Limestone, Sinkholes, and Karst Assessments
Where, when, how, and why sinkholes form are complex geologic questions. Sinkhole formation can damage structures and infrastructure, particularly in areas that were developed without proper assessment. The potential for sinkhole formation must be considered when preparing to develop a site. Areas that are susceptible to sinkhole formation require additional site work and planning in order to minimize additional costs associated with the prevention or remediation of sinkholes. Some structures may be incompatible with sinkhole prone areas. Without a proper assessment of proposed development sites in carbonate settings, unanticipated costs may be incurred, or worse yet, features may be overlooked that result in building or infrastructure failures in the future. Municipal ordinances in areas underlain by carbonate bedrock often require an assessment of the sinkhole hazard prior to approving a land development plan.
Assessment of Karst Features for Site Development
In the eastern United States, sinkholes occur in areas underlain by carbonate bedrock, such as limestone and dolomite. The susceptibility of carbonate bedrock to sinkhole formation depends on characteristics of the rock, such as the bedrock structure, chemistry, fabric, and impurities. Areas underlain by carbonate bedrock that are susceptible to sinkhole formation frequently have characteristics visible on the surface that are known as karst features. Karst features such as pinnacles, closed depressions, lineaments, fracture traces, and disappearing streams indicate that special precautions must be taken during site development. GeoServices can assess the location of potential karst issues with an assessment that may include some or all of the following activities:
- Desktop study of the bedrock characteristics and mapped features.
- Historical aerial photograph review to look for site changes or features indicative of karst development.
- Site inspection to look for indications of karst features.
- Subcontracted geophysical investigations.
Assessment of the Cause of Site Failures
Carbonate bedrock dissolves very slowly into the rainwater that seeps through the soil and into cracks in the rock. These cracks enlarge below the surface, hidden beneath the surface soils for a time. Eventually, a triggering event collapses the soil bridge into the bedrock opening, causing a sinkhole on the ground surface. This is a natural process, which may or may not be obvious even to a trained eye before the surface collapse. If collapse results in the failure of a structure, it is necessary to determine why the failure occurred, to avoid any additional damage. The answer to this question can be complex due to numerous potential causes such as:
- Poor planning during the initial development.
- Failure to address features that should have been recognized as having the potential to cause a failure.
- Site drainage design that resulted in the concentration of infiltrating surface water into an area susceptible to sinkhole formation.
- Alterations in surface drainage as a result of other development that result in the concentration of surface runoff.
- Leakage of water supply, waste water, or storm water lines resulting in the discharge of large quantities into the subsurface in an area susceptible to sinkhole formation.
GeoServices has experience addressing the causes of site failures. Through a careful examination of the facts, combined with an understanding of the subsurface processes, GeoServices can assess the cause of the failure and help you in planning to avoid the potential for future failures.