地基条件对仰斜式挡墙地震响应影响及墙高限值研究

Seismic responses of inclined retaining walls on different foundations and wall height limit suggestions

摘要:

地基条件和墙高是影响挡土墙地震响应特征的重要因素。建立不同地基条件的仰斜式挡土墙有限元时程分析模型,以墙身外倾最大危险状态为最不利时刻,研究地基条件和墙高对挡墙动力响应及墙-土相互作用的影响特征,并以满足力学检算和墙身位移限值为出发点,提出同时考虑地基条件和地震峰值加速度PGA的仰斜式挡墙墙高控制建议。结果表明:岩质地基挡墙墙背动土压力沿墙高呈中部大、上下小的凸形分布,大震下土压力较中震时有小幅减小;基底反力呈墙踵为0、墙趾集中的三角形图式,且随PGA和墙高的增加踵部脱空趋势更为明显;土质地基挡墙因墙底地基土变形对墙后填土的牵连作用,填土跟随墙身运动的趋势加剧,墙背动土压力与PGA呈正相关并沿墙高近似呈线性分布,于墙底处最大;墙身往复摆动使踵趾端地基土体塑性变形较基底中部明显,基底反力峰值向中部转移;根据最不利时刻稳定性、承载力检算,考虑对墙身位移合理限制,提出地震区仰斜式挡墙的允许墙高在设防PGA不超过0.2g时为8 m,0.4g大震下硬质岩地基挡墙可达8 m,软质岩地基挡墙不宜超过6 m,碎石土、砂质黏土地基挡墙不宜超过4 m。

Abstract:

Foundation conditions and wall height affect the seismic response of retaining walls. In this study, a finite element time-history analysis model of inclined retaining walls on different foundations was established to study the influence of foundation condition and wall height on the dynamic response of retaining walls and wall-soil interaction in the most unfavorable moment. To meet the requirements of mechanical calculation and wall displacement limit, we proposed the height control of the inclined retaining wall considering the foundation condition and peak ground acceleration (PGA). The results show that the dynamic earth pressure of the retaining wall on the rock foundation was large in the middle and small at both ends, showing a convex shape along the wall height. In addition, the earth pressure under large earthquakes was reduced slightly compared with that under medium earthquakes. The contact pressure beneath the foundation was zero at the wall heel and concentrated at the toe, and this finding became more evident with an increase in PGA and wall height. For the retaining wall on the soil foundation, the backfill behind the wall followed the wall movement owing to the traction effect caused by the deformation of the foundation soil. The dynamic earth pressure at the back of the wall was positively correlated with PGA and approximately linearly distributed along the wall height and was the largest at the wall bottom. The reciprocating motion of the retaining wall made the plastic deformation at both ends of the base more important than that in the middle, and the peak value of reaction force was transferred to the middle. According to the calculation of stability and bearing capacity at the most unfavorable time and reasonable restriction on wall displacement, in the seismic area, the allowable height of the inclined retaining wall was 8 m when the PGA was less than 0.2g. Moreover, when the PGA was 0.4g, the allowable heights of the retaining wall on hard rock foundation, soft rock foundation, and gravel soil and sandy clay foundation were 8, 6, and 4 m, respectively.