Design of Helical Piles for Heavily Loaded Structures

Abstract

Over the past 20 years the square shaft solid steel helical screw pile has come into expanded use as a permanent deep foundation element in new construction of heavily loaded structures, i.e., column loads in excess of 445 kN (100,000 lbs). This increased use, along with recognition by every national building code in the United States of at least one manufacturer's helical screw pile, emphasize the importance of helical screw pile technology as it pertains to new construction. This paper presents an introduction to design methodology for heavily loaded helical screw piles in new construction common to all manufacturers of helical screw piles, covers pile load capacity, installation torque versus capacity, discusses the helical screw pile as a pure axially loaded element where special consideration is given to pile placement for lateral load transfer such as seismic and wind forces, discusses pile grouping and pile cap design, concrete to pile shaft load transfer hardware, settlement, long-term creep, corrosion, slenderness buckling of the pile shaft, water migration along the shaft in expansive clays, discusses the refusal condition, covers the economics of helical screw pile technology, especially in difficult soils, tight access and environmentally sensitive areas, or where schedule improvement is required, and lists the manufacturers of helical screw piles and how they can be contacted. He paper concludes with a case history of a project where helical screw piles were designed and installed for new construction under a heavily loaded structure. The helical screw pile is a viable and accepted deep foundation for construction if new heavy structures that should e considered anytime a deep foundation is contemplated.