Soil Testing in Construction: Why it's Required & What Are Its Methods

Feb 25 2024

Archana Ajith Beena

Soil testing for building construction is one of the most important factors for every project, even though it is the most overlooked during construction planning. It ensures the foundation is safe, long-lasting, and appropriate for the project. The safety and longevity of our construction are not only determined by the surface we can see. It is also important to understand what is happening underneath it. There are various techniques for testing soil, but the one you use will depend on the characteristics of the soil. Facts indicate that soil testing for construction is rare in India, even though sixteen soil testing facilities were set up across the country in 1955.

In this blog, Brick&Bolt gives detailed information about soil testing for construction, its importance, and methods for testing soil in construction.

What is Soil Testing?

Soil testing determines the soil's physical and chemical characteristics of soil, giving important information on its fertility, load-bearing capacity, structural composition, and overall health. This procedure is essential in many areas, including environmental research, building, and agriculture, since it helps those involved make reasonable decisions regarding the properties of the soil and its suitability for particular uses. 

Testing the soil before building aids in choosing the foundation to make. Evaluating your soil before the building begins helps determine the project's stability.

Importance of Soil Testing in Construction

  • As mentioned above, soil testing aids in choosing the building's foundation. 
  • The depth and length of the selected foundation of the building are also determined by soil testing.
  • The possibility of foundation issues and the most effective building techniques are ascertained from the findings of soil testing.
  • The level of the water table in the soil can be determined by soil testing.
  • Soil testing determined that the water table level suggests possible problems with the building's foundation and interior humidity.
  • The mineral and chemical composition of the soil can influence the choice of building material.
  • If a soil analysis method reveals the presence of sulfur, the building's foundation is shielded using cement resistant to sulfur. 
  • The importance of soil testing in determining soil reactivity must be considered. The term "soil reactivity" describes how the soil responds to specific environmental factors, such as moving, contracting, or expanding.
  • When developing multistory structures or apartments, soil testing is very important.
  • This guarantees that there are no disastrous accidents or collapses.

Soil Testing

Methods for Testing Soil in Construction

After discussing the importance of soil testing for buildings, let's examine typical soil tests conducted in India:

soil testing

1. Moisture Content Test:

Various moisture content tests are frequently employed in the construction industry to determine the soil's water amount. These techniques include the alcohol method, radiation method, sand bath method, Pycnometer method, torsion balance method, calcium carbide method, and oven-drying method The oven-drying method, which involves weighing the sample soil, drying it at 110 degrees, and then considering it again to determine the difference, is the most widely used technique for determining moisture content.

These examinations support appropriate compaction, stable foundations, and high-quality construction materials. The moisture content test yields vital information about the water content of the soil, which is used in several engineering calculations and the design of slopes, retaining walls, and foundations.

The following are some important kinds of tests for moisture content in construction:

Oven Drying Method : 

One of the most precise and often applied techniques is the oven-drying method. A wet sample of soil is taken and weighed. At the same time, it's dried in an oven at a predetermined temperature (usually about 110 degrees Celsius). Then, the sample is weighed again to determine the moisture content based on the weight difference.

Calcium Carbide Method:

Using the calcium carbide method, soil samples are combined with the chemical, which produces acetylene gas when mixed with water. The soil's moisture content directly affects the amount of gas generated.

Torsion Balance Method:

The torsion balance method can be used to assess the weight loss of a soil sample after drying. It is beneficial in both field and lab applications.

Pycnometer Method: 

This technique measures soil moisture content by utilising a glass container called a pycnometer that has been calibrated. The sample's moisture content is determined by measuring the change in volume after it has been saturated with water. Because of its accuracy, it is extensively utilised in scientific settings.

2. Atterberg Limits Test

This kind of test is used to determine the fine-grained soil's essential water content. The qualities of fine-grained soil can be measured using three limits:

Shrinkage limit: 

The water content at which soil changes from a semi-solid to a solid state is known as the shrinkage limit. The amount of water that can fill the spaces in the soil is calculated using a mathematical formula.

Plastic limit: 

A soil thread measuring 3.2 mm in diameter will start to crumble at the water moisture content, known as the plastic limit. To make the soil sample plastic, it is combined with water. After that, the dirt is formed into a ball and rolled into 3 mm threads. If these threads cannot break, the procedure is repeated using less water and a fresh soil sample. This keeps happening until the thread finally breaks.

Liquid limit: 

The water content at which soil begins to behave like a liquid is known as the liquid limit. Casagrande's liquid limit apparatus measures the soil's liquid limit. It consists of a cup with a rising and falling gadget.

3. Specific Gravity Test:

The density ratio of water to the substance's density determines the specific gravity of any given material. The type of material being tested and the level of precision needed are two examples of the elements that influence the method chosen.

Glass Jar Method:

A glass jar method includes a known-volume glass jar filled with a precisely weighed mixture of soil and water, ensuring that all air bubbles are removed and the soil settles to the bottom. When the particles settle, the water is moved to a measurable extent. Weighing the jar both with and without soil and determining the weight of water displaced will allow you to estimate the specific gravity of the soil.

Measuring Flask Method: 

This technique involves weighing a known volume of soil added to a measuring flask. After adding water to the flask, the weight is once more measured. Specific gravity can be calculated for soil with irregular forms because of the weight variation.

Density Bottle Method:  

This technique determines the density of fine-grained soil. This method is especially helpful in the geological engineering and construction fields, where a thorough understanding of soil qualities is essential for determining the suitability of a site, the design of a foundation, and the overall viability of a project.

4. Dry Density Test

In the dry density test, the weight of the soil particles in a given sample is used to calculate the dry density of the soil. The soil's specific gravity and void ratio determine its dry density, which is then used to categorise the soil into three densities: loose, medium dense, and dense. There are three ways to finish this test: replacing the sand, using a core cutter, or using water displacement.

Water Displacement Method: 

This technique measures the rise in water level after adding a known volume of soil to a known-volume container. After that, the specific gravity of the water is taken into account, and the weight of the soil and the change in water level are used to calculate the dry density.

Core Cutter Method: 

A soil core is extracted using a cylindrical core cutter inserted into the ground at a predetermined depth. The weight and volume of the extracted core can be measured to compute dry density.

Method for Replacing Sand: 

This technique involves digging a hole in the earth, removing the dirt, and then adding a known weight of sand to replace it. The soil volume is calculated using the amount of sand needed to fill the hole, and the dry density can be ascertained by weighing the soil.

The choice of method relies on various criteria, including soil type, equipment availability, and project requirements. These methods offer multiple approaches to estimating the dry density of soil. Precise dry density measurements are necessary for the soil to be properly compacted during construction and for foundations and structures to be stable and able to support loads.

5. Proctor’s Compaction Test

This test aims to determine the compaction characteristics of the soil. The soil is first allowed to air dry, then split into smaller samples and treated with 3–5% water. After being hammered into place inside the Proctor compaction mould, these are removed and allowed to dry to ascertain their dry density and water content.

It is imperative to underscore the importance of the test results:

In the construction sector, the outcomes of the Proctor compaction test are vital. They offer important information about how the soil will respond to the pressure and weight of a building or other structures. Engineers can decide how much soil to compact during construction by knowing the soil's ideal moisture content and maximum dry density. In addition to eliminating settlement problems and guaranteeing the built project's durability and duration, the soil is compacted to the proper level. In addition, the test results are a crucial component of the soil testing procedure for building projects since they aid in selecting suitable building materials and techniques.

The tests above can guarantee a strong, safe, solid foundation for your building project while saving significant money on foundation installation. There are many advantages to soil testing, including determining the required type, preventing foundations from being rested on substandard soil or at an insufficient depth, identifying corrosive soil, recognising the potential for soil liquefaction after an earthquake, etc.

Therefore, investing in soil testing before starting any building work will help you save money and lives!

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