Lake06 - Harry Poulos has done a lot of work on the topic. Attached is a simplified design procedure for designing piled rafts. He states that this probably isnt suitable for detailed design but for a first stab it should be sufficient. He has done some comparison with the results from hes design procedure compared to Plaxis results and they agreed pretty well. This is shown in the paper.
I had a quick look at the calcs but got stuck on developing the load settlmement graph, cant remember what exactly stumped me. I never re-visited it....