RETAINING WALL DESIGN

ERT352FARM STRUCTURES

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INTRODUCTION• Retaining walls are used to retain earth or other

material in a vertical or nearly vertical position at location where an abrupt change in ground level occurs.

• This caused the retained earth to exert a lateral pressure on the wall, thereby tending to overturn, side and settle the retaining wall.

• Failure of retaining wall as shown in figure below.

TYPE OF RETAINING WALLS

• There are many types of retaining structures and generally divided into two main categories namely gravity wall and cantilever wall.

• The following are some commonly used walls in Malaysiao Gravity wall

• Depends on its own weight to provide the necessary stability

• Usually constructed of plain concrete or stone masonry

• Height of wall < 3 m

TYPE OF RETAINING WALLS (cont.)o Cantilever wall

• Most common type of retaining structures • Economical for height up to 8 m• Consists of a vertical cantilever spanning

from a large rigid base slabo Counterfort wall

• Used where the overall height of wall is too large to be constructed economically as cantilever

• The wall and base are tied together at intervals by counterfort or bracing walls

• Economical for high of walls above 6 - 7 m backfill

o Butrress wall• Similar to counterfort wall but the bracing

is constructed in front of the wall.• Provides free usable space in front of the

wall

TYPE OF RETAINING WALLS (cont.)o Gabion wall

• Made of rectangular containers (basket) which are filled with stone and stacked on one other.

• Can conform to ground movement, dissipate energy from flowing water and drain freely

o Crib wall• Constructed by interlocking individual boxes

made from timber or pre-cast concrete members.

• The boxes filled with crushed stone or other coarse granular materials.

o Tie back • A horizontal wire or rod or helical anchor used

to reinforce retaining walls for stability• Resists forces that would cause the wall lean

o Keystone• Made up from concrete segmental block units• Using interlocking systems• Offers aesthetic appeal, cost efficiency, easy

installation and strength.

ANALYSIS AND DESIGN• The design of RC retaining

wall can be divided into two fundamental stages as follow:o Stability analysis

• Lateral force due to earth pressure constitutes the main force acting on the retaining wall, tending to make it overturn, slide and settle.

o Element design and detailing• 3 elements of retaining wall

(eg.: stem, toe slab and heel slab) are designed as cantilever slabs to resist the designed moments and shear forces.

Safety factor for stability analysis

Example:• Design a cantilever wall to retain earth with

horizontal backfill which subjected to surcharge of 10 kN/m2. the top of the wall is 4.0 m above the ground level and foundation depth may be taken as 0.9 m below ground level with a safe bearing capacity 170 kN/m2. Assume the backfill has a unit weight of 19 kN/m3 and an angle of shearing resistance of 350. The coefficient of friction between soil and concrete is 0.45. Use fck = 30 N/mm2, fyk = 500 kN/m2 and nominal cover = 45 mm

Solution:

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