Experimental study on the influence of crack penetration rate on long-term strength and deformation characteristics of expansive soil

There are a large number of cracks frequently distributed within expansive soil, which significantly affects the mechanical properties of the soil. To explore the influence of the crack penetration rate on the creep properties of expansive soil, geomembrane was selected to simulate the internal cracks of the soil mass, and triaxial creep tests under unloading paths were carried out. The research results demonstrate that cracks have an obvious weakening effect on the strength of expansive soil. As the crack penetration rate increases, the ultimate failure deviatoric stress of the specimens shows a linear decreasing trend. During the unloading creep test, under relatively low deviatoric stress, the creep curves exhibit the characteristics of attenuated creep and steady-state creep. With the increase in the deviatoric stress level, the creep curves start to display the characteristics of accelerated creep, and shear failure occurs within a short period of time, resulting in relatively large axial deformation. In the process of creep of expansive soil, its stress-strain isochronous curves deflect significantly, transitioning gradually from linear characteristics to nonlinear ones, and presenting obvious nonlinear variation characteristics. Before the specimens are completely damaged, the axial strain rates under the action of deviatoric stresses at all levels gradually decrease from their initial values, and as the deviatoric stress increases, the initial creep rates at the corresponding levels show an increasing trend. Based on the isochronous curve method, the long-term strength value of expansive soil containing cracks was established. The results indicate that under the action of long-term loads, the long-term strength of the soil mass is significantly reduced, approximately accounting for 54.5 - 60.5% of the ultimate failure deviatoric stress. According to the creep characteristics of expansive soil, an exponential creep empirical model was established in this paper, and the test results were fitted. The fitting accuracy is above 0.97, showing good applicability. The research results can provide a reference for the long-term stability issues of soil containing cracks.