Indirect foundation has many applications and is required in many occasions:
- In the consolidation of direct foundations with insufficient bearing capacity to support the superstructure;
- In the restoration and/or repair of foundations damaged by external physical-chemical agents (settlements, erosion at the foot of bridge piers);
- In the consolidation of lands before execution of direct foundations;
- In the realization of tie rods/anchors (applications in rock fall barriers and tie rods for the variation of the tilting of bulkheads).
The most common use of micropiles in urban areas is to build bulkheads and/or diaphragms known as “berliners”, since the size of the necessary equipment is small.
The bulkheads consist of a series of micropiles of appropriate length disposed along a straight line (staggered grid called “quinconce”) and built at variable center distances (from 30 to 70 cm), depending on the soil characteristics and the excavation heights.
The bulkheads are widely used for the support of the excavation face, allowing to operate safely and safeguarding other people’s property; they are a viable alternative to concrete diaphragms, steel sheet piling, jet grouting diaphragms and pre-fabricated bulkheads, etc.
Berliners are widely used in urban environments because, during the works, the drilling of micropiles:
- do not induce vibrations in the ground (driving of sheet piles);
- do not use bentonites for the support of the hole (diaphragms in c.a.);
- do not pollute acoustically (pile driver for prefabricated diaphragms cac).
Micropiles are generally created on site (not pre-fabricated), with small equipment (hydraulic probes, drillers) that permit the execution inside buildings. In spacious outdoor construction sites, drill rigs of considerable size and weight up to 300 quintal are used.