New device for measuring drilled shaft bottom sediment thickness

Abstract The sediment thickness at the bottom of a drilled shaft before the placement of concrete plays a significant role in the development of drilled shaft bearing capacity and settlement, especially for an end-bearing shaft where side shear resistance is limited and only end-bearing resistance is considered significant. Load tests have demonstrated that conscientious bottom cleaning is necessary to achieve suitable load transfer in end-bearing. Inspection and measurement of the bottom sediment thickness before concreting is challenging, expensive, and often time consuming for contractors and inspectors when direct visual inspection is not possible, as for shafts drilled through slurry or water. The Ding inspection device (DID) was developed by John Z. Ding for measuring the sediment thickness at the bottom of a drilled shaft without human access into the excavation. Laboratory model tests and field comparisons to the miniature shaft inspection device (mini-SID) have demonstrated repeatability and accuracy of sediment thickness measurements using the device.