The Role of Antecedent Conditions in Sinkhole Formation and Collapse Mechanisms

Aims
The main aims of the proposed research are to:
- Explore the geotechnical properties of materials susceptible to sinkhole formation. This includes determining which particular materials are likely to be weakened by long periods of dry weather followed by heavy rain, and which combinations of these conditions are likely to result in the greatest likelihood of sinkholes forming. Meeting this aim will improve understanding of the stability of these materials when supporting foundations over emerging cavities, and could facilitate the prediction of sinkholes in areas where land has already been developed, which could be used to prevent injury and potential loss of life.
- Investigate the mechanisms involved in the development of different types of sinkhole, such as the softening and failure of historic chalk workings. An understanding of the physics involved in these failures could inform additions to building regulations and design codes for infrastructure and structures in areas susceptible to sinkholes.

Method
In order to meet the aims listed, the following research method is proposed:
- A geotechnical desk study to identify suitable sites for sample extraction. This will be done using existing literature, as well as the BGS sinkhole database.
- Samples of clay, chalk and other rocks will be taken from the selected locations at different times of the year, with technical support and drilling equipment to be provided by BGS. These samples will be used to determine a ground profile for the site.
- The geotechnical properties of the samples, such as the relationship between water content and strength will be tested. This will be carried out in lab facilities provided by BGS.
- Based on the geotechnical properties and ground profile of the site, scale models of typical sinkhole prone formations will be produced for testing in a centrifuge, to generate typical in-situ stresses. This will require the use of further samples or of synthetic soil material. The centrifuge is an existing facility at the University of Sheffield.
- A technique for simulating aging effects of different antecedent conditions on the models will be developed. This may require new equipment such as drying and humidifying devices. The technique will be verified by comparison of artificially aged rocks with naturally weathered rocks.
- Rock and soil models with different moisture contents, and ageing conditions will be produced.
- These models will be tested in the centrifuge and their failure mechanisms studied and classified using image analysis techniques, such as particle image velocimetry, and calculated back analysis.
- The relationship between water content, strength and ageing conditions will be analysed and the critical combination resulting in the most sinkholes determined.