The Modified Proctor Test: Enhancing Soil Bearing Capacity through Compaction

Introduction of Modified Proctor Test

Bearing capacity of the soil is one of the most important factors which should be considered during the construction of any structure or building. Before starting construction it is necessary that the bearing capacity of the soil should be checked on the site.

In this article, you will get to know about the Modified Proctor Test and the difference between the Modified Proctor test and Standard Proctor test.

If the bearing capacity of the soil which is available on the site, is not as per the requirement then there are only two solutions. The first solution is to construct the foundation at the greater depth so that the total load can transmit into the deep underground strata of the soil.

The second solution is to improve the bearing capacity of the soil by using various methods. Compaction of the soil is one of the most widely used methods for the improvement of soil bearing capacity.

Compaction of the soil is increasing the density of the soil by the application of Mechanical energy. In the compaction process, the density of the soil is increased by reducing the air voids in the soil.

The Theory of compaction was firstly developed by the R. Proctor while building a dam in the United States of America.

Purpose of Compaction

The Compaction of soil is done for the various purposes which are as follows

1. The compaction of the soil is done to increase the density.
2. Compaction process help to decrease the permeability of the soil.
3. It will help to increase the shear strength of the soil and bearing capacity of the soil.
4. It will reduce the settlement of the structure after the construction.
5. Compaction also helps to reduce the danger of piping which is required for seepage control of the Dams.
6. Compaction process to increase the resistance towards the erosion of soil.

Modified Proctor Compaction Test

The Modified proctor test is widely used for the determination of the compaction of the different types of soils and their properties with a change in the water content.

The Modified proctor compaction test also determines the relationship between dry density and the water content of the soil. The one of the main purpose of the process of compaction is to increase the shear stress of the soil by reducing its permeability and compressibility.

Modified proctor test is also known as heavy compaction test and widely used in situations where heavy compaction is needed.

Apparatus Required for the Modified Proctor Compaction Test

There are various Apparatus are required for performing the modified proctor compaction test are as follows.

1. The cylindrical metal mould which is either 100 mm diameter and 1000 cubic cm volume or 150 mm diameter and mm 2250 cubic cm.
2. Thermostatically controlled oven with the interior of non-coding material to maintain the temperature between 105-degree celsius and 110-degree celsius.
3. The sample extruder which consists of Jack extruding compacted specimen from the mould.
4. Sieves of 75 mm, 19 mm, 37.5 mm IS sieves.
5. Balance of capacity 15 kg and sensitivity of 1 gram.
6. Metal rammer and mixing tools.

Modified Proctor Test Procedure

The step by step procedure of modified proctor test is as follows

Step 1. Take the representative sample of dried soil of about 5 kg.

Step 2. Sieve the sample properly through the 19 mm sieve.

Step 3. Add a suitable amount of water in the soil and mix it thoroughly.

Step 4. In case of sandy or gravel soil at about 3 % to 5 % of water and for cohesive soil such as clay soil ad 12% to 15% percent water in the soil.

Step 5. Take the weight of the mould with the base plate attached to the nearest one gram. Record the weight as W1.

Step 6. Attach the extension collar with the mould.

Step 7. Take the volume of the soil in the mould in each layer such that it’s compacted height is about one-third of the total height of mould.

Step 8. Compact the moist soil into the mould that different five layers which should be approximately equal.

Step 9. Each player should be compacted with 25 number of blows with the help of 9 kg rammer.

Step 10. The rammer should be a drop from the minimum height of 450 mm above the soil so that it should be compacted properly.

Step 11. After the completion of the compaction process remove the extension collar and level up the top of the mould properly with the help of straightedge.

Step 12. Take the weight of mould with the compacted soil to the nearest 1 gram and note it as W2.

Step 13. Remove the compacted soil from the mould and place it on the tray.

Step 14. Now take out a sample from that specimen for determining water content in that soil.

Step 15. Take a number of the result by adding an increment of water in the soil sample such as for the gravel and sandy soil add water 1% to 2%.

Step 16. For cohesive and clayey soils add water about 2% to 4%.

Step 17. The minimum 5 reading should be taken, then the graph is plotted between the dry density of the soil and moisture content.

Step 18. The graph will give the value of optimum moisture content at the maximum dry density.

Calculations of Modified Proctor Test Procedure

Calculate the bulk density Yw in g /cm³ of each compacted specimen from the equation is as follows

Yw = (m2 – m1) / Vm

m1 = Weight of mould with the base plate.

m2 = Weight of mould with the compacted soil.

Vm = Volume of mould in cm³

Calculate the dry density Yd in g/cm³ from the equation are as follows

Yd = Yw / (1+W/100)

Ye = Bulk density

W = % of moisture content

1. The percentage of the moisture content of the soil which is corresponding to the maximum dry density shall be reported as the optimum moisture content.
2. The optimum moisture content of the soil is defined as the water content at which the soil can be compacted to the maximum dense state.

Standard Proctor Test Procedure as Per Is Code: Is:2720

1. Standard proctor test is also known as Light compaction Test. Standard proctor test is used to achieve controlled compaction of the soil in the field.
2. Standard Proctor Test is used to determine the optimum moisture content at the maximum dry density. This test gives the relation between dry density and moisture content for the particular soil sample.

The step by step procedure of standard proctor test is as follows

1. First, upon, take the sample of 16 kg of air-dried which passes through 20 mm IS sieve.
2. Applied water to bring the water contains about 10 % which is less than the estimated optimum water content.
3. Keep the soil sample in the airtight container for about 20 hours to ensure thorough mixing of the water with the soil.
4. Divide the sample into the six equal parts and clean the mould and take the weight of it.
5. Apply grease to the inside of the mould base plate and collar and assemble properly the mould and the Base plate together.
6. Take one part of the sample and filled mould in three layers and apply 25 number of blows to each layer.
7. The hammer which is used for blowing should weight 6 kg any two-beat drop from the height of 310 mm.
8. Then scratch each layer with a spatula before putting in the next layer.
9. Remove the collar and trim the compacted soil flush with the top of the mould with a straight edge.
10. Take the weight of the mould with the soil to the nearest gram and extract the soil from the mould with the extruder.
11. Cut the soil sample in the middle and take the represented you sample in the airtight container from the middle of the cut surface.
12. Calculate the water container and bulk density.
13. Then calculate the dry density using bulk density and water content values.

Standard Proctor Vs Modified Proctor

The difference between the standard proctor test and modified proctor test is as follows

FAQ: Modified Proctor Test

What is the Modified Proctor Test?

The Modified Proctor Test is a laboratory test used to determine the optimal moisture content at which a soil type will achieve its maximum dry density. This test helps in understanding how different soils react to compaction and is crucial for construction projects requiring heavy compaction.

Why is the bearing capacity of soil important in construction?

The bearing capacity of soil determines its ability to support the loads applied by a structure. If the soil’s bearing capacity is insufficient, the structure may settle unevenly, leading to potential damage or failure.

How does the Modified Proctor Test differ from the Standard Proctor Test?

The main differences are:

1. The Modified Proctor Test uses a heavier rammer (4.89 kg) compared to the Standard Proctor Test (2.6 kg).
2. The height of free fall in the Modified Proctor Test is 450 mm, while in the Standard Proctor Test it is 310 mm.
3. The soil is compacted in five layers in the Modified Proctor Test, compared to three layers in the Standard Proctor Test.
4. The compactive effort in the Modified Proctor Test is 2700 kg/m³, whereas mk.   in the Standard Proctor Test it is 592 kg/m³.

What apparatus is required for the Modified Proctor Test?

The apparatus required includes a cylindrical metal mold, thermostatically controlled oven, sample extruder, sieves, balance, metal rammer, and mixing tools.

What are the steps involved in the Modified Proctor Test procedure?

Key steps include:

1. Taking a representative sample of dried soil.
2. Sieving the sample.
3. Adding water and mixing thoroughly.
4. Compacting the soil in layers in a mold using a rammer.
5. Weighing the mold with compacted soil.
6. Determining the water content and dry density of the soil.

How is the dry density calculated in the Modified Proctor Test?

Dry density is calculated using the formula: Yd=Yw1+W100Y_d = \frac{Y_w}{1 + \frac{W}{100}}Yd​=1+100W​Yw​​ where YwY_wYw​ is the bulk density and $W$ is the percentage of moisture content.

What is the purpose of soil compaction?

Soil compaction is done to:

1. Increase soil density.
2. Decrease soil permeability.
3. Increase shear strength and bearing capacity.
4. Reduce settlement post-construction.
5. Decrease the danger of piping for seepage control.
6. Increase resistance to erosion.

What does the graph plotted between dry density and moisture content represent?

The graph represents the relationship between dry density and moisture content, showing the optimum moisture content at which the soil achieves maximum dry density.

Why is it important to determine the optimum moisture content of soil?

Determining the optimum moisture content is crucial as it ensures the soil can be compacted to its maximum density, providing better stability and bearing capacity for construction projects.

What are some key differences in the procedure of the Standard Proctor Test?

The Standard Proctor Test involves:

1. Using a lighter rammer and lower drop height.
2. Compacting the soil in three layers.
3. Applying 25 blows per layer with a 6 kg hammer dropped from 310 mm.
4. Using a sample of 16 kg of air-dried soil passing through a 20 mm sieve.