S2- Standard Proctor Test.docx

TEST NAME: STANDARD PROCTOR TEST Reference Standard: BS 1377:1975, Test 14; ASTM D 698; AASHTO T 99 1.0 Introduction Soil compaction can be a very economical method of soil improvement, and it is often used to make ground suitable for the foundations of roads and buildings. It is also used in the placing of soil fills and in the construction of earth dams to ensure suitable soil properties. The compaction is normally achieved through the input of energy into the soil by impact, kneading, vibration or static means. Compaction is a process that brings about an increase in soil density or unit weight, accompanied by a decrease in air volume. There is usually no change in water content. The degree of compaction is measured by dry unit weight and depends on the water content and compactive effort. For a given compactive effort, the maximum dry unit weight occurs at optimum water content.

Figure 1 Dry density-moisture content relationship for soil

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2.0 Principles When soil is compacted usually by mechanical means, the solid particles are packed more closely together, thus increasing the soil density while air is being removed. The size of the individual soil particles does not change, neither is water removed. If the percentage of air voids is zero, that is, the soil is totally saturated. Increasing the water content for a saturated soil results in a reduction in dry unit weight. The relation between the moisture content and dry unit weight for saturated soil is known as the zero air voids line.

Figure 2: Soil solid particles are packed more closely together when compacted

3.0 Objectives i)

To determine the relationship between the dry unit weight and the moisture content using the standard rammer in Proctor method.

ii)

To determine the maximum dry density and the optimum moisture content of a given soil

4.0 Apparatus i) ii) iii) iv) v) vi) vii) viii)

Standard compaction mold (with base plate and collar) Standard compaction hammer (24.5) 10 to 12 moisture content cans Steel straightedge Sample extruder Large mixing pan Large spoon Soil mixer (or other mixing tools, e.g., trowel, spoon or spatula)

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Figure 3: British Standard 1 liter compaction mould (left) and 2.5 kg rammer for BS ‘light’ compaction test (right)

5.0 Procedure i)

Prepare about 3 to 4 kg of air-dry soil.

ii)

Pulverize soil and use only the ones passing No. 4 (4.75 mm) sieve.

iii)

Conduct test for the first point at w of about 5% (by weight). Mix soil thoroughly.

iv)

Weight the compaction mold (i.e., without the collar and base plate) and record in data sheet.

v)

Check the volume of mold (volume of standard mold is 1000 cm3)

vi)

Fix the mold with the collar to the base plate.

vii)

Apply a quantity of moist soil in the mould such that when compacted it occupies a little over one third of the height of the mould. Apply 25 free fall blows from 300 mm above the soil by using the rammer. Distribute the blows uniformly over a surface.

viii)

Repeat the procedure above for the following two layers and make sure there is excess soil on top of the mould.

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ix)

Detach collar and base plate.

x)

Strike out soil at the top of mold by using the straightedge.

xi)

Weight the mold and soil and record its mass on data sheet.

xii)

Extrude soil from mold using the extruder.

xiii)

Take soil samples and determine w (2 moisture content determination for each compaction points).

xiv)

Conduct at least 4 compaction points, i.e., sat at moisture content of about 5%, 10%, 20% and 30% (by weight of dry soil).



6.0 Result & analysis 1.

The dry unit weight γd can be computed from

where γt

= =

 d 

t 1m

wet unit weight of the soil W (g)  9.81 (kN/m3) V (cm3 ) W = mass of the wet compacted soil sample V = volume of soil

m

=

where G

=

specific gravity of the soil (assume G =2.70)

γw

=

unit weight of water 9.81 kN/m3 (or density 1.0 g/cm3)

S

=

degree of saturation

2.

moisture content of the compacted soil W m = w = W  Ws Ws Ws Ws = mass of the dry soil sample Ww = mass of water Gγ w To plot the zero air void curve γd  1  (mG/S)

For zero-air-voids or 100% saturation, S = 1. 3. To calculate the amount of water to be added to the soil assume the initial moisture content is 1.5%, and the mass of the soil is 2500g. Then

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1.5% 

2500  Ws Ws

which may be solved for the mass of dry soil Ws which we take to remain constant. Recalling that the assumed initial weight of water in the soil Ww = 0.015 Ws and that Ws is constant, if the first required water content is 10%, the extra mass of water required W w can be calculated W 10% - 1.5%  w  0.085 Ws Subsequent water to be added to change the moisture content by 3% can be found from W 3%  w  0.03 Ws

7.0 Discussion i) ii) iii)

From the test results, what is the maximum dry density and the optimum moisture content of the soil sample Explain the zero air void line State factors affecting

8.0 Conclusion Compaction of soil is an important process, as it helps it of achieve certain physical properties necessary for its proper behavior under loading: for example, proper compaction of an earthen dam or a highway embankment reduces the chances of its settlement, increases the shear strength of the soil due to its increased density and reduces the permeability of the soil. Mechanical compaction is one of the most common and cost effective means of stabilizing soils. An extremely important task of geotechnical engineers is the performance and analysis of field control tests to assure that compacted fills are meeting the prescribed design specifications. Design specifications usually state the required density (as a percentage of the “maximum” density measured in a standard laboratory test), and the water content. In general, most engineering properties, such as the strength, stiffness, resistance to shrinkage, and imperviousness of the soil, will improve by increasing the soil density. To sum up, the objectives of this experiment which are determining the relationship between the dry unit weight and the moisture content using the standard rammer in Proctor method and the maximum dry density and the optimum moisture content of a given soil have been achieved.

MYMT@2006

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