为研究大断面砂质黄土隧道的合理台阶开挖工法,以中兰铁路最长的黄土隧道为研究对象,在室内土工试验获取围岩参数的基础上,采用数值模拟方法对比分析了三台阶法、三台阶七步法和三台阶临时仰拱法与超前管棚组合下的围岩变形控制效果,并考虑施工进度和造价因素,优选出合理工法。开展现场测试工作,评价了优选工法的有效性,结果表明:(1)对于拱顶沉降和水平收敛,三台阶临时仰拱法和三台阶七步法控制效果相当,三台阶法最差;(2)对于掌子面挤出位移,三台阶临时仰拱法控制效果最优,三台阶七步法控制效果最差;(3)对于三台阶临时仰拱法,围岩压力沿洞周分布较小,小于规范中松动压力计算值,围岩处于弹塑性状态,钢拱架弯矩较小,轴力较大,呈现小偏心受压特征,且安全系数均小于规范容许值。综合数值模拟和现场测试结果,三台阶临时仰拱+超前管棚组合工法兼顾了施工速度和围岩变形控制需求,可作为大断面砂质黄土隧道的优选工法。
In order to study the reasonable bench excavation method for large cross-section sandy loess tunnels, the longest loess tunnel of the Zhongwei to Lanzhou Railway is used as the research object. Some geotechnical tests in laboratory were carried out to obtain the surrounding rock parameters. The numerical simulation method was used to compare and analyze the deformation control effects of surrounding rock under the combination of three bench method, three bench seven step method, and three bench temporary inverted arch method with advanced pipe shed support, and consider construction progress and cost factors, a reasonable construction method was selected. Field test effort was carried out and the effectiveness of the reasonable construction method was evaluated. The research results show that: (1) For the settlement and horizontal convergence of the arch, the control effects of the three bench temporary inverted arch method and the three bench seven step method are equivalent, with the three bench method being the worst. (2) For the extrusion displacement of the work face, the three bench temporary inverted arch method has the best control effect, while the three bench seven step method has the worst control effect. (3) The on-site test results of the three bench temporary inverted arch method indicate that, the distribution of surrounding rock pressure along the tunnel circumference is relatively small, less than the calculated value of loose pressure in the specifications, and the surrounding rock is in an elastic-plastic state. The bending moment of the steel arch is small, the axial force is large, showing the characteristics of small eccentric compression, and the safety factor is less than the allowable value of the specification. (4) Based on the comprehensive numerical simulation and on-site testing results, the three bench temporary inverted arch and advanced pipe shed combination construction method takes into account the construction speed and surrounding rock deformation control requirements, and can be used as the optimal construction method for large cross-section sandy loess tunnels.
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