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Major works are underway to support construction of the new State Library Station. The new station at the northern end of Swanston Street will improve access to some of the Melbourne’s most popular destinations including the State Library of Victoria, RMIT, and the Queen Victoria Market, and cater for the area’s growing student population.

Pile top removal process during piling works.

Piling works at State Library Station

Facts at a glance

500 piles

About 500 piles will be installed across the five State Library Station sites

Piles will be bored to a depth of approximately 50m across the five sites

50m

What we are doingTo construct the new State Library Station, we will be undertaking excavation at five sites in the north of the CBD (Franklin Street East, Franklin Street West, A’Beckett Street, La Trobe Street, and Little La Trobe Street). Before excavation commences, over 500 piles will be installed across the sites to a maximum depth of approximately 50 metres. These new foundations will enable excavation and station construction works to be safely carried out underground.

We will excavate to a maximum depth of approximately 50 metres using ‘top down’ and ‘bottom up’ construction methods.

The ‘bottom up’ method involves excavating the box down to its maximum depth before starting the construction and fit out of the station. The ‘top down’ method involves construction of each level during excavation before fit out of the station starts.

Surfaces will then be reinstated above the station.

Cut-off level

1 2 3 4 5

Expanding agent

Flasks

Plastic sleeves

METRO TUNNEL PILING WORKS AT STATE LIBRARY STATION 32 METRO TUNNEL PILING WORKS AT STATE LIBRARY STATION

Stages of piling Start of the pile top removal process

As the piles are constructed, there will be some instances where the top of the pile may need to be removed. Where possible to avoid hammering, we use a more innovative method to cut the piles. The method involves the use of an expanding mortar to create pressure and generate a horizontal cut, so the top layer of concrete can be easily removed by a crane. This helps minimise the need to use jack hammers and excavators in the process, reducing noise, dust and vibration impacts on the surrounding community.

Following the removal of the top layer of concrete, a temporary concrete capping beam is cast on top of completed piles to prevent any displacement during subsequent excavation works.

The pile top removal process

1. Polyethylene sleeves are placed over the reinforcement cage down to the desired cut off level

2. An arrangement of purpose designed flasks are fixed to the reinforcement cage to the cut off level inside the concrete

3. The concrete is then poured into the hole

4. During concrete curing, excess water reacts with the flasks, creating expansive stress to crack the concrete

5. In this process, the pressure from the expanding agent forms a perfectly horizontal crack at cut-off level

6. The top layer of concrete can then be removed using a crane and the breaking back of the pile is complete.

SETTING UP THE RIG

Deliver the rig to site and move it into position

DRILLING

Drilling holes into the ground using a core barrel, and excavating material

STEEL REINFORCEMENT

Removing the material and inserting a prefabricated steel reinforcement cage into the hole

CONCRETE POURING WITH TREMIE PIPE

Pouring concrete into the hole to form the pile. Once the concrete sets, the pile is complete

CAPPING THE PILES

Once the piles are constructed, the top layer of concrete is removed and topped by a capping beam to prevent lateral displacement.

Artist impression of State Library Station entrance, opposite Melbourne Central

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It should be noted that this information is current at the time of printing, however due to unforeseen circumstances, changes may occur. Please visit metrotunnel.vic.gov.au for the latest updates.

Authorised and published by the Victorian Government, 1 Treasury Place, Melbourne.

Construction partner:

Design &Construction

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The use of heavy machinery such as piling rigs, cranes and excavators can generate medium to high levels of noise and some vibration at various stages of construction.

While every effort is made to minimise impacts from construction, a project of the size and scale of the Metro Tunnel can have an impact on the comfort of people living, working or studying near construction sites. We recognise there are some sensitive buildings and stakeholders located close to the State Library Station worksite.

Prior to works commencing, qualified consultants have and will continue to undertake extensive modelling of the predicted noise and vibration impacts.

This will allow us to determine appropriate mitigation strategies, and ongoing discussions with key stakeholders to allow us to identify any additional mitigation measures that may be required.

Mitigation measures may include (but are not limited to) offering periods of respite, selecting less noisy equipment, shielding noise sources, and installing acoustic timber hoarding around the site.

Noise and vibration monitoring will continue throughout the project to inform the construction process, validate the modelling, and demonstrate compliance with the Metro Tunnel Environmental Performance Requirements (EPRs).

Piling works are complete at the Franklin Street East and A’Beckett Street sites. Piling works will start at the Franklin Street West and La Trobe Street sites in late 2018. It is expected that piling will start at the Little La Trobe Street sites in mid-2019.

At the completion of piling, shaft excavation will commence across all sites and continue until the end of 2021.

State Library Station construction will take around five years.

The Metro Tunnel is on track to be completed by 2025.

How long will it take?Managing noise and vibration