D45 FACE THE CHALLENGE

A rectangular channel has width 3 m and depth 2 m. If velocity = 2 m/s, calculate discharge.

• 12 m³/s
• 10 m³/s
• 8 m³/s
• 6 m³/s

Answer explanation

Q = A × V = 3×2×2 = 12 m³/s

Calculate total dry volume of materials required for 1 m³ of concrete.

• 1.52 m³
• 1.44 m³
• 1.60 m³
• 1.35 m³

Answer explanation

Dry volume = Wet volume × 1.52 (to account for shrinkage and voids)

Assertion (A): More water in concrete mix reduces strength. Reason (R): High W/C ratio increases porosity.

• Both A and R are true and R is correct explanation
• Both A and R are true but R is not the correct explanation
• A is true, R is false
• A is false, R is true

Answer explanation

Higher W/C increases porosity, reducing strength.

1. In RCC, minimum cover depends on exposure condition. 2. Cover is mainly to resist shear.

• Only 1 is correct
• Only 2 is correct
• Both correct
• Both incorrect

Answer explanation

Cover is for protection from corrosion and fire, not for shear.

1. Plane table surveying gives real-time plotting. 2. It is suitable for large-scale detailed surveys.

• Only 1 is correct
• Only 2 is correct
• Both correct
• Both incorrect

The minimum diameter of main bars in slab reinforcement is:

• 6 mm
• 8 mm
• 10 mm
• 12 mm

Answer explanation

The minimum diameter of main bars in slab reinforcement as per IS 456:2000 Clause 26.5.2.2 is 8 mm for high yield strength deformed bars (HYSD) and 10 mm for plain bars.

So, for modern practice using HYSD bars (which is the most common), the minimum is 8 mm.

Which dam type requires strong abutments to resist horizontal thrust?

• Gravity
• Arch
• Buttress
• Earth

Answer explanation

Arch dams push load to abutments — requires strong sides.

Which defect is caused due to insufficient curing of plaster?

• Flaking
• Blistering
• Efflorescence
• Crazing

Answer explanation

Crazing results from rapid drying and shrinkage.

The bearing capacity of soil is least for:

• Rock
• Gravel
• Silt
• Clay

Answer explanation

Clay has lowest SBC due to poor drainage and compressibility.

A free vortex has:

• Constant velocity
• Constant angular velocity
• Constant circulation
• No flow

Answer explanation

Free vortex has constant circulation and decreasing angular velocity.