Quarry tunnel a ‘golden opportunity’

Hornsby Quarry, located in New South Wales, operated as a hard rock quarry from the early 1900s. It was last operated by CSR, which mined it for road base and aggregates, but was acquired by the Hornsby Shire Council in May 2002 after the quarry became unviable due to the poor quality of excavated material and unsafe due to its decreasing stability as excavation deepened.

The council resolved to fill the quarry with virgin excavated natural material, and an opportunity to do so recently arose after the NSW Government approved the proposed NorthConnex Motorway ? twin 9km tunnels that would link the M1 and M2 motorways ? in March this year. 

According to the Hornsby Advocate, NSW Roads and Maritime Services contacted Hornsby Shire Council offering to use spoil from the project to fill Hornsby Quarry. However, Hornsby Mayor Steve Russell is opposed to the proposal because it would require ?a truck a minute for years? through Hornsby?s CBD to transport the excavated material.

Construction engineer and Hornsby local Chris Jones added that these frequent truck movements would only be moving enough spoil to partially fill the quarry. Jones noted that according to reports prepared for council, approximately four million cubic metres of spoil would be required to stabilise Hornsby Quarry, and that NorthConnex had only proposed to transport 40 per cent ? about one million cubic metres ? of its project?s spoil to Hornsby with the remaining 60 per cent to be delivered to western Sydney.

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Seeing an opportunity to provide a solution that would benefit their community, Jones and fellow Hornsby locals Ian and Nola Ezzy of Ezzy Architects formed the QFill joint venture and pitched a new proposal to the council: to build a 2km tunnel for the purpose of transporting the NorthConnex spoil underground to the quarry. 

Russell referred to the QFill proposal as a ?golden opportunity?. ?I like the QFill option if it’s economically feasible as it provides a solution to filling our quarry whereby the trucks can operate 24/7 without disrupting the businesses and residents of Hornsby,? he told Quarry. ?The alternative is a truck and trailer every minute and a half, five days a week for eight years, or an unsatisfactory remediation attempt that doesn’t allow the full potential of the site to be realised.?

Jones said that he had initially been considering a conveying system to move the spoil through the tunnel but that Russell had had a different plan in mind. ?I envisaged that it would be a small-bore tunnel just sufficient to carry material and service the conveyors but then the councillor [Russell] said it would be great if that tunnel was big enough so that it could become a permanent link between the Hornsby CBD and the freeway,? Jones explained.

As a result, QFill is now proposing a larger, two-way tunnel that will eventually be able to accommodate road traffic, thus negating the need for a conveying system. ?It?s cheaper just to leave the spoil on the truck and tip it straight into the quarry instead of handling it twice with a conveyor,? he said. 

Jones suggested that the council might also be supporting the proposal because it gave NorthConnex a good reason to move more spoil to the quarry, meaning the abandoned site could be rehabilitated in a shorter period of time. 

?[NorthConnex?s proposed one million cubic metres of project spoil] would only fill up 25 per cent of Hornsby Quarry,? he said. ?Securing the balance of three million cubic metres may take many years to secure from other projects.?

Jones explained that if NorthConnex were to transport all of its spoil to western Sydney, it would involve about 200 million tonne kilometres to transport, whereas it would only require 50 million tonne kilometres to transport the spoil to Hornsby Quarry, cutting haulage costs by about 75 per cent. 

?The proposal is a benefit to the community but whether it will be seen as a benefit or a cost to the NorthConnex builders is still unknown,? Jones said. 

Russell has been vocal with his own support of the proposal but stated that he was unable to say at this stage whether or not the wider Hornsby community agreed with him. ?The QFill proposal is one of many that have been put to the council. I think it would have community support if it provided new vehicular access to the M1 and the community gained a major new sports and parklands asset in the remediated quarry site at no cost or little cost to council,? he stated. 

A NSW Roads and Maritime Services spokesperson said that a decision had not yet been made on the destination for the NorthConnex spoil but that a resolution would be reached soon. 

Construction of the NorthConnex Motorway is scheduled for early 2015.