下穿隧道开挖对松散堆积边坡稳定性影响的物理模型试验研究

Physical model test study on steady state effect of underpass tunnel excavation on loose deposit slope

隧道与边坡的空间展布特征、边坡岩体结构特征、隧道开挖工序、其他影响外因等直接关系到隧道和边坡的协同稳定特性。为探究复杂地质条件下隧道-边坡体系的稳定性,以深圳部九窝弃土场堆积体边坡为研究对象,通过物理模型试验探索隧道下穿开挖扰动影响松散堆积体边坡的变形机理。首先,基于隧道和边坡实际几何特征和空间展布特征,确定最佳相似比,构建上覆松散堆积体边坡的物理模型;然后,开展了降雨条件下大断面隧道下穿开挖与未开挖两种工况的物理模型对比试验,通过分析降雨条件下坡体内部含水率、孔隙水压力和土压力的变化规律,揭示了降雨条件下在松散堆积体边坡下方开挖大断面隧道导致边坡失稳的变形机制;最后,采用具有负泊松比特性的恒阻大变形锚索,提出大跨度隧道的围岩NPR(Negative Poisson’s Ratio)锚索控制措施,并通过数值模拟进行控制效果验证。研究结果表明:经过一定的降雨历时,松散堆积边坡的破坏由表层扩展到深层,主要变形模式为冲蚀型冲沟;隧道下穿开挖会形成较大范围的松动圈和临空面,当边坡冲沟掏蚀区与隧道松动圈重叠后,隧道内易发生涌水、局部塌方等灾害,继而诱发上覆边坡出现局部滑塌破坏现象。采用NPR锚索对下穿隧道围岩进行高预紧力应力补偿控制,隧道拱顶下沉和上覆边坡变形均得到有效控制,为类似工程背景的隧道支护和边坡加固方案的设计提供新的思路。

The spatial distribution characteristics of tunnel and loose dump slope,the structural characteristics of slope rock mass,the excavation procedure of tunnel,and other influencing factors are directly related to the cooperative stability characteristics of tunnel and loose dump slope.In this paper,the deformation mechanism of the loose dump slope affected by tunneling disturbance is explored by a physical model test in a waste dump in Shenzhen.Firstly,the optimal similarity ratio is determined based on the actual geometric characteristics and spatial distribution characteristics of tunnel and loose dump slope,and the physical model of overlying loose dump body slope is constructed.Then,under the condition of rainfall,a comparison of physical model experiments is conducted for the large-span tunnel excavation with two kinds of the working condition of under-excavation and without excavation.By analyzing the slope body internal moisture content,pore water pressure,and earth pressure under the conditions of rainfall,the deformation mechanism of the slope instability caused by excavating large-span tunnel under loose dump slope with the condition of rainfall.Finally,using the constant resistance and large deformation anchor cable with negative Poisson ratio,the control measures of the NPR(Negative poisson’s ratio)anchor cable in the surrounding rock of the large-span tunnel are proposed,and the control effect is verified by numerical simulation.The results show that after a certain rainfall duration,the failure of the loose dump slope extends from surface to deep,and the main deformation mode is erosion gully.When the slope gully cut area overlaps with the tunnel loose circle,water gushing and local collapse are easy to occur in the tunnel,and then the local collapse of the overlying slope is induced.The NPR anchor cable is used to compensate for the high preload stress of the surrounding rock of the underpass tunnel,and the subsidence of the tunnel vault and the deformation of the overlying slope are effectively controlled,which provides a new idea for the design of tunnel support and slope reinforcement schemes with a similar engineering background.