Chapter 5

Question 1

Failure of retaining wall

Answer 1

• Fracture
• Overturning
• Rotation

Question 2

Factors affecting stability

Answer 2

• Nature, type of soil
• Type of wall
• Material used

Question 3

Active earth pressure

Answer 3

Tends to move or overturn the wall

Question 4

Passive pressure

Answer 4

Reactionary pressures which react in the form of resistance to the movement of the wall

Question 5

Main types of retaining wall

Answer 5

• Gravity wall
• Cantilever retaining wall
• Counterfort wall
• Buttress wall

Question 6

Gravity wall

Answer 6

• Made of plain concrete
• Depends entirely on its weight for stability
• Used for walls not exceeding 2m

Question 7

Cantilever retaining wall

Answer 7

• Constructed of reinforced concrete
• Wall may be cast-in-situ or precast sections
• Suitable for heights up to 7m

Question 8

Counterfort wall

Answer 8

Triangular shaped wall which connects the top to the back of the footer

Question 9

Buttress wall

Answer 9

Identical to a counterfort wall except the support wall is on the outside of the retaining wall

Question 10

Other types of retaining walls

Answer 10

• Concrete crib wall
• Anchored sheet pile wall

Question 11

General requirements of formwork

Answer 11

• Strength
• Alignment
• Quality of Surface Finish
• Economy

Question 12

The formwork should be strong enough to carry (Strength)

Answer 12

• Dead weight of concrete
• Live load from men and machines used in placing of concrete
• Impact loading caused by concrete being discharged into the formwork

Question 13

Surface finish of concrete may be (Quality of Surface Finish)

Answer 13

• Smooth
• Textured
• Exposed aggregates

Question 14

Economy

Answer 14

To minimise formwork wastage, the correct usage and repeated reuse must be considered

Question 15

Before formwork can be removed the concrete must have (Striking of formwork)

Answer 15

• Sufficient strength to support itself
• Sufficient surface hardness to resist damage
• Sufficient curing to give a reasonable colour finish to the concrete

Question 16

General requirements governing design of formwork

Answer 16

• Safety
• Structural safety
• Durability

Question 17

Types of cofferdam

Answer 17

• Sheeted types
• Double-skin types
• Gravity and crib types

Question 18

Advantages of cofferdam

Answer 18

• Provides safe environment to work
• Steel sheet piles are easily installed and removed
• Materials can be reused on other projects

Question 19

Disadvantages of cofferdam

Answer 19

• Special equipment required
• Relatively inexpensive
• Very time consuming and tedious

Question 20

Cofferdam construction

Answer 20

• Open-cut
• Top-down
• Bottom-up

Question 21

Methods of support for excavation

Answer 21

• Excavation supported by sheet piling
• Excavation supported by reinforced concrete diaphragm wall
• Excavation supported by secant piles

Question 22

Methods for basement waterproofing

Answer 22

• Interior sealants
• Interior water drainage
• Exterior waterproofing

Question 23

Terms used in retaining wall

Answer 23

Surcharge, Stem, Front face, Rear face, Toe, Base, Heel, Downstand beam

Question 24

Reasons to leave formwork permanently

Answer 24

• Difficulty of removing the formwork
• High cost of removing the formwork
• Formwork can also be used as wall finish

Question 25

Alignment

Answer 25

Joints should be smooth and have no surface irregularities