Quiz-02-Summer10

Quiz-02-Summer10 - unit weight of 19 kN/m 3 The SPT...

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Solution to Quiz No. 2 1. (2 points). Briefly describe the difference between the standard penetration test (SPT) and the Dutch cone penetration test (CPT) as a means of site investigation. Comparison between the SPT and the CPT SPT CPT 1 Type of soil Best for G and S Best for soft M and C 2 Samples Disturbed samples obtained No samples 3 Drilling Borehole required No boring required 4 Results Estimates bearing capacity Bearing capacity and settlement 5 Type of test Dynamic test Static test 6 Procedure A 2”-diameter split spoon sampler is driven 18” into the ground by a 140# hammer dropped 30”. Only the last 12” are recorded as the “ N ” value. A conical probe is jacked into the ground at a constant rate of 10 to 20 mm/s. The cone tip’s resistance q c and the side sleeve friction q s are measured. The total q t = q c + q s . 2. (8 points). An SPT was performed at a site where a 10 foot square foundation is to be constructed at a depth of 6 feet below the surface in medium-dense sand, with a
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Unformatted text preview: unit weight of 19 kN/m 3 . The SPT recorded blows were 3-5-7 to penetrate the split samplers 18 inches. The water table is 16 feet below the surface. Estimate the angle of internal friction. The raw SPT value is N = 5 + 7 = 12 (that is, only the last two sets of 6” penetrations). Assume the use of a US-style donut hammer efficiency is E m = 0.45, and the other parameters C B = 1.00, C S = 1.00, C R = 0.75. With these values, the SPT corrected to 70% efficiency can use the table of correlations based on the N’ 70 , ( 29 ( 29 ( 29 ( 29 ( 29 ' 70 0.45 1.00 1.00 0.75 12 6 0.70 0.70 m B S R E C C C N N = = = That corrected SPT N’ 60 is then corrected for depth, ( 29 ( 29 ( 29 ( 29 ( 29 ' 70 70 100 100 6 10 2 19 corrected N N depth effectiveunit weight m-= = = The table of correlations suggests that for a medium-dense sand, an angle of internal friction is about 33º....
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