Prediction and Treatment of Water Leakage Risk Caused by the Dynamic Evolution of Ground Fissures in Gully Terrain

Groundwater leakage in the loess gully terrain is one of the main hazards of coal seam mining at shallow burial depth. The burial depth of the 5−2 coal seam is less than 50 m from the ground in the gully of the study site. The fissures that expand upward after mining can easily penetrate the ground to form a water-conducting channels. During rainy periods, there is a potential risk of groundwater leakage. In order to reveal the characteristics of plane development and the dynamic evolution of gully ground fissures, the typical U-shaped gully in the northern Shaanxi coal mine was studied using the field measurement methods of “On-site measurement” and UAV aerial photography. Based on the experimental platform of ground fissure leakage developed and designed by the team, an indoor test model corresponding to the actual situation was established. In addition, the mathematical models of actual flood inrush, fissure width, and flood flow in the channel were established. The actual mine water flow and the mine drainage capacity were compared and analyzed, thus proposing criteria for classifying gully mining ground fissure collapsed water hazards. These criteria can provide theoretical references for predicting fissure leakage hazard zones in the ground gully of shallow buried coal seams. According to the development height of the water-conducting fissure zone (WCFZ), the treatment methods of ground fissures in gullies under different security conditions were designed, which was applied in the field with good results. The results showed that the treatment methods in this paper could effectively prevent the leakage of groundwater in the gullies along the ground fissures.

A Framework for Risk-Based Cost–Benefit Analysis for Decision Support on Hydrogeological Risks in Underground Construction

Construction below the ground surface and underneath the groundwater table is often associated with groundwater leakage and drawdowns in the surroundings which subsequently can result in a wide variety of risks. To avoid groundwater drawdown-associated damages, risk-reducing measures must often be implemented. Due to the hydrogeological system’s inherent variability and our incomplete knowledge of its conditions, the effects of risk-reducing measures cannot be fully known in advance and decisions must inevitably be made under uncertainty. When implementing risk-reducing measures there is always a trade-off between the measures’ benefits (reduced risk) and investment costs which needs to be balanced. In this paper, we present a framework for decision support on measures to mitigate hydrogeological risks in underground construction. The framework is developed in accordance with the guidelines from the International Standardization Organization (ISO) and comprises a full risk-management framework with focus on risk analysis and risk evaluation. Cost–benefit analysis (CBA) facilitates monetization of consequences and economic evaluation of risk mitigation. The framework includes probabilistic risk estimation of the entire cause–effect chain from groundwater leakage to the consequences of damage where expert elicitation is combined with data-driven and process-based methods, allowing for continuous updating when new knowledge is obtained.

A Survey Method on Groundwater Sources and Preferential Flow Paths In Urban Limestone-Based Residential Districts

Residential districts dominated by limestone are likely to be impacted by undesirable groundwater seepage accidents. Such groundwater seepage can generally give rise to loss of life and property. To control groundwater seepage, increasingly accurate and reliable methods for surveying are becoming indispensable. We proposed a survey method to confirm groundwater sources and preferential flow paths in urban limestone-based residential districts via ground penetrating radar (GPR) and time domain electromagnetic method (TDEM). Firstly, we established the geophysical exploration plan after careful analysis of available hydrogeological survey data including terrain, stratum distribution and water table. Survey lines were designed parallel to existing urban roads and perpendicular to the ground. Next, we used GPR and TDEM to detect gravels in the permeable layer and water-rich regions in the aquifer. Drilling method was adopted for comparisons to resulting images. Finally, integrated interpretation indicated accurate measures of groundwater sources, main preferential flow paths and the preliminary classification of groundwater leakage risk in a study region. The feasibility and effectiveness of the GPR and TDEM survey method were verified in the hydrogeological survey at the Lingxiucheng Residential District in China, where a thick limestone layer existed and groundwater leakage accidents had occurred in basements of houses. The method had high reliability for limestone topographies and was improved to be an effective and low-cost solution to overcome physical limitations of existent buildings and traffic jams in urban areas. Therefore, our research can be extended to similar projects and related problems to help better map urban limestone-based residential districts and reduce groundwater seepage.