Loose material drawn onto the auger and flighted upwards is called ‘entrainment’ and results in excess use of concrete and ground settlement.
We use the latest computer controlled cased flight auger pile system In these specific ground conditions. This allows the continuous flight auger to bore within a casing that penetrates with the auger. If hard layers are encountered at depth, no material can be entrained onto the auger because it is inside a protective casing.
As the pile is concreted, the casing is withdrawn. This system has been used very successfully in tight urban sites and, in particular, to install very accurate retaining walls, with no settlement of the ground during pile construction.