考虑基坑宽度及软弱土层厚度的基坑抗隆起稳定可靠度研究

坑底隆起破坏是导致基坑失稳的关键因素之一。对坑底隆起的影响因素展开研究工作,分析基坑宽度以及软弱土层厚度对坑底隆起变形以及基坑抗隆起稳定可靠度的影响规律。首先,建立不同工况的基坑开挖有限元模型,获取坑底不同特征点的隆起变形值,分析其变形规律,进而构建基于隆起变形限值的坑底抗隆起失效极限状态函数,最后采用蒙特卡罗法对坑底进行概率分析。数值模拟结果表明:当软弱土层厚度足以使隆起破坏滑动面贯通时,窄基坑的坑底两侧隆起变形大,中间小,宽基坑隆起变形规律与之相反;两种类型基坑坑底隆起变形都随基坑宽度增加而增大。改变软弱土层厚度,坑底各特征点隆起变形值随之变化,当为窄基坑时,坑底隆起变形依旧是中间小,两侧大;当基坑为宽基坑时,随软弱土层厚度增加,隆起变形随之增大,且坑底中心隆起变形逐渐超过两侧隆起变形;依据变形规律得到不同宽度基坑隆起破坏滑动面贯通时的软弱土层厚度。坑底抗隆起稳定可靠度与基坑宽度、特征点位置以及软弱土层厚度有关,坑底的稳定状态以及可靠度最低的特征点位置随基坑宽度以及软弱土层厚度变化而变化。

结合工程实例浅谈岩土工程可靠度

目前,综合国内外情况看,采用概率极限状态设计法为原则研究岩土工程的可靠度分析方法是发展的大趋势。但是由于岩土的变异性大,区域性强,故对其研究迟迟没有全面展开。本文结合具体的工程来对基坑抗倾覆的可靠度进行研究:根据基坑的破坏模式,结合具体的工程实例对支护抗倾覆稳定性的可靠指标进行了计算和分析。并根据现行规范设计方法进行校准提出了抗倾覆稳定性目标可靠指标的建议值。

Reliability analysis of anti-pull piles under excavation

The impact of excavation on the reliability of anti- pull piles is studied, and three cases of reliability analysis, named reliability of ultimate limit state （ULS）, reliability of serviceability limit state （SLS） and reliability of system （SYS） are studied. The reduction factor of the pile capacity is used to calculate the reliability indices for the three cases. The ratio ξ of the pile capacity of SLS to the pile capacity of ULS has a significant influence on the reliability indices of SLS and SYS. The mean value μξ of the ratio ξ： is considered as a random variable to study the reliability indices of SLS and SYS. The numerical example demonstrates that the excavation depth and the excavation diameter are proved to have significant influences on the reduction factor of the pile capacity and the reliability indices. The reliability indices decrease with the increase in the excavation depth, and the excavation diameter has a considerable influence on the reliability index when the excavation is relatively deep. In addition, μξ has a significant influence on the reliability indices of SLS and SYS. For a more accurate estimation of μξ, further research should be conducted to study μξ.