昔格达地层隧道围岩灾变特征及致灾因子研究

Research on the Disaster Induced Factors and Disaster Characteristics of the Surrounding Rock in Xigeda Strata Tunnel

研究目的:西南地区面积分布较为广阔的昔格达地层,因其遇水易泥化等特点严重影响着成昆铁路沿线隧道工程的建设,因此对其展开研究具有一定的现实与工程意义。本文对昔格达地层隧道围岩破坏形态进行现场调研,通过现场采样、室内试验、数值模拟、现场监测和理论分析等手段对昔格达地层隧道围岩灾变特征与致灾因子进行深入研究。研究结论:(1)隧道穿越昔格达地层出现灾变数量多,尤其出现拱顶沉降、水平收敛过大、仰拱隆起基底突泥和掌子面塌方等典型灾变模式;(2)昔格达地层隧道围岩含水率在0%~25%范围内时,拱顶沉降、水平收敛、仰拱隆起和掌子面挤出变形等位移变化趋势较为一致,开挖过程中随着含水率的逐渐增大,隧道围岩变形越来越明显,当含水率从25%渐变到30%时,各部位的位移变化急剧增大,含水率在30%时,隧道各部位的累积沉降值达到隧道灾变状态,因此可将含水率25%定为昔格达地层隧道灾变临界值,含水率30%定为昔格达地层隧道围岩灾变值;(3)通过建立灾变因子指标体系,构造判断矩阵并赋值,利用层次分析法确定各因子的权重,灾变源因子影响权重最大的为昔格达地层自身地质及岩体力学性质因子0.625 0,其次是水文地质因子0.238 5,水文地质因子主要为地下水指标影响最大;(4)本研究结论可为西南地区昔格达地层隧道安全快速施工提供指导。

Research purposes： Because of the characteristics of argillization induced by water, the widespread Xigeda strata in the Southwestern areas severely impact the tunnel engineering construction along the Chengdu -Kunming Railway. Thus, it is of significance to carry out the study on Xigeda strata tunnel. We made field research on the catastrophe pattern of Xigeda strata tunnel, deeply studied the catastrophe feature and mechanism of the tunnel surrounding rock in Xigeda strata by means of field sampling, indoor test, numerical modeling, field monitoring, theoretical analysis and the like. Research conclusions：（ 1 ）When the tunnel crosses the Xigeda strata, catastrophes appear, for example, the large sedimentation of vault, big horizontal convergence, the hunching and mud burst of the inverted arch, and the collapse of face and other typical catastrophe patterns. （2） When water content ranges within 0% and 25%, the displacement changes trends of the vault crown settlement, the horizontal convergence, the uplifting of the inverted arch, and the extracted deformation of face are basically the same. Moreover, with the gradual increase of water content during the excavation process, the deformation of the tunnel surrounding rock becomes clearer. Especially when water content gradually changes towards the value of 30% from that of 25% , the displacement changes of those parts increase sharply and when the water content reaches 30%, the accumulated sedimentation values of every part of the tunnel reach the tunnel catastrophe state. Thus, 25% of the water content can be marked as the critical value of the catastrophe of the Xigeda tunnel, while 30% of that is the catastrophe value. （3） We establish the judgment matrix and evaluate it through setting up the index system of catastrophe factor and then determine the weight of every factor by using the analytic hierarchy process. The catastrophe source factor that influences the weight most is the geology of Xigeda itself and the rock mass mechanics with the factor being 0. 625 0, followed by the factor of hydrogeology, which is 0.238 5, groundwater index is the most important factor in hydrogeological factors. （4）The conclusions obtained can provide guidance for the rapid and safe construction of Xigeda strata tunnel in the Southwestern Areas.