Question 4 A sample of a clay soil deposi, upon which a lightly-loaded structure

Question

Question 4 A sample of a clay soil deposi, upon which a lightly-loaded structure is to be constructed, had the following properties Total Volume 100cm3 Total Mass 170grams Moisture Content (mass basis) = 16% Specific Gravity of Solids 2.70 (a) Calculate the relative proportions, on a volume basis, of solids, water and air in the sample. (6 marks) (b) The sample was then soaked for 12 hours and the total volume increased to 105cm3, with a corresponding increase in moisture content (mass basis) to 25%. Is the sample now saturated? (4 marks) (c) Outline the reason(s) why some clay soils swell more than others. (5 marks)

Explanation / Answer

(a) Mass = density * volume

Volume = Mass/density

given that specific gravity = 2.70

Thus, the density would be 2.70 g/cm3.

Total mass = 170 g

Mpisture Content (mass basis) = 16%

Thus mass of the moisture present = (170*16/100) g or 27.2 g

Thus mass of the total solids present in the soil system = (170-27.2) or 142.8 g (as the mass of the air present in the soil is negligible)

Now volume of the soil solid Mass / Density or (142.8/2.7) or 52.9 cm3

We know the density of water is 1 g/c3,

Thus, the volulme of of water = (27.2/1) or 27.2 cm3

Therefore volume of air present in the soil sample = (100-27.2-52.9) or 19.9 cm3

Thus the relative proportion, on a volume basis, of solids, water and air in the sample would be 52.9 : 27.2 : 19.9

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