CENTRIFUGE MODELING OF PILE GROUPS IN SAND (FOUNDATIONS)

The behavior of pile groups in soils has not been thoroughly understood even in the simpler conditions. Analytical and numerical methods tend to ignore the viscoplastic behavior of the soil and do not reproduce exactly the field response.;Pile group analysis in sands has been the subject of very limited study due to the great cost involved in testing full-scale groups and the drawbacks of testing scale models at one gravity. Centrifuge testing is a technique that allows the small-scale modeling of stresses and strains in the soil.;A method to instrument, install, and test piles and pile groups in the centrifuge was developed from this research. Thirty-five tests were conducted to analyze soil-pile behavior. The main conclusions achieved were as follows. (a) Model scaling was validated. (b) There is good agreement between observed and theoretically calculated bearing capacity for single piles in sand. (c) There is a substantial difference in bearing capacity between one-gravity and centrifuge model pile group tests. Centrifuge pile group efficiencies were lower than one-gravity model efficiencies, but correlated well with previous uplift test results. (d) The contribution of the pile cap to bearing capacity is substantially larger than the predictions given by previous researchers. (e) The load transferred to the pile tips increases as the gross load increases and as the number of piles in the group increases. (f) The deformations at failure loads for the centrifuge tests are 10 to 15 times lower for floating pile groups and 3 to 4 times lower for piled groups, as compared to values derived using theory of elasticity methods. (g) Settlement ratios correlated well with model and full-scale tests previously reported. Current empirical methods overpredict the settlement ratios for pile groups. (h) The center pile, in a five-pile group, takes more load than the corner piles. This contradicts results derived from theory of elasticity methods, but is in agreement with previously reported full-scale tests.;Centrifuge modeling of pile groups in sand proved to be achievable and presents an interesting method to improve the understanding of pile group behavior.