Evolutionary Mechanism Of Water Inrush Through Filling Structures In Tunnels And Engineering Applications

Groundwater can flow into tunnels through intact materials, joints and fissures, as well as faults and karst conduits. The mechanical mechanism and evolutionary process of water inrush through faults and karst conduits have been investigated systematically in the present study using a literature review, theoretical analysis, software development, experimental testing and numerical simulation. The MATLAB platform was used for software package development, and the PFC3D software was used for numerical simulation analysis.(1) A novel research method is proposed for the analysis of the internal instability of granular soils to identify which type of water inrush will occur. To verify the feasibility and accuracy of the novel method, four unimodal parametric PSD models and one bimodal parametric PSD model are compared, and dozens of soil specimens are studied. To determine the optimal parameter values of the PSD models, a software package termed Analysis Software for Internal Stability of Granular Soils (ASISGS) is developed, which can also obtain the secant slope curves of soil PSDs automatically. A new synthetic chart is proposed for the analysis of the internal instability of granular soils, and the evaluation results are in good agreement with experimental tests.(2) The microscopic mechanisms of suffusion initiation and development are revealed. The theoretical formulas and models previously proposed for determining the critical hydraulic condition of suffusion initiation are compared first, and then a new formula and a new theoretical model are proposed based on the seepage force and the variable section capillary model, respectively. For calculation and comparison of these formulas and theoretical models, a software package termed Calculation Program for Critical Hydraulic Gradient (CPCHG) is developed. The force condition and equilibrium state of coarse particles under seepage flow are studied and expressed in mathematical terms, and the critical hydraulic gradient of soil skeleton deformation is proposed.(3) An experimental testing apparatus is developed for systematic research on the seepage failure of filling materials in faults and karst conduits subjected to seepage flow. The apparatus comprises an axial load application system, a pressurized water supply system, a permeameter cell, a particle collection system, a water collection system and a data acquisition system. A series of experiments on internally-unstable granular soils with and without different clay contents, respectively, was conducted under different axial stresses. The variations of flow rate and hydraulic conductivity with the hydraulic gradient under different conditions are analyzed. The effects of axial stress and clay content on the evolutionary process and the critical hydraulic condition are investigated, and the typical evolutionary process and phenomena of seepage failure are summarized.(4) The mesoscopic evolutionary process of seepage failure of non-cohesive filling materials under unidirectional seepage flow is reproduced by secondary development of the PFC3D software. The effect of seepage direction on the evolutionary process of seepage failure is studied by doing numerical simulations under different seepage directions. The variations of porosity and flow rate with increasing hydraulic gradient are monitored, as well as the migration pathways of fine particles. Numerous basic scaling relationships and their limitations for a DEM scale model are summarized first, and then a new set of scaling relationship is proposed using a governing equation approach for the DEM simulation of fluid-solid coupling problems, and numerical simulations of the seepage failure with different scaling relationships indicate that it is more reasonable and accurate than other scaling relationships.(5) Several factors are selected as evaluation indices for risk assessment of water inrush, and two evaluation index systems used in the design and construction stages, respectively, are established. An innovative and effective method named Attribute Interval Evaluation Theory (AIET) is proposed for risk assessment of water inrush. The AIET can not only quantitatively prioritize risks by combining consequences and probability of occurrence, but also analyze the reliability of the evaluation results. Since the AIET method is subjected to a large amount of calculations, a practical software termed AIET software is developed. Engineering applications indicate that the AIET can be successfully used in evaluating the risks of geological disasters.