Recent trends in underwater in-situ soil testing

It is recognized that currently available underwater soil sampling techniques provide a disturbed sample for laboratory analysis, especially for shear strength testing which is a useful parameter in designing and assessing the behavior of offshore structures. Test results have indicated that the ratio of in-situ vane to laboratory vane strengths varies from one to more than three. Hence, measurement of the soil strength properties in situ is suggested as a means of enhanqing data quality. Available significant information concerning the recent trends in underwater in-situ soil testing has been summarized. There are a number of underwater activities such as pipeline projects, cable installation, harbor dredging, and light underwater installations, which require investigation of the properties of near-surface deposits only. Among the shallow penetration in-situ testing tools available, free falling type of dynamic penetrometer, and submersible platforms equipped with a cone penetrometer or vane testing device (such as DOTIPOS) show greatest promise. In conclusion, there are three primary methods for collecting geotechnical information from an offshore site, namely: interpretation of acoustic records, sampling and laboratory testing, and in-situ testing. Each method has its own particular advantages and limitations and it is usually best to employ all three methods and correlate the results to gain optimum information return.