Field experiment on hydraulic channel sealing via grouting to prevent groundwater pollution in karst region
The karst regions in Southwest China are characterized by intense karstification, complex hydrogeological conditions, and well-developed karst conduits with pronounced spatial heterogeneity. These factors contribute to the inherent vulnerability of karst groundwater systems, rendering them highly susceptible to contamination. Additionally, large-scale mining activities in these areas generate substantial volumes of wastewater and waste materials, exacerbating groundwater pollution. Consequently, the development of scientific technologies for the prevention, control, and assessment of groundwater pollution is of significant importance. This study focuses on the Zimudang mining area in Guizhou Province, where curtain grouting experiments were conducted to seal identified karst conduits, targeting the dominant hydraulic pathways of groundwater contamination. Real-time, in-situ monitoring using electrical resistivity methods was employed throughout the grouting process to evaluate the effectiveness of the sealing measures. The Zimudang depression is a critical surface water convergence area within the study area, where the converging surface water is transformed into groundwater through the K20 drainage cave located beneath a steep cliff on the northeastern side of the depression. Mining activities have compromised the water-blocking function of the F1 fault, altering groundwater flow so that it converges toward the mined-out areas and mining tunnels. Within the mining area, the K20 drainage cave serves as a channel for the concentrated recharge of groundwater from atmospheric precipitation. Upon entering the K20 drainage cave, the principal karst hydraulic conduits extend roughly in an east–west direction. Taking into account the characteristics of subterranean river channels, topography, and surface structures, the site for the curtain grouting test was selected in the northern part of the tailings pond. Drilling and borehole TV surveys were conducted at the site. Analysis of core logs and borehole TV results confirmed significant karst development in the underlying strata, which serve as the dominant hydraulic pathways for groundwater contamination migration, thereby validating the suitability of the test site. To ensure that the grout solution thoroughly permeated and filled fractures and karst caves, high-pressure intermittent grouting was adopted. The grouting was performed sequentially from ZJ08 to ZJ01, followed by a second round after the injected grout had cooled. Throughout the entire grouting process, high-density resistivity and transient electromagnetic methods were employed to monitor changes in formation resistivity. In this experiment, one high-density electrical measurement line and 11 transient electromagnetic measurement lines were deployed. Three electrode configurations-Wenner, dipole, and Schlumberger-were utilized, with measurement depths of 15 m, 15 m, and 17 m, respectively. All three configurations demonstrated a clear increase in formation resistivity within the grouted zone, with the low-resistivity regions adjacent to the boreholes exhibiting more pronounced improvements after grouting. For instance, among the transient electromagnetic measurement survey lines (S3, S5, S7, S8, S10, and S11), significant increases in formation resistivity were observed in lines S3, S5, S7, and S8, indicating effective grouting and sealing. In contrast, lines S10 and S11 showed either negligible changes or a decrease in resistivity after grouting. This discrepancy is attributed to the fact that line S10 was situated beyond the grouting influence zone due to its distance from the grouting wells, while line S11 exhibited localized resistivity reductions, likely caused by the displacement of water from karst caves and fractures as grout infiltrated these features. Analysis of the geophysical monitoring data revealed that when survey line layouts are constrained by factors such as topography, the high-density electrical method is more suitable for detecting shallow resistivity variations in areas with limited terrain, whereas the transient electromagnetic method is more effective for probing deeper subsurface electrical properties. To quantitatively assess the grouting effectiveness, formation porosity was derived from resistivity measurements using Archie’s formula. By comparing porosity variations before and after grouting, the grout diffusion area was delineated, and the effectiveness of blocking groundwater pollution pathways was evaluated. For instance, in measurement lines S3, S5, S7, and S8, the grout diffusion area within a 2-meter radius of the grouting wells ranged from 21.42 m2 to 99.32 m2. The maximum reduction in formation porosity reached 65.7%, averaging 39.9%. This study demonstrates that electrical resistivity monitoring enables real-time, in-situ evaluation of the grouting sealing effectiveness in karst conduits. In addition, by converting resistivity data into formation porosity for quantitative analysis, it is possible to accurately delineate the grouting diffusion area and sealing range, thereby assessing whether key hydraulic pathways have been effectively sealed. This approach provides robust technical support for evaluating the performance of curtain grouting in blocking the dominant groundwater contamination pathways in karst regions.
Hydrochemical characteristics and genesis analysis of hot springs in the Changtan area, Chongqing
This study takes the natural and artificially drilled hot springs as the research objects located in the northwest wing of the Fangdoushan anticline in Changtan Town, Wanzhou District, Chongqing City. It systematically examines their hydrochemical characteristics, heat storage conditions, and genetic mechanisms, revealing the unique formation process of the low-temperature Cl-Na type hot springs in the high-uplift anticline region. The hot springs in the study area are located within the carbonate rock layers of the Lower Triassic Jialingjiang Formation (T1j), and are controlled by the combined effect of the Fangdoushan anticline structure and local hydrogeological conditions. Through hydrogeochemical analysis, geothermal temperature scale calculations, and hydrogeological conceptual model analysis, the following key conclusions are drawn: 1. Chemical characteristics and genesis of water (1) The chemical composition of the hot spring water is classified as Cl-Na type (according to the Piper three-line graph). The pH is weakly alkaline (7.26 to 7.87). The mineralization degree is significantly higher than the regional background level, TDS up to 11.25 g·L−1. The proportions of Cl− and Na+ are 36.72% and 55.37%, respectively.(2) The high mineralization degree stems from the concentrated halogen dissolution and filtration in the tidal flat-lagoon facies strata of the Triassic Jialingjiang Formation (T1j), as well as the water-rock interactions during the deep circulation processes (such as dolomite dissolution and sodium growth petrification). Additionaly, sulfate reduction reactions involving microorganisms (e.g., H2S generation) and long-range migration (>10 km) further enhance ion enrichment.(3) The content of Sr2+ among the trace elements is notably high (37.06 mg·L−1), and its source is closely related to the water-rock interactions involving carbonate rocks and gelatinate layers in the Triassic Jialingjiang Formation (T1j). 2. Heat storage conditions and circulation mechanism (1) The calculation of geothermal temperature scales (quartz, chalcedony, and quartzite) shows that the heat storage temperature ranges from 54 ℃ to 78 ℃, with an average of 65.4 ℃, classifying it as a low-temperature geothermal system. Based on the ground temperature gradient, the circulation depth is estimated to be approximately 2,000 meters.(2) The heat storage layer is composed of interbedded limestone and dolomite from the Triassic Jialingjiang Formation (T1j), which overlies the mudstone of the second section of the Badong Formation (T2b2), the clastic rocks of the Triassic Xujiahe Formation (T3xj), and the sand-mudstone of the Jurassic system. Together, these formations create a water-proof and heat-insulating cover layer, thereby forming a closed heat storage structure. 3. Groundwater recharge sources and heat sources (1) Recharge sources: Atmospheric precipitation in the exposed area of the Triassic Jialingjiang Formation (T1j) at the core of the Fangdoushan anticline infiltrates in through karst fissures and sinkholes, generating deep runoff.(2) Runoff path: Groundwater migrates deeper along the fault-fracture system at the wing of the anticline, absorbs heat from the surrounding rock, and undergoes dissolution and filtration, with a retention time of several hundred years.(3) Heat source: There is no additional heat source, such as magmatic activity. The heat originates from the normal geothermal gradient (2.5 to 3.0 ℃·100 m−1), and the formation of the heat reservoir is driven by the warming of the stratum. 4. Three-dimensional genesis conceptual model (1) After the infiltrating as atmospheric precipitation, the water migrates deeper along the fracture network at the core of the anticline. It undergoes long-path circulation (approximately 2,000 meters) and slow warming, accompanied by intense water-rock interaction with salt-bearing carbonate rocks. (2) Deep faults, such as the outer dam reverse fault, act as secondary hydrothermal channels that locally supplement solutes and heat; however, the main heat source remains the natural warming of the crust. (3) Hydrogeological sections reveal that the combination of an aquifer and impermeable layer under the control of anticline structures, is the key to the occurrence and migration of thermal fluids. The mudstone of the Triassic Badong Formation (T2b) effectively blocks vertical heat loss and maintains the stability of thermal reservoirs.
Hydrogeological processes of large karst spring in southeastern Yunnan affected by the combined influence of natural and engineering disturbances
Large karst springs are important surface water resources and play a particularly significant role in the vast karst mountainous regions. In China, research on large karst springs has a long history with remarkable achievements, but it is predominantly concentrated in northern regions. However, studies on large karst springs in southern regions still remain insufficient and require deeper and broader investigation. In recent years, due to the frequent occurrence of extreme weather events and the intensified human engineering activities in southern karst areas, large karst springs have been faced with ecological and environmental challenges. Therefore, it is urgent to conduct scientific and targeted analyses of the hydrological processes of karst springs in south China under multifactorial disturbances. The eastern part of Yunnan is widely recognized as one of the most prominent and typical regions for environmental issues related to large karst springs in south China’s karst area. This study focuses on the Xiaolunan large karst spring in southeastern Yunnan. Persistent drought in the region, combined with tunnel dewatering within the spring area, has disrupted the discharge dynamics of the Xiaolunan karst spring, causing abnormal fluctuations. Based on hydrogeological investigations and regional hydrochemical and isotopic tests, this study identified the genetic characteristics of the spring, its recharge sources, and hydraulic connections with the tunnel project. Using synchronous monitoring data of precipitation, spring discharge, and tunnel borehole water levels, we analyzed their variation trends and correlations. Finally, a hierarchical groundwater flow system for the spring area was constructed to enhance understanding of the hydrological processes in large karst springs. The primary findings of this study are as follows: (1) The recharge area of the Xiaolunan large karst spring is located within the Honghe River Basin. During groundwater runoff, the water transitions from phreatic to confined conditions and eventually rises and discharges as a spring due to fault obstruction. After surfacing, the spring water flows downhill into the Pearl River Basin’s water system. Therefore, the Xiaolunan large karst spring is a fault-controlled uplifted spring with cross-basin recharge. The hydrogen and oxygen isotopes of the spring closely align with the atmospheric precipitation line, indicating that its recharge originates from atmospheric precipitation. Hydrochemical ion signatures show that tunnel construction drainage has impacted the hydrological processes of the large karst spring. (2) Precipitation in the spring area exhibits marked seasonality under the influence of the plateau monsoon climate. The borehole water level generally shows a downward trend, primarily caused by continuous dewatering from tunnel construction. Over a two-year period, under the combined influence of precipitation changes and tunnel disturbances, the discharge of the large karst spring remained stable. The time-series curves were categorized into two types: asymmetric sharp peaks characterized by steep rises and falls, and relatively gentle, wave-like undulations. The exhibited a weak correlation with precipitation, with a lag time of 1 to 2 months during certain periods. (3) Multiple crustal uplifts since the Neotectonic Movement have caused spatial shifts in the erosional datum within the spring area, which have sequentially evolved into the present-day local and regional flow systems. The impacts of tunnel construction have created an intermediate flow system within a specific part of the spring area. The combined synergistic effects of the intrinsic properties of the regional flow system and the local flow system maintain the dynamic balance of large karst spring discharge across different hydrological periods, while also reducing the spring’s sensitivity to precipitation events. The intermediate flow system induces groundwater capture and pressure relief in the karst aquifer, directly leading to a reduction in discharge from the large karst spring. Continuous drainage of static groundwater reserves from the aquifer by the tunnel will cause the drawdown cone to expand progressively, increasingly threatening spring discharge. To protect the water resources of the large karst spring, it is recommended that the tunnel construction strictly implement water sealing and discharge limitations. Grouting and sealing of excavated sections should be promptly carried out, with particular focus on outer lining gaps and sections containing concentrated runoff channels, to minimize groundwater extraction. During the tunnel’s operational period, borehole water levels and spring discharge should be continuously monitored, and their recovery dynamics should be consistently tracked.
Numerical study on hydraulic failure characteristics of deep-buried solution-fissured limestone as an inrush prevention layer
In tunnel engineering in karst areas, the tunnel mud and water inrush is one of the most common geological disasters. These events significantly impact tunnel construction, safe operation, and the safety of personnel and equipment, particularly in tunnels with large burial depths located in water-rich karst areas. Numerous factors affect tunnel mud and water inrush, including tunnel burial depth, groundwater pressure, surrounding rock stress, and the characteristics of the water inrush prevention layer-such as its thickness, karstification rate, fissure density, and mechanical strength. The water inrush prevention layer refers to the rock mass situated between the tunnel and groundwater, serving as the critical barrier that prevents groundwater from rushing toward the tunnel free face. The strength of the rock mass in this inrush prevention layer determines its capacity to resist groundwater pressure. Key factors affecting its overall strength include the thickness, karstification rate, fissure density, and mechanical strength of the prevention layer. The development of solution-fissures within this rock mass reduces its effective thickness and structural integrity, thereby diminishing its ability to withstand groundwater inrush toward the tunnel free face. To investigate the impact of the development of solution fissures in the limestone inrush prevention layer on its failure characteristics under hydraulic action in deep tunnels, limestone samples were collected, and tests were conducted to determine the physical and mechanical parameters of rock. The true density, tensile strength, elastic modulus, Poisson’s ratio, cohesion, and internal friction angle of the limestone material were obtained. Four different models for water inrush prevention were designed with the use of finite difference numerical simulation software. These models are square-rectangular in shape, with cylindrical holes cut opposite each other in the middle of the upper and lower surfaces, but not completely through. The remaining middle layer forms a disc-shaped batholite that serves as the water inrush prevention layer. Shallow circular holes and strip-shaped grooves are cut on the upper surface of this disc-shaped water inrush prevention layer, representing the solution fissures developed within the water inrush prevention layer. The circular holes and strip-shaped grooves differ among the four models, representing varying karstification rates. Based on this, the models were assigned the measured physical and mechanical parameters. Numerical simulations of the model for inrush prevention batholitel were conducted under fixed geostress at a depth of 1,000 m, with gradually increasing water pressure at an interval of 50 m after constraining the bottom and surrounding areas of the model. The maximum shear stress and maximum shear strain increment of the model’s force response are used as the criteria to analyze the characteristics of each stage of the model’s force deformation and failure, as well as the stress-strain distribution contour maps. The similarities and differences among the four models were compared. The research findings show that: (1)The deep-buried solution-fissured limestone used as inrush prevention batholitel undergoes four stages of deformation and failure under high geostress and gradually increasing water pressure: elastic deformation, plastic deformation, residual strength, and failure. (2) The higher the karstification rate of the deep-buried limestone used as an inrush prevention batholite, the lower the critical water pressure required to cause hydraulic failure of this batholite. A relationship curve between the critical water pressure for failure of the inrush prevention batholite and the karstification rate has been established. (3) Under the effect of water pressure, the inrush prevention batholite without solution fissures is more susceptible to tensile failure near the upper surface, mixed tensile-shear failure around the lower surface, and tensile failure in the central area of the lower surface. (4) The development of solution fissures affects the distribution of stress and strain within the inrush-prevention batholite. Under the effect of water pressure, the inrush-prevention batholite with solution fissures is more prone to mixed tensile and shear failure at the edges and tips of the solution fissure zones, compressive shear failure at the periphery of the lower surface of the batholite, and tensile failure in the central area of the lower surface. (5) Tensile and shear deformations at multiple adjacent solution fissure tips tend to interconnect, forming a continuous tensile and shear fracture zone. Under water pressure, the inrush prevention batholite may experience tensile failure, tensile-shear failure, compressive-shear failure, or a combination of these failure modes, depending on the development of the solution fissures. The research findings offer valuable insights into the deformation and failure characteristics of hydraulic fracturing in deeply buried rock formations, aiding in the prevention of water inrush.
Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
2025, 44(6): 1144-1157.
doi: 10.11932/karst20250602
2025, 44(6): 1158-1172.
doi: 10.11932/karst2025y021
2025, 44(6): 1173-1185, 1197.
doi: 10.11932/karst2025y009
Founded in 1982 bimonthly
ISSN: 1001-4810
CN 45-1157/P
Editor-in-chief: Jiang Zhongcheng
Sponsor: Chinese Academy of Geological Sciences
Sponsored by: Institute of Karst Geology, Chinese Academy of Geological Sciences
Cosponsor: International Research Center on Karst under the Auspices of UNESCOKarst Geology Committee of Geological Society of ChinaSpeleology Committee of Geological Society of China
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