The former Hanson Concrete Batching Plant at Blackwattle Bay was constructed in the early 1970’s and served as a key Sydney cement batch plant for nearly 50 years. Liberty Industrial was engaged by Hanson Concrete to remove the harbourside Batching Plant to make way for the harbourside Sydney Fish Market redevelopment.
This involved the demolition of all above ground structures including the demolition of the large reinforced concrete aggregate storage bins situated on the site boundary alongside a busy public road and a concrete batch plant situated on the wharf as well as the removal of the interconnecting conveyor systems and administration buildings.
As much of the infrastructure to be demolished was situated on the wharf structure, a structural assessment of the wharf was undertaken as well as a thorough geotechnical assessment of the surrounding areas of the site in order to segment the site into various zones with machine weight and impact load limits for each.
Liberty Industrials 66t Kocurek modified Volvo EC480 Excavator fitted with three stage high reach boom configured for 24m of reach, equipped with a 3.5t hydraulic shear was used to demolish the majority of the Batch Plant structure in a sequenced top down manner. With the structure located entirely on the wharf, the machine’s movements were limited to a specific footprint as guided by the structural engineering assessment.
The Batch Plant structure consisted of four cylindrical steel silos each with an internal dividing wall, and an overhead bin consisting of 12 internal dividing walls. Due to the limited movements and strict weight and impact load limits on the wharf, the tanks had to be demolished in square metre sections to allow immediate loading out from site.
The main conveyor that fed the aggregate storage bins was removed by a large mobile crane as it was suspended partially over a live substation and located on the site boundary. Extensive planning was required to enable a 350t crane within the restricted space, with the manoeuvrability being limited by the seawall at the adjoining wharf and a 1.8m wide stormwater culvert running through the site. Once set up the 350t crane had to navigate an overhead electrical line located within its slew radius. The largest lift was a section of conveyor with a 36m span weighing 23.5t.
The feed conveyor to the batch plant had to be demolished by controlled induced collapse as it was 2m from and parallel to the wharf edge. This wharf slab area did not permit the use of the high reach excavator. The induced collapse method was designed to focus the initial impact load of the conveyor down through the plinth and piles which supported it, by hinging it at its lower support point which eliminated the possibility of unnecessary overload on the wharf section below it. Precautionary load spreader grids were placed underneath the conveyor which would spread the load to additional local piles. A 25t excavator was used to induce the collapse, once the conveyor was on the ground, it was used with a 2.5t hydraulic shear to downsize and remove the conveyor.
Liberty Industrial’s 200t custom built Kocurek modified Hitachi Ex1200 High Reach Demolition Excavator fitted with concrete cracking attachment’s was deployed to carry out the demolition of the iconic 32m high, 4800m3 capacity reinforced concrete aggregate storage bin structure situated on the site’s perimeter.
This excavator was fitted with a range of attachments including a 6t Concrete Cracker, a 4t Concrete Cracker and a 3t Concrete Pulveriser.
The structure consisted of six square concrete bins with a steel roof housing the conveyor headgear and distribution components. The bins were supported by 24 columns, had concrete structure to a height of 24m with 600mm thick heavily reinforced walls. Concrete cores confirmed a concrete strength of 70Mpa. The steel structure that housed the head frames and roof peaked at a height of 32m and consisted of a steel frame covered by corrugated iron sheeting.
The cones at the base of the bins were demolished first, this allowed the steel roof to be demolished by cut & drop methods, starting with the internal components followed by the top of the roof and lastly the sides.
The northern face of the structure was directly in line with the sea wall and suspend wharf area and the southern face of the structure was the site boundary. Directly adjacent to the site boundary was a bicycle and pedestrian footpath, an overhead electrical service at a distance of 2.5m from the structure, and a high volume 4 lane public road that had to remain in service and uninterrupted at all times.
Prior to demolition works on the storage bins starting a B-Class Hoarding (10kpa rated) was erected along the footpath with a heavy demolition Scaffolding reaching to full height to prevent debris from falling into the public domain. To enable safe demolition of the eastern and western walls up to the scaffold elevation a 6m wide by 24m high demolition screen suspended from a mobile crane utilising conveyor belt was designed and constructed. This was the first time a demolition screen of this type has ever been used in Australia.
Structural and geotechnical assessments confirmed that the machine had to be assembled and work from the west side of the aggregate bins only, an 800m² area of which it could only occupy 400m² as it needed to stay a minimum of 6m away from the sea wall. Due to the uncontrolled fill discovered, survey points were established to monitor any movement in the ground slab whilst the machine was working.
The demolition of the aggregate storage bins was a sequenced top down method, starting from the North Western corner of the structure, working along the northern elevation to the eastern face, and steadily working in towards the southern elevation.
The southern wall posed the highest risk and most challenging activity of this project as it formed the site boundary and with no closure to the pedestrian road was permitted, public safety was our biggest concern.
For this task a 3t single ram hydraulic pulveriser was fitted to the 200t High Reach which pulverised the material on the internal side of the structure ensuring majority of the concrete rubble fell inside the bins and not onto the scaffolding.
The scaffolding decks were lined with structural ply wood and carpet on the two levels closest to the top, which prevented material from falling through the scaffold or between the scaffold and the bin. All residual rubble on the scaffold was cleared by hand with the two levels of boards and protection measures rotated down the scaffolding as demolition progressed ensuring two levels of protection were maintained throughout.
Throughout the project constant environmental monitoring was required to ensure noise, dust, vibration and water discharge were maintained within strict limits. All stormwater and demolition water run-off from the site was diverted, captured and treated to ensure no uncontrolled discharge into the pristine Sydney Harbour.
The project was shortlisted as a finalist for the 2020 World Demolition Awards in the ‘Contract of the Year Under US$1 Million’ award category.