Volume 13, Issue 1, January 2019
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Performance Assessment of Wave Equation Analysis for Driven Steel H-piles in IGM (RESEARCH PAPER)
Pramila Adhikari, Ph.D Candidate, Yrgalem Z. Gebreslasie, Kam W. Ng, Ph.D., and Shaun S. Wulff, Ph.D.
Among the hammer, driving system, pile, and soil (geomaterial) models used in the wave equation analysis for driven pile foundations, geomaterial model exhibits the highest uncertainties in terms of its static and dynamic behaviors. In particular, intermediate geomaterials (IGMs) are transitional geomaterials with a high variation in strength and compressibility parameters. The SPT N-values of IGMs are often greater than the maximum allowable value of 60 in the Wave Equation Analysis Program (WEAP) for a static geotechnical analysis. Furthermore, it is practically infeasible to treat the IGMs as a hard rock input unless the unit shaft resistance and end bearing can be estimated. Due to this current limitation, the paper presents research outcomes and recommendations for wave equation analyses of driven piles in IGMs. An electronic database was developed to compile 26 test steel H-piles bearing on or driven into IGMs. Two different approaches were used for quantifying toe quake values in the analyses. The first approach used the default toe quake values generated by WEAP, and the second approach defined the toe quake values as a ratio of pile dimension to 120 (D/120) and 0.04 for IGM-soil and IGM-rock, respectively. The comparison between the resistances determined from bearing graph analysis and Case Pile Wave Analysis Program (CAPWAP) was performed, and resistance factors for WEAP in IGMs were calibrated. The performance of the WEAP in IGMs was found to be in close agreement with the CAPWAP with a resistance bias of 1.07 and a Coefficient of Variation (COV) of 0.30 for the first approach. Changing the toe quake values to D/120 and 0.04 for the respective geomaterials in the second approach improved the resistance bias to 1 with no change in variability. Overall, this paper presents useful information for engineers and practitioners for determining the drivability and resistances of piles driven in IGMs using the WEAP.
IGM, WEAP, pile resistance, toe quake, driven pile, intermediate geomaterials