Application of Digital Image Cross Correlation to Study Sinkhole Collapse

This paper presents the results of a study using a transparent soil experimental technique and numerical modeling to detect 3D deformations resulting from submerged cavities that lead to a sinkhole. Excessive deformations from underground activity beneath highway pavements could lead to sinkhole collapse. The formation of a sinkhole is often sudden and can lead to extensive damage and loss of life, especially in urban areas. The use of transparent soils permitted the visualization of internal ground deformations which allowed for comprehensive evaluation of the extension of failure. A series of finite element analyses have also been carried out for the tests conditions. The observed sinkhole, at the surface, is found to be a small indicator of the final size and magnitude of the internal deformations as a subsequent funnel-shaped depression developed with a hole at the center. The modeling results emphasized the need to extend the repair zone following sinkhole collapse by a minimum distance that equals twice the cavity diameter away and ahead of the developed hole. Results of this study are believed to be of practical interest for predicting surface and internal ground deformations following sinkhole collapse which could be useful for the stability assessment of underground utilities and the development of a restoration plan after collapse occurred. The results also provided approximate bounds to areas affected by the sinkhole allowing for collapse risk to be assessed. 1. Introduction Sinkholes are depressions that develop at the soil surface due to stress release in the soil beneath. They could develop naturally like in karst terrains, due to dissolution of limestone and the subsequent subsidence above the depression, or as a result of human underground activities such as horizontal directional drilling (HDD) or tunneling operation. They could also be formed due to leaking sewer or culvert by washing away surrounding soils. Risk of sinkhole collapse will continue to increase due to increased urbanization which intensifies the need to utilize underground space to accommodate large utility systems, subways, and highways, thereby decreasing traffic congestion and allowing preservation of aboveground space. A sinkhole may develop on a roadway when an opening is formed, either beneath or within the subgrade layer, followed by the flowing of layers above into this opening. Such sinkholes require immediate and costly repairs to avoid further traffic delays and closures. The current maintenance approach to this problem is to quickly remove and/or repave