★ what is retaining wall ?
a) Retaining wall is a structure designed and constructed to resist the lateral pressure of soil, when there is a desired change in ground elevation that exceeds the angle of repose of the soil.
a basement wall is the one kind of retaining wall. This reduction lowers the pressure on the retaining wall.
b) A retaining wall is a structure that retains any material and prevents it from sliding away it is designed so that to resist the material pressure of the material that it is holding back.
c) retaining wall are generally used to retain Earth or other material to maintain unequal levels on on two faces.
-Retaining walls are used in the construction of basement below ground level.
-Retaining wall can be constructed with Masonry as well as reinforced concrete.
-In case of masonry retaining wall, the thickness of wall increases with height because masonry resist the lateral pressure by its weight thus it is called gravity retaining wall.
-The reinforced concrete retaining wall resist the lateral pressure by structural action such as bending.
† Types :-
1) Gravity retaining walls
Reinforced concrete retaining walls
2) Cantilever retaining wall
3) CounterFort/buttressed retaining wall.
-It is that type of retaining Wall relies on their huge weight to retain the material behind it and achieve stability against failures.
-Gravity retaining wall can be constructed from concrete, stone or even brick masonry.
-Gravity retaining wall are much thicker in section.
-Geometry of these walls also help them to maintain the stability.
2) Cantilever retaining walls :-
Cantilever retaining walls are most commonly and widely used type of retaining wall.
|Fig show the parts|
A) Vertical stem :-
Vertical stem in cantilever retaining wall resist Earth pressure from back fill side and bends like a cantilever.
-Thickness of cantilever slab is larger at the base of stem and it decreases gradually upwards due to reduction of soil pressure with decrease in depth
B) Base stem :-
-The base slab from the foundation of the retaining wall. it consists of a heel slab and the toe slab.
-The Heel slab acts as a horizontal cantilever under the combined action of the weight of retaining earth from the top and the soil pressure acting from the softing.
-The toe slab also acts as a cantilever under the action of the soil pressure acting upward.
The stability of the wall is maintained by the weight of the Earth fill and On The heel slab together with the self weight of the structural element of the retaining wall.
-Cantilever type retaining walls are suitable up to 5 m depth of back fill.
– When the height of earth to be retaining exceeds 5 m the bending moment developed in the stem, heel and toe slabs are very large with results in large thickness of structural element becomes uneconomical.
– That’s counter fort type retaining walls is adopted for large Heights.
– Counter-fort retaining wall consist of stem, toe slab and heel slab as in case of cantilever retaining wall. but it is also consists of counter-forts are regular interval which divides the stem.
– The stem with combination of counter-forts behave like a toe slab with varying width.
– The stem and heel slabs are effectively fixed to Counter-forts so that the stem bends horizontally between the Counter-forts due to lateral Earth pressure.
– Thus, the thickness of stem and heel slab is considerably reduced due to the reduction of movement due to fixity of these slabs between the Counter-forts
# Causes of retaining wall failure.
1) Improper reinforcement Placement.
2) Saturated back-fill.
3) Weep holes that do not weep.
4) Design error
5) Calculation errors.
6) Unanticipated loads
7) Mistakes in utilizing software.
8) Detailing errors.
9) Foundation issues.
10) In adequate specification and notes.
11) retaining wall age.
# Loads and forces acting on retaining walls.
1) Lateral Earth pressure.
2) Surcharge loads.
3) Axial loads.
4) Wind on projection of stem.
5) Impact forces.
6) Seismic Earth pressure.
7) Seismic wall self-weight forces.
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