2. [10] The following chart was developed for a particular compaction equipment

Question

2. [10] The following chart was developed for a particular compaction equipment by using a specific soil type. It is required to compact the soil using the same equipment to achieve a dry unit weight of at least 106.5 1b/ft3. Considering the cost of using the equipment, state the thickness of each layer and the number of roller passes to achieve the required dry unit weight. Note: the diagram is drawn to scale Dry unit weight, a (lb/ft3) 104 100 108 0 0.00 Number of roller passes 0.50 2 1.00 4 1.50 15 45 1.83 15.72 16.00 16.50 17.00 Dry unit weight, y (kN/m3)

Explanation / Answer

Sol- To find the best combination make permutations -

The final layer of soil has to be 6 ft thick.

i) If 2 passes of roller for a soil depth of .5 ft (approx.) and 5 passes for 3.5 ft depth of soil then we will get desired density for 6 m soil layer.

ii) If we pass the roller on 3 ft layer for 2 times and then again 3 ft layer is laid and roller is passed 2 times the desired density with 6 ft soil layer is acheived.

Rest all combination for density- 16.54 kN/m^3 will result in large no of roller passes thus more cost.Thus the best one is second one.

The roller will be passed total 4 times- 2 times on each layer.

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