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Design is unacceptable if degree of utilization is >

100%

© The selection of an appropriate angle of friction between the base of the wall and the ground is a matter of engineering judgement. The constant volume angle of friction, 9cv, is the minimum likely value for a soil and thus it is considered that it would be unreasonable to adopt a design value of lower than 9cv.

© The drained sliding resistance excludes any influence of effective cohesion. This is conservative but reflects the likelihood that adhesion would not be generated along a soil/concrete interface. Furthermore, the vertical action should be taken as favourable since this reduces the sliding resistance.

© The formulae for bearing capacity and load inclination factors are those given in Annex D of EN 1997-1. As the wall is effectively a strip footing, shape factors are not required. Depth factors are not given in Annex D.

© Since the water level could rise to the base of the wall, the submerged weight density (Yk,fdn ~ Yw) should be used in this equation.

© For drained conditions, bearing is critical and indicates a higher degree of utilization than for the undrained case (99% vs 59%, both for Combination 2). Under drained conditions, the requirements of Eurocode 7 are just met.

The fact that bearing resistance is more critical in the drained case is contrary to the normal expectation that situations improve with time, i.e. bearing and sliding resistances should be greater for the drained situation. This suggests a lack of compatibility between undrained and drained parameters at low effective stresses. However, engineers are not traditionally comfortable using high values of effective c' and/or 9 in clays that would give such compatibility.

© The results for Design Approaches 2 and 3 are presented in summary only. The full calculations are available from the book's website at www.decodingeurocode7.com.

Design Approach 2 applies factors greater than 1.0 to actions and resistance. Sliding is critical in DA2 and the degree of utilization (104%) is higher than Eurocode 7 allows.

Design Approach 3 applies factors greater than 1.0 to structural actions (i.e. the self-weight of the concrete) and material properties. Bearing is critical and the degree of utilization (102%) is marginally unacceptable under Eurocode 7.

11.11.3 T-shaped gravity wall retaining wet fill

Example 11.3 re-considers the design of the T-shaped gravity wall from Examples 11.1 and 11.2 (shown in Figure 11.10), allowing for the absence of a drain that is fully effective in the long term. (Alternatively, this example could represent the situation where a drain is positioned behind the wall stem, not behind the heel.) This potentially leads to a build-up of water behind the wall, as shown in Figure 11.11.

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