8.5 Construction of earth retaining structures and reinforced slopes

8.5.1 General

8.5.1.1 The construction procedure of all earth retaining structures and reinforced slopes shall conform with the requirements which are common to all types of reinforced fill structures, as itemized in this section.

8.5.1.2 In addition, the construction procedure should conform with the recommendations which are specific to the relevant type of reinforced fill structure, as set out in the instructions provided by the supplier of the reinforcement and of the facing system, if applicable. Examples are given in Annex C.

8.5.1.3 The construction of all reinforced fill structures shall be executed layer-wise and in stages, where the placing and fixing of the facing elements, if any, and the reinforcement alternates with the deposition, spreading, levelling and compaction of the fill material.

8.5.1.4 If the reinforced fill structure has different foundation levels construction should usually start at the lowest foundation level.

8.5.2 Placement of facing

8.5.2.1 For all facing systems, special construction arrangements, adequate temporary bracing systems, such as props, wedges, clamps, steel angles etc, or formwork shall be used. At every stage of the construction, it shall be ensured that any new course of facing is stable while additional layers of backfill are placed and compacted behind or above it, before it can be effectively held back by the reinforcements.

8.5.2.2 All temporary bracing systems or formwork with the exception of lost formwork shall be removed as soon as they are no longer necessary.

8.5.2.3 Special construction arrangements shall be used, at every stage of the construction, to ensure that the final geometry is as required by the design and within the specified tolerances. Such arrangements may comprise the adjustment of the facing units to a required horizontal and vertical alignment, batter or slope to compensate for the anticipated gradual deformation of the reinforced fill structure itself but not for settlements or movements of the foundation.

8.5.2.4 The horizontal spacing with respect to overlapping, alignment and level, and the vertical alignment, batter or slope of any new course of facing units or formwork shall be checked and adjusted if needed, during the progression of the construction.

8.5.2.5 Particular attention shall be paid to the horizontal spacing, with respect to overlapping, alignment and level, as well as the vertical alignment, batter or slope of the initial course, as accuracy in this phase helps to ensure a rapid and well aligned construction of the complete structure.

8.5.2.6 Jointing material and bearing pads, if any are required by the design, shall be installed, as any new course of facing units is put in place and secured.

8.5.3 Placement of reinforcements

8.5.3.1 The reinforcement shall be laid on an even surface and connected to the facing, if applicable, using the connection method particular to the facing system as specified by the design.

8.5.3.2 It shall be ensured that the non-rigid reinforcement is tight and that any slack has been removed, in order to minimize any deformation during the mobilization of tensile forces in the reinforcement. This may be achieved by pulling the reinforcement tight and holding in this position while it is covered with fill.

8.5.3.3 Reinforcement should be placed as perpendicular as possible to the facing or to the sloped face unless specified otherwise in the design. A transverse overlap may be used at the junction of adjacent pieces of sheet type reinforcement if specified in the design.

8.5.3.4 In the presence of obstacles such as pipes, columns, piles, manholes etc it may be necessary to skew or shift a reinforcement from its designated location in either the horizontal or vertical direction. For sheet-type reinforcements it may be necessary to cut a hole into the reinforcement. Unless such alterations are explicitly permitted by the design they shall be ratified by the designer.

8.5.3.5 Reinforcement with vertical bends should be placed on a preformed mound of backfill. Sharp bends which affect the reinforcement strength shall be avoided unless allowed for in the design.

8.5.3.6 Reinforcements should extend in one continuous piece in the main load carrying direction. Where joints in that direction are unavoidable, the design shall specify an appropriate on site jointing method. The joints may be formed using methods such as bolting, welding, sewing of geotextiles, bodkin joints, etc. or designed overlaps.

8.5.3.7 Polymeric reinforcement may be prone to degradation when exposed to sunlight and therefore should be covered with fill within a specified time of laying. Where no such time is specified, exposed reinforcement should be covered within 24 hours of placement.

8.5.3.8 In general, the placement of sheet material may be disrupted by wind uplift. Where this is likely, the material should be locally ballasted.