裂缝对膨胀土抗剪强度指标影响的试验研究

基于室内直剪试验，测定了膨胀土经历干湿循环后的抗剪强度指标。试验基本反映了膨胀土在干湿循环过程中裂缝的开展现象，揭示了正是由于裂缝的开展使膨胀土强度降低。结果表明，无论是黏聚力还是内摩擦角随裂缝的开展，都会产生一定程度的衰减，相比之下，裂缝对黏聚力的影响更加突出，对其取值也应更为谨慎。膨胀土的抗剪强度随裂缝的开展而衰减的规律符合双曲线模式，提出反映膨胀土抗剪强度随干湿循环次数增加，实际上是随裂缝的开展，而降低规律的经验公式。工程实际中膨胀土的抗剪强度反映的是包含各种裂隙的土体复合强度，因此在设计中，强度参数的取用应以考虑裂隙作用的土体强度为基本依据。所建议的方法可以使今后研究膨胀土裂隙的发生、发展对抗剪强度的影响变得相对简单，具有可操作性。

Test study of influence of crack evolution on strength parameters of expansive soil

The strength parameters are obtained with consideration of influence of wetting and drying cycles by an experiment based on laboratory direct shear test. The test basically reflects the phenomenon of crack evolution with wetting and drying cycles and reveals that crack evolution results in strength degradation. The results show that both cohesion and internal friction angle will attenuate along with crack evolution. Comparatively, cohesion index will be affected more obviously by crack and its determination should be more cautious. The law of attenuation accords with hyperbola; and the empirical expressions are proposed, which show that the relationship between attenuation of shear strength with increase of wetting and drying times is in fact with crack evolution. The expansive soil in engineering practice includes all kinds of cracks; therefore, in the design, the selection of strength parameters should consider the crack in the expansive soils. As the same time, the test method proposed makes the research of influence of crack evolution on the strength characteristics relatively simple and feasible.