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Six Storey Apartment Building

Weak sub-soil under a heavyweight concrete 6-storey apartment block in Christchurch had settled after the 2010-2011 earthquakes causing the building to suffer differential settlement of up to 70mm. The situation was rectified using Jet Grouting to strengthen the sub-soil and JOG integrated computer grouting to raise the building back to its design levels.

six storey apartment

The Challenge

The challenge was twofold; first to improve the strength and stability of the sub-soil under the foundations to better protect the structure from future seismic activity and second to level and lift the 6 storey structure to its design levels.

What was done and achieved

Continuous robot surveying of multiple points around the structure was set up and the output linked to the computers controlling the pumps and valve monitors.

22 Jetcrete columns were installed under the critical load points of the building to support and transfer loads down to the gravels. These columns are sometimes called “soilcrete” as they are a mix of cementitious grout and natural sub-soil formed by controlled injection of the grout into the ground and simultaneous removal of excess material.

With a stable foundation in place the JOG integrated computer grouting process was used to lift and level. 20 injection ports were installed through the concrete foundations, down to the top of the Jetcrete columns. Controlled high mobility grout was then pumped through the ports to top of the jetcrete columns. The computers using the data from the robot survey equipment individually controlled the rate of grout injection to each port. This grout injection process lifted the building to the required levels.

It took 10 working days to set up, install the 22 columns and then remove the Jetcrete equipment. A further 10 working days were required to install the JOG computer-controlled levelling equipment, level the building back to the agreed lift requirement and then remove the equipment.

The building was brought back to level precisely as required and the sub-soil greatly strengthened to better protect the structure from future seismic activity.

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