Soil Structure Interaction Analysis of a Dry Dock

Abstract

Pile foundation is one of the most popular forms of deep foundations and is widely used for supporting water front structures in weak soils characterized by low shear strength and high compressibility, and also in structures which are subjected to heavy lateral loadings and moments. The lateral forces are mainly due to berthing forces and lateral earth pressure due to unstable slope as a result of dredging or siltation etc. Conventionally API guidelines and Vesic equation are used to analyze the laterally loaded piles. The study of laterally loaded pile in active soil wedge requires a proper assessment of soil structure interaction phenomenon involving the interaction between pile surface and the surrounding soil. The instability of soil wedge can occur due to self weight, surcharge load, dredging, siltation and earthquake force. Laterally loaded piles are analyzed by methods derived from the classical beam on elastic foundation mode in which the soil support is approximated by a series of independent elastic spring. The soil spring constants estimated from API guidelines and Vesic equations are not suitable for piles located in active soil wedge. Hence a numerical study is carried out for on dry dock in site specific soil and in dense sand, in order to study the behaviour of piles in active soil wedge. Based on the P-Y curves plotted for piles located in active soil wedge, appropriate reduction factor is obtained for API guidelines for dense sand. From reduction factors, it is concluded that the effect of active soil wedge decreases with increase in distance from the crest of the wedge. Profile of the active soil wedge using P-Y curve plots from Plaxis results closely matches with the theoretical soil slip plane. Soil spring constants are estimated from the modified API curves and are used to model the dry dock in Staad pro for dense sand in order to validate the results.