小净距隧道中夹岩对拉锚杆控制机制与工程应用

小净距隧道中夹岩受到两侧开挖的剧烈扰动，处于单向或双向受力的不利状态，严重影响施工安全，而预应力全长注浆对拉锚杆常用于中夹岩的主动支护。为阐明对拉锚杆的作用模式和控制机制，建立相应的力学模型和解析方法，开展实测验证，并进行参数分析和工程应用。研究表明：对拉锚杆为中夹岩提供强力水平约束，并提高岩体力学性能，发挥挤压加固作用；对拉锚杆利用剪切摩阻改善浅层围岩受力状态，同时锚固深部岩体，具有承载传力效果；对拉锚杆轴力和剪应力均由两侧向中间非线性衰减，作用范围局限于浅层中夹岩，实测结果验证了理论方法的合理性；进行了对拉锚杆的参数分析，提出了对拉锚杆临界长度、合理锚杆直径等工程建议；结合京张高铁长城站小净距隧道实践，主动增强对拉锚杆设计参数，变更后围岩压力、拱顶沉降和水平收敛的实测均值分别降低12.2%、14.1%和10.2%，保障了隧道开挖的安全。

Control mechanism and engineering application of pillar-reinforcing bolt in closely spaced tunnels

Due to the severe disturbance between closely spaced tunnels, the rock pillar is in the unfavorable state of single or double-direction compression, and the construction safety is seriously affected. Therefore, the prestressed and grouted pillar-reinforcing bolt is widely used to support the rock pillar actively. The mechanical models and analytical methods are established to clarify the function modes and control mechanism of the pillar-reinforcing bolt. The theoretical approach is verified by field test, the influencing parameters are analyzed, and the corresponding engineering applications are carried out. The results show that the pillar-reinforcing bolt can provide strong horizontal restraint on the rock pillar, improve the mechanical properties of the rock mass, and has the extrusion reinforcement effect. The pillar-reinforcing bolt also utilizes friction resistance to improve the stress state of the shallow surrounding rock and anchor the deep rock, which has the load transfer effect. The axial force and shear stress of the pillar-reinforcing bolt decrease nonlinearly from both outsides to the insides, and the function range is limited within the shallow layer of the rock pillar. This trend is verified by field measured data. The parameter influences on the mechanical behavior of the pillar-reinforcing bolt are systematically analyzed, and the critical bolt length and reasonable bolt diameter are proposed accordingly. Based on the engineering practice of the closely spaced tunnels in the Great Wall Station of Beijing Zhangjiakou high-speed railway, the design of pillar-reinforcing bolt is actively enhanced. After the design change, the average values of surrounding rock pressure, crown settlement, and horizontal convergence are reduced by 12.2%, 14.1%, and 10.2%, respectively. The safety state of closely spaced tunnels is significantly safeguarded.