Bespoke Teretek® Application Stabilises Heritage Church Foundations

When deep excavation works commenced as part of a major infrastructure project in Sydney, underground voids and subsidence were quickly identified at the site.

Immediate action was required to enable continuation of the project works, while protecting the foundations of a heritage church situated adjacent to the excavation site. Originally constructed in the 19th century, the church is a treasured local icon, and preserving the historically important building was a priority of the project.

Mainmark was contracted to stabilise the ground at the project site, including the church perimeter, to help prevent further subsidence and fill the voids that had formed, while protecting the structural integrity of the church.

After receiving Dynamic Cone Penetration (DCP) test results from geotechnical engineers, and conducting a thorough evaluation of the site, Mainmark identified Teretek® engineered resin as the ideal solution for stabilising the sandy soil ground composition at the site.

Due to the heritage status of the church, access to the historic building foundations was restricted to a 10m deep pit at the adjacent excavation site, which was surrounded by a 1m thick retaining wall.

A unique application method was formulated which involved injecting the resin solution horizontally behind the retaining wall surrounding the excavated pit, in order to reach the difficult-to-access foundation ground beneath the church.

Despite the complexity of the site and extensive wet weather conditions in the lead up to works, Mainmark was able to complete the project in just four days, two days earlier than originally planned.

Mainmark was required to improve the ground at the project site, compacting and densifying the sandy soil to stabilise the site for major excavation and construction works while helping to ensure the historic church was protected from further ground movement.

Due to the church’s heritage status, the solution needed to be delivered from a nearby excavated pit. It was important for the solution to be delivered with minimal impact to the major infrastructure project works underway at the site.

Before commencing this complex project, geotechnical engineers undertook a series of DCP tests to analyse the soil integrity, and confirm the required solution to improve and stabilise the ground beneath the church foundations.

Mainmark recommended their proprietary Teretek® engineered resin injection solution to stabilise the sandy soil at the site. Teretek® is a non-invasive and cost-effective method for ground improvement and filling voids. It is suitable for most soil types, and quick to apply.

While Teretek® is usually applied vertically into the ground along the perimeter of an affected structure, it wasn’t possible in this instance because of the restricted access to the foundations of the church due both to its heritage status not allowing access from within the church, and due to the proximity of the church on the edge of the deep pit excavation. Therefore, the only access point was via the 10m deep pit located beside the church, which was surrounded by a 1m thick retaining wall.

To overcome site access challenges, an elevated work platform was used within the pit to enable Mainmark technicians to apply the Teretek® via four horizontal injections behind the surrounding retaining wall. Each injection reached a depth of approx. 4m to strengthen the foundation ground directly beneath the church footings.

Once injected into the sandy soil, the engineered resin immediately expands into the voids, compacting the loose soil and adding volume. When applied, the Teretek® immediately increased the ground density and bearing capacity of the soil at the site, which was confirmed with additional DCP testing following application.

Despite wet weather causing extremely muddy conditions, and the horizontal application method which extended the time required to inject the solution, works were successfully completed within a shorter than anticipated timeframe of just 4 days. The Mainmark team worked seamlessly alongside the infrastructure project team, delivering the solution without impacting construction or delaying overall project timelines in any way.