A recent engineering study evaluated the axial behavior and capacity of driven piles in calcareous sands by performing a series of static and cyclic axial load tests on a fully instrumented pile in samples of two calcareous sands. The samples were prepared at various densities and cement contents in a large test drum capable of applying separate vertical and lateral confining stresses. The samples were characterized by performing cone penetration tests (CPTS). The model pile was instrumented to measure end bearing, skin friction and lateral stress. The results indicated that the behavior of driven piles in calcareous sand, although complex, follows various definitive patterns and that most of the commonly utilized design methodologies for piles in calcareous soils are in doubt. The results of this study also concluded that the load capacity of driven piles in calcareous sands is closely related to CPT data.
Calcareous sands extensively exist in coastal regions and shallow water areas of continental shelves. The behavior of calcareous sands is long recognized to be significantly different from that of most terrestrial sands (1, 2, 3, 4, 5). There exist considerable experimental data to indicate that the skin friction resistance of driven piles in uncemented and partially cemented calcareous sands is, in general, considerably lower than that in silica sands (l, 2, 4, 5, 6, 7, 8). Various investigations have postulated a number of attributing factors in trying to explain this phenomenon with little or no quantitative proof, since available literature data on the behavior of driven piles in calcareous sands are limited.
Except for important facilities where costly and time-consuming full-scale pile load tests can be conducted to increase design confidence, current pile design in calcareous sediments generally relies on applying a significant amount of engineering judgment and often using large factors of safety to account for various uncertainties and lack of knowledge (5, 6, 9, 10). Cost and safety considerations dictate the need for developing a better understanding of axial behavior aimed at developing a rational design methodology for driven piles in calcareous sands. This study was conducted as part of continuing effort to reach this goal. The study involved the performance of a series of laboratory load tests on an instrumented model pile to (1) understand soil-pile interaction mechanisms, (2) determine the contribution of end bearing, side friction and shear transfer mechanisms* and (3) correlate the findings with laboratory and in-situ engineering properties of the calcareous sands to establish a simple and rational design methodology.
The laboratory model pile load test program was designed to evaluate the effects of calcareous sand type, density, confining pressure and cementation on the axial behavior and capacity of driven piles in calcareous sands. Thus, the test program essentially consisted of performing a series of laboratory static and cyclic load tests on a fully instrumented pile driven into samples of two calcareous sands. The two calcareous sands were obtained from the beaches in Key West, Florida (Florida sand) and Hawaii (Hawaiian sand). As summarized in Table 1, sixteen laboratory load tests were performed.
