# 3 Methods to determine the field density of soil

Written By Sourabh Negi

I cover structural design, construction technology and building materials.

Compaction of the soil at the field should be such that the desired unit weight of the soil at optimum moisture content could be achieved. The engineer has to conduct a test for soil compaction to check whether the soil is compacted at the desired unit weight. Various methods for checking the field density of soil area available. These methods measure the dry unit weight of the soil and the moisture content.

• Sand replacement method
• Core cutter method
• Water displacement Method

## Sand Cone Method or Sand Replacement Method

The sand replacement method is a field method to determine the field density of soil. The sand pouring apparatus consists of a sand pouring cone at the base and a cylinder at the top. There is a shutter between the cylinder and the cone. The first step is the calibration of the cylinder to determine the mass density of sand. Sand passing through a 600-micron sieve and retained on a 300-micron sieve should be used. Sand should be clean, uniform, and dry.

### Calibration of apparatus

• Determine the internal volume of the calibrating container either by filling it with water and measuring the volume or by measuring the dimensions of the calibrating cylinder.
• Now fill the sand pouring cylinder with clean sand up to the 10 mm from the top. Determine the weight of the cylinder (W1).
• Place the sand pouring cylinder over the calibrating container. Now oen the shutter and allow the sand to fill the calibrating container and cone of the sand pouring cylinder. Close the shutter when there is no movement of sand. Weight the pouring cylinder (W3).
• Again refill the cylinder and put it over a glass plate. Open the shutter and allow the sand to fill the cone of the pouring cylinder. Now weigh the sand on the glass plate. Let this weight be W2.
• Now, the calibration part of the test is completed.

### Procedure for field density of soil

• Clean an area of about 450 mm square and level it. Place the metal tray with having a central hole over the surface.
• Excavate the soil through this central hole for about a depth of 150 mm in a cylindrical shape having the diameter as that of the hole.
• collect the excavated soil in the metal container and wight it. Let the weight be W.
• Remove the metal tray and fill the sand pouring cylinder with clean sand for a depth of about 10mm from the top and determine the weight W1.
• Place the pouring cylinder directly over. Now, open the shutter and allow the sand to pour into the hole until there is no movement of the sand.
• Close the shutter and remove the sand pouring cylinder and weigh it. Let the weight be W4.
• Take a small sample of the excavated soil and determine its moisture content using the oven-dry method.

Let just understand the procedure by using the example:

The calculation for dry density of soil

## Core cutter method

This is the easiest and widely used method of determination of field density of soil as well as dry density of soil. It consists of a cylindrical core cutter that is pressed into the soil so that it is filled with the soil. The cutter is then removed from the ground and weighed. The dry density is determined as

ρ = γ/(1+w)

### Equipment required

Cylindrical core cutter of 100 mm internal diameter and 130 mm height. Steel rammer of weight 9 Kg and height 900 mm. Steel dolly 25 mm high and dia same as that of core cutter., weighing machine, palette knife

#### Procedure for field density of soil

• Measure the internal diameter and height of the core cutter.
• Determine the weight of the core cutter (W1).
• Clean the area of about 300mm square from debris and grass where a test is to be done and level it.
• Place the Dolley over the core cutter and press the core cutter into the ground using a rammer of 6 kg weight.
• Continue to do so until the Dolley protrudes about 1.5mm above the ground surface.
• Remove the soil from the surrounding of the core cutter and take out the core cutter.
• Now remove the Dolley and trim the soil from the top and bottom of the core cutter using straight edge.
• Weight the core cutter filled with soil W2
• REemove the soil from the core cutter and take a representative sample of the soil to determined the water content.

Let just understand the procedure by using the example

Dry density = 1.82g/ml

## Water displacement method

In this method, the soil specimen is coated with paraffin wax so as to make it impervious. The total volume of the waxed sample is determined by knowing the water displaced by the specimen. The volume of soil sample without was is calculated as

V= Vt – (Wt-W)/ρp

Where Wt = weight of the waxed specimen

w= weight of soil sample

Vt = Volume of waxed specimen

V= volume of soil sample

ρp = density of wax

Dry density of soil sample = (W/V)/ 1+w

### Procedure for field density of soil

• Take a soil sample and trim it to the regular shape. Soil samples should not have re-entrant corners. Weight the soil Sample (W).
• Melt some paraffin wax and apply it to the soil sample using a brush. One layer of wax dries up, put another layer using a brush.
• Measure the weight of waxed soil sample Wt.
• Fill the water displacement apparatus with water. Close the valve when overflow starts.
• Place the measuring jar below the overflow tube and open the valve.
• Immersed the waxed specimens very slowly into the apparatus. With the immersion water from the apparatus starts overflowing and this overflowed water is collected in a measuring jar.
• Determine the volume of the overflowed water Vt.
• Take out the waxed specimen from the apparatus and dry it. Remove the wax applied to the specimen by peeling.
• Take the representative sample for water content determination.

Example for easy understanding

Let density of paraffin wax = 0.90g/ml

Dry density of soil sample = 1.77g/ml

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1. How many testing of FDD