Earth retaining structures are frequently found in civil engineering practice because of the need to resist lateral pressures from soil often due to unbalanced earth distribution on earth surface or from manmade creations. There are different and configurations of earth retaining system which depends on purpose and choice of the designer. For structural design purposes, Reynold et al (2008) gave the following common systems of earth retaining structures:
- Cantilever walls on spread base
- Gravity wall
- Embedded wall (propped)
- Embedded wall (anchored)
- Reinforced soil
- Soil nailing
- Simple cantilever walls and
- Cantilever walls with counterforts
The structural design of retaining walls just as other civil engineering structures considers the loads (actions) coming on the retaining wall. The retaining wall may be subject to vertical or horizontal loads applied at any point to the base or wall stem. It may also be subject to surcharge loads applied as area loads directly behind the wall. The analysis calculations check the stability of the retaining wall with regard to sliding and overturning as well as checking the maximum base pressures (see Retaining Wall Design). The design calculations check the stem and base in flexure and shear and will include crack width checks if required. At the completion of the design, reinforcement arrangement sketch is produced which can be used on actual site construction.
Example (Example 6.4 of Soil Craig textbook)
Details of a cantilever retaining wall are shown in Figure 1 below, the water table being below the base of the wall. The unit weight of the backfill is 17 kN/m3 and a surcharge pressure of 10 kN/m2 acts on the surface. Characteristic values of the shear strength parameters for the backfill are cˡ = 0 and ɸˡ = 36o. The angle of friction between the base and the foundation soil is 27o (i.e. 0:75ɸ). Analyse the wall and produce design calculations according to the limit state (EC7) approach?
Unit weight of concrete being taken as 25 kN/m3.
Figures 2 to 7 shows the various actions taken in order to design the retaining wall. Figure 2 is the user interface of the software for retaining wall design. From definition of geometry of retaining wall (Figure 3) to definition of soil details (Figure 4), the surcharge load was defined in Figure 5, while the density of the material of the retaining wall which is concrete in our case was defined in Figure 6. You can see from Figure 2 that the various checks of stability, overturning and bearing pressure all passed. Therefore, the reinforcement details produced in Figure 7 would be satisfactory for the geometry and he applied loads.
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