干湿循环效应对风化砂改良膨胀土抗剪强度影响研究

Influence of Wet-Dry Cycles on the Shear Strength of Expansive Soil Modified by Weathered Sand

将风化砂按10％,20％,30％,40％,50％比例掺入膨胀土中,分别进行0～5次干湿循环,然后采用四联直剪仪进行直剪试验,研究干湿循环作用对风化砂改良膨胀土抗剪强度的影响.试验结果表明：①内摩擦角在第1次干湿循环之后有小幅度的提高,随着干湿循环次数的继续增大,内摩擦角逐渐减小,最后趋于稳定;黏聚力随干湿循环次数的增加,呈二次函数形式衰减;②抗剪强度随着干湿循环次数的增加而衰减,且在第2、第3次循环过程中,衰减幅度最大,之后逐渐减小最后趋于稳定.综合考虑干湿循环次数以及掺砂比例对抗剪强度指标的影响,当掺砂比例为30％时,膨胀土抗剪强度最高,且可有效抑制膨胀土由于干湿循环效应所导致的抗剪强度的衰减,能够达到路基填筑用土的标准,更重要的是降低改良后土体对季节气候变化的敏感性,抑制其在干湿循环效应下抗剪强度的降低,确保工程建设的安全.

To research the influence of wet-dry cycles on the shear strength of expansive soil modified by weathered sand,indoor direct shear tests were carried out by quad direct shear apparatus. Before the shear tests,the expansive soils were first mixed with weathered sand in a ratio of 10%,20%,30%,40%,and 50% respectively,and then treated by wet-dry cycles for 0-5 times. Results showed that: 1) after the first wet-dry cycle,internal friction angle increased slightly. As the number of wet-dry cycle increased,the internal friction angle gradually decreased and finally became stable. With the increase of wet-dry cycles,cohesion decreased in a quadratic function. 2) Shear strength declined with the increase of wet-dry cycles. The decline reached the maximum in the second and third cycles,and then gradually mitigated and finally stabilized. When the mix rate of weathered sand was 30%, the shear strength of expansive soil reached the maximum,and the attenuation of shear strength induced by wet-dry cycles could be effectively alleviated. Moreover,the sensibility of modified expansive soil to seasonal climate change could be reduced,and the project safety is ensured.