9.3 Actions, geometrical data and design situations

9.3.1 Actions Basic actions

(1) The actions listed in 2.4.2 (4)P should be considered. Weight of backfill material

(1)P Design values for the weight density of backfill material shall be estimated from knowledge of available material. The Geotechnical Design Report shall specify the checks, which shall be made during the construction process to verify that the actual field values are no worse than those used in the design. Surcharges

(1)P Determination of design values for surcharges shall take account of the presence, on or near the surface of the retained ground, of, for example, nearby buildings, parked or moving vehicles or cranes, stored material, goods and containers.

(2) Care should be taken in the case of repeated surcharge loading such as imposed by crane rails on a quay wall. The pressures induced by such surcharges can significantly exceed those due to the first loading or those resulting from static application of a load of equal magnitude. Weight of water

(1)P Design values for the weight density of water shall reflect whether the water is fresh, saline or charged with chemicals or contaminants to an extent that the normal value needs amendment. Wave and ice forces

(1)P Design values for forces imposed by reflected waves or by ice forces shall be selected on the basis of locally available data for the climatic and hydraulic conditions at the site.

(2)P When selecting design values for static forces imposed by a sheet of ice, the following shall be taken into account:

  • the initial temperature of the ice before warming begins;
  • the rate at which the temperature increases;
  • the thickness of the ice sheet. Seepage forces

(1)P Seepage forces due to different ground-water levels behind and in front of a retaining structure shall be considered as they may change the earth pressure behind the wall and reduce the earth resistance in front of the wall. Collision forces

(1)The determination of design values for collision impact forces, caused by, for example, waves, ice floes or traffic, may take account of the energy absorbed by the colliding mass and by the retaining system, e.g. by fenders and/or guide structures.

(2) For lateral impacts on retaining walls, the increased stiffness exhibited by the retained ground should be considered.

(3) The risk of the occurrence of liquefaction due to lateral impact on embedded walls should be investigated.

(4)P The impact load of an ice floe colliding with a retaining structure shall be calculated on the basis of the compressive strength of the ice and the thickness of the ice floe. The salinity and homogeneity of the ice shall be considered in calculating the compressive strength. Temperature effects

(1)P The design of retaining structures shall take into account the temporal and spatial effects of abnormal temperature changes.

(2) These effects should be considered particularly when determining the loads in struts and props.

(3) The Structural Fire Design Parts of the material related Eurocodes should be consulted when dealing with the effects of fire.

(4)P Special precautions, such as selection of suitable backfill material, drainage or insulation, shall be taken to prevent ice lenses forming in the ground behind retaining structures.

9.3.2 Geometrical data Basic data

(1)P Design values for geometrical data shall be derived in accordance with the principles stated in Ground surfaces

(1)P Design values for the geometry of the retained material shall take account of the variation in the actual field values. The design values shall also take account of anticipated excavation or possible scour in front of the retaining structure.

(2) In ultimate limit state calculations in which the stability of a retaining wall depends on the ground resistance in front of the structure, the level of the resisting soil should be lowered below the nominally expected level by an amount Δa. The value of Δa should be selected taking into account the degree of site control over the level of the surface. With a normal degree of control, the following should be applied:

  • for a cantilever wall, Δa should equal 10 % of the wall height above excavation level, limited to a maximum of 0,5 m;
  • for a supported wall, Δa should equal 10 % of the distance between the lowest support and the excavation level, limited to a maximum of 0,5 m.

(3) Smal er values of Δa, including 0, may be used when the surface level is specified to be controlled reliably throughout the appropriate execution period.

(4) Larger values of Δa should be used where the surface level is particularly uncertain. Water levels

(1)P The selection of design or characteristic values for the positions of free water and phreatic surfaces shall be made on the basis of data for the hydraulic and hydrogeological conditions at the site.

(2)P Account shall be taken of the effects of variation in permeability on the ground-water regime.

(3)P The possibility shall be considered of adverse water pressures due to the presence of perched or artesian water tables.

9.3.3 Design situations

(1)P The following items shall be considered:

  • variations in soil properties, water levels and pore-water pressures in space;
  • anticipated variations in soil properties, water levels and pore-water pressures in time;
  • variation in actions and in the ways they are combined;
  • excavation, scour or erosion in front of the retaining structure;
  • the effects of compaction of the backfilling behind the retaining structure;
  • the effects of anticipated future structures and surcharge loadings or unloadings on or close to the retained material;
  • anticipated ground movements due, for example, to subsidence or frost action.

(2) For waterfront structures, ice and wave forces need not be applied simultaneously at the same point.

Eurocode 7 Geotechnical design Part 1 : General rules