基于双强度折减法的浅埋偏压隧道安全性与破坏模式研究

基于双强度折减系数法,探究了以特征部位沉降、最大塑性应变和最大主应力是否突变及塑性区发展作为隧道失稳判据的适用性。基于双强度折减理论,采用不同埋深与高跨比、不同地表坡度及不同围岩级别,对浅埋偏压隧道进行了安全度分析,探讨了浅埋偏压隧道的破坏模式。结果表明,拱顶沉降对隧道围岩失稳有很好的突变响应,建议采用拱顶沉降作为隧道的围岩稳定性判据;黏聚力c及内摩擦角φ对隧道稳定安全系数的贡献受地表坡度及围岩级别影响较大;浅埋偏压条件下隧道开挖后产生的潜在破裂面主要有5处,不同破坏模式下的破裂面状态不同。

Profound probe into the safety and failure mode of shallow layer buried bias tunnel based on the double strength coefficient reduction method

Based on the double strength reduction coefficient method,this paper intends to make an exploration of the applicability of the tunnel instability criteria with the settlement of the specific parts,the maximum plastic strain and the maximum principal stress mutation and the development of the plastic zones through the ABAQUS finite element analysis.At the same time,we have also compared and analyzed the safety degree of shallowburied tunnel with the bias pressure on the basis of the double strength reduction theory through examining the different buried depths,the height-span ratios and the surface gradients.What is more,the failure modes of the shallow tunnel with the eccentric pressure has also been discussed as to the different surrounding rock levels from the point of view of the safety analysis.The results of our research prove that the vault settlement should have a close catastrophic reaction to the settlement instability of the tunnel surrounding rocks,which can be used to test the stability criteria of the tunnel surrounding rocks.As for the contribution of the tunnel stability safety factors,the cohesion c and internal friction angleφmay have a great impact on the slope of the surface and the grade of the surrounding rock.For instance,under the condition of the surrounding rock at grade IV,the shortest path of the strength reduction tends to gradually decrease with the increase of the buried tunnel depth.At the same time,the safety factor of the surrounding rock of the tunnel calculated may turn to decrease continuously by the use of the shortest path method.In addition,the shortest path of the strength reduction may also gradually decrease while the tunnel span remains constant with the increase of the tunnel height.At the same time,with the excavation of the tunnel going on under the shallow partial pressure,there may occur 5 kinds of potential crack or rapture surfaces,with their surface state being ruptured differently under the different failure modes.Therefore,the double strength reduction method can be seen profitable and applicable to analyze the stability of the surrounding rocks of the bias tunnel in excavation and provide some reference for the tunnel excavation.