Current Limitations and Challenges of Driven Piles in Rock as Demonstrated Using Three Case Studies in Wyoming

Abstract

There are currently no static analysis methods available for estimating the geotechnical resistance of a driven pile in rock. According to the American Association of State Highway and Transportation Officials (AASHTO), the limiting factor for a pile in rock is its structural capacity. The estimation of its structural axial capacity depends strongly on an effective length factor (K) and its unbraced length (L). These parameters significantly depend on its soil confinement along the pile and rock support at its toe, which lead to a large discrepancy between estimated and measured resistances. In this paper three case studies of completed pile projects in Wyoming are presented to highlight the limited knowledge and challenges pertaining to present design and construction practices of driven piles in rock. Steel H-piles were installed at Burns South, Casper and Torrington sites in Wyoming. Static analysis method were used to estimate the geotechnical resistances of these piles. Wave Equation Analysis Program (WEAP) and Case Pile Wave Analysis Program (CAPWAP) were used to verify their performances during construction. Structural capacities of these piles were also calculated. The results of the studies show that the static analysis methods and structural analyses yield inconsistent pile resistance estimations. Several recommendations are proposed: 1) develop an analytical method for piles in rock; 2) conduct full-scale load test of piles in rock; 3) characterize rock properties; and 4) develop a relationship of percent pile bracing, soil properties and embedded pile length.