Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 545

In summary, grout filling of members increases the strength of a member but
does add mass to the structure.
Grout filling of members requires the same equipment as specified above for
joint grouting.

Grouting of Piles
Platform loads may be transferred to steel piles by grouting the annulus between
the jacket leg (or sleeve) and the pile. The load is transferred to the pile from the
structure across the grout. Experimental work indicates that the mechanism of
load transfer is a combination of bond and confinement friction between the
grout and the steel surfaces and the bearing of the grout against mechanical
aids, such as shear keys.
Centralizers should be used to maintain a uniform annulus or space between
the pile and the surrounding structure. A minimum annulus width of 1 1/2
inches (38 mm) should be provided where grout is the only means of load trans-
fer. Adequate clearance between pile and sleeve should be provided, taking into
account the shear keys outer dimension.

Note that packers should be used as necessary to confine the grout. Proper
means for the introduction of grout into the annulus should be provided, to mini-
mize the possibility of dilution of the grout or formation of voids in the grout.
The use of wipers or other means of minimizing mud intrusion into the
spaces to be occupied by piles should be considered at sites having soft mud
bottoms.

'

Computation of Allowable Axial Force
Until now there has been little research into the transfer of axial force from the
pile to the leg through the grouting. The transfer of axial force from the pile to
the leg is accomplished by the bond strength between the pile and the leg through
the grouting. The allowable axial load transfer should be calculated as the smaller
value from pile or leg of the force calculated by a multiplication of the contact
area between the grout and steel surfaces and the allowable bond strength due
to axial load f ba .
The value of the allowable bond strength due to axial load, f ba ,shouldbetaken
as 0.138 MPa for API loading conditions 1 and 2, and 26.7 psi (0.184 MPa) for
loading conditions 3 and 4, where the API loading conditions are:

1. E o +D L +L max
2. E o +D L +L min
3. E D +D L +L max
4. E D +D L +L min
where E o is the operating environmental condition, D L is the dead load, L max and
L min are the maximum and minimum live load, respectively, and in both cases the
live load is appropriate to the normal operating condition of the platform. E D is
the design environmental condition in extreme environmental conditions.