我国西南部山区隧道施工期支护结构力学行为特征案例分析

为研究我国西南部山区隧道施工期支护结构所面临的重大问题，将雅安—康定、汶川—马尔康高速公路的典型隧道作为案例，归纳总结施工期存在的高地应力、软弱围岩、断层破碎带、次生地质灾害等潜在危险源，通过现场实测数据深入分析不同危险源环境下支护结构体系的力学行为特征。研究结果表明： 1）当隧道穿越软弱围岩时，围岩强度低、自承载能力差，接触压力、钢拱架应力均显著高于普通围岩隧道，二次衬砌分摊荷载比例显著上升； 2）当隧道穿越断层破碎带时，支护结构受力需要较长时间才能稳定下来，其力学行为呈现出3阶段演化规律，前期快速降低、中期缓慢降低、后期基本稳定； 3）当隧道洞口穿越松散堆积体时，坡体稳定性易受到扰动，其支护结构力学行为具有显著的偏压特性，围岩压力主要集中在深埋侧； 4）高地应力与围岩强度联合控制着围岩稳定性与支护结构体系的力学行为，高地应力硬岩隧道也具有一定的流变时间效应，但由于硬质围岩的强度较大、稳定性较好，支护结构受力相对较小，安全储备较高； 5）高地应力软岩隧道的围岩压力与结构受力显著升高，其支护结构力学行为在施工期便呈现出明显的流变特性，开挖约200 d后，仍然保持着缓慢增长。

Cases Analysis of Mechanical Behavior Characteristics of Tunnel Supporting Structure in Mountainous Areas in Southwest China

Serious potential risks, such as high geo stress, weak surrounding rock, fault and fracture zone, secondary geological disasters, etc., are existing in the tunnel supporting structure in mountainous areas in southwest China during construction phase. As a result, cases analysis are carried out on Ya′an Kangding High speed Tunnel and Wenchuan Ma′erkang High speed Tunnel so as to analyze the mechanical behaviour characteristics of tunnel supporting structure under different potential risks based on site monitoring data. The analytical results show that: (1) The contact pressure and steel arch stress of tunnel in weak surrounding rock with low strength and self bearing capacity are much higher than those of tunnel in common surrounding rock, and the load sharing ratio of secondary lining increases significantly. (2) When the tunnel passes through fault and fracture zone, the stabilizing time for supporting structure stress is quite long, and the mechanical behavior of the supporting structure presents three stage evolution law, i.e. falling quickly in the early stage, slowly decline in the middle stage, and becoming stable in the final stage. (3) As for portal section of tunnel passes through loose deposits, the stability of slope is easily disturbed, the mechanical behavior of the supporting〖HJ1.5mm〗structure has significant asymmetric characteristics, and the surrounding rock pressure mainly concentrates on the deep buried side. (4) The geo stress and rock properties jointly control the stability of surrounding rock and the mechanical behavior of supporting structure; the high geostress hard rock tunnel also has certain rheological time effect, but due to the greater strength and stability of the hard surrounding rock, the supporting structure is relatively less stressed and the safety reserve is higher. (5) The surrounding rock pressure and structural force of soft rock tunnel with high geo stress increase significantly, and the mechanical behavior of the supporting structure shows remarkable rheological characteristics during the construction period, even after about 200 days of excavation, it still growing slowly.