Developing a Simplified Model for the Design of Rafts with Settlement Reducing Piles

The simplified method to design a ground bearing raft with settlement reducing piles described by Burland (1995) has been implemented. The implemented method is based on iterative geo technical and structural analyses carried out using linear elastic geo technical models. The design process starts with the simulation of a ground bearing raft of a certain thickness to establish the location of the settlement reducing piles. Interactive soil-structure analyses are then performed to optimise the design of the foundation system. Structural analyses of a raft are carried out using column loads reduced by the estimated capacity of the piles. The reaction forces resulting from these analyses are then input into the geo technical model to derive new spring stiffnesses for the subsequent iterations of the structural analyses. The geotechnical and structural iterative analyses are carried out until the two models showed consistent predictions of settlements, proving that the spring stiffnesses of the structural model could more realistically simulate the ground response. In the implemented model the pile capacities are calculated using full base and shaft resistance. This does not restrict the type of piles to be installed and enables the adoption of more cost efficient shorter piles, including CFA piles. Upper and lower bound of the estimated pile capacities are adopted for structural checks, to be validated by pile tests.