膨胀土的强度及其测试方法

Shear strength of expansive soil and its test method

膨胀土的强度参数是膨胀土边坡稳定分析的基础。膨胀土的特殊性以及膨胀土边坡失稳机理的复杂性使得膨胀土强度指标的获取和取值十分困难。以往对于膨胀土的强度曾开展过大量的研究工作,但无论是研究体系,还是试验方法以及强度取值原则都存在一定的差异。人们关注到膨胀土裂隙的存在,却又难以实测到裂隙面上真实的强度指标;关注到膨胀土的非饱和特性,并试图用含水率变化引起的强度衰减来解释边坡的失稳机理;然而,无论采用何种理论,都难以将膨胀土的强度与边坡的失稳机理有机的联系在一起,造成在实际工程中数值分析与边坡实际稳定状态不符的现象。仅从强度理论上讲,膨胀土仍然是一种黏性土,仍然应符合莫尔–库仑强度准则。所不同的是,由于裂隙的存在,使得膨胀土的强度时而显示出均匀介质的特性,时而显示出非均匀介质的特性。因此,研究膨胀土的强度特性,不可避免的要研究裂隙以及裂隙对强度的影响问题。在大量现场工作和室内试验研究的基础上,重点探讨了裂隙对膨胀土强度的影响,提出对于膨胀土的强度应以土块强度和裂隙面强度两套指标进行描述,而土块强度又应区分为有胀缩裂隙和无胀缩裂隙两类,并进一步提出了不同强度的测试方法。

Shear strength parameters are necessary for slope stability analysis of expansive soil. It is difficult to obtain the shear strength parameters of expansive soil because of particularity of expansive soil and complexity of failure mechanism of expansive soil slopes. The researches on the shear strength of expansive soil are availabe, including research system, test methods and valuing principle of shear strength parameters. Focusing on the existence of fissures, it is difficult to measure the shear strength of fissure-plane. At the same time, researchers attempt to reveal the failure mechanism of expansive soil slopes through reduction of shear strength resulted from decrease of water content based on unsaturated soil mechanism. However, the previous records have failed to provide reasonable relationship between slope failure mechanism and shear strength of expansive soil, which leads to failure of numerical analysis in modelling the stability of slope stability in the engineering practice. In the view of shear strength theory, expansive soil is clay and follows the Mohr-Column criterion. Owing to the existence of fissures, expansive soil has the characteristics of both homogeneous and heterogeneous media. So the effect of fissures on the shear strength of expansive soil should be studied in the researches on shear strength behaviour. Based on the in-situ and laboratory tests, it is suggested that the shear strength of expansive soil should be described by the strength of soil block without fissure plane and strength of fissure-plane, and the strength of soil block should be divided into strength with shrinkage crack and without shrinkage crack. Finally, the test method for the shear strength of expansive soil is proposed.