68_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

68_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 -...

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X9 o Insert accelerometer and load cell into rod string under hammer to measure energy entering rod system (ASTM 04633-86, Pile Dynamics Inc.). Then correct N value. o Many years of SPT experience were accumulated before energy measurements and many correlations were developed. The average energy for these correlations is in the range 50-60% of theoretical (E max = 140 Ib x 30" = 4,200 in-Ib). (metal on metal hammer impact - instantaneous peak force during impact may exceed 25,000 Ibsl) o Common to use N values for liquefaction potential calculations. These methods have used N 60 (60% energy, ASTM 06066) as the "standardized" blow count. o Bowles (1996) suggests to correct blow count N to 70% theoretical energy and then further to 1 tst (=95.76 kPa) overburden pressure to obtain N'70 (overburden correction mostly useful to characterize the deposit): N 70 = CN x N X 711 X 112 X 113 X 114 where 11i = adjustment factors from (and computed as shown) N!,o = adjusted N using the subscript for the Erb and the ' to indicate it has been adjusted CN = adjustment
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Unformatted text preview: adjusted CN = adjustment for effective overburden pressure p~ (kPa) computed [see Liao and Whitman (1986)]5 as eN = (9~~6r Factors 1); Country United States! Nonh America Japan United Kingdom China Hammer for 111 Average energy ratio E, Sampler correction 1b Remarks R-P = Rope-pulley or caIhead 'Ill = E,.IE". = E,/70 For U.S. lriplauto w/E, = 80 'Ill = 80/70 = 1.14 E rt X Nt = E r2 X N2 N is too high for L < 10 m Without liner 'Il3 = 1.00 With liner: Dense sand, clay = 0.80 Loose sand = 0.90 Borehole diameter correctiOD 1)4 Base value N is too high with liner Hole diameter:t 6O-l20mm ISOmm 200mm 'Il4 = 1.00 = LOS = US Base value; N is too small when there is an oversize hole • DlIta synthesized from Riggs (1986). 8kemplOD (1986), Scbmertmann (19780) and Seed et at. (1985). t '14 . .. 1.00 for all diameter hollow-stem lIugers where 8FT is lllkCD through the stem....
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