topic 7 Geo

Question 1

Give two types of shallow foundation and describe each.

Answer 1

1. Pad foundation - usually constructed to support structural R.C. columns, stanchions or isolated brick piers.
2. Strip foundation - normally provided for load-bearing walls and for rows of columns that are closely spaced.

Question 2

For strip foundation, state the requirements for its concrete thickness.

Answer 2

1. The concrete thickness must be bigger than slab’s projection from the wall it supported.
2. Thickness, t > 150mm

Question 3

Determine two situations when it is more suitable to use raft foundation over pad or strip foundation.

Answer 3

1. When the individual pad or strip foundation occupy more than 50% of the area of the structure
2. When the soils beneath the structure consist of varying compressibility

Question 4

Determine five situations when it is more suitable to use pile foundation.

Answer 4

1. No firm bearing strata exists at a reasonable depth and the applied loading is uneven.
2. The pumping of sub-soil water would be too costly.
3. Highly compressible soils near the surface.
4. Shrinkable clayey soil beneath the structure.
5. To solve the problem due to the moisture changes in the soil.

Question 5

Piles could be classified in two ways. Briefly describe how the piles are classified.

Answer 5

By the ways their bearing capacities are derived:
1. friction piles
2. End bearing piles

By the methods of installation:
1.displacement
2. Non displacement

Question 6

List ten possible problems occurring during the installation of a pile.

Answer 6

1. Overdriving the pile
2. Driving the pile using the wrong hammer weight
3. Deflected off location by
   obstructions
4. Ground heaving
5. Tensile cracking during driving
6. Consolidation in sand due to piling
7. Confusion between chiselling and socketing
8. Concrete placement and mix design
9. Necking of pile due to incorrect casing withdraw method
10. Boring in unstable soils may cause breakthrough of soil wall