Design for serviceability

Design values of earth pressures for the verification of serviceability limit states must be derived using characteristic soil parameters, taking account of the initial stress, stiffness, and strength of the ground; the stiffness of structural elements; and the allowable deformation of the structure. These earth pressures may not reach limiting (i.e. fully active or passive) values.

Calculations of wall movement are not necessarily required to verify the avoidance of serviceability limit states. As discussed in Chapter 8, Eurocode 7 acknowledges that deformations can be kept within required serviceability limits provided 'a sufficiently low fraction of the ground strength is mobilised'. [EN 1997-1 §2.4.8(4)]

For conventional structures founded on clays, the serviceability limit state may be deemed to have been verified by an ultimate limit state calculation, provided the ratio of the characteristic bearing resistance Rk to the applied serviceability loads Ek is at least equal to three:

YR ,sls in which yR,SLS = a partial resistance factor > 3. [en 1997-1 §6.6.2(16)]

Since Eurocode 7 fails to provide a method for calculating the displacement of gravity walls, when such calculations are required, simple rules such as those given in CIRIA 5169 could be used. The settlement 's' (in mm) of a gravity wall in a coarse-grained material can be estimated from:

where q = bearing pressure (kPa), B = the breath of the wall (m), and N = standard penetration test blow count. In an overconsolidated clay: = 15qB

cu where cu = the foundation soil's undrained strength and the other symbols are defined above.

Limiting values for the allowable wall and ground displacements must take into account the tolerance to those displacements of supported structures and services. [en 1997-1 §9.8.2(1)P]

See Chapter 12 for further discussion of Eurocode 7's serviceability requirements for retaining structures.

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