Practical considerations for diminishing piled rafts on weak layered soils
Alluvial deposits are abundant in the world especially in coastal areas. Due to their young geological formation, very stiff strata are not normally obtained even at great depth, which maximizes the cost of conventional foundation variants for heavy weight structures. This paper presents basic considerations for optimized design of foundations of high-rise buildings on alluvial soils of the West African coastal city of Lagos by using piled rafts. Soil parameters have been determined from interpretation of extensive soil data from test records of different high-rise building projects within the area and back analysis of static pile load test results. Effects of raft thickness, pile length and spacing on the load-settlement behaviour of piled rafts were studied by employing threedimensional non-linear Finite-Element Analysis. Normalized curves for practical loads in the area were produced to enhance design of piled rafts for similar conditions. The extensive parametric studies with uniform length piles and uniformly distributed external loads indicated the advantage of having widely spaced piles for reducing the foundation costs. Analysis results of a specific highrise building in Lagos were found to be in good agreement with the findings of the parametric studies and previous researches with comparable input parameters.