Question

An Standard Penetration Tests was performed using an standard sampler at a depth of 45 ft in silty sand of unit weight 125 lb/ft3. The blow counts for the first, second and third 6-inch increment of the test were 8, 13, and 16, respectively. The ground water table at the test location was at 12 ft below the ground surface. The rod length was 15 ft, and the bore hole size was 6 inch Calculate corrected SPT N-value. (I inch-25.4 mm)

Answer 1

Solution:- Given:- -Depth of test locahion =45 ft = 13.F16 m -Depth f und water table = 12 ft St means test loCation i Below GWT - Unit wt. 46/f 125x 4.45 XI /m sily sand = 125 -3 (0.3048)3 19.644 KNM Overburden Prewre at test locatton P 13.716 x19.644 269.4 KNM observed Blou Counts= 8, 13, 16 Uncorrected N-value 13 +16 29. Novo Vasious cofrectiong to be applied are- over burden pressure Correction CCN): As per Liao & Whitman (1986) b.5 95.76 where P. 0ver burden Presuse in KNm 0.5 gs.76 0. 596 O.6 269.44 B Drill Sod CorrecHon (Cd) & Bore hole dia Correcton (Cb) Bowles (1996) As per for Tod leng th 4-lom) Ce0.85-0-g5) Cd 0.87 . FoY 15 ft, Cb 1.05 7 for Bohe dia 6 inch

N-Value after oberbur den Coreetin No - CN N 0.6 X29 = 17.4 No18 N-value after Submergence Correcten CN,-15) Ne = 15+ = 15+ ( 18-15) 1 2 16.5 N-Value aftes drillod Corr ecHon 4 Bore hole dia Corre cHon- NNe CCb = 16.5 X 0.87 X 1.05 15. 07 1 Hence Corrected N- Value = 15 )