Specific Gravity of Soil Solids

The City College of New York

Department of Civil Engineering

CE 345: Soil Mechanics

Instructor: Dr. George Mylonakis

LAB EXPERIMENT #2:

DETERMINATION OF SPECIFIC GRAVITY OF SOIL SOLIDS

Introduction

The specific gravity of a given material is defined as the ratio of the weight of a given volume of material to the weight of an equal volume of distilled water at 4C. It is denoted by Gs and is defined as

s

Gs =

w

where,

s = unit weight of soil solids only

w = unit weight of water at 4 C

or,

Ws / V

Gs =

Ww / V

where,

Ws = weight of soil solids

Ww = weight of water

V = volume of soil = volume of water

Note: This test is applicable for soil particles smaller than 4.75 mm in size.

Table 1. Range of Gs for Different Soil Types

Apparatus

1. Volumetric flask (500ml)

1. Thermometer

1. Balance sensitive to 0.01g

1. Distilled water

1. Vacuum pump

1. Evaporating dishes

1. Oven

1. Spatula

1. Plastic squeeze bottle

Procedure

1. Weigh about 100-120g of representative sample of well-pulverized air-dried soil. Place this sample into the flask.

1. Add distilled water until flask is about two-thirds full.

1. Attach the flask to a vacuum for 15-20 minutes.

1. After the de-aerating process is complete, carefully add distilled water up to the 500ml mark. Be careful not to reintroduce air into the flask. This is done by adding water very slowly. Dry the neck of the flask above the mark with paper towels.

1. Record the weight of the flask (W1) to the nearest 0.01g as well as its temperature.

1. Empty the flask into an evaporating dish. Use the plastic squeeze bottle to rinse the inside of the flask, making sure no soil is left inside.

1. Place the dish in the oven to dry it to a constant weight.

1. Clean the flask. Repeat steps 3 and 4.

1. Record the weight of the flask (W2) to the nearest 0.01g.

1. Determine the weight of dry soil in the evaporating dish (W3).

Calculation

1. W1 = weight of the flask + soil + distilled water filled to mark.

1. W2 = weight of the flask + distilled water filled to mark.

1. W3 = weight of the dry soil.

1. W4 = weight of equal volume of water = W2 + W3 – W1.

1. Gs at TC = specific gravity at TC

W3

Gs at TC =

W4

6. The specific gravity is generally reported on the value of the density of water at 20C

W3

Gs at 20C = * 

W4

where,

ρw at TC

 =

ρwat 20C

Table 2. Values for  at Varying Temperatures.

DATA SHEET: Determination of Specific Gravity of Soil Solids

Description of soil:______

Sample No.:______

Location:______

Tested by:______

Group No.:______

Date:______

Volume of flask at 20C: 500ml

Temperature of the test:______

 (from Table 2.):______

Average Gs =______

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