Structural Evaluations
Damage to structures can result from many mechanisms in addition to sinkhole activity. Inadequate support beneath the foundation, insufficient compaction of bearing soils prior to construction, decay and compression of organic-laden soils, shrink-swell movement of highly active clay soils, erosion of surficial soils and densification of load bearing soils due to extreme changes in the water table are but a few.
Determining the presence of active sinkholes is sometimes difficult in lieu of obvious surface depressions or collapse features and is usually dependent on identifying raveling soils extending up towards the ground surface from subterranean voids or cavities. Isolated loose or soft zones, losses of circulation or an undulating limestone surface beneath a structure are not necessarily indicative of active karst or sinkhole activity.
In 2005, the Florida Geological Survey issued Special Publication Number 57 titled Geological and Geotechnical Investigation Procedures for Evaluation of the Causes of Subsidence Damage in Florida. This document recognized the need to clarify a loss due to a sinkhole and reads as follows, “Solution action on subsurface limestones is present throughout all of Florida and can be found at most locations at depth. The term ‘sinkhole activity’ has been used to suggest that subsurface, dissolution related features distant in terms of geographic vicinity or depth from the structure in question represent the process that has caused damage to the structure. This is not the case until the movement of geologic materials into the solution feature, void or cavern phenomena are near enough to the surface to cause a sinkhole loss.”