Karst Collapse Research Articles

Characteristics, influencing factors, and prediction of fractures in weathered crust karst reservoirs: A case study of the Ordovician Majiagou Formation in the Daniudi Gas Field, Ordos Basin, China

The study of fractures in karst reservoirs is a hot spot in the field of geosciences. In this article, we conducted a systematic study on the characteristics, influencing factors, and prediction methods of karst reservoir fractures of the Ordovician Majiagou Formation in the Daniudi Gas Field, China. Both weathering and tectonic fractures are mainly developed in the Ma 5 member of the Majiagou Formation. The former is categorized into surface weathering, steep wall tensile and karst collapse fractures, and the latter is made of tensile and shear fractures. The palaeo‐temperatures of the fracture filling inclusions range from 90 to 140°C, peaking at 111–120°C, which are derived from oxygen isotopes of −7.9 to −17.5‰, with average −14.1‰ from the same filling inclusions. Integrations of regional tectonic activities, inclusion tests, and stable isotope analysis recognizes four formation periods of fractures since the Caledonian. The factors controlling the development degree of the karst reservoir fractures include lithology, petrophysical properties, rock layer thickness, structural deformation strength, and karst palaeomorphology. The buckling thin plate simulation results show a good positive correlation between the maximum principal stress and tensile fracture density. The same positive correlation is also observed between the shear stress and fracture density. The ancient karst landforms have strongly affected the distribution of weathering fractures. Surficial weathering fractures occur typically in the weathered residual monadnocks, while steep wall tension ruptures in areas near geomorphic steep ridges, and karst collapse fractures in karst residual monadnocks and karst pit areas.

Risk Control of Karst Collapse----A Case Study of Linyi City

Karst collapse is a common geological disaster, and groundwater level is the main influencing factor of karst collapse in Linyi City. This article uses the established groundwater flow model to propose a method for controlling karst collapse: to make the karst water level not lower than the control level. Based on this method, three different groundwater extraction schemes were designed in the study area, and calculation analysis was performed in conjunction with water level control points. The results show that in the future, the amount of karst water exploitation in the urban area of Linyi City will be reduced by 11.65×104m3/d compared with the current situation, The reduced groundwater volume will be solved by the surface water project of the Andi reservoir in Linyi City, which can control the danger of karst collapse.

Near-surface site investigation and imaging of karst cave using comprehensive geophysical and laser scanning: a case study in Shandong, China

The karst development of Jiao Dong Peninsula in Shandong Province has formed a unique karst landform, and has become one of the typical karst areas in the north of China. Karst collapse occurred during the construction of high-speed railways and caused many environmental problems. To reveal the development situation of karst area in Shandong, the conventional surface geophysical techniques were used for karst exploration and location of key area. And the results of drilling verification were in good agreement with the results of geophysical exploration. At the same time, the new technology in the field of surveying and mapping 3D laser scanning technology, is cited in the engineering geophysical exploration, and the key issue is the shape and size of the karst. It makes up for the shortcomings of traditional geophysical exploration technology that can only be qualitative and cannot be quantitatively analyzed. It realizes the transformation of karst exploration from regional detection to single cave exploration, and better implements the concept of information construction. It has contributed to the smooth progress of the project and environmental protection.

Damage Characteristics and Mechanism of a 2010 Disastrous Groundwater Inrush Occurred at the Luotuoshan Coalmine in Wuhai, Inner Mongolia, China

On 1 March 2010, a disastrous groundwater inrush occurred at the Luotuoshan coalmine in Wuhai (Inner Mongolia, China). Great effort was taken during the post-accident rescue. However, triggered by a large amount of groundwater rushed in from the Ordovician limestone aquifer underlying the No.16 coal seam through the fractured sandy claystone and the karst collapse column, it caused great damage, including 32 deaths and direct economic losses of over 48 million yuan. The groundwater inrush originated from the floor heave in the air return gallery of the No.16 coal seam. The peak inflow rate was 60,036 m3/h. The gallery excavation under conditions caused by the incompletely recognized hydrogeological environment induced the accident. The unidentified spatial distribution of the karst collapse column triggered the accident directly. The high-pressure groundwater accumulated in the collapse column and the gallery excavation, which caused the redistribution of the in situ stress, contributing to progressive fractures in the floor of the No. 16 coal seam. Eventually, an intensive water-conductive passage consisting of the fractured floor and the karst collapse column formed. Administratively/technically, that mandatory regulations on gallery excavation were not carried out which contributed the accident. Moreover, the poor awareness about groundwater inrush recognition and quick remediation also contoirbuted to the disastrous extent of the accident.

Groundwater Hydrogeochemical Processes and the Connectivity of Multilayer Aquifers in a Coal Mine with Karst Collapse Columns

Understanding groundwater hydrogeochemical processes and the connectivity of multilayer aquifers in a coal mine with karst collapse columns (KCCs) is very important for mine safety and groundwater resource management. In this study, 52 groundwater samples from the main aquifers in the Xieqiao coal mine (Anhui Province, China) were analyzed using hydrochemical, multivariate statistical methods, and stable isotope analyses. In the Permian aquifer, the main hydrogeochemical processes are halite and silicate dissolution and sulfate reduction, followed by cation exchange, while in the Carboniferous and Ordovician aquifers, the main hydrogeochemical processes are carbonate, gypsum, and halite dissolution, followed by cation exchange. This causes the hydrochemical characteristics of these two aquifers to be similar. The Permian aquifer contains less SO42−, more HCO3− concentration, and a concentration ratio of SO42− to HCO3− less than 0.25 due to sulfate reduction, which allows the Permian aquifer to be distinguished easily from the other two. Both hierarchical cluster and stable isotope analysis show that water samples from both aquifers appear to have been mixed via the KCCs, which may serve as a potential channel for groundwater inrush into the coal mine. These results may assist in accurately predicting potential water inrush sources in this coal mine as well as in other mines.

Seismic attribute selection for machine-learning-based facies analysis

Interpreters face two main challenges in seismic facies analysis. The first challenge is to define, or “label,” the facies of interest. The second challenge is to select a suite of attributes that can differentiate a target facies from the background reflectivity. Our key objective is to determine which seismic attributes can best differentiate one class of chaotic seismic facies from another using modern machine-learning technology. Although simple 1D histograms provide a list of candidate attributes, they do not provide insight into the optimum number or combination of attributes. To address this limitation, we have conducted an exhaustive search whereby we represent the target and background training facies by high-dimensional Gaussian mixture models (GMMs) for each potential attribute combination. The first step is to choose candidate attributes that may be able to differentiate chaotic mass-transport deposits and salt diapirs from the more conformal, coherent background reflectors. The second step is to draw polygons around the target and background facies to provide the labeled data to be represented by GMMs. Maximizing the distance between all GMM facies pairs provides the optimum number and combination of attributes. We use generative topographic mapping to represent the high-dimensional attribute data by a lower dimensional 2D manifold. Each labeled facies provides a probability density function on the manifold that can be compared to the probability density function of each voxel, providing the likelihood that a given voxel is a member of each of the facies. Our first example maps chaotic seismic facies associated with the development of salt diapirs and minibasins. Our second example successfully delineates karst collapse underlying a shale resource play from north Texas.

范各庄井田岩溶陷落柱特征及成因机理研究

范各庄井田岩溶陷落柱特征及成因机理研究

Seepage Property of Crushed Mudstone Rock in Collapse Column

The karst collapse column composed of crushed rocks and fine argillaceous or clay particles is easy to form the fissure channels between the coal seam working face and the confined limestone aquifer under mining and causes water inrush disasters with the loss of underground water resource, economic losses, and casualties. It is of great necessity to understand the seepage properties of crushed rock in karst collapse column for the prevention of water inrush and the protection of underground water resource. A self‐developed seepage test system is used in this paper to conduct laboratory experiments on seepage properties of crushed mudstone specimens. The effects of the particle size distribution, the porosity (specimen height), and the hydraulic pressure on the water flow velocity and the permeability of crushed specimen are analyzed. The results indicate that the permeability of specimen increases with the particle size, porosity, and hydraulic pressure. It can be known from the comparative experiments of progressive hydraulic pressure on one specimen and variable hydraulic pressure on different specimens with constant particle size and porosity that more fine particles leak out from the specimen with repeated application of hydraulic pressure on one specimen. Therefore, the permeability of one specimen is bigger than that of different specimens under the condition of same hydraulic pressure.

Determining the Seepage Stability of Fractured Coal Rock in the Karst Collapse Pillar

The karst collapse pillar (KCP) is a common geological structure in the coal mines of northern China. KCPs contain many fractured coal rocks, which can easily migrate under the action of high‐pressure water. The destruction or instability of the cementation structure between the rocks can directly induce coalmine water‐inrush accidents. To study the seepage stability of cemented and fractured coal rock under triaxial pressures, a self‐designed triaxial seepage testing system was used and the permeability k and non‐Darcy factor β of the cemented and fractured coal rock were tested. Furthermore, the 1D non‐Darcy seepage equations were used to calculate the evolution criteria of the seepage loss stability. The results show the following: (1) The cemented structure in the KCP under the triaxial pressures can be easily destroyed. The damaged coal and rock body mainly exists in bulk form, and the permeability depends mainly on the effective stress of the particles. (2) The seepage process in the KCP structure is a combination of pore flow, fracture flow, and pipe flow, and the transition of the seepage state is closely related to the change in the magnitude of β. (3) Under the long‐term effect of confined underground water, the migration of small fractured particles in the KCP will increase the structural porosity. If the parameter βk2 reaches the threshold value, the seepage system will evolve into a pipeline flow state, eventually causing a water‐inrush accident.

An overview of surface water hazards in China coal mines and disaster-causing mechanism

Surface water is not only an important water supply to mining region but also the cause of severe water burst accidents in coal mines. In China, surface water is categorized as a major water hazard that has inflicted serious property losses and casualties not seen in the rest of the world. Based on the analysis of the distribution and characteristics of 47 major mining accidents caused by surface water in China coal mines, this paper summarizes the disaster-causing mechanism of surface water hazards in coal mines. Main research results are as follows: (1) coal mine accidents caused by surface water mainly occur in spring and summer with large rainfall; particularly in summer when 70% of such coal mine accidents took place, (2) natural water channels include valleys and gullies, surface tension fissures, water-conducting faults, and karst collapse caves in mountain areas; (3) artificial water channels include underground structures in abandoned mines (such as shafts and roadways), water-conducting cracks resulted from mining activities, and illegal mining of water and sand-resistant coal (rock) pillars. Through the analysis of engineering cases, this paper puts forward prevention and control measures of surface water hazards of coal mines. The results of this paper can be of reference to other countries tasked to treat surface water hazard while protecting surface water resources.

Modeling Rock Fracture Propagation and Water Inrush Mechanisms in Underground Coal Mine

Water inrush in underground mines is a major safety threat for mining personnel, and it can also cause major damage to mining equipment and result in severe production losses. Water inrush can be attributed to the coalescence of rock fractures and the formation of water channel in rock mass due to the interaction of fractures, hydraulic flow, and stress field. Hence, predicting the fracturing process is the key for investigating the water inrush mechanisms for safe mining. A new coupling method is designed in FRACOD to investigate the mechanisms of water inrush disaster (known as “Luotuoshan accident”) which occurred in China in 2010 in which 32 people died. In order to investigate the evolution processes and mechanisms of water inrush accident in Luotuoshan coal mine, this study applies the recently developed fracture-hydraulic (F-H) flow coupling function to FRACOD and focuses on the rock fracturing processes in a karst collapse column which is a geologically altered zone linking several rock strata vertically formed by the long-term dissolution of the flowing groundwater. The numerical simulation of water inrush is conducted based on the actual geological conditions of Luotuoshan mining area, and various materials with actual geological characteristics were used to simulate the rocks surrounding the coal seam. The influences of several key factors, such as in situ stresses, fractures on the formation, and development of water inrush channels, are investigated. The results indicate that the water inrush source is the Ordovician limestone aquifer, which is connected by the karst collapse column to No. 16 coal seam; the fracturing zone that led to a water inrush occurs in front of the roadway excavation face where new fractures coalesced with the main fractured zone in the karst collapse column.

Review of the advanced monitoring technology of groundwater–air pressure (enclosed potentiometric) for karst collapse studies

This paper presents an overview of the groundwater–air pressure monitoring technology for karst sinkholes. Karst collapses often occurred rapidly without prior warning. The early warning for potential karst collapses has been one of the most challenging problems around the world. In fact, many karst collapses are kind of sudden geohazards and mainly induced by abrupt changes of hydrodynamic conditions within karst conduit systems. Traditionally, only groundwater level monitoring was applied to monitoring the karst collapses, which did not reflect the hydrodynamic conditions within karst conduit systems. The monitoring technology of groundwater–air pressure was proposed by the Institute of Karst Geology, China in 1998 to study the formation mechanisms, monitoring and forecast of karst collapses. This technology has been improved in the past 20 years and applied to collapse risk assessment, triggering factor evaluation, and controlling drawdown of the groundwater levels during underground civil engineering works at 11 study sites. This advanced technology is characterized by improved borehole drilling, special sealing technique of borehole orifice, and high-frequency data logging. The recommended logging interval is at least 5–20 min to capture the transient changes of groundwater–air pressure within karst conduit systems. The pressure transducers used in this technique are retrievable and can be reused or recycled.

Mechanism of Shallow Soil Cave–Type Karst Collapse Induced by Water Inrush in Underground Engineering Construction

Water inrush disasters are the main cause of karst collapse. In this study, a physical model test was conducted to investigate the mechanism of karst collapse. The formation, expansion, and variation of a soil cave induced by water inrush were studied, including the expansion pattern of soil cavities, the voids between the bottom of the hole, cavity disengagement, wall collapse, and soil cavity expansion. The variation of shear stress in soil under the dynamic change in groundwater level was simulated and analyzed using a finite-difference method. When the groundwater level falls, the expansion and collapse of a soil cave are caused by the concentrated action of shear stress on the arch foot of the soil cave. Results of this study deepen the understanding of karst collapse induced by water inrush in underground engineering and provide guidance for the prevention and control of karst ground collapse.

Collapse dolines susceptibility mapping using frequency ratio method and GIS in Sahel-Doukkala, Morocco

This study aims firstly, to build the collapse dolines susceptibility maps in the Sahel-Doukkala area of central Morocco, using the modified frequency ratio (FR) method. Secondly, to determine the relationships between factors responsible for collapse doline occurrence and their spatial distribution. To accomplish these objectives, a total of 58 collapses were identified in the field and integrated into the Geographic Information System (GIS) database. A collapse inventory map was prepared from the locations of the identified collapses. This inventory was subdivided randomly in two equal groups, one for FR model development and one for model validation. In this study, six parameters that control the development of karstic collapse dolines were selected. These factors are slope, appearance, elevation, geological nature of the terrain, distance from the underground drainage axis and, distance from faults. The combination of the chosen factors allowed the creation of Collapse Dolines susceptibility map of the study area. The validity of the obtained model was verified using the Area Under the Curve (AUC) highlighting a high prediction degree. The FR value obtained for Collapse dolines susceptibility were comprised between 2.5 and 25.8, these levels have been divided into five susceptibility classes: very low, low, moderate, high and very high. Overall, the obtained results show that the study area was dominated by very low and low or moderate susceptibility classes. However, the Sahel and the NW part of the study area was characterised by a concentration of high and very high classes. Moreover, the AUC value of 90% was obtained, which indicates the reliability of the susceptibility map for the karst collapse. This study’s findings can help decision-makers in land use planning and preventing areas of potential collapse.

Investigation on failure behavior of collapse column in China's coal mine based on discontinuous deformation numerical method.

Karst collapse column is a serious geological disaster in China’s coal mines. There are various karst collapse columns in coal mine areas, such as Huainan, Huaibei, Xingtai, Lu’an. And they have seriously affected mining safety and geological environment. The present research is focused on analyzing subsidence mechanism and dynamic collapse process. Based on mechanical analysis of thin plate theory, a detailed model of collapse column slipping and bending fracture is constructed to gather the critical conditions of the collapse column roof. The sensitivity parameters analysis shows that both the radius and roof thickness of cave have a great influence on the sliding instability and bending fracture. Meanwhile, the buried depth also affects bending failure. The discontinuous deformation analysis (DDA) method is used to simulate and analyze the collapse process. The numerical results indicate that the stability of inverted funnel collapse column is dominated by the bending stress of roof strata. The movement of columnar collapse column is mainly caused by sliding instability. However, the funnel collapse column is relatively stable, and does not change in the same condition. The displacement field analysis shows that the collapse range of inverted funnel collapse column is obviously larger than that of columnar collapse column, in which its maximum displacement is approximately 1.5 times that of the columnar collapse column. There is no large area collapse on the upper part of the funnel collapse column, and the block system is relatively stable. The principal stress field analysis proves the above results.

Study on risk assessment method of Karst collapse—Taking the Karst collapse in Linyi urban areas as an example

Karst collapse is one of main important geological disasters in Linyi city of Shandong Province. In this article, risk assessment of present and forecast situation of karst collapse have been done by the method of fuzzy comprehensive evaluation based on level analysis at the first time. The hazardous assessment, the vulnerability and the expected loss have been assessed, and then the risk assessment map of karst collapse at present is obtained and prevention and control work of karst collapse is expected to develop. It puts up availability exploration on prevention of the same geohazards, and provides a reference pattern.

On the Nature of Seismic Phenomena in Platform Areas: A Case Study of Belarus

When compiling historical earthquake catalogs, the main problem is to validate the reliability of information to exclude false reports. Detailed descriptions from reliable sources contribute to more precise intensity assessment. Additionally, in low-active territories, very important problem of identifying the nature of the event has to be solved. Earthquakes generated by tectonic or other activity (such as landslides or karst collapses) may have similar descriptions. Recently, cryoseisms have also been considered a possible source of the ground surface shaking. Seismic events in Belarus reported based on noninstrumental data and having fundamentally different interpretations in different publications are studied. The analysis is based on original information from primary sources. It is shown that two out of four seismic events are cryoseisms, while the other two are not related to the territory of Belorussia.

Effect of particle erosion on mining-induced water inrush hazard of karst collapse pillar

As a typical disaster-causing geological structure, karst collapse pillar (KCP) is widely distributed in coalfields of northern China. The interior of KCP is filled with loose and weakly cemented rock masses. Fine particles can be eroded under the hydraulic pressure and the disturbance of the coal mining operation. Then, water inrush pathway can be formed easily, resulting in water inrush hazard. The release of untreated coal mine water can pollute the environment and waste the limited water resource in China. To investigate the particle erosion effect on the water inrush mechanism of KCP, FLAC3D numerical investigations were conducted to simulate the water flow process of KCP in the mining floor during the coal seam excavation, according to the stress-seepage coupling model with the consideration of the particle erosion. Besides, the evolution of shear stress field, seepage field, and plastic zone along was obtained as working plane advances. Meanwhile, the influence of the thickness of a waterproof rock floor and the hydraulic pressure of aquifer on the formation of water inrush pathway was analyzed. Numerical results indicated that: (1) Shear failure of the KCP near the side of the working plane occurs under the effect of mining excavation; then, the KCP connects with the damage area around the working plane; finally, the water inrush pathway is formed. (2) Water inrush disaster will not occur immediately when the KCP is connected with the damaged area around the working plane; it only occurs when the KCP is completely exposed in the mining. (3) With the mining advances, the thinner the waterproof rock floor and the greater the hydraulic pressure of the aquifer, the easier the groundwater can lead up, and the KCP tends to be damaged with the formation of water inrush pathway.

A Targeted Grouting and Water Blocking Method Based on Hydrological Tracer Testing and Its Engineering Applications

Hydrological tracer testing is an effective way to determine the law of recharge and the transport of groundwater. In karst collapse mine water treatment, the hydrological tracing test can determine information such as the runoff velocity and the pattern of underground runoff, so that targeted grouting becomes possible. In this paper, NaCl was used as a tracer, and the content of the tracer was determined by the chloride ion selective electrode method. The NaCl concentration–time curve was plotted, and we obtained a tracer test method that can determine the runoff of the karst quantificationally. The method can quantificationally obtain the groundwater transport velocity, runoff pattern, and connectivity. This combination of grouting rate, grouting pressure, and setting time realized the localized targeted grouting and achieved a significant water damage control effect.

Research on karst collapse pillar imaging of water-rich area in coal mine

Research on karst collapse pillar imaging of water-rich area in coal mine