Group Index Test Report

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4.3.3 Group index
To evaluate the quality of a soil as a subgrade material, the Group Index (GI) is also used along with the groups and subgroups of the soil. Group index is a function of the liquid limit, plasticity index, and the amount of material passing the 0.075mm sieve. A group index of 0 indicates a “good” subgrade material and a group index of 20 indicates a poor subgrade material (AASHTO, 2000). Group index is calculated using the following formula.
GI = (F-35) [0.2 + 0.005(LL-40)] + 0.01(F-15) (PI-10)
Where F= percent of fine passing sieve size 0.075mm LL = Liquid Limit PI = Plastic Index
When the group index for soils belonging to groups A-2-6 and A-2-7 is calculated the partial group index for PI should
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It measures that force needed to push 49.6mm diameter plunger very slowly 1.25mm/min into a compacted cylindrical soil sample. The test is usually carried out on saturated specimen from which +20mm stones have been removed, as this impede run penetration.
For the present study three point CBR tests performed on materials compacted with optimum water content and for this, three specimens were prepared. The specimens are compacted using three different compactive efforts (i.e. 10, 30, 65 blows per layer) to obtain unit weights both above and below the desired unit weight. After allowing specimens to take on water by soaking for 4 days each specimen were subjected to penetration by a cylindrical rod. This load is divided by the load required to force the piston to the same depth in a standard sample of crushed stone (a high quality crushed stone material with a CBR value of 100%) AASHTO, 1993. Results of stress (load) versus penetration depth are plotted to determine the CBR for each specimen. The CBR at the 95% maximum dry density is determined from a graph of CBR versus dry unit weight according to the project technical
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The weight of an empty bottle was determined using a weighing balance. The bottle was filled with distilled water to the brim and its weight determined. 10gram soil sample of passing sieve size 2mm added into empty bottle and its weight determined appropriately. Water was added about half to three-fourth of the pycnometer and soaked for 10 minutes then partial vacuum were applied to the contents for 10 minutes, to remove the entrapped air; latter water added to the brim and its weight determined. The test was done at 20ᵒc water

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