The 900 mm deep concrete anchor pile footing is intended to provide support to the pile in vertical cantilever action by horizontal bearing against the ground.
Softer material above good ground
If there is a layer of softer material above the good ground, the lateral support for cantilever action is less than intended. This lack of support can sometimes manifest itself by the building vibrating during the spin cycle of a washing machine.
The problem can be overcome by choosing braced piles, which are not as susceptible to lack of lateral support. However, it would be better to engage a structural engineer to modify the design to maintain the integrity of the subfloor bracing system.
