Teretek® | Severe cracking and lateral twisting
Multi-level 1940s apartment building | NSW, Australia | 2020
The owner of a multi-level block of units located in NSW contacted Mainmark after detecting large cracks in the building’s internal and external walls. The cracks were visible in most walls and the floors were becoming noticeably uneven. The situation had deteriorated over several months with significant cracking and unlevel floors indicating major structural issues due to severe differential settlement.
The heritage-listed brick apartment block was constructed in the late 1940s. The property’s construction included concrete strip footings, double brick walls, timber floors and a tiled roof. The building’s strip footing foundations were situated on silty clay soil which had become affected by water ingress from an old, abandoned stormwater pipe. The soft soil conditions had caused the building’s upper level to twist laterally, resulting in extensive cracking throughout the building. Structural damage to the footings, stairways and walls was also a serious safety and liveability concern to the occupants.
For example, one of the upper-level units had large cracks in the foyer, main bedroom and living room, with engineers detecting approximately 90mm of lateral movement in the plane of the walls. The outdoor stair bridges and supports had disconnected from the main structure, making access to the unit unsafe. The exterior brick façade also had enormous cracks running down the full height of the building, giving the impression that the building had split in two.
The internal floor joists had been built into the walls using an old ‘socketing’ technique, an indication of construction techniques used at the time the complex was built. Therefore, as the building shifted the floorboards and joists were being extracted from their supports.
A structural investigation confirmed the floor levels at both the front and back of the building had dropped by up to 34mm and large separation cracks averaging 50mm wide had formed. In addition, the external doors and side staircases appeared to be falling away from the building.
A significant degree of building lift was required to raise the structure back to within 5mm of its original level. As the building was on the NSW State Heritage Register for Residential Flat Buildings, Mainmark also needed to ensure that the building’s structural aesthetics were not significantly altered.
This incredibly complex project was completed in just three days using Mainmark’s Teretek® resin injection solution with the result exceeding the customer’s expectations.
The primary objective was to stabilise and re-support the building to prevent further sinking and reduce the tilt of the walls. This involved compacting and strengthening the weaker foundation soils to form a bearing pad which would enable the structure to be lifted off, returning it to within 5mm of its original level at both the front and back.
Mainmark recommended remediating the block of units using their proprietary Teretek, a two in one ground improvement and re-levelling solution. Teretek is an engineered polyurethane resin that expands when injected into the ground.
Before commencing the project, Mainmark worked with the client’s structural forensic and geotechnical engineers to clearly understand the site’s ground conditions. Test pits and Dynamic Cone Penetration (DCP) tests were undertaken to confirm the location and cause of the problem as well as verify the ground bearing capacity required to support the building.
While traditional concrete underpinning was considered, the process would have been too time consuming and costly; significant excavation would have been required, putting further strain on the severely cracked building. Teretek was identified as a more cost-effective and time-efficient solution that also provided greater flexibility, allowing engineers to carefully re-level the building in manageable increments which could be monitored and adjusted as needed, minimising the risk of further structural damage.
Teretek was injected into the soil beneath the building’s foundations in a process similar to keyhole surgery, with the solution strategically targeting the weakest points. This allowed Mainmark to achieve its objective of raising the building back to within 5mm of its original levels. The successful lifting and re-levelling process also enabled Mainmark to reduce the large cracks in the walls, with many cracks narrowing to within a few millimetres. Interior repairs were then undertaken to restore the building’s former heritage aesthetic which included structural stitching, rendering, and painting.
“I’ve completed a number of jobs with Mainmark and their operators make all the difference – getting the right people involved in a problem is key to preventing ongoing issues. Mainmark’s Teretek resin injection solution is a major game changer in the ground remediation industry. It’s affordable, safe, easy to deliver and you can easily make adjustments as you go to ensure accurate and guaranteed results are achieved, which is not always the case when using other remediation techniques.”
The project’s forensic engineer, Daniel Lee from Fairdinkum Technical Services, was impressed with Mainmark’s approach to the challenging project.