Changes in Properties of Clay Surrounding Cast in situ Piles

Often pile load carrying capacity is derived from friction between pile and the surrounding soil. This magnitude of friction mobilised, in the main, depends on pile material, properties of the soil and method of construction. In terms of construction, piles may be either pre-formed or cast in situ. Cast in situ piles are formed by boring a hole and filling it with concrete. It is envisaged that water and both calcium and hydroxyl ions migrate from the fresh concrete to the surrounding soil and have an impact on soil properties. An experimental study was undertaken to examine the extent of soil (Oxford clay) around the pile was affected by fresh concrete. Time related study included load tests on model piles. The investigation showed that there was about 4% increase in the moisture content of the surrounding soil soon after fresh concrete was placed and with time this dissipated. It showed that there was an increase in both hydroxyl and calcium ions in the vicinity of the pile. These also affected the adhesion factor, which increased with time to a limiting value. Time related tests showed that there was a small increase in pile load capacity with time.