Polyurethane (PU) resin has been used as an innovative and effective method for re-levelling structures including residential homes for more than 40 years. The idea of using PU resin for ground strengthening was originally introduced by a Scandinavian company to help address ground movement and subsidence that can occur each year due to Europe’s extreme weather cycle, which freezes then thaws the ground.
The science behind polyurethane (PU) resin as a ground engineering solution is a homogenous mixture in two parts. When the homogenous resin is injected into the soil, it instantly reacts, forming a rapidly expanding foam that seeps into any ground voids and fissures, filing gaps and creating a bonding effect with the soil particles. The pressure from the expansion of the resin compacts the surrounding soil to significantly strengthen the ground, increasing the bearing resistance of the soil without increasing the weight or overburdening the soil. When the solution is injected beneath a structure, the expansion pressure lifts the structure, remediating differential settlement without the need to excavate.
Mainmark’s founder, Philip Mack, introduced polyurethane resin as a ground strengthening solution to Australia after researching ground engineering innovations following the 1989 Newcastle earthquakes. After remediating a number of earthquake affected buildings, Philip saw an opportunity to use the solution to re-level sunken slabs. He subsequently travelled to Scandinavia to investigate bringing this technology to Australia.
However at the time, there was skepticism about the effective use of resin as a ground strengthening solution due to the lack of scientific evidence. The idea that there was a quick, cost effective and non-invasive way to lift a building’s foundations without the need for expensive concrete underpinning was hard for the industry to conceptualise, and there were no design tools to assist engineers.
It wasn’t until Professor Olivier Buzzi, chief investigator with the ARC Centre of excellence for Geotechnical Science Engineering and lecturer at the University of Newcastle undertook an investigation in 2007, exploring the structure and properties of expanding PU in the context of foundation remedial works, that Australian engineers started to take notice.
Professor Buzzi wrote a research paper which was co-authored by Mark Yasumasa Sasaki, a Mainmark long-term employee, titled Structure and properties of expanding polyurethane foam in the context of foundation remediation in expansive soil, which concluded that the injection of expansive polyurethane resin was an effective method for remediating differential settlement. The University of Newcastle funded research also concluded that polyurethane expanding resins were suitable to use underneath building foundations and that the expanding resin didn’t impede the reactivity of clay soils. Professor Buzzi’s research was a breakthrough in gaining wider acceptance of polyurethane resin as a ground strengthening solution within the wider engineering community. Until this point, the only scientific research available was based on European soils that didn’t consider Australian soil types; specifically reactive clay.
Yet while this research was a major milestone, Mainmark has continued to push the boundaries by independently supporting further research. The company had a theory about a new technique using polyurethane resin to remediate seismic liquefaction. Following the 2010 and 2011 earthquakes in the Canterbury region of New Zealand, more than 15,000 homes were demolished due to the effects of liquefaction. This initiated a series of resin injection trials in a designated zone severely affected by liquefaction known as the Christchurch Red Zone.
Mainmark’s liquefaction mitigation trials using resin injection were first initiated in 2013 in partnership with the New Zealand Earthquake Commission (EQC) using a small sample of Mainmark’s engineered resins. The sample was tested in a number of different ways, including earthquake simulations with full strength shake and explosives. However while the outcome was positive, the sample was relatively small and more robust data was required.
In 2016, a second round of Red Zone trials commenced in partnership with the Ministry of Business, Employment, and Innovation (MBIE) and the EQC. This time the research was conducted under the supervision of a team of engineers and independent international peer reviewers using pre and post ground investigations, geophysical testing including CPT, cross-hole shear-wave velocity testing and seismic dilatometer testing (DMT). The tests were carried out approximately two metres below the ground improvement zone and post testing the test area was hydra-excavated to observe the resin structure in the ground. The trial injection panels were then analysed to determine the outcome of the resin structure. The outcome was overwhelmingly positive, with vastly improved ground density and stiffness, significantly reduced surface damage and an improvement in the static bearing capacity.
These encouraging outcomes, and the results from numerous subsequent projects such as the Seaview Wastewater Treatment Plant liquefaction mitigation project using Mainmark’s proprietary Terefirm™ Resin Injection, continue to drive Mainmark toward further innovation. The Seaview project in Wellington, New Zealand, was the first of its kind whereby the client has proactively prepared the ground beneath critical infrastructure to prevent failure or downtime during a seismic event.
Mainmark has since taken its research trials even further, conducting a series of blast testing of the Red Zone Trial site with the US Department of Science in an effort to further understand how the resin material behaves in soils under extreme earthquake simulations. The results are expected to be released later this year.
By James O’Grady
James O’Grady is a Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years’ experience in structural engineering, construction materials and ground treatment.