Micropiles, also called minipiles, pin piles, needle piles, or root piles, have been in use in Europe since the 1950s and have grown in popularity globally. They are small-diameter piles, usually less than 300 mm, and are particularly suitable for:

1. Supporting structural loads at sites with restricted access or low headroom.

2. Retrofi tting/rehabilitating distressed structures.

3. Underpinning.

4. Excavation and retention systems with restricted access.

5. Seismic retrofi t.

6. Expansive soils.

They are also used as alternatives to conventional piles and as anchors in retaining systems and slopes. The method of construction depends on the application .
The design of micropiles requires several steps and several years of appropriate experience. It is beyond the scope of this textbook. The reader may refer to “FHWA, Micropile Design and Construction Guidelines, Implementation Manual, Publication No. FHWA-SA-97-070, 2000” for design information.

SUMMARY:
Piles are used to support structural loads that cannot be supported on shallow foundations. The predominant types of pile material are steel, concrete, and timber. The selection of a particular type of pile depends on availability, environmental conditions, pile installation methods, and cost. Pile load capacity cannot be determined accurately because the method of installation invariably changes the soil properties near the pile. We do not know the extent of these changes. The equations for pile load capacities and settlement are, at best, estimates. Load capacities from pile load tests are preferred, but these tests are expensive and may only be cost-effective for large projects.