CFA pile behaviour in very stiff lodgement till

Abstract

The design of CFA piles in the stiff/hard lodgement till that underlies most of Dublin is usually based on published experience from similar piles in other soils that lack the high density and stiffness of this till. The results of load tests on two instrumented test piles are presented, one 450 mm in diameter and 12·3 m long and the other 600 mm in diameter and 11 m long, which were loaded to 3·15 MN and 4·5 MN respectively. A 1 m long instrumented dummy pile was formed at the same time as the prototype and was tested in the laboratory to confirm the calibrations for use in interpreting the instrumentation. The instrumented piles showed that high average shaft resistances of 230 kPa and 270 kPa were mobilised, which were of similar magnitude to those recorded on an instrumented driven pile in this lodgement till that was reported previously. The pile load tests indicate an estimated Nc value of about 7 for the bearing capacity factor in ultimate end resistance, which is less than the value of 9 normally used and considerably less than a value of about 55 estimated from the tests on the driven pile. The results also indicate a change in the load–pile-head deflection curves with time, which could be related to disturbance of the ground caused by the construction process.

Comparative Investigation of Axial Bearing Performance and Mechanism of Continuous Flight Auger Pile in Weathered Granitic Soils

“…From a series of model tests, Kassem et al [2] observed that the axial capacity of CFA piles is approximately twice of that of bored piles, which is attributed to an increase of the pile diameter by the high-pressure pumping of concrete and a higher interface roughness caused by auger rotation. Farrell et al [7] reported a shaft resistance of 230 kPa in lodgement till, which was of a similar magnitude of the driven pile. Such a finding contradicts the viewpoint of O'Neill [15], in which the bearing capacity of driven piles excels significantly over that of augered piles.…”

“…He found that the shaft resistance is independent of the relative density of sand, but strongly correlated to the cone penetration test (CPT) or standard penetration test (SPT) result. Other works were extended to soft clay [5], silty soil [6], lodgement till [7], and mixed soil [8]. Moreover, Pession and Tsuha [9] has developed a CFA-based energy pile and examined its in-field performance with different configurations in layered soil.…”

3D Roughness Measurement of Failure Surface in CFA Pile Samples Using Three-Dimensional Laser Scanning

“…In the CFA pile construction, the grouting is injected direct after excavation of a borehole in the CFA pile and hence the soil collapse can be minimized by confining of grouting in the borehole. Since the CFA pile is mainly constructed on weak ground conditions, studies have been conducted to estimate the bearing capacity and the behavior of CFA piles in various grounds (Farrell and Lawler, 2008, Gavin et al, 2009, Battista et al, 2016, Loveridge and Cecinato, 2016). In the CFA pile, the loss of ground can affect the bearing capacity of the pile (Leznicki et al, 1992 [8]).…”