基坑工程排桩内支撑围护结构局部破坏安全风险评价方法研究

目前"排桩+内支撑"围护结构在深基坑工程中应用广泛,而排桩破坏易引发基坑支护结构连续破坏。为解决基坑工程缺乏定量评估连续破坏风险手段的问题,基于结构承载力冗余度理论,结合基坑支护结构破坏风险抵抗破坏系数进行安全风险等级划分,有效量化基坑连续破坏风险,并制定相应的风险控制对策。依托某地铁车站明挖基坑工程,采用拆除构件法,对不同条件下基坑排桩破坏进行三维数值模拟,分析结构承载力冗余度,开展安全风险评价。研究表明,排桩破坏会对剩余基坑支护结构产生重要影响,其中邻近桩最大弯矩值增长30%以上;结构承载力冗余度安全风险评价因子对基坑连续破坏的风险等级判定具有重要影响,对于常规地铁车站基坑工程,建议安全风险评价因子大于0.4,以保障施工安全。

Engineering Risk Analysis of Foundation Pit Partial Over-excavation on Inner Bracing and Row Piles Supporting Structure

At present,the inner bracing and row piles supporting structure is widely used in deep foundation pit engineering.However,the failure of piles is an important risk to foundation pit support structure damage.In order to solve the problem of the lack of quantitative evaluation of continuous failure risk in foundation pit engineering,based on the redundancy theory of structural bearing capacity,this paper put forward the resistance failure coefficient which can comprehensively evaluate the failure risk of foundation pit supporting structure.Safety risk levels were divided,the continuous failure risks of foundation pit were effectively quantified,and the corresponding risk control countermeasures were formulated.Based on a subway station open excavation foundation pit project,the method of demolishing components was adopted.A 3 D numerical simulation of the failure of piles of foundation pit under different conditions was carried out.The redundancy of structural bearing capacity was analyzed,and the safety risk assessment was carried out.The results show that:piles failure have an important impact on the remaining foundation pit supporting structure,in which the maximum bending moment of adjacent piles increases by more than 30%;the safety risk assessment factor of structural bearing capacity redundancy has an important influence on the determination of the risk level of continuous failure of foundation pit.For conventional subway station foundation pit engineering,it is suggested that the safety risk assessment factor should be greater than 0.4 to ensure the construction safety.