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Soil Mechanics and Foundation Engineering - Engineering

Q1:

For determing the specific gravity of soil solids, using a pycnometer of 500 cc., the following data is available : Weight of dry empty pycnometer = 125 g Weight of dried soil and pycnometer = 500 g Weight of dried soil and distilled = 850 g water filled in pycnometer up to top The specific gravity of soil soilds, is

A 2.0

B 2.25

C 2.50

D 2.75

ANS:C - 2.50

Weight of soil solids = 500-125 = 375g.
The weight of water when the soil is also present in the pycnometer = 850-500 = 350g.
the Weight of water when water fills pycnometer = 500cc * 1g/cc = 500g (Since the unit weight of water is 1g/cc).
Therefore weight of equal volume of water = 500-350 = 150g.
Specific gravity = (Weight of soil solids)/(Weight of equal volume of water) = 375/150 = 2.5. SG = Wt of dry soil/Distilled water.

Wt of dry soil = 500 - 125,
Wt of distilled water = 850 - 500,
(no need to find W4, the density of pure water or anything else). W1= Wt. of pycnometer = 125 g.
W2 = Wt. of pycnometer + Wt. of dry soil = 500 g.
W3 = Wt. of pycnometer + wt. of dry soil + wt. of water = 850 g.
W4 = Wt. of pycnometer + wt. of water = 500*1 + 125 = 625g,
where density of pure water = 1g/cc, volume of pycnometer = 500 cc.
G = (Wt. of dry soil)/(Wt. of water of equal volume (means equal to the volume of dry soil).
G = (W2-W1)/((W4-W1)-(W3-W2)).
Hence, G = (500-125)/((625-125)-(850-500)).
G = 375/(500-350).
G = 375/150.
G = 2.5. W1 = 125.
W2 = 500.
W3 = 850.

W4 = 500*1+125 = 625.
Md = 375.

W4 = W3-Md+Md/G.
G = 2.5.