Public safety reassured by new retaining wall for unit block

CHALLENGES

Strata Engineering Solutions was called to assess a cracked and leaning retaining wall on the boundary of a block of apartments in Cremorne, NSW. The failing wall, which threatened to collapse onto a frequently-used public pathway, was presenting a risk to public safety and compromising the overall serviceability and appeal of the property. On assessment, SES engineers determined that the existing retaining wall wouldn’t be salvageable, and advised that a new retaining wall of reinforced concrete block would need to be designed and constructed. Adapting the intended design to deal with unforeseen underground obstructions, and preserving an existing footing when removal of the original wall showed it could be incorporated into the new design, were some of the ways SES helped deliver the desired results with savings on costs and time taken to complete the project for the property owners.

SOLUTIONS

SES inspected on-site works at each stage of the project. Large tree stumps below the ground couldn’t be seen until revealed by excavation for the commencement of works. The tree stumps impacted on the intended footing design, so SES designed some concrete beams into the new retaining wall footing which would accommodate the tree stumps but still maintain the integrity of the new wall. An existing footing, only discovered once the original wall was removed, was incorporated into the new design by SES, saving time and costs on the project for the property owners.

Prior to the contractor pouring concrete for footings, SES ensured that steel reinforcement installed by the contractor would meet or exceed the design requirements in terms of materials, size, length, embedment, and spacing, for the full length of the footings. Once approved by SES, the concrete was poured to the full extent of the area in a single occurrence. The ‘ag line’ drainage installed by the contractor was noted by SES to the owners as needing the plumber to obtain relevant certificates if connecting to the Council surface drain.

On inspection of the masonry blockwork prior to core-filling, SES observed that the masonry ties used by the contractor at the location of expansion joints, to every course of blockwork, were smaller than the design specification but installed at a greater frequency than originally specified. SES considered this variation by the contractor and confirmed that the intent of the design specification was still being met. Expansion joints were inspected and approved for filling with a flexible sealant. Upon successful completion of the structural works, the owners of the property elected to complete the aesthetic detailing independently.

RESULTS

With the new retaining wall completed, people walking along the Council footpath next to the property can feel safe once again. Matching with the surrounding walls, the new retaining wall has also improved the property aesthetic and ‘street appeal’, which in turn helps to protect the investment of property owners.

• Collapses
• Compliance Issues
• Mortar Defects
• Structural & Aesthetic Issues