What is the field density of soil?
The mass of soil per unit volume of any field or site is known as the field density of soil. Before the construction of any structure on the site, we need to test the field density of the soil.
There are generally two methods used to calculate the field density of soil. They are given below one by one with calculation.
Why field density is necessary?
The calculation of the field density of soil is necessary because it tells us the condition of the site. It tells us the bearing capacity, compaction ratio, hardness, and moisture content in the soil. With the help of this information, we can design structures like buildings, dams, and bridges on the proposed site.
If we construct any structure without field density, then there may be various faults in construction like unequal settlement, unwanted settlement, etc.
Methods of calculating field density of soil
1) Core cutter method
2) Sand replacement method
I) Core cutter method
A standard core cutter apparatus figure 2.4 is used in this experiment for taking out a sample from the ground. The various steps to be followed for the determination of field density are as follows:
- Find the mass of the clean core cutter (M₁).
- Clean and level the ground where the density is to be determined.
- Press the cylinder cutter into the ground soil to its full depth with the help of a steel rammer.
- Remove core cutter from soil layer excavating the soil surrounding the cutter.
- Find the mass of the cutter with a soil sample from the field (M₂)
Mass of soil (M) = M₂-M₁
Volume of soil (V) = Volume of cutter
where, H=130 mm
d = 100 mm
Density (𝜌 ) = M/V
Figure for Core cutter method are given below
II) Sand replacement method
The sand replacement method consists of making a hole into the ground. The excavated soil is weighed. The volume of the hole is determined by replacement with sand. Knowing the weight of excavated soil and the volume of the hole, the in-situ unit weight can be easily determined. There is the following procedure for finding the unit weight of soil by sand replacement method is as follows:
- The site is cleaned and a square tray with a central hole in it is placed on the cleaned surface.
- A hole of diameter equal to the diameter of the hole in the tray and a depth of about 10-15 cm is made in the ground.
- The excavated soil is collected in a tray and weighed and its water content is determined.
- The pouring cylinder is filled with sand to about 3/4 capacity and its weight is taken and its density is also known.
- The cylinder is then placed over the hole and the tap is opened and the sand is allowed to run to fill the excavated whole and conical end.
- When no further flow of sand takes place, the tap is closed and the bottle with the remaining sand is weighed. The weight of sand filling the cone of the bottle is taken separately. The observations and calculations are as follows:
Weight of soil in the hole =W₁
Weight of pouring cylinder + Sand before pouring = W₂
Weight of cylinder + Sand, after pouring = W3
Weight of sand filling conical funnel = W4
Weight of sand filling hole = W2-W3 -W4
Unit weight of sand = 𝛾
Fig:- Sand Pouring cylinder and calibrating container for sand-replacement method.
Calculation for field density of soil by sand replacement method
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