Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 379

Some penetration under the self-weight of the pile is normal. For soft soil
conditions, particular measures are taken to avoid an uncontrolled run.
Piles are then driven or drilled until pile refusal. Pile refusal is defined as the
minimum rate of penetration beyond which further advancement of the pile is
no longer achievable because of the time required and the possible damage
to the pile or to the hammer. A widely accepted rate for defining refusal is
300 blows/ft (980 blows/m).
Figure 5.51 shows the insertion of one pile into another one.
The shims are inserted at the top of the pile within the annulus between
the pile and jacket leg and welded afterward. This metal-to-metal connec-
tion is achieved by a hydraulic swaging tool lowered inside the pile and
expanding it into machined grooves provided in the sleeves at two or three
elevations.
This type of connection is most popular for subsea templates. It offers
immediate strength and the possibility to re-enter the connection should swaging
prove incomplete.
Grout is extensively used to

“ cement ” the annulus between pile leg and

jacket sleeve. An annular gap of 50 - 100 mm is usually selected. The grout

should flow from the bottom up.
The mix is generally cement plus water. Fly ash may be used to replace part
of the cement in order to reduce heat of hydration. Silica fume may be added to

(b)

(a)

FIGURE 5.52 (a) Resting the pile on the jacket. (b) Pile padeye for lifting.