Explanation

• Free vortex — rotation driven by gravity, no external energy input, velocity increases toward the center
• Example of a free vortex: water swirling down a drain

Additional information 

• Forced vortex — rotation driven by an external force (like a rotating impeller), velocity increases with radius

Explanation

• By the middle-third rule, the resultant must fall within the middle third of the base
• Max allowable eccentricity e=B/6 to avoid tension
• Keeps entire foundation in compression

Additional information 

• B/4: This would allow tension over part of the base.

Explanation

• Fly ash replaces cement (Portland cement)
• Because it has pozzolanic properties (reacts with lime + water to form cementitious compounds)
• Improves workability, durability, long-term strength; reduces heat of hydration

Explanation

• The coefficient of friction is generally greatest for Rock 
• Rock — highest friction due to angular, rough, interlocking mineral surfaces

Additional information

• Sand — moderate, since grains are more rounded and can roll over each other
• Clay — lower, because fine clay particles are smooth and can also hold water, which lubricates
• Silt — lowest, being very fine, smooth particles

Explanation

• Punching shear is maximum at the Critical section around the column
• Located at a distance of d/2 (half the effective depth of the slab) from the face of the column or concentrated load.