Specific Gravity • This number indicates how much heavier/lighter a material is than water. • In soils, SG refers to the mass of solid matter of a given soil sample as compared to an equal volume of water.
Specific Gravity • For example: A material with SG of 2 is twice as heavy as water (2x 62.4 lbs/ft3 ) = 124.8 lbs/ft3 • Equation Form: SG = Ms/VsΥwater • We use the SG of soils to calculate other engineering properties like the volume of solids in a sample…. • This leads to the phase diagram (like last class) and… • S, n, e
Specific Gravity Soil Solids Water W = 187.2 lbs W= 62.4 lbs SG= 187.2/62.4 = 3.0 1 ft3 1 ft3
General Ranges of SG For Soils • Sand 2.63 – 2.67 • Silt 2.65-2.7 • Clay & Silty Clay 2.67-2.9 • Organic Soils <2.0
Procedures For Specific Gravity LabASTM D 854 See Chapter 3, Page 55 For Your Data Sheet APPARATUS: 500 ml flask Ice Heating Plate Thermometer C Scale (readability .1g) Evaporating Dish Distilled Water
Procedures (Method B) • Dry specimens to constant mass in oven at 110 C. • Select a 500 ml flask and record mass (g) • Fill with distilled water to 500 ml line and record mass (g) • Record temperature of water in degrees Celsius (T1). • Pour 2/3 of water back into distilled container
Weigh out 100g of sandy soil and transfer to flask • Add distilled to 2/3 full and boil gently for 10 minutes • Bring temperature back to T1 using cooling bucket w/ice. • Add distilled to 500 ml line and record mass (g) • Record mass of evaporating dish (g) • Pour ALL sample into dish and dry to constant weight. • Record mass of oven dried dish/sample. • Complete calculations on data sheet, including correction for temperature …. SG is always reported at 20 C. • See page 44 for correction factors.