地震作用下非饱和土主动土压力极限分析半解析法

地震是诱发边坡失稳的主要因素之一,重力式挡土墙作为一种广泛采用的岩土支挡结构,有必要对其地震稳定性问题进行深入的研究.为有效评估地震作用下非饱和填土的主动土压力,基于极限分析上限原理和拟动力法,提出一种半解析水平片分法,计算具有非线性分布特征的非饱和土重力和地震惯性力所做外功率,并构建功能平衡方程,得到非饱和填土主动土压力显示半解析解.通过与解析解对比,验证该方法的合理性,并通过算例分析,揭示吸力效应的强化机制和非饱和填土主动土压力的地震响应规律.结果表明:忽略吸力效应会高估填土的主动土压力,吸力的强化作用不仅取决于填土类型,还与地震动特性密切相关;水平和竖向地震动对土压力有较大影响, 土压力系数峰值随土剪切模量的增加略有增加并向负方向移动,随地震周期的增加略有增加并向正方向移动;填土倾角较大时,坡顶附加荷载的影响更加显著;对于倾角大于100°的填土,墙G土界面摩擦角较大时,土压力相对较高.

Semi-analytical method for the limit analysis of active earth pressure of unsaturated soil under seismic action

Earthquake is one of the main factors that induce slope instability. As a widely used geotechnical retaining structure, the seismic stability of gravity retaining walls remains a popular topic in geotechnical engineering. A semi-analytical horizontal slice method is proposed on the basis of the upper bound limit theory and the pseudodynamic approach to evaluate the active earth pressure of unsaturated filling soil under seismic action effectively. The work rates of unsaturated soil gravity and seismic inertia force with evident nonlinear distribution characteristics were computed to formulate the energy balance equation. The semi-analytical solution of active earth pressure was formulated explicitly according to the equation and then compared with the analytical solution to validate the proposed method. Parametric analyses of the impacts of soil suction and seismic excitations on the earth pressure estimations were also conducted. The findings demonstrate the following: (1) the active earth pressure is overestimated when soil suction is disregarded in the analyses. The suction effect relates not only to the type of filling soil but also to the characteristics of ground motion. (2) The active earth pressure depends significantly on the horizontal and vertical ground motions. The peak earth pressure slightly increases with the soil shear modulus and moves toward the negative direction; as the seismic period increases, the peak earth pressure slightly rises and moves toward the positive direction. (3) The impact of surcharge load on the earth pressure becomes increasingly evident in filling soil with large inclination angles. For filling soil with an inclination angle larger than 100^°, the earth pressure becomes markedly pronounced with large soil-wall friction angles.