Problems in pile construction - Piling Engineering - page 270

Figure 7.13 Defect in pile shaft caused by water. (Photograph courtesy of CIRIA, London.)
Figure 7.14 The effect of a large water-filled cavity. (Photograph courtesy of CIRIA, London.)
danger that debris can be dragged into the pile shaft, particularly if large cavities exist.
Dry voids may form where thin gravel layers exist or where piles are formed in fill.
The formation of such voids can be reduced by the use of a vibrator to insert the pile
casing. Obviously, if there is any doubt that satisfactory pile shafts will be constructed,
thin permanent casings should be used to support the soil.
Where slumping of concrete into voids has occurred, topping up the pile shaft with
fresh material frequently leads to problems (Figure 7.16).
Debris may be dislodged by removal of the casing or by the placement of additional
concrete and incorporated in the pile shaft.