In-situ Mechanical Property and Mechanism Analysis of Shallow Expansive Soil under the Influence of Water Content and Fissures

The mechanical properties of shallow expansive soil are crucial to expansive soil engineering. However, few effective test methods have been available to measure the in-situ mechanical properties of shallow expansive soil. This paper attempts to test the effects of water content and fissures on the mechanical properties of shallow expansive soil under a natural state by in-situ CBR and resilience modulus tests. The evolution characteristics of shrinkage fissures in expansive soil were recorded and observed. The fissure connectivity coefficient is used to express the degree of fissure development and the integrity of soil structure. The CBR strength and resilience modulus of expansive soil increase first and then decrease with the decrease of water content and the increase of fissure development degree, and reach the peak near the optimal water content. It is effective to use the inverse hyperbolic sine function to fit the relationship between soil mechanical parameters, water content, and fissure connectivity coefficient. When the water content is higher, the influence of water content on soil mechanical properties is great. When the water content is lower, fissures are more developed, and the influence of fissures on soil mechanical properties is dominant.