梁锚结构加固浅埋隧道洞口软弱地层的承载特性研究*

针对隧道洞口埋深浅且软弱围岩稳定性差这一问题，提出在地表增设混凝土框架梁，设置扩大头锚杆与框架梁连接并深入软弱围岩，运用数值模拟分析“混凝土框架梁-扩大头锚杆”结构加固软弱地层后的力学特性。研究结果表明:采用“混凝土框架梁-扩大头锚杆”加固隧道洞口软弱地层，k=0.4时，相比于没有加固对照模型，隧道最大拱顶沉降值下降68.7%，隧道最大边墙收敛值下降15.1%，初期支护最大等效应力减小12.7%；建立不同加固区围岩松动压力分散系数k下的数值模型，通过拱顶沉降结果与加固区围岩松动压力分散系数的线性拟合，提出采用加固结构后的隧道拱顶沉降规律与围岩松动压力计算方法。

Study on bearing characteristics of weak stratum at portal of shallow-buried tunnel reinforced by beam-anchor structure

Aiming at the problem of shallow buried depth and poor stability of weak surrounding rock at the tunnel portal,being different from the traditional grouting combined with advance support to reinforce the surrounding rock,it was proposed to add the concrete frame beam on the ground surface,set up the bit expanded anchor rods connecting with the frame beam,and go deep into the weak surrounding rock.The mechanical characteristics of weak stratum reinforced by the “concrete frame beam and bit expanded anchor rods” structure were analyzed by numerical simulation.The results showed that after applying the “concrete frame beam and bit expanded anchor rods” to reinforce the weak stratum at tunnel portal,when the dispersion coefficient of loosening pressure of surrounding rock in the reinforcement area was k=0.4,compared with the control model without reinforcement,the maximum vault settlement of the tunnel decreased by 68.7%,the maximum side wall convergence of the tunnel decreases by 15.1%,and the maximum equivalent stress of initial support decreased by 12.7%.The numerical model under different k values was established,and through the linear fitting between the vault settlement results and k,the tunnel vault settlement law and the calculation method of loosening pressure of surrounding rock after using the reinforcement structure were proposed.