ORCID Profile
0000-0003-2254-3914
Current Organisation
University of Leipzig
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Publisher: Copernicus GmbH
Date: 23-11-2018
Abstract: Abstract. Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth ∕ diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth ∕ diameter values in each material type may partly reflect sinkhole growth trends.
Publisher: Copernicus GmbH
Date: 29-07-2019
Abstract: Abstract. The 2-D distinct element method (DEM) code (PFC2D_V5) is used here to simulate the evolution of subsidence-related karst landforms, such as single and clustered sinkholes, and associated larger-scale depressions. Subsurface material in the DEM model is removed progressively to produce an array of cavities this simulates a network of subsurface groundwater conduits growing by chemical/mechanical erosion. The growth of the cavity array is coupled mechanically to the gravitationally loaded surroundings, such that cavities can grow also in part by material failure at their margins, which in the limit can produce in idual collapse sinkholes. Two end-member growth scenarios of the cavity array and their impact on surface subsidence were examined in the models: (1) cavity growth at the same depth level and growth rate (2) cavity growth at progressively deepening levels with varying growth rates. These growth scenarios are characterised by differing stress patterns across the cavity array and its overburden, which are in turn an important factor for the formation of sinkholes and uvala-like depressions. For growth scenario (1), a stable compression arch is established around the entire cavity array, hindering sinkhole collapse into in idual cavities and favouring block-wise, relatively even subsidence across the whole cavity array. In contrast, for growth scenario (2), the stress system is more heterogeneous, such that local stress concentrations exist around in idual cavities, leading to stress interactions and local wall/overburden fractures. Consequently, sinkhole collapses occur in in idual cavities, which results in uneven, differential subsidence within a larger-scale depression. Depending on material properties of the cavity-hosting material and the overburden, the larger-scale depression forms either by sinkhole coalescence or by widespread subsidence linked geometrically to the entire cavity array. The results from models with growth scenario (2) are in close agreement with surface morphological and subsurface geophysical observations from an evaporite karst area on the eastern shore of the Dead Sea.
Publisher: Copernicus GmbH
Date: 16-07-2018
Publisher: Copernicus GmbH
Date: 16-07-2018
DOI: 10.5194/SE-2018-62
Abstract: Abstract. Mechanical and/or chemical removal of material from the subsurface may generate large sub-surface cavities, the destabilisation of which can lead to hazardous ground collapse and the formation of enclosed depressions termed sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard, but is a challenging task due to the involved high strains and material discontinuities. Here we present a 2D Distinct Element Method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, step-wise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and Boundary Element Method models of a deep void space in a linear elastic material. Secondly, we explore the effects of material properties on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geomechanical parameters of three model materials that reflect literature and field-based estimates for three materials in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden, but also due to an inhibition of stabilising stress arching. Fourthly we compare our model sinkhole geometries to observations at the Ghor al-Haditha sinkhole site on the eastern shore of the Dead Sea in Jordan. Sinkhole depth to diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth/diameter values in each material type may partly reflect sinkhole growth trends.
Publisher: Copernicus GmbH
Date: 29-01-2019
DOI: 10.5194/SE-2019-20
Abstract: Abstract. The 2D Distinct Element Method (DEM) code (PFC2D_V5) is here used to simulate the evolution of subsidence-related karst landforms, such as single and clustered sinkholes, and associated larger-scale depressions. Subsurface material in the DEM model is removed by a feedback loop to produce an array of cavities this simulates a network of subsurface groundwater conduits growing by chemical/mechanical erosion. The growth of the cavity array is coupled mechanically to the surroundings such that cavities can grow also in part by material failure at their margins, which in the limit can produce in idual collapse sinkholes. Two end-member growth scenarios of the cavity array and their impact on surface subsidence were examined in the models: (1) cavity growth at the same level and at the same in idual growth rate (2) cavity growth at progressively deepening levels with varying in idual growth rates. These growth scenarios are characterised by differing stress patterns across the cavity array and its overburden, which are in turn an important factor for the formation of sinkholes and uvala-like depressions. For growth scenario (1), a stable compression arch is established around the cavity array, hindering sinkhole collapse into in idual cavities and favouring block-wise subsidence across the whole cavity array. In contrast, for growth scenario (2), the stress system is more heterogeneous, such that local stress concentrations exist around in idual cavities leading to stress interaction. Consequently, sinkhole collapses into in idual cavities occurs by shear or tensile failure of the overburden, and these sinkholes lie within a larger scale depression linked to the cavity array as a whole. The results from models with growth scenario (2), which also account for variations in mechanical properties of the overburden, are in close agreement with surface morphological and subsurface geophysical observations from a karst area on the eastern shore of the Dead Sea.
Location: Germany
Location: No location found
Location: No location found
Location: Germany
No related grants have been discovered for Djamil Al-Halbouni.