Designing foundations around sinkholes

There is an increasing awareness among developers and owners, of the need to conduct subsurface exploration studies before planning a project. The use of geophysical methods in subsurface exploration has been established to be valuable in locating sinkhole activity and suggesting pro-active measures. However, the value of geophysical exploration to supplement geotechnical investigation has not yet been stressed, primarily out of cost concerns. Ground penetrating radar and electrical resistivity tests, which were used to determine void spaces below proposed buildings are gaining wider acceptance. As a result of information obtained from geophysical tests, foundation designs were modified, to use post-tensioned mats or to include grouting. An improved grouting technique that controls the volume of grout being pumped is also discussed. This paper is an attempt to document some case studies which resulted in making design improvements to mitigate the effects of known sub-surface solution activity. These case studies illustrate the use of geophysical exploration methods in adding value to the engineered design.