Complex basement shoring solution for high-rise

The project

Adore is a mixed-use high-rise currently under construction in Southport on Queensland’s Gold Coast. The 14-storey development combines 74 residential apartments with ground floor retail and a two level underground car park.

The challenge

Limited site access and excessive stepping in the basement design were two of the main challenges the project team faced in delivering temporary works to support construction at Adore.

Although stepping is reasonably common, the quantity of the horizontal and vertical steps that were required to achieve the basement design at Adore created complexities for the ground engineer:

• In four different areas of the basement, the capping beam was stepping in plan.
• The capping beam also had five different reduced levels (RL), which meant the design was stepping vertically at five different locations.
  
  

Site restrictions presented another considerable challenge for the client, with site access limited to just one street – despite Adore’s corner location.

The solution

In September 2019 Coates Hire was appointed to deliver the temporary hydraulic shoring and bracing of the capping beam level of the basement structure at Adore. Having worked closely with our client (PCA Ground Engineering) and developer (Draycon Building) during the final design phase, Coates Hire was more than ready to step up and provide support.

Better access

To improve access for basement construction Coates Hire’s design focused on minimising the use of cross lot struts – replacing them with a higher capacity MP250 hydraulic strut spanning 21.5m and weighing approximately 8.5 tonne. Smaller MP 150 struts were used to provide additional support in the corners and a MP 50 strut was designed and used for the smallest internal span.

“This highly efficient and cost effective hydraulic shoring solution eliminated the need for a welded bracing solution and significantly reduced the requirement for basement shoring – improving the installation schedule by 50%,” explains Stephen Reghenzani, Coates Hire Temporary Works Engineer – Services.

In supporting excavation, the installation of struts had to be completed in three stages to accommodate limited access and a tight excavation schedule. Crane radius restrictions further exacerbated these challenging site conditions. To work around these issues and move the struts into place PCA devised a clever combination of lifting solutions – ranging from a 30 tonne excavator to a mobile crane and tower crane.

PCA Ground Engineering sees great value in the solution that Coates Hire designed. “The use of an internal bracing system was critical to the construction methodology at Adore, as Draycon was unable to use typical tie-back anchors.” explains Ash Moghaddas, Business Development Manager for PCA Ground Engineering. ”This solution also provided the additional space and better access that we needed for construction at Adore.”

Design efficiency

To achieve a practical solution for shoring the two-level basement at Adore, Coates Hire consulted with the client and developer during design to modify the layout of the basement stepping. To accommodate a change in height of 650mm from varying design RLs bespoke vertical end bearing plates were designed and fabricated.

“The overall design and installation of our solutions created considerable efficiencies and flexibility for the client,” says Stephen. “We designed a shoring system that could be mobilised quickly and installed in multiple stages, and an efficient solution to accommodate the stepping,” he says. “Our designs allowed for a fast and highly streamlined installation and de installation process that prevented unnecessary interruptions to the major contractors and subcontractors.”

According to PCA Ground Engineering Coates Hire’s collaborative approach and direct contact with Draycon helped to fast-track the temporary works design process. “By cutting out middle man we knew that technical information could be accurately passed on, and that no detail would be missed,” says Ash. “The open and flexible communication our project team was able to achieve at Adore further enhanced the working relationship and mutual trust that Coates Hire and PCA share.”

Reflecting on Coates Hire’s selection, Stephen believes that this strong and growing relationship gave PCA Ground Engineering the confidence to work with Coates Hire. “Our critical thinking during design and problem solving approach during installation also helped to secure our involvement, and allowed Coates Hire to play an important part in the success of this project,” Stephen concludes.

Temporary works installation commenced in October 2019 and was completed in February 2020. Construction is scheduled for completion in 2021.