Drilling Secant Wall
Secant pile walls are constructed such that space is left between alternate ‘primary’ piles for the subsequent construction of ‘secondary’ piles. Construction of ‘secondary’ piles involves boring through the concrete in the ‘primary’ piles hole in order to key ‘secondary’ piles between. The secondary pile is the one where steel reinforcement cages are installed.
Secant piled walls can either be true hard/hard, hard/intermediate (firm), or hard/soft, depending on design requirements. Hard refers to structural concrete and firm or soft is usually a weaker grout mix containing bentonite.
All types of wall can be constructed as free standing cantilevers, or may be propped if space and sub-structure design permit. Where party wall agreements allow, ground anchors can be used as tie backs.