The temporary casing and CFA auger are drilled into the ground simultaneously but in opposite directions. The casing’s cutting shoe drilling easily through hard layers and prevents flighting of material above that may undermine existing structures. Piles are formed in the same way as conventional CFA, with concrete pumped through the hollow stem as both the auger and casing are withdrawn. Reinforcement cages are installed following concreting of the pile.
Cased secant piled walls are built in the same was as when using rotary bored methods; for hard/soft walls. The unreinforced primary piles are installed first. Secondary piles are installed by cutting through the cured primary pile concrete to form the reinforced piles. The higher vertical tolerance of cased CFA piles means verticality is maintained along their entire length, making walls watertight.
Van Elle can installed secant piled retaining walls of piles of up to 750mm diameter and 38.5m depth.