MODELING THE EFFECT OF EXCESS PORE-WATER PRESSURE ON THE BEARING CAPACITY OF FULL DISPLACEMENT PILES IN GROUP: A CASE-STUDY IN PARMA (ITALY)

Excess pore-water pressure development during installation of piles into saturated clays is of primary importance and strongly affects pile bearing capacity and settlements. Such a problem is well known in literature, but excess pore-water pressure magnitude prediction, and then that of the bearing capacity, is an open research topic. In addition, excess pore-water pressure may increase greatly when numerous piles are installed in a relatively small area - as in the case of a pile group foundation - thus leading to a non-negligible modification of stress conditions at the soil-pile interface and, as a consequence, to a temporary reduction of ultimate load-bearing capacity. The paper focuses on the interpretation of load-test data performed on several auger-screw piles (full displacement), part of an important soil improvement intervention in Parma (Italy). The analysis of load test showed low values of ultimate load bearing capacity of the tested piles. Hence, the need to investigate the evolution of excess pore-water pressure with time and its relationship with the ultimate pile bearing capacity. In addition, special attention is dedicated to the study of possible mechanisms standing beneath the superposition of excess pore-water pressure effects among adjacent piles. Eventually, in order to give a consistent theoretical explanation of the recorded data, a simplified model is introduced. Such a model could be applied to similar case studies.