Study on pressure distribution characteristics of typical conduit-fracture medium in southwest karst area
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摘要: 在岩溶发育区进行地下水资源开发、矿山开采及基础施工等工程活动时，都必须查明区域地下水流场及岩溶发育特征。以西南岩溶典型管道–裂隙介质含水层为研究对象，本文将裂隙的发育角度、导水通道中水流的流速、地下水供水形式等因素概化为裂隙开度、流量（管径、溢水高度）、裂隙与管道夹角三种因素，分析了管道–裂隙介质内的压强分布特征，揭示了影响因素与压强分布的响应规律。研究结果表明：管道–裂隙介质中，裂隙面内地下水形成的“水墙”，能够降低上下游管道内水流的流速，“水墙”越厚流速降低越大。提出了管道占优和裂隙占优的概念，管道占优表示涌水点或示踪剂接收点水流主要来源于上游管道介质，少量或无来源于裂隙介质；裂隙占优则表示涌水点或示踪剂接收点水流主要来源于与其相连接的裂隙介质，少量或无来源于上游管道介质。裂隙面内压强分布呈现对称的“漏斗”型分布，且管道口附近区域存在一个影响半径，影响程度为裂隙开度大于管道裂隙夹角大于流量。Abstract:
The southwest karst region of China is a unique area characterized by abundant groundwater resources and a fragile ecological environment. Its typical conduit-fracture dual aquifer system exhibits significant heterogeneity and anisotropy, which directly result in complex and variable groundwater recharge, flow, and discharge processes. These characteristics present numerous challenges to engineering activities such as regional groundwater development and utilization, mining, transportation, and foundation construction. When undertaking engineering projects in such areas, failure to accurately understand the flow dynamics and pressure distribution of groundwater within conduit-fracture media can lead to serious issues, including water inrush, mud outbursts, water resource wastage, groundwater contamination, and ecological damage. Therefore, systematically elucidating the hydraulic properties of these media is a critical prerequisite for addressing core hydrogeological problems in karst regions. This study focuses on the typical conduit-fracture medium aquifer in the southwestern karst region. Addressing the limitations of existing research—which primarily emphasizes macro-scale hydrological processes and lacks quantitative analysis of micro-scale pressure distribution and interpretation of water-conducting dominance relationships—this paper employs a combined approach of theoretical generalization and laboratory experiments. Complex factors influencing groundwater pressure distribution, such as fracture development angle, flow velocity within water-conducting channels, and groundwater supply mode, are systematically distilled into three adjustable key parameters: fracture aperture (three levels: 1 cm, 3 cm, 5 cm), flow rate (using pipe diameters of φ16 mm, φ21 mm, and φ26 mm combined with overflow heights of +3 cm, +5 cm, and +10 cm), and the angle between fracture and conduit (three levels: 60°, 70°, and 90°). An independently developed three-dimensional visual indoor test system is utilized, integrating four modules: water supply, fracture, conduit, and monitoring & data acquisition. This system offers precise parameter control and intuitive visualization of hydraulic phenomena. High-frequency, high-precision data on pressure and flow velocity within the conduit-fracture medium are collected using pressure sensors, paperless recorders, and flowmeters. Each experimental condition is repeated three times to ensure the reliability of the results. The experimental results demonstrate a significant "water wall" effect in the conduit-fracture medium: groundwater accumulating on the fracture surface forms a water-blocking "water wall" that effectively reduces flow velocity in both upstream and downstream conduits. The thickness of this "water wall" is positively correlated with the fracture aperture. When the fracture aperture increases from 1 cm to 5 cm, the pressure at the conduit mouth rises by approximately 3.1% compared to the baseline, accompanied by a more pronounced reduction in flow velocity. Based on differences in groundwater recharge sources, this paper innovatively introduces the concepts of "conduit dominance" and "fracture dominance. dominance refers to scenarios where water flow at the water gushing point or tracer receiving point primarily originates from the upstream conduit medium, with minimal contribution from the fracture medium. Conversely, fracture dominance describes cases where water flow mainly depends on recharge from the connected fracture medium. This classification offers a new theoretical framework for identifying groundwater recharge sources in karst areas. Additionally, the pressure distribution on the fracture surface exhibits a symmetrical "funnel" shape, with the funnel center aligned with the conduit mouth. A distinct influence radius exists around the conduit mouth, which first decreases and then increases as the fracture aperture grows (27 cm at 1 cm aperture, 24 cm at 3 cm, and expanding again at 5 cm). This influence radius is not significantly affected by changes in flow velocity. Quantitative analysis clarifies the relative importance of three factors affecting pressure distribution: fracture aperture > angle between conduit and fracture > flow rate. Specifically, the pressure at the conduit mouth when the angle is 90° is 4.4% lower than at 60°, and pressure decreases by approximately 1.9% as the flow rate increases from 228.3 mL/s to 874.0 mL/s. This study addresses the gap in systematic research on the micro-pressure distribution within conduit-fracture media in the southwest karst region. Its findings not only enhance the understanding of groundwater flow mechanisms but also provide valuable experimental data and theoretical support for engineering applications, including the identification of groundwater runoff channels, precise development and protection of groundwater resources, and the prevention and control of mine water inrush disasters in karst areas. This research holds significant practical importance for ensuring regional engineering safety and promoting sustainable ecological development. -
图 6 竖向距离50 cm处管道口附近压强值
Figure 6. Pressure value near the conduit entrance at a vertical distance of 50 cm
表 1 试验工况设计
Table 1. Test condition design
影响
因素裂隙开
度/cm管径
φ/mm溢流高
度/cm裂隙管道
夹角/°裂隙开度 1 26 +3 90 3 5 流量 1 16 +3 90 21 26 26 +3 +5 +10 裂隙–管道夹角 1 26 +3 60 70 90 
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