Test: Soil Mechanics- 1 - Civil Engineering (CE) MCQ

Plasticity index (PI) is the range of water content over which the soil remains in the plastic state. Mathematically defined as,

Plasticity Index = Liquid Limit (w_L) – Plastic Limit (w_p)

1. Water content is the ratio of the mass of water to the mass of solids. It can be greater than 100%.
2. The degree of saturation has ranged from 0% to 100%.
3. The porosity cannot be greater than 100%.
4. The void ratio of soil can be greater than 1.

• Loess is an Aeolian Sediment i.e. transported by winds.
• These contain fine particles like silt and clay (typically in the 20–50 micrometer size range). 
• Loess is uniformly graded soil. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs.

Lacustrine soil: Soil which is deposited from suspension in fresh still water of the lakes is known as Lacustrine soil. Lacustrine deposits are sedimentary rock formations which formed in the bottom of ancient lakes. 

Alluvial Soil: Soil which is been deposited from suspension in running water is known as Alluvial soil. It is transported soil formed by physical wheathering.

Aeoline Soil: Soil which is formed due to transportation by wind is known as Aoeline soil. It is also a transported soil.

Marine soil: Soil which is deposited from the suspension in sea water is known as marine soil.

Voids ratio: It is defined as the ratio of the total volume of voids to the volume of solids in a given soil mass.

Void ratio, e = V_v / V_s

e > 0, voids ratio has no upper limit

V_v = air void (Va) + water filled voids (Vw)
Calculation:

Given,

V_a = 1/6 of V

V_w = 1/3 of V

V_v = Va + Vw = V/2

Specific gravity of solids is the ratio of weight of given volume of solids to the weight of equivalent volume of water at 4° C.

Specific gravity is usually reported at 27°C and determined using pycnometer. It is given by 

W₁ = Mass of empty volume of pycnometer

W₂ = Mass of pycnometer + Mass of moist sample

W₃ = Mass of pycnometer + soil + water

W₄ = Mass of pycnometer full of water

G_s = Specific gravity of soil solids

Total volume of soil, V = 10 m³

∴ V_V = 0.4 × 10 = 4m³

Volume of solids, V_s = V – V_V = 10 – 4 = 6 m³

Mass of solids, W_s = V_s G_s Y_w = 6 × 2.68 × 1000 = 16080 kg

Moisture content = 0.12

So, Mass of water = 0.12 × 16080 = 1929.6 kg

Volume of water = 1929.6/1000 = 1.929 m³

So, phase diagram can be shown as

For full saturation, the amount of air has to be replaced by water.

So, water to be added = 2.071 × 1000 = 2071 kg

Dry unit weight is given by

η_a = 0.05

G = 2.70

ω = 0.35

η_d = 13.19 kN/m³

η_a = a_cη

η → porosity

a_c → aircontent

a_c = 0.1269
a_c = 12.70%

And, e s_r = wG

⇒ e × 1 = 0.40 G

⇒ G = 2.97
Shrinkage limit, w_s = 
Where, G_m = Mass specific gravity at dry state

Dry density of soil at excavation site,

∴ Volume of excavated soil =
= 1000 × 1.1/1
= 1100 m³