考虑锚杆腐蚀作用的岩质边坡系统可靠度分析

SYSTEM RELIABILITY ANALYSIS OF ROCK SLOPES CONSIDERING ROCK BOLT CORROSION

锚杆腐蚀是导致锚固工程事故的重要原因之一,为此,主要研究锚杆腐蚀作用对锚固岩质边坡系统可靠度的影响。首先,在系统分析现有钢筋腐蚀模型及锚杆腐蚀试验数据基础上,确定锚杆腐蚀模型。分析与腐蚀作用相关的锚杆自由段屈服失效模式和锚固段锚杆与注浆体界面黏结失效模式,进而确定相应的锚固边坡失效模式。给出基于蒙特卡洛模拟的边坡时变系统可靠度分析方法,并以锚固岩质边坡为例证明所提方法的有效性。结果表明:K.A.T.Vu和M.G.Stewart提出的钢筋腐蚀模型适用于分析处于密闭潮湿和干湿交替环境条件之间的锚杆腐蚀作用。在锚杆服役的前期,自由段锚杆的腐蚀作用对边坡稳定性的影响较大,而在后期锚固段锚杆的腐蚀作用对边坡稳定性的影响开始变得较大,并且锚杆服役后期锚固力和边坡系统失效概率的变化幅度明显大于前期。边坡系统失效概率随锚杆握裹层厚度的增加而减小,随注浆体水灰比的增加而增大,当握裹层厚度和水灰比达到一定值时,边坡系统失效概率随时间增大的程度并不明显。

A large number of engineering accidents have demonstrated that the failures of rock bolts are mainly induced by the corrosion of reinforcing steel bars.This study aims to investigate the effect of rock bolt corrosion on the system reliability of anchored rock slopes.A uniform corrosion model for rock bolts and its applicable environmental conditions are first examined based on systematical analysis of the existing corrosion models for reinforcing steel bars and the experiment data for rock bolt corrosion.Two failure modes related to rock bolt corrosion are determined.They are the yield failure mode of rock bolts at free section and the bond failure mode at the bolt-grout interface,respectively.Then,the failure models of anchored rock slope corresponding to those of rock bolts are established.A method for estimating the time-variant system reliability of rock slopes based on Monte Carlo simulation is presented.Consequently,an example of anchored rock slope with a single slip surface is presented to demonstrate the validity and capability of the proposed methods.The results indicate that the corrosion model proposed by K.A.T.Vu and M.G.Stewart is suitable for rock bolts subjected to environmental conditions of humidity and drying/wetting cycles.The rock bolt corrosion at free section has a more significant influence on the stability of rock slopes at the early stage,whereas the effect of rock bolt corrosion at anchored section becomes more obvious at the later stage.Moreover,the variations in the anchored force of each rock bolt and the system probability of slope failure at the later stage are more significant than those at the early stage.The system probability of slope failure decreases with the increasing thickness of the rock bolt cover,while increases with the increasing water-to-cement ratio of the grout.However,the system probability of slope failure does not significantly increase with time,when the thickness of the rock bolt cover and water-to-cement ratio of the grout reach certain values,respectively.