Dynamically Cast-in-Place Piles-PDF

PDF

Pdf Summary

The article describes Dynamically Cast-in-Place (DCIP, or Franki-type) piles and a conservative method for estimating their capacity from Standard Penetration Test (SPT) N-values. The method applies Nordlund’s empirical driving formula, which relates allowable load to hammer blows, hammer weight and drop height, and expanded-base concrete volume. The author correlates its constant, K, with SPT N-values using more than twenty pile-load-test records from Alberta and British Columbia. Predicted capacities were generally below observed failure loads.<br /><br />DCIP installation involves driving a heavy-walled tube into the ground using a compacted concrete plug, then expelling small charges of zero-slump concrete under high-energy hammer blows to form a dense, expanded base. The pile shaft is constructed dynamically or formed with a permanent casing and plastic concrete. The method is particularly useful for installing piles through soft, wet or loose soils to a competent bearing layer, for design loads up to about 400 kips.<br /><br />The proposed correlation should not be extrapolated beyond its stated range: the chart excludes N-values below 10, where adequate base formation may be difficult, and values above 80 may reflect cobbles rather than representative soil strength. Base construction should use more than one 5-cubic-foot charge in many conditions, but no more than five; if adequate resistance is not achieved, the pile should be driven deeper.<br /><br />Advantages include reduced soil and water contamination, densification of the base and surrounding soil, and potential shaft-friction gains. Limitations include vibration, soil displacement and possible movement or damage to nearby piles and structures. Reinforcement, pile spacing, concrete quality and site monitoring require careful attention. Overall, the formula and correlation are presented as useful, conservative tools for capacity estimates, construction guidance and inspection.

Keywords

Dynamically Cast-in-Place piles

Franki-type piles

SPT N-values

Nordlund driving formula

pile capacity estimation

expanded-base concrete

pile-load-test records

conservative design

soft wet loose soils

pile installation methods