Quantifying settlement reduction from two design codes for piles in London clay

Piled foundations generally fail due to excessive settlements causing damage to the supported structure. While various methods are available to predict pile settlements, historically codes of practice have relied upon large factors of safety to ensure pile plunging is sufficiently unlikely. This can lead to confusion between serviceability and collapse limit states as both are concerned with limiting settlements. Modern codes of practice do require the serviceability limit state to be considered independently. However, guidance is rarely provided as to the specific method of predicting settlement and in some cases the expressed expectation is that this condition is satisfied for a pile designed according to the collapse limit state. Therefore, quantifying the settlement reduction provided by a design code is of interest to the engineer as this allows the level of design conservatism to be evaluated. However, this can only be done with a sufficiently large database of pile load tests in the soil deposit of interest. In this paper, two design codes are applied to a dataset of pile tests in London clay. Measured settlements are then obtained from load-test results and compared with those obtained from an unfactored ‘α-method’ analysis to obtain the settlement reduction provided by the design code