Proprietary internal bracing solution keeps four-level basement construction on track

When steel supply and site issues ruled out anchored shoring, Coates stepped up to deliver a more efficient, flexible and cost effective hydraulic retention system

The project

A new three-storey, specialist medical centre is currently under construction on Panorama Parade in Blacktown, NSW, adjacent to Blacktown Hospital. Two residential dwellings were demolished to make way for the new facility, which will feature a radiology centre and a range of other specialist rooms. Once complete, a four-level basement will provide off street parking for up to 72 cars. 

Head contractor, Stevens Construction, enlisted Coates to provide a full hydraulic shoring solution to support the excavation and construction of the basement. 

The challenge

To allow for construction to begin, an area close to 1200m2 had to be excavated to depths ranging from 13m to 16m. Designing a solution to achieve this proved particularly challenging, because of the need to: 

• Excavate a large area

• Support high structural loads, while allowing sufficient space for excavation and construction

• Accommodate discrepancies between the shoring design and excavation site

• Work in very close proximity to a high-pressure gas main that supplies Blacktown Hospital and runs adjacent to the site on Panorama Parade.

According to John Russell, Project Manager for Stevens Construction, the original shoring tender specified structural steel. However, the cost and availability of steel later threatened to blow out the construction schedule and budget.

When anchor rights could not be obtained on the four neighbouring boundaries, the client turned to Coates for an alternative solution.

The solution

Coates worked closely with the client and structural engineer Birzulius to design a two-level hydraulic retention system to support all four sides and levels of the basement structure. 

Robust
Coates’ utilised its entire range of struts to deliver this solution. 

“We used 12 struts, starting from MP50s (50 tonne capacity) all the way up to the MP250s (250 tonne capacity) at capping beam level,” explains Shereen Amin, Coates Senior Engineer – Structures. “An additional 13 struts were used at the lower level, the largest being the MP250 Super Tubes.”

“These struts had to span significant distances. At capping beam level, they ranged from 5.5m to 29m in length; at the lower level, they spanned 5m to 28.5m,” Shereen continues. “As the site has an irregular shape, and the capping beam was at different levels on each side, Coates also fabricated custom end-bearing plates for most of the hydraulic struts at capping beam level, and special connections to transfer the loads to the shoring wall and maintain continuity of the waler beam.”

Flexible
After starting work on site, small discrepancies were found between the drawings and the excavation, however the flexibility of Coates’ proprietary solution could easily accommodate this discovery. 

“If adjustments are needed once excavation and prop installation has begun, our flexible hydraulic system allows these changes to be made,” says Shereen. “This reduces the cost and delay of making these changes, and brings value to Coates customers.” 

To ensure the safety and integrity of the shoring solution, Coates provided in-house design and installation certification, and used telemetry to remotely monitor the structural load and displacement. Vibration monitoring was also used by Stevens Construction throughout piling, excavation, and during the installation of ground floor propping to Panorama Parade, to safeguard against damage to the high-pressure gas main that sat just centimetres away.

The client was also able to successfully design and install a stretcher stair around the struts, providing safe access and egress to the excavation site. 

The impact

Basement construction is nearing completion on Panorama Parade, and plans for the removal of the temporary works are being finalised. Using a Coates hydraulic retention system successfully helped the client to keep construction on track, on budget, and without incident. 

Having reached this stage, and previously implemented a similar small-scale Coates solution, John understands the value this system offers. In the right conditions, he would take this approach again.

“On top of the delays that we would have experienced waiting for steel, there was just no buy-back value in a fabricated steel shoring approach for this project,” says John. “The original structural steel system required us to buy steel at as much as $3500 per tonne, but we would then have cut it up and sent it away at a fraction of that price. The beauty of the Coates solution is that it is available, customisable and it can be reused.”

Connect with Coates today for expert advice on your next temporary works or excavation project. Or learn more about Coates Engineering Solutions