Secant piles are reinforced concrete elements installed in a sequence of primary and secondary in order to form retention systems. Their execution takes place in stages. First of all, a reinforced concrete guide wall is constructed to set out the correct position of the secant piles and ensure the good initial overlapping between primary and secondary ones.
Primary piles are then installed by means of a clockwise rotating auger which simultaneously drives a “rotary bored” core barrel into the ground. The core barrel is provided of a cutting casing shoe made of special steel where hard material (widia) plates are mounted, suitable also for blocks, boulders and unreinforced concrete crossing.
Once the drilling has been performed and the bore is fully cleaned out reinforcement cages are installed. Such cages – which normally are 12-14 meters long – are coupled on site by welding them on the longitudinal bars or on metal clamps.
After reinforcement cages installation, concrete is pumped by means of a special supply conveyor which shall be submerged of at least 2 meters, while the core barrel is progressively removed.
The most modern equipment is equipped with a complete set of tools capable of constantly monitoring all the execution phases, measuring the main characteristics of the pile construction process: digging depth, thrust, torque, digging time..
The instrumentation gives the operator the possibility of constantly checking the construction of the pile and can be electronically connected to a data logger which provides, among other things: name of the project; stake number; date; construction time; pile diameter.
After having carried out a series of primary piles and, in any case, at least 24 hours have elapsed since the casting of the same (necessary for the maturation of the concrete) the “secondary” pile is executed. The project may prescribe, depending on static and hydraulic needs, interpenetrations between the more or less accentuated piles.