EARTH RETAINING STRUCTURES.ppt
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Retaining walls are used to retain earth or other material in a vertical position where there is an abrupt change in ground level. This causes lateral pressure on the wall from the retained material. There are four main types of retaining walls: gravity walls, which rely on their own weight for stability; cantilever walls, the most common type for heights up to 8 meters, consisting of a vertical stem and base slab; counterfort walls, which have transverse supports called counterforts to reduce bending moments for heights over 7 meters; and buttress walls, similar to counterfort walls but with supports located in front instead of behind.
EARTH RETAINING STRUCTURES.ppt
- 2. Retaining walls are used to retain earth (or other material) in a vertical (or nearly vertical) position at locations where an abrupt change in ground level occurs. It causes the retained earth to exert a lateral pressure on the wall, thereby tending to bend, overturn and slide the retaining wall structure.
- 4. 1. Gravity walls 2. Cantilever walls 3. Counterfort walls 4. Buttress walls
- 5. GRAVITY WALLS The gravity wall provides stability due to its own weight and therefore, it is massive in size. It is usually built in stone masonry, and occasionally in plain concrete. Plain concrete gravity walls are not used for heights exceeding about 3 m, for economic reasons.
- 6. CANTILEVER WALL The cantilever wall is the most common type of retaining wall and is generally economical for heights up to about 8 m. The structure consists of a vertical stem, and a base slab. Base slab is made up of two components i.e. a heel slab and a toe slab. All three components behave as one-way cantilever slabs. The stem acts as a vertical cantilever under the lateral earth pressure. The heel slab acts as a (horizontal) cantilever under the action of the weight of the retained earth. The toe slab also acts as a cantilever under the action of the resulting soil pressure (acting upward). The stability of the wall is maintained by the weight of the earth on the heel slab plus the self weight of the structure.
- 8. For large heights, in a cantilever retaining wall bending moments develops in the stem. Heel slab and toe slab become very large and require large thickness. Bending moments (and hence stem slab thicknesses) can be considerably reduced by introducing transverse supports, called counterforts. These counterforts are spaced at regular intervals of about one-third to one-half of the wall height. They interconnect the stem with the heel slab. Such a retaining wall structure is called the courrterfort wall, and is economical for heights above (approx.) 7m. The counterforts subdivide the vertical slab (stem) into rectangular panels and support them on two sides. Counterforts themselves behave as vertical cantilever beams of T- section of varying depth.
- 10. The buttress wall is similar to the counterfort wall except that the transverse stem supports, called buttresses and are located in the front side. They interconnect the stem with the toe slab (and not with the heel slab, as with counterforts). Although buttresses are structurally more efficient (and more economical) than counterforts, the counterfort wall is generally preferred to the buttress wall as it provides free usable space (and better aesthetics) in front of the wall.