Variations in excavation construction periods for fissured soil transportation engineering lead to differing unloading rates, which affect the soil's mechanical properties. This study utilizes a triaxial testing system to conduct monotonic and cyclic loading undrained shear tests on undisturbed fissured samples as well as remolded samples subjected to three distinct unloading rates. The K0 consolidated samples are regarded as soil mass that undergoes no unloading during testing. The findings indicated that the initial unloading rate influences the reloading shear mechanical properties of undisturbed and remolded specimens. The effects of unloading rates differ between undisturbed and remolded soil, a discrepancy attributed to inherent fissures. Specifically, undisturbed soil exhibits significant damage at low unloading rates due to fissures, while remolded soil experiences strength augmentation due to compaction with decreased unloading rates. Similarly, unloading will cause a loss of strength. Structural disparities result in the monotonic loading strength of undisturbed specimens being higher than that of remolded ones. In contrast, remolded specimens demonstrate greater dynamic strength under cyclic loading, likely because fissures deform, diminishing overall dynamic strength. Subsequent microscopic analysis, utilizing SEM images, along with a discussion of macroscopic inherent fissures, elucidated the impact of unloading rate on soil damage mechanisms, advancing the understanding of fissured soil behavior post- unloading. The study of mechanical properties of fissured soil following varying unloading rates is crucial for comprehending its damage mechanism and determining post-unloading soil strength parameters, providing valuable insights for practical applications in soil engineering.

The selection of structural strength indicators is of utmost importance for slope engineering safety. This paper, with the backdrop of the destruction of high liquid limit clay layers in the Huai River slope, aims to investigate the influence of dry-wet (D-W) cycles on the structural and mechanical properties of undisturbed high liquid limit clay. Through unconfined compression tests, scanning electron microscopy (SEM) tests, and triaxial shear tests, the structural behavior, stress-strain curves, porewater pressure-strain curves, and effective stress paths of undisturbed samples taken at three different angles and reconstituted samples were analyzed under the condition of maximum drying stress with 0 and 1 D-W cycle. Based on the impact of D-W cycles on the effective stress path, the shear failure mode of structurally high liquid limit clay under the influence of D-W cycles was identified. A method for evaluating the anisotropic level of structural clay after experiencing D-W cycles was proposed. The test results show that compared with reconstructed soil, the undisturbed high liquid limit clay with structure is more significantly affected by the D-W cycle. After D-W cycles, the CU shear strength of high liquid limit clay increased significantly. The failure mode transitioned from a hardening-shear dilation mode to a softening-partial shear contraction-partial shear dilation mode. The appearance of the phase transition state (PTS) point may be attributed to the partial action of effective stress on cracks inside the sample, resulting in shear contraction. D-W cycles weakened the structural properties (anisotropy) of high liquid limit clay.