Numerical simulation study on shear resistance of anchorage joints considering tensile-shear fracture criterion of 2G-NPR bolt

2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has signifcant efects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under diferent tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verifed by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.

Geomechanics model test and numerical simulation of 2G-NPR bolt support effect in an active fault tunnel

Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.

新型NPR锚杆支护系统抗动力冲击试验研究

为应对深部洞室开挖过程中可能出现的高应力岩爆、冲击地压及外部爆炸等动力冲击作用下造成的洞室围岩非线性大变形,何满潮院士研究团队研发了具有均匀大变形、颈缩明显消失、屈服平台消失等实验现象的2G-NPR(Second Generation Negative Poisson’s Ratio)锚杆新材料,并在此基础上,形成了2G-NPR锚杆支护工程岩体的刚柔性结构系统大变形控制技术。为了深入研究爆炸强冲击作用下2G-NPR锚杆支护工程岩体的整体动态响应规律及力学行为,后续将其应用于国防和人防工程中。在爆炸试验现场研究了爆炸冲击波在花岗岩中的衰减模型,确定了爆炸所需的装药参数,获得了PR锚杆支护复合结构和2G-NPR锚杆支护复合结构洞室的支护参数;对比研究了在爆炸冲击过程中2种不同支护体系中拱顶峰值压力、拱顶拱肩拱底加速度、锚杆轴力以及围岩的动力学响应和相互作用规律,揭示了不同支护洞室的抗冲防爆特性及其破坏模式。研究结果表明:2G-NPR锚杆能抵抗更强的平面冲击载荷,能量吸收分摊比例占比高,在地下防爆支护中具有显著能量吸收特征,能够起到传统锚杆支护无法比拟的支护效果。此外,针对地下洞室开挖引起围岩应力状态的改变,提出洞室开挖应力补偿理论,并得到了锚杆锚固端各应力分量和位移分量的理论解,为后续洞室支护研究提供理论参考。