DISCUSSION ON PAPERS 13–16 Design and site control

MR FLETCHER, Paper 14

The main piers of the Orwell Bridge each transmit 35 000 t vertical load with groups of 121 piles 1 m in diameter.

The responsibility placed on the foundation designer of a major bridge is considerable. Not only do the piles have to control settlement, but also piling is always a critical path activity. It can generally be said that if the foundations are completed on programme, the bridge should also be completed on programme. The psychological effect on management and work force of seeing the pile caps completed on time is tremendous.

On this project two basic decisions helped to fulfil this. First, in spite of the variability of the chalk within the length of the bridge, the pile type, diameter and spacing and the pile cap details were standardized and, second, a preliminary trial pile contract was let, sited such that permanent works piling could start in that area immediately the main contract was let. This meant that the piling contractor did not have to spend the first few weeks on site carrying out trial pile tests to ascertain the required pile lengths.