Earth Pressure Analysis and Retaining Walls

Earth Pressure Analysis and Retaining Walls

Copyright: © 2015 |Pages: 98
DOI: 10.4018/978-1-4666-6505-7.ch006
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Retaining walls are structures used not only to retain earth but also water and other materials such as coal, ore, etc. where conditions do not permit the mass to assume its natural slope. In this chapter, after considering the types of retaining wall, earth pressure theories are developed in estimating the lateral pressure exerted by the soil on a retaining structure for at-rest, active, and passive cases. The effect of sloping backfill, wall friction, surcharge load, point loads, line loads, and strip loads are analyzed. Karl Culmann's graphical method can be used for determining both active and passive earth pressures. The analysis of braced excavations, sheet piles, and anchored sheet pile walls are considered and practical considerations in the design of retaining walls are treated. They include saturated backfill, wall friction, stability both external and internal, bearing capacity, and proportioning the dimensions of the retaining wall. Finally, a brief treatment of earth pressure on underground structures is included.
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6.1 Lateral Support In Geotechnical Engineering

Engineering structures such as retaining walls, trenches and braced excavations, basement walks, culverts, sheet piles, bulkheads and coffer dams have a common purpose - to provide lateral support for a mass of soil. They are used in a variety of engineering projects, Figure 1. In highway construction for example, retaining walls are often used to hold back cuts or fills where space is inadequate for the appropriate side slopes. Bridge abutments and foundation walls that support earth fills are also designed as retaining walls. So also are basement walls. The pressure exerted by the soil on these structures is known as earth pressure and must be determined before a satisfactory design can be made. The lateral pressure which acts on a particular structure depends upon the boundary and the deformation conditions behind the structure, the physical and strength properties of the soil, the imposed loading and the type of retaining structure. The earth on the high side of a retaining structure is called the backfill and usually includes natural soils as well. This terminology differs from the more general one in which backfill is the material placed to fill an excavation.

Figure 1.

Applications of lateral support

Retaining walls are structures used not only to retain earth but also water and other materials such as coal, ore, etc; where conditions do not permit the mass to assume its natural slope. However, the main function of retaining walls is to stabilize hillsides and control erosion. When roadway construction is necessary over rugged terrain with steep slopes, for example, retaining walls can help to reduce the grades of roads and the land alongside the road. Some road projects lack available land beside the travel way, requiring construction right along the toe of a slope. In these cases, extensive grading may not be possible and retaining walls become necessary to allow for safe construction and acceptable slope conditions for adjacent land uses. Where soils are unstable, slopes are quite steep, or heavy runoff is present, retaining walls help to stem erosion. Excessive runoff can undermine roadways and structures, and controlling sediment runoff is a major environmental and water quality consideration in road and bridge projects. In these situations, building retaining walls, rather than grading excessively, reduces vegetation removal and reduces erosion caused by runoff. In turn, the vegetation serves to stabilize the soil and filter out sediments and pollutants before they enter the water source, thus improving water quality.

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