Calculate the measured SPT N-value (blows per foot), N 60, and ( N 1) 60 assuming that the vertical effective stress σ′ vo = 50 kPa. Assume that E m = 60% (i.e., E m = 0.60), the borehole diameter is 100 mm, and the drill rod length is 5 m. These values are close to meeting the criteria for undisturbed soil sampling.Ģ.2 A standard penetration test SPT was performed on a near surface deposit of clean sand where the number of blows to drive the sampler 45 cm was 5 for the first 15 cm, 8 for the second 15 cm, and 9 for the third 15 cm. Calculate the clearance ratio, area ratio, and indicate if the sampling tube meets the criteria for undisturbed soil sampling.ĭ i = D o − 2 t (where t = wall thickness)įrom Table 2.8, inside clearance ratio = 100 ( D i − D e)/ D e = 100 (2.87 − 2.84)/2.84 = 1.06%įrom Table 2.8, area ratio = 100 ( D o 2 − D e 2)/ D e 2 = 100 (3 2 − 2.84 2)/2.84 2 = 11.6% 2.1 A sampling tube has an outside diameter D o of 3.00 inches, a tip diameter D e of 2.84 inches, and a wall thickness of 0.065 inches.
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