Articles | Volume 9, issue 6
Research article
23 Nov 2018
Research article |  | 23 Nov 2018

Geomechanical modelling of sinkhole development using distinct elements: model verification for a single void space and application to the Dead Sea area

Djamil Al-Halbouni, Eoghan P. Holohan, Abbas Taheri, Martin P. J. Schöpfer, Sacha Emam, and Torsten Dahm

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.

Short summary
Sinkholes are round depression features in the ground that can cause high economic and life loss. On the Dead Sea shoreline, hundreds of sinkholes form each year driven by the fall of the water level and subsequent out-washing and dissolution of loose sediments. This study investigates the mechanical formation of sinkholes by numerical modelling. It highlights the role of material strength in the formation of dangerous collapse sinkholes and compares it to findings from a field site in Jordan.