Case history: Pile Foundations of a Large Gantry Crane

Direct motivation for the present study was the reconstruction of the existing gantry crane foundation situated in one of the major factories in the Northern part of Poland. The problem has been analysed in connection with the excessive settlement of the part of the track founded on the approximately 9-meter thick layer of non-compact embankment. One of suggestions of repair works assumed the carrying out of the jet-grouting columns under the beam. It seemed that random fluctuations in flexibility or bearing capacity of piles had resulted in large random fluctuations of bending moments of the beam. A static scheme as well as random model has been proposed. Then a procedure of evaluating random fluctuations of bending moments, based on Monte Carlo method, has been elaborated. The procedure can serve the cases when piles work within the elastic range, as well as in the cases when some piles under the beam are over-loaded and the load has to be carried by other piles. The computations have provided evidence for a considerable influence of the fluctuation of the pile bearing capacities on the bending moments. The extent of that effect, of course, depends, first of all, on the bearing capacity fluctuation range, measured by the coefficient of variation. It can be demonstrated that in the situation when the limiting bearing capacities of the piles have been exceeded, the positive correlation causes a considerable increase of the absolute value of the bending moments. When accompanied by the high values of the reliability index, the values of bending moments obtained from the probabilistic analysis may considerably exceed the moments from the deterministic computations.