proctor compaction test

TITLE: STANDARD PROCTOR COMPACTION TEST

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To obtain the relationship between water content and dry unit weight by using the standard  proctor compaction test. To determine the maximum dry unit weight and optimum water content.

INTRODUCTION

As described in Geotechnical Engineering, soil being a particulate medium contain pore spaces, which may or may not be filled with water. When the soil which has high void ratio, subject to external forces, the soil particles will be pushed to fill the voids spaces, as a results the soil will be subjected to large deformations. Therefore, it is required to reduce the void spaces of partially saturated loose soil deposits to improve strength, reduce compressibility and conductivity. In the construction of highway embankments, earth dams, and many other engineering structures, loose soils must be compacted to increase their unit weights. Compaction increases the strength characteristics of soils, which increase the bearing capacity capacit y of foundations constructed over them. Compaction also decreases the amount of undesirable settlement of structures and increases the stability of slopes of embankments. Smooth- wheel rollers, sheepsfoot rollers, rubber-tired rollers, and vibratory rollers are are generally used in the field for soil compaction. c ompaction. Vibratory rollers are used mostly for the densification of granular soils. Vibroflot devices are also used for compacting granular soil deposits to a considerable depth. Standard proctor compaction test is to establish es tablish a relationship between dry density and moisture content for a soil under controlled conditions. R.R. Proctor (1933) was the first t o develop a method of assessing compacted fill that has since become a universal standard and the test is known as standard  proctor test. Standard proctor test is also known as light compaction test as per BIS. AASHO AASHO developed a modified test to give a higher standard of compaction and is known as modified proctor test. The same is also known as heavy compaction test as per BIS. In the proctor compaction test, a soil sample s ample is compacted into a standard mold shown in figure 4. The total volume of the mold is 1000cm^3. Compaction of the soil is carri ed out using the standard hammer shown in figure 4. The hammer has a 2.5kg ram, which can be lifted 300mm and dropped.

THEORY

Compaction is the process of densification of soil by reducing air voids and the degree of compaction of a soil is measured in terms of its dry unit weight. Determination of the dry density and moisture content of a soil under given compaction effort can be obtained from these equations shown below. Bulk unit weight of the soil ( ᵞbulk) ᵞbulk = bulk = (solid weight of soil inside the mold + moisture weight)/ volume of the mold

(Mass of the air within the voids of soil is neglected) Dry unit weight of the soil ( ᵞdry) ᵞdry = ᵞbulk / (1+ water content)

Water content = (Mass of water) / (dry mass of soil) %

Then the graph of the dry unit weight verses water content can be plotted. It gives a curve shown in figure 1, and from that curve the maximum dry unit weight and optimum moisture content c an be found.

Figure 1. Compaction curve

Figure 2. Zero air void line

If all the air of soil could be expelled by compaction, the soil would become fully saturated or the soil is at zero zer o air voids condition. Practically it is impossible to attain full saturation by compaction, the line showing the relationship between dry density and water content at saturation is called zero air void line or theoretical saturation line. Zero air void line is shown in figure 2.

APPARATUS

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Cylindrical metal mold, which is fitted with a detachable base plate and removable extension collar (figure 4) Metal rammer with 50mm diameter face, weighting w eighting 24.4KN, sliding freely in a tube that controls the height of drop to 300mm Sample extruder (jack) for removing compacted material from t he mold Metal tray Balance sensitive to 0.1g and 0.01g Drying oven with temperature ranges from 105◦C to 110◦C Desiccator Trowel or scope Straight edge  No 4 sieve (4.75mm) Water sprayer

Figure 3. Test Apparatus

Figure 4. Mold with Collar and Rammer

PROCEDURE

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The compaction mold was set to the base plate without the removable collar and weighed. Then the removable collar was attached. Around 3kg representative specimen of the air dried soil sample was obtained and all the lumps were broken. The soil passed through no.4 sieve was collected to a t ray. Water was added to the soil and mixed thoroughly to get a homogeneous soil sample. The test was started with a water content lower than the optimum. The mold assembly was placed on the ground and soil was added to the mold so that it was about half full. The soil was compacted by applying 25 blows of the rammer dropping from the controlled height of 300mm and ensured a uniform distribution of blows. A second approximately equal layer of soil was placed in the mold and compacted it with 25  blows as before. Procedure was repeated with a third layer, la yer, which should bring the compacted soil level in the extension collar to about 6mm above the level of the mold body. Extension collar was removed carefully. The excess soil was cut and leveled off to the top of the mold. The small cavities resulting from the removal of stones were filled with fine materials. Excess soil on the base plate was removed carefully using a brush and weighed (Soil + mold + base plate). The base was removed and the mold was set on the sample extruder, the sample was removed from the mold. Some amount of Soil was collected from top, middle and bottom to determine the water content. Those Soil samples were put into the dry oven for water content determinati on. The material in the tray tra y was broken up and water was added to the soil with the spr ayer. Then the soil was mixed thoroughly. thoroughly. The compaction process was kept repeating with increasing of the water content until five runs had been made and soil became very wet and sticky.

Figure 5. Sequence of applying blows

Figure 6. Soil layers in the mold 

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. The proctor compaction test was carried out suc cefully and obtained a curve that satisfied satis fied the objectives. Clearly identified the relationship between the dry densit y and the water content of a soil and reasons r easons to have that change was studied.

RFERENCES

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Compaction of soil-process-necessity-and-theory-of-compaction.  Z.Khan Available at: http://www.yourarticlelibrary.com/geography/compaction-of-soil-processnecessity-and-theory-of-compaction/45567/ [Last accessed: 21th September 2016] Proctor soil compaction Available at: http://www.naturalbuildingblog.com/proctor-soil-compaction-test/ [Last accessed: 19th September 2016] soil-compaction-test (2015) Available at: http://www.vertekcpt.com/blog/soil-compaction-test-intro#.V-IJNPl97IU [Last accessed: 18th September 2016] BRAJA M. DAS. Principles of Geotechnical Engineering. Seventh Edition