Improved Soil Characterization For Pipe Piles In Sand In Api Rp-2A

ABSTRACT In the offshore, most foundations are steel pipe piles and most of them are designed using the API RP 2A guidelines. For axial capacity of piles in sand the current guidelines in many cases show definite discrepancies when compared against actual load capacities of piles. An updated data base analysis shows that there are three major weaknesses in the current guidelines with respect to soil characterization:the consideration of the lateral earth pressure coefficient, K, as a constant (1. O or 0.8);the consideration of the unit point bearing resistance, q, as a linear function of depth; andthe absence of an unambiguous soil parameter determination process based on reliable in situ test results. Due to the erroneous assumption of a constant K, the API RP 2A guidelines show a "length effect;" it tends to under predict the capacity of shorter piles and over predict the one of longer piles. Consideration of q as a linear function of depth coupled with a step function bearing capacity factor, Nq, also contribute to over prediction for long piles, and wide variation in the prediction between users for short piles. The absence of an unambiguous in situ test method simply add to the overall discrepancies in the predictions. In this paper, specific modifications to the current API RP 2A guidelines are proposed on the basis of a data base analysis to account for the discrepancies arising from (a), (b), and (c) above. These modifications will reduce the discrepancies in the current API RP 2A method and increase the accuracy of the prediction of axial capacity of pipe piles in sand. Furthermore this will make the method fundamentally more consistent with soil behavior in deep foundations. INTRODUCTION The American Petroleum Institute (API)1 published its first set of recommended practice for planning, designing, and constructing fixed offshore platform in 1969. Since then it gained worldwide popularity and usefulness in the geotechnical community. However, along with the success it also drew criticisms, which led to its improvements2 over the years. This paper includes the results of a data base analysis of pipe piles in sand. The current data base is the updated version of a previous load test data base3 of piles in sand. THE DATA BASE Most offshore foundation piles are piles. In this paper the updated data the load tests of pipe piles in sand, It driven steel pipe base only includes consists of 60 load tests at 18 onshore sites. Most of the tests are from the United States, with a few from Canada, Holland, Taiwan, Israel, Yugoslavia and Japan. The references to the sites including other relevant information are shown in Table 1. The load tests of at least 11 of the 18 sites had already been considered in the revision and/or in the formulation of the API RP 2A previously.