Calcareous sand present a particular challenge for offshore foundation engineers. The paper presents a summary of the properties of calcareous sands pertinent to pile design and reviews modifications that have been proposed to make the standard design methodologies more suitable for application in calcareous sands.

Analyses of 33 pile load tests performed in calcareous sands are presented, the measured capacities from each of which is compared with the predicted values computed using the API RP 2A (1993) recommendations with the modifications proposed by Datta et al. (1980) and the Jardine and Chow (1996) method.

The results of the analyses clearly demonstrate that the application of the Imperial College pile design method to calcareous sands is dangerous, and that predictions based on the moditications proposed by Datta et al (1980) are also, on average, non-conservative, However, simple modifications are proposed which yield predications for shaft resistance of driven displacement tubulars In calcareous sands which are consistently safe, and statistically more reliable than compared methods.


Recent research into the behabiour of piles driven in silica sands has identified important shortcomings in the physical models that underpin the widely adopted API RP 2A offshore pile design procedures (Lehane, 1992). Jardine and Chow(1996) have proposed new design methods which capture the key features of behavior more realistically, and so allow axial capacity to be predicted with greater accuracy. However, Jardine and Chow specifically state that their procedures are unsuitable for use in calcareous sand. This limitation is inconvenient because calcareous sand present perhaps the most taxing challenge to offshore pile designers.

It it well known that methods for estimating the axial capacities of steel tubulars in silica sand can be severely non-conservative in calcareous formations The current API RP 2A document (API 1993) notes that :

"..Available data suggests that driven piles in these soils may have substantially lower design strength parameters than those recommended" cementation may increase end bearing capacity, but results in a loss of lateral pressure and a corresponding decrease in frictional capacity?.

While Khorshid et al (1998) reported that at the North Rankin site (offshore Western Australia):

" Following the initial pile penetration, approximately 47 metres, this pile free fell to 114 metres below mudline as a result of the first hammer blow and no further piles of this type were installed."

Several modifications have been proposed to make the standard design methodologies more suitable for design in calcareous sands, but none has yet received sufficiently broad approval to be incorporated sufficiently broad approval to be incorporated into the forthcoming API/ISO recommendations, and so be adopted for industry-wide use.

This paper considers how the Jardine and Chow (1996) procedures might be modified for application in calcareous sands. Some introductory comments are made first on the properties of calcareous sand, and a brief review given of existing proposals for design of piles within them. A database of field tests and site investigations is then described which is used to test both an existing ?calcareous sand? design approach

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