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Soil testing is the most important part of a pre-construction checklist. The stability, retentivity, and resistance of an entire building depend on it. The soil engineers test the composition of the soil, in order to determine the construction factors. Strong soil, which gets the pass to construct a building on it, has adequate density for bearing the construction load and does not settle or compact post-construction. In regards to moisture, the soil does not expand or contract excessively. Therefore, it is highly necessary to test the soil standard before you get or give approval for the construction.

Importance of soil testing

With soil being of the utmost importance, as is the base of the foundation of a building, we have jotted down some of the most crucial benefits of soil testing.

Bearing capacity

Primarily, the soil testing gives an estimation of the bearing capacity of the soil. It requires holding and balance the weight of the structures.

Physical and chemical compositions 

Chemical compositions of a soil
The chemical composition of soil determines the behavior pattern of it

You can measure the physical and chemical composition of the soil easily. This determines the presence of impurities inside the soil. This is important because the choice of construction material may also be affected by the chemical and mineral composition of the soil. If an analysis of the soil reveals that it contains sulfur, then the sulfur resisting cement is used to protect the foundation of the buildings.

Geotechnical investigation 

The geographical reaction such as the effects of weather, climate, and other natural occurrences on the soil gives a rough estimation of how the soil will resist any disasters like earthquakes, landslides, or avalanches.  

Settlement behavior 

The settlement behavior of the soil is important to measure the stabilization. If the soil is weak, it will settle easily, erode, and may claim lives. 

Laying the building foundation  

building foundation
The construction of a foundation begins right after the passing of the soil test

To lay the foundation of the building, soil testing is an important determiner to decide the length and depth of the pillars. These pillars are put in the soil for laying the foundation of the building. All the possible foundation problems depend on the results of the soil testing. 

Water table level

Most importantly, the water table level is one of the key problems to the foundation. Soil testing gives an insight into the water level of the soil. Through this soil, engineers determine the moisture, humidity, dampness, and mineral components of the soil. 

Soil testing methods

There are multiple soil testing methods. Some of them are theoretically determined, some of them need heavy equipment to find out. Different methods are for determining different factors. Many of the methods have multiple tests for determining a particular soil testing method. In this blog, we will discuss one of the methods which are common in Bangladesh. 

Atterberg Limit Test 

atterberg limit test
The Atterberg Limit test using Casagrande’s liquid limit device

The Atterberg limit test is the experiment to find out the properties of fine grain soil at different conditions applied. There are three levels of performing Atterberg limit tests on soil. These tests consist of multiple pieces of equipment which the soil engineers use for determination.  

Shrinkage Limit Test

The shrinkage limit test is to determine, whether the water content in the soil is adequate enough to fill the soil voids. The below formula is to calculate the SLT: 

In a given soil sample Ws = (M2 – M1)n – (V1 – V2) Pw / M2

Where,

M1= initial mass

V1= initial volume

M2= dry mass

V2= volume after drying and

Pw = density of water

The result Ws determines the shrinkage limit. From that, we can find out the volumetric shrinkage of the soil. Let us say that the average value of the shrinkage limit is 10.67, and volumetric shrinkage is 0.71%. At the shrinkage limit, if the water content diminishes, air enters the voids of the soil. As a result, the volume of the voids remains constant.

Plastic Limit Test

In this test, add water to the soil sample in order to make it plastic enough to shape them into small balls. After leaving that ball in the glass plate, roll them into threads of 3mm diameter. See if the threads break. If they don’t break below 3mm diameter, we can understand water content is more than the plastic limit. Reduce water content in that case, keep on repeating the same procedure until the soil crumbs under 3mm. The water content measurement for the crumbling is the plastic limit of soil.

Liquid Limit Test

Casagrande’s liquid limit device is an important piece of equipment for this test. It consists of a cup that moves up and down carrying the soil. When you move the cup up and down with the help of the handle the groove closes at some point. Note down the number of blows required to close the groove. After that water content of the soil is determined. Repeat this procedure 3 times and draw a graph between log N and the water content of the soil. Water content corresponding to N=25 is the liquid limit of soil. 

These are some of the important elements of soil testing methods and their importance. Construction engineers do the appropriate testing to ensure proper safety and security. Henceforth, the soil test results can only help to determine the infrastructure and design along with space allocation of a construction. 

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