DA Bruce, BSc, PhD, CEng, MICE, MIWES, MASCE, MHKIE, FGS. This paper was first published in GE’s July 1986 edition.
Enhancement by toe/ground contact grouting
When long piles are constructed through very difficult and variable soft ground conditions to bear on hard fresh rock, it is understandable that problems are occasionally encountered with soft sediment inclusions at the bases. Despite due skill and attention on the part of the contractor, circumstances often conspire to defeat the intention to provide absolutely clean bases and intimate, continuous pile-rock contact. Equally, in cohesionless soils under high hydraulic gradients, the natural resultant base instability will confound the best efforts to remove disturbed sediment. Occasionally, other constructional problems may occur, such as delays prior to concreting allowing settling of suspended sediment from the flushing medium.
The presence of the resulting soft and highly compressible inclusions is detected by coring, sonic testing, load te ting and/or analysis of construction records and inevitably the first reaction is to condemn the pile. However, the author has been involved in a number of recent cases where successful remedial works have been minimal in reiation to the costs involved in pile replacement (which has no guarantee of more satisfactory behaviour, and which may simply not be feasible given physical or logistical restraints).