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New Zealand
Sub-industry
Residential Apartments
Problems
Earthquake induced differential settlement
Location
Christchurch, NZ
Year
2020
Solutions
Ground Improvement
Technology
JOG Computer-Controlled Grouting
JOG Computer-Controlled Grouting Re-levels Multi-Storey Apartment Building in Christchurch
Summary
West Fitzroy Apartments is a seven-storey building located in the heart of Christchurch New Zealand, consisting of 70 privately owned serviced apartments.
The complex, which was constructed from heavy pre-cast concrete panels, had suffered from differential settlement of approximately 135mm following the 2010 and 2011 earthquakes and subsequent aftershocks.
Geotechnical investigations found the settlement had been caused by liquefaction induced ground deformation which had occurred in a relatively planar manner. The apartment owners and the body corporate sought a solution to return the building to pre-earthquake levels, however, any remediation work needed to be undertaken with extreme care to avoid causing additional stress on the building.
After considering several different re-levelling options, including traditional screw piles and jacking techniques, Mainmark’s JOG Computer-Controlled Grouting solution was selected due to its extremely precise application method and proven ability to re-level large, complex structures.
The multi-storey building also needed to be lifted without damaging an adjacent newly built Returned Services Association (RSA) property, as well as an adjacent carpark building.
The West Fitzroy project set a new benchmark for Mainmark as the tallest building successfully re-levelled using JOG Computer-Controlled Grouting. Mainmark was able to draw on its extensive international expertise to assist with the project by utilising team members from its operations in Japan, the UK, and Australia, despite the work coinciding with New Zealand’s COVID-19 shutdown.
Objectives
Mainmark was required to re-level the seven-storey building, targeting planar tolerances of less than 5mm, subject to the building’s ground conditions and structural tolerance during the lifting process. The re-levelling works also needed to be undertaken without disturbing the newly built building next door or the adjacent carpark building.
Mainmark’s re-levelling works had to be completed to a tight timeframe and before any structural strengthening and refurbishment works could commence.
Solution
Mainmark used their proprietary JOG Computer- Controlled Grouting to lift and re-level the seven- storey West Fitzroy apartment block. JOG is a unique, multi-point injection process for re-leveling large
and complex structures using an extremely precise, computer-controlled methodology.
Due to the scale of the project, Mainmark worked closely with the client’s project manager, engineers and building contractor to ensure the application process was undertaken in stages using a systematic and carefully managed approach that included client sign-off at the end of each stage.
Mainmark inserted a total of 65 JOG Computer- Controlled Grouting injection points across the entire internal floor slab and around the building’s perimeter targeting the foundation footings. The work was undertaken in 5 incremental stages to ensure the lifting induced flexural gradients across the slab were re- levelled in line with the structural specifications.
Traditional surveys and Trimble monitoring technology were used to capture real-time movement of the building, with new surveys completed before and after each stage of the injection works to verify and record the degree of re-levelling achieved at each point.
To ensure that the neighbouring buildings were protected, Mainmark created a retaining wall between the West Fitzroy Apartments and the RSA building by installing piles down to 2.5m deep along the site’s western boundary. A trench was then dug between the southern wall to break the friction in the ground between the two structures.
Suresh Nagaiya, the client’s project manager at DMP Ltd, who was contracted by the body corporate
to oversee the re-levelling work, was extremely impressed with how the work was carried out, commenting, “I found Mainmark to be technically competent and very professional in their approach. They delivered the financial and contractual outcomes we were looking for. Their team was very easy to work with and their commitment to client service is to be commended. We look forward to working with them again in the future.”
The body corporate was also impressed by Mainmark’s ability to complete the project during the COVID-19 shutdown period, which required the crew to quickly adapt to strict hygiene and social distancing protocols and staffing constraints due to travel restrictions. Despite the additional challenges, Mainmark was able to successfully complete the project on time and below budget.
The West Fitzroy Apartments is now re-levelled, strengthened to 90% of the new building standards and fully refurbished. This was all achieved within 12 months of residents moving out. The residents and tenants have moved back in with universal praise, thanks to the large part played by Mainmark.
Resources
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JOG Computer-Controlled Grouting Re-levels Multi-Storey Apartment Building in Christchurch
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