retaining walls. retaining wall basic function – to retain soil at a slope which is greater than...

RETAINING WALLS

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

Retaining wall failure at the Shin-Kang Dam

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:1. Overturning of the wall does not occur2. Forward sliding does not occur3. Materials used are suitable4. The subsoil is not overloaded

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

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

Types of walls

• Mass retaining walls

• Cantilever walls

• Counterfort retaining walls

• Precast concrete retaining walls

• Precast concrete crib-retaining walls

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

Typical example of mass retaining walls

BRICK MASS RETAINING WALL

Brick retaining wall

Stone retaining wall

Typical example of mass retaining walls

MASS CONCRETE RETAINING WALL WITH STONE FACINGS

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

Cantilever wall

Two basic forms:-• A base with a large heel

• A cantilever with a large toe

Cantilever LCantilever T

Cantilever walls

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

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

application

Precast concrete retaining walls

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.