1. RETAINING WALLS

2. RETAINING WALL
Basic function – to retain soil at a slope which is greater than it would naturally assume, usually at a vertical or near vertical position

4. Retaining wall failure at the Shin-Kang Dam

5. Design of retaining wall
retaining walls have primary function of retaining soils at an angle in excess of the soil’s nature angle of repose.
Walls within the design height range are designed to provide the necessary resistance by either their own mass or by the principles of leverage.
Design consideration:
Overturning of the wall does not occur
Forward sliding does not occur
Materials used are suitable
The subsoil is not overloaded

6. Factors which designer need to take account
Nature and characteristics of the subsoil's
Height of water table – the presence of water can create hydrostatic pressure, affect bearing capacity of the subsoil together with its shear strength, reduce the frictional resistance between the underside of the foundation
Type of wall
Materials to be used in the construction

8. Failure of retaining wall (dam) due to water pressure..

9. Types of walls Mass retaining walls Cantilever walls
Counterfort retaining walls
Precast concrete retaining walls
Precast concrete crib-retaining walls

10. Mass retaining walls
Sometimes called gravity walls and rely upon their own mass together with the friction on the underside of the base to overcome the tendency to slide or overturn
Generally only economic up to 1.8 m
Mass walls can be constructed of semi-engineering quality bricks bedded in a 1:3 cement mortar or of mass concrete
Natural stone is suitable for small walls up to 1m high but generally it is used as a facing material for walls over 1 m

11. Typical example of mass retaining walls
BRICK MASS RETAINING WALL

12. Brick retaining wall
Stone retaining wall

13. Typical example of mass retaining walls
MASS CONCRETE RETAINING WALL WITH STONE FACINGS

14. Cantilever walls
Usually of reinforced concrete and work on the principle of leverage where the stem is designed as a cantilever fixed at the base and the base is designed as a cantilever fixed at the stem
Economic height range of 1.2 m to 6 m using pre-stressing techniques
Any durable facing material can be applied to the surface to improve appearance of the wall

15. Cantilever wall

16. Two basic forms:- Cantilever L Cantilever T A base with a large heel
A cantilever with a large toe
Cantilever L
Cantilever T

18. Cantilever walls

21. Counterfort retaining walls
Can be constructed of reinforced or prestressed concrete
Suitable for over 4.5 m
Triangular beams placed at suitable centres behind the stem and above the base to enable the stem and base to act as slab spanning horizontally over or under the counterforts

25. Precast concrete retaining wall
Manufactured from high-grade pre cast concrete on the cantilever principle.
Can be erected on a foundation as permanent retaining wall or be free standing to act as dividing wall between heaped materials which it can increase three times the storage volume for any given area
Other advantages- reduction in time by eliminating curing period, cost of formwork, time to erect and dismantle the temporary forms
Lifting holes are provided which can be utilized for fixing if required

26. application

28. Precast concrete retaining walls

29. Pre cast concrete crib-retaining walls
Designed on the principle of mass retaining walls
A system of pre cast concrete or treated timber components comprising headers and stretchers which interlock to form a 3 dimensional framework or crib of pre cast concrete timber units within which soil is retained
Constructed with a face batter between 1:6 and 1:8
Subsoil drainage is not required since the open face provides adequate drainage.