Geohazards form a unique set of problems for existing structures. These hazards can be classified in many ways. For the purpose of this and future articles, an abbreviated list of hazards would consist of:
- Sinkholes (Karst) and Land Subsidence
- Landslides and Earth Movement
- Weathering of Sediment and Soil
- Strength of Earth Materials
- Earthquakes and Tsunamis
- Rivers and Floods
- Severe Weather (Hurricanes and Tornadoes)
Sinkholes and Subsidence
Among the most common problems, which may result in material loss to structures in Karst terrain, are those resulting from subsidence of the ground due to to natural processes of sinkhole development. Issues involving the cause of soil subsidence usually occur during the construction process in the development of Karst terrains. The solution of limestone bedrock taking place beneath a cover of sediment is the usual cause of sinkholes. Certainly, other causes exist. Unexpected, localized subsidence of the ground can be catastrophic or inexorably slow.
Different areas of the country suffer from different degrees of the potential problem. Case histories are perhaps the best method of gaining insight into the complexities and varieties of the problem. Investigation of an existing issue should begin with having an investigator who has a thorough understanding of the localized hydrogeologic processes. Initially the definition of “sinkhole” should be on a policy-by-policy basis to evaluate if a claim is warranted.
"All subsidence issues are not sinkholes."
The photographs above show a collapsed parking lot which resulted from a failed, 30 year old storm sewer pipe.