NPR锚索支护下相交隧道围岩变形规律及破坏机理

Deformation law and failure mechanism of surrounding rock of intersecting tunnel supported by NPR anchor cable

城市交通逐渐向地下发展,地下立交中相交隧道数量日益增加。为探究复杂地质条件下相交隧道的变形规律,以深圳南龙地下立交隧道相交隧道段为工程背景,通过物理模型试验探索相交隧道在开挖支护及超载状态下的变形机理。首先自主设计三维模型试验系统,并通过相似理论计算,进行了多种岩样及支护材料的配制;其次在模型搭建完成后,基于开挖补偿理论,利用缩尺NPR(Negative Poisson’s Ratio)锚索对相交隧道进行开挖支护。通过对隧道应变、位移及NPR锚索轴力的分析,得到隧道开挖状态下的应力重分布特征;最后,对隧道进行超载试验,结合数据及现象分析,揭示了相交隧道合建结构的围岩破坏机理。研究结果表明:相交隧道在开挖贯通时,合建区域岩体因隧道开挖产生应力损失,会对已经开挖支护完的隧道造成轻微影响。隧道贯通加载时,相交隧道的破坏分为3个阶段:拱顶应力集中区沉降阶段、合建结构的破坏阶段和隧道洞口破坏阶段。具体表现:首先是上层隧道合建区域拱顶开始出现沉降,然后下层隧道出现底鼓,最后应力传播至边界,使得洞口上方垮塌。试验中采用NPR锚索对相交隧道进行支护,现象和数据表明,开挖阶段隧道合建区的沉降影响到NPR支护段,由于NPR锚索的高应力补偿特点,支护段并未出现明显沉降。试验验证了NPR锚索在相交隧道的支护效果,可为类似工程支护提供一种新的思路。

Urban traffic is gradually developing into underground,and the number of intersecting tunnels in under⁃ground interchanges is increasing.In order to explore the deformation law of intersecting tunnels under complex geo⁃logical conditions,taking the intersecting tunnel section of the Shenzhen Nanlong underground interchange tunnel as the engineering background,the deformation mechanism of intersecting tunnels under excavation support and over⁃load conditions was explored through physical model tests.Firstly,a three⁃dimensional model test system was designed independently,and a variety of rock samples and supporting materials were prepared by similarity theory calculations.Secondly,after the completion of the model,based on the excavation compensation theory,the intersec⁃ting tunnel was excavated and supported by the reduced⁃scale Negative Poisson’s Ratio(NPR)anchor cable.Thro⁃ugh the analysis of tunnel strain,displacement,and NPR anchor cable axial force,the stress redistribution characteris⁃tics of tunnel excavation were obtained.Finally,the overload test of the tunnel was carried out.Combined with the data and phenomenon analysis,the failure mechanism of the surrounding rock of the intersecting tunnel joint construction area was revealed.The results show that when the intersecting tunnel is excavated,the stress loss of the rock mass in the joint construction area due to tunnel excavation will slightly impact the tunnel excavated and supported.When the tunnel is loaded through,the failure of the intersecting tunnel is divided into three stages:the settlement stage of the vault stress concentration area,the failure stage of the joint construction area,and the failure stage of the tunnel portal.The specific performance is as follows:first,the vault of the upper tunnel joint construction area begins to sink,then the bottom drum of the lower tunnel appears,and finally,the stress spreads to the boundary,cau⁃sing the collapse above the tunnel entrance.The test uses the NPR anchor cable to support the intersecting tunnel.The phenomenon and data show that the settlement of the tunnel joint construction area during the excavation stage af⁃fects the NPR support section.Due to the high⁃stress compensation characteristics of the NPR anchor cable,there is no obvious settlement in the support section.The test verifies the supporting effect of the NPR anchor cable in intersec⁃ting tunnels,which can provide a new idea for the similar engineering support.