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Project Profile Z18 W009

Mainmark raises and re-levels home in Upper Hutt

Sub-industry
Office Building
Problems
Earthquake induced differential settlement
Location
Christchurch, NZ
Year
2014
Solutions
Ground Improvement
Technology
JOG Computer-Controlled Grouting

Teretek raises and re-levels home in Upper Hutt

Summary

When the glass sliding door of a family home in Upper Hutt, New Zealand, became misaligned, the homeowner suspected it was due to ground subsidence as the family home was built on a steep slope. A subsequent ground engineering report pointed to poor localised soil bearing capacity which was most likely caused by an ancient waterway.

Soil instability had resulted in voids forming under the home’s foundation slab which had caused the slab floor to crack and the sliding door to become misaligned. The concrete slab had dropped by approximately 54mm at one point.

The affected area spanned 20m2 and following a site inspection, several areas under the slab were determined to be hollow. Visual examinations also revealed some voids under the slab were 100mm thick and had nominal reinforcing.

Mainmark used its proprietary Teretek® engineered resin injection solution to fill the voids and lift the slab back to level in a uniform and controlled manner. The deep injection method also improved the bearing capacity of the ground 500mm to 1000mm below the injection level. This additional ground strengthening procedure has minimised the chances of further subsidence affecting the home.

The project was successfully completed in a single day.

Objectives

To minimise costs and the risk of damage to the home, it was important that the project be carried out without any excavation.

The requirement was to fill the voids under the slab, then re-support and raise the foundation by 54mm to bring the floors back to level, which would realign the sliding door and close up the cracks in the slab. Mainmark planned to achieve this by injecting Teretek® resin directly beneath the sunken foundations, then slowly lift the slab, monitoring it constantly using laser levels to ensure it retained its integrity.

Solution

Mainmark’s proprietary engineered resin injection solution, Teretek®, was used to fill the voids, stabilise the foundation soil, raise and re-level the slab, and remediate cracked sections of the home.

Teretek® was specified because it could improve the foundation ground while raising and re-levelling the slab in a single application without any need for excavation. This solution was a far more cost- effective alternative to traditional underpinning processes, which can be expensive and disruptive. The Teretek® resin is injected into the ground, via very small injection tubes, at specified points. When the expanding polyurethane enters the ground, the components mix together and expand, filling the voids, strengthening the ground, and re-levelling the slab.

Mainmark completed this project quickly, and the homeowner was able to avoid the time and cost involved in excavating and pouring new concrete. This fast completion time also minimised disruption to the homeowner while delivering peace of mind that the home was on more stable ground.

According to the homeowner: “the Mainmark team did a great job and I’m very happy with the outcome. The team were on time, worked solidly and were clean and tidy. They were professional, knowledgeable and kept me informed of what was happening throughout the project.”

Resources

Download a pdf version of this project here

Teretek raises and re-levels home in Upper Hutt
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