These structural elements can be distinguished into three categories, depending on their diameter: large-diameter piles, medium-diameter piles, and small-diameter piles (also known as micropiles). Among their different employments, they can be used for example as deep-reaching foundations when the upper layers of the soil have scant weight-bearing capacity or an excessive tendency to compression - namely, when it is not possibile to apply the usual superficial foundations; they can also be used as bulkheads (if the piles are laid next to one another) for the stabilization of natural or artificial escarpments and unstable cut slopes, or to heighten the safety of natural slopes that are subject to landslides.
The construction of piles is obtained by means of ground-drilling operations with total removal of a soil portion. In some cases, iron piles must be driven into the ground down to the desired depth, and drilling muds and foams must be used if particular conditions of the soil make it necessary (e.g. when the soil is melted and/or scarcely cohesive). After having cleaned out the drilled hole, a hollow metal structure made of type B450C steel cages is driven into it, and castings of concrete are executed. This very last phase must be carried out with particular technological expedients if a certain amount of water is found in the soil.
These elements are employed when deep foundations give rise to problems that can’t be solved by means of other technological devices. They are helpful both during the execution phase (as they imply the use of handy equipment in narrow spaces) and during the employment phase (thanks to their small dimensions and to the minimal impact they have on pre-existing structures). Micropiles are special small-diameter piles endowed with a conspicuous weight-bearing capacity that can be used to sustain foundations, underpinnings and abutments. They are executed by means of rotation or rotary percussion, employing techniques similar to those adopted to realize the other types of piles, and can be placed
either in a bulkhead configuration or in contiguous groups (the so-called root piles), in a vertical or sub-vertical position. In the Italian praxis, the root-pile consist of a tubular steel reinforcement (a.k.a. tube), hosed to improve its continuity and supplied, if necessary, with check valves for low-pressure injections of cement mixtures, with the addition of admixture to obtain a strengthened interspace between the steel tubular core and the soil surrounding it. Perforations can be either air-driven, involving the use of down-hole hammers for operations of rotary percussion, or liquid-driven (namely using admixtured perforating fluids) by means of abrasive tools called claw-bits or by simple rotation.