Sinkholes are alarming and dangerous events, they have a worldwide occurrence, and are imposing a potential risk to urban communities and the widely developed built environment. Losses due to catastrophic sinkhole collapse, foundation, pavement and structural repairs, occur more often, due to the increased pressure to develop even on sinkhole prone land, and the aging of existing water supply infrastructure in the majority of cities. Remote sensing earth observation methods have proved to be valuable tools during the last two decades in long-term sinkhole hazard assessment. Satellite air borne and ground earth observation methods have primarily facilitated the wide detection of continuous displacement on the earth's crust. National sinkholes catalogues are necessary for town planers decision makers, and government authorities. In many instances the ground collapse is the result of water ingress from old poorly maintained leaking pipelines, or extensive dewatering activities. In the current study a comprehensive review of the current literature is presented in order to show experiences from South Africa and present recent mapping using PSInSAR methodology in Centurion South Africa.
Unexpectedly occurring sinkholes caused by shallow submerged voids are one of the key problems of intensively built-up post-mining areas. Five percent of Poland’s territory is still under the influence of post-mining deformation. Impending sinkholes, which tend to develop randomly over very large areas, cannot be detected by using traditional geophysical methods. Moreover, geodetic measurement methods like Global Positioning System (GPS) analyses, tachymetry, laser scanning, or photogrammetry may be useful only for the registration of the dimensions and locations of sinkholes that have already occurred. Here, we investigate an area in Upper Silesia, Poland, where 345 sinkholes were recorded over a period of more than 20 years (1992–2013). Most of the events occurred in intensively built-up areas, and thus, these sinkholes posed a direct threat to the population. In the test area, 11 sinkholes were detected with a maximum depth of 16m and maximum dimension of 25 m. The root cause of sinkhole formation was the collapse of post-mining shallow voids. We used satellite radar technology to detect and monitor ground movements potentially associated with the impending sinkholes. The findings showed that the application of Persistent Scatterer Interferometry can support the identification of zones where sinkholes will occur, given adequate spatio-temporal sampling. A stack of Envisat Synthetic Aperture Radar (SAR) images acquired between March 2003 and August 2010 was used in the analysis, and the results confirmed that precursory ground movements were detectable at an early stage of sinkhole development. The land subsidence rate observed prior to sinkhole collapse was not constant in time. Accelerated ground movements within 100m of an observed sinkhole were detected. We conclude that satellite measurements may provide significant support in the early identification of areas prone to sinkhole occurrence.
Presented research focused on the development of a novel methodology for sinkhole risk assessment above shallow caverns in a salt mine. The research was carried out for the Wieliczka Salt Mine, which is registered on the UNESCO list and visited by near around 2 million tourists every year. The main assumption of the investigation was to estimate root cause of sinkhole occurrence on the surface. Based on the arch pressure theory the vertical stress in the roof of salt caverns was established. Constructed three-dimensional model of underground mine allowed to determine the stresses between the caverns. Furthermore, the caverns which were hazarded by roof collapse were indicated. Hybrid solution was supported by multicriteria risk analysis based on Analytic Hierarchy Process carried out in Geographical Information System. Spatial analysis led to the identification of caverns potentially influenced by other risk factors. Developed final risk maps were based on four the most significant risk factors leading to sinkhole occurrence. Vulnerability maps developed with support of Analytic Hierarchy Process indicated areas where habitants and infrastructure are exposed to sinkhole occurrence. Merging risk maps with vulnerability maps led to final hazard map, where urban areas susceptible to sinkhole occurrence were shown. In conclusion, the research carried out proved that combined spatial analysis with theoretical solution may pave the way for reliable sinkhole risk assessment above shallow caverns.
The present research focuses on the definition of a novel methodology for sinkhole risk assessment above shallow salt mines. The research were carried out on the area above the salt mine, a World Heritage site. The study of vertical stresses on the basis of a theoretical state of rock mass deformation in the area of test chambers was performed. Furthermore, the risk of chamber collapse due to ventricular stress exceeding the limit specified in the zone were calculated based on the arch pressure theory. The final stage of the research consists of spatial analysis that leading to the identification of chambers potentially influenced by other risk factors. The research shown in the article strongly suggests that combined spatial analysis with analysis may lead to reliable sinkhole risk assessment methodology.
Underground exploitation of mineral resources is often carried out in a watered rock mass. Dewatering of rock layers disturbs its geomechanical equilibrium, consequently resulting in deformations occurrence on the terrain surface. Furthermore, modeling of rock strata dewatering and related land subsidence is still a complex issue, mostly due to unambiguous qualitative and quantitative characteristics of rock mass. Presented research aimed at determination of dynamics of hydrogeological changes and land subsidence induced by water withdrawal in fractured rock strata. They were carried out in the area of “Bogdanka” hard coal mine in Poland, at a depth of 1000 m, in a multi-layered aquifer system. Spatio-temporal distribution of depression cone and land subsidence in the period 1982-2018 was analyzed. Furthermore, based on the results of observations of water table in aquifers, land subsidence and geomechanical characteristics of rock mass, trend lines of logarithmic functions were estimated. Afterward, based on logarithmic functions, prediction of water table fluctuation and land subsidence was carried out in the entire area of hard coal mining in the period 2018-2025. Subsequently, a novel time factor was introduced. It determines the delay of deformation occurrence on the terrain surface induced by rock strata dewatering as a function of time and distance from drainage center. Finally, computation results were successfully compared with field data. On the whole, the presented research provide better insight into mechanics of lands subsidence development and water flow in the fractured rock mass due to rock strata dewatering accompanying underground exploitation of mineral resources.
The research is focused on the feasibility analysis of a numerical model describing the field of strains generated by mining-induced subsidence caused by a deep underground coal extraction, which may contribute to the formation of Earth fissures. The finite elements method and Knothe’s theory were used in the research. The geomechanical modeling was applied for defining zones of strains and maximum horizontal deformations of the terrain. Knothe’s theory was employed for defining boundary conditions of the geomechanical model. The parameters of the empirical and geomechanical models were scaled out on the basis of geodetic surveys in the mining area. The results of geomechanical modeling were compared with the geodetic surveys to select the best model. The presented research confirmed high congruence between the results of modeling with the finite elements method and observations of vertical movements on the surface. The results of modeling also confirmed the assumed highest stress in areas where earth fissures were observed. The proposed solution may be a new research tool applicable to areas where earth fissures potentially occur. © 2018, Academy of Sciences of the Czech Republic. All rights reserved.
The geodetic measurements optimization problem has played a crucial role in the mining areas affected by continuous ground movement. Such movements are most frequently measured with the classical geodetic methods such as levelling, tachymetry or GNSS (Global Navigation Satellite System). The measuring techniques are selected with respect to the dynamics of the studied phenomena, surface hazard degree, as well as the financial potential of the mining company. Land surface changes caused by underground exploitation are observed with some delay because of the mining and geological conditions of the deposit surroundings. This delay may be considerable in the case of salt deposits extraction due to slow convergence process, which implies ground subsidence maximum up to a few centimeters per year. Measuring of such displacements requires high precision instruments and methods. In the case of intensely developed urban areas, a high density benchmark network has to be provided. Therefore, the best solution supporting the monitoring of vertical ground displacements in the areas located above the salt deposits seems to be the Sentinel 1-A radar imaging satellite system. The main goal of the investigation was to verify if imaging radar from the Sentinel 1 mission could be applied to monitor of slow ground vertical movement above word heritage Wieliczka salt mine. The outcome of the analysis, which was based on DInSAR (Differential SAR Interferometry). technology, is the surface distribution of annual subsidence in the period of 2015-2016. The comparison of the results with levelling confirmed the high accuracy of satellite observations. What is significant, the studies allowed to identify areas with the greatest dynamics of vertical ground movements, also in the regions where classical surveying was not conducted. The investigation proved that with the use of Sentinel-1 images sub centimeters slow vertical movements could be obtained.
Treść: Problem optymalizacji pomiarów geodezyjnych na obszarach poddanych wpływom ciągłych deformacji powierzchni terenu wciąż stanowi wyzwanie. Pomiary ruchów powierzchni na terenach górniczych najczęściej wykonywane są przy wykorzystaniu klasycznych metod geodezyjnych takich jak niwelacja, tachimetria czy pomiary GNSS. Technika pomiarowa jest dobierana w odniesieniu do dynamiki zjawiska, stopnia zagrożenia powierzchni terenu i potencjału finansowego, którym dysponuje zleceniodawca. Przekształcenia powierzchni terenu obserwowane są z pewnym opóźnieniem w stosunku do czasu prowadzenia wydobycia. Opóźnienie to wynika m.in. z warunków górniczo-geologicznych otoczenia złoża i jest zdecydowanie największe w przypadku prowadzenia wydobycia soli. Powolna konwergencja podziemnych wyrobisk powoduje osiadania powierzchni terenu dochodzące maksymalnie do kilku centymetrów rocznie. Pomiar tego typu deformacji wymaga wysokiej precyzji, a w przypadku intensywnego zagospodarowania powierzchni terenu również znacznej gęstości sieci pomiarowej. Dlatego też, optymalnym rozwiązaniem wydaje się być wykorzystanie zobrazowań radarowych satelity Sentinel 1-A jako metody wspierającej monitoring przemieszczeń pionowych powierzchni terenu na terenach znajdujących się nad złożem solnym. Prezentowane badania dotyczyły analizy możliwości wykorzystania zobrazowania satelitarnego pochodzącego z misji Sentinel dla wsparcia monitoringu deformacji powierzchni terenu na obszarze miasta Wieliczka na bazie technologii DInSAR. Wynikiem przeprowadzonych analiz jest powierzchniowy rozkład rocznych przyrostów osiadań w okresie 2015-2016 nad konwergującymi wyrobiskami górniczymi. Otrzymane wyniki, poddane analizie dokładnościowej poprzez ich porównanie z pomiarami geodezyjnymi realizowanymi na liniach obserwacyjnych, potwierdziły bardzo wysoką dokładność pomiarów satelitarnych. Prowadzone badania pozwoliły na wyłonienie rejonów o największej dynamice ruchów pionowych, również w strefach, w których klasyczne pomiary geodezyjne nie są prowadzone. Abstract: The geodetic measurements optimization problem plays still a crucial role in the mining areas affected by continuous ground deformation. Measurements of that movements are most frequently conducted using the classical geodetic methods such as: levelling, tachymetry or GNSS. Measuring technique is selected with respect to the dynamics of chosen phenomena, surface hazard degree, as well as the financial potential of the mining entrepreneur. Land surface changes caused by underground exploitation are observed with some delay due to mining and geological conditions of the deposit surroundings. This delay reaches the highest values in case of salt deposits extraction due to slow convergence process that implies ground subsidence maximum up to a few centimetres per year. Measurement of the deformation of this type requires high precision instruments or methods, and in the case of intensively developed urban areas, use of high density of benchmark network. Therefore, the best solution supporting the monitoring of vertical ground displacements in the areas located above the salt deposits seems to be application of the Sentinel 1-A radar imaging satellite system. The present study involved the analysis of the possibility of applying satellite monitoring of surface deformation for Wieliczka town, using imaging radar from the Sentinel 1 mission. The outcome of the analysis - based on DInSAR technology - is the surface distribution of annual growth of settlements above mining excavations affected by convergence process in the period of 2015 – 2016. Comparison of the results with levelling – that has been carried out on benchmark network – confirmed the high accuracy of satellite observations. What is significant, the studies allowed to identify the areas characterized by the greatest dynamics of vertical ground movements, also in the regions where classical geodetic measurements are not conducted.
The analysis of mining-induced sinkholes occurrence is a very important problem as far as the spatial development optimization is concerned. Research conducted within this paper was oriented to revealing the applicability of GIS and the associated AHD method for estimating the risk of discontinuous deformation occurrence on the surface. The qualitative factors were accounted for in the sinkhole risk assessment, thus creating bases for the research. These elements play an important role in the process of sinkholes formation; however they were not used in prediction models. Another assumption lied in minimizing the number of variables in the model. Accordingly, the most important qualitative and quantitative risk factors were finally selected, on the basis of which the risk of cave-ins occurrence on the surface could be calculated. The results of estimations of zones with sinkholes potential were verified. The places of actual and high-risk potential discontinuous deformations were compared. The congruence between predicted values and actual observations of sinkholes was very high. The results of presented research prove the necessity to evaluate the sinkhole hazard in view of qualitative factors.
Treść: W przypadku kopalń soli problem zachowania bezpieczeństwa w rejonie wyrobisk komorowych i na powierzchni terenu jest niezwykle złożony. Na przebieg procesu deformacji w górotworze solnym mają wpływ zarówno własności geomechaniczne różnych typów soli, jak i cały szereg czynników górniczych, geologicznych i hydrogeologicznych wpływających na potencjalne ryzyko wywołania zapadlisk czy deformacji ciągłych na powierzchni terenu. Przy tak złożonym zagadnieniu zasadnym i optymalnym rozwiązaniem wydaje się być wykorzystanie Systemów Informacji Geograficznej (GIS), które umożliwiają integrację wielu czynników i pozwalają na wyłonienie stref o szczególnym zagrożeniu zapadliskowym. Analizy przestrzenne zrealizowane w GIS pozwoliły na wyłonienie rejonów, w których wzajemny układ komór jest niekorzystny i w których wytężenia górotworu solnego mogłyby prowadzić do znacznego zaciskania się wyrobisk komorowych. W rejonach tych istnieje prawdopodobieństwo między poziomowej migracji pustki z poziomów niższych do wyższych. W badaniach opracowano koncepcję zintegrowanego systemu oceny zagrożenia złoża solnego opartego o funkcjonalność analityczną GIS w ujęciu estymacji prawdopodobieństwa między poziomowej migracji pustki poeksploatacyjnej. Abstract: The problem of safety in historic salt mines is an extremely complex issue. The process of deformation in rock masses related not only to geomechanical properties of different types of salt, but also a whole range of mining, geological and hydrogeological factors affecting the potential risk of causing sinkholes or continuous deformation on the surface. With such a complex issue a reasonable and optimal solution seems to be the application of Geographic Information Systems (GIS), which support the integration of multiple factors. Spatial analysis carried out in GIS enables detection of the areas with unfavorable chambers distribution that could lead to increase strains in rock mass and significant tightening of the excavation chamber. In those areas there is a likelihood of cross-level void migration from low to high levels. A new concept of an integrated system of risk assessment salt deposits based on the analytical functionality of GIS in terms of the probability of cross-level void migration has been presented.
The problem of sinkhole hazard estimation in the former and present mining areas still remains unsolved. This issue is frequently associated with numerous factors causing that phenomenon. The origin of that factor is not only related to the mining and geological condition of the rock masses in the vicinity of sinkhole. The correct interpretation of grounds for discontinuous deformation occurrence in a given area is particularly important in densely built-up areas. The analyses presented were focused on the identification of risk factors which may have influence on the process of discontinuous deformation occurrence and their spatial analysis. Fuzzy set theory and kernel density estimation support dealing with uncertainty of potential risk factors. The correlation has been established between distribution of this factors and spatial distribution of places where discontinuous deformations occurred. Four the most significant risk factors were taken into account in order to develop probability maps of sinkhole occurrence Presented approach is based on analytical hierarchy process, which enables integration of that factors. In the investigation both quantitative and qualitative factors were taken into consideration. While modelling discontinuous ground surface deformations, such an approach allows for consideration of complex mining and geological conditions. The effectiveness of the presented solution was verified by comparing probability maps of sinkhole occurrence with the observed sinkholes.
Abstract Anthropogenic movements of the rock mass generate strains and displacements on the surface, creating environmentally negative effects and hazards for buildings and infrastructure. The level of uncertainty of the theoretical model is important while predicting this kind of impact and the related hazards. Uncertainty is connected to the degree to which the actual properties of the modeled medium are generalized and with the error of the assumed parameters and variables, i.e. input data in the modeling. The reliability of the prediction is a function of the above factors, regardless of the type of the applied model. The recipient of the prediction results is principally interested in border values of strains or displacements, which can create hazards for the users of the analyzed terrain. In the case of particularly sensitive objects it is also necessary to calculate the range of border values for a given statistical significance value. The authors present one possible way of incorporating the uncertainty of a model used for spatial prediction of strains of the rock mass and surface, taking into account the influence of uncertainty of parameters of the model. A 3D stochastic model of the rock mass movement was analysed and the uncertainty was estimated statistically using the Monte Carlo method. The obtained results were GIS-integrated, allowing the border contour line of strains on the surface to be determined in the area of the planned mining activity. This solution was then applied to a copper ore deposit extracted with an underground mining method, resulting in a prediction of a negative impact of horizontal strains.
Reliable evaluation of linear objects resistance is an essential problem in highly developed areas which are subjected to seismic tremors and continuous surface deformations. Results of analyses of pipeline failures generated by continuous surface deformations are discussed in this paper. The development of a failure in a water pipeline under the influence of a 10-year subsidence of terrain to a depth of 4 m and horizontal deformations to 9.0 mm/m is presented. The research is focused on evaluating the reliability of approximate method which is presently used for assessing pipeline resistance. The more thorough investigation based on empirical data from a region subjected to intense and continuous surface deformations allowed for the estimation of factors having a decisive influence on the pipeline resistance. This result is crucial for further works on modeling hazard in this type of objects. The obtained risk factors and their rank will create basis for construing a new model for assessing linear objects hazard with continuous deformations.