Stirling Council
Retaining wall - Dunblane

Job description/ scope

Following the failure of the existing retaining wall a local structural engineer was engaged to investigate the reason for the collapse and provide rectification requirements. The consequent onsite meeting provided the following information :

• the original wall was of poor construction
• low quality materials had been used previously
• not carried out to the engineers specification.

The construction of retaining walls are primarily used for holding back soil from a building, structure or in our instance a footpath to the adjoining property.

Retaining walls are commonly constructed of concrete, steel and brickwork and their main objective is to prevent a down slope movement of soil or to resist lateral pressure.

Works Completed by Burnbrae Contracts

Following our pre-start meeting with the client and the structural engineer, the procedures below were agreed as safe working practice :

• removal of existing footpath
• phased foundation digs and subsequent phased foundation pours after steel cage instalments allowing 7 days between pour
• retaining wall constructed in phased manner to ensure stability of adjacent ground with temporary propping as required
• at junction of pours provide dowel bars to ensure continuity between top and bottom base mesh and stem mesh
• shutter and pour mass concrete block, tied into steel foundation cage to reinforce existing garden return wall
• 350mm retaining wall constructed with 150mm cavity, wall ties formed using galvanised T6 bar at staggered 450mm horizontal and 900mm vertical centres
• stem poured in 2 equal lifts, concrete placed no sooner than 5 days after building of brickwork. Pockets at 675mm centres left to allow cleaning of cavity prior to concrete pour
• repeat retaining wall process to achieve required height
• cavity fill with concrete, slab and cap off to top of wall allowing 5 day curing time
• apply 2no coats of R.I.W waterproofing to rear of retaining wall ensuring weep holes are kept clear
• granular backfill to be contained within a geo textile filter membrane
• re-build wall profile to match existing, using brick to brick ties to ensure stability
• clear site
• handover meeting/ sign-off