Report on Design and Construction of Drilled Piers (ACI 336.3R-14)

Description

This report addresses design and construction of drilled pier foundations constructed by digging, drilling, or other-wise excavating a hole in the subgrade that is subsequently filled with plain or reinforced concrete. Although structural design and construction of drilled pier foundations are the primary objectives of this report, relevant aspects of geotechnical engineering are also discussed, as variations in subgrade properties have a critical influence on design, construction, and subsequent performance. Successful drilled pier design, construction, and performance requires reliable data on the applied loads and supporting subgrade. Because construction limitations often govern design, combined cooperation among the geotechnical engineer, structural engineer, and drilled pier contractor are essential.

This report is generally limited to piers of 30 in. (760 mm) or larger diameter, made by open or slurry stabilized construction methods. A 30 in. (760 mm) diameter boundary is an arbitrary size. Although smaller-diameter drilled piers have been designed and installed in accordance with this report, it is difficult to detect sidewall collapse. Refer to ACI 543R for concrete piles having diameters smaller than 30 in. (760 mm), piles installed by the use of hollow stem augers, or other pile types. Also beyond the scope of this report are rectangular columns on spread footings in deep excava-tions and foundations constructed without excavations by methods such as mortar intrusion or mixed-in-place.

Piers installed by tapping or ramming concrete or aggre-gate into an excavated shaft are beyond the scope of this report. Engineers and contractors have used the terms “cais-sons,” “foundation piers,” “bored piles,” “drilled shafts,” and “drilled piers” interchangeably. The term “drilled pier” is used in this report. A drilled pier with an enlarged base can be called a belled caisson, belled pier, or drilled and under-reamed footing. Drilled pier foundations excavated and concreted with water or slurry in the hole have been called slurry shafts, piers installed by wet-hole methods, or piers installed by slurry displacement methods