强度参数都有不同程度的降低,其中黏聚力降低幅度较大,摩擦角降低幅度较小。试验结果表明干湿循环诱发膨胀土裂隙发育,抗剪强度迅速衰减,是导致膨胀土工程失稳破坏的主要因素。

In order to obtain the characteristics of strength of field expansive soil including cracks caused by wetting-drying cycles,the specimens both with and without undergoing wetting-drying cycles are tested by means of the field large shear apparatus.When the expansive soil does not undergo wetting-drying cycles,the shear stress reaches the peak value quickly and then reduces gradually;the stress-strain relations show the obvious softening.When the expansive soil undergoes wetting-drying cycles,the peak shear stress is much less than the values of expansive soil and the characteristics of softening are less obvious compared with those of the expansive soil which does not undergo wetting-drying cycles.The shear strength of expansive soil undergone wetting-drying cycles decreases to some degree compared to that of undisturbed expansive soil,and the decreased degree of cohesion is much greater than that of friction angle.It is shown that crack propagation due to wetting-drying cycles result in the reduction of shear strength,and it is the major factor to lead to instability and damage of projects in expansive soil areas.