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Types of Soil Tests in Building Construction

Importance of Soil Testing

Soil testing is one of the first steps after purchasing a piece of land when you plan to build a house.  The first step in construction planning is soil testing to determine whether the site is suitable for building any structure to prevent terrible events.

The types of soil tests show the physical and structural characteristics of the soil, which help to define the type of construction foundation that should be put forth. Knowing the soil’s moisture content, mineral density, permeability, and bearing capacity provides insight into the factors to take into account when building foundations and other earthworks.

The foundation is the initial and most crucial stage of construction; even a tiny flaw or damage can cause the entire building to fail or collapse. The building’s foundation guards it and keeps out any physical pressures that might arise from the subsoil. It supports and preserves the load bearings from the structure to the ground.

To support the weight of the building, the soil must possess all necessary physical and chemical qualities. The rate of settlement and bearing capacity of the soil are both determined through soil testing and analysis. The length and depth of the pillars needed to build the foundation are also determined by these tests.

Only soil testing can determine the amount of water in the soil, which helps to determine the foundation’s humidity level. It is important to make a note of how soil moves and responds to water both in its presence and absence. In general, clay soil moves more readily than sandy soil.

The removal of vegetation is also very significant since weeds and the roots of previously cut trees can cause soil to move. These several elements all have an impact on the foundation settlement, endangering the building.

Types of Soil Testing

Test for Moisture Content

 This test is used to figure out how much water and moisture is present in the soil. There are several techniques, including the alcohol method, the calcium carbide method, the oven drying method, the sand bath method, and the radiation method.

The results of the Oven Drying method, which defines moisture content as the mass of water that can be removed from soil by heating at 105 to 110°C, are the most accurate of all the methods.

Only soil testing can determine the water table level, which helps to determine the humidity level in the foundation.

A crucial factor in building construction is the moisture content or water content of the soil. It is determined using a variety of techniques, including:

  • Oven-drying technique
  • Using calcium carbide
  • Method of tension balance
  • Pycnometer approach
  • Sand bath technique
  • Radiation technique
  • Alcohol technique

Specialised Gravity Test

 The results of this test reveal the soil’s saturation level and void ratio. The void ratio is described as the relationship between the volume of the void and the volume of the solids in the soil.

The optimal range for the specific gravity of soil for construction is 2.65 to 2.85. The soil should have porous matter, heavy materials, and low-value organic content.

The ratio of the unit weight of soil particles to that of water is known as the specific gravity of the soil. Numerous methods determine it.

  • Using a density bottle
  • Pycnometer approach
  • Gas jar technique
  • Reduced shrinkage approach
  • Method of measuring a flask

Test of Dry Density on Soil

The term “dry density of soil” refers to the weight of soil particles in a specific volume of sample. The void ratio and soil-specific gravity affect the dry density of the soil. Soil is divided into dense, medium-dense, and loose categories based on dry density values.

Core cutter, sand replacement, and water displacement methods are used to determine the dry density of soil.

Testing Soil Dry Density using a Core Cutter

To cut the dirt in the ground and raise the cutter with a soil sample, this method employs a cylindrical core cutter with standard dimensions. The sample that was removed is weighed and recorded. Finally, the sample’s water content is identified, and using the relationship shown below, dry density is computed.

Testing Soil Dry Density using the Sand Replacement Method

In this procedure as well, a hole is made in the earth by removing soil to determine its dry density. The sand of known dry density is uniformly distributed across the hole. Therefore, the volume of the hole can be determined by dividing the amount of sand put into the hole by its dry density. So, using the method above, we can get the dry density of the soil.

Atterberg Limits Soil Testing

Atterberg provided three limitations that demonstrate the characteristics of fine-grained soil under various conditions to estimate the essential water content of fine-grained soil. The restrictions include liquid, plastic, and shrinkage limits. Individual tests are used to calculate these limitations, as shown below.

Test of Liquid Limit on Soil

Casagrande’s liquid limit gadget, which consists of a cup with a sliding up and down mechanism, is utilised in this test. The cup is filled with a soil sample, and using the right tool, a groove is made in the centre of the cup. The groove eventually closes as the handle is used to raise and lower the cup.

Keep track of how many blows are necessary to close the groove. The soil’s water content is then calculated. Draw a graph between log N and the soil’s water content after completing this process three times. The soil’s maximum liquid capacity corresponds to a water content of N=25.

Soil-based Plastic Limit Test

Take a little sample of dirt, add water to make it more malleable, and then roll it into a ball. After some time has passed, place the ball in the glass plate and roll it into threads that are 3 mm in diameter.

If the threads hold together after being rolled to a diameter of less than 3 mm, then the water content exceeds the plastic limit. If so, lower the water quantity and keep going until crumbling starts at 3 mm in diameter. Finally, determine the soil’s water content because that value is nothing more than a plastic boundary.

Test for Maximum Shrinkage in Soil

The soil’s water content is just enough to fill the spaces left by the shrinkage limit. The saturation level at that point is 100%. Therefore, lowering the shrinkage limit does not affect the soil’s volume. For the provided soil sample, it is calculated using the formula below.

Where M1 is the initial mass.

The initial volume is V1.

Dry mass = M2

V2 = volume after drying

Pw is the water’s density.

Proctor’s Soil Compaction Test

To find out how compaction affects soil, Proctor’s test is used. Simply said, soil compaction is the densification of the soil while eliminating air voids. The amount of compaction is determined by the soil’s dry density.

Given soil sample was sieved through a 20 mm and a 4.75 mm sieve for the Proctor’s Compaction Test. A particular ratio is used to combine the percentage passing 4.75mm and the percentage remaining at 4.75mm.

It should be given water and left in an airtight container for 20 hours. Mix the soil, then divide it into six to eight pieces. Place the mould in the desired location, then add one part of the soil, three layers thick, and smash it with 25 blows for each layer.

Weight the soil and mould after removing the base plate. Take a tiny sample of the soil from various strata and conduct a water content test after removing the mouldy soil. Determine the soil’s dry density and water content from the values; graph them; and record the soil sample’s maximum dry density and ideal water content at the highest point on the curve.

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