Earth pressures on spillthrough abutments

The earth pressures exerted by cohesionless backfill against spill through abutments have been investigated by instrumenting two full size structures with vibrating wire earth pressure cells which were calibrated in soil under laboratory conditions. The abutment deformations were recorded with inclinometer tubes and precise surveying techniques, and the column bending was measured using vibrating wire strain gauges. The earth pressures were found to be influenced by the concrete expansion during hydration which caused transverse bending of the columns after the capping beam pour, as well as longitudinal backward rotations and bending of the abutments after the deck slab pours. High residual lateral earth pressures were exerted against the rear of the capping beams due to heavy compaction of the backfill at this level, thus causing the abutment to rotate forwards and become effectively propped by the deck slab. Traffic loading and deck slab temperature fluctuations were found to cause seasonal earth pressure variations. The lateral earth pressure profiles as predicted by the existing design methods were found to be totally unrepresentative of the Wisley results, and a modified design approach has been proposed. Model tests were performed in the laboratory to investigate the behaviour of embedded laterally loaded columns within a spill through abutment. At small lateral displacements, the friction of the soil against the column sides was found to contribute significantly to the total soil resistance. Soil deformations were measured using specialised photography and the interaction between columns was found to be negligible. A nuclear density probe was compared with other common methods of measuring the in-situ density of compacted backfill. A modified resin impregnation technique was developed to measure the density variations within a laboratory test specimen of dry sand.