Geotechnical and Underground Engineering Problems Caused by Water Action

1. Introduction

Geotechnical engineering is an interdisciplinary field bridging earth science and engineering construction that primarily focuses on the mechanical behavior and stability of rock and soil masses under natural and engineering-induced disturbances. Extensive engineering experience has demonstrated that water serves as a critical factor governing the engineering properties and stability of geotechnical materials, with water influencing geological environmental evolution and engineering activities [1,2,3,4]. Entering the 21st century as major projects such as large-scale water conservancy and hydropower facilities, transportation tunnels, and mineral resource development advance into regions with complex geological conditions, water-induced geotechnical engineering problems have become increasingly prominent. This trend requires a more in-depth understanding of the mechanisms through which these problems occur and the innovation of prevention and control technologies [5,6,7,8].

Water significantly alters the physical and mechanical properties as well as the stress environment of rock and soil masses, resulting in various geological hazards. Taking the Three Gorges Reservoir area as an example, numerous landslides have been closely associated with seasonal rainfall and the periodic fluctuation of the reservoir’s water level [9,10,11]. Rainfall infiltration increases the saturation of the sliding mass, elevates pore water pressure, and reduces effective stress. Concurrently, the rise and fall in the reservoir level alter the seepage pressure on the bank slope and soften the rock and soil through soaking. These combined effects attenuate shear strength, ultimately causing rock and soil instability [12,13]. Similarly, water inrushes during deep mining operations are often related to the accumulation and sudden release of energy within rock masses under high, confined water pressure [14,15]. The water and mud inrush disasters encountered during tunnel excavation originate from construction disturbances that disrupt the original hydrogeological equilibrium, activating high-pressure water-bearing systems [16,17]. The liquefaction of saturated sandy soils under seismic loading is a typical manifestation of a rapid rise in pore water pressure, causing the soil to lose its shear strength [18,19,20]. Land subsidence in coastal areas due to groundwater over-exploitation and submarine landslides caused by submarine slope instability are directly related to changes in pore water pressure or seepage [21]. These cases adequately illustrate that water is not only a fundamental element of the geological environment hosting rock and soil masses but also a crucial triggering and controlling factor in the evolution of their instability.

Currently, addressing the complex challenges due to water–rock interactions requires systematic research that integrates multidisciplinary methods and advanced technologies. High-precision numerical simulations and physical model tests have become essential tools for revealing the mechanisms underlying these interactions [22,23,24]. Additionally, field monitoring and data analysis are crucial for model validation and practical guidance [25,26]. Looking ahead, the sustainable development of geotechnical engineering requires continuous innovation in the following areas: First, refined numerical simulation techniques must be developed that can more realistically represent complex water–rock–soil coupling processes, particularly in areas such as unsaturated seepage, chemo-mechanical coupling, and multiphase flow [27]. Second, enhanced real-time monitoring and intelligent early-warning technologies for engineering geological hazards must be developed based on big data and artificial intelligence, thereby increasing the proactivity and accuracy of risk prevention and control [28,29,30,31]. Third, new low-carbon, environmentally friendly, and efficient technologies, materials, and methods must be devised for geotechnical reinforcement and groundwater control, such as ecological slope protection and intelligent drainage systems [32]. Fourth, systematic research must be deepened into the evolution of geological environments under the combined effects of extreme climate events (e.g., heavy rainfall, drought) and major engineering activities (e.g., reservoir operation, deep mining) to provide scientific and technological support for the safety throughout the engineering life cycle [33].

Accordingly, this Special Issue, titled “Geotechnical and Underground Engineering Problems Caused by Water Action,” includes 11 thematic papers. The following provides a brief overview of their contents, which primarily cover valley deformation induced by reservoir impoundment, the impact of tunnel excavation on groundwater systems, particle migration and erosion in geotechnical materials due to groundwater seepage, the discharge capacity of hydraulic structures (such as flood relief shafts), water and salt transport and remediation in saline–alkali lands, as well as the triggering and evolution mechanisms of landslides, debris flows, and other geological hazards under the influence of precipitation and groundwater. The research approaches include numerical simulations, field monitoring, and experimental analyses, with a core focus on engineering safety, geological hazard prevention, and environmental impact assessment within the water cycle.

2. An Overview of the Published Articles

Water is one of the core forces driving the genesis and evolution of geotechnical engineering problems. Given the increasingly complex engineering geological conditions and environmental challenges, the mechanisms underlying water–rock interactions must be deeply understood and the interdisciplinary integration as well as innovative development of monitoring, simulation, and prevention technologies must be actively promoted. This understanding will guarantee the safety of the construction and operation of major projects as well as the effective protection of the geological environment, thereby facilitating the coordinated development of geotechnical engineering and the natural environment. The 11 papers in this Special Issue cover research topics related to this theme.

Contribution 1 propose a semi-analytical solution for predicting the early recession segment in a finite-length horizontal unconfined aquifer following steady initial conditions. The solution is constructed via linear perturbation and a Sturm–Liouville eigenvalue problem. By deriving a large-eigenvalue asymptotic solution describing the aquifer’s immediate response to the cessation of recharge, an exact analytical expression for the early outflow rate versus time was obtained, and its valid time range was explicitly defined. The authors further described the analytical connection between this solution and classical recession theory. The proposed solution serves as a benchmark for related numerical simulations and verifications.

Contribution 2 addressed the problem of predicting water hazards in separated layers in coal mining. They constructed a spatial volume calculation model that couples a criterion based on strata bending deflection with the developmental stage of the separated layer. By integrating an improved stepwise comparison combination method and thin elastic plate theory, the model can dynamically and precisely predict the developmental stage, spatial location, and water accumulation volume of a separated layer. Validation using the 21,301 working face in Cuimu Coal Mine, Shaanxi Province, demonstrated that the methods’ prediction accuracy and reliability for the location of separated layer development and the risk of water inrush are significantly higher than those of prior methods. The study further indicated that changes in the morphology of the separated layer directly affect the volume of accumulated water, and traditional methods exhibit significant errors after long-distance mining. These findings provide crucial technical support for effective early warnings and the prevention of water hazards from separated layers in mines.

Contribution 3 systematically investigated the discharge capacity and evolution of the flow regime of a flood relief shaft through hydraulic model tests and FLOW-3D numerical simulations. The authors found that the discharge head controls the flow regime: free-surface flow occurs when the head is below 0.8 m; intermittent flow occurs between 0.8 and 1.2 m, transitioning to pressurized full-pipe flow when exceeding 1.2 m. The findings also demonstrated that increasing the height of the discharge window can significantly enhance discharge capacity (the discharge of the eighth layer was approximately 30% higher compared to that of the first layer), but increasing the height of the discharge window also raises the risk of intermittent flow. Consequently, the authors recommend controlling the operational head to below 0.8 m to balance discharge requirements with flow regime stability. The study provides a basis for the design and safe operation of tailings pond flood discharge systems.

Contribution 4 investigated the ameliorative effects of applying furfural residue combined with different contents of flue gas desulfurization gypsum on the water–salt transport and infiltration characteristics in saline–alkali soil in Ningxia through simulation experiments. Based on fixed leaching water volume and furfural residue application, three treatments with d desulfurization gypsum application rates were established. The results indicate that this combined application measure reduces soil alkalinity by an average of 36.7% as well as promotes water infiltration and surface desalination by enhancing the soil’s hydraulic conductivity. However, excessive application can lead to salt accumulation in deeper layers. The authors clarified that infiltration parameters exhibit a power or linear relationship with time and validated the applicability of the Philip model for simulating the infiltration process under these conditions. Ultimately, an optimized application of 7.5 t/ha furfural residue combined with 22.5 t/ha desulfurization gypsum was proposed for local saline–alkali soil reclamation.

Contribution 5 systematically investigated the coupled relationship between groundwater dynamics and soil water–salt variations under subsurface pipe drainage conditions in the Yinbei region of Ningxia through field monitoring and laboratory tests. The study revealed wide seasonal fluctuations in groundwater depth and salinity, with soil salinity synchronously varying. Soil salinity linearly decreased with increasing groundwater depth and exhibited an exponential correlation with groundwater salinity. Based on these findings, the authors developed a quantitative relationship model incorporating groundwater salinity, depth, and soil salinity, the reliability of which was validated (R² = 0.7238). The researchers elucidated the key water and salt transport patterns in subsurface drainage systems, providing a scientific basis for the remediation of saline-alkali soils as well as the regulation of water and salt in similar regions.

Contribution 6 focused on Erlian Village in the eastern Guide Basin of the upper Yellow River, conducting a systematic analysis of the distribution characteristics, material composition, and genesis of the debris flow fans in the area. The authors particularly explored the feedback relationship between the debris flow activity and the evolution of the Yellow River channel. In the area, at least 66 debris flow gullies and 20 large accumulation fans have developed. Since 16 ka B.P., the Yellow River channel has undergone an evolutionary process dominated by the accumulation, erosion, and re-accumulation of debris flow fans. Notably, the deposition of late-stage fans (since 8 ka B.P.) has continuously constrained the channel, causing it to shift southward by at least 1.25 km. Through a chronological study, five accumulation phases were identified within the late-stage debris flow fans. These findings provide an important case study and theoretical basis for a deeper understanding of debris flow hazards and their long-term impact on channel evolution in the upper Yellow River.

Contribution 7 investigated the valley contraction deformation issue in the Baihetan high arch dam. They developed a hybrid model that integrates transient seepage numerical simulation with statistical analysis. They employed numerical simulation to characterize the complex seepage field at the dam site after reservoir impoundment. Subsequently, monitoring data were used to quantify the contribution of various factors influencing the seepage field, with predictions based on time-series extrapolation. The valley deformation in the dam area is projected to be mitigated by June 2028. The study not only provides critical evidence for assessing the safety of the Baihetan Dam but also offers a significant methodological reference for studying similar engineering geological problems through the developed hybrid prediction approach.

Contribution 8 investigated the hydro-environmental impact of tunnel excavation drainage on a confined karst groundwater system within a typical anticlinal structure based on the Wufu Tunnel project in Chongqin. Through the systematic monitoring of flow rates and water levels at multiple points including the tunnel, boreholes, and springs, and employing methods such as statistical testing and wavelet analysis, the researchers revealed the mechanisms through which the karst aquifer and surface water bodies respond to tunnel drainage and precipitation. The researchers found that tunnel drainage is the dominant driver of hydrological dynamic changes, with its impact far exceeding that of rainfall. Tunnel drainage has significantly altered the regional groundwater flow pattern, causing local flow field reversal and reconstructing the recharge–runoff–discharge regime of the groundwater system. The study provides an important basis for assessing and managing the hydrological effects in the environment of similar tunnel engineering projects.

Contribution 9 employed the computational fluid dynamics–discrete element method (CFD-DEM) to investigate the migration of fine particles in loose soil driven by groundwater seepage, with a focus on the influence of key factors such as particle size ratio, particle count, and weight. The results indicate a distinct mechanistic shift in the migration behavior of fine particles in loose soil. When the particle size ratio is ≤5, fine particles primarily accumulate on the surface of the porous medium, and the degree of accumulation intensifies with an increase in their own weight or quantity. However, when the particle size ratio exceeds 5, the size ratio becomes the dominant factor controlling migration distance. A larger size ratio leads to particles migrating farther, resulting in a significantly larger proportion of accumulation in the mid-to-rear regions. The study reveals how the dominant particle migration mechanism changes with conditions, providing theoretical insights for understanding and preventing geotechnical issues such as internal soil erosion and slope instability induced by seepage.

Contribution 10 employed molecular dynamics simulations to systematically investigate the effects of temperature (298.15–363.15 K) on the structure, dynamics, and mechanical properties of interlayer water in three typical clay minerals (kaolinite, montmorillonite, and pyrophyllite). By analyzing mean square displacement, density profiles, hydrogen bond dynamics, and stress distributions, the mechanisms of the interactions between water’s molecular structure and thermal motion were revealed. The authors found that the diffusivity of water and the stability of the hydrogen bond network are strongly dependent on temperature, with montmorillonite demonstrating the strongest water retention capacity and the most stable hydrogen bond structure. Furthermore, the pronounced interlayer confinement effect at low temperatures weakens as temperature increases, and the stress distribution reflects the response of interfacial mechanical behavior to thermal perturbations. The study provides a critical high-resolution theoretical foundation for understanding and predicting the macroscopic performance of clay–water systems in environments with varying temperatures.

Contribution 11 studied a large-scale landslide induced by slope toe excavation and heavy rainfall along the Jiaxi Highway in Qinghai Province. Through field data analysis and numerical simulation (combined with the strength reduction method), the mechanisms of the landslide and landslide risks were accurately identified (predicting a slip of 1960 mm and a safety factor of 1.26 under natural conditions). The researchers proposed and implemented a comprehensive treatment scheme involving “cut and fill combined with a sheet pile wall”. This scheme significantly increased the slope safety factor (to over 2.16 after treatment) and effectively controlled displacement (reduced to approximately 17.6 mm). Continuous monitoring and rainfall simulation verified the long-term stability trend of the slope post-treatment. The study provides a reliable methodology and a case reference for identifying the cause of and selecting engineering treatments for highway landslides under similar geological conditions.

3. Conclusions

The safety and stability of geotechnical engineering are deeply rooted in a profound understanding of the intrinsic behavior of geological masses. Among the numerous influencing factors, water plays a central role, serving as not only the host medium for rock and soil but also a key factor controlling their mechanical behavior and stability. As human engineering activities increasingly advance into regions with more complex geological conditions, the understanding of the mechanisms of water–rock interactions and the capability to control them will be directly related to the success and safe operation of major projects.

The research findings compiled in this Special Issue collectively showcase current cutting-edge explorations addressing the complexity of water–rock interactions, reflecting an innovative trend of multi-scale and multi-method integration.

(1)

At the macro-engineering scale, studies are focusing on the interaction between water and large-scale projects. For instance, research on valley deformation at the Baihetan high arch dam integrates transient seepage simulation with monitoring data statistics, enabling the accurate prediction of long-term deformation. The analysis of the Chongqing Wufu Tunnel, through hydrological monitoring, reveals the profound impact of tunnel drainage on the regional groundwater system, leading to flow field reversal. These studies provide a scientific basis for assessing the lifecycle safety and controlling the environmental impact of major engineering projects.

(2)

At the material and mechanism scales, research is advancing toward more refined levels. The use of a coupled CFD-DEM simulation reveals the mechanistic transition governing the migration of fine particles driven by groundwater seepage. Molecular dynamics simulations show, from an atomic perspective, the influence of temperature on the structure and mechanical properties of the interlayer water in clay minerals. These breakthroughs in mechanistic understanding establish a solid theoretical foundation for understanding macroscopic phenomena, such as internal erosion and soil softening.

(3)

Regarding prevention/control and improvement technologies, the research reflects a shift from passive response to active regulation. For the large landslide on the Qinghai Jiaxi Highway, the mechanism was accurately identified through precise numerical simulation, leading to the development of an effective and comprehensive treatment scheme involving “cut and fill combined with a sheet pile wall”. For the saline–alkali soils in Ningxia, simulation experiments identified optimal measures for applying soil amendments to enhance water and salt transport. Furthermore, in-depth research on the discharge capacity and flow regimes of flood relief shafts directly informs the safety design of projects such as tailings ponds.