Modified Proctor Test for Soil: A Comprehensive Guide

Soil compaction testing is an essential part of any construction project. It helps to ensure that the soil is suitable for the intended use and can support the weight of any structure built on it.

One of the most commonly used methods for soil compaction testing is the Proctor Test. However, over the years, this test has undergone a few modifications to make it more efficient and accurate.

In this article, we will delve into what the Modified Proctor Test for soil is, how it differs from the Standard Proctor Test, and the procedure involved in conducting it.

Read More: Standard Proctor Test – Its Apparatus, Procedure & Test Report

Modified Proctor Test for Soil

The Modified Proctor Test for soil, on the other hand, is a modified version of the Standard Proctor Test that uses a heavier compaction effort and a larger mold. It was developed to better simulate the compaction effort of heavy machinery used in the field.

The Modified Proctor Test for soil is generally more accurate than the Standard Proctor Test, as it better simulates the actual conditions under which the soil will be compacted.

Procedure for Conducting the Modified Proctor Test for Soil

Apparatus for the Modified Proctor test as follows,

1. Cylindrical-shaped mold having an inside diameter of about 10 cm and a volume equal to 1000 cu. cm or inside diameter 15cm and volume are equal to 2250 cu. cm.

2. Oven which is thermostatically controlled and can keep samples at 105° C and 110° C temperatures continuously.

3. A Sample Extruder Tool

4. Sieve of standard size – 19 mm, 75 mm,

5. Capacity balance of 15 kg with an accuracy of 1 gm.

6. Rammer has a 4.5 kg (10 lbs) weight & free fall of 457 mm (18 Inches).

7. Moisture Containers

8. Straightage made of steel

9. Weight balance having accuracy up to 0.01 gm

IS Code For Modified Proctor Test

For the modified proctor test following is code is used,

IS-2720-PART-8 is used for the Modified Proctor Compaction Test and Heavy Compaction Test

Read More: Read More: Standard Penetration Test (SPT Test) – Procedure, Test Report

Modified Proctor Test Procedure

The stepwise procedure for the revised Proctor test is as follows,

• Take around 5 kg of dry soil sample.
• Pass these samples of soil through a 19 mm Sieve.
• Add a specified % of water by the weight of the soil sample. Add 3% to 5% water by weight of the soil sample while soil nature is gravel or sandy type and 12 to 15% water by weight of the soil sample for cohesive soil like clay soil.
• Measure the weight of the mold with the attached base plate as W1.
• Now, Collar assembly to the mold.
• Fill the mold with soil in 3 layers such that each layer is compacted with standard rammers 25 blow.
• Compaction of each layer should be done with a minimum 45 cm free fall of the rammer hammer which ensures proper compaction of soil in the mold.
• As the soil compaction is finished with the rammer, remove the top collar from the mold and level the soil sample with a tool called straight.
• Measure the weight of compacted soil with the mould as W2.
• Take out soil samples from the mold and spread them on a separate tray.
• Collect at least 3 soil samples to determine the water content of the soil.
• Repeat the above steps by increasing or decreasing the amount of water added to a soil sample. Take at least 3 to 5 readings to achieve more accurate results.
• Calculate the Dry density of each soil sample and plot a graph between water content and the dry density of the soil.
• Water content at the highest dry density will give the relationship between maximum dry density and optimum moisture content.

Calculation of Modified Proctor Test

The bulk density of soil (Ym) is calculated by using the following formula,

Yw = (W2 – W1) / Vm

W1 = Mould Weight with Baseplate.

W2 = Compacted soil with mould.

Vm = Mould Volume in cm³

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

Yd = Yw / (1+W/100)

W = % moisture content of the soil

Which the soil can be compacted to the maximum dense state.

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