非饱和膨胀土总强度指标随饱和度变化规律

Variation of the total shear strength of unsaturated expansive soils with degree of saturation

建立在有效应力基础上的非饱和土强度理论公式参数测试复杂、不便于工程应用,而包含吸附强度的总强度指标也能反映非饱和土的强度特性且易于获取。为此,以土水特征曲线为理论依据,采用抽气饱和、风干脱水法控制试样的饱和状态,用常规直剪仪对不同状态下的宁明膨胀土进行固结快剪试验,得到其总强度指标随含水量、饱和度的增大而衰减的变化规律。其中,黏聚力、内摩擦角的对数和含水量之间以及内摩擦角与饱和度之间成线性关系;黏聚力随饱和度的变化可用二次抛物线描述。对该规律的普遍性还用廖世文、卢肇钧同类试验结果的分析来加以检验。此外,针对膨胀土路堑边坡滑坍的特点,对如何将非饱和膨胀土总强度指标用于边坡稳定性分析进行探讨,研究结果可为工程应用提供参考。

The shear strength formula for unsaturated soils, based on the effective stress principle, is difficult to apply in engineering practice, because of the complications in measurements of its parameters. However, the indices of total shear strength including suction strength not only can express the features of the strength of unsaturated soils, but also can be easily obtained. For this reason, several groups of Ningming expansive soil specimens were kept under a certain range of saturations by using vapor extraction and air-drying methods, according to the theory of soilwater characteristic curve. Then, a series of tests on the specimens were conducted with consolidation and quick shearing method using a conventional direct shear apparatus. The total shear strength decreases with increase of saturation degree. Furthermore, the relationships between the logarithm of cohesive force, frictional angle and saturation degree are linear; the variation of cohesive relationship. This relationship was also validated by force with saturation degree can be described by a the test results obtained by Liao Shiwen and Lu parabolic Zhaojun. Application of the indices of total shear strength to slope stability analysis was also discussed.