Karst Collapse Research Articles

Study on field and numerical analysis of karst collapse as railway hazard

The vulnerability of karst ecosystems and the weak mechanical performance of caves pose hidden risks in railways, leading to increased karst collapses. To analyse karst collapse as a railway hazard, the Beijing–Guangzhou railway line in China was selected to identify karst features, using the multi-source frequency domain method because of its operational advantages. Abaqus was also used to numerically analyse the factors (dynamic loading, groundwater fluctuations, over-burden thickness) affecting the collapse mechanism. The study reveals diverse stratigraphy, transitioning from a Quaternary layer to stable rock formations. A notable finding is that the presence of a karst cavity in the railway embankment significantly increases the vertical dynamic displacements, particularly within the soil layer, by 72%, highlighting the significant impact of karst sections on soil dynamics. The study also reveals that due to the groundwater table fluctuations from the subsoil surface to the subgrade surface, the maximum displacement increases by 73% in the subgrade section of the railway embankment. The authors consider soil overburden thickness to validate confirmation of reliability through field data and theoretical study. The findings offer crucial insights for managing karst hazards, enhancing railway safety and ensuring durable infrastructure in challenging geological conditions.

Inventory and geomorphological analysis of karstic collapse dolines in Sahel-Doukkala (Morocco)

Inventory and geomorphological analysis of karstic collapse dolines in Sahel-Doukkala (Morocco)

Risk Assessment of Multi-Hazards in Hangzhou: A Socioeconomic and Risk Mapping Approach Using the CatBoost-SHAP Model

As the global push for sustainable urban development progresses, this study, set against the backdrop of Hangzhou City, one of China’s megacities, addressed the conflict between urban expansion and the occurrence of urban geological hazards. Focusing on the predominant geological hazards troubling Hangzhou—urban road collapse, land subsidence, and karst collapse—we introduced a Categorical Boosting-SHapley Additive exPlanations (CatBoost-SHAP) model. This model not only demonstrates strong performance in predicting the selected typical urban hazards, with area under the curve (AUC) values reaching 0.92, 0.92, and 0.94, respectively, but also, through the incorporation of the explainable model SHAP, visually presents the prediction process, the interrelations between evaluation factors, and the weight of each factor. Additionally, the study undertook a multi-hazard evaluation, producing a susceptibility zoning map for multiple hazards, while performing tailored analysis by integrating economic and population density factors of Hangzhou. This research enables urban decision makers to transcend the “black box” limitations of machine learning, facilitating informed decision making through strategic resource allocation and scheduling based on economic and demographic factors of the study area. This approach holds the potential to offer valuable insights for the sustainable development of cities worldwide.

Numerical research on disastrous mechanism of seepage instability of karst collapse column considering variable mass effect

In order to reveal the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect, a variable mass fluid–solid coupling mechanical model of water inrush is established, by considering the random distribution characteristics of a collapse column. Taking Qianjin coal mine as the research background, based on the Weibull distribution theory, the heterogeneous distribution characteristics of rock mass is described, and COMSOL Multiphysics numerical simulation software is employed to simulate the seepage characteristics and inrush water changes in collapse columns under different conditions of homogeneity, water pressure, and initial porosity. The research results show that the greater the homogeneity is, the more water conduction channels are formed, and the porosity increases accordingly, when considering the influence of different homogeneity on the seepage characteristics of broken rock mass, which eventually leads to water inrush accidents and a sharp increase in water inflow. Besides, when studying the seepage evolution law of different water pressures on a broken rock mass, an elevation of water pressure dramatically increases the porosity and seepage rate of the water. Over time, the broken rock particles gradually migrate and the fine particles are transported and eroded by the water flow, resulting in changes in the seepage characteristics and the formation of potential water diversion channels. Finally, when taking into account the effect of different initial porosity on the fractured rock mass seepage characteristics, the greater the original porosity is, the higher the seepage velocity is, and the particle migration increases the permeability. This leads to a more pronounced conductive water passage formation, which reveals the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect.

Characteristics and an accumulation model of a bauxite gas reservoir in the southwestern Ordos Basin

A significant breakthrough has been made in natural gas exploration in the aluminum (Al)-bearing rock series of the Permo-Carboniferous System in the Longdong (LD) region of the Ordos Basin, and this has sparked great interest in studying bauxite reservoirs within the oil and gas industry. Although recent research has focused on the depositional environment and reservoir well logging identification, there is still a lack of understanding regarding the characteristics, formation mechanism, and accumulation model of bauxite gas reservoirs. This knowledge gap hinders the rapid exploration of this new type of gas reservoir. Based on core observations, major and trace element analyses, whole-rock X-ray diffraction, thin section examination, and scanning electron microscopy (SEM), the pore types, physical properties, reservoir formation mechanisms and accumulation models of the bauxite reservoirs were determined. The results are as follows: (1) The main mineral components of the Al-bearing rock series are diaspore and clay minerals. The bauxite that formed by the weathering, leaching, sedimentation and diagenesis of the parent rock has a high diaspore content and secondary dissolution pores. (2) Bauxite with a high aluminum content has a high porosity and permeability and can be used as a potential natural gas reservoir, and the reservoir space is mainly composed of dissolution pores. There is a strong correlation between the aluminum content and porosity, indicating that high Al2O3 or diaspore contents can serve as reliable indicators for an effective reservoir. (3) The overlying coal-bearing source rocks and the underlying karst are key to bauxite reservoir formation. The concurrent presence longitudinally of coal, bauxite, fractures, and karst collapse offers valuable guidance for the exploration of natural gas in bauxite within the Ordos Basin. These findings have significant implications for natural gas exploration in Al-bearing rocks in North China and other regions.

Study on the Hydrochemical Characteristics and Evolution Law of Taiyuan Formation Limestone Water under the Influence of Grouting with Fly Ash Cement: A Case Study in Gubei Coal Mine of Huainan, China

The hydrogeological conditions of Huainan Coalfield are complex. The Taiyuan formation limestone water (Taihui water) in this area is a direct threat to the water source of the 1# coal mining floor. In order to prevent and control water disasters, Gubei Coal Mine adopted ground high-pressure grouting with fly ash cement to block the hydraulic connection between the Taiyuan formation limestone aquifer and the Ordovician limestone aquifer. However, the injected slurry will destroy the original hydrochemical balance of Taihui water and change its hydrochemical characteristics. Taking the influence area of the 2# karst collapse column in the Beiyi 1# coal mining area of Gubei Coal Mine as an example, a total of 25 Taihui water samples were collected. The hydrochemical characteristics and evolution law of Taihui water before and after grouting are studied via the multivariate statistical method. The research methods include constant index statistics, Piper diagram, correlation analysis, ion combination ratio, and saturation index analysis. The results show that after grouting, the concentrations of Na+ + K+, Ca2+, Mg2+, and Cl− in Taihui water decrease, while the concentrations of SO42− and HCO3− increase. The average values of PH and TDS become larger. The hydrochemical types of Taihui water are more concentrated, mainly HCO3-Na and Cl-Na. The correlations between conventional indicators decrease. According to the analysis of ion combination ratio, dissolution, cation exchange, and pyrite oxidation mainly occur in Taihui water, and these effects are enhanced after grouting. The saturation index results show that after grouting, the saturation index of dolomite, calcite, and gypsum is significantly reduced, and the saturation index of rock salt is slightly increased. The conclusion of this study is that the hydrochemical characteristics of Taihui water are greatly affected by fly ash cement. Moreover, because fly ash cement contains a lower calcium oxide content than ordinary Portland cement, the effect of fly ash cement on the ion concentration of Taihui water and the resulting hydrogeochemical effect are significantly different. Therefore, in the treatment of mine water disasters, the hydrogeochemical evolution law affected by fly ash cement grouting should be identified.

Exploration and prediction of high pressure dynamic water hidden collapse column in coal mines

Hidden collapse column associated with high pressure dynamic water is a main cause of major water inrush accidents in North China type coal fields. Taking the structural abnormality area discovered in 11603 working face of Daizhuang Coal Mine as an example, underground three-dimensional high-density electrical method, advanced exploration of underground drilling and curtain grouting were used to detect the existence of collapse column, and analyzed the water conductivity of collapse columns based on the hydraulic connection analysis of the 13th limestone and Ordovician limestone aquifers. Finally, it is determined that this abnormal area is a strong water filling collapse column originating from the upper Ordovician strata runoff zone (inferred to be within a range of 30 to 100 m below the Ordovician limestone top interface), developed to a height of 12th limestone. Based on the fact that the water yield and water pressure of underground directional drilling, the grouting pressure of curtain grouting, and the amount of cement injected are external quantitative factors that reflect the existence of hidden karst collapse columns during the process of detecting hidden karst collapse columns, and in combination with the feature that deep learning can fully independently learn abstract knowledge expression, a prediction model based on convolutional neural networks is constructed. According to the established network model, it was found that among the 12 sets of actual measurement data, only one data point indicated the absence of a collapse column. The prediction accuracy reached 91.6%, which meets the practical needs.

Fractal mechanical model of variable mass seepage in karst collapse column of mine

Currently, the study of karst collapse column water inrush mechanism often ignores the effect of pore structure, and the traditional fractal seepage model ignores the effect of nonlinear seepage velocity field on model permeability. In order to solve this problem, the fractal seepage theory is combined with variable mass seepage theory, and the influence of seepage velocity field on model permeability is considered. The fractal seepage model of the third flow field of the settling column is established and improved, and the influence of different pore structure parameters and nonlinear seepage parameters on the macroscopic seepage of the settling column is analyzed.

Experimental study on the seepage mutation of natural karst collapse pillar (KCP) fillings over mass outflow.

Conduction between the unique geological formation karst collapse pillar (KCP) and the fractures caused by mining in the coal seam floor can lead to catastrophic water inrush disasters in many coalmines in Northern China. It is widely recognized that seepage mutation induced by the migration/loss of KCP fillings (highly broken rocks filling the fractured rocks) happens during occurrence of the KCP-related water inrush. However, roles of fluid path (mining-induced fracture) scale and KCP filling porosity in seepage mutation evolution remain unclear. Here, we conducted seepage tests on natural KCP fillings containing rock particles of different sizes. The filling specimens were deformed to different porosities from 14 to 26% through axial compression, and small to large fluid paths were simulated by seepage plates with distinct pore sizes from 2.5 to 12.5mm. We found that seepage mutation occurs with significant permeability enhancement by 2 orders of magnitude under a pore diameter of 12.5mm and a specimen porosity of 26%. There is a strong linear relationship between specimen permeability and Reynolds number (Re) over seepage mutation. The mutation is caused by the sudden collapse of the specimen skeleton and subsequent quick outflow of the particles. Therefore, it is inferred that the KCP-related water inrush is more likely to happen when highly porous KCP fillings are present and mining-induced fractures are well developed.

Mechanical Response Law and Parameter Influence Analysis of Karst Tunnel Dynamic Excavation

To ensure the stability of the tunnel structure, this paper simulates the excavation process of shield tunneling in karst areas, and monitors the top of the arch, the bottom of the arch and the waist of the arch within the influence of the cave. It obtains the displacement and stress change laws under the influence of the upper cave and the lower cave. Finally, the main factors causing karst collapse in tunnels are explored through orthogonal tests. The results indicate that the displacement of the surrounding rock within the influence of the cave decreases and the stress increases. When the cavity and the tunnel reach the safety limit distance, the effect of the lower cavity on the stress around the tunnel is more obvious than that of the upper cavity. The results of the orthogonal test show that when the cavity is above the tunnel, the tunnel burial depth has the greatest influence on the stability of the surrounding rock; when the cavity is below the tunnel, the cavity height has the greatest influence on the stability of the surrounding rock.

Retracted: Study on Early Warning of Karst Collapse Based on the BP Neural Network

Retracted: Study on Early Warning of Karst Collapse Based on the BP Neural Network

Characteristics and evolution of karst collapse columns in the Huainan coalfield

Karst collapse columns (KCCs) seriously affect the mining safety of deep coal seams. This study systematically summarizes and analyzes the development of KCCs, and classifies the different development stage to identify their development stages and evolutionary process in the Huainan coalfield. The evolution models for KCC development are given, combining with the exploration strata data from boreholes, the groundwater flow data of regional field, the hydrogeochemical data from the relative aquifers of KCC, and the hydrodynamic parameters. The results show that first types of KCCs are discovered in Liuzhuang and the Pansan mine, which is broken and disorganized, with a high degree of filling and cementation, and with the low permeability and velocity, and lower storage capacity. The KCCs in the Xieqiao and Zhangji mine have various morphologies and size differences. Their internal rocks are broken and semi-cemented, with a coefficient of permeability between 0.2 and 0.5 m/d and a specific discharge between 0.1 and 0.2 L/s•m. The KCCs are located in the cone of depression and are part of a sink area with moderate water-richness, where upper and lower aquifers have close hydraulic connections with mixed water quality. The internal core of the KCCs in the Gubei Mine is close to the center of the cone of depression which is highly broken and disorganized, with a high permeability, and a specific discharge more than 1.5 L/s•m. The intensity of runoff increases as its vertical depth also increases, especially the local areas are a higher hydraulic conductivity. Based on comprehensive hydrogeological characteristics, the KCCs development is divided into three stages: growing stage, declining stage, and dead stage. According to their characteristics of different stages, a series of evolutionary processes are established. Combining the sedimentological, karstological, and hydrogeological theories, some measures have been taken for prevention and control of mine water hazard in the various developmental stages. Hence, this research not only provides a new classified approach for KCC stages, but also an essential reference for a better understanding the mechanism of water inrush of KCCs in Northern China.

Sensitivity Analysis of Mechanical Parameters of Collapse Roof of Carbonate Rock Deep Buried Oilfield

Carbonate rock oilfields account for two-thirds of proven marine carbonate oilfield reserves, which are the primary way to increase future oil and gas energy reserves. Cave collapses occur during the process of oil reservoir development, seriously affecting oil production. In order to reveal the collapse failure mechanism of carbonate karst caves and predict whether the fracture cave type oil reservoir will collapse before drilling, a binary depth reduction method for determining the critical collapse depth of karst caves is proposed based on the Tahe fracture cave type oil reservoir. The sensitivity of karst cave collapses to multiple factors is analyzed, and a prediction formula for the critical collapse depth of karst caves with changes in the deformation modulus, the internal friction angle, and the cohesion is established through multiple regression analysis. By calculating and analyzing the numerical values of a large number of operating conditions under different mechanical parameters, the failure process, failure mode, and the change law of collapse depth during the Tahe oilfield destruction process were obtained. We used the established formula for predicting the collapse depth of karst caves to predict and analyze the actual distribution of karst caves in the Tahe oilfield. The calculation and analysis results showed that in the karst cave failure mode characterized by vertical shear failure, the cohesive force is the most sensitive factor affecting cave collapse, followed by the internal friction angle. The deformation modulus is hardly sensitive to the influence of the karst collapse. Through the geomechanical model test, the result verified the accuracy and reliability of the calculation results. The research results will provide necessary theoretical support for the large-scale safe extraction of deep petroleum resources, increase oil production in China, and have important theoretical significance and engineering application value.

Mechanical model and numerical simulation of the formation of karst collapse columns in the Huainan coalfield of Northern China

Karst collapse columns (KCCs) are channels where groundwater and gas gather, and they pose a great threat to mining safety. In this study, a mechanical model and criterion for the roof collapse of KCCs were established, and simulations were performed to analyze the formation mechanism of KCCs in the Huainan coalfield of Northern China. The results showed that the roof collapse and upward development of KCCs were facilitated by increasing the cave radius of the KCC basement and decreasing the groundwater pressure, single-layer thickness of the roof strata, lateral pressure coefficient of the rock mass, and cohesion and internal friction angle between fractures. The KCC formation process in the Huainan coalfield could be divided into four stages: (I) early collapse, (II) middle-early rapid collapse, (III) middle-late slow collapse, and (IV) late filling compaction. The simulation results were generally consistent with actual KCCs observed in the Huainan coalfield, which verified the theoretical analysis. The results of this study provide an important reference for the formation mechanism and evolution of KCCs in Northern China.

The Seepage Evolution Mechanism of Variable Mass of Broken Rock in Karst Collapse Column under the Influence of Mining Stress

When the collapse column of overburden is disturbed by the working face, the grain loss in the karst collapse column occurs by the dissolution and corrosion of groundwater, thereby inducing the water inrush disaster. The test samples are prepared based on the fractal theory and the Talbol grading theory, and the seepage evolution law of fractured rock in collapse column under triaxial stress is studied, by employing the triaxial seepage test equipment. Besides, the seepage mechanics model of broken rock is established and calculated in the COMSOL Multiphysics, and the water-conducting channel under mass loss condition in the collapse column is further elucidated. The research results indicate that the loss ratio of mass is inversely proportional to the Talbol power index, and grain mass loss rate increases with the decrease of the Talbol power index. During the infiltration process, the evolution of pore structure is related with grain size distribution. With the increase of the Talbol power index, the overall porosity increases. Grain loss is an internal factor in seepage loss stability. Flow speed is accelerating, and seepage pathways are communicated with each other to induce the water inrush disaster.

The Magnitude 4.5 Earthquake in the Karst Area of Guizhou on 21 August 2021: An Extremely Shallow Earthquake with a Closing-Crack Source

AbstractGuizhou province is located in a karst development area in China, and there are many moderate earthquakes, among which extremely shallow earthquakes are likely to cause damage to buildings, transportation lines, and other engineering facilities. Accurate focal depth and moment tensor can provide vital information for earthquake disaster assessment and karst collapse monitoring in karst areas. The network in the study area is relatively sparse, and the velocity structure is complex. For shallow earthquakes, the shallow velocity structure may cause certain errors in the inversion of the focal depth and mechanisms. In this study, based on the surface-wave information of regional stations, the shallow velocity structure is inverted. Based on the updated velocity model, we obtain the focal depth and mechanism of the Mw 4.5 earthquake on 21 August 2021 in Guizhou province. The results show that the optimal focal depth is about 2 km, and the moment of horizontal closing crack (M​crack) accounts for about 31% of the full moment tensor. The first motions of the P wave at the near-seismic stations of the earthquake are negative, similar to the typical collapses. However, compared to mining collapse earthquakes, the proportion of closing-crake components is relatively low. The dominant double-couple source of the earthquake is a thrust fault, which is consistent with the distribution of faults in the study area. It is speculated that a collapse in the karst area, resulting in negative P-wave polarities and about 31% closing-crake source, induced the shallow earthquake.

Characteristics and mechanisms of human‐induced earthquakes in China from the QuakeQuake database

Based on the collation and collection of a large number of data, we construct an induced earthquake database, QuakeQuake, and report a total of 193 human‐induced earthquake cases in China. 155 human‐induced earthquakes in China recorded in the global‐induced earthquake database (HiQuake) are revisited and re‐arranged by compiling the Chinese literature. The human‐induced earthquakes in QuakeQuake database are classified into three levels of reliability, strong, moderate and weak levels, based on both human‐induced processes and seismic activity. Three main categories including reservoir‐induced earthquakes, mine‐induced earthquakes and other induced earthquakes in China are sorted based on data recording and types of the induced earthquakes. Most of the induced earthquakes with strong level in QuakeQuake database are mainly minor earthquakes (3 ≤ M < 4.5). The focal depth of reservoir‐induced and mining‐induced earthquakes is within 30 and 8 km deep, respectively. The active type of source faults of the large induced earthquakes is mainly thrust type with the highest proportion. The largest observed magnitude of the induced earthquakes (MMAX) correlates positively with the injection/extraction volume, reservoir dam heights, reservoir capacity and lithology of the reservoir area. Nine volume intervals corresponding to each induced earthquake type are figured out. Based on the analysis of the mechanisms of human‐induced earthquakes in China, the main mechanisms of surface mass loading are karst collapse or gas explosion, pore water pressure effect and gravity energy release. Underground material extraction is mainly induced by the compaction of different reservoirs. Two injection types of underground material are gas injection and water injection. Gas injection is related to continuous stress loading and unloading. Two induction mechanisms of water injection are the increase of fault pore pressure and the change of fault load condition.

The impact of various geological factors on the real estate valuation using AHP analysis: case studies from Turkey.

Turkey's diverse geology causes natural disasters that kill and damage towns every year. Population growth in unstable areas without geological variables in value studies endangers people and real estate. This study examines how geological factors affect house values, which are often overlooked in applications. The analytical hierarchy process (AHP) was used to analyze conventional parameters, geological factors, and priorities for three provinces in Turkey with unique geological properties in surface water, groundwater, active faults, and karstic collapse. The AHP analysis was performed in the Ankara-Cankaya district (Ilkbahar quarter), Bolu-Gerede district, and Konya-Karapinar district, test locations with unique geological properties in terms of surface water, groundwater, active faults, and karstic collapse in various regions of Turkey. Statistical software analyzed the test location survey data. The results show that surface water, groundwater, active faults, and karstic collapse all affect real estate value. The findings suggest that house valuation requires multidisciplinary building site investigations with appropriate methods. This reduces the risk of making unreliable decisions and eliminates uncertainties, resulting in reliable results. The geological factors that determine a house's value are crucial to reducing disaster-related deaths and property damage.

Karst collapse and gypsum-filled veins in Eocene outcrops, Dammam Dome, Saudi Arabia: Causes and implications

• Differential weathering of Dammam Dome through uplift and erosion. • Factors affecting Dammam Dome geomorphology. • Gypsum-filled veins on the Dammam Dome due to karst collapse. • Results from this study can be related with water and hydrocarbon reservoirs. A recent road cut through Dammam Formation outcrop on the Dammam Dome in Dhahran, Saudi Arabia exposed an array of open fractures and gypsum-filled veins. The widespread array of fractures in the road cut was mostly contained within Saila Shale member and consisted of horizontal, vertical, and oblique extensional fractures, most were filled with gypsum. The gypsum veins are of varying thickness with the largest exceeding 2.5 inches. Vertical gypsum veins, similar to those encountered at the road cut, were found in adjacent areas. Thin layer of gypsum (about 1 inch) was also observed in the Rus Formation. The open fractures, in the Saila and Midra Shales members, were devoid of gypsum fill. Most of the open vertical and horizontal fractures were interpreted to be recent with indications of triggered by the excavation work. The open fractures and filled veins cover a stretch of about 250 ft. across the road cut that also exposed what was interpreted as a local karst collapse. Horizontally-layered and continuous rocks overlying the collapse indicated that it was a paleo structure. The causal mechanism for fracture formation and subsequent fill was associated with deformations accompanying post-karst collapse. Here, natural fracturing and fluid transport were not synchronous events. Insights from this interpretation offered an explanation for widespread surface structures with major and subtle morphologies on the Dammam Dome. These insights also highlighted the significance of collapse in the modification of the Dammam Dome over a geological timescale. The unstable nature of gypsum, prevalent in Dammam Formation in the Dammam Dome, has potential implications for integrity of anthropogenic structures such as roads and building foundations.

Model Test Analysis of Groundwater Level Fluctuations on Karst Cover Deformation Taking the Monolithic Structure of Guilin as an Example

Engineering practice and real-life cases show that the geological conditions of the Guilin overlying karst site are complex. In particular, the groundwater, which drives the accelerated formation of soil cavities, and the thickness of the overlying soil layer, which affects the speed of the groundwater subsidence process. Therefore, this paper is based on a physical model to evaluate the effects of groundwater level changes caused by different factors on the deformation of karst cover. The model tests are simulated for different cover thicknesses (6 cm, 9 cm, 12 cm, 15 cm, 18 cm) under rainfall and other recharge, cavity supply, and drainage conditions at the same density (1.40 g/cm3) and initial water content (30%), respectively. The results show that with the increase of rainfall and other recharge time, the basic change trend of different cover thicknesses is that the infiltration curve changes faster at the beginning and slows down at the end, but the thicker the cover, the slower the overall deformation; at a certain rate of cavity recharge and drainage, the thicker the cover, the smaller the deformation caused by the fluctuation of groundwater level. The cavity recharge makes the cover displacement obvious, in the order of 0.304 cm, 0.173 cm, 0.118 cm, 0.068 cm, and 0.056 cm. After the formation of the cavity, the rainfall, other recharge, and the cavity supply and drainage accelerate the destruction and deformation of the soil body and the upward development of the cavity. The research results provide theoretical support for the subsequent prevention and control of karst collapse in covered karst areas, and have certain practical engineering significance.