The major difference in classification and testing procedures of terrigenic and submarine soils is reviewed, and suggestions have been made for modifications which may be necessary for better understanding of the behaviour of submarine sods. Among the subtopics discussed in this chapter are (a) submarine sods, (b) Sampling disturbances, (c) laboratory tests, and (d) in-situ tests.

INTRODUCTION

Some of the earlier developments m offshore technology took place in the relatively shallow and friendly waters of the Gulf of Mexico. However, in the past three decades, offshore structures have been built in deeper waters, sometimes even more than 300 m deep, and in more difficult soil profiles and very hostile environments. Since land-based geotechnical engineering is the root of marine geotechnology, many of the developments in the latter were extensions of basic conventional geotechnology to suit oceanic environments.

Over the past 25 years, several state-of-the-art reviews have been presented on various sub divisions of the marine geotechnology (Noorany and Gizienski, 1970; Noorany, 1972; Silva, 1974; Eide, 1974; Sangrey, 1977, Fotch and Kraft, 1977; Anderson et al. 1979; Sulivan, 1980; Marshland and Windle, 1982; De Ruiter and Richards, 1983; Lee, 1985; Richards and Zuidberg, 1985; McClelland, 1975; Dayal, 1978). In most of the reviews, sampling and in-situ tests of submarine sediments have been emphasized, perhaps because they involve unique and expensive equipment, and much of the thrust of marine geotechnology has been towards the development of this equipment. However, very little is said about the applicability of the conventional geotechnical approach to marine geotechnology. This is not to say that there is any fundamental difference between terrigenic sods and submarine soils. Both obey the same fundamental principles of particulate mechanics, and both consolidate, shear and allow water passage m essentially the same way. The differences are mainly: the origin of submarine soils, the performing of laboratory and field tests, and loading conditions.

The major differences between geotechnical engineering on land and m marine environments are in the following areas:

  • submarine sods,

  • sampling disturbances,

  • laboratory testing and

  • in-situ testing. This chapter renews these differences and summarizes a comparative study between submarine sods and terrigenic sods. The emphasis is on those areas where substantial differences exist between the two types of soils, and the objective is to outline the modification which may be necessary for classification and testing of submarine sods.

SUBMARINE SOILS

The classification and testing of submarine sods implies some knowledge about the properties of the "sod" material, its distribution, depositional environments and state of stress. Although much of this information may be well known, nevertheless it may be useful to summarize certain aspects prior to focusing on the main points.

The sea floor is primarily formed from depositional processes, m contrast to the land which is formed primarily m an erosional environment. As a consequence, marine sediments exhibit more uniformity than is normally found on land (Lee and Clausner, 1979). Submarine sediments can be broadly classified on the basis of whether the sediments are land derived (terrgeneous) or are the result of marine activity (pelagic).

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