EXPERIMENT # 3
COMPACTION TEST
Job
To determine the maximum dry density at optimum moisture content for a given soil sample by standard and modified Proctor Test.
Reference
ASTM D698: Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3(600 kN-m/m3))
ASTM D1557: Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft3 (2,700 kN-m/m3))
Objective of the experiment
Soil placed as engineering fill (embankments, foundation pads, road bases) is compacted to a dense state to obtain satisfactory engineering properties such as, shear strength,
compressibility, or permeability. Also, foundation soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and water content needed to achieve the required engineering properties, and for controlling construction to assure that the required compaction and water contents are achieved. Apparatus Mold Manual rammer Extruder Balance Drying oven Mixing pan Trowel #4 sieve Moisture cans Graduated cylinder Straight edge
Related Theory
Density of soil
Density is simply the ratio of weight (mass) and volume. For soils, following different types of densities are used,
Bulk Density, 𝛾 =𝑊 𝑉 Dry Density, 𝛾 =𝑊𝑠 𝑉 = 𝑊𝑑 𝑉 Density of soilds, 𝛾 =𝑊𝑠 𝑉𝑠
Standard and Modified Tests
The differences between Standard and Modified Proctor Tests can be understood from the following figures.
Optimum Moisture Content
The moisture content at which the dry density of a sample is maximum or optimum is known as the Optimum Moisture Content.
From the sample result of a compaction test given, it can be observed that the dry density increases with increase in moisture content till maximum dry density is achieved at optimum moisture content. After this the dry density starts to decrease with further increase in moisture content.
Relative Compaction
Relative compaction or degree of compaction is given as
𝑅𝐶 = 𝛾𝑑 𝑓 𝛾𝑑 𝑚𝑎𝑥
× 100 Where
𝛾𝑑 𝑓 = In-situ density
𝛾𝑑 𝑚𝑎𝑥 = Maximum density achieved in field
Relative Density
Relative density of free draining, granular materials is given as
𝑅𝐷 = 𝛾𝑑 𝑚𝑎𝑥(𝛾𝑑 𝑓− 𝛾𝑑 𝑚𝑖𝑛)
𝛾𝑑 𝑓(𝛾𝑑 𝑚𝑎𝑥− 𝛾𝑑 𝑚𝑖𝑛)× 100 Where
𝛾𝑑 𝑚𝑖𝑛 = Minimum density achieved in field
Procedure
1. Determine the mass and volume of the mold without collar and with or without base plate.
2. Sieve the soil using # 4 sieve and divide it into at least 4 (preferably 5) specimens.
3. Use approximately 2.3 kg or 5.9 kg (4 in or 6 in mold respectively) of soil for each specimen.
4. Prepare the specimens by adding moisture contents such that they bracket the estimated optimum moisture content.
5. Moisture content should be varied by about 2% but not exceeding 4%, so that to get at least two specimens dry and two specimens wet of optimum.
6. Assemble and secure the mold and collar to the base plate. Compact the soil in 3 or 5 layers as required giving 25 blows per layer using the appropriate rammer. The top surface of the sample should not extend more than ¼ in into the collar.
7. After compacting the sample remove the collar and strike off the excess soil with a straight edge. Any holes left in the surface should be filled with the trimmed soil and pressed with fingers.
8. Take the mass of the mold and the compacted soil with or without the base plate. 9. Remove the material from the mold and take a specimen for moisture content
determination.
10. Following compaction of the last specimen, compare the wet unit weights to ensure that a desired pattern of obtaining data on each side of the optimum water content will be attained for the dry unit weight compaction curve. Plotting the wet unit weight and water content of each compacted specimen can be an aid in making the above
evaluation. If the desired pattern is not obtained, additional compacted specimens will be required.
Analysis
Determine the moisture content of each specimen by oven drying method.
Calculate the bulk density (unit weight) and subsequently the dry density (unit weight) of each specimen using the following formulas respectively
𝛾𝑏= (𝑀𝑚+𝑠− 𝑀𝑚) × 9.81 1000 × 𝑉 𝛾𝑑 = 𝛾𝑏 1 + 𝑤 Where 𝛾𝑏 = Bulk density (KN/m3)
𝑀𝑚+𝑠 = Mass of mold + compacted soil (Kg) 𝑀𝑚 = Mass of mold (Kg)
𝑉 = Volume of mold (m3) 𝛾𝑑 = Dry density (KN/m3)
𝑤 = Moisture content from oven drying method
a) Plot the results of both standard and modified tests on a graph with moisture content as abscissa and dry density (unit weight) as ordinate.
Test Results
Optimum Moisture Content = 12.5 % Maximum Dry Density = 1.86 (g/cm3)
Comments
This moisture content is used for the compaction of subgrade or subbase/base in the field. 95% of Maximum Dry Density is achieved in field.
OBSERVATIONS AND CALCULATIONS
COMPACTION TEST
Moisture Content determination
Standard Proctor Test
Specimen Number 1 2 3 4 5
Can Number 3 4 5 6 7
Weight of empty can + lid, W1 7.78 7.71 7.5 8.1 7.7 Weight of can + lid + moist soil,
W2 11.78 10.71 10.7 11.1 10.3
Weight of can + lid + dry soil,
W3 11.48 10.41 10.3 10.70 10.02
Weight of soil solids, WS 3.70 2.7 2.84 2.60 2.32 Weight of pore water, WW 0.29 0.30 0.40 0.40 0.4 Moisture Content, w 7.9 11.1 12.5 15.3 17.6
Dry Density determination
Standard Proctor Test
Volume of mold, V =944 cm3
Specimen Number 1 2 3 4 5
Mass of mold, 𝑀𝑚 1933 1933 1933 1933 1933
Mass of mold + soil, 𝑀𝑚+𝑠 3457.2 3721.2 3909.0 3782.5 3715.2 Bulk density, 𝛾𝑏 1.615 1.894 2.093 1.959 1.888
1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 0 2 4 6 8 10 12 14 16 18 20 Dry Den sity Moisture Content
