Restoring Support to a Pump Station Switch Room

The single-storey masonry switch room was situated on reclaimed estuarine land and founded on a concrete slab approximately 300 mm thick. Ongoing differential settlement had caused cracking in the internal and external masonry walls, particularly around door and window openings.

Geotechnical investigations identified highly variable and compressible ground beneath the structure. The subsurface profile included uncontrolled historical fill, poorly compacted cohesive material and a very loose saturated sand layer, with groundwater encountered approximately 2.5 m below ground level. These conditions provided inconsistent foundation support and were considered to be contributing to the movement affecting the slab and masonry.

Investigations included borehole drilling, dynamic cone penetrometer testing, installation of groundwater monitoring equipment and foundation pit inspections. The findings highlighted the need to improve the founding soils and re-establish support beneath the switch room.

The original construction program had not allowed for underpinning works. With a retrofit planned, the client needed an efficient repair method that could address both the underlying ground conditions and the resulting masonry damage while limiting additional delays.

The treatment approach drew on the available geotechnical investigations, service location information and levels recorded during the site inspection. Deep resin injection targeted the weak subsurface materials, with ground improvement undertaken between approximately 0.5 m and 3.5 m below ground level.

Mainmark injected approximately 700 kg of Teretek® expanding polyurethane resin to improve the supporting ground and re-establish support beneath the switch room floor. Controlled injection also re-levelled the perimeter footings, addressing the differential movement affecting the structure.

To repair the damaged masonry, helical ties were installed across affected cracks and the brickwork was repointed. The crack stitching connected the masonry across the damaged areas, helping redistribute loads and restore continuity within the walls.

Helical ties and repointing repaired the cracked masonry, restoring integrity to the damaged asset.

The combined works were completed over two days, enabling the planned switch room retrofit to proceed with minimal impact on the original construction program despite the unanticipated need for underpinning.

By combining treatment of the supporting ground with repairs to the superstructure, Mainmark addressed both the foundation support issues and the associated masonry damage within a short delivery period.

Mainmark provides ground engineering solutions for utilities, helping asset owners address settlement, restore foundation support and extend the service life of existing infrastructure. This project demonstrates how ground improvement and targeted repairs can work together to rehabilitate an asset while limiting disruption to planned works.