The physical properties of a soil provide insight into the identification of the soil and the determination of its properties and load response. These properties can be determined by performing a laboratory analysis on undisturbed soil samples obtained during the test drilling process.

The laboratory analysis must be performed in accordance with the following ASTM standard:

D-854: Soil Specific Gravity Test Method

It should be noted that laboratory analyzes are performed under controlled conditions using demanding materials and equipment. The results of such analyzes can be considered accurate.

A field sample of undisturbed soil will contain three separate and distinct constituents: solids, water, and air.

One of the important properties to be determined in the laboratory analysis is that of the weight-volume relationship of these ingredients. The composition of this soil sample can be illustrated visually as shown in Fig-1, where: V stands for volume, W stands for weight, and the subscripts a, with whom, and s represent air, water and solids.

Weight to volume ratio of soil
Weight to volume ratio of soil

The general procedure for determining weight and volume is specified below:

Step 1.

Select the sample to be tested and determine the total volume v. The units of volume are usually cubic centimeters (cm3).

Step 2.

Weigh the sample to determine the weight w, in gr. Note that this weight includes both the weight of the water and the solids.

Step 3.

The weight of the solid components w. must now be determined. The sample is first oven dried at a constant temperature of 105 to 115 degrees Celsius. This will expel all free water from the sample. If there are clay particles in the sample, the drying process also removes the absorbed water molecularly bonded to those particles.

The sample that remains after the drying process consists exclusively of solid components, the weight of which can now be determined.

Step 4.

The weight of water Wwith whom originally present in the sample can be determined by subtracting the weight of the solids from the original weight of the sample:

Wwith whom = WWs

Step 5.

The water volume Vwith whom, corresponding to the weight of water found in step 3, can now be calculated. Remember that density is the ratio of weight to volume, and that the density of water is 1 g/cm3; therefore:

Vwith whom = Wwith whom

Step 6.

The volume of solids v can be determined by placing the solids from step 3 in a container of known volume and filling the container with water whose volume is accurately measured. The difference between these two volumes represents the volume of the solids.

The weights and volumes obtained by these measurements can be used to determine important physical properties of the in-situ soil from which the undisturbed sample was obtained.


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