Abstract
This thesis covers the investigation into the design and performance of the piled raft foundation for the recently completed shops and offices building complex on the south side of Victoria Street, London. In particular, an attempt has been made to determine the proportion of the total load supported by the piles, using simple calculation techniques. The ability to predict accurately this share out of foundation loading between piles and raft could have a marked influence in saving costs in foundation design. An attempt has also been made to predict foundation settlement with a piled raft foundation, taking into account the non-linear soil strata and heave effects from the removal of the considerable depth of overburden, in the basements. Comprehensive site investigations were carried out; initially for Blocks B. and C, and later for Block D. The results from these site investigations were used for the initial design of the piled foundations, but were found to give very conservative results. Four test piles were constructed and tested to verify the initial pile design for Blocks B and C, The test piles were instrumented with vibrating wire strain gauges in an attempt to determine the distribution of load down the pile shafts and on the pile bases. The results from these test piles showed that much higher stresses could be applied to the ground than had been indicated in the soil investigation report. Three further test piles were tested for Block D and gave similar results to the test piles for Blocks B and C. The various considerations affecting the choice of foundation design are discussed and the validity of the initial assumptions are compared with the actual performance of the foundations as derived from the results recorded by the instrumentation of the foundations. In order to monitor the dispersion of loading through the foundation system, vibrating wire strain gauges were built into the working piles and vibrating wire soil cells were installed under the rafts and at the bottom of piles. The test piles were also instrumented to record the distribution of shear forces on the shaft and the end bearing forces. The building construction was phased, commencing in 1971, but all of the blocks, Block B, C, and D are now completed and occupied. The last two were monitored for some time after their occupation.