Basement Shoring

The project

Tenor by Sanchi is a multi-residential project currently under construction at Teneriffe, near the Brisbane CBD. From its riverside location the completed eight storey, three basement level development will offer 46 one, two, three and four bedroom apartments.

The problem

The design team faced two major challenges in delivering temporary works for the capping beam level and 2nd basement (2B) level at Tenor. These challenges included the need to avoid obstruction by designing the struts to avoid the lift core and future tower crane location; and managing the horizontal and vertical stepping. Other design factors that contributed to the complexity of this project included:

A large basement footprint, which created a 20m span for cross lot struts. Variance in reduced levels (RL), which required high-capacity shear connection details on the waler system. The need for custom-designed shear plates and stops to combat shear force loads on the corner struts. Limited site access also inhibited the large craneage used to move the struts and waler beams into place. Combatting these issues required a high degree of precision and customisation throughout the design and installation phase.

The solution

In June 2019 GCB Constructions engaged Coates Hire’s engineering team to provide design services and specialist temporary works equipment to enable the early stages of construction at Tenor. This project team has since completed the design and successful installation of a robust – yet relatively unobtrusive – hydraulic shoring and bracing solution for Tenor’s three-level basement structure.

This highly customised design included approximately 100 linear metres of waler beams and 20 hydraulic struts, comprising:

6 MP250 Heavy Duty Hydraulic Struts

13 MP150 Heavy Duty Hydraulic Struts

1 MP50 Medium Duty Hydraulic Strut

1 System 100 prop

1 System 60 prop

Super-sizing support for better access

Ensuring unobstructed access to the basement during excavation and construction was a priority at Tenor, explains Stephen Reghenzani, Coates Hire Temporary Works Engineer – Services.

“By using higher capacity MP250 struts we were able to reduce the amount of cross lot struts in the design, which opened up the basement area,” says Stephen. “Three of the MP250 struts were used to secure the basement while the remaining MP250s supported the large loads on the corner struts.”

“Given the quantity of cross lot struts required on the 2nd basement level, this design layout was particularly important to allow for efficient excavation,” Stephen continues. “Designing the struts to avoid the lift core and future tower crane location also required our team to perform detailed design analysis to balance all of the various constraints.”

Highly customised design

Coates Hire’s proprietary MEGA Brace waler system was used on the lower basement level at Tenor, supported by gallows brackets – creating a waler system that required high capacity shear connection details. In addition to the shear plate design, Coates Hire designed and fabricated shear stops to ensure adequate load capacity for the waler and strut system, and utilised shear clamps to combat the shear force loads on the corner struts.

Another complex aspect of the design was the need for custom connections to accommodate the difference in RL that varied from 0.15 to 0.45m in height around the perimeter of the capping beam. In one particularly challenging corner of the basement a height change of 1.15m caused the struts to slope – a system 60 prop was used here to provide additional support.

Supporting project success

GCB Constructions Senior Project Manager, Kevin Alexander, believes Coates Hire has been instrumental to the success to-date of construction at Tenor.

“We presented Coates Hire with the challenge of delivering a basement retention bracing solution for Tenor. The time frame was short, the design could not impede construction, and we required it to minimise obstructions,” explains Kevin.

“Coates Hire delivered on this goal, and provided a high degree of service, customisation and coordination” Kevin continues. “They showed initiative to maintain our works programme in both design and installation phases. Working with Coates Hire meant that the job was done safely and to schedule.”

Other notable project achievements include:

Providing a solution that allowed the client to meet their time and cost objective for bracing the basement excavation. Helping to eliminate the need for a welded bracing solution and extensive hot works. (Hot works would have required considerable crane time on an inner city site with limited access.) Formulating an efficient and cost effective hydraulic shoring solution to reduce the bracing schedule by 50%* and reduce the basement shoring significantly. Achieving flexibility for the client with a shoring solution that could be quickly mobilised and applied in multiple stages. Coates Hire’s contribution also allowed for a streamlined installation and de-installation process that could occur without impacting the major subcontractors and main contractors.

Temporary works commenced in December 2019, with de-installation of basement level 2 in April 2020 and basement level 1 in May 2020.