28.02.2013 Views

Building Design and Construction Handbook - Merritt - Ventech!

Building Design and Construction Handbook - Merritt - Ventech!

Building Design and Construction Handbook - Merritt - Ventech!

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

SOIL MECHANICS AND FOUNDATIONS 6.25<br />

Values of water content (w) can vary from essentially 0% up to 1200%. A water<br />

content of 0% indicates a dry soil. An example of a dry soil would be near-surface<br />

rubble, gravel, or clean s<strong>and</strong> located in a hot <strong>and</strong> dry climate, such as Death Valley,<br />

California. Soil having the highest water content is organic soil, such as fibrous<br />

peat, which has been reported to have a water content as high as 1200%.<br />

Specific Gravity of Soil Solids (G). The specific gravity (G) is a dimensionless<br />

parameter that is defined as the density of solids (� s) divided by the density of<br />

water (� w), or G � � s/� w. The density of solids (� s) is defined as the mass of solids<br />

(M s) divided by the volume of solids (V s). The density of water (� w) is equal to<br />

1 g/cm 3 (or 1 Mg/m 3 ) <strong>and</strong> 62.4 pcf.<br />

For soil, the specific gravity is obtained by measuring the dry mass of the soil<br />

<strong>and</strong> then using a pycnometer to obtain the volume of the soil. Table 6.5 presents<br />

typical values <strong>and</strong> ranges of specific gravity versus different types of soil minerals.<br />

Because quartz is the most abundant type of soil mineral, the specific gravity for<br />

inorganic soil is often assumed to be 2.65. For clays, the specific gravity is often<br />

assumed to be 2.70 because common clay particles, such as montmorillonite <strong>and</strong><br />

illite, have slightly higher specific gravity values.<br />

Total Unit Weight (� t). The total unit weight (also known as the wet unit weight)<br />

should only be obtained from undisturbed soil specimens, such as those extruded<br />

from Shelby tubes or on undisturbed block samples obtained from test pits <strong>and</strong><br />

trenches. The first step in the laboratory testing is to determine the wet density,<br />

defined as � t � M/V, where M � total mass of the soil, which is the sum of the<br />

mass of water (M w) <strong>and</strong> mass of solids (M s), <strong>and</strong> V � total volume of the soil<br />

TABLE 6.5 Formula <strong>and</strong> Specific Gravity of Common Soil Minerals<br />

Type of mineral Formula<br />

Specific<br />

gravity Comments<br />

Quartz SiO2 2.65 Silicate, most common type of soil<br />

mineral<br />

K Feldspar<br />

Na or Ca Feldspar<br />

KAlSi3O8 NaAlSi3O8 2.54–2.57<br />

2.62–2.76<br />

Feldspars are also silicates <strong>and</strong> are<br />

the second most common type of<br />

soil mineral.<br />

Calcite CaCO 3 2.71 Basic constituent of carbonate rocks<br />

Dolomite CaMg(CO 3) 2 2.85 Basic constituent of carbonate rocks<br />

Muscovite varies 2.76–3.0 Silicate sheet type mineral (mica<br />

group)<br />

Biotite complex 2.8–3.2 Silicate sheet type mineral (mica<br />

group)<br />

Hematite Fe 2O 3 5.2–5.3 Frequent cause of reddish-brown<br />

color in soil<br />

Gypsum CaSO 4�2H 2O 2.35 Can lead to sulfate attack of concrete<br />

Serpentine Mg 3Si 2O 5(OH) 4 2.5–2.6 Silicate sheet or fibrous type mineral<br />

Kaolinite Al 2Si 2O 5(OH) 4 2.61–2.66 Silicate clay mineral, low activity<br />

Illite complex 2.60–2.86 Silicate clay mineral, intermediate<br />

activity<br />

Montmorillonite complex 2.74–2.78 Silicate clay mineral, highest activity<br />

NOTE: Silicates are very common <strong>and</strong> account for about 80% of the minerals at the Earth’s surface.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!