中国岩溶

Hydrogeochemical characteristics and circulation model of deep geothermal resources in Tianjin

ZHANG Qiuxia, LIU Donglin, YUE Dongdong, YANG Li, FENG Zhaolong, LI Shengtao

2025, 44(3): 445-461. doi: 10.11932/karst20250301

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Geothermal resources, as a pivotal renewable and environmentally benign energy source for advancing green development and establishing a clean energy system, hold immense potential for exploitation in Tianjin. Tianjin is situated in the northern region of the North China Plain, and its geothermal resources are predominantly distributed in the southern plain area, south of the Ninghe–Baodi Fault. These resources encompass porous thermal reservoirs within the Neogene Minghuazhen Formation and the Guantao Formation, as well as bedrock fracture-type thermal reservoirs in the Ordovician, Cambrian, and Mesoproterozoic Wumishan Formation (Jixian System). By integrating hydrochemical and isotope geochemical signatures, this study aims to quantitatively evaluate the mixing proportions of deep geothermal fluids and to systematically elucidate the circulation patterns of deep geothermal reservoirs, thereby providing a theoretical basis for the sustainable development of Tianjin’s geothermal resources.Sampling and analytical testing of geothermal fluids indicated a pH range of 7.08 to 8.43, suggesting a weakly alkaline nature. The TDS ranged from 762.1 to 6,040.4 mg·L⁻¹, averaging at 1,768.97 mg·L⁻¹. Along the flow path, the anionic composition of the geothermal fluids exhibited significant shifts, transitioning from ${\rm{HCO}}_3^{-}$ dominance to Cl⁻ and ${\rm{SO}}_4^{2-}$dominance. This transition was accompanied by an increase in TDS. Both porous geothermal reservoirs and bedrock fracture-type geothermal reservoirs displayed distinct spatial zonation in their hydrochemical characteristics. An in-depth analysis using Gibbs plots and ion ratio coefficients demonstrated that water-rock interactions are the key factors influencing the chemical composition of geothermal fluids. Specifically, Cl⁻ and Na⁺ primarily originate from the dissolution of salt rocks. In contrast, Ca²⁺ and Mg²⁺ ions are mainly affected by the dissolution of carbonate minerals. Furthermore, cation exchange processes resulted in an increase in Na⁺ concentrations and a corresponding decrease in Ca²⁺ and Mg²⁺concentrations. Gypsum dissolution also served as a significant source of ${\rm{SO}}_4^{2-}$ in geothermal fluids. The dissolution of gysum induced a common ion effect that promoted the precipitation of CaCO₃, further reducing the concentrations of Ca²⁺ and ${\rm{HCO}}_3^{-}$. Isotopic analysis of hydrogen and oxygen revealed that atmospheric precipitation is the primary source of recharge for geothermal fluids. However, the isotopic drift observed in most geothermal fluids indicated that they did not originate directly from local precipitation. Instead, these fluids underwent deep circulation, with lateral recharge serving as the main mode of replenishment. During circulation, these fluids exchanged oxygen isotopes with the surrounding rocks.Plotting the geothermal fluids on the Na-K-Mg ternary diagram showed that all samples fell within the partially equilibrated and immature fields, indicating that either (i) the fluid–rock system has not reached cationic equilibrium, or (ii) the ascending deep fluids have been diluted by shallow cold water. Consequently, cationic geothermometers are not recommended for estimating reservoir temperatures. Calculations by PHREEQC software showed quartz and chalcedony to be in supersaturation or near saturation, suggesting that SiO₂ geothermometry can reliably estimate temperatures. Reservoir temperatures derived from the quartz geothermometer were generally higher than those from the chalcedony geothermometer and exceeded the measured wellhead temperatures. Therefore, we adopted the quartz geothermometer results as representative of the reservoir temperature. The estimated thermal storage temperature range in the study area was between 67.06 °C and 121.38°C.Using the silicon-enthalpy hybrid model, we analyzed deep circulation temperatures and cold water mixing in geothermal fluids. The cold water mixing ratios ranged from 0.01 to 0.77, resulting in estimated deep circulation temperatures of the geothermal fluids between 94.54 °C and 160.90°C. To ascertain the maximum circulation depth of the geothermal fluids, we integrated the reservoir temperatures derived from both the quartz geothermometer and the hybrid model, along with the average geothermal gradient. The quartz geothermometer results indicated that the thermal circulation depth of the middle reservoir ranged approximately from 1,828.27 m to 3,150.24 m. Conversely, the hybrid model calculations revealed a deeper maximum thermal circulation depth for the deep reservoir, ranging from 2,383.28 m to 4,279.28 m.Based on the aforementioned study, we have developed an initial conceptual model for geothermal fluid circulation. This model divides the area along the Ninghe–Baodi Fault, designating the recharge zone mainly in the bedrock-exposed region of Jixian county to the north. Atmospheric precipitation infiltrates through this and adjacent deep faults, entering enclosed and semi-enclosed thermal reservoirs in the southern plain. As the precipitation flows, it is progressively heated by underlying heat sources. Over extended geological periods, the dissolution of calcite and dolomite reaches equilibrium in the groundwater, maintaining a stable HCO₃⁻ concentration. Meanwhile, Ca²⁺ and Mg²⁺ undergo processes such as cation exchange and adsorption, leading to their gradual reduction. In contrast, highly soluble rock salt results in significant accumulation of Na⁺ and Cl⁻ during prolonged migration. Consequently, the geothermal fluids exhibit high concentrations of Na⁺, Cl⁻, and TDS. Furthermore, the mixing of cold water with the geothermal fluids along their flow path has contributed to the current characteristics of geothermal resources in the study area. This study is of great significance for understanding the genetic mechanisms, occurrence modes, and geochemical evolution patterns of underground thermal water.

Analysis of hydrochemistry and pollution characteristics in manganese-related industrial watersheds

GONG Xiaoyu, ZHANG Zhongqian, LI Wei, XIE Weisong, ZHU Ling, XU Lei, YE Liangkai, ZHANG Shaojian, WANG Chengcheng, ZHU Bin, AN Siwei, HUANG Daikuan

2025, 44(3): 462-476. doi: 10.11932/karst20250302

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The counties of Xiushan in Chongqing, Songtao in Guizhou, and Huayuan in Hunan are home to the enterprises producing Electrolytic Manganese Metal (EMM) in China and form China’s "Manganese Triangle". Although the development of the manganese industry has driven economic growth, it has also caused significant ecological and environmental damage. Statistically, the production of 1 ton of EMM generates 6 tons to 10 tons of electrolytic manganese slag. The leachate from fresh slag is acidic (pH≈5) and contains high concentrations of ammonia nitrogen (565 mg·L⁻¹ to 792 mg·L⁻¹), manganese (936 mg·L⁻¹ to1,460 mg·L⁻¹), and sulfate (9,250 mg·L⁻¹ to 11,400 mg·L⁻¹). Additionally, the leachate contains high levels of ions such as nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg). Rainfall and surface water can dissolve these soluble components, facilitating their migration into the environment. However, due to inadequate anti-seepage measures and complex geological conditions, the leachate has not been fully collected and treated, leading to contamination of surrounding soils and surface water bodies. Hence, to better understand the impact of the manganese industry on the environment, this study investigated the hydrochemical characteristics and pollution patterns in the Songtao River Basin. Water samples from potential pollution sources and receptors were collected during both the rainy season (May) and the dry season (September), respectively. Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF) were used to identify the controlling factors affecting the hydrochemical characteristics of surface water in the study area.The findings are as follows:(1) Electrical Conductivity (EC) and Total Dissolved Solids (TDS) exhibited the following decreasing trend: leachate from manganese slag yard > landfill leachate > polluted groundwater from two wells > surface karst spring > surface water. Mn concentrations generally followed the order: leachate from manganese slag yard > polluted groundwater from two wells > landfill leachate > surface water > surface karst spring. The nitrogen in surface water and surface karst springs primarily existed in the form of NO$_3^{-}$-N, while in other instances, nitrogen mainly appeared as NH$_4^{+}$ -N. In surface water, NH$_4^{+}$ and Mn concentrations exceeded 13% and 9.6% of the permitted levels, respectively. (2) the pH of the landfill leachate had a pH above eight, and the chemical composition included SO₄ ·Cl-Na·K. In contrast, the leachate from the manganese slag yard exhibited a pH value ranging from weakly acidic to neutral (pH 4.64 to 7.17), with a chemical composition of SO₄-Mg. The surface water and surface karst spring water were dominated by HCO₃-Ca·Mg type water. Interestingly, the polluted groundwater from two wells, although classified as groundwater, exhibited a SO₄ -Mg·Ca type due to the influence of the leachate from manganese slag. (3) in the rainy season, surface water demonstrated substantial dilution effects, whereas specific indicators within waste leachate exhibited a significant percolation. Meanwhile, chemical indicators in other water bodies exhibited minimal variation between the rainy and dry seasons.(4) both PCA and PMF extracted four main influencing factors, identifying geochemical processes, the manganese industry, and domestic pollution as the primary contributors to the hydrochemical characteristics. Factor 1 (F1) in PCA and Factor 4 (F4) in PMF exhibited consistent patterns, primarily associated with HCO$_3^{-}$, Ca²⁺, Mg²⁺, and TDS. These factors represent the combined effects of geochemical processes, with an average contribution rate of 52.99%. F4 in PCA aligned closely with Factor 3 (F3) in PMF, where Mn as the dominant loading variable, indicated pollution from the manganese industry, contributing an average of 5.06%. F3 in PCA and F1 in PMF, characterized by K⁺, Cl⁻, and Na⁺, represented domestic pollution, with an average contribution rate of 16.44%. However, due to the overlapping signatures of pollutants from both manganese industrial emissions and domestic sources, neither method can accurately quantify the individual contribution rates of these two pollution sources to the contamination of the water environment in the study area. By comparing the chemical compositions of surface karst springs, and according to the synchronous trends of manganese and ammonia nitrogen concentrations along the Songtao River, it can be inferred that surface water continues to be affected by both manganese slag storage and domestic pollution.This highlights the need to sustain and strengthen remediation efforts targeting manganese-related industrial activities, slag yards, and domestic pollution in the Songtao River Basin. Additionally, localized monitoring of manganese and ammonia nitrogen should be enhanced to identify pollution pathways and prevent untreated leachate from slag yards and other pollution sources from being directly discharged into surface water. Furthermore, stricter supervision and regulation of domestic pollution discharges are essential to ensure that domestic sewage and pollutants are not released untreated into surface water.

Genesis analysis of karst groundwater inrush and prediction of its water inflow in the Huxitai Tunnel

SHAO Changjie, WANG Lei, LIU Huidong, CUI Yongxing, LIU Wei

2025, 44(3): 477-487, 518. doi: 10.11932/karst20250303

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Tunnel water inrush is one of the primary threats to tunnel construction safety, not only posing risks during the construction but also creating long-term hidden dangers for the post-construction operation and maintenance. This issue is particularly severe in karst tunnels, where dense karst fractures and conduit networks will lead to rapid water inrush responses to precipitation. Extreme rainfall events can trigger the instantaneous and massive water influxes, making tunnel water inrush in karst regions especially serious. Therefore, it is critical to elucidate the formation mechanisms of tunnel water inrush and to predict water influxes during extreme rainfall conditions in order to address water inrush challenges and ensure safety of tunnel construction in karst regions.The Huxitai Tunnel is examined here as a case study. This tunnel is a critical component of Linjian Expressway, located in the subtropical humid zone of Eastern China, characterized by abundant preciptation and complex geological conditions.The tunnel tranverses through the Carboniferous Huanglong Formation (C₂h) and the Chuanshan Formation (C₂c) limestones, which features well-developed karst conduits, abundant water, and high permeability. These features result in significant water inrush problems, increased construction challenges, and heightened safety risks. Since the beginning of tunnel construction, water inrush events in varying degrees have occurred in the limestone sections of the tunnel.To investigate the causes of water inrush in the Huxitai Tunnel under karst geological conditions and to estimate its influxes, this study conducted detailed field investigations and in-situ tests to analyze the hydrogeological conditions of the water inrush sections and to determine the groundwater flow systems. Based on the hydrogeochemical characteristics and hydrogen-oxygen isotopes of groundwater, the study analyzed the pathways of karst groundwater flow and the mechanisms of water inrush. It also estimated the contributions of different water sources to the tunnel water inrush by employing the isotopic end-member mixing model. Using precipitation infiltration methods and groundwater dynamics principles, the study calculated groundwater recharge rates and the proportion of tunnel water inrush relative to total recharge, while predicting the maximum water influx in the tunnel during extreme rainfall events. The findings include as follows.(1) According to the pathways of groundwater flow, the tunnel region is divided into three groundwater flow systems: the Caoyuanxi groundwater flow system, the Fenshuijiang karst groundwater flow system, and the Dakengxi–Chaipingli groundwater flow system. The karst water inrush section (K65+100-K65+360) lies within the Fenshuijiang karst groundwater flow system, which consists of the Huanglong Formation and the Chuanshan Formation limestone characterized by intensive karst development, abundant water influx, and high risks.(2) Karst groundwater in the tunnel area is primarily recharged by precipitation, which infiltrates through sinkholes and karst conduits. The hydrochemical characteristics of tunnel water inrush are similar to those of underground river discharge, dominated by carbonate rock dissolution, reflecting a mixture of karst water and sandstone water. Karst water vertically infiltrating from the Huanglong Formation and the Chuanshan Formation limestone accounts for 70% to 79% of tunnel water inrush, with 21% to 30% contributed by lateral sandstone water.(3) During the runoff process, the recharge of groundwater from atmospheric precipitation amounts to 19,324.89 m³·d⁻¹, of which 48.29% is discharged through the tunnel.Under non-extreme rainfall conditions, the predicted water influx into the Huxitai Tunnel is 10,684.89 m³·d⁻¹; however, during extreme rainfall events, the maximum predicted water influx can reach up to 79,364.13 m³·d⁻¹.To sum up, these results provide a quantitative decision-making basis for the prevention and control of water inrush in the Huxitai Tunnel, and also serve as valuable references for similar studies on water inrush of karst tunnel.

Influence of mosses on the weathering features of sandstone and carbonate rocks in the subalpine region of western Sichuan

LIU Han, PU Wanqiu, WANG Panpan, HUANG Chengmin

2025, 44(3): 488-499. doi: 10.11932/karst20250306

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Sichuan Province is located in the Southwest China, with its western mountainous area serving as a transitional zone between the Qinghai-Xizang Plateau and the Sichuan Basin. The climate is complex, characterized by abundant rainfall, and the terrain is mainly mountainous, featuring significant variations in elevation. The geological conditions are complex, tectonic activities are frequent, and geological disasters occur regularly. In addition, with the increasing intensity of human activities, exposed slopes and rock masses are widely distributed. The weathering and detachment of rock fragments can easily trigger secondary disasters, posing potential threats. The widespread presence of rocky slopes makes these areas prone to such events, underscoring the urgent need for ecological restoration. Mosses play a critical role in ecological succession and soil formation on rock surfaces, acting as pioneer species that promote the development of thin soil layers. Exploring the impact of moss growth on rock weathering processes is beneficial for finding ways to promote ecological restoration. This study aims to investigate the weathering processes and mechanisms in this region by analyzing weathered rock bodies and bedrock properties under varying weathering conditions to elucidate their microscopic characteristics. Additionally, the influence of moss growth on rock weathering was further investigated. We collected samples from carbonate rocks and sandstones at various sites within several counties in western Sichuan Province. Our study focused on sites with varying degrees of moss coverage and differing weathering durations. The analyses included examining the microstructural features of weathered rock surfaces, assessing mineral composition, and analyzing elemental variations to understand how mosses interact with these geological materials. These investigations were conducted by using electron microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) for mineral composition, energy-dispersive spectroscopy (EDS), and other analytical techniques.The results indicate that as weathering progressed, the breakdown of mineral crystal structures, the development of fractures in the rock mass, and the formation of secondary minerals occurred in both sandstone and limestone. These processes were accompanied by the infiltration of iron oxides and organic matter, and they intensified over time. Notably, sandstone exhibited a more pronounced weathering response during the early stages compared to limestone. During the weathering of carbonate rocks, a large amount of secondary minerals was produced, and the mineral composition evolved from simple to complex. In contrast, the main component of sandstone weathering has consistently been quartz; as weathering progressed, secondary minerals disappeared, and the mineral composition shifted from complex to single. The elemental content in limestone did not change significantly during the early stages of weathering, while the elemental content in sandstone changed markedly. In total, results show that the weathering of carbonate rocks is predominantly chemical, whereas physical weathering is more pronounced in sandstone.Furthermore, the impact of mosses on rock weathering is complex. For carbonate rocks, initial weathering stages exhibited minimal elemental changes with moss presence; however, with prolonged exposure, significant modifications in structural integrity and chemical composition occurred. The percentage of carbon and other elements, such as calcium and magnesium, changed markedly, due to the bioerosion effects of moss-generated organic acids, with carbon increasing and calcium and magnesium decreasing. Microstructural analysis revealed that moss-covered rocks exhibited deeper and wider fissures compared to their bare counterparts. This increase in fissure size is correlated with the mechanical and biochemical actions of mosses, which exploited small crevices to enhance their growth and further facilitate the weathering process. Over time, mosses create a conducive environment for microbial activity, which adds to the biochemical weathering of the rock substrate. When mosses grew on the surface of sandstone, it exacerbated the already intense physical weathering of sandstone during the early stages and resulted in compositional changes. Overall, moss growth accelerates the weathering process of rocks, but its influence is not significant during the early stages.The findings indicate that mosses significantly contribute to both the physical and chemical weathering processes of rocks, which in turn influence soil formation and ecological stability. These insights have important implications for ecological restoration strategies on exposed rock slopes, particularly in areas susceptible to erosion and geological instability. By harnessing the natural weathering capabilities of mosses, we can develop sustainable methods for restoring degraded landscapes and mitigating ecological risks associated with exposed rock surfaces. For the ecological restoration of limestone slopes, the use of mosses is more effective than its application on sandstone, as it provides protective benefits over time. Therefore, it is essential to consider the differences in rock types when we select suitable plants for ecological rehabilitation. Future studies should explore the long-term effects of moss-induced weathering on soil development and ecosystem restoration, particularly in sensitive mountainous regions.

Analysis of the influence of tunnel engineering on groundwater resources in karst mountain areas: A case study of a tunnel in Wushan county of Chongqing City

WEN Jinmei, WU Tao, LI Xian, JIANG Chen, CHEN Li, LIU Sheng, MENG Li

2025, 44(3): 500-509. doi: 10.11932/karst20250304

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Tunnel construction can disrupt the groundwater balance, impacting the drainage of both surface water and groundwater, as well as causing other eco-environmental effects. This study takes a water-diversion tunnel as the research object. Prompted by a pronounced decline in the storage of the adjacent reservoir of the tunnel, it integrates hydrogeological surveying and tracer tests to characterize the altered recharge–flow–discharge conditions, elucidate the hydraulic interactions between the tunnel and the surrounding groundwater system, and quantitatively evaluate the tunnel’s impact on the observed reservoir-storage variations.Field investigations indicate that groundwater in the study area can be divided into three categories: karst water from carbonate rock fissures, karst water from fissures characterized by carbonate rock interbedded with clastic rock, and karst water from pores and fissures characterized by mudstone interbedded with silty mudstone. The water bearing formations of karst water from carbonate rock fissures consist of the Lower Triassic Jialingjiang Formation (T₁j) and the Daye Formation (T₁d³⁺⁴) along the axis and wings of an anticline. These units exhibit significant water abundance and are well developed with karst landforms, such as karst depressions, sinkholes, caves, and underground rivers. Karst water from fissures characterized by carbonate rock interbedded with clastic rock occurs within the first and third members of the Middle Triassic Badong Formation (T₂b¹⁺³) along the axis and wings of a syncline. The water abundance of the formation is moderate, and karst features are only locally developed. Karst water from pores and fissures characterized by mudstone interbedded with silty mudstone is primarily stored in the second member of the Middle Triassic Badong Formation (T₂b²) and exhibits comparatively low water abundance. Groundwater recharge is derived primarily from atmospheric precipitation and surface water bodies such as reservoirs and fish ponds. Due to the large terrain cutting, the speed of surface water runoff is fast.The catchment of the reservoir is located west of the axis of the water-diversion tunnel on the southeast wing of the anticline. Exposed strata comprise limestone, dolomitic limestone, dolomite, and rock-solution breccia of T₁j and T₁d³⁺⁴, as well as limestone, argillaceous limestone, argillaceous dolomite, and mudstone of T₂b. Within the Jialingjiang and Daye Formations, sinkholes, depressions, and dissolution fissures are well developed, facilitating efficient infiltration of rainwater through karst conduits to the saturated zone. Although karst development is weak in the Badong Formation, secondary structures have intensely fractured the rock mass; rainwater recharge, therefore, occurs dominantly through fissures. Overall, the catchment exhibits favorable groundwater recharge conditions. After infiltration, groundwater migrates southwestward along either longitudinal karst conduits or fissure networks. The deeply cut watercourse in which the reservoir is located, along with the dense network of tributary gullies, ultimately leads to the discharges of groundwater in the form of karst springs within these gullies.The water-diversion tunnel crosses the anticline, traversing limestone and dolomite of T₁d and T₁j, with T₁j serving as the principal aquifer. The anticlinal axis functions as a watershed, resulting in the southern and northern segments of the tunnel each forming an independent groundwater system. The tunnel site is deeply cut, resulting in poor recharge conditions. Scattered precipitation accumulates only within the upper narrow peak-cluster depressions, subsequently infiltrating vertically along sinkholes. Southwest of the tunnel, the reservoir catchment consists of T₁j, T₁d, and T₂b formations, which are characterized by well-developed sinkholes, karst depressions, and corrosion fissures that create favorable discharge conditions. Following rainfall events, groundwater is directed southwestward along longitudinally oriented karst conduits. These conduits are cut by gullies, where groundwater ultimately discharges as karst springs. Before the construction of the water-diversion tunnel, atmospheric precipitation infiltrated through surface karst depressions, sinkholes, dolines, or corrosion fissures to recharge groundwater. Afterward, a portion of the precipitation flowed through the aquifer and discharged in the form of an underground river along the riverbank. Another portion of flowed through the runoff that crossed fissures perpendicular to the structural trend, and discharged in the form of karst springs (including the S01 spring point) or underground rivers within the gully and watercourse that cut the south-eastern wing of the anticline. The spring points exposed in the gully and watercourse were the main source of water supply for the reservoir. Because the water-diversion tunnel intersected the transition zone between the vertical and horizontal circulation cells of the karst aquifer, its excavation repeatedly intersected underground rivers and cave systems. Severe water inflows were encountered, resulting in twelve springs within a 3-km radius becoming either completely or partially dewatered. Springs located to the southwest of the tunnel were less affected than those to the northwest.Analytical calculations indicate that the influence radius of the water-diversion tunnel on surface water and groundwater extends from 649 to 2,073 m, covering 13.7 km². The overlapping area of the reservoir catchment is 4.02 km². Tracer tests confirm a strong hydraulic connection between the surface sinkholes located above the tunnel, and the drainage outlet of the water-diversion tunnel and several spring points. Consequently, a portion of the reservoir’s recharge has been diverted to runoff at the tunnel exit and subsequently discharged, thereby reducing the storage capacity of the reservoir. The findings demonstrate that the alteration of regional groundwater recharge–flow–discharge conditions induced by the tunnel project is the primary cause of the observed decline in groundwater-derived inflow to the nearby reservoir.

Hydrogeochemical characteristics of classical karst regions in Slovenia

MIAO Ying, ZHANG Cheng, Mitja Prelovsek, XIAO Qiong

2025, 44(3): 510-518. doi: 10.11932/karst20250305

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Groundwater plays an important role in supplying drinking water, as well as supporting industrial and agricultural activities worldwide, especially in karst regions. Due to the unique spatial distribution of soil and water resources in these areas—where soil lies above and water below—groundwater is particularly vulnerable to water quality degradation and flood-related environmental issues. Slovenia is an important country along the Belt and Road route and is also recognized as the birthplace of karst research. Karst groundwater serves as a vital resource for both the livelihoods and agricultural production in the karst regions of Slovenia. Covering more than half of the country’s territory, these karst regions are characterized by vast land and sparse population, making karst groundwater one of the most critical natural resources for its national economic development. The main environmental problems in Slovenia include water security, imbalanced spatial and temporal distribution of water resources, and flooding. Hence, it is of great significance to investigate the situation of karst groundwater in Slovenia.Under the exemplary role of the Belt and Road Initiative, this study is supported by the China-Slovenia Belt and Road Joint Laboratory Project on Karst Geology (currently in preparation) within BRI framework. It involves field investigations and sampling conducted in collaboration with the Karst Institute of Slovenia. The objectives are to elucidate the processes and patterns of the Dinaric karstification and its cycles of carbon, water and calcium, analyze the formation and distribution background of this karst system, and compare it with the subtropical karst system in China. The findings are expected to be applicable to other karst regions along the Belt and Road route, enhancing China’s understanding to key resource and environmental challenges in these areas. This study will provide background information on geology, geomorphology, resources, and environment to national authorities for formulating subsequent development strategies, thereby contributing to national diplomacy concerning the environment and resources. In this study, karst geological investigations and sampling were carried out in the Postojna karst basin in Slovenia, obtaining hydrochemical and isotopic data of karst groundwater in this country. Preliminarily analysis and research are currently underway. The results show as follows. (1) The quality of karst groundwater in Slovenia is excellent, with groundwater remaining in its natural state. Parameters such as water temperature, pH, conductivity, and concentrations of anion and cation remain stable within fixed ranges throughout the year. Fluctuations, when they occur, are mostly affected by natural environment variations rather than human activities. (2) Comparative analysis with hydrochemical data from the Lijiang Basin in the karst areas of southwest China reveals that the hydrochemical types in karst areas are predominately controlled by water-rock interactions, with negligible influence from other factors.(3) Analysis of hydrogen and oxygen isotopic characteristics of groundwater shows that atmospheric precipitation serves as the primary recharge source for karst groundwater in the study area. Influenced by weathering and leaching processes in carbonate aquifers and other types of rock, groundwater exhibits typical HCO₃⁻-Ca²⁺ type. (4) The concentrations of common pollutants, such as nitrate, are far below the safety limit for drinking water quality set by the World Health Organization. The primary sources of these contaminants are soil nitrogen derived from natural processes. During the dry season, groundwater at some sampling sites exhibits contamination from domestic sewage and livestock manure.

Study on laboratory acid erosion characteristics of carbonate rocks in different formations under hydrodynamic action

ZHANG Jiaxin, CHU Xuewei, FU Hai, ZHANG Qilin, ZONG Shaokang

2025, 44(3): 519-531. doi: 10.11932/karst20250307

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In Southwest China, carbonate rocks are extensively distributed, and their unique dissolution features pose significant challenges to engineering construction in this region. This study focused on Guizhou Province, located in the core area of the karst regions in Southwest China. A phosphogypsum stacking site with potential leakage risks and intense karst development in the surrounding area was selected as the study area. The pH values of the phosphogypsum leachate, measured in the field at the landfill, ranged from 1.12 and 2.64. The dissolution characteristics of carbonate rocks are expected to change in such an acidic environment. While existing studies have mainly investigated the dissolution effects on carbonate rocks by altering the single factor, the combined influence of lithology, fluid state, and acid concentration on carbonate rocks dissolution remains underexplored. In order to study the dissolution mechanism of carbonate rocks after the original environmental change, five strata samples in the area of Fuquan City, Guizhou Province were collected in this experiment. These samples included limestone of the Lower Triassic Maocaopu Formation (T₁m), dolomite of the Anshun Formation (T₁a), limestone of the Middle Triassic Qingyan Formation (T₂q²), limestone of the Falang Formation (T₂f²), and dolomite of the Late Aurora Dengying Formation (Z₂dy). Indoor dynamic simulation experiments on dissolution were carried out under different acid concentrations and hydrodynamic conditions.The research results show: (1) Compared with the rock samples of the Maocaopu Formation, which have a relatively uniform mineral composition with a calcite content of 96.72%, the Falang Formation contains 47.22% calcite and 51.93% dolomite. Differences in the connectivity of the contact surfaces between these minerals result in the easy detachment of the surface material from the rocks. (2) At a pH value of 1, the difference in the amount of dissolution per unit area between limestone and dolomite is significant. The amount of dissolution per unit area of the dolomite from the Qingyan Formation, the Maocaopu Formation, and the Falang Formation increases by 12% to 32%, compared with that of dolomite from the Anshun Formation and the Dengying Formation. When the pH value is raised to 2, increasing the rotational speed of the disk does not result in a significant increase in the amount of dissolution per unit area for either limestone or dolomite. (3) Under hydrodynamic conditions of 200 rpm, the CaO/MgO ratio of the dolomite from the Falang Formation is 17.83, with an acid-rock reaction rate constant of 0.964×10⁻⁶. In contrast, the limestone from the Maocaopu Formation has a CaO/MgO ratio of 65.59 and an acid-rock reaction rate constant of 1.023×10⁻⁶. Under hydrodynamic conditions of 400 rpm, the difference between the acid-rock reaction rate constants of the Falang Formation and the Maocaopu Formation is 5.38×10⁻⁶. The difference in CaO/MgO ratios between the two formations is significant; however, the difference in acid-rock reaction rate constants of the Falang Formation and the Maocaopu Formation is not substantial under high hydrodynamic force. In conclusion, in acidic solutions, the chemical reaction rates (R) of the five rock groups follow the order: the Qingyan Formation>the Maocaopu Formation>the Falang Formation>the Anshun Formation>the Dengying Formation. During the dissolution of carbonate rocks, three factors interact: hydrodynamics, acid concentration, and lithology. Higher acid concentrations amplify the differences in dissolution caused by variations in hydrodynamic conditions. Conversely, increased hydrodynamic activities accentuate the influence of differences in tuff rock properties on dissolution. Under the erosive action of acidic water, the uneven erosion arises from differences in the properties of both the acid and the rock—such as compound content, mineral composition, and crystal morphology—resulting in the formation of irregular erosion channels.

Morphological characteristics and geological significance of karst landforms developed in red-bed strata of the western Sichuan foreland basin

YU Lei, FAN Shijie, LIANG Hong, YU Tianqi, WANG Bo, MAI Gaofei

2025, 44(3): 532-543, 571. doi: 10.11932/karst2025y006

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As a uniquely developed karst type in terrestrial clastic rocks, red-bed karst is widely distributed across the mountainous terrain of the western Sichuan foreland basin. Its development rules and evolution model differ significantly from those of traditional carbonate karst systems. Although academic research on traditional carbonate karst has reached a relatively advanced stage, systematic investigations into the spatial distribution characteristics, genetic mechanisms, and evolution models of red-bed karst still require in-depth exploration. In recent years, transportation tunnels and water resource allocation projects in western Sichuan have frequently encountered geological hazards such as water inrush and collapses caused by red-bed karst. These engineering-induced changes in water environment have become increasingly severe. Therefore, systematically revealing the spatial distribution patterns of red-bed karst and exploring its formation mechanisms are not only critical for deepening the scientific understanding of red-bed karst development, but also of great significance for ensuring the safety and sustainability of major engineering projects in mountainous areas of western Sichuan.This study is supported by the National and Sichuan Provincial Water Network Key Project—the Dadu–Minjiang Water Diversion Project. Based on red-bed karst morphology data collected during the engineering investigation phase in the Lianhua Mountain area (southern segment of the Longmenshan Fault Zone and western margin of the western Sichuan foreland basin), this study applied comprehensive mathematical statistics and digital terrain analysis methods. By quantifying the parameter characteristics of red-bed karst landforms, it clarified their spatial distribution patterns (including planar distribution and vertical zoning) and examined the driving factors behind the spatial differentiation of red-bed karst landforms, as well as the impact of neotectonic movements on the evolutionary stages of red-bed karst geomorphology.The results show: (1) Vertical distribution of red-bed karst landforms exhibits a significant elevation aggregation effect. Karst springs are primarily concentrated in the elevation ranges of 797 m to 852 m, 962 m to1,017 m, and 1,037 m to 1,292 m, while karst depressions are predominantly distributed at 775 m to 875 m, 1,075 m to 1,175 m, and 1,575 m to 1,675 m. Results from K-function and kernel density analyses indicate that the spatial distribution of red-bed karst landforms is significantly scale-dependent, with rock mass solubility and fracture density serving as the main controlling factors. Further analysis shows that red-bed karst depressions tend to aggregate in areas with high concentrations of soluble components in clastic rocks and well-developed groundwater runoff paths. Karst springs in red-bed strata are generally characterized by rapid recharge, short flow paths, low discharge, and a scattered distribution from multiple points. However, in regions with intense tectonic activities, large karst springs with concentrated discharge can still be developed, though their scale is significantly smaller than that of springs in carbonate karst areas under similar tectonic conditions.(2) As a typical karst feature in red beds, depressions show smaller morphological parameters (e.g., major axis, minor axis, perimeter, and area) compared to those developed in carbonate rocks, with a significantly negatively skewed distribution, indicating smaller scales in red-bed strata. The eccentricity (E) predominantly ranges from 0.75 to 1, and the compactness coefficient is mainly concentrated in the interval of 1 to 1.6, suggesting simpler edge morphology of red-bed karst depressions.(3) The spatial distribution pattern of Hypsometric Integral (HI) values further reveals that red-bed karst development is strictly controlled by tectonics and lithology, indicating that the overall geomorphic evolution of the study area has reached the mature stage. In the area where calcareous conglomerate is distributed, the drainage basin landforms exhibit significantly higher HI values than the regional average due to the highest solubility of the rock mass. This results in geomorphic evolution predominantly in the youthful stage, corresponding to active karst development. However, the low degree of actual evolution of karst landforms in these basins highlights a tectonically induced geomorphic rejuvenation process. The core of the Gaojiachang Anticline and the limbs of the Nanbaoshan Syncline, characterized by intensive structural fracture development, actively respond to tectonic uplift and are currently undergoing geomorphic rejuvenation.These results reveal significant differences in spatial distribution patterns and formation-evolution models between red-bed karst and carbonate karst. This study examines the spatial differentiation characteristics of red-bed karst and its primary developmental drivers, thereby enriching the theoretical framework of red-bed karst research. The findings provide a theoretical basis for analyzing potential red-bed karst hazards in transportation and water diversion projects in this region.

Spatial differentiation and trade-off /synergy relationship of soil fertility in typical karst peak-cluster depressions

MA Guobin, QIN Xingming, HU Baoqing, QU Zihan, SUN Qi

2025, 44(3): 544-554. doi: 10.11932/karst2025y005

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A scientific evaluation of soil fertility levels in karst peak-cluster depressions at a grid scale is essential for implementing precise fertilization and conservation strategies at the regional level. To provide targeted support for the effective management and cultivation of soil fertility in these depressions, this study selected typical peak-cluster depressions in Pingguo City, Guangxi, as the research object. A 500 m×500 m grid was employed as the evaluation unit, and soil data were collected through a combination of field sampling and Kriging interpolation. An index system was developed, incorporating pH, organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK) and land use types. The Analytic Hierarchy Process (AHP) was utilized to determine the weights of these indicators, and a multi-factor comprehensive evaluation method was applied to assess the overall soil fertility. Furthermore, semi-variance functions, spatial clustering models (including global and local Moran’s I), and Spearman’s correlation coefficients were employed to systematically analyze the spatial differentiation characteristics of soil fertility and the trade-off/synergy relationships among the indicators.The results indicate that: (1) spatial differentiation is significant: TN, TP and OM contents generally exhibit a decreasing pattern from the northeast to the southwest, with weak spatial correlation (nugget coefficient>75%). This pattern is mainly influenced by anthropogenic stochastic activities, such as fertilizer application and planting methods. In contrast, pH value demonstrates the strongest spatial correlation with a nugget coefficient of 17%, which is predominantly governed by the structural factors of the karst geological background. Additionally, the spatial distribution of TK is largely opposite to that of TN, TP and OM. (2) The overall soil fertility is characterized by a relatively deficient level, with an average value of 2.93. Grid cells classified as moderate (Grade 3), relatively deficient (Grade 4), and deficient (Grade 5) account for 86.88% of the total area. Spatially, soil fertility exhibits a differentiation pattern of being higher in the northeast and lower in the southwest. High-fertility zones are concentrated in low-slope forestlands and agricultural lands in the northeastern region, while low-fertility zones are found in sloping farmlands, construction sites, and steep-slope forestlands in the northwestern area. (3) Significant trade-off/synergistic effects exist among indicators: TP, TN and OM show significant synergy effects in enhancing comprehensive fertility (Spearman’s correlation coefficient>0.389), with contribution rankings as TP>TN>OM. However, TK exhibits a significant trade-off relationship (negative correlation) with the other four indicators (TN, TP, OM and pH), particularly showing the strongest trade-off effect with TN. Spatial agglomeration analysis indicates that OM, TN, TP, and TK exhibit strong spatial autocorrelation (Moran’s I>0.47), with predominant agglomeration type being “low-low” synergy-weakening patterns, while “high-high” synergy-enhancing patterns are mainly distributed in the northeastern agricultural land area. The relationship between land use and spatial synergy/trade-off effects of OM and TN is generally moderate. In conclusion, soil fertility in typical karst peak-cluster depressions is relatively low and exhibits significant spatial heterogeneity, with complex trade-offs and synergies among nutrients. Accordingly, it is proposed that differentiated measures targeting different fertility grades and spatial areas should be implemented, including soil and water conservation, optimization of fertilization structures (with a focus on phosphorus and nitrogen synergy supplementation, as well as potassium balance), and adjustments to land-use planning to achieve effective enhancement and sustainable management of soil fertility.

Dynamic simulation of land use and its response to the ecosystem service value in Puding county from 1973 to 2030

LI Yue, FENG Xia, WU Luhua

2025, 44(3): 555-571. doi: 10.11932/karst2024y036

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Puding county is located in the west-central part of Guizhou Province, covering a total area of 1,091 km². It experiences a humid subtropical monsoon climate, characterized by an average annual precipitation of 1,378.2 mm and an average annual temperature of 15.1 ℃. As of 2021, Puding county had a resident population of 376,300, including an urban population of 144,900, resulting in an urbanization rate of 38.51%. The county’s annual Gross Domestic Product (GDP) was 15.463 billion yuan, with the value added of the primary industry contributing 2.808 billion yuan, reflecting a year-on-year increase of 8.2%. The value added of the secondary industry was 4.785 billion yuan, a year-on-year increase of 10.06%, while the value added of the tertiary industry contributed 7.870 billion yuan, up 11.10%. This region is characterized by the typical development of karst geomorphology, and it frequently faces ecological challenges such as soil erosion and rocky desertification. Therefore, uncovering and predicting the impacts of land use change on Ecosystem Service Value (ESV) in karst mountainous areas under different scenarios is of great significance for maintaining regional ecological security, enhancing the value of ecosystem services, and formulating ecological protection and restoration policies. In order to deeply analyze the land use patterns and their response to ecosystem service value over an extended time series in Puding county, research and discussion were carried out across the three temporal dimensions: past, present, and future. This study aims to provide a scientific foundation and valuable insights for the sustainable development of ecosystems in the study area.Based on five periods of land use data from 1973, 1989, 2003, 2010 and 2020, the equivalent factor method, which incorporates localized adjustments of food prices, was used to assess the ESV for each historical period. Additionally, the PLUS model was applied to simulate land use and ESV changes projected for 2030 under three scenarios, natural evolution, ecological protection, and economic development. The results indicate as follows. (1) The area of cultivated land in Puding county decreased sharply from 1973 to 2020, with a total reduction of 25.08% over the last 50 years. In contrast, the areas of forest land and construction land increased annually, with increases of 6,338.56 hm² and 9,408.00 hm², respectively. (2) The ESV of the study area from 1973 to 2020 was recorded at 3.100 billion yuan, 2.238 billion yuan, 2.598 billion yuan, 3.277 billion yuan, and 3.510 billion yuan, respectively, exhibiting a general fluctuating upward trend. Regarding the ESV of various land types, the ESVs of forest land, grassland, and watershed all showed annual increases from 1989 to 2020, serving as main contributors to the overall increase in ESV. Specifically, in terms of the value of individual ecosystem service functions, hydrological regulation and climate regulation services made the most significant contribution to ESV, with the combined total of these two services accounting for 47.97% of the total ESV. (3) In the natural evolution scenario, the ecological protection scenario, and the economic development scenario projected for 2030, the areas of cultivated land, grassland, and unused land in Puding county are all expected to decline, mainly converted into forested land and construction land. Notably, the area of cultivated land is projected to experience the greatest loss under the ecological protection scenario, amounting to 5,196.42 hm². The spatial distribution across the three simulation scenarios shows that the area of construction land is point-surface in the central part of the study area. (4) The ESVs for the natural evolution scenario, ecological protection scenario, and economic development scenario are projected to be 3.638 billion yuan, 3.778 billion yuan, and 3.597 billion yuan, respectively, all of which exceed the ESVs recorded for the study area in 2020. From a spatial distribution perspective, the ESVs for Puding county as a whole present the characteristics of being higher in the east and west and lower in the center. Furthermore, the ESV of each land use type has passed the sensitivity test, indicating strong credibility in the results.

Mechanisms and pathways of realizing the value of karst ecological products in Hebei Province

ZHANG Yu, FU Yue, XIONG Kangning, YAN Jiawang, ZHANG Zefu, NING Youze, ZHENG Peng

2025, 44(3): 572-586. doi: 10.11932/karst2025y010

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The karst ecological environment is characterized by fragility, sensitivity, vulnerability, heterogeneity, and limited natural regenerative capacity. The ecosystem formed through karst ecological restoration and conservation provides essential ecological products (eco-products) for human beings. Realizing the value of these products is an important initiative for addressing human-land conflicts in fragile environments, sustaining the benefits of ecological restoration, promoting the sustainable development of poverty alleviation efforts, and practicing the principle that "lucid waters and lush mountains are invaluable assets".Hebei Province, which surrounds Beijing and Tianjin, is characterized by high terrain in the northwest and low terrain in the southeast, with a variety of landforms. Two major mountain ranges, the Yanshan Mountains and the Taihang Mountains, cover 48.1% of the total area of the province. China is implementing restoration and protection projects for karst forest ecosystems through the Three-North Shelterbelt Forest Program. These ecosystems are ecologically significant, as they contribute to the conservation of water, soil, and biodiversity. They serve as primary providers of eco-products and form a crucial ecological security barrier for the North China Plain. Recognizing the intrinsic value of eco-products in this region is essential, as it will act as a key driver for transforming green mountains into invaluable assets in the karst ecologically fragile areas—an approach that reflects distinctive Chinese and Hebei characteristics. Therefore, given the unique features of the karst terrain in Hebei, it is imperative to assess the value of eco-products based on localized data. This approach will enhance the realization of their value and optimize transformation rates in response to environmental heterogeneity and other factors. This study holds significant academic and reference values for Hebei and even the broader northern karst regions.In the karst regions of Hebei, the Three-North Shelterbelt Forest Program has implemented large-scale karst ecological restoration and protection efforts, but raising critical questions: Can these ecosystems further optimize their service functions? Can they provide additional high-quality eco-products to meet people’s growing need for a beautiful environment? Can green mountains be effectively transformed into invaluable assets? The chain process of karst eco-products valuation, value transformation, and the value realization mechanisms and pathways becomes the key scientific challenge underlying the technical bottlenecks that must be addressed in this region.The realization of the value of eco-products refers to the process of transforming their ecological value into economic profits through the rational development and utilization of eco-products under the premise of maintaining ecosystem stability and integrity. The mechanisms for realizing the value of eco-products include policy, market and technology approaches to promote the value realization. The total economic value of eco-products transformed through various pathways is termed the amount of value transformed. Addressing the shortcomings of the existing eco-product mechanisms and pathways—such as low premium effects and inefficient value transformation—this study employs 35 regions in Hebei with the karst area exceeding 10% of the total area as a case study. Based on localized data accounting, it calculates the Gross Ecological Product (GEP) and evaluates the value transformation rate of eco-products. By analyzing influencing factors from the perspective of value transformation efficiency, this study proposes mechanisms and pathways to enhance the realization of eco-product value. The results show that the GEP of karst regions in Hebei in 2022 was 602.822 billion yuan, the value transformed from eco-products was 217.211 billion yuan, and the value transformation rate is about 36.03 %. Material products and cultural service products contributed 35.21% of the value transformation rate, representing the most effective eco-products in the karst regions of Hebei, while regulating services contributed only 0.83 %. The study reveals the existence of fragile ecosystem mechanisms, imperfect safeguard mechanisms, and a limited range of realization pathways in the karst regions of Hebei. Accordingly, differentiated improvement strategies are proposed: at the mechanism level, it is suggested to strengthen ecological protection and restoration, improve basic security and establish long-term incentives; at the level of implementation pathway, a trigram model encompassing government leadership, market-driven mechanisms, and government-market coordination should be introduced.

Mechanisms and critical criteria of coverd karst collapses under extreme rainfall conditions

PAN Zongyuan, SHU Rui, DAI Jianling, MENG Yan, LEI Mingtang, JIA Long, MA Xiao, BAI Bing

2025, 44(3): 587-597. doi: 10.11932/karst20250308

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In recent years, the increasing occurrence of covered karst collapses triggered by rainfall conditions has posed a threat to human life and property safety. According to field investigations and statistical data, the triggering factors of karst collapses can be categorized into natural and human factors, with 40% of these collapses attributed to natural causes. Natural factors, such as rainfall, earthquake, tsunami, etc., exert different effects on the development of karst collapses. Notably, most karst collapses are associated with extreme rainfall conditions, indicating a correlation between rainfall and the occurrence of collapses. At present, research of the impact of rainfall on karst collapses mainly focuses on pressure changes in groundwater and air, the effects of increased load, vertical permeability deformation, and saturation erosion caused by rainfall infiltration. However, there is a scarcity of studies providing quantitative analyses of the evolution process of karst collapses triggered by rainfall. Therefore, understanding the mechanisms of karst collapses under extreme rainfall conditions has been considered as a key research objective. Based on field investigations, a hydrogeological structural model has been developed, taking into account the hydrogeological conditions and the presence of covered karst collapses in the study area. Subsequently, a physical model of these collapses has been constructed to simulate their formation process under rainfall conditions. To enhance the understanding of the mechanisms of karst collapses and to further refine methods for preventing their occurrence, the dynamic characteristics of pore water pressure, earth pressure, and displacement of overburden materials have been monitored and analyzed through model testing. In addition, the coupling effect among pore water pressure, earth pressure, and displacement of overburden materials has been comprehensively analyzed, along with the formation processes, collapse types, and triggering factors associated with these events.The results show that: (1) The pore water pressure, earth pressure, and displacement of overburden layers under extreme rainfall conditions exhibit synchronous deformation patterns and present as a strong correlation with different evolution stages of karst collapses. As the rainfall intensity and frequency increase, the pore pressure and earth pressure of overburden materials also rise continuously, which is related to water retention capacity of overburden layers. Additionally, variation in displacement of overburden materials reflects the formation process of karst collapses. When a collapse occurs, displacement of overburden materials manifests as a rapid variation curve. (2) Under extreme rainfall conditions, karst collapses can be categorized into two types: creep failure and compression-shear fracture. In the case of creep failure, the pore pressure and the earth pressure of overburden materials exhibit similar form peak-cluster fluctuations. The dynamic curves of pore pressure and earth pressure experience homogeneous variations, while both pressures constantly increase. The displacement of deeper layers initially increases and then decreases, whereas the displacement of the upper and middle layers gradually increases with the frequency of rainfall cycles. Furthermore, in the compression-shear fracture type, the pore pressure, earth pressure, and displacement display isolated peaks, which sharply increase over a short period before decreasing. (3) The formation process of creep failure type of karst collapse involves softening, water loading, and corrosion absorption, leading to soil damage, the increase and enlargement of pores and cracks, and ultimately resulting in forming ground collapses. This type of karst collapses is the result of circulation and accumulation effects of softening, water saturation and increased load, and soil damage. Conversely, the formation process of the compression-shear fracture type of karst collapses consists of softening and water loading, followed by vertical shear failure of the roof and subsequent ground collapse. This suggests that karst collapses are mainly induced by water saturation, increased load, and soil damage.The critical early warning criteria of karst collapses in the study area should take into account the different overburden thicknesses: (1) When the overburden thickness is 0.5 m, the critical pore water pressure in the study area is 17.95 kPa to 19.1 kPa, the critical earth pressure is 15.3 kPa to 17.3 kPa, and the critical displacement is 589.95 μm to 928.4 μm. (2) When the overburden thickness is 1.0 m, the critical pore water pressure is 23.55 kPa to 25.55 kPa, the critical earth pressure is 17.75 kPa to 20.95 kPa, and the critical displacement is 770.7 μm to 988.6 μm. (3) When the overburden thickness is 1.5 m, the critical pore water pressure is 29.15 kPa to 30.4 kPa, the critical earth pressure is 20.25 kPa to 26.5 kPa, and the critical displacement is 967.25 μm to 1,087.5 μm. The overburden thickness is positively correlated with the critical criteria of covered karst collapses, which indicates that a thicker overburden layer provides better anti-collapse properties. This paper focuses on the mechanisms and critical criteria of rainfall-induced karst collapses. However, during rainfall infiltration, a relatively impermeable layer forms within the overburden layer, and fluctuations in the groundwater level will compress the air in the cavity of rock and soil materials, resulting in a complex water-soil-air coupling effect. Understanding this coupling effect and the collapse mechanism is of great significance for improving the mechanism theory of karst collapses, which will be further studied in the following experiments.

Development law and influencing factors of covered karst in Shaoguan New District

CHEN Hui, GONG Jinzhao, GUAN Zhende, ZHANG Wenping, ZHANG Yunfei, XIE Changyang, XU Yao

2025, 44(3): 598-608. doi: 10.11932/karst20250309

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The carbonate rock in the Shaoguan New District is widely distributed, and the covered karst caves are well-developed, exerting a significant influence on engineering construction and restricting the city’s construction and development. Through research on the karst types, karst development and its stratum lithology combinations, geological structures, and groundwater relationships in the Shaoguan New District, we summarized the karst development patterns and main controlling factors. The findings provide valuable guidance for the planning and urban construction of the Shaoguan New District. The covered karst area in the Shaoguan New District is mainly distributed in the valley plain and is roughly divided into three regions by the surrounding hills: the Xilian–Gantang karst valley, the karst syncline basin in Furong New City, and the terrace of the Beijiang River in the Jiangwan Area, encompassing a total area of 35 km². Horizontally, controlled by regional northeast-oriented structures and the distribution of soluble rocks, etc., karst in the study area is generally distributed in a northeast-oriented band. According to the lithology combination, groundwater recharge and runoff conditions, geological structures, topography, and detection rates of karst caves in boreholes, the degree of development of covered karst can be classified into four levels: extremely strong development, strong development, moderate development, and weak development. The area characterized by extremely strong karst development is approximately distributed in a northeast-oriented band, with a detection rate of karst caves generally exceeding 60%. This area can be broadly categorized into three types. The first type is mainly affected by lithology combinations, exemplified by the region surrounding Furongwan–Shaoguan Avenue–Hengda City, which is located near the lithological contact zone between the Hutian Formation and the Zimenqiao Formation. The second type is mainly affected by geological structures and lithology, as seen in Baoneng Mansion and the northeastern side of Xiahu Village located in the core of the Furong Mountain Syncline. The stratum lithology consists of the limestone and dolomitic limestone in the Hutian Formation, which is brittle and leads to highly developed rock joints and fractures, thereby providing favorable spaces and channels for groundwater activities. The third type is mainly affected by groundwater recharge and runoff conditions. For example, the Zhangwuling in Jiangwan and the Gantang Industrial Park are located in areas of strong runoff where groundwater discharges into the river. The intense groundwater activities in these locations provide favorable hydrodynamic conditions for karst development. The area characterized by strong karst development has a wide area and is mainly distributed in Xilian Town–Muxi Industrial Park, Gantang Industrial Park, the Furong Syncline Basin, and the south of Baimang Reservoir. The detection rates of karst caves range from 30% to 60%, and these caves are mostly distributed in the areas of groundwater runoff. The area characterized by moderate karst development is mainly distributed in Muyang Avenue–Muxi Industrial Park, Chishui New Village, the New Party School, and Cuntou, etc. The detection rates of karst caves range from 10% to 30%, and the soluble rocks are mainly from the Shidengzi Formation. The area characterized by weak karst development is mainly distributed in the peripheral regions of moderate development, and the detection rates of karst caves are generally less than 10%. Vertically, there are significant differences in karst development within the study area, which exhibit a diminishing trend as the depth increases. From shallow to deep, the area can be divided into four zones: extremely strong development, strong development, moderate development, and weak development. The zone of extremely strong karst development extends from the bedrock surface to a depth of 40 m, with detection rates of karst caves in the 20 m to 40 m depth range reaching 45%. These karst caves are mostly filled with silty clay. The zone of strong karst development is distributed at depths of 40 m to 60 m below the surface, where the detection rate of karst caves is 35%. In this zone, the karst caves are mainly fully filled or semi-filled. The zone of moderate karst development is distributed at depths of 60 m to 80 m below the surface, with a detection rate of karst caves being 20%. These caves are mainly semi-filled or unfilled. The zone of weak karst development is distributed at depths greater than 80 m, where the detection rate of karst caves is less than 10%. In this zone, the karst caves are mostly empty, with a few being semi-filled. The degree of karst development results from the interaction of various factors. Among the three areas of covered karst, the karst basin of Furong New Town is located in the core of the Furong Mountain Syncline structure, where the geological strata mainly consist of pure carbonate rocks, including the limestone and dolomitic limestone of the Hutian Formation, which are inherently brittle. The influence of the syncline structure has led to significant fracturing of the rock in the core area, providing optimal conditions for groundwater flow and dissolution. Additionally, the basin is located within a region of active groundwater flow, characterized by strong hydraulic action that can facilitate the formation and development of karst. Therefore, the overall degree of karst development in the karst basin of Furong New Town is stronger than that observed in the Xilian–Gantang karst valley and the terrace of the Jiangwan karst river.

Landslide susceptibility assessment in the western Changyang section of the Qingjiang River Basin based on InSAR technology and random forest algorithm method

MENG Xiaojun, XING Zhao

2025, 44(3): 609-620. doi: 10.11932/karst2025y001

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The Qingjiang River Basin, a typical karst mid-mountain geomorphic region where carbonate rocks constitute 72% of the lithology, has been extensively influenced by long-term geological processes. Quaternary loose deposit layers, mixed with soil and rock, are extensively distributed along both banks. These layers exhibit poor stability and are prone to frequent landslide disasters, such as the Pianshan landslide and Maoping landslide. Traditional landslide susceptibility assessments typically rely on static historical data and linear models, such as the information content method and the Analytic Hierarchy Process (AHP). However, these approaches are limited in their ability to capture the nonlinear characteristics of landslide evolution. To improve the timeliness and accuracy of the assessment, this study integrates Small Baseline Subset-InSAR (SBAS-InSAR) surface deformation monitoring technology with the random forest machine learning algorithm to conduct dynamic landslide susceptibility assessments in Ziqiu town and Yuxiakou town, covering a total area of 251.89 km² in Changyang county, Hubei Province.Based on the landslide development patterns in the study area, this study selects 12 evaluation indicators from four categories—topography, geology, hydrology, and human engineering activities—as the landslide susceptibility indicators for the region. It employs the Random Forest model for comprehensive susceptibility assessment. Due to the poor timeliness and inaccuracy of landslide data in traditional evaluation models, the study utilizes the latest Sentinel-1A radar data and applies the SBAS-InSAR method to obtain up-to-date surface deformation data to replace the conventional landslide data. The interpretation results show that the central and western parts of the study area are predominantly characterized by subsidence points, with a small number of uplift points, while the eastern region exhibits a greater distribution of uplift points. The density of surface deformation points decreases from the southern to the northern part of the study area. Along the Qingjiang River, surface deformation points are more densely distributed. From the western part of the study area to Ziqiu Town, subsidence points dominate, while from Ziqiu town to the eastern part of the study area, uplift points are more prevalent. Most of the surface deformation points are located around towns and villages. In Yuxiakou town, both subsidence and uplift points are present, while Ziqiu town mainly features uplift points. The surface deformation points are mainly located in hard carbonate rock formations, with densely distributed deformation points typically found on both sides of fault zones. The rock mass on either side of the fault is subjected to intense compression, leading to fracturing, which forms a fractured zone. The uneven distribution of stress on both sides can easily trigger landslides. Additionally, the comparison of surface deformation points with other evaluation factors reveals that these points are predominantly distributed in areas with slopes ranging from 8° to 25°, elevation differences between 10 m and 30 m, and proximity to construction land such as houses and roads, where human engineering activities significantly influence surface deformation.The 12 evaluation indicators and SBAS-InSAR interpretation results were used as training datasets, and the random forest method was employed to assess landslide susceptibility. The importance of the evaluation factors, as determined by the random forest classification prediction model, indicated that Quaternary thickness and engineering geological rock groups were significantly more influential than the other factors. This suggests that when the surface deformation rate is used as an indicator to evaluate landslide susceptibility levels, geological factors are predominant. The hardness and stability of the rocks, as well as the thickness of the Quaternary deposit layers, determine the scale and severity of landslides induced by surface deformation. Factors such as the influence range of river systems, elevation difference, and slope have relatively high importance values. Within a certain influence range of river systems, water level fluctuations may significantly affect landslide stability. Areas with greater elevation differences and steeper slopes exhibit higher surface deformation rates, consequently increasing the probability of landslides. The remaining factors have little impact on the prediction results; except for the distance to the fault, all are related to human engineering activities. This suggests that when the surface deformation rate is used as an indicator for landslide susceptibility assessment, human engineering activities may alter certain original landforms and potentially trigger surface deformation and landslides, although their influence is relatively limited.The calculation results indicate that the areas classified as extremely high-risk and high-risk for landslide hazards in the western section of Changyang, within the Qingjiang River Basin, account for a substantial proportion, reaching 32.22%. These areas are mainly concentrated near Ziqiu town on the eastern side of the study area and along the banks of the Qingjiang River, which aligns well with the spatial distribution of historical landslides. The Quaternary deposit thickness, engineering geological rock groups, and river systems are identified as the dominant controlling factors for landslide susceptibility. Areas characterized by thicker Quaternary deposits, interbedded with soft and hard rock layers, and the distance proximity to rivers (within 200 meters) demonstrate significantly higher probability of landslides. The ROC curve analysis of the hazard assessment model shows that the random forest model incorporating InSAR technology can effectively capture landslide susceptibility, achieving a high AUC value of 0.90. This model exhibits strong predictive performance and reliability, providing a novel approach to landslide susceptibility assessment and valuable decision-making support for governmental disaster prevention and mitigation efforts.

Monitoring of surface deformation and its spatiotemporal characterization in Tongling City of Anhui Province based on time-series InSAR of Sentinel-1 data

YANG Chen, JIN Yuan, DENG Fei, SHI Xuguo

2025, 44(3): 621-631, 644. doi: 10.11932/karst20250310

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Tongling City, located in the south-central part of Anhui Province on the southern bank of the middle and lower reaches of the Yangtze River, lies within the hilly region of the riverine plain and experiences a subtropical humid monsoon climate. With a total area of 2,991.87 square kilometers, it is a crucial region within the Wanjiang Economic Belt. Renowned as the "Ancient Copper Capital of China", Tongling is abundant in natural resources, particularly minerals, including copper, sulfur, iron, gold, silver, coal, and limestone. As a significant mining area in China, there are currently 220 licensed mines in Tongling, which are extracting 30 million cubic meters of ore annually, with a total mining and processing output exceeding two billion yuan. The carbonate rock strata in Tongling are highly developed, with a cumulative thickness of over 1,500 m. These strata are primarily concentrated in the Middle-Upper Carboniferous to Lower Permian and Middle-Lower Triassic geological periods. Due to factors such as mining dewatering and groundwater pumping, Tongling has been vulnerable to geological hazards such as karst collapses.The sites with potential geological hazards are typically found in regions exhibiting clear signs of surface deformation. Real-time monitoring of surface deformation allows for comprehensive identification of the sites with potential geological hazards and timely early warnings. The simple monitoring methods, such as pile-embedding and painting to observe known hazard sites, have been employed; however, these techniques cannot capture large-scale subsidence data, making it difficult to detect and monitor unknown hazards. In recent years, Interferometric Synthetic Aperture Radar (InSAR) has been widely used as a large-scale, high-precision deformation monitoring tool. It offers several advantages over traditional methods, including all-weather capability, continuous operation, extensive spatial coverage, and high accuracy. With the development of time-series InSAR techniques like Persistent Scatterers InSAR (PSI) and Small Baseline InSAR (SBAS-InSAR), high-precision surface deformation monitoring using coherent pixels within InSAR data has become increasingly important in identifying and monitoring geological hazards.This study focuses on Tongguan District and Yi’an District in Tongling City, situated in the south-central part of Anhui Province, along the southern bank of the middle and lower reaches of the Yangtze River. The study area boasts extensive soluble rock distributions and rich mineral resources like gold, silver, copper, iron, and sulfur, with a mining history spanning over 3,500 years. Consequently, geological hazards like karst collapses and mining collapses are prevalent. Fig.1 marks 130 locations of historical karst collapse, primarily concentrated near Shizishan in Tongguan District. Fig.1a illustrates the terrain and karst development within the study area, while Fig.1b depicts the landform, characterized by higher terrain in the south and lower, flat terrain in the north (the Yangtze River alluvial plain, with elevations ranging from 6.5 to 20 m) and hilly terrain in the south (with significant topographic relief and elevations generally between 50 and 250 m, peaking at 493 meters at Tongguan Mountain).This study utilizes SBAS-InSAR technology to process Sentinel-1 data covering Tongling City, identifying local deformation zones from 2015 to 2021, including the Xinqiao Mining Area, Laoyaling, Bijia Mountain, and Liuguo Chemical Plant. The maximum deformation rate, observed in the Xinqiao Mining Area, is approximately 118 mm/yr. Analysis of these deformation zones indicates that the combined effects of karst geological conditions and human activities like mining have contributed to the observed deformation characteristics. Notably, deformation in the Laoyaling tailings pond is also influenced by rainfall. Our findings demonstrate that InSAR technology can be effectively employed for large-scale geological hazard identification and monitoring, providing vital information for disaster prevention and control. For areas with significant deformation, it is recommended to install corresponding ground monitoring measures to assess risks in detail. With the launch of China’s land exploration satellites and future satellite missions, abundant SAR satellite data will become available for more detailed analysis of deformation characteristics, enabling more precise monitoring and assessment of hazard sites. InSAR technology will play an increasingly critical role in disaster monitoring in this region.

Mechanism of karst ground collapse and evaluation of disaster risk in Chengnan community, Yingde City, China

WANG Heng, YAO Yijuan, ZHAO Kui, CHEN Yudao, QIN Jiaxiao

2025, 44(3): 632-644. doi: 10.11932/karst2025y007

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Karst ground collapse is one of the most common geological hazards in karst areas. It is characterized by concealment, sudden occurrence and inhomogeneity, along with various other complex features. Understanding the mechanisms of karst ground collapse and conducting risk assessments for such events are of great significance for urban development and engineering construction. In November 2020, a large-scale karst ground collapse occurred in Chengnan community of Yingde City, Guangdong Province. A total of 31 collapse pits were identified, predominantly exhibiting elliptical and circular shapes, and spatially distributed in three strips. The duration was notably lengthy, resulting in relatively severe disaster impacts.Comprehensive investigation results and analysis show that the karst ground collapse in the study area primarily occurred in the main groundwater runoff zone, which is characterized by relatively thick overlaying layers and significant karst development. The spatial distribution of the strip align with the arrangement of three fault zones in the study area. In the vicinity of a sewage treatment plant, the stacking of karst caves is evident, characterized by a significant cumulative thickness of the caves, high permeability of the rock layers, and loose overlying soil with low cohesion. These factors created fundamental conditions for the concentrated occurrence of ground collapse. In the study area, the triggering mechanisms of karst ground collapse are influenced by frequent fluctuations in the water levels of the nearby Beijiang River, as well as human activities that involve groundwater pumping and draining. These factors induce hydrodynamic effects, including subsurface erosion and vacuum suction erosion of groundwater. Additionally, the presence of sewage leakage near the sewage treatment plant at the center of the study area altered hydrochemical properties of groundwater, resulting in chemical dissolution. Therefore, the primary mechanisms driving karst ground collapse in this area are chemical dissolution and hydrodynamic effects.In order to facilitate the formulation of targeted preventive measures, we selected eight susceptibility indicators and two vulnerability indicators after screening each indicator factor in the study area. These indicator factors were combined with the Analytic Hierarchy Process (AHP) to establish a comprehensive index model of karst ground collapse risk suitable for the study area. By leveraging GIS spatial analysis functions, we conducted a relatively accurate risk assessment of the study area. The results show that the risk of karst ground collapse in the study area can be categorized into two levels: high-risk and moderate-risk. The high-risk zone is mainly distributed around the sewage treatment plant and cement plant area, comprising 70.83 % of the total study area. Conversely, the moderate-risk zone is mainly located in the northwest corner of the study area, accounting for 29.17 % of the total.In conclusion, it is recommended to strengthen the dynamic monitoring and management of groundwater, along with implementing measures to prevent and control surface sewage seepage. These actions are essential to protect the region from ground collapse hazards and to reduce the risk of disasters.

Mapping and characteristic analysis of karst areas along the Belt and Road

QIN Zhengfeng, XU Qi, JIA Min, BI Xueli, YANG Xiangpeng

2025, 44(3): 645-656, 668. doi: 10.11932/karst20250311

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The region along the Belt and Road is a critical global hub for energy production and supply, containing 55% of the world’s oil reserves and 76% of its natural gas reserves. Carbonate rock oil and gas reservoirs hold an extremely important position in global hydrocarbon resources. Statistics show that carbonate reservoirs account for approximately 70% of the world’s total oil and gas resources, 50% of proven recoverable reserves, and 60% of global production. By the end of 2013, there were 53 UNESCO World Heritage Sites featuring karst landscapes worldwide, including 42 designated as World Natural Heritage Sites. The stunning karst landscapes and unique cave formations have become major tourist attractions, while the abundant karst water resources and carbonate rock oil and gas reserves support human survival and development. The karst regions along the Belt and Road encompass over 50% of the global karst areas, which coincide with intensive human activities. In the context of global change, these regions face prominent environmental challenges, including karst drought, rocky desertification, water pollution, and severe geological hazards such as collapses and depression waterlogging, posing substantial threats to regional eco-environmental security.Supported by a project of the China Geological Survey, this study employed MODIS Reprojection Tool (MRT) and the Environment for Visualizing Images (ENVI) software to conduct remote sensing interpretation of collected datasets, including annual precipitation, mean temperature, evaporation, elevation data, and satellite imagery. A specialized map of the karst geological environment along the Belt and Road was compiled, which laid a foundation for further classification of key types of karst belt along the route and serving the International Karst Science Program. By integrating remote sensing images, geological maps, literature, and other data, and combining with field verification, this study has compared the karst characteristics of plateaus, large slopes, plains, and coastal areas within their geological and climatic contexts. The main conclusions are as follows.(1) Karst distribution areas along the Belt and Road span about 12.3 million km², representing over half of the global karst coverage. Among the countries along the Belt and Road, China, Russia, and Kazakhstan have the largest karst areas, ranking as the top three in terms of karst coverage.(2) The characteristics of karst distribution under different elevations, temperatures, rainfall levels, and evaporation rates along the Belt and Road are quantitatively analyzed. Karst areas located between 0 m and 1,000 m in elevation account for 74% of the total karst area, whereas those above 3,500 m represent only 8%. Karst areas with surface temperatures above 9 ℃ comprise 65.3%, while those below 9 ℃ account for 34.7%. Regarding annual rainfall, karst areas receiving 0 mm to 210 mm constitute 31% of the total area, those receiving 210 mm to 540 mm account for 32%, 540 mm to 840 mm cover 18%, and areas with annual rainfall exceeding 840 mm represent 19%. Additionally, karst areas with evaporation rates below 205 mm account for 51.4% of the total.(3) A comparative analysis of karst development conditions and controlling factors in Ethiopia, Croatia, Turkey, Iran, Thailand, and South China reveals that the lithology and tectonics of soluble rocks serve as intrinsic drivers of karst development, establishing the fundamental framework for karst processes. Meanwhile, climate acts as an extrinsic driving force, with both factors jointly shaping the development of karst landforms. Taking the karst in South China as an example, this study analyzes the influence of tectonic uplift on the differentiation of karst landforms. Distinct vertical hydrological profiles and erosion-dissolution base levels have been formed during different geological periods. To adapt to changes in these base levels, karst geomorphological zones have been developed at varying elevations. Moreover, the significant disparities in elevation also induce variations in climate, hydrology, and tectonic conditions, which in turn cause geomorphological differentiation in karst landforms. Meanwhile, China’s Qinghai-Xizang Plateau on the first terrain ladder is characterized by high altitude, low temperatures, and scarce rainfall. The development of modern karst is limited in this region, exhibiting only micro-karst formations on rock surfaces. In contrast, Southwest China (Yunnan, Sichuan, and Chongqing), located on the second terrain ladder, experiences abundant rainfall and steep slopes. This area undergoes intense fluvial downcutting, forming canyons and peak-cluster valleys. Meanwhile, Guangxi (China), Thailand, and other Indochina Peninsula plains lie on the third terrain ladder. These areas are characterized by a hot, humid climate and low-elevation terrains near sea level, exhibiting vigorous surface and subsurface karstification and developing classic karst landforms such as peak-cluster valleys, peak-forest plains, and isolated-peak plains.

Study on karst development characteristics using cross-hole radio imaging method: A case of karst detection of Jifucun aqueduct in the Central Yunnan Water Diversion Project

QIN Ruidong, SUN Guanjun, LU Kai, SHI Cunpeng, LU Mingxuan, LI Wei, DU Lixuan

2025, 44(3): 657-668. doi: 10.11932/karst20250312

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Karst development represents a common geological phenomenon, giving rise to a variety of hazards during engineering construction. These risks include structural cracks, tilting, and even building collapses, posing significant challenges to project progress, safety, and cost efficiency. To effectively address these issues, karst exploration plays a crucial role in engineering construction, as it facilitates the identification of geological anomalies and the mitigation of potential dangers. Moreover, it provides a solid foundation for project implementation. In areas characterized by karst development, a comprehensive understanding of the perils associated with this geological phenomenon becomes imperative. Therefore, placing a greater emphasis on karst exploration becomes indispensable for us to adopt effective prevention and treatment measures that ensure project quality and safety.The Jifucun aqueduct, situated in Songgui town of Heqing county, Yunnan Province, is a vital component of Segment I of Dali of the Central Yunnan Water Diversion Project. The geological composition surrounding the aqueduct route consists of the Upper Triassic Zhongwuo Formation (T₃z), which comprises limestone intermixed with muddy limestone. Surface karst features are predominantly characterized by dissolution grooves and small sinkholes, while underground karst formations consist of dissolution caves, fractures, and gaps. The thickness of strongly dissolved and weathered limestone in the aqueduct area generally ranges from 9 m to 50 m. The pile foundation structure exhibits non-uniformity, which gives rise to concerns regarding the deformation and stability of the karst foundation.In this study, cross-hole Radio Imaging Method (RIM) was employed to detect the karst development at the position of each pile foundation of the aqueduct piers. By integrating the results from drilling core data and borehole panoramic digital images, a comprehensive comparative analysis was conducted to discern the characteristics and patterns of karst development within the study area.The RIM observation data, based on the established criteria for evaluating data quality, achieves the highest classification: Class I. By extracting (quasi) curves of horizontal synchronous electric field intensity from the complete set of observational data for a given section, valuable insights can be obtained regarding the approximate location of subsurface karst and the overall integrity of the underlying rock mass. Through meticulous data preprocessing, including a comprehensive review of the observation system parameters and the removal of erroneous data points, the inversion process employs the Simultaneous Iterative Reconstruction Technique (SIRT) to determine the absorption coefficient of the electromagnetic wave between the two boreholes. Significantly, the areas exhibiting notably high absorption anomalies in the inversion results closely align with the findings obtained from core drilling data and panoramic digital images of boreholes.The detection results reveal that the curves of horizontal synchronous observation effectively illustrate the depth range of distribution of subsurface anomalies. Furthermore, the RIM provides valuable insights into the boundaries, shapes, and absorption coefficients of these abnormal areas, yielding significant geological information regarding the form, extent, and intensity of underground karst development. Additionally, they illuminate the regional scope and fragmentation degree of the rock mass fracture zone. The RIM results accurately depict crucial geological details, including the location and shape of underground karst and the integrity of the rock mass, and they demonstrate a high degree of concurrence with the karst anomalies revealed through borehole panoramic digital imaging and results of drilling cores. Hence, the RIM emerges as a reliable and efficient method for detecting karst formations, offering direct insights into the developmental traits and extent of underground karst, which serves as a valuable scientific reference for the planning and implementation of aqueduct engineering projects.

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2025 Vol. 44, No. 3

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Current Issue 2025 Vol. 44, No. 3

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Current Issue
2025 Vol. 44, No. 3