浅埋黏土层大跨度隧道施工技术与塌方风险分析

Construction Technology of Large-span Tunnel in Shallow Clay Stratum and Collapse Risk Analysis

为了研究黏土层浅埋大断面隧道洞口施工的塌方风险,从围岩地质条件与隧道设计特点两个角度分析了依托隧道工程的洞口施工难点,并提出相应施工工法和加固措施。在隧道典型段落的掌子面采用地质雷达进行短距离超前地质预报,以预报结果为基础,再综合考虑隧道水文和地质条件、施工状态和隧道管理水平,选择了围岩级别、隧道埋深、地下水、开挖方式、隧道跨度与施工水平作为塌方风险评估因素。以100多座典型隧道的塌方事故资料作为依据,提炼塌方事故主要致灾因子及其发生频率,采用频数统计法计算各风险因素的客观权重,通过专家对风险因素评分与层次分析法计算和获取各因素的主观权重和分配权重,再通过工程中广泛使用的Karwowski模糊隶属度函数确定各风险因素不同风险等级的隶属度,以此构建权重矩阵与隶属度矩阵,计算出隧道塌方综合风险隶属度,根据最大隶属度原则确定塌方风险等级。最终形成了一套黏土层浅埋大断面隧道塌方风险评估模型,将塌方风险评估模型应用到依托工程大罗山隧道中,结果表明:隧道评估段塌方风险结果为IV级,属于危险级别;洞内实际开挖引起地表发生塌陷,围岩含水丰富,评估和开挖揭露的塌方风险等级具有较高的一致性,验证了该风险评估模型的可靠性和适用性。

To research the construction collapse risk in the entrance of large-span tunnel in shallow buried clay stratum,the difficulties during the entrance construction of supporting tunnel project are analyzed from the aspects of geological conditions of surrounding rock and tunnel design characteristics,and the corresponding construction method and reinforcement measures are put forward.Geological radar is used for short range advance geological forecast in the tunnel face of typical section.Based on the forecast result and considering hydrology and geology conditions,construction status and management level of the tunnel comprehensively,the level of surrounding rock,tunnel buried depth,groundwater,excavation method,tunnel span and construction level are selected as collapse risk assessment factors.Based on the collapse data of more than 100 typical tunnels,the main disaster factors and the occurrence frequency of these collapses are extracted,the objective weight of each risk factor is calculated by frequency statistical method.The subjective weight and the distribution weight of each factor are calculated and obtained by expert scoring and analytic hierarchy process.The Karwowski fuzzy membership function,which is widely used in engineering,is used to determine the membership degrees of different risk levels for risk factors.Then,the weight matrix and the membership matrix are established,the comprehensive risk membership degree of tunnel collapse is calculated,and the risk grade of tunnel collapse is determined according to the principle of maximum membership degree.A set of collapse risk assessment models for large cross-sectional clay layer shallow buried tunnel is formed finally,and the model is applied to the support project of the Daluoshan tunnel.The result shows that(1)the collapse risk in the evaluation section of the tunnel is grade IV,which belongs to the dangerous level;(2)the actual excavation in the tunnel causes the surface collapse,the surrounding rock is rich in water,and the collapse risk level by assessment and excavation exposure is highly consistent,which verified the reliability and applicability of the risk assessment model.