Three-inch diameter piston cores collected from the Gulf of Mexico undergo a large number of geological and soil engineering tests in order to determine relationships between various physical parameters. Electrical resistivity logs are run to determine zones of interest. Cone penetrometer and vane shear measurements are being made on these zones and samples collected for water content, density, grain size, plasticity and carbonate content analyses. Additional samples are collected for absolute resistivity calibration, pore water properties consolidation and triaxial (CU) tests. Lithological, structural and textural characteristics are also examined.
The vane shear and cone penetrometer readings are correlated with triaxial tests. Comparison of all abovementioned parameters and other parameters derived from those measured indicates interesting relationships and clearly reveals that many of the fast tests adequately describe the general characteristics of the material, as long as a number of the time-consuming experiments, such as triaxial testing, are conducted for calibration purposes. Horizontal correlation can be done with shallow penetration high resolution subbottom profiling while in situ electrical resistivity logging can replace detailed coring that is normally required for determining sedimentary characteristics.
Several types of investigations are being carried out in the marine environment by industry, universities, research and service groups and by government and state agencies. The purposes of such investigations primarily are applied research and economics rather than pure research. In spite of the intensity of work in many disciplines, a tremendous overlap of effort takes place, partly due to the confidential nature of the work and partly due to lack of communication. Engineers, geologists, oceanographers, biologists, ecologists, environmentalists, planners, administrators and others not only speak different languages, but are also too occupied to pay enough attention to other workers. This, in addition to lack of funds for all necessary research, often leads to duplication and an uneconomical approach to a problem.
This paper is not intended to solve this complex problem but we have attempted to demonstrate the 'value of teamwork among different specialists. Different techniques, some well known, will be discussed on their relevance and then comparisons will be drawn.
It soon becomes apparent that the state of knowledge of marine sediments is limited. Certain techniques are applied that are very time-consuming, require highly skilled technical ability, and allow the presentation of detailed answers. Other techniques are less accurate but require considerable less ship time and laboratory work. A combination of both approaches is ideal, especially when the time-consuming ones are used for calibrating the faster techniques.
The upper few tens of meters of the sediment column are important from an economic, as well as a scientific, viewpoint. With the tremendous number of structures being erected upon the bottom and the pipelines and cables being laid within the bottom, an increasing number of studies must concentrate upon sediment properties and the vertical and horizontal extent of specific layers. The most obvious method is to obtain cores and to describe and analyze them. Coring is an expensive and time-consuming process. It is neither possible nor desirable to eliminate coring entirely; however, there are methods that help reduce this process to a minimum.
