Chapter 5 Flashcards
Failure of retaining wall
- Fracture
- Overturning
- Rotation
Factors affecting stability
- Nature, type of soil
- Type of wall
- Material used
Active earth pressure
Tends to move or overturn the wall
Passive pressure
Reactionary pressures which react in the form of resistance to the movement of the wall
Main types of retaining wall
- Gravity wall
- Cantilever retaining wall
- Counterfort wall
- Buttress wall
Gravity wall
- Made of plain concrete
- Depends entirely on its weight for stability
- Used for walls not exceeding 2m
Cantilever retaining wall
- Constructed of reinforced concrete
- Wall may be cast-in-situ or precast sections
- Suitable for heights up to 7m
Counterfort wall
Triangular shaped wall which connects the top to the back of the footer
Buttress wall
Identical to a counterfort wall except the support wall is on the outside of the retaining wall
Other types of retaining walls
- Concrete crib wall
- Anchored sheet pile wall
General requirements of formwork
- Strength
- Alignment
- Quality of Surface Finish
- Economy
The formwork should be strong enough to carry (Strength)
- 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
Surface finish of concrete may be (Quality of Surface Finish)
- Smooth
- Textured
- Exposed aggregates
Economy
To minimise formwork wastage, the correct usage and repeated reuse must be considered
Before formwork can be removed the concrete must have (Striking of formwork)
- Sufficient strength to support itself
- Sufficient surface hardness to resist damage
- Sufficient curing to give a reasonable colour finish to the concrete
General requirements governing design of formwork
- Safety
- Structural safety
- Durability
Types of cofferdam
- Sheeted types
- Double-skin types
- Gravity and crib types
Advantages of cofferdam
- Provides safe environment to work
- Steel sheet piles are easily installed and removed
- Materials can be reused on other projects
Disadvantages of cofferdam
- Special equipment required
- Relatively inexpensive
- Very time consuming and tedious
Cofferdam construction
- Open-cut
- Top-down
- Bottom-up
Methods of support for excavation
- Excavation supported by sheet piling
- Excavation supported by reinforced concrete diaphragm wall
- Excavation supported by secant piles
Methods for basement waterproofing
- Interior sealants
- Interior water drainage
- Exterior waterproofing
Terms used in retaining wall
Surcharge, Stem, Front face, Rear face, Toe, Base, Heel, Downstand beam
Reasons to leave formwork permanently
- Difficulty of removing the formwork
- High cost of removing the formwork
- Formwork can also be used as wall finish
Alignment
Joints should be smooth and have no surface irregularities
