Planning and design considerations in karst terrain

Abstract

This article discusses the various steps that the authors feel are necessary to the successful progression of an engineered project sited in karst terrain. The procedures require a multidisciplined approach with liaison and cooperation among the various parties to the project.

Initially, the prospective owner must have sufficient understanding of the potential engineering problems to incorporate the engineering geologist into the early stages of any planned acquisition. The first step in an investigation should include a review of the available geologic information, aerial photo interpretation, consultation with the State Geological Survey, and a geologic reconnaissance of the prospective site and surrounding area.

A go-no-go decision as to purchase can often been made at an early time. Although, in some instances, more study is needed for a particularly intriguing property.

The second stage should consider the various planning alternatives that are feasible based upon the limited available information. At this stage planning/purchase decisions can be made as to purchasing options, value of the property, design constraints, and the possible economic penalties that could be associated with the potential site construction. Various planning and construction alternatives should be considered in this phase of the work.

The third stage should include a site investigation program of moderate size, consisting of test pits and/or exploratory borings. The borings should be drilled using water as the drilling fluid, with an experienced crew and qualified technical inspection. The authors find the use of geophysical techniques can be extremely misleading unless used in conjunction with exploratory drilling. Successful evaluations using geophysical procedures occur only under ideal conditions.

The geotechnical viability of the plan and preliminary design should be investigated in the fourth phase. Additionally, the physical parameters required for the design of structures founded atop cavities can be obtained at this time. Several support schemes which incorporate cavity roof thickness, rock strength, and cavity space are discussed.

Possible construction procedures include excavation and dental concrete, grouting, piers or piles to sound rock, or moving to another area. The relative economies of these procedures are discussed in relation to the size and depth of the soil or rock cavity, possible future cavity formation, magnitude of loading and acceptable safety factors.