The Standard Penetration Test (SPT) N value is corrected for overburden pressure using the relation (Peck, 1974):
Choose the correct answer
N_c = N (no correction needed)
N_c = 0.77 log(2000/sigma_v) x N where sigma_v is effective overburden (kPa), applicable for sigma_v > 25 kPa
N_c = N x depth
N_c = N / 2
Correct Answer
B. N_c = 0.77 log(2000/sigma_v) x N where sigma_v is effective overburden (kPa), applicable for sigma_v > 25 kPa
Why is this the answer?
SPT N correction for overburden: Peck correction: N_c = 0.77 log(2000/sigma_v) x N for sigma_v > 25 kPa (no correction for sigma_v = 1 ton/ft2 = 100 kPa). Also water table correction: if water table is within B above footing: N_corrected = 0.5 N + 15 (Terzaghi). Corrected N used for bearing capacity and settlement.
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