干湿循环对粉砂土改良膨胀土裂隙及强度影响

为探究黄泛区粉砂土改良膨胀土路基在干湿循环作用下裂隙发育与强度的影响规律,设计并开展了室内干湿循环试验,分别进行了11%、13%、15%、17%四种不同含水率下改良膨胀土经历不同干湿循环次数的直剪试验,然后采用MATLAB开发的图像处理技术对干湿循环作用后的土样裂隙进行定量分析,探讨改良膨胀土的裂隙率和抗剪强度的关系。结果表明:随着含水率的增大,改良膨胀土的裂隙率、黏聚力和内摩擦角逐渐减小; 当含水率一定时,裂隙的发展随干湿循环次数的增加而增大,改良膨胀土的黏聚力和内摩擦角随着裂隙率的增大而减小; 当含水率为11%时,前两次干湿循环作用导致改良膨胀土的裂隙快速发展,裂隙率曲线较陡,黏聚力下降较快,但是内摩擦角变化不大,改良膨胀土的裂隙率和黏聚力的判定系数达到0.95; 当含水率为17%时,前4次干湿循环作用下改良膨胀土的裂隙虽然发育迟缓但裂隙率增长较快,4次干湿循环之后裂隙率的增长变得不明显,裂隙率曲线较平缓,黏聚力和内摩擦角下降较少,改良膨胀土的裂隙率和黏聚力的相关系数仅为0.70。

Influence of Dry-wet Cycle on Crack and Strength of Silty Sand Improved Expansive Soil

In order to explore the influence law of crack development and strength of silty sand improved expansive soil subgrade in the Yellow River flood area under the action of dry-wet cycle, the indoor dry-wet cycle tests were designed and carried out. Direct shear tests of improved expansive soil under four different moisture contents of 11%, 13%, 15% and 17% were carried out respectively. Then, the image processing technology developed by MATLAB was used to quantitatively analyze the cracks of soil samples after dry-wet cycle, and the relationship between the crack rate and shear strength of improved expansive soil was discussed. The results show that the crack rate, cohesion and internal friction angle of the improved expansive soil decreases gradually with the increase of water content. When the moisture content is constant, the development of cracks increases with the increase of dry-wet cycles, and the cohesion and internal friction angle of improved expansive soil decrease with the increase of crack rate. When the moisture content is 11%, the first two dry-wet cycles lead to the rapid development of cracks in the improved expansive soil. The crack rate curve is steep and the cohesion decreases rapidly, but the internal friction angle changes little. The correlation coefficient between the crack rate and the cohesion of the improved expansive soil reaches 0.95. When the moisture content is 17%, although the cracks of the improved expansive soil develop slowly under the first four dry-wet cycles, the crack rate increases rapidly. After the four dry-wet cycles, the growth of the crack rate becomes insignificant, the crack rate curve is relatively flat, and the decreases of cohesion and internal friction angle are less. The correlation coefficient between the crack rate and cohesion of the improved expansive soil is only 0.70.