7 Design considerations

7.1 General

7.1.1 The design shall produce contract documents to enable works to be constructed which fulfil the specified requirements with respect to safety, serviceability, economy and durability, taking into account the expected service life.

7.1.2 The design of reinforced fill structures shall be based on EN 1990 and EN 1991. Since EN 1997-1 does not presently cover the detailed design of reinforced fill structures, the design of these structures shall currently be carried out using national standards. See Foreword for further comments.

7.1.3 The reinforced fill technology shall be compatible with the method of construction and be selected at the design stage.

7.1.4 The design shall enable construction to be achieved within realistic tolerances. Generally speaking reinforced fill structures as such are flexible and can deform during and after construction. The design should, therefore, take into account reasonable construction tolerances in regard to vertical and horizontal alignments, levels and layout. Special consideration should be made to allow for necessary deformations when reinforced soil structures are combined with or located adjacent to rigid structures.

7.1.5 A design brief shall be prepared which details the works to be constructed, the scope of the work carried out in the design, the required design life and any hazard associated with operation of the works.

7.1.6 When some latitude is left in the selection of the materials or systems to be used, the design brief should emphasise the particular requirements of the project that shall influence the final selection decision.

7.1.7 Possible consequences of failure, in terms of risk to life, potential economic losses and inconvenience including disruption of services, shall be taken into account early in the design stage, in accordance with the categories given in EN 1997-1.

7.2 Additional Design Considerations

7.2.1 Loading conditions, including accidental loads and transient loads during construction, climatic effects and hydraulic conditions, shall be taken into account for both permanent and temporary reinforced fill structures. This also includes seismic loads in seismically active areas.

7.2.2 The effects of permanent and temporary reinforced fill structures on any adjacent structures shall be taken into account.

7.2.3 Hydraulic conditions shall include the effects of hydraulic loading and effects on durability arising from any contact with water or contaminants.

7.2.4 Consideration shall be given to the ability of the reinforced fill structure to tolerate anticipated magnitudes of total and differential settlement, frost heave, deformation and movement. Where necessary, such settlements, deformations and movements of reinforced fill structures shall be monitored as the construction progresses, for comparison with the predictions (see 7.4.5).

7.2.5 Where appropriate special consideration shall be given to drainage during the construction phase.

7.2.6 Consideration shall be made of any restrictions on construction such as environmental conditions, including noise and vibration, tidal working, climatic conditions and any phasing of construction.

7.2.7 Where the origin and properties of the fill materials to be used are not known at the design stage the design assumptions shall be stated in the design documents.

7.2.8 For reinforced fill structures with a vegetative cover on the facing the special construction guidelines of the supplier of the facing system should be considered to ensure permanent vegetation.

7.3 Design amendments

7.3.1 Amendments may be necessitated by either unforeseen conditions or planned modifications arising out of use of an observational method.

7.3.2 Amendments necessitated by unforeseen circumstances, such as changes in ground or hydraulic conditions, shall be reported immediately in accordance with clauses 4.2 and 4.3.

7.3.3 If the construction activity requires a change to the structure as defined in the design documents then this shall only be carried out after the design has been checked and modified accordingly.