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Florida Agricultural and Mechanical University Division of Engineering Technology Spring 2017 Soil Mechanics & Foundations ETC 3211 Assignment Just solve problems: 5.1, 5.2, 5.6, 5.7, 5.11 Problems 5.1 State whether the following are true or false. a. In the same soil, the optimum water content would be greater for stan- dard Proctor compaction test than for modified Proctor compaction test. b. Relative compaction cannot exceed 100%. c. Sheepsfoot rollers are very effective for compacting clays. d. Strength of compacted clay is higher when compacted dry of optimum than wet of optimum. e. Hydraulic conductivity of a compacted clay is higher when compacted dry of optimum than wet of optimum. 5.2 It is proposed to carry out a laboratory compaction test on a 2.5 kg soil sample currently at a moisture content of 10.0%. How much water should be added to raise the moisture content to 16.0%? 5.3 Given G, = 2.75, calculate the zero-air-void unit weight for a soil in kN/m² at w = 5%, 8%, 10%, 12%, and 15%.
5.4 The results of a standard Proctor test are given below. Determine the max- imum dry unit weight of compaction and the optimum moisture content. Weight of metall Volume of Proctor mold (cm) Moisture content in the mold (N) (%) 943 14.5 943 18.46 10.2 943 20.77 12.3 943 17.88 14.6 943 16.15 16.8 5.6 5.5 For the soil described in Problem 5.4, if G, -2.72, determine the void ratio and the degree of saturation at optimum moisture content. The results of a standard Proctor test are given in the following table. Determine the maximum dry density (kg/m') of compaction and the optimum moisture content. Mass of wet soil Moisture Volume of Proctor mold in the mold content (cm³) (kg) (%) 943.3 1.68 943.3 1.71 10.6 943.3 1.77 12.1 943.3 1.83 13.8 943.3 1.86 15.1 943.3 1.88 17.4 1.87 19.4 943.3 943.3 1.85 21.2 5.7 A field unit weight determination test for the soil described in Problem 5.6 yielded the following data: moisture content = 10.5% and moist density - 1705 kg/m³. Determine the relative compaction. 5.8 The in situ moisture content of a soil is 18% and the moist unit weight is 16.5 kN/m³. The specific gravity of soil solids is 2.75. This soil is to be exca- vated and transported to a construction site for use in a compacted fill. If the specifications call for the soil to be compacted to a minimum dry unit weight of 16.27 kN/m' at the same moisture content of 18%, how many cubic meters of soil from the excavation site are needed to produce 7651 m² of compacted fill? How many 178 kN truckloads are needed to transport the excavated soil? 5.9 A proposed embankment fill requires 3500 m' of compacted soil. The void ratio of the compacted fill is specified as 0.65. Four borrow pits are available, as described in the following table, which lists the respective void ratios of the soil and the cost per cubic meter for moving the soil to the proposed construction site. Make the necessary calculations to select the 8.4 9.9
pit from which the soll should be bought to minimize the cost. Assume G to be the same at all pits. Borrow pit Void ratio Cost (S/m³) 0.85 9 1.2 6 0.95 7 0.75 10 5.10 The maximum and minimum dry unit weights of a sand were determined in the laboratory to be 17.5 kN/m² and 14.8 kN/m. What would be the relative compaction in the field if the relative density is 70%? 5.11 Laboratory compaction test results on a clayey soil are listed in the table. Moisture content (%) Dry unit weight (kN/m²) 14.80 17.45 18.52 18.9 12 18.5 14 16.9 Following are the results of a field unit weight determination test on the same soil with the sand cone method: • Calibrated dry density of Ottawa sand= 1570 kg/m² • Calibrated mass of Ottawa sand to fill the cone = 0.545 kg • Mass of jar + cone + sand (before use) = 7.59 kg • Mass of jar + cone + sand (after use) - 4.78 kg • Mass of moist soil from hole = 3.007 kg • Moisture content of moist soil = 10.2% Determine a. Dry unit weight of compaction in the field b. Relative compaction in the field 5.12 For a granular soil, the following are given: • G₁ = 2.60 • Liquid limit on the fraction passing No. 40 sieve - 20 • Percent retained on No. 4 sieve-20 Using Eqs. (5.8) and (5.9), estimate the maximum dry density of compac tion and the optimum moisture content based on the modified Proctor test. 5.13 For a sand with 3% fines, estimate the maximum relative density of compac tion that may be obtained from a standard Proctor test. Given: the median grain size, D 1.9 mm.