HOW TO DETERMINE UNIT WEIGHT OR DENSITY OF SOIL?

Density Test of Soil

Purpose:

This lab is performed to determine the in-place density of undisturbed soil obtained by pushing or drilling a thin-walled cylinder. The bulk density is the ratio of mass of moist soil to the volume of the soil sample, and the dry density is the ratio of the mass of the dry soil to the volume the soil sample.

Standard Reference:

ASTM D 2937-00 – Standard Test for Density of Soil in Place by the Drive-Cylinder Method

Significance:

This test is used to determine the in-place density of soils. This test can also be used to determine density of compacted soils used in the construction of structural fills, highway embankments, or earth dams. This method is not recommended for organic or friable soils.

Equipment:

  • Straightedge
  • Balance
  • Moisture can
  • Drying oven
  • Vernier caliper

Density test of soil

Test Procedure:

(1) Extrude the soil sample from the cylinder using the extruder.

(2) Cut a representative soil specimen from the extruded sample.

(3) Determine and record the length (L), diameter (D) and mass (Mt) of the soil specimen.

(4) Determine and record the moisture content of the soil (w).

(Note: If the soil is sandy or loose, weigh the cylinder and soil sample together. Measure dimensions of the soil sample within the cylinder. Extrude and weigh the soil sample and determine moisture content)

Data Analysis:

(1) Determine the moisture content of soil (click here to read moisture content test procedure)

(2) Determine the volume of the soil sample

V = (πD2L)/4 in cm3

(3) Calculate bulk density (ρt) of soil

ρt = Mt/V in g/cm3

or unit weight γt = ρt * g

(4) Calculate dry density (ρd) of soil

ρd = ρt/(1+w) in g/cm3

or dry unit weight γd = ρd* g

Article written by

Prof. Krishna Reddy, UIC

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