PILING RESEARCH IN BELFAST SOFT CLAY

This article outlines some research at the Department of the Environment (Northern Ireland) geotechnical test bed site at Kinnear near Belfast. The main sections of Kinnear's continuing programme are: (1) lateral load tests and combined vertical and lateral load tests on instrumented drive precast concrete single piles; (2) site characterisation involving in situ and laboratory testing; and (3) tension and compression loading on five-pile pile groups and single piles, using 250mm square precast concrete piles instrumented in varying degrees. The programme has led to some interesting unexpected results. The geology of the site was investigated by boreholes and piezocone tests. The site has about 2m of alluvial clayey sand and silt overlying about 7m of soft, sensitive clay with high plasticity. Sand of medium density lies under the clay. The water table is 1m below ground surface. It was found that lateral load pile tests are likely to indicate a lower lateral stiffness for the soil than would be developed under combined loading in service, but that the presence of a vertical load may contribute to sudden collapse as movements increase. A pile's response to lateral load depends critically on the soil properties near the ground surface. The group test showed that group stiffness is less than that of a single reference pile.