重力式挡土墙地基抗震承载力探讨

Discussion on seismic bearing capacity of gravity retaining wall’s foundation

高烈度地震区重力式挡土墙由于地基承载力不足导致墙身失稳是一种较常见震害类型。基于拟静力法原理,利用极限分析上限定理对地震作用下挡土墙地基极限承载力进行求解,通过典型算例分析了极限承载力随地震动峰值加速度的变化关系与机理,讨论了地基土强度参数对其变化趋势的影响,提出了同时考虑设防烈度和地基土性的挡土墙地基抗震容许承载力修正方法及相应修正系数取值建议。结果表明:设防烈度在9度及以内时,随着地震动峰值加速度增加,挡土墙地基极限承载力近似呈线性下降,下降速率与地基土黏聚力呈负相关性,而受内摩擦角的影响不显著;地震作用加剧挡土墙基底荷载倾斜与偏心导致地基破坏区缩减是造成极限承载力下降的主要原因;设防烈度大于7度时,挡土墙地基抗震容许承载力较天然工况下有所降低,8度和9度设防烈度对应的修正系数约为0.9和0.7。

Loss of bearing capacity of gravity retaining wall’s foundation leading to instability of wall body occurred frequently in high intensity earthquake-hit areas.Based on pseudo-static approach and upper-bound theorem of limit analysis,the ultimate bearing capacity of retaining wall’s foundation under seismic load is solved.By means of a typical case,the variation of the ultimate bearing capacity with peak acceleration of ground motion and its mechanism as well as the influence of strength parameters of foundation soil on it are analyzed.Finally,a correction method with suggested correction factor related to both seismic fortification intensity and soil property were proposed for seismic allowable bearing capacity of gravity retaining wall’s foundation.The results show that the ultimate bearing capacity decreases approximately linearly as peak acceleration increases when seismic fortification intensity isn’t more than 9 degree.The attenuation rate of ultimate bearing capacity is negatively correlated with cohesion of foundation soil,but not significantly affected by internal friction angle.Main cause of the decrease is that earthquake aggravates the inclination and eccentricity of base load causing reduction of failure zone of foundation.The allowable bearing capacity in seismic condition is less than that in natural condition when seismic fortification intensity is more than 7 degree,the correction factorψ’for 8 and 9 degree are approximately 0.9 and 0.7 respectively.