Work is underway at Bowline Wickham, a luxury residential development being constructed by Eastern Pacific alongside the Newcastle Interchange, a major transport hub serving the city, in NSW. Due for completion in 2024, the 16-storey development will feature commercial and residential lots.
In early 2022 Coates was engaged by civil works and retention specialist Keller to provide an internally braced retention solution for Bowline’s 3-level basement structure.
The shoring solution for this large basement excavation was determined by the site’s size, location and ground conditions.
Bowline is situated close to the Hunter River, resulting in poor soil stability and a naturally high water table. Excavating the southern half of the basement to a depth of 10m in these conditions - an area of approximately 42 x 25m - created high loads for the internal bracing and additional water management challenges for Keller.
“We needed a high-capacity lateral support system, and as Coates’ proprietary system is one of the largest capacity solutions available on the market, they were a good fit for delivering this solution,” says Eric Lin, Design Engineer for Keller.
Ground anchoring under neighbouring properties was Keller’s preferred option, to provide clear spacing within the basement with minimal obstruction to work around. However, this was not possible on the southern boundary due to the adjacent rail asset. “To safely excavate close to the rail corridor and interchange, Keller needed a solution that could utilise both ground anchors and internal bracing,” explains Coates Temporary Works Design Engineer, Jorge Valencia.
Design criteria issued by Transport for NSW required the basement retention system to achieve deflection of 20mm or less throughout installation, excavation and construction. “This required high-capacity support and the ability to apply pre-load,” says Jorge. “Keller also needed to be alerted quickly if the deflection deviated outside of this range.”
Accommodating a 1.1m step in the capping beam level from one side of the excavation to the other was another significant design challenge for the project team.
A telemetry-enabled system allowed Keller to monitor displacement at all times
Keller designed an anchored retention system for the northern half of the excavation and collaborated with Coates to design a 2-level wirelessly monitored internal bracing system for the southern half. The design incorporated a range of bespoke technologies and innovations:
- The top level feature 7 x MP150 and MP250 standard and Super Tube hydraulic struts connected to the capping beam. Coates designed and fabricated custom end bearing plates to connect three of these struts to the capping beam in the southwest corner to achieve the necessary angle and rotation to accommodate the 1.1m capping beam step.
- On the lower-level, Coates’ proprietary HW500 waler was fitted to the retaining wall, supported by a further 7 struts. This heavy-duty modular waler system was developed by Coates in response to growing customer demand for high-capacity structural support and used here for the first time.
- Coates’ new MP375 hydraulic ram was also used on four lower-level struts. With a considerably thicker wall than the MP250 ram, the MP375 is the highest capacity double-acting hydraulic ram available in Australia.
- The 914 tube is another solution custom developed by Coates for this excavation. With an outer diameter of 914mm, these tubes were applied to three lower level struts, allowing greater loads to be supported between the MP250 strut sections and the Super Tubes. This proved particularly useful for longer struts, where space for the Super Tubes is limited.
The MP375 strut connected to the HW500 waler system
Working with Coates Engineering Solutions was a positive experience for Keller. “Coates were professional, proactive and able to respond quickly to questions and provide the support that we needed,” says Eric.
The use of telemetry sensors allowed Keller to accurately measure the displacement and rotation between the two ends of the props. “In conjunction with other instruments and survey monitoring, Coates’ solution provided a good indication of where the movement was in the wall and created a much clearer picture of how the whole system was performing,” says Eric.
Using Coates’ hydraulic struts instead of prefabricated steel struts improved the performance of Keller’s basement retention system. “You can normally fabricate sections to the right size with made-to-order steel propping systems. The downside is that you can’t pre-load these sections,” says Eric. “But with Coates’ hydraulic shoring system, pressure can be pre-loaded during installation to support the wall and minimise deflection.”
The modular design also saved Keller time during transportation and installation. “Compared to the anchoring that we installed at the northern end of the site, installing Coates hydraulic shoring solution seemed quite quick and straightforward,” says Eric. “Despite the need to brace from within the excavation, it was also reasonably easy to work around.”
Connect with Coates’ Engineering Solutions team to find out how Coates can improve the cost efficiency, reliability and safety of your next excavation.
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