高堆石坝土工格栅抗震加固效果分析

Aseismic strengthening effect of geogrid in high rockfill dam

强震区高堆石坝坝顶堆石体常由于地震加速度放大效应处于不稳定状态,目前比较经济有效的抗震措施是在坝顶一定范围内加筋来提高堆石体的强度和自稳能力。土工格栅以其与土石体相互作用的优越性而被广泛运用于土石坝坝顶抗震加固工程。以240 m高长河坝心墙堆石坝为例,分析土工格栅对强震区坝顶堆石体的抗震加固效果。运用时程法对加筋坝体进行动力反应分析,利用动力响应应力结果并结合Newmark滑块法理论,采用滑面应力分析有限元法对加筋限制高堆石坝地震永久变形的工程效果进行研究和探讨。结果表明,动力作用下格栅所受最大拉力远小于其抗拉强度,且加筋基本不影响坝体动力反应结果。可一旦坝坡发生滑移,加筋能使地震永久位移减少40%～50%,有效限制坝顶堆石体侧向滑移,提高了坝体抗震稳定性。抗震稳定性又对加筋长度与竖向加筋间距敏感,较适宜的加筋长度及间距分别为40～60 m和1～4 m。

Rockfill is unstable because of the magnification of earthquake acceleration on the top of high rockfill dams located in strong earthquake areas.To improve the strength and stability of the rockfill,reinforcement for the rockfill at the upper part of dams is an economical and effective measure.Geogrid has been widely used in aseismic reinforcement because of its superiority in interaction with rock and earth.240 m-high Changhe Dam core rockfill dam is taken as an example,and the aseismic strengthening effect is analyzed when geogrid is used in the rockfill of dam crest.Dynamic response of the reinforced dam is analyzed by means of the time-history method.The results are introduced into the finite element method for slip surface stress analysis to investigate the effectiveness of restricting permanent deformation of high reinforced rockfill dams based on the Newmark＇s sliding mass method.The results indicate that during the earthquake the force on the geogrid is much less than its tensile strength,and reinforcement has little influence on the dynamic response of the dam.But once slope slips,the reinforcement reduces the permanent deformation up to 40%~50%,limits lateral movement of the rockfill at the dam crest effectively and improves the aseismic stability of high rockfill dams.The stability is sensitive to reinforced length and vertical spacing,and their rational values are 40~60 m and 1~4 m respectively.