Pile Design and Construction Practice, Fifth edition

experience to give reasonably reliable results when operated and interpreted by specialists.
The method does not give reliable results in jointed precast concrete piles, however.
The dynamic response method consists of mounting a vibrating unit on the pile head and
interpreting the oscillograph of the response from the pile. This method is again quite
widely used.
Ground-probing radar techniques are being developed to assist in locating existing
foundations and piles for potential reuse (2.21) .
The main advantage of specifying integrity testing of all or randomly selected piles while
pile installation is underway is that it encourages the piling contractor to keep a careful
check on all the site operations. However, the methods do not replace the need for full-time
supervision of the piling work by an experienced engineer or inspector.
Integrity testing will indicate if a pile is badly broken but not hair cracks; the anomalies
shown up may need to be checked by another method. The limitations of integrity testing
were demonstrated by experiences of a field trial competition in The Netherlands (7.5) . Ten
different precast concrete pile shapes with different forms of defect were installed in drilled
holes. The average score from 12 specialist firms competing in the trials was four correct
identifications out of the 10 shapes, but the suitability of the test conditions has been criticized.
Somewhat better results from a comparative blind testing are reported by Iskander et al. (11.29)
for pulse echo and impulse response methods. Defects as small as 6% of the cross-sectional
area of bored piles in varved clay were correctly identified. Cross-hole tomography was not
as effective but was able to identify the pile lengths and lateral locations of the defects.
11.6 References
Ground investigations, contracts and testing 537
11.1 BINNS, A. Rotary coring in soils and soft rock for geotechnical engineering, Geotechnical
Engineering, Vol. 131, No. 2, Institution of Civil Engineers, London, 1998, pp. 63–74.
11.2 TERZAGHI, K. and PECK, R. B. Soil Mechanics in Engineering Practice, 2nd edn, John Wiley,
New York, 1974, p. 114.
11.3 JOUSTRA, K. Comparative measurements on the influence of the cone shape on results of soundings,
Proceedings of the European Symposium on Penetration Testing, Stockholm, 1974.
11.4 CEARNS, P. J. and McKENZIE, A. Application of dynamic cone penetrometer testing in East Anglia,
Symposium or Penetration Testing in U.K., Thomas Telford, London, 1988, pp. 123–7.
11.5 WROTH, C. P. and HUGHES, J. M. O. An instrument for the in-situ measurement of the properties of
soft clays, Proceedings of the 8th International Conference, ISSMFE, Moscow, 1973, 1.2,
pp. 487–94.
11.6 HUGHES J. M. O. and ERVIN, M. C. Development of a high pressure pressuremeter for determining
the engineering properties of soft to medium strength rocks, Proceedings of 3rd Australian –
New Zealand Conference on Geomechanics, Wellington, Vol. 1, 1980, pp. 243–7.
11.7 MADDISON, J. D., CHAMBERS, S., THOMAS, A., and JONES, D. B. The determination of deformation
and shear strength characteristics of Trias and Carboniferous strata from in situ and laboratory
testing for the Second Severn Crossing, Advances in Site Investigation Practice, C. Craig (ed.),
Institution of Civil Engineers, Thomas Telford, London, 1996, pp. 598–609.
11.8 MARCHETTI, S. In situ tests by Flat Dilatometer, Proceedings of the American Society of Civil
Engineers, Vol. 106, No. GT3, 1980, pp. 299–321.
11.9 WHITTLE, R. W. Recent developments in the cone pressuremeter, Proceedings of the
International Conference on Advances in Site Investigation Practice, Thomas Telford, London,
1996, pp. 533–54.
11.10 MARSLAND, A. Large in-situ tests to measure the properties of stiff fissured clays, Building
Research Establishment, Current Paper CP1/73, Department of the Environment, January 1973.