(1). Modified proctor compaction test of soil -
The modified proctor compaction test of soil, because of heavy vehicles and need for higher compaction the modified proctor test was developed to give a higher standard of compaction. It is referred to as modified AASHO test. This procedure is similar to standard proctor test , except for the application of higher compaction effort. The difference standard proctor test with modified proctor test is that the soil is compacted in 5 layers, with rammer of mass 10 16 (4.54 Kg) and height of fall of 18 inch (45.72 cm). IS: 2720 (Part VII) – 1965 recommends the use of 4.89 Kg rammer with a drop of 45 cm for heavy compaction.
(2). Comparison of Compactive Energies
Compactive energy used in standard proctor test
=2.5× 30.48 × 25×3/945
= 6.05 Kg - cm/ml
Compactive Energy used in modified proctor test
= 4.54 × 45.72 × 25 × 3.
= 27.46 Kg - cm/ml 945
(3.) Field compaction methods -
Three methods of compaction are rolling, ramming and vibrating and the three categories of compaction equipments are roller, rammer and vibrator.
Rollers are usually of three types -
(i) Smooth wheel rollers
(ü) Sheep foot rollers
(iii) Pneumatic tyred rollers.
(i) Smooth wheel rollers are of three types.
(a) The conventional three wheel type with two large smooth faced steel whe in the rear and one smaller smooth faced drum in the front weighing from 20 to 150 KN.
(b) Tandem rollers weighing from 10 to 140 KN,
(c) The three axle tandem rollers weighing 120 to 180 KN
Short Answer Type Questions
1. In Heavy Compaction Test the weight of rammer is -
(a) 2600 gm
(b) 2900 gm
(c) 4500 gm
(d) 4900 gm
Answer: (a)
2. The aim of compaction test is to get values of -
(a) maximum void ratio and moisture content
(b) density and moisture content
(c) dry density and maximum moisture content
(d) maximum dry density and optimum moisture content
Answer: (d)
3. If specific gravity of soil solids of a soil having optimum moisture content 16.5% and maximum dry density 1.57 gm/cc, is 2.65, void ratio at optimum moisture content is:
(a) 0.488(b) 0.588(c) 0.688 (d) 0.788
Answer: (c)
4. A rough estimate of the moisture content and achieved dry density of a soil mass, being compacted during construction under OMC conditions, can be obtained using an instrument, called: -
(a) proctor's needle
(b) hydrometer
(c) lactometer
(d) shear van
Answer: (a)
5. Optimum moisture content is the moisture content when
(a) dry density is maximum (b) shear strength is maximum
(c) permeability is maximum (d) settlement is maximum
Answer : (a)
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