Buried Karst Research Articles

Multiple contamination sources, pathways and conceptual model of complex buried karst water system:constrained by hydrogeochemistry and δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr isotopes

Karst groundwater contamination has emerged as a worldwide environmental and health hazard. Karst aquifers, even for the buried karst systems, have strong contamination sensitivity and great pollution risk due to the good pipe fracture connectivity. The large burial depth and invisible hydrologic connectivity pose a challenge for the diagnosis of the contamination sources and identification of the contamination pathways of buried karst aquifers. To address it, a comprehensive application of hydrogeological and hydrogeochemical investigation combined with multiple isotopes (δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr) were performed to elucidate the multiple contamination sources and migration pathways of contaminants in Jinci Spring, a complex buried karst water system. The results obtained highlight that the hydrological connectivity and source availability determine the specific contamination process in buried karst aquifer. Karst aquifer under the river channel is observed to be influenced by the vertical infiltration of polluted river water as indicated by elevated chloride levels (mean 79.4 mg/L) and higher δ2H (mean −8.8 ‰) and δ18O (mean −64.5 ‰) values. Evidenced by the excess of sulfate (mean: 1454 mg/L) and depleted δ34S (mean: −1.6 ‰), the lower karst aquifer may receive the leaking recharge of the mining waste water in the overlying coal seams. The occurrence of nitrate in karst water may be induced by reverse recharge from neighboring confined quaternary aquifers, indicated by the elevated nitrate concentration (15.0–50.8 mg/L) with high 87Sr/86Sr ratios (mean 0.7124). Our findings suggest that over-pumping of deep karst waters may produce additional pollution sources by altering the natural recharge relationship between montanic karst waters and the neighboring pore waters within the basin. Research in this paper improves our understanding of groundwater pollution and hydrological connectivity in buried carbonate aquifers and the protection of karst water resources.

Fine Detection and Analysis of Hidden Karst in Wellsite with Quasi-Three-Dimensional TDEM Based on Lateral Constraint

Considering that karst caves, underground rivers, and dissolution fractures in shallow carbonate formation in the Sichuan Basin are extremely developed, leakage, failure and plugging difficulties are easy to occur in the drilling process. The TDEM was used to carry out the exploration of hidden karst geological bodies in well QM2, and the quasi-three-dimensional inversion based on lateral constrain was used to invert the TDEM data. Three NW trending anomalous bands were identified in the lower Triassic Jialingjiang Formation within the range of drilling, consisting of seven relatively low-resistivity anomalous zones. Under the guidance of TDEM quasi-three-dimensional inversion resistivity data, the low-resistivity karst development area is avoided, and the specific drilling location of well QM2 is determined. No karst cave and underground river were drilled in the later drilling process of well QM2, as well as no instability phenomenon occurred. It indicates that the TDEM detection results are consistent with the actual drilling, and the quasi-three-dimensional TDEM inversion interpretation data based on lateral constraints is reliable and can accurately detect the buried karst in the wellsite.

Characteristics of shallow buried karst and its safety distance to tunnel in wuxi city, China

Subway tunneling construction in shallow buried karst region is a common challenge. Survey boreholes and cross-hole seismic CT data showed that 29 karst caves exist at elevation of −17 m to −37 m in Si–He section of the Wuxi Metro Line 4, which are consisted of 18 filled caves and 11 empty caves and constitute substantial dangers to the stability and quality of metro construction projects. Based on their size, position, and type of filling, we divided these shallow karst caves into four types. Aimed at exploring the instability of the tunnel after excavation, numerical analyses have been developed by using the Finite difference method. Both the effects of the distance between tunnel and karst caves and the effects of the filling of the cavities on the overall stability of the rock mass around the tunnel have been investigated. According to the design criteria, safety distance between tunnel and karst caves was determined. The monitoring data of tunnel during excavation proved the rationality and accuracy of the analysis results. The research results can provide technical reference for the design and construction of other proposed tunnels that are located in the regions of shallow buried karst in Jiangsu Province.

The Analyses of Land Use and Prevention in High-Density Main Urban Areas under the Constraint of Karst Ground Subsidence: Study of Wuhan City, China

The development and utilization of land in the main urban area have significantly impacted the stability of the regional geological environment through various means, such as increased load and subway construction, primarily manifested as rock and soil mass deformation leading to geological hazards. Therefore, it is worth exploring how to reduce the occurrence of karst ground subsidence (KGS) through reasonable land development and control measures in the main urban areas with large-scale developments of buried karst formations. This study focuses on the main urban area of Wuhan City. An evaluation model for KGS was constructed using the analytic hierarchy process (AHP) and comprehensive index evaluation method by analyzing the geological conditions that affect KGS. The susceptibility zoning of KGS was obtained with GIS spatial analysis technology. The results show that the susceptible areas can be divided into extreme, high, medium, and weak susceptibility, accounting for 4.93%, 15.30%, 33.21%, and 46.56%, respectively, which are consistent with the distribution density of past KSGs. Furthermore, by selecting the subway construction as a human activity type, it indirectly discusses the influence of land development intensity on KGS. The results show that past KSGs are mainly concentrated in areas with high engineering construction density and significant land development intensity. Based on the above, strategies for regional land development and prevention and control of KGSs are proposed.

Investigation of buried karst sinkholes under a bog using ground penetrating radar (GPR) and electrical resistivity tomography (ERT)

AbstractActive evaporite karst processes in the Baltic states are associated with a few relatively small regions where gypsum rocks can be found close to the Earth's surface. One of these areas lies in the vicinity of the Pandu bog. However, such a possibly active karst region, which is covered by peat and in which the mapping of karst formations is complex, has not been previously investigated. In this study, we present a buried and peat‐filled karst cover‐collapse sinkhole mapping approach that involves a combination of ground‐penetrating radar (GPR), electrical resistivity tomography (ERT) and conventional boreholes. A detailed map of the bog's substratum topography was constructed from a geophysical surveying dataset. It reveals 15 distinctly expressed sinkholes with diameters of several tens of metres. Overall, 140 potential sinkholes were also mapped using remote sensing data in the vicinity of the bog. Higher electrical resistivity anomalies were identified inside the peat; they coincide with scatter‐free zones in GPR data and water layers in boreholes. Highly disturbed internal peat layering was also detected in these sinkholes. It is suggested that these water layers and disturbed peat layering may have formed due to the subsidence of the lower peat layers, and thus they represent relatively younger sinkholes. This is also supported by evidence from orthophoto maps, which showed the formation and disappearance of surficial lakes and depressions on the bog surface. Our results revealed the presence of active and widespread karst processes under the bog that have not been previously noticed despite the fact that they have implications for the assessment of geohazards in this area.

Karst detection by geophysical methods using microseismic sounding

Research aim is to test a technique for detecting buried karst using microseismic sounding based on spectral amplification of horizontal displacements. The main research tasks include the construction and analysis of geoelectric and microseismic sections. Methodology. The microseismic background was recorded using the OMAR-2s autonomous seismic station (Institute of Geophysics Ural Branch RAS, Ekaterinburg) in the frequency band 1–1000 Hz. Low-frequency horizontal seismic receivers from OYO Geospace Corporation were used as sensors. Vertical electrical sounding (VES) was carried out by a set of ERA-MAX equipment (SPC “ERA”, St. Petersburg) using a symmetrical Schlumberger installation at a frequency of 4.88 Hz, at currents of 5–50 mA. VES processing consisted in quantitative one-dimensional inversion according to the IPI2Win program (Moscow State University, Moscow). Results. Experimental and methodological work on the study of microseisms, accompanied by VES, was carried out on two karst sites of the Sverdlovsk region. Based on the results of processing, geoelectric and microseismic sections were constructed to determine the conditions of occurrence of bedrock and loose sediments covering them, as well as to identify local anomalies associated with karst manifestations. The results of electrical exploration and seismometry are in good agreement with each other and are confirmed by geological data. Conclusions. Vertical electrical sounding makes it possible to distinguish karst by the high contrast of the resistances of the host bedrock (limestone) and terrigenous filler material (clay, loam). Microseismic sounding makes it possible to delineate karst zones by high values of spectral amplification of weakly consolidated karst deposits, relatively low levels of microseisms in bedrock. Thus, on the basis of complex electrical and microseismic soundings, it is possible to confidently identify the areas of development of karst processes.

Hydrochemical characteristics and health risk assessment of groundwater in karst areas of southwest China: A case study of Bama, Guangxi

The southwest karst area is considered to have the most vulnerable groundwater environment in China. Groundwater quality is an important factor restricting sustainable economic development. In this study, traditional water chemistry method, water quality index (WQI), and hazard index (HI) were applied to comparatively analyze the hydrochemical characteristics of groundwater and the water quality in the exposed karst region (EKR) and buried karst region (BKR) in Bama, a typical karst area in southwest China. Generally, the main water type was Ca/Mg–HCO3. Due to the predominance of dissolution of carbonate rocks in EKR and silicate rocks in BKR, higher total dissolved solids (TDS), Ca and HCO3− concentrations, and lower H2SiO3 content were detected in groundwater in EKR compared with BKR. As affected by weathering of rocks such as lead-zinc ore, the maximum concentrations of Zn and Sr were 11.23 mg/L and 13.30 mg/L, showing that mineral water resources are widely distributed in Bama. The ion ratios and isotope abundances (δD and δ18O) in groundwater samples indicated stronger evaporation and rock-water interaction in EKR than BKR. Human activities exerted a more significant influence on the water quality in EKR compared to BKR. The mean WQI value also suggested that the groundwater quality was better in BKR (9.56) than EKR (12.17). Although 95.7% of the water samples in the study area were classified as excellent based on their WQI values, 4.3% of the water samples still had significant health risks (HI > 1) due to the high Sb, Zn, As, and Sr concentrations. It is recommended to reduce anthropogenic pollution in EKR and develop a plan for clean production of mineral water industry according to local conditions, which will help the sustainable development of the local economy.

A rapid sediment pulse induced by glacial melting during the MIS 8/7e transition buried well‐developed karst in the Railton Valley, Tasmania, Australia

Recent catastrophic sinkhole collapse caused by regional water table lowering induced by quarrying has led to the partial exhumation and reactivation of a buried karst cave system in the floor of the Railton Valley in the lowlands of northern Tasmania, Australia, and widespread sinkhole development. Extensive silty sediments exposed in sinkholes, OSL dated to approximately 237 ka, are interpreted to be lacustrine deposits derived from rapidly deposited glacial outwash. The silty sediments have mineralogy consistent with derivation from a source in the upper Mersey catchment rather than locally and are interpreted to be the product of rapid melting of the Mersey Valley glacier during the MIS 8/7e transition. Thick Last Glacial alluvial fan and Holocene flood‐plain deposits mantle the lacustrine sediments. Exposures of glacial erratics and weathered till in streambeds provide further evidence that the valley was impacted by earlier Pleistocene glaciations.

Karst geology and mitigation measures for hazards during metro system construction in Wuhan, China

Karst geology is widely distributed in China; the great differences in natural conditions bring it an array of characteristics in different regions. There is a huge area of the buried karst in Wuhan, exhibiting a unique, but complicated engineering geological environment. This paper summarizes the geological conditions in Wuhan, with special focus on its karst geology. At present, a total of six karst belts have been detected, and they were divided into five structure types. For shield tunnelling in karst region, some problems such as water ingress or mud inrush, partial ground collapse, damage or failure of shield machine, and metro operation and management issues may be raised as a result of the activity of the karst geology. To prevent occurrence of possible hazards, a series of countermeasures suggested for hazard and risk mitigation were discussed in this paper. A case history, where the study section belongs to the Wuhan metro line 6, is referred to evaluate effectiveness of the adopted treatment measures. The feedbacks demonstrated that water ingress was successfully avoided, and ground deformation was effectively controlled in the study section throughout the construction phase. This study can provide significant reference information and experience for metro tunnel constructed in karst region.

Characteristics, Controlling Factors, and Formation of Shallow Buried Karst in Eastern China: A Case Study in the Wuxi Metro Areas, Jiangsu Province

ABSTRACT Karst-related geo-disasters often occur in karst regions during underground construction. In recent years, a number of shallow buried karst features have been discovered in eastern China. Survey boreholes show that karst caves exist at depths of 26–30 m and 33–36 m, which are typical of shallow buried karst. Using cross-hole seismic computed tomographic techniques, 36 geological anomalies consisting of 26 mud-filled caves, three empty caves, and seven fissure zones/loose lens bodies were detected. Most of the karst caves were oblate or oval. After determining the scale of and the connection between the caves, the study area was divided into two areas to provide advice on the treatment of caves during construction. An analysis of the development characteristics of the karst suggests that karst is controlled by several key factors, including topography, structural features, groundwater conditions, and human activities. Following an analysis of these factors and field studies of the process of formation of the shallow buried caves, solutions are proposed to prevent karst-related geo-hazards. The research results can be used in the design of foundations for buildings that are located in regions that include shallow buried karst in eastern China.

A Buried Landslide Block in a Section of Middle Jurassic Deposits in the Moscow Region

A section of Upper Carboniferous and overlying Jurassic sediments in the area of a buried karst depression in the northwestern part of Moscow was studied. According to conodont zoning, it was revealed that in the section of the karst depression the Perkhur Formation directly lies on the Voskresensk Formation altered by karst processes. It was shown that the absence of the Neverovo Formation in the section is associated with landslide deformations, which occurred in the Middle Jurassic (Kudinovo) time, that is, the movement of a block of the Perkhurovsky limestones, which was located hypersometrically higher on the slope of the karst paleodepression.

A buried landslide block in the section of Middle Jurassic deposits in Moscow region

A section of the Upper Carboniferous and overlying Jurassic sediments in the area of the buried karst depression in the northwestern part of Moscow was studied. According to conodont zonality, it was revealed that, in the section of the karst depression on the Voskresensk Formation altered by karst processes, the Perkhurovo Formation directly lies. It was shown that the missing in the section Neverovo Formation is associated with the origin of landslide deformations in the Middle Jurassic (Kudinovskoye) time — the movement of a block of Perkhurovo limestones, which are located hysometrically higher on the slope of the karst paleodepression.

Processes leading to the re-activation of a sinkhole in buried karst and the subsequent drying of waterfalls in a small catchment located in northern Indiana, USA

Processes leading to the re-activation of a sinkhole in buried karst and the subsequent drying of waterfalls in a small catchment located in northern Indiana, USA

Geochemistry of the fracture-cave calcite of the Ordovician Yingshan Formation and its paleokarst environment in the Tazhong area, Tarim Basin, China

The fracture-cave reservoir of the Yingshan Formation is an important oil and gas producing zone in the Tarim Basin. Karstification occurs at the top surface of the carbonate rocks of the Yingshan Formation on the northern slope of the Tazhong area due to a short exposure, so abundant fracture-cave spaces are formed. On the basis of the data of nearly 49 samples obtained from 21 wells, the carbon and oxygen isotopes of the fracture-cave calcite were analyzed. The carbon and oxygen stable isotopic characteristics recorded during paleokarstification were discussed to provide geochemical evidence for predicting the distribution of the fracture-cave reservoirs, as well as to understand the genetic mechanism of karst fracture-caves and the fluid properties and paleo-hydrological conditions of paleokarstification. The fracture-cave calcite can be divided into three types based on its carbon and oxygen isotope values, which indicate three types of paleokarst environments with different fluid properties. Type I calcite has similar carbon and oxygen isotope values to the bedrock of the Yingshan Formation, with δ13C values of − 2.0 to 1.1‰ and δ18O values of − 5.76 to − 8.16‰. These values indicate that the calcite was precipitated in the eogenetic karst environment of the Yingshan Formation. Type II calcite has a δ13C value of − 2.13 to 1.0‰ and a δ18O value of − 12.41 to − 8.0‰. It has a similar δ13C value, but a significantly negative oxygen isotope value compared with values of the bedrock of the Yingshan Formation, indicating a buried karst environment. Type III calcite has an extremely negative δ18O value (δ18O value < − 14.50‰), indicating hypothermal karst genesis. Its formation is related to magma or deep hydrothermal fluids. No calcite with atmospheric freshwater genesis and significantly negative δ13C and δ18O values was found in the samples, indicating that the formation of fracture-caves is weakly affected by atmospheric freshwater. The main reservoir space of the Yingshan Formation is karst caves. The calcite in the karst cave fillings belongs to type I, indicating an eogenetic karstification environment. Therefore, the formation of the fracture-cave reservoirs of the Yingshan Formation in the Tazhong area is related to eogenetic karstification, which occurred during exposure and mainly contributed to the formation of the reservoir spaces.

Fractal Prediction of Grouting Volume for Treating Karst Caverns along a Shield Tunneling Alignment

Karst geology is common in China, and buried karst formations are widely distributed in Guangdong province. In the process of shield tunneling, the abundant water resources present in karst caverns could lead to the potential for high water ingress, and a subsequent in situ stress change-induced stratum collapse. The development and distribution of karst caverns should therefore be identified and investigated prior to shield tunnel construction. Grouting is an efficient measure to stabilize karst caverns. The total volume of karst caverns along the shield tunneling alignment, and its relationship with the required volume of grouts, should be evaluated in the preliminary design phase. Conventionally, the total volume of karst caverns is empirically estimated based on limited geological drilling hole data; however, accurate results are rarely obtained. This study investigates the hydrogeology and engineering geology of Guangzhou, the capital of Guangdong province, and determines the fractal characteristics of the karst caverns along the tunnel section of Guangzhou metro line no. 9. The karst grouting coefficients (VR) were found to vary from 0.11 in the case of inadequate drilling holes to 1.1 in the case where adequate drilling holes are provided. A grouting design guideline was furthermore developed in this study for future projects in karst areas.

Mechanics Parameter Optimization and Evaluation of Curtain Grouting Material in Deep, Water-Rich Karst Tunnels

Mud and water often gush suddenly during the construction process of deep buried karst tunnels, which may cause serious accidents and result in major economic losses. Accordingly, for tunnels buried in deep rich water districts, discovering how to effectively control water gushing and ensure the stability of surrounding rock has great influence on the safety of engineering construction. The case study in this paper simulates the water-rich section of Dou-mo tunnel from Shanghai to Kunming of China. Numerical analysis was used to simulate the construction of the curtain grouting section and to evaluate the effects of the various curtain grouting parameters. The optimal grouting parameters were selected and then evaluated by applying them to the grouting method. The results show that (1) the grouting effect is the most notable one when the thickness of the grouting circle is outside the 4 m range of the tunnel contour. (2) In the same circle, the grouting quantity of the same ring is presented as a wave form. Therefore the number of the same ring grouting holes should reduce and increase the distance between the adjacent grouting holes appropriately to reduce the number of grouting holes and speed up the grouting progress.

Study of geology and Carboniferous subcrop topography upon engineering geological mapping of Moscow territory

Abstract Carboniferous deposits in Moscow are composed of interlaying carbonate and clay-marl massifs. The roof of Carboniferous deposits occurs at a depth 5–150 m below the surface. It has been affected by several generations of river erosion. Carbonate layers consist mainly of limestones karstified to a different extent. Suffosion development in overlaying sandy-clayey and sandy horizons resulting in karst-suffosion sinkholes and surface subsidence are related to the ancient buried karst forms. The geological map of Carboniferous deposits is compiled to a scale of 1: 10 000 for the entire territory of Moscow. The map shows the geological structure at the roof of Carboniferous deposits. It also displays the spatial distribution of various stratigraphical and lithological series of Carboniferous system, the subcrop topography of the Carboniferous deposits and thalwegs of pre-Jurassic and pre-Pleistocene (pre-glacial) buried river valleys and gullies. The specifics of karst development in Carboniferous limestone massifs are studied. Karstification and fracturing distribution is analysed in connection with the ancient topography. The geological map of Carboniferous deposits is one of the principal maps for compiling the map of karst and karst-suffosion hazard and the map of engineering geological zoning of Moscow.

REAL KARST COMPONENT OF THE LANDSCAPE DEVELOPMENT IN THE SMOLENSK LAKE COUNTRY

The karst processes took part in the formation of the natural complexes in the Belorussian-Baltic region of the East-European Plain since the Devon. Role of the karst is not confined to areas of exposed forms of karst denudation and sporadic accumulation of derivative calcium carbonate. Under the quaternary cover of glacial and fl uvio-glacial deposits there are large buried karst complexes developed under the conditions similar to recent landscapes of the low latitudes. Relic karst forms, including the buried ones, look more prominent than exposed ones and have wider expansion.

Chinese karst geology and measures to prevent geohazards during shield tunnelling in karst region with caves

Karst landscapes are widely distributed in China, and buried karst is widespread in Guangdong. This study mainly focuses on buried karst or karst caves which are underground at depths of up to 50 m and can significantly affect engineering construction activity. The karst caves, which are widely distributed in Guangdong Province, have the following features: high fissure water content, high rock permeability, prone to collapse, variable shapes, and irregular distribution. When a shield tunnel is constructed in this kind of environment, hazards, such as sink holes, the ingress of water or stones, and damage to the constructed tunnels may occur. Thus, karst caves need to be treated before tunnel construction. This paper presents a procedure for karst cave treatment to mitigate possible hazards during shield tunnelling in karst regions. The construction procedure includes field investigation, judgment, treatment, and effectiveness check. The treatment criteria, grouting material, construction steps, and effectiveness check for the karst cave treatment are introduced in detail. A field test on shield tunnelling excavation was conducted using the karst cave treatment in the karst region of Guangzhou, China. Field investigations include testing the unconfined compressive strength (UCS) of borehole samples of grouting materials, standard penetration test (SPT), core recovery (CR), ground surface settlement and building settlement. All of the UCS values of the borehole samples are greater than 0.2 MPa, the modified SPT values are more than ten, and the CR values are greater than 90 %. The measured values of ground surface settlement and building settlement are all within the allowable ranges. All of the test results demonstrate the applicability of this treatment process in karst regions.

Introduction to special section: Karst

The term karst derives from the name of an area of Slovenia and generally refers to the result of weathering or dissolution of limestone, dolomite, anhydrite, or other soluble rocks. Karst and ancient, buried karst (paleokarst) affects hydrocarbon exploration and production, hydrogeology, and near-