Due to differences in loading conditions type of structures, and construction methods onshore foundation design experience cannot be directly transplanted to offshore situations. Progressive load, transfer mechanism of pile and surrounding soil is important to assess unit shaft frictional resistance of long open-ended pipe piles driven into marine siliceous sands. The key factors influencing the shaft friction are: pile length, structure and relative density of sand, pile soil load transfer characteristics, soil plugging and method of driving and loading. These items are hereinafter described in detail. A number of pile load tests performed in China are cited for illustrations. Future work is finally suggested in this paper,
For fixed offshore oil production platforms, pile foundations sometimes are indispensable under certain subsoil conditions, construction facility limitations, and environmental circumstances. Due to differences in loading conditions, type of structures, and construction methods, design requirement for pile foundation of offshore structures are quite different from those of inland structures. Thus, onshore experience cannot be directly transplanted to offshore designs. It is generally recognized that engineering experience on sea, so far, are still inadequate for confident design and construction of offshore structures. Limited working conditions, high cost of investment, and, as a rule, lack of sufficient time for design etc. give geotechnical engineers a solemn challenge Owing to improper design and construction of foundations of offshore structures, disasters involving losses of human lives an investments have happened from time to time. How to explore new approachs for better uncle standing pile foundations of offshore structures becomes a pressing problem.
It is generally considered appropriate using piles driven into sand strata for endearing purpose. Sometimes piles are driven through statisfied layers of soft clay and sand deposits to a great depth for obtaining required load carrying capacities. Seabed scour, potentially liquefied zones or unstable foundations due to soil movements etc. may also necessitate using piles to ensure safety. Piles are also used to compact loose san deposits for increasing their bearing capacities. Nevertheless, adopting jetting or other feasible construction methods to sink piles in dense sand often make pile capacity highly indefinite. While more information are available for determining pile tip resistance particularly in end-bearing sand stratum, far less data have been published on shaft resistance. Because of this situation, gross pile load capacity in sand cannot be properly assessed. In China, a few pile load tests have been performed in coastal and offshore regions. The main purpose is to ascertain end-bearing capacity of piles driven into sand strata. However, pile load tests on uniform sand deposits are very scarce even in land constructions and geotechnical data are usually poor. This makes it difficult to analyze pile?s frictional capacity in sands. Generally, unsophisticated procedures have been adopted in assessing pile capacity by making static pile load tests on site and/or by complying with specifications set forth by relevant government engineering departments and local codes. Practically no work has yet been carried out in China on investigating pile capacity in calcareous sands.
