Geotechnical investigations were carried out at three sites offshore India. The carbonate content varied in a wide range from 15% to 96%. A study, based on laboratory and field tests, was conducted to understand the effect of varying percentage of carbonate content on the engineering properties of deep penetration piles. laboratory tests included to study stressstrain characteristics of calcareous soils, the effect of bentonite on soil-grout interface, effect of cyclic load and sensitivity whereas field tests data were analysed to understand the effect of soil set-up as a function of time on the driving resistance and ultimate static capacity of the pile. Based on this experience, suggestions are incorporated to modify the limiting values of unit frictional resistance and end bearing for deep penetration piles in calcareous soils.
Environmental conditions have been reported to be favourable for the deposition of carbonate sediments between the latitudes 30 degrees N and 30 degrees S (17). In confirrnity with this observation, the presence of high carbonate content in sand, silt and clay has been found to be a typical geotechnical feature encountered off all the coasts of India, and particularly so on the western coast. Offshore construction activities are likely to increase in the near future off the west coast of India at the three sites as indicated in Fig. 1. Geotechnical investigations were carried out at these sites using barge with diver operated rig, self elevating mobile rig, survey boat and a twin craft forming a catamaran. Typical soil profiles are illustrated in Figs. 2, 3 and 4 for site I, II and III respectively. The percentage of carbonate content in different types of soils as observed at the three sites under consideration is indicated in Table 1. It will be observed that the variations in carbonate content at the three sites are as follows:
Site I22 to 96%
Site II25 to 52%
Site III 15 to 19%
This indicates that carbonate content varies in a wide range from 15% to 96%, and the calcareous deposit is encountered in different degrees of creep and stages of recrystallization.
The main variables in carbonate sediments are Classified as mineral composition, origin, grain size and strength i.e. degree of in duration. The engineering properties are mainly affected by grain size and fast depositional changes, and differ significantly from those of silica sands, silts and clays. In order to understand the effect of carbonate content on the geotechnical properties, laboratory and field studies were carried out.
This paper briefly describes the results of the tests conducted to study the engineering properties of calcareous soils affecting the behaviour of deep penetration piles.
