New Device for Measuring Drilled Shaft Bottom Sediment Thickness-Article

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The article presents the Ding inspection device (DID), developed to measure sediment thickness at the bottom of drilled shafts without requiring personnel to enter the excavation. Sediment can reduce end-bearing capacity, yet measuring it is difficult in shafts constructed under water or slurry. Conventional weighted-tape estimates are subjective, while the established shaft inspection devices are heavy, costly, and time-consuming to operate.<br /><br />The DID is lowered to the shaft base on a cable. Its three narrow legs penetrate the sediment and rest on the firmer material below, while a lightweight plate rests on the sediment surface. The difference in penetration is read as sediment thickness. A digital version uses a position sensor for submillimeter measurement precision; resetting it by lifting the device allows measurements at multiple locations. The device weighs about 8 kg, and a trained operator can generally complete an inspection in under 10 minutes.<br /><br />Laboratory tests with sand and clay showed close agreement between DID measurements and a manual thickness gauge. Field comparisons at sites in Virginia and Florida found results generally consistent with those from the mini-SID, although the DID tended to report somewhat greater thicknesses. Calculations indicated that penetration of the legs into the shaft base and of the plate into the sediment has negligible effect on readings for typical engineering applications.<br /><br />The authors conclude that the DID offers a practical, repeatable inspection method, particularly where sediment is relatively uniform. More field testing is needed to establish correlations with existing devices across soil types. Coarse gravel or cemented particles may require a specially configured DID.

Keywords

Ding inspection device

sediment thickness

drilled shafts

shaft inspection

end-bearing capacity

underwater excavation

slurry construction

position sensor

mini-SID

field testing