含水率差异对膨胀性红黏土隧道施工力学行为的影响

膨胀性红黏土因其特殊的水敏性,使得自身遇水膨胀,是造成隧道围岩失稳的重要原因。 为建立含水率与膨胀率的关系,从 而明确含水率变化对大断面膨胀性红黏土隧道及支护结构受力变形的影响,以银西高铁庆阳膨胀性红黏土隧道为研究背景,通过 现场监测确定围岩含水率波动范围;结合室内试验建立含水率与膨胀性和抗剪强度的对应关系;将土体含水率变化条件下的膨胀 关系同材料受热膨胀特性进行联系,利用ABAQUS内置的温度应力场模拟湿度应力场,分析不同含水率作用下隧道围岩压力、衬砌 结构内力与变形量值的重分布规律。 结果表明: 开挖后不同含水率最终趋于饱和时,随着初始含水率的降低,围岩及支护结构受 力增大,仰拱与拱脚处相对位移提高,拱顶、拱腰与边墙处相对位移降低,整体安全系数逐渐降低;对开挖后洞周平均含水率20.7% 而言,最终趋于饱和时围岩压力安全系数为2.2,衬砌安全系数为1.1,围岩相对位移为0.97%;相比于围岩压力和衬砌结构受力, 含水率变化对洞周围岩变形影响最大;基于特殊地质情况,建议将隧道预留变形量提至150~180 mm。

Influence of Water Content Difference on Construction Mechanical Behavior of Expansive Red Clay Tunnel

The expansive red clay easily expands in water due to its special water sensitivity, which is a main reason for instability of tunnel surrounding rock. In order to learn the relationship between the water content and expansion ratio of red clay to determine the influence of the water content on the stress and deformation of large cross-section expansive red clay tunnel and supporting structure, the fluctuation range of water content in surrounding rock of Qingyang expansive red clay tunnel on Yinchuan-Xi′an High-speed Railway is monitored. And then the correspondence between water content and expansibility and that between water content and shear strength are established by laboratory tests. Finally, the expansion relationship under the variation of water content and that under thermal condition are studied; the temperature stress field built in ABAQUS is used to simulate the humidity stress field; and the redistribution laws of the surrounding rock pressure, internal force and deformation of lining structure under different water contents are analyzed. The results show that: (1) When the water content tends to be saturated after excavation, the stresses of surrounding rock and supporting structure increase, the relative displacements of invert arch and arch foot increase, the relative displacements of crown, arch waist and sidewall decrease, and the integral safety factor decreases with the initial water content decrease. (2) Under the average water content of tunnel surrounding rock after excavation, 20.7%, the final safety coefficient of surrounding rock pressure is 2.2, the final safety coefficient of lining is 1.1, and the final relative displacement of surrounding rock is 0.97%. (3) The influence of water content on surrounding rock deformation is the largest, followed by that on surrounding rock pressure and lining structure. (4) The reserved deformation of the tunnel is recommended to be 150-180 mm based on the special geological conditions.