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

134SLT have a similar trend. The magnitudes are sometimes significantly different which isattributed to the current CAPWAP signal matching procedure of using constant damping andquake values to achieve a best match.Referring to the ∆R/R EOD distribution based on SLT (the dashed line), Figure 3.15shows that the ∆R/R EOD increased by about 5% in the top 5 m (16.4 ft) thick soil layer, whichwas characterized with relative large C v values ranging between 0.107 cm 2 /min (0.017in 2 /min) and 0.089 cm 2 /min (0.0142 in 2 /min) and small SPT N-values ranging between 6 and9. The ∆R/R EOD continued to reduce to a depth of about 11 m from the ground surface,where the surrounding cohesive soil layer has the smallest C v of 0.051 cm 2 /min (0.008in 2 /min) and the highest SPT N-value of 22. With the combined effects of the overburdenpressure and the reduction in SPT N-value from 22 to 13 below the 11 m (36 ft) depth, the∆R/R EOD indicated a peak increase of about 25%. This observation suggests a directrelationship between pile setup along the shaft and the coefficient of consolidation, and aninverse relationship between pile setup and the SPT N-value (or a direct relationship with thehorizontal coefficient of consolidation as indicated by Figure 3.4).Besides comparing with SPT N-value and coefficient of consolidation, pile setup wascompared with other soil properties (overconsolidation ratio (OCR), compressibility index(C c ) and plastic index (PI)). Figure 3.15 reveals an inverse relationship between themeasured PI and the ∆R/R EOD . For instance, within the cohesive soil layers with low PIvalues of 5.6% and 8.6% at 3 m (10 ft) and 14 m (13 ft), respectively, the shaft resistancesincreased. In other words, a pile embedded in a cohesive soil with low PI will experience alarge ∆R/R EOD at a given time. Furthermore, Zheng et al. (2010) concluded that a lowcompressive cohesive soil with a small C c value dissipated the excess pore water pressurefaster. Relating this conclusion to pile setup, the C c value will have an inverse relationshipwith ∆R/R EOD . However, Figure 3.15 reveals no such inverse relationship, especially at the11 m (36 ft) depth where ∆R/R EOD reduced with the lowest C c of 0.124. Furthermore, arelationship between pile setup and OCR could not be established in Figure 3.15.