裂隙岩体隧道建造对地下水环境影响的高效随机模拟方法

The analysis of tunneling induced impact on groundwater environment in fractured rocks faces many difficulties, such as the difficulty in delineating the impact range and defining boundary conditions; the difficulty in modeling complex rock-tunnel-drainage system; the scarcity and spatial variability of seepage parameters; the difficulty in defining priors in uncertainty methods and the formidable calculation cost; and the difficulty in effectively using the tunnel inflow measurements. To address the above issues, this research focuses on the following three aspects: multi-scale modeling techniques, stochastic simulation, and interacting mechanism between tunnel and rock seepage field. The research contents include: (1) establishing a mixed “watershed-rock-tunnel-groundwater” multi-scale seepage model, dynamic coupling of the mixed multi-scale model, and its parallel computation; (2) defining priors based on similarity criteria of tunneling sites and the Bayesian multi-source data fusing technique, and proposing an modified “approximate Bayesian computation” methodology to improve the efficiency of stochastic simulation; and (3) constructing an equivalent seepage model to simplify tunnel drainage system on the basis of numerical simulation and laboratory tests. The research objective is to explore the interacting mechanism of seepage field between tunnel drainage system and surrounding rocks, and to form a systematic “watershed-rock -tunnel-groundwater” modeling and analysis method. Our goal is to provide a theoretic solution for analyzing tunneling induced environmental impacts under conditions of uncertainty.

岩体隧道修建对地下水环境影响分析经常遇到如下困难：计算范围及边界条件难以确定；难以全面考虑围岩-隧道-防排水系统渗流场复杂模型；渗流场计算参数采样数据少，空间变异性大；不确定性方法的先验分布难以给定，且计算量大；隧道涌水量实测数据难以有效利用等。针对上述问题，本课题从多尺度模型、随机模拟方法、隧道与围岩渗流场相互作用机理三个方面出发，开展以下研究：①建立“流域-岩体-隧道-地下水渗流场”混合多尺度分析模型，研究多尺度模型动态耦合方法和并行计算方法；②研究基于隧道工程环境相似性准则和贝叶斯数据融合的先验参数分布确定方法，以及改进的“近似贝叶斯计算”方法，提高随机模拟效率；③在数值模拟和室内试验基础上，提出隧道防排水系统的等效渗透模型。课题旨在探明隧道防排水系统与围岩渗流场相互作用机理，形成系统的“流域-岩体-隧道-地下水渗流场”建模与分析方法，为岩石隧道修建对地下水环境影响分析提供理论支撑。

隧道工程建设过程中的地下水排放一方面可能会影响隧道的安全，另一方面会降低地下水位并对生态环境产生影响。现有隧道排水引起地下水位降深分析方法对地形、地下水流动和水文地质参数过于简化，无法反映地下水位降深的不确定性。为了考虑了裂隙岩体渗透特性不确定性、断层带和复杂地形的影响，基于地下水渗流场数值模型和贝叶斯定理，利用隧道涌水量实测值作为条件值，提出了地下水降深随机建模方法。该方法能够考虑复杂地形因素，在施工前初步预测地下水降深及排水量，在施工期根据实测数据不断更新预测值，通过设置误差区间灵活地进行预测，并可以考虑水文地质参数对预测的不确定性影响。研究揭示了岩性空间分布对地水位下降有着决定性的作用，是地下水位降深沿隧道轴线呈现不规则且不连续分布的根本原因。该方法为工程和水文地质资料较为贫乏的山区隧道地下水长期影响提供了定量的分析方法。