Civil Engineering Reference
In-Depth Information
Figure 7.2
Buckling of sheet steel piling. (Photograph courtesy of CIRIA, London.)
experiment with different types of shoe. If obstructions in fill are causing the problem,
pre-boring may be resorted to.
7.1.2.2 Control of final set
In some soil types difficulty may be experienced in achieving the desired set, and
both increases and decreases of the set some time after piling have been noted. The
pile driving process frequently results in an increase in pore-water pressures within
a few diameters of the pile. Dissipation of these pressures leads to an increase in
adhesion, and hence set, with time. If the set-up is rapid, cessation of driving to splice
the pile, etc., may cause difficulty in re-starting the pile. In extreme cases refusal can
result (Figure 7.4).
Piling into chalk or other soft carbonate rocks can present special problems,
particularly with low-displacement piles, such as H-piles. Breakdown and lique-
faction of a thin layer of rock around the pile may lead to very low driving
resistances. Table 7.1 shows the driving records for steel H-piles in Upper Chalk
at Newhaven. Driving resistances were very low compared to the values expected
from the Standard Penetration Test results. Pile tests showed that the piles had an
