碎石锚固试验被用于证实锚固破碎岩体中存在压力拱，但压力拱的概念较为抽象，难以理解和应用。为研究锚固破碎岩体中压力拱的形成机制与锚杆的作用，克服颗粒锚杆批量生成与预紧难题，利用三维颗粒流程序（PFC^3D）开发碎石锚固试验的数值模拟方法，开展系列碎石锚固数值试验，直观展示压力拱的形成，揭示压力拱的形成机制与成因，分析并验证锚杆在压力拱形成中的具体作用。在此基础上，提出极破碎岩体锚杆加固的建议。研究结果表明：① 锚杆加固碎石体内会形成拱形承载结构压力拱，压力拱由碎石咬合而成，碎石体全部质量由压力拱承载，压力拱的稳定依靠拱下碎石支撑。② 压力拱形成于碎石在锚杆作用下的自适应运动过程。移除碎石箱底板后，底部碎石向下运动，导致上部碎石重力向周边转移，在周边碎石形成拱腿，拱顶部位碎石在侧向约束作用下彼此咬合形成拱顶，最终以底托板为基础形成压力拱。③ 压力拱的形成和稳定需满足4个条件：强力的底部基础、足够的侧向约束、适当的碎石厚度和平衡的拱下碎石。④ 锚杆在压力拱形成和稳定中发挥侧向约束作用、支撑作用和护表作用。在成拱过程中，锚杆通过预紧提供侧向约束力，使碎石具有足以成拱的咬合能力。在压力拱形成后，锚杆通过对拱下碎石提供支撑和护表使其平衡，维护压力拱的稳定。锚杆预紧有助于增强侧向约束作用和支撑作用。⑤ 大范围极破碎岩体加固应围绕压力拱的形成，充分发挥锚杆的侧向约束、支撑和护表作用，包括提高锚杆预紧力、增大锚杆杆体粗糙度、减小锚杆间距、增大托盘尺寸等。

The gravel bolting tests has been used to verify the existence of pressure arch in bolted fractured rock,however,the pressure arch is difficult to understand and used due to the abstract concept.In order to study the formation mechanism of pressure arch and the functions of rockbolts in bolted fractured rock,the numerical simulation of gravel bolting tests by using the Particle Flow Code in 3 Dimensions(PFC^3D)was achieved through developing the methods of batch generation and pretension for rockbolts simulated by particles.A series of gravel bolting tests were performed to visualize the pressure arch and reveal its formation mechanism and causes.The functions of rockbolts in gravel bolting tests were analyzed and verified.Base on the above,some suggestions were made for bolting in extremely fractured rock.The results show that:① A pressure arch can be formed in bolted gravel pack,which is an arched load bearing structure made of interlocked gravel particles.The load of the whole gravel pack is carried by the pressure arch,and the stability of pressure arch depend on the support from the gravel below the pressure arch.② Pressure arch is formed in the adaptive motion process of gravel particles under bolting.After the removal of bottom plate of gravel box,the gravity of upper gravel shifts to the periphery due to the downward movement of bottom gravel,forming arch legs in surrounding gravel.The gravel particles at the top of the arch interlock each other to form the vault,resulting in a formation of pressure arch based on the backing boards.③ The formation of a pressure arch needs to meet four conditions:a strong bottom base,a sufficient lateral constraint,a proper thickness of gravel pack and some balanced gravel particles below the arch.④ Lateral restraint,support and surface retention are exerted by rockbolts to gravel particles in gravel bolting tests.In the formation of a pressure arch,the rockbolts are pretensioned to generate lateral restraint on the gravel pack,so that the gravel particles have sufficient interlocking capacity for arching.After the formation,the rockbolts can maintain the stability of pressure arch by providing support and surface retention for gravel particles below the pressure arch.The pretention of rockbolts helps to increase the lateral restraint and supporting effect.⑤ The lateral restraint,supporting and surface retaining effects of rockbolts should be fully developed to build up a pressure arch in a large scale extremely fractured rock,including increasing pretension force,increasing the roughness of the rockbolt bodies,reducing the spacing between rockbolts,enlarging the size of plates and installing mesh,etc.

1 碎石锚固试验的数值模拟实现

2 碎石锚固数值试验与压力拱形成

   2.1 碎石锚固数值试验

   2.2 压力拱的形成

   2.3 压力拱的成因

3 锚杆作用分析

   3.1 侧向约束作用

   3.2 支撑作用

   3.3 护表作用

4 对极破碎岩体锚杆加固的建议

5 结论