Karst Development Research Articles

Effects of Thalassinoides ichnofabrics on the petrophysical properties of the Lower Cretaceous Lower Glen Rose Limestone, Middle Trinity Aquifer, Northern Bexar County, Texas

The combined Edwards and Trinity aquifer system is the primary source of freshwater for the rapidly growing San Antonio and Austin metropolitan areas. The karstic Lower Cretaceous (Aptian–Albian) Lower Glen Rose Limestone (GRL) contains the middle Trinity aquifer and has been subdivided into six hydrostratigraphic units (HSUs) with distinct hydrologic characteristics. These HSUs were first identified in the subsurface via core examination at the Camp Stanley Storage Activity (CSSA) in northern Bexar County, Texas and were then correlated to associated gamma-ray and resistivity logs. The Trinity aquifer system is a telogenetic karst and fluid flow is directed primarily through solution-enhanced faults, fractures, and pervasive Thalassinoides networks because matrix porosity of both transmissive and confining HSUs is very low. Meteoric water infiltrates the Trinity aquifer through vertically-oriented faults and likely moves laterally through biogenic pores. Two 7.62cm diameter GRL cores and well logs from monitoring wells CS-MW9-CC and CS-MW5-LGR recovered from the CSSA were used to characterize the effect such large-scale Thalassinoides networks have on the petrophysical properties (resistivity and natural gamma-ray) of four HSUs (Honey Creek, Rust, Doeppenschmidt, and Twin Sisters HSUs). Resistivity logs show that resistance values >300Ω-m correlate with well-developed biogenic porosity and values of 650Ω-m are associated with solution enhancement of the Thalassinoides networks. These high resistivity zones are cyclical and are identified in muddy confining units, even when no changes in lithology or karstic development are identified. Pervasive Thalassinoides networks act as starting points for wide spread dissolution and lead to advanced karst development in transmissive HSUs. Natural gamma-ray logs do not reflect hydrologic characteristics directly, but are inversely correlated to resistivity logs and display m-scale cyclicity. Resistivity logs suggest that Thalassinoides networks are interconnected throughout strata within the GRL and when coupled with natural gamma-logs, the lateral distribution of these networks within HSUs can be correlated. Identifying such fluid pathways is of particular importance for wells not located in proximity to major faults and karstic features.

Geomorphology of karst features in the northeast of Khuzestan, Iran

Zagros mountain range (ZMR) contains the most karstic carbonate formations in Iran. Because of the broad expansion of folded and fractured carbonate rocks, well-developed karstic features occur in the southwest of ZMR. The study area, which occupied 794 km2, is located in the ZMR of Khuzestan province and mostly is covered with Asmari Formation. In the study area, the most important karstic formations are the Asmari and the Ilam-Sarvak Formations and the two examples of karst plains (Polje) were created through tectonic activities and dissolution process of water in the Asmari Formation. Geological setting and climate condition are the most important factors of karst development in the study area. The region has a wide variety of developed karstic features. Accordingly, the purpose of this paper is to identify and introduce karst features of the study area including polje, karst valley, doline, waterfall, ponor, lapiez, rain pit, cave and karst spring.

Late quaternary speleogenesis and landscape evolution in the northern Apennine evaporite areas

AbstractGypsum beds host the majority of the caves in the north‐eastern flank of the Apennines, in the Emilia Romagna region (Italy). More than six hundred of these caves have been surveyed, including the longest known epigenic gypsum cave systems in the world (Spipola‐Acquafredda, ~11 km). Although this area has been intensively studied from a geological point of view, the age of the caves has never been investigated in detail. The rapid dissolution of gypsum and uplift history of the area have led to the long‐held view that speleogenesis commenced only during the last 130 000 years.Epigenic caves only form when the surface drainage system efficiently conveys water into the underground. In the study area, this was achieved after the dismantling of most of the impervious sediments covering the gypsum and the development of protovalleys and sinkholes. The time necessary for these processes can by constrained by understanding when caves were first formed.The minimum age of karst voids can be indirectly estimated by dating the infilling sediments. U–Th dating of carbonate speleothems growing in gypsum caves has been applied to 20 samples from 14 different caves from the Spipola‐Acquafredda, Monte Tondo‐Re Tiberio, Stella‐Rio Basino, Monte Mauro, and Castelnuovo systems. The results show that: (i) caves have been forming since at least ~600 kyr ago; (ii) the peak of speleogenesis was reached during relatively cold climate stages, when rivers formed terraces at the surface and aggradation caused paragenesis in the stable cave levels; (iii) ~200 000 years were necessary for the dismantling of most of the sediments covering the karstifiable gypsum and the development of a surface mature drainage network.Besides providing a significant contribution to the understanding of evaporite karst evolution in the Apennines, this study refines our knowledge on the timescale of geomorphological processes in a region affected by rapid uplifting. Copyright © 2016 John Wiley & Sons, Ltd.

Assessment of a Pipeline Route in a Karst Terrain, Florida, USA

A pipeline, known as Sabal Trail Pipeline, for natural gas transport has been proposed to extend from Alabama to Florida, passing through a very fragile and mostly uncovered karst terrain in Florida. There is considerable concern as to the structural integrity of the pipeline as well as its potential impacts on the environment, particularly on groundwater quality of the Floridan aquifer. Using Geographic Information Systems, this study examines the extent of karst in the proposed trail route and suggest two new alternative routes with significantly less karst development. Mean depression density within 5 km of the proposed Sabal Trail route is 5.2 depressions per km2, with a spatial coverage of 12.2%. Depressions within the alternative route have significantly lower density -2.1 depressions per km2 and much smaller spatial coverage; 5.7%. The routes were also compared with respect to intersected land cover categories.

重庆某隧道区岩溶水系统划分与系统特征研究

为了查明黔恩高速公路仰头山隧道隧址区岩溶水发育特征，在分析其工程地质条件的基础上，将仰头山隧道岩溶水系统进行划分，并对各系统的含、隔水介质、水文地质结构、岩溶发育情况及排泄量等进行了分析，最终得出各岩溶水系统与隧道间的关联与影响。 In order to find out the karst water development characteristics in the Yangtoushan tunnel site area of Qian-En Expressway, based on the analysis of the geological engineering conditions, the karst water system is divided in parts, and the analysis on the aquifer and aquiclude medium, the hydrogeological structure, the karst development and excretion and so on are conducted. We obtain the correlation and influence between the karst water system and the tunnel at last.

On connection of modern geodynamic processes in carbonate rocks with tectonic activization of Petrivs’k-Kreminna fault

The given paper considers the connection of modern geodynamic processes in carbonate rocks with the tectonic activation of Petrivs’k-Kreminna fault. It is emphasized that faults in the region are the channels of the upward heat and mass transfer.The unloading of deep formation waters and endogenous fluids in the area Petrivs’k-Kreminna and other faults results from heat and mass transfer, which is brought about by the motions of lithospheric blocks of Donets’k folded structure.The present tense dynamic state of the geological system manifests itself in the constant uplifting of the hanging wings of Svyatohirs’k brachyanticline at a speed of 1,3-2,5 mm a year. Earthquakes with the focal depth of ~10 km are associated with periodic geodynamic stress relaxation in the Archean-Proterozoic basement complex in the ancient geologically closed submeridional fault that intersects within Svyatohirs’k structure with the Petrivs’k-Kreminna fault. The modern and most recent tectonic activation of the latter is evidenced in the formation of hypogenic hydrogeochemical anomalies, accompanied by hydrochemical inversion. The groundwater here exhibit alkaline reaction (pH up to 8,2), an increased temperature (19- 27 °C) in the range of 0-300 m and a high content of hypogenic trace elements, among which carbon dioxide takes pride of place.The presence of CO2 increases the aggressiveness of underground water towards carbonate rocks, resulting in a chemical geodynamic process referred to as karst. Furthermore, abnormal physical and chemical properties of groundwater bring about suffusion processes in loamy, chalk strata of rocks. These geodynamic processes are associated with geological risks for buildings of Svyatohirs’k monastery.The study found that: 1) the tectonic activation of the Petrivs’k-Kreminna fault in various and, above all, the modern and contemporary periods of Alpine tectonogenesis is the dominant energy basis of geodynamic processes, including seismic activity; 2) carbon dioxide as atmospheric and deep genesis present in the groundwater of different types, is the major factor in the development of carbonate karst in Svyatohirs’k brachyanticline; 3) the isotopic analysis of δ13C and δ18O in aragonite chalk powder clearly showed that recrystallization of chalk into aragonite occurred involving deep formation waters saturated with endogenous (metamorphogenic or mantle) CO2.

Buildings and constructions safety operation on karstic territories of the Samara city

During the last 20-25 years the geological structure of the city has considerably changed due to different anthropogenic and technological factors. The geotechnical situation of the Samara city needs to be specified. In the first place, it is about karstic territories that are under active man-induced impact. Water utilities leakage, snow melting and rainfalls cause carbonates soakage which results in carbonates damage and karst appearance accompanied by cavities in the earth shell of different size and shape. Karst changes the current eco and geological system – the natural landscape. These deformations are highly disadvantageous for buildings and constructions on karstic territories, as they can lead to serious circumstances - partial or full building failures. Besides, karst and suffosion have recently become more frequent, which directly endanger human safety and even life. This paper presents results of the analysis of karst and suffosion development on the territory of Samara. It observes geotechnical problems of using karstic grounds as structure bases, gives reasons for necessary geotechnical monitoring at the stage of examination, as well as reasons for implementation of anti-karstic engineering and technical measures during building erection and operation.

RELATIONS BETWEEN KARST AND THE NEOGENE PALEO-BELAYA VALLEY NETWORK, SOUTHERN CIS-URALS REGION

Miocene-Pliocene tectonic movements transformed considerably the landscape of South Urals and drove spatial patterns and intensity of Earth surface processes. Deepening of river valleys in Paleo-Volga and Paleo-Ural drainage systems facilitated ground water action. Geological section in paleo-valleys of Belaya, Ufa, Bystriy Tanysh, Dioma and other rivers includes up to 200 m thick Late Miocene – Pliocene clayey unit that may favor both drainage and screening of aquifers depending on local hydrogeological conditions. In the former case, karst processes are intensified due to the increased pressure gradients and ground water velocities along the sides of paleovalleys that are composed of Carboniferous and Lower Permian gypsum and limestones. In case of shielding, rising flows of highly mineralized water are discharged in the form of large karst springs (“Krasniy Klyuch”, and others.). Along with natural control factors (lithology, tectonics, hydrogeology, etc.), present-day karstic processes development are controlled by economic activity. Karst and suffosion (underground erosion) are often activated by growth of cities and development of new lands. Neogene and modern valleys promote karst development in Lower Permian gypsums in the Ufa agglomeration where 63 karstic fieds were found. In the last 25 years, 70–80% of hazardous cases related to kasrt intensification were induced by technogenic waterlogging. Karstic and suffusion processes threaten the exploitation of Yumaguzinskaya and – Pavlovskaya Hydropower stations that were constructed on karst prone carbonate rocks at the Belaya and Ufa palevalleys.

Hydrogeochemical features of karst development under current conditions

Karst is regarded as a geological and physicochemical process of interaction between the natural water and soluble rock. Its development is possible only under non-equilibrium conditions in the “groundwater–congruently soluble rock” system. It is shown that intense karst development, leading to the formation of underground cavities and passages, is possible in the presence of advective transport of dissolved substance, which can redistribute its considerable amounts in a relatively short time. The specific features of karst development are considered in the case of its manifestation in carbonate, sulfate, and chloride rocks.

Editorial: Flow and Transformation in Porous Media

Fluid flow in transforming porous rocks, fracture networks, and granular media is subject to considerable current interdisciplinary research activity in Physics, Earth Sciences, and Engineering. Examples of natural and engineered processes include hydrocarbon recovery, carbon dioxide geo-sequestration, soil drying and wetting, pollution remediation, soil liquefaction, landslides, dynamics of wet or dry granular media, dynamics of faulting or friction, volcanic eruptions, gas venting in sediments, karst development and speleogenesis, ore deposit development, and radioactive waste disposal. Hydrodynamic flow instabilities and pore scale disorder typically result in complex flow patterning. In transforming media, additional mechanisms come into play: compaction, de-compaction, erosion, segregation, and fracturing lead to changes in permeability over time. Dissolution, precipitation, and chemical reactions between solutes and solids may gradually alter the composition and structure of the solid matrix, either creating or destroying permeable paths for fluid flow. A complex, dynamic feedback thus arises where, on the one hand, the fluid flow affects the characteristics of the porous medium, and on the other hand the changing medium influences the fluid flow. This Research Topic Ebook presents current research illustrating the depth and breadth of ongoing work in the field of flow and transformation in porous media through 15 papers by 72 authors from around the world. The body of work highlights the challenges posed by the vast range of length-and timescales over which subsurface flow processes occur. Importantly, phenomena from each scale contribute to the larger-scale behavior. The flow of oil and gas in reservoirs, and the flow of groundwater on catchment scale is sensitively linked to pore scale processes and material heterogeneity down to the micrometer scale. The geological features of the same reservoirs and catchments evolved over millions of years, sometimes as a consequence of cracking and fracture growth occurring on the time scale of microseconds. The research presented by the authors of this Research Topic represents a step toward bridging the separation of scales as well as the separation of scientific disciplines so that a more unified picture of flow and transformation in porous media can start to emerge.

Bioturbation-influenced fluid pathways within a carbonate platform system: The Lower Cretaceous (Aptian–Albian) Glen Rose Limestone

The Aptian–Albian Glen Rose Limestone (GRL) is an argillaceous shallow-marine carbonate deposit on the Central Texas Platform and contains the upper Trinity aquifer and the upper part of the middle Trinity aquifer. The GRL is divided into Upper and Lower GRL members, which have been further subdivided into hydrostratigraphic units (HSUs). This study uses an integrated ichnological and sedimentological approach to record changes in ichnofabric index (ii) as a proxy for bioturbation within the GRL and relates these changes to fluid flow. Fluid pathways within HSUs are controlled by the complex interaction of faults and fractures, karst development, and large-scale bioturbation-influenced porosity and permeability. The effect of bioturbation-influenced porosity as an aquifer characteristic is the least studied of these factors. Post-depositional solution enhancement of ichnofossils is also common and has increased lateral and vertical fluid connectivity in some HSUs. Most GRL strata are dominated by Thalassinoides networks, but also contain Palaeophycus, Planolites, Ophiomorpha, Serpulid worm tubes, rhizoliths, and Cruziana. Thalassinoides are commonly filled with coarser sediment than the surrounding matrix and act as fluid conduits within an otherwise low permeability matrix. Beds with ii3–4 and burrows with permeable fill transmit water readily. Beds with ii5–6 are commonly muddy and heavily homogenized, restricting fluid flow. Grainstone beds commonly have ii1–2 and are well cemented, restricting fluid flow to low intergranular flow. Pore systems dominated by Thalassinoides ichnofabrics, such as the GRL, are difficult to characterize on a large scale using many laboratory methods because they create heterogeneous flow paths depending on difference in permeability between the matrix and burrow fill. Understanding the effects of bioturbation-influenced porosity and permeability on subsurface fluid pathways is vital for creating a geologic and hydrostratigraphic framework for the Trinity aquifer.

Morphometric comparisons between automated and manual karst depression inventories in Apalachicola National Forest, Florida, and Mammoth Cave National Park, Kentucky, USA

Karst depression catalogs are critical to assessing the hydrology and geohazards of an area; yet, the delineation of these features within a landscape can be a difficult, time-consuming and subjective task. This study evaluates the efficacy of karst depression inventorying using an automated fill-difference method operating on high-resolution lidar-derived digital elevation models (DEMs). The resulting catalog is compared with existing karst depression inventories for two low-development areas of the USA, Mammoth Cave National Park (MACA) and Apalachicola National Forest (ANF), where karst depressions have been mapped previously using a manual closed-contour approach. The automated fill method captures 93 and 85 % of these previously mapped karst depressions at MACA and ANF, respectively. Field observations and topographic analysis suggest that the omitted features were likely misclassified within the existing catalogs. The automated routine returns 797 and 3377 additional topographic depressions, at MACA and ANF, respectively, which are not included in the existing catalogs. While the geology of ANF is mostly homogenous Quaternary deposits, the newly identified, typically smaller-scale depressions found within MACA tend to be disproportionally located in non-carbonate-dominated formations, where the development of karst may be restricted by geologic heterogeneity. Within both areas, the size distributions of the two inventories are statistically identical for features larger than ~103 m2 in area or ~3 m in depth. For individual depressions captured by both methods at MACA, the automated fill-difference routine tends to return a slightly larger estimate of depression size and aggregate small depressions into larger ones. Conversely, at ANF, some low-relief depressions may be disaggregated by the fill-difference technique, with a trend toward smaller estimated depression areas when the automated method is employed. The automated fill-difference method, operating on high-resolution lidar-derived DEMs, can reproduce and expand the existing inventories of karst depressions, while minimizing false detections that may be inherent within pre-existing catalogs.

Amplitude of late Miocene sea-level fluctuations from karst development in reef-slope deposits (SE Spain)

A prograding late Miocene carbonate platform in southern Spain revealing different sea-level pinning points was analysed with the aim to increase the accuracy of reconstruction of past sea-level changes. These pinning points are distinct diagenetic zones (DZ) and the position of reef-framework deposits. DZ1 is defined by the dissolution of bioclastic components and DZ2 by calcitic cement precipitation in dissolution pores. Calcite cements are granular and radiaxial fibrous, and are of meteoric origin as deduced from cathodoluminescence, EDX spectroscopy, as well as from δ13C and δ18O isotope analyses. DZ3 has moldic porosity after aragonitic bioclasts with minor granular calcitic cements. DZ1 and DZ2 indicate karstification and the development of a coastal palaeoaquifer during a sea-level lowstand. DZ3 diagenetic features are related to the final subaerial exposure of the section during the Messinian Salinity Crisis. Facies and diagenetic data reveal a complete cycle of sea-level fall (23±1m) and rise (31±1m). A robust age model based on magneto- and cyclostratigraphy for these deposits places this cycle between 5.89 and 5.87Ma. Therefore, for the first time, this work allows a direct comparison of an outcrop with a pelagic marine proxy record of a specific Neogene sea-level fluctuation.

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.

Morphometric analysis of karst depressions on a mediterranean karst massif

Dolines are the most typical landform in karst landscapes. They play an important role in karst hydrogeology; they are effective sediment traps that provide information about past climates and karst evolution, and can also be indicators of tectonic activity. The morphometic analysis of those depressions can help in their study and interpretation. However, detailed identification and delineation of dolines becomes increasingly difficult when the study area is very large, of limited access or covered by vegetation. Here, we have used a method developed by the authors for automatic identification and delineation of karst depressions based on the use of a pit removal algorithm. Next a complete morphometric analysis of the karst depressions has been carried out. The main advantage of the methodology is that by delineating and identifying the depth of each doline from its rim, many morphometric statistics can be obtained, including the relation of doline depth and area with respect to altitude, the main doline orientations, doline density, the fractal dimension of doline area and frequency, and point field analysis, among others. The results are interpreted from a geomorphological point of view and the mapped dolines can be easily integrated into geomorphological mapping. A case study is presented from the large Sierra Gorda karst massif in southern Spain, where 3100 depressions have been identified. A strong structural control of doline shape and orientation is demonstrated; the main areas of doline density are highlighted and doline size is shown to follow a fractal law.

Tectonic evolution and paleokarstification of carbonate rocks in the Paleozoic Tarim Basin

Thick carbonate rocks were developed in the depression of the Tarim craton during the Cambrian–Middle Ordovician periods. The compressional tectonic movement during the Middle Caledonian–Hercynian created the paleouplifts, which became the base for the paleokarst in the Ordovician carbonate rocks. Based on the large quantity of seismic, drilling, and geological outcrop data, this study analyzed the paleokarst development in relation to the multi-stage tectonic movements in the Paleozoic Era and different stages of karstification and hypothesized paleogeomorphology and paleokarst water system of those stages. Fractures from the tectonic movements in the carbonate and non-carbonate rocks were essential for water cycle, and therefore, the karst development in deep carbonate rocks. Paleokarsts in the Tarim Basin can be classified into four major types based on the paleogeomorphology, degree of karstification, and the layering, i.e., Tahe type, gentle hill type, high steep hill type, and covered-semi-open type. Relatively, the Tahe type was mostly on hill slopes and had the strongest karstification, the gentle hill type often located in the plain areas or basin bottoms and had least karstification, the high steep hill type was controlled by faults and had medium karstification, the semi-open type was controlled by precipitation and hydraulic gradient, and fracture passages and karst caves were mostly developed along major fractures. Overall, the paleokarsts of the Ordovician carbonate rocks in the Tarim Basin can be characterized by long geologic history, multiple development stages, deep burial depth, and various karst types.

Structure and evolution of collapse sinkholes: Combined interpretation from physico-chemical modelling and geophysical field work

In karst rocks (limestone, anhydrite, gypsum, etc.), water flowing through fissures and bedding partings can enlarge voids either by physical or chemical dissolution. Within a geologically short period of time, the increase in void space creates a large secondary porosity typical for soluble rocks, which is responsible for preferential flow through the karst rock, often through cave systems with passages reaching the meter-scale and more. This large-scale voids in the sub-surface can initiate collapse of the overburden, either through wall or roof breakdown, and the initial void created by dissolution can migrate upwards and finally cause a surface collapse and create a collapse sinkhole. While the dissolution part of this evolution is in the order of 10,000–100,000years, the final mechanical collapse can occur on time scales of days.We have studied a typical collapse sinkhole site in the southern Harz Mountains in Germany, with anhydrite (partly converted to gypsum) as soluble rock in the sub-surface. We discuss geophysical measurements (gravity, electrical resistivity tomography, self potential, magnetics) from the location to identify the local collapse sinkhole signal and the possibility to separate the collapse sinkhole signal from the broader geological signal of the study site. We model the initiation of sub-surface voids with our numerical tool KARSTAQUIFER, a 3D karst evolution model describing flow and dissolution in karst rocks. We apply this numerical model to predict collapse sinkholes in a locality in the Harz Mountains.

Analysis of rock quality designation (RQD) and Lugeon values in a karstic formation using the sequential indicator simulation approach, Karun IV Dam site, Iran

The hydraulic properties of hard rock and karst formations are typically highly heterogeneous. Quantification of the groundwater flow in these media is a complicated process with numerous uncertainties. There are several approaches to overcome this problem. Stochastic simulation is one of the promising approaches for quantification of the intrinsic uncertainty in karst formations. In the present research, the sequential indicator simulation was used as a tool for the simulation of the hydrogeological and geotechnical properties of a karstic formation at the Karun IV dam site, Iran. In this regard, two variables of interest, RQD and Lugeon, were considered as criteria for the development of karst. One hundred realizations of these variables were produced and then combined to obtain an expected value and the probability of exceeding a threshold value for each cell. The results showed a weak negative correlation between the expected values of RQD and Lugeon. Also, it was determined that the geologic structures (i.e., faults) and lithology play an important role in the development of karst in the study area. A decrease in the simulated values of Lugeon was observed with increasing depth of karstic layers and the distance from faults. The results of this study helped to overcome the intrinsic uncertainty in karst media and to present a conceptual model of karst development. This approach can be applied in other dams for the evaluation of risk and uncertainty of hydrogeological parameters.

Analysis and prevention of sinkhole collapses during the reconstruction and extension of Guang-Qing freeway, china

The Guang-Qing freeway reconstruction and extension project is located in Guangdong province, China, extending from Guangzhou city to Qingyuan city. The total project length is 57.6 km, 33 km of which is in a karst area where sinkhole collapses are common. Therefore, there were concerns about the safety and security of the roadbed, bridge piles, and other structures associated with the original roadway. The study addresses karst development, covering layer (overburden), and external factors that contribute to catastrophic sinkhole collapse along the project. The study found that the formation of sinkhole collapses is affected significantly by the degree of karst development and soil characteristics, including thickness. Collapses may be triggered directly by external factors that disturb the natural equilibrium. Such factors include heavy rainfall that impacts soil and groundwater conditions, as well as vibration and groundwater flow disruptions that are caused by pile construction and other engineering activities. Prevention measures were adapted to local conditions and optimized based upon safety, reliability and cost-effectiveness.

A model of karst systems of the Usturt plateau (Middle Asia)

The issues relating to the structure and development of desert karst is currently one of the least studied problems. The goal of the research efforts presented in this paper was to create a model of karst systems in the Usturt Plateau and, primarily, of the systems formed by the prevailing numerous surface karst landforms. The model is based on the following main assumptions: the process of emergence of the karst phenomena is probabilistic and occurs independently at non-intersecting sites; the probability of emergence of one depression at a reference site depends only on its area. The increase of the dimensions of a karst landform is a random process that occurs independently of other karst landforms, its speed is governed by random factors, and it is directly proportionate to the existing dimensions of the landform. The model does not assume constancy of climatic characteristics. The testing was conducted at several reference sites of the Usturt Plateau. The research allowed us to reach the following conclusions: the karst depressions of the Usturt Plateau, which are the typical forms of desert karst, are governed by the Poisson distribution of their centres and by the lognormal distribution of their dimensions, similar to the karst depressions in a humid climate. The results may be used in assessments of karst hazard for linear and areal structures, as well as for small-dimensional structures.