三维非饱和土边坡拟动力稳定性分析初探

Three-dimensional seismic stability of unsaturated soil slopes using pseudo-dynamic approach

边坡在地震作用下极易失稳破坏且通常伴随明显的三维破坏特征,增加边坡阶数并结合抗滑桩等加固措施可有效提高边坡的动稳定性,广泛用于滑坡灾害防治中。基于极限分析上限原理并结合拟动力法,将塑性变形理论扩展至非饱和土中,改进已提出的半解析水平片分法,计算具有非线性分布特征的非饱和土重力、地震惯性力和抗滑桩侧阻力所做外功率和表观黏聚力的功率耗散率,与解析解对比,验证了该方法的合理性。通过算例分析,探究了非饱和土边坡的地震响应规律,揭示了吸力对边坡地震稳定性及抗滑桩加固效果的强化作用。结果表明:吸力对边坡稳定性的贡献可达15%~30%,且与地震动特性密切相关,地震波达到峰值时,吸力效应得到显著加强;水平加速度系数和土体剪切模量对边坡地震稳定性影响较大;地震作用下边坡将出现明显的“浅层”滑动现象。

The seismic excitation remains the main factor in triggering the slope failures that present three-dimensional(3D)features universally.The slopes combined with anti-slide piles are the effective reinforcement techniques in improving the slope stability and are widely employed in slope failure preventions.Based on the upper bound limit analysis theorem and the pseudo-dynamic approach,the plasticity deformation theory is extended to unsaturated soils,and a modified horizontal slice method is proposed to calculate the work rates of unsaturated soil gravity,seismic inertial forces and pile lateral resistance forces as well as the energy dissipation rate of apparent cohesion that are all characterized with nonlinear distribution features.The semi-analytical method is validated through comparisons with the analytical solutions.A series of parametric analyses are conducted regarding the seismic responses of unsaturated soil slopes.The improvements in seismic slope stability due to soil suction are studied systematically.The results show that the slope safety is underestimated by 15%~30%when the soil suction is not considered in the analyses.The suction effects depend on the seismic excitations and are enhanced significantly when the seismic wave approaches the peak.The horizontal acceleration coefficient and soil shear modulus both have a great influence on the slope stability.The critical slip surface becomes much shallower under excitation conditions.