Improved Wave Equation Analysis of Steel H-Piles in Shales Considering LRFD and Economic Impact Studies

Abstract

Shale is a transition material harder than soil and softer than hard rock. Treating shale as soil-like material in the Wave Equation Analysis Program (WEAP) could result in several construction challenges such as early pile refusal and pile damage. To overcome these limitations, this paper presents the development of improved WEAP methods for steel H-piles driven in shale including load and resistance factor design (LRFD) recommendations. Our parametric study reveals a significant effect of damping factors of shale on the bearing graph analysis and the determination of ultimate pile resistance. Using load test data of 32 steel H-test piles driven onto shale in Kansas, a back-calculation procedure was adopted to yield recommended dynamic parameters for shale, which are incorporated into two proposed WEAP methods. A range of damping factors from 0.03 to 0.97 s/m are recommended for two proposed WEAP methods, shale types, and weathering conditions. The accuracy and efficiency of the proposed methods and default WEAP method were validated and compared using 44 dynamic load test results and data of 2 static pile load tests at the end of driving. Furthermore, 49 dynamic test results at the beginning of restrike condition were also used for comparison. The LRFD resistance and efficiency factors were calibrated for the three WEAP methods for analyzing shale pile resistances. An economic study reveals that the three WEAP methods, on average, overpredict the weight of steel pile per load demand ranging from −0.01 to −0.05 kg/kN. Among the three methods, the proposed WEAP-UW-R will yield the least excess steel weight, on average, during construction, which will alleviate construction challenges encountered in the current practice, such as higher construction costs and longer durations.