Soil testing is the first and most important step in construction. Before starting actual construction work, engineers must have all relevant details about the construction site. The soil testing report provides this information.
The term soil boring refers to digging a hole in the earth to collect soil samples. These samples are then sent to soil testing laboratories for detailed analysis. Soil testing report includes the chemical composition of the soil, the nature of the soil, its porosity, whether the soil is loose or compact, and other relevant details.
All such details are available in this soil testing report, which helps the construction manager to decide how to proceed with the construction of a building.
What is Soil Boring?
Soil boring is also known as geotechnical boring. The purpose of soil boring is to collect soil samples from different spots of the construction site. Samples are of two types, disturbed and undisturbed soil samples. Both are important to get a correct overview of the soil.
Rigs are used to dig a hole in the earth, which may go as deep as 70 to 100 meters, depending on the nature of the soil. Soil texture may not be the same in an entire construction area. To get a complete overview of the site, samples are collected from different locations. For an average-sized site, at least 4-5 samples from other site areas must be collected.
Types of Soil Boring
There are different techniques of soil boring in practice these days. Some of these are:
- Auger Boring – It is the simplest type of boring; hence costs less. Effective on all soil types except rocky areas.
- Wash Boring – This type of boring is useful for loose and sandy soils.
- Rotary Drilling – Rotary drilling is used where the earth is rocky.
- Percussion Drilling – Useful method of boring where the soil is hard or has relatively soft rocks. But the soil samples collected with this type of boring are disturbed samples, which may not be suitable for some tests.
In most cases, scientists prefer undisturbed soil samples. This gives a true picture of the soil on the site. Generally, the auger boring method is preferred by experts in areas having non-rocky earth. For more details on soil boring, you may visit the official website of Boring Americans.
What is Soil Testing Report?
Soil samples collected from the site are analyzed in specialized soil testing labs. Some tests are done on the spot, while most of the analysis is carried out in laboratories. After a careful and scientific analysis, a soil test report is compiled.
This soil test report is the basic document that helps the construction managers to decide on different phases of construction, such as foundation, depth of foundation, the height of the building, material to be used in construction, especially in the foundation, and so on.
Understanding Soil Tests
The most common tests that are required for a construction site may include:
- Gravity Test – The gravity of soil is an important factor. It is the ratio of solid soil to water. Mostly “density bottle method” is used to determine the specific gravity of the earth.
- Moisture Level Test – Moisture plays a critical role in construction. It is not restricted to only construction, but it also has an impact on the future of the building. The most common method used to determine moisture content in the soil is the “oven dry method.” It is a simple method. The weight of the sample is recorded. Then the sample is placed in an oven for 24 hours to dry. The dried-up sample is again weighed. The difference between the two is the water content in that particular sample.
- Compaction Test – This test gives us the compaction characteristics of the soil. Air is removed from the soil sample by using densification technology. The more compact the soil, the more stable will be the building constructed on it.
- Dry Density Test – It is the weight of the soil particles in the soil sample. Based on the dry density, the soil is categorized as loose, medium dense, and dense soil.
- Atterberg Limits – Atterberg limits are liquid limit, plastic limit, and shrinkage limit. These limits determine the water level in a soil sample.
Laying of Foundation
Foundation is the most important part of any structure. The entire building structure is going to be built on this foundation. It has to bear the entire load of the building. It provides stability and strength to the whole structure.
Soil testing plays an important and key role in determining the type and depth of the foundation. For this very purpose, various tests are done on the soil. These may include:
- Direct shear test
- Standard penetration test
- Vane shear test
- Un-drained shear strength
- Groundwater and permeability test
- The static cone penetration test
These are some of the tests which are necessary to decide about the number of pillars, size of pillars, and most importantly, depth of pillars. Ultimately these pillars have to bear the load of the building. So, they must be strong and reliable to give the required strength and stability to the building.
Based on the soil test report that provides the chemical composition of the soil, construction managers will decide the quantity and type of material required to lay a reliable foundation.
Composition of Soil
- The biological composition of an ideal soil is 25% air, 25% water, 45% minerals, and 5% organic matter.
- The chemical composition of soil includes saline content, Ph of Soil, micro and macronutrients, and soil contaminants. Salinity, Ph, and contaminants are important in construction.
- The physical composition of soil includes texture, structure and drainage, and water-holding capacity. The soil texture means the ratio of sand, silt, and clay in any given sample.
- All these properties of soil are important to decide the types and quantity of materials to be used in the construction of a building.
Role of Soil Testing in Construction
- It helps in the selection of appropriate quantity and type of material to be used in construction.
- Soil testing helps in laying a reliable and strong foundation that may bear the load of the entire structure and provides stability.
- Careful implementation of soil test reports may reduce the time and cost of completing the project.
- Analysis of the chemical composition of soil will help select the right type of materials or any additional materials that may be required for construction on that particular site.
- It also helps to determine the useful life of the building and how we can increase it. Normally a high-rise building should have a useful life span of more than 50 years.
Things to Remember During Soil Boring and Testing
Always use appropriate tools and machinery for boring. Hire qualified professional people for the boring job. Select reputable laboratories to get authentic test reports to ensure the maximum possible accuracy and authenticity of the soil test reports.
The possibility of human error always exists. So, try to avoid any possibility of human error, both in the collection and analysis of soil samples and the compilation of test reports. Remember, the success of your project depends on it.
Construction is a very sensitive matter. Much investment is involved in it. It’s a matter of the safety of the people who will be the occupants of this building, either for living or any commercial activity. As such, the safety, strength, and reliability of the building are crucial.
Soil boring and testing are key to the success of any construction project. A lot depends on it, may that be the cost or the stability of the building. Wise implementation of test reports may save many work hours that may reduce the overall cost.
The cost incurred on soil testing may pay back in terms of reducing overall project costs and, most importantly, in the reliability and safety of the building. Never compromise on it. It’s not only your investment, but the life of so many people is at stake.
Also read: Shrinkage and Plastic Limit of Soil
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