Re-levelling a 20,000m² Warehouse

A detailed level survey of the building revealed variations of up to 120 millimetres within the floor slabs and the steel superstructure compared to the original “as built” documented site levels. The building’s construction consists of a 180 millimetre thick fibre reinforced concrete slab on ground, a steel portal frame with perimeter precast concrete dado panels supported by independent internal and perimeter pad footings, sheet metal cladding, and a lightweight roof.

A review of the pre-construction geotechnical investigations revealed that the building platform included imported fill material up to 8 metres in depth. Historical records indicated that the site had been subject to a flooding event soon after construction, resulting in loss of fines within the foundation soils during the drawdown of the subsiding floodwaters.

This subsidence mechanism led to the formation of voids beneath the floor slab, loss of contact and support, differential settlement and dishing. The subsidence also resulted in differential settlement of the pad footings and superstructure, stressing the building’s structural elements.

The Client engaged Mainmark to develop a suitable solution to restore the superstructure and floor slabs to their original design tolerances and make them fit for purpose.

Once the final detailed design, including the target levels and tolerances, was agreed upon, Mainmark commenced the level correction works.

The priority was to restore the pad footings and the building’s superstructure to the designated target levels. This was done following a pre-agreed sequence that covered the entire building footprint. To prepare for the level correction, each pad footing was drilled, and injection tubes were installed to depths of up to 2.5 metres below the finished floor slab. These tubes enabled the application of Teretek resin, which gradually lifted the structure. The level correction itself was carried out through a series of controlled injection ‘sweeps’ across large floor sections. This method allowed for a gentle, step-by-step raising of the superstructure, helping to avoid the creation of new stresses within the building. As part of this phase, the precast concrete dado panels were also injected and levelled to ensure their alignment with the corrected structure.

The slab level correction works began once the pad footings and superstructure were within the desired level tolerances across a given area.

Multiple Teretek® injection rigs and  numerous injection guns enabled large floor areas to be injected simultaneously to effectively ‘float’ the slab back to the target level and mitigate the potential for any new damage to the slabs.

Once the level correction of the floor slab was complete, a final injection phase known as ‘stitching’ was applied beneath the floor slab construction joints to ensure slab edges were supported.

This approach enabled the project to be completed on time and within a budget significantly less than the cost of the alternate traditional demolition and replacement method.

The Teretek® solution successfully level-corrected the significant differential settlement to the slabs and footings, ensuring that the facility is within level tolerances for the safe use of forklifts, high-level racking, and warehouse operations.

By collaborating closely with the Client and their subcontractors, Mainmark successfully met the Client’s critical timeline while prioritising safety, efficiency, and quality.