standard proctor

8/11/2019 Standard Proctor

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Soil Lab Experiment: Standard Proctor

Introduction

The Proctor compaction test is a laboratory method of experimentally determining

the optimal moisture content at which a given soil type will become most dense and

achieve its maximum dry density. The term Proctor is in honour of R. R. Proctor, who

in 1933 showed that the dry density of a soil for a given compactive effort depends

on the amount of water the soil contains during soil compaction.

Theory of Soil compaction

Compaction is the process by which the bulk density of an aggregate of matter is

increased by driving out air. For any soil, for a given amount of compactive effort, the

density obtained depends on the moisture content. At very high moisture contents,

the maximum dry density is achieved when the soil is compacted to nearly

saturation, where (almost) all the air is driven out. At low moisture contents, the soil

particles interfere with each other; addition of some moisture will allow greater bulk

densities, with a peak density where this effect begins to be counteracted by the

saturation of the soil.

Objective

1. Increasing the bearing capacity of foundations

2. Decreasing the undesirable settlement of structures

3. Control undesirable volume changes

4. Reduction in hydraulic conductivity

5. Increasing the stability of slopes


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Equipment and apparatus

1. Mould

2. Rammer

3. Manual Rammer

4. Balance

5. Mixing pan

6. Trowel

7. Straight edge

8. Hammer

9. Lids

10. Drying oven11. Steel ruler

12. Soil

Procedure

1. Lumpy soils are pulverized to small sizes by using a rammer and 3 kg of the

soil is weighted2. The weight of the soil sample as well as the weight of the compaction mould

with its base (without the collar) is determined by using the balance and

record the weights.

3. Compute the amount of initial water to add by the following method

a) Assume water content to be at 8 percent

b) Compute water to add from the following equation

Water to add in ml =

Where water to add and the soil mass are in grams

4. The water is the measure out, the water is added to the soil, and the soil is

then mixed thoroughly using the trowel until the soil gets a uniform colour


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5. The compaction based is then assembled to the mould, some soil is placed in

the mould and the soil is compacted in the three of equal layers specified by

the type of compaction method employed .27 of drops of the rammer per layer

is applied to the soil .The drops should be applied at a uniform rate not

exceeding around 1.5 seconds per drop, and the rammer should provide

uniform coverage of the specimen surface

6. The soil should completely fill the cylinder and the last compacted

7. Layer must extend slightly above the collar joint. If the soil is below the collar

joint at the completion of the drops, the test point must be repeated.

8. The collar and trim off is carefully removed from the compacted soil so that it

is completely even with the top of the mould using the trowel. The top layer of

the soil is trimmed by using steel ruler

9. The compacted soil is weighted while its in the mould and to the base, and

the mass is recorded. The wet mass of the soil is determined by subtracting

the weight of the mould and base.

10. The soil from the mould is removed by using hammer and straight edge is

used to take some wet soil and is placed in the weighted lid and placed it in

the drying oven.

11. The dried soil is then weighted and the water content is determined.

12. Step 1-11 is repeated buy using different soil and different amount of water.


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Analysis

1) Calculate the moisture content of each compacted soil specimen by using the

average of the two water contents.

2) Compute the wet density in grams per cm3 of the compacted soil sample by

dividing the wet mass by the volume of the mould used.

3) Compute the dry density using the wet density and the water content

determined in step 1. By using the following formula:

4) Plot the dry density values on the y-axis and the moisture contents on the x-

axis. Draw a smooth curve connecting the plotted points.

5) On the same graph draw a curve of complete saturation or zero air voids

curve. The values of dry density and corresponding moisture contents for

plotting the curve can be computed from the following equation:


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6) Identify and report the optimum moisture content and the maximum dry

density. We have recorded the method of compaction used on data sheet.


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Example Calculations

Gs= 2.7(assumed)

w=1.0 g/cm3

Assumed w sat% Calculated Pd (g/cm3)

9 2.17

12 2.04

6 2.32

15 1.92

18 1.82


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Discussions

The optimum water content is the water content that results in the greatest density

for a specified compactive effort. Compacting at water contents higher than (wet of )

the optimum water content results in a relatively dispersed soil structure (parallel

particle orientation ns) that is weaker , more ductile, less pervious, softer, more

susceptible to shrinking, and less susceptible to swelling than soil compacted dry of

optimum to the same density. The soil compacted lower than (dry of) the optimum

water content typically results in a flocculated soil structure (random particle

orientations) that has the opposite characteristics of the soil compacted wet of the

optimum water content to the same density.


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Reference

http://www.uic.edu/classes/cemm/cemmlab/Experiment%209-Compaction.pdf

Appendix
http://www.uic.edu/classes/cemm/cemmlab/Experiment%209-Compaction.pdfhttp://www.uic.edu/classes/cemm/cemmlab/Experiment%209-Compaction.pdfhttp://www.uic.edu/classes/cemm/cemmlab/Experiment%209-Compaction.pdf

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