Pile Design and Construction Practice, Fifth edition

124 Piling equipment and methods
not occur, or when 1000 litres of fluid had been injected to limit hydrofracture of the soil
below the gravel.
Shaft grouting of cast-in-place piles and barrettes entails rupturing the outer skin of the
pile and pushing it against the surrounding soil. This increase in lateral pressure is intended
to cause local increases in the soil density which had become loosened or softened by the
pile construction and thereby enhance the shaft resistance of the pile. When shaft grouting
in granular soils, cementation of the soil particles may occur and voids and fissures become
filled giving improved contact between pile and soil. The usual technique is to install 50 mm
diameter steel tubes-à-manchette around the perimeter of the reinforcement cage for the
depth to be treated, with non-return connections to the surface. The manchettes on the tubes
at 1 m centres are cracked at pressures up to 80 bar and flushed with water after allowing the
concrete to cure for 24 hours and each sleeve pressure grouted 10 to 15 days thereafter.
Littlechild et al. (3.18) report on a series of tests on 20 shaft grouted, cast-in-place piles in soft
marine clay underlain by alluvial deposits of stiff clay and dense to very dense sand in
Bangkok. The measured shaft resistances for the shaft grouted piles, ranging from 150 to
320 kN/m 2 , were approximately double those without shaft grouting. The test piles were
reloaded more than one year after grouting and showed no loss of resistance in either
the clay or sands. Core samples along the pile/grout interface showed grout infilling cracks
and fissures in the concrete and a grout zone 20 to 30 mm around the pile with some
cementation of the sands.
3.4 Procedure in pile installation
Each class of pile employs its own basic type of equipment and hence the installation methods
for the various types of pile in each class are the same. Typical methods are described below
to illustrate the use of the equipment described in the preceding sections of this chapter.
Particular emphasis is given to the precautions necessary if piles are to be installed without
unseen breakage, discontinuities or other defects. The installation methods described in this
section are applicable mainly to vertical piles. The installation of raking piles whether driven
or bored is a difficult operation and is described in Section 3.4.11.
BS EN 1536 and BS EN 12699 deal with the execution of bored and displacement piles
respectively. However, in many respects the guidance on installation in these new codes is
not as comprehensive as that contained in BS 8004. For example, BS EN 12699 does not
comment on appropriate penetration, stroke, drop or weight of hammer, simply requiring
that a suitable hammer or vibrator be used to achieve the required depth or resistance
without damage to the pile.
3.4.1 Driving timber piles
Timber piles are driven by drop hammer or single-acting hammer after pitching them in a
piling frame, in crane-suspended leaders or in trestle guides. The Swedish piling code
requires the hammer to weigh at least 1.5 times the weight of the pile and helmet with a minimum
of 1 tonne. Diesel hammers, unless they are of the light type used for driving trench
sheeting, are too powerful and are liable to cause splitting at the toe of the pile. The heads
of squared piles are protected by a helmet of the type shown in Figure 3.20. Round piles are
driven with their heads protected by a steel hoop. A cap is used over the pile head and hoop,
or packing can be placed directly on the head.