Engineers specializing in the study of the earth (geotechnical engineers) gain valuable information about the underlying traits of soil through an examination and measuring specific gravity in soil:.
The term denotes the comparison between the weight of a particular soil volume and the weight of an equal volume of water.
What might seem like a straightforward calculation, in fact, opens up a window to understanding vital soil features such as the density of its particles, its porous nature, and the structural support it can provide.
Measuring specific gravity in soil, though, isn’t as simple as it sounds. It demands a deep knowledge of varied methods and the utilization of appropriate instruments. Whether utilizing standard tables or sophisticated lab equipment, specialists apply diverse techniques to evaluate this soil property.
The precision of these measurements is paramount, as they are central to sectors like construction, water distribution, and land farming.
These assessments directly guide decisions that have far-reaching implications on both economic and safety fronts.
This blog will guide you through the complex ideas, procedures, and tools linked with analyzing the specific gravity of soil.
Keep Reading: Master Precision: Your Essential Guide to Measurement Tools.
What is Measuring Specific Gravity in Soil?
Measuring specific gravity in soil is an essential concept with broad applications. To put it in simple terms, it is the ratio of the weight of a particular volume of soil to the weight of an equal volume of water. It is a dimensionless quantity that offers a glimpse into the very heart of the land’s nature.
Earth is a complex mixture of minerals, organic matter, air, and water. Understanding these properties of different soils helps reveal crucial information about their composition and structure. Specifically, knowing the specific gravity aids in determining various soil properties such as void ratio, degree of saturation, and soil density. These properties are vital for foundation design, stability of soil embankments, and settlement estimations for engineered soil fills.
Generally, it tends to fall between 2.65 to 2.85 for most soils. As you can imagine, the value is higher for fine dirt than coarse, granular dirt.
How Do You Perform a Specific Gravity of Soil Sample Test?
You can determine the specific gravity of the soil in several ways. Specific gravity tests can be performed using various methods, each with its own advantages and drawbacks.
Here are a few methods to test this critical soil property:
Bench Technique for Measuring Specific Gravity in Soil
A specific gravity bench is a piece of specific gravity lab equipment that allows you to weigh suspended samples in water. Using a bench effectively determines the specific gravity of hardened concrete, aggregates, refractory brick, bituminous mixtures, and other similar materials.
To perform the specific gravity of soils test using a bench, follow these steps:
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- Dry the soil sample and weigh it.
- Submerge the test specimen in water and weigh it again.
- Calculate the specific gravity of soil by dividing your first measurement (weight in air) by your second measurement (loss of weight in water).
You use the following formula to calculate the value:
The specific gravity of soil = Weight in air/ loss of weight in water
Flask Technique Using Distilled Water
A Le Chatelier flask is the second most commonly used piece of equipment for measuring specific gravity in soil particles. However, this method is more effective for powdered materials, such as limes, slag, and hydraulic cement.
To perform the specific gravity test using a flask, follow these steps:
- Dry the soil sample and crush it into a powder.
- Measuring specific gravity in soil with an accurate weight of the sample (say 2 grams)
- Pour the weighed mass into a volumetric (Le Chatelier) flask.
- Fill the flask with distilled water just below the top of the bulb and note how much water you added.
- Roll the flask at an incline to remove any air bubbles without letting any water leak.
- Fill the flask with enough water to reach the 500 ml mark. Again, take note of how much water you have added.
The specific gravity of soil solids calculation is slightly more complex for this method than the bench method.
To begin, you must find the density of soil solids (Ps) by dividing the mass of the oven-dried soil sample by 500 minus the volume of distilled water added to reach 500 ml. The calculation will appear as such:
Ps = Ms/(500-Vw)
Now that you have the density of soil particles, you are measuring specific gravity in soil solids (SG). To find it, divide the density of soil by the density of distilled water (Pw), which is 1,000 kg/m3.
The calculation should then be:
SG = Ps/Pw
Pycnometer Technique for Soil Samples
It is a widely used laboratory method for determining the specific gravity of soil. A pycnometer is a specialized glass or metal container equipped with a thermometer and a precisely fitted stopper through which air bubbles can be expelled using a vacuum pump.
A known volume of dry soil is placed into the empty pycnometer, and then a liquid (usually distilled water) is added to fill the container.
After removing all entrapped air bubbles, the pycnometer is weighed, and the weight of the soil and liquid together is determined. The process is then repeated with only the liquid (usually distilled water) to obtain a reference weight, allowing for the calculation of the soil’s specific gravity values.
