Lab Report #3
Determination of the Optimum Moisture Content and the Maximum Dry Unit Weight of Compaction Using Standard Proctor Test
The purpose of this report is to determine the maximum dry unit weight of compaction and optimum moisture content of a soil sample using Standard Proctor Test. These values are essential in determining the maximum moisture needed to achieve the highest strength characteristics of soils in the construction of engineering structures. It has been determined that the optimum moisture content of the soil sample is 22.7% and the maximum dry unit weight of compaction is 15.77 kN/m3.
Submitted by: Julius Rey D. Baniqued
Group Mates: Renz Gian Cavida Ephraim Madanguit Christian Paul Maranan
Roland Mondano Jr. Marc Neil Rabin
Date Performed: October 21, 2015 Date Submitted: November 4, 2015
I. Objectives
Determine the optimum moisture content of the soil sample using Standard Proctor Test.
Determine the maximum dry unit weight of the soil sample using Standard Proctor Test. II. Materials Soil Sample Mold Rammer Weighing Scale Oven Sieve #4 Mixing Pan Containers III. Methodology Yes No Record the mass of mold.
Place one layer of wet soil in the mold and compact it with 25 blows using a rammer. Do
this for three layers.
Soil does not extend >6 mm above the top of the
mold. Discard the trial. Record the mass of specimen + mold. Obtain a representative portion of the compacted
specimen and determine the moist mass and
oven-dried mass.
Repeat procedure using another set of soil in increasing water content until mass of specimen + mold of trial i is less than that of
IV. Data and Results Compaction Curve Mmd = 4509.5 g V = 939.537 cm3 Trial 1 2 3 4 5 6 Mt (g) 6020 6132.5 6203 6223.5 6350.5 6334 Mc (g) 8 8.5 9.18 8.84 10.4 8.2 Mcms (g) 73.5 50.5 75.62 66.52 75.54 82.33 Mcds (g) 68.92 45.86 66.72 58.52 63.81 65.24 w (%) 7.52 12.42 15.47 16.10 21.96 29.96 ρm (g/cm3) 1.61 1.73 1.80 1.82 1.96 1.94 ρd (g/cm3) 1.50 1.54 1.56 1.57 1.61 1.49 γd (kN/m3) 14.66 15.07 15.31 15.41 15.76 14.65
Table 1: Raw and Calculated Data for required values of compaction curve
Mmd = mass of mold
V = volume of mold
Mt = mass of mold and soil specimen
Mc = mass of container
Mcms = mass of container and moist representative portion of soil specimen
Mcds = mass of container and oven-dried representative portion of soil specimen
w = water content
ρm = moist density of compacted soil specimen
ρd = dry density of compacted soil specimen
γd = dry unit weight of compacted soil specimen
Equations used: Sample Computations (Trial 1):
100% Saturation Curve
The average dry unit weight calculated was 15.14 kN/m3. Additionaly, from the sieve analysis performed in previous experiment, it was determined that the soil is composed mostly of sand. Using the table (Das, 2010), we classify the soil as loose uniform sand with an estimate void ratio, e, of 0.8.
Figure 1: Void ratio, moisture content and dry unit weight of typical soils (Das, 2010) Using the equation,
Gs = 2.78.
Calculating the completely saturated water content,
Trial 1 2 3 4 5 6
gammad 14.66 15.07 15.31 15.41 15.76 14.65
wsat 30.78 28.98 27.97 27.55 26.15 30.83
Table 2: Values for 100% Saturation Curve
Figure 2: Compaction and 100% Saturation Curve y = -2019.2x4 + 945.71x3 - 155.53x2 + 18.914x + 13.784 y = -23.428x + 21.869 14.4 14.6 14.8 15 15.2 15.4 15.6 15.8 16 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Compaction Curve 100% Saturation Curve Poly. (Compaction Curve) Linear (100% Saturation Curve)
Diffentiating best fit equation of the compaction curve and equating it to zero, the optimum moisture content of the soil sample is determined to be 22.7%. Substituting this value to the best fit equation of the compaction curve, the maximum dry unit weight is determined to be 15.77 kN/m3.
V. Analysis and Discussion
It can be observed that as the moisture content is increased and the same compaction effort is used, i.e. 25 blows per layer, the dry unit weight is increased. This happens because water acts as a softening agent which makes the soil particles slip and move to a more dense position (Das, 2010).
However, when certain moisture content is reached, any addition to the moisture content will decrease the dry unit weight of the soil. This occurs because the water takes the space that could have been taken by the soil particles (Das, 2010). The moisture content in which the maximum dry density is achieved is the optimum moisture content. It was determined that the optimum moisture content of the soil sample is 22.7% and the maximum dry density is 15.77 kN/m3.
It can be observed there is no point in the compaction curve to the right of the 100% saturation curve which is expected in accord to theory. Also, the shape of the wet side of the optimum of the compaction curve follows the shape of the 100% saturation curve.
Compaction also has effect on hydraulic conductivity and strength. As the soil increases its unit weight by compaction, the hydraulic conductivity decreases because the pore spaces are taken by soil particles. The minimum hydraulic conductivity occurs at the optimum moisture content. Beyond the optimum moisture content, the hydraulic conductivity increases because the pore spaces are taken by water instead of the soil particles (Das, 2010). Compaction increases the strength of soils if compacted on the dry side of the optimum because of the increase in dry unit weight, thus, its bearing capacity and decreases the potential settlement of structures built on the soil. The opposite happens if the soil is compacted on the wet side of the optimum.
VI. Conclusion
Through the Standard Proctor Test, it has been determined that the optimum moisture content of the soil sample obtained from the field is 22.7% and the maximum dry unit weight is 15.77 kN/m3.
VII. References
ASTM D698-12e2, Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 ft-lbf/ft3 (600 kN-m/m3)), ASTM International, West Conshohocken, PA, 2010, www.astm.org
