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Warehouse earthquake damage remediated 

05 September 2019

Mainmark has revealed how it helped to re-level the floors of two warehouses in Christchurch New Zealand that were damaged by earthquakes. 

A large retail warehouse building constructed of precast tilt panels supported by pad footings and beam construction had experienced differential settlement of up to 60mm along approximately 250 lineal metres of the perimeter foundations due to seismic events. 

Approximately 800 sq m of the internal floor slab-on-grade also required void filling and level correction. 

The first job was to correct the settlement along the 250m perimeter section and second was to fill all voids under the 800 sq m of floor and to re-level the area. It was essential to absolutely minimise interruptions to operations.

Using JOG computer-controlled grouting, a continuous circuit of 64 injectors were installed beneath the foundations of the building to facilitate a lift that was uniform, incremental and controlled. Continuity of foundation support was maintained throughout the correction.

JOG operations were carried out during daylight hours from outside the building to minimise any interruption to the tenants’ daily operations. 

Void Filling and Slab Lifting operations were completed at night outside of the tenant’s normal trading hours.

The perimeter was successfully corrected to target levels utilising the JOG method in 17 working days from initial mobilisation. 

Avoiding disruption to the retail operations, a further 12 working night shifts were required to void fill and adjust/correct internal floor levels.

Raised and re-levelled 

The ground floor slab of an occupied food distribution centre was re-levelled. The racking systems and machinery remained in place and operational and the client was caused minimal downtime. 

Several areas within this food industry distribution centre suffered subsidence during the Darfield Earthquakes that affected Christchurch, New Zealand. The loading dock, the cold storage area, the north wall and the dry store had subsided. Tilt panel wall settlement of 90mm was the major concern. The slab settlement correction required was relatively minor because the main floor slabs in the cold storage section were post-tensioned, although the tilt panel slab footings required re-levelling.

Mainmark deployed Deep-Injection and Slab-Lifting methods where proprietary, engineered structural resins were injected to correct the 1,200 sq m floor slab in the dry store, and the 600 sq m loading dock. Laser level measurements were taken to ensure that various locations on the site were treated to achieve the desired lift and return walls to plumb, in accordance with the engineer’s specifications. The teams worked in confined spaces in the cold storage area, in addition to working in open warehouse areas and locations with racking systems in place. 

All the warehouse areas and the cold storage area were re-levelled to within 10mm tolerances. This decision saved the client significant costs which would have been incurred, if he had decided to demolish and rebuild the facility.