An SPT log is given below. The SPT was performed with a safety hammer using the standard ASTM split spoon sampler with a liner. The borehole diameter is within the recommended range. The sand is normally consolidated, and the water table is very deep. The unit weights of the sandy clay, silty clay, and sand are equal to 17, 15, and 20 kN/m', respectively. For the sand layer extending from 8.5 to 21 ft, estimate the relative density DR and the peak friction angle op from the following depths where SPT measurements are available: 9.3, 14, and 19 ft (samples 4, 6, and 8, respectively). Depth Water levels (f) able Water USCS Graphic I During drilling 2 After completion Samples SPT Descriptions results Remarks 0 GRAVEL 3,4,4 CL Dark brown, moist, medium stiff, SANDY CLAY - 5 3.3.3 CL Brown, very moist, soft, SILTY 2.1.3 CLAY with sand seams 10 7.6.6 Brown, slightly moist to moist. 10,12,14 medium dense, fine to medium grained, SAND with trace - 15 SP silt and gravel 7,7.10 7,8,12 6.6.7 Boring 20 caved to Brown, moist, medium dense, fine 7,15,15 18 ft upon SP to medium grained, SAND with auger little gravel 10 9.15,13 -25 removal 11 9,10,11 SM Brown, slightly moist, medium dense, SILTY SAND 12 5,7.8 -30 Boring terminated after 30 ft 35 Ground water was not encountered during drilling or upon completion