Jie Zhang

The influence of soil water content and contaminant injection pressure on the migration behaviour of p-Xylene (one of the organic pollutants in Benzene Toluene Ethylbenzene & Xylene) is investigated in the unsaturated zone using the controlled laboratory sandbox experiments. The results show that, at equivalent migration distances, higher soil water content leads to longer migration durations and reduces transport velocities, whereas greater injection pressure promotes faster contaminant movement. These findings highlight the governing role of water saturation in the water–oil–gas three-phase system, in which increased water content decreases the relative permeability of the oil phase and retards capillary-driven BTEX transport. Unlike many previous studies in which contaminants commonly migrate downward toward the groundwater table, the BTEX in this study did not reach the water table and exhibited partial upward migration. Overall, the results provide experimental-scale insight into key mechanisms governing BTEX transport in unsaturated sandy media and serve as a reference for improving predictions of contaminant fate and migration pathways in field settings.

To investigate the seepage behavior in a single fracture, a nonlinear seepage model based on boundary layer theory was developed. An analytical formula for calculating nonlinear flow in a single fracture was derived, providing a new method for assessing non-Darcy flow in single fractures. The flow in this formula consists of two parts: the viscous layer and the inertial layer. When the undetermined coefficient λ is equal to 0.5, the formula is simplified to the traditional cubic law. Under high hydraulic gradient conditions, the formula can be simplified for practical use. COMSOL software was used to explore the relationships between fracture length, fracture width, hydraulic gradient, and flow rate under high hydraulic gradient conditions. Additionally, a semi-empirical formula for calculating non-Darcy flow in single fracture was derived. The flow rates calculated using the proposed method were compared with those obtained from the Forchheimer equation, the Schrauf model and the cubic law. The results confirmed the accuracy and effectiveness of the proposed analytical formula.

In areas with complex hydrogeological conditions, the tracer test method is often used as an effective means in hydrogeological surveys. According to the results of tracer tests, hydrogeological parameters, including hydraulic gradient and permeability coefficient, fracture network leakage passages and their scale, and groundwater flow rate and direction can be quantitatively determined. This paper takes the upper reservoir of Yongxin Pumped Storage Power Station in Jiangxi Province as the research object, and focuses on the complex hydrogeological conditions of the upper reservoir. Three sets of tracer tests and multiple sets of single-hole flow rate and direction tests were conducted on the left and right banks of the reservoir and near surface gullies. The results showed that ZKS18 received tracers in all three tests, which indicates a close hydraulic connection between ZKS18 and the left bank, right bank, and surface gullies within the reservoir. Based on the single or multiple peak values of the tracer, it was determined that there are 1–6 leakage passages in the fractured rocks, with leakage passage sizes of 0.1–0.4 mm. According to the single-hole flow rate and flow direction tests, a self-developed instrument was used to determine the groundwater flow rate and flow direction at different depths in the test holes, which yielded results that were basically consistent with the results of the three-hole method. These results provide a basis for the use of tracer tests in hydrogeological surveys for water conservancy and hydropower engineering, and anti-seepage design of upper reservoirs.

Due to its poor hydro-physical properties and other characteristics, argillaceous dolomite is susceptible to seepage failure under high water pressure, affecting the seepage stability of a rock mass. To ensure the safety of the project, when the argillaceous dolomite is present, it is necessary to study the conditions pertaining to its seepage failure. Taking the argillaceous dolomite of Jurong Pumped Storage Power Station as the research object, the spatial distribution, occurrence, scale, degree of weathering, and mechanical and hydrogeological characteristics of the argillaceous dolomite were studied. Through on-site water pressure tests and laboratory variable head tests, the permeability characteristics of argillaceous dolomite were analyzed, and the hydraulic conductivity of the argillaceous dolomite in the upper reservoir and underground powerhouse areas was quantified. The argillaceous dolomite specimens were collected, and seepage failure tests were conducted to determine the critical water pressure for its seepage failure. Based on the results of the laboratory tests, a numerical model of groundwater flow was established. By changing the water level of the upper reservoir and the measures of the anti-seepage and drainage, the seepage stability of the argillaceous dolomite was discussed. The actual water pressure of argillaceous dolomite in the underground powerhouse area was identified during the operation of the Jurong pumped-storage power station. The calculations show that when fully enclosed anti-seepage and drainage measures are taken for the underground powerhouse, the maximum head of water is 98 m, which is lower than the critical water pressure of seepage failure for the argillaceous dolomite. Therefore, no seepage failure will occur. The results provide a scientific basis for the anti-seepage and drainage design of the underground powerhouse area.