S - Kam Ng PhD Dissertation Final.pdf - Digital Repository of CCEE ...

123with CAPWAP analysis at different times of restrike. The reference pile resistances at theEOD (R EOD ) were based on CAPWAP analysis of PDA data. For comparison purposes, apredominant soil type along the pile shaft and a weighted average SPT N-value (N a ) weredetermined for each data source. Figure 3.1 shows that pile resistances typically increaseimmediately after the EOD and the rate of increase decreases with time. The extent of setup,however, varies between sites. It can be observed in general that piles embedded in a soilprofile with a relatively smaller N a value (i.e., weighted average SPT N-value) exhibited ahigher resistance ratio (R t /R EOD ), indicating a higher pile setup. However, the test pilereported by Lukas & Bushell (1989) exhibited a higher resistance ratio than that of Fellenius(2002) despite similar N a values for both sites, confirming that setup is influenced by othersoil parameters. Although the mechanisms of pile setup are related to the increase in lateralstresses and the dissipation of pore water pressure, consolidation test results, in-situ lateralstresses, and pore water pressure measurements were not reported by the authors.Recognizing the difficulty in understanding the pile setup based solely on the data availablein the literature, the current study focused on collecting sufficient and good-quality soil datafor performing accurate pile setup evaluations, including SPT N-values, vertical coefficientof consolidation (C v ), horizontal coefficient of consolidation (C h ) using PiezoconePenetration Test (CPTu), over consolidation ratio (OCR), and Atterberg limits.Besides the aforementioned pile setup reported by other researchers, pile setup wasalso realized using the PIle LOad Test (PILOT) database that currently reports qualityassured historical pile load test data available in Iowa (Rolling et al. 2010). Using eight setsof data, Ng et al. (2010) reported an average of 39% increase in vertical load resistance ofsteel H-piles after five days of the EOD when comparing the measured pile resistance fromstatic load tests with the initial pile resistance at the EOD estimated using WEAP. Thisfinding confirmed the occurrence of pile setup in cohesive soils at a regional setting, wherefour different geological formations (i.e., loess, loess on top of glacial, Wisconsin glacial andloamy glacial) exist as shown in Figure 3.2.