Significance of In-Situ and Laboratory Tests for Design of Foundations in Granular Carbonate Soils (1991)

Abstract Various in situ and laboratory tests that have been used to study the behavior and engineering characteristics of granular carbonate sediments are described and evaluated. Based on success or failure of these different test procedures (in terms of foundation performance) in situ and laboratory tests are recommended to make future geotechnical investigations in these soils more cost effective while meetin8 the technical demands of designing foundations in a material that is not well understood. Such standardization schemes will lead to significant improvements in soil characterization procedures and ultimately pave the way for improved foundation design methods. It is hoped that this will lead to development of rational geotechnical investigation programs rather than the arbitrary selection of tests and test procedures which may not always be appropriate. Introduction On a global basis, use of in situ and laboratory tests for foundation design in a siliceous environment has more or less been standardized over the last 30 years and more. For geotechnical investigations in granular carbonate deposits, no such standard exists and in situ and laboratory tests applicable to siliceous soils are often utilized in an attempt to describe the behavior andengineering characteristics of carbonate sediments. The resulting foundation design has had, in many cases, severe economic impact on a project, mainly from remedial work that has been necessary to improve foundation performance (de Matos and de Mello, 1982; Dutt et al., 1985; King and Lodge, 1988). In this paper, commonly used in situ tests are described and it is shown how some of these tests have been used (successfully and unsuccessfully) to select pile design parameters in granular carbonate soils. It is shown that, in general, in situ tests have had limited success and that there is a shift in emphasis toward more meaningful laboratory tests. This change in emphasis stems from a growing erception that in situ tests do not provide reliable data in nonhomogeneous. partially cemented, granular carbonate aeposits: Also contributing to this negative sentiment is the high cost to benefit ratio associated with most in situ test procedures. Successes and failures of various laboratory tests that have been tried to develop meaningful definition of soil conditions are described. Index for grain crushability, once thought of as the most important parameter affecting soil-pile behavior, is shown to have minimal impact, and the significance of photomicrographs of thin sections and soil compressibility is demonstrated. Finally, both in situ and laboratory tests are identified which show promise for describing material behavior and rovide reasonable material properties for Foundation design. In Situ Testing In the early days of geotechnical site investigations in carbonate deposits (in the seventies), testing of carbonate soils was limited to a suite of index tests such as grain size analysis, specific gravity, carbonate content, and Atterberg limits, and a few drained triaxial compression tests. As it became increasingly evident that results from these conventional laboratory tests on carbonate soil samples were inadequate for predicting in situ soil structure interaction, there was a widespread support and recognition in the industry for in situ testing. The following paragraphs describe some of the important in situ tests that have been used in attempts to improve foundation design practice in carbonate soils.