Case study on the mechanics of NPR anchor cable compensation for large deformation tunnel in soft rock in the Transverse Mountain area,China

横断山区软岩大变形隧道NPR锚索补偿力学案例研究

A study was conducted to analyze the deformation mechanism of strongly weathered quartz schist in the Daliangshan Tunnel,located in the western Transverse Mountain area.A large deformation problem was experienced during the tunnel construction.To mitigate this problem,a support system was designed incorporating negative Poisson ratio(NPR)anchor cables with negative Poisson ratio effect.Physical model experiments,field experiments,and numerical simulation experiments were conducted to investigate the compensation mechanical behavior of NPR anchor cables.The large deformations of soft rocks in the Daliangshan Tunnel are caused by a high ground stress,a high degree of joint fracture development,and a high degree of surrounding rock fragmentation.A compensation mechanics support system combining long and short NPR anchor cables was suggested to provide sufficient counter-support force(approximately 350 kN)for the surrounding rock inside the tunnel.Comparing the NPR anchor cable support system with the original support system used in the Daliangshan tunnel showed that an NPR anchor cable support system,combining cables of 6.3 m and 10.3 m in length,effectively prevented convergence of surrounding rock deformation,and the integrated settlement convergence value remained below 300 mm.This study provides an effective scientific basis for resolving large deformation problems in deeply buried soft rocks in western transverse mountain areas.

针对西部横断山区大亮山隧道强风化石英片岩大变形问题,分析了强风化石英片岩的变形机理,利用负泊松比效应的NPR锚索补偿力学行为进行支护设计,并进行了物理模型实验、现场实验和数值模拟实验。结果表明,地应力高、节理裂隙发育程度高和围岩破碎程度高是大亮山隧道软岩大变形的主要原因,采用长、短NPR锚索组合的补偿力学支护体系,可使隧道内部的围岩保持足够的反支护力(350 kN左右)。通过对比NPR锚索支护体系与大亮山隧道原支护体系,得出大亮山隧道采用6.3 m和10.3 m相结合的NPR锚索支护体系可有效地防止围岩的变形收敛,综合沉降收敛值在300 mm以下。该研究为西部横断山区深埋软岩大变形隧道的支护提供了有效的科学依据。