卸荷损伤原状膨胀土剪切力学特性试验研究

通过GDS三轴试验系统对经历3种卸荷速率损伤后的原状南阳膨胀土样进行再加荷不排水三轴伸长剪切试验，同时考虑了超固结比与固结状态的影响。试验结果表明，膨胀土再加荷剪切力学特性与初始卸荷速率有关。在相同的轴向应变下，初始卸荷速率越小，其偏应力单调越小。在主应力方向改变前后，其应力?应变关系曲线斜率显著变化。相同固结方式与超固结比状态下，孔隙水压力均表现为先增大后减小趋势，孔隙水压力峰值应变随卸荷速率增大而减小。无论是等压固结还是K0固结，初始卸荷速率越大，不排水剪切强度越大。膨胀土样经历了初始卸荷损伤后，再加荷常规三轴伸长试验所得剪切强度均低于无损伤时的强度。以膨胀土破坏强度所得损伤度SD低估了卸荷速率对膨胀土的损伤程度，建议采用孔隙水压力峰值强度进行膨胀土边坡设计计算。原状膨胀土力学性状随卸荷速率损伤的演化规律受卸荷阶段轴向应变大小及裂隙性综合影响。

Experimental study on shear mechanical properties of unloading damaged undisturbed expansive soil

To study the mechanical characteristics of unloading rate damage effect for Nanyang undisturbed expansive soil, the unloading-reloading undrained triaxial shear test was conducted with three unloading rates (0.02 kPa/min, 0.2 kPa/min and 2 kPa/min) through the GDS triaxial test system. The effect of over-consolidation ratio and consolidation state have also been studied. Test results showed that the shear mechanical properties of expansive soil are related to the initial unloading rate. Under the same axial strain, the deviatoric stress is smaller with lower initial unloading rate. The slope of stress-strain curve changed significantly before and after the principal stress direction rotation. Under the same consolidation state and over-consolidation ratio, pore water pressure increased first and then decreased. Peak pore water pressure strain decreases as the unloading rate increases. As the unloading rate decreases, the tangential modulus of the undisturbed expansive soil decreases monotonously. The higher the initial unloading rate, the greater the undrained shear strength. After the initial unloading damage of expansive soil sample, the shear strength obtained by reloading conventional triaxial elongation test was lower than that of non-damage soil sample under both isotropic consolidation and K0 consolidation. The damage degree SD obtained by the failure strength qf of expansive soil greatly underestimated the damage degree of the damage rate to expansive soil. It is recommended to use the strength of peak pore water pressure qumax to design and calculate the slope of expansive soil. The mechanical properties evolution of undisturbed expansive soil with unloading damage rate is influenced by the axial strain and cracking character.