Z.H. Xu

An enriched K-means clustering method for grouping fractures with meliorated initial centers

An enriched K-means clustering method for grouping fractures with meliorated initial cluster centers is proposed. Selection of the initial cluster centers is based on a gathering degree function and a hierarchical clustering method. A simplified Xie-Beni cluster validity index is applied to determine the optimal number of clusters automatically. The effectiveness of the proposed clustering method is demonstrated by using synthetic data and field data compiled from literatures. The gathering degree concept used in the density-based method is helpful in seeking suitable initial cluster centers. It alleviates the influence from the selected arbitrary threshold to get a more stable clustering result. The procedure to automatically remove fractures belonging to the obtained cluster center with the hierarchical clustering method is more natural than using the pre-defined radius. Additional advantage of the algorithm is that its convergence is fast, and it can be easily implemented for geological mapping result analysis.

Flow Characteristics and Escape-Route Optimization after Water Inrush in a Backward-Excavated Karst Tunnel

AbstractIn this study, using the background of Qiyueshan high-risk karst tunnels, flow characteristics and escape-route optimization after water inrush in a backward-excavated karst tunnel are researched. First, five case studies are simulated and investigated under different velocities of water inrush. One special probing line is selected, respectively, in the left tunnel, cross passage, right tunnel, and along the height direction of the tunnel centerline. For each probing line, the corresponding velocity and pressure curves are obtained based on the numerical simulation results. The change rules of velocity and pressure under the five water-inrush velocities are analyzed and concluded. Then, focusing on one velocity of water inrush, the variation laws of velocity and pressure in a plane are analyzed and discussed by selecting a series of probing lines. Flow characteristics of water after inrushing in a backward-excavated tunnel are summarized. Finally, for such cases, the optimized escape routes are ma...

An Innovation Simulation Method for Flow State Evolution Laws of Water Inflow and Inrush in Course of Tunnel Excavation (Part I: Theories)

Hydrologic and engineering geological conditions of underground engineering and mining are highly complex. Geological hazards, especially water inflow or inrush, often occur during constructions. In order to get an insight into flow state evolution laws of water inflow and inrush in karst regions, as well as the influence of tunnel excavation, a numerical simulation method was proposed with COMSOL Multiphysics. Three water flow laws, Darcy’s law, Brinkman equations and incompressible Navier-Stokes equations, are coupled and linked with each other. Water pressure and velocity can be analyzed in the course of excavation, and it can be used for further study of risk control of water inflow and inrush.

A spiral variable section capillary model for piping hydraulic gradient of soils causing water/mud inrush in tunnels

An innovative spiral variable-section capillary model is established for piping critical hydraulic gradient of cohesion-less soils causing water/mud inrush in tunnels. The relationship between the actual winding seepage channel and grain-size distribution, porosity, and permeability is established in the model. Soils are classified into coarse particles and fine particles according to the grain-size distribution. The piping critical hydraulic gradient is obtained by analyzing starting modes of fine particles and solving corresponding moment equilibrium equations. Gravities, drag forces, uplift forces and frictions are analyzed in moment equilibrium equations. The influence of drag force and uplift force on incipient motion is generally expounded based on the mechanical analysis. Two cases are studied with the innovative capillary model. The critical hydraulic gradient of each kind of sandy gravels with a bimodal grain-size-distribution is obtained in case one, and results have a good agreement with previous experimental observations. The relationships between the content of fine particles and the critical hydraulic gradient of seepage failure are analyzed in case two, and the changing tendency of the critical hydraulic gradient is accordant with results of experiments.