Blasting at the cutting edge

The Western Highway ? Anthonys Cutting Realignment Project, west of Melbourne, involves the straightening and duplication of five kilometres of freeway from Harkness Road, Melton West to Bacchus Marsh Road, east of Bacchus Marsh. The highway forms part of the Route 8 between Melbourne and Adelaide and is a vital interstate freight route linking Melbourne, Ballarat and western Victoria.

The new freeway alignment is intended to avoid the steep hills and tight curves through Anthonys Cutting, near Melton West. The new road alignment will provide full freeway conditions with a dual carriageway and four new bridges along the main alignment. The largest structure crosses Djerriwarrh Creek and will be 165m long and 32m high. Once completed it will be the tallest precast match cast bridge in Australia. The works will also include an overpass to carry Bulmans Road, in Melton West, and two new Melbourne-bound access ramps at Hopetoun Park Road. Part of the new freeway is being constructed through an old quarry at Hopetoun Park. The quarry was once an operational silica sand production facility, but was closed when VicRoads purchased the land in 1996.

All the fill for the project is being excavated from the site itself. ?The project is a balanced cut to fill operation, so we are cutting into the hill and utilising that fill to build up the road in other areas,? declared Rod Jeffrey, Alliance general manager for the Anthonys Cutting Alliance, which comprises VicRoads, John Holland and AECOM and is responsible for the planning, design and management of the freeway construction. The Federal and Victorian Governments are jointly funding the $200 million project as part of the Nation Building Programme and the Victorian Transport Plan.

Major works commenced on the project in February 2010, with former Prime Minister Kevin Rudd and the Victorian Government Ports Minister Tim Pallas turning over the first sod. As of August 2010, one million cubic metres of material has been extracted and relocated of a total (estimated) 1.5 million cubic metres. The balanced cut to fill operation involves cuts up to 25 metres in depth and a drill and blasting operation was employed to break up the rock below the surface. It is estimated that the realignment will be finished by early 2012 and should improve safety and reduce travel times and transport costs for all vehicles large and small, with drivers able to travel this new section at 110 kilometres per hour.

Rod Jeffrey explained that the Alliance was established in August 2009. ?We?re an Alliance framework, rather than  a standard design and construct. VicRoads wanted a more collaborative framework, and one of the reasons for this was the risks and uncertainty associated with complex geology.

?There has been extensive geotechnical investigations completed in the area,? Rod explained. ?We have had a geotech team on-site testing and drilling since about September [2009] and their findings have helped to design the construction process. Based on those investigations, it was determined that a balanced cut and fill operation would be employed.?

Matthew Maltman, the construction manager for the project, explains how extensive geotechnical site investigation along the length of the alignment identified a layer of what he described as ?newer volcanic basalt? of varying strengths crossing the proposed alignment and in all excavation areas. The higher strength basalts were overlying the more weathered basalts and it was decided to quickly excavate through the harder basalt to reach the material below. It was the weathered basalt that was intended to be used as Type A aggregate to build up the road to the west and to construct embankments for the four structures along the new alignment.

In early trials, D10 and D11 dozers had limited success in ripping up the hard basalt. As Matthew explained, the dozers did not ?break up the material to a manageable size?. The ripped material was greater than one metre in most instances, when maximum particle sizes of 500mm were required for use of the rock in ?rock fills?. Consequently, Matthew said the decision was taken that blasting was ?the most efficient method of constructing that material in order to build a better project as soon as possible?.

The rock to date has been extracted in five ways:
1. Blasting. The basalt material below the surface needs to be blasted so that it can be broken into smaller pieces that can then be excavated.
2. Ripping. Using a large dozer, rock is ripped from the ground in larger pieces.
3. Excavation. After blasting, the shattered material is dug out from deep under the surface.
4. Crushing. The excavated rock is crushed so that it can be used as fill to build up the road.
5. Stripping. Softer materials such as the fill and gravel are dug up and then used throughout the project to build up the new road.

For the drill and blast process, John Holland commissioned Impact Drilling, a Melbourne-based quarry and surface mining drilling contractor whose expertise covers a wide range of blasting services from small to intermediate diameter blast holes or presplit blast holes for both large and small quarry enterprises. Impact Drilling also offers environmental monitoring for air blast and ground vibration and has supported environmental projects, including the rehabilitation of depleted quarry sites. Its clients have included major quarrying businesses such as Boral, Hanson and Holcim and a number of smaller quarrying operations in Victoria, southern New South Wales and South Australia. In addition to performing contract work for quarries, Impact Drilling has also worked on major infrastructure and freeway projects, including Stage 3 of the Craigieburn bypass and now the Western Highway – Anthonys Cutting Realignment Project.

Matthew explained that Impact Drilling was selected because it provided the most competitive of the tenders that John Holland received and had the necessary resources to commence works promptly and ramp up if needed. ?Impact Drilling was also able to provide the Alliance with a considerable amount of information that was able to assist with our assessment of the feasibility for blasting versus alternative methods,? he said.

Between March and April this year, Impact Drilling conducted 16 blasts at Anthonys Cutting. On the day, Quarry visited Anthonys Cutting, Rodney Krins, the general manager of Impact Drilling, was involved in the tenth blast on the site of the old silica quarry (this followed a successful ninth blast there a few days earlier), which would eventually make way for the off-ramps onto the freeway. He described blasting on this project as unique and more challenging compared to blasting in a quarry. In particular, he and his crew spent more time carefully designing each blast so that it would not impact on nearby residents and the environment.

?Quite a few of the shots have constraints because we are near particular structures, including residential housing estates, power lines and optic fibre cables for telecommunication. Based on those constraints and environmental limitations, Impact Drilling designs the shots to keep within certain parameters,? Rodney explained. ?There?s particular limits on the amount of vibration you?re allowed near houses, power lines and optic fibres. Depending on limitations, we will adjust standard blasting methdology such as reducing the amount of explosives we are putting into each hole. We may have to have a smaller diameter hole, closer patterns to still move the rock but not so violently. Again, most of it is dependent on buildings and utilities. Where we are firing today is probably one of the easiest areas. It?s over at the quarry face.?

He also had to take into account environmental considerations, not just stakeholder concerns. ?Another of the constraints was that we weren?t allowed to send rock rolling down the hill into the creek. We had to be very careful with our blast design and tie-up, to ensure it all stayed on top of the hill. As you can see, the area was kept clear of any loose or blasted material, leaving the creek in pristine condition. Our blast design team had created another great result for all parties concerned.?

For this blast, Impact Drilling used 10 tonnes of bulk explosives supplied by Orica Quarry Services, which is located at nearby Deer Park. In all, using a combination of Sandvik?s Pantera 1100 and Ranger drill rigs, Impact Drilling bored 308 holes of 89mm, with a stemming of three metres and drill metres of 2400m. The bulk in the shot was 17,600m3 ? resulting in overburden of 42,000 tonnes of rock (one cubic metre of rock would weigh around 2.6 tonnes).

All of these factors were integral to a successful, yet non-disruptive blast process, especially in what is predominantly agricultural ground.
?The blast operation was very well managed and had little to no impact on the neighbouring environment or residents,? explained Matthew Maltman. ?Impact Drilling was able to calculate the blasts correctly to minimise the impact and to use whatever techniques they needed to make sure each blast was controlled.?

Rodney Krins said that ?safety is paramount at Impact Drilling, not only the drilling and blasting, but everything?. Prior to blasting any particular area, a detailed analysis of the geological make-up was completed. A geological profile was mapped for the entire alignment based on a series of bores taken during the site investigations. The profile was mapped using the Vulcan Modelling software. During the analysis of the geological profile, the depth of each of the different materials including clay, hard basalt, weathered basalt and any underlying formations was measured.

From this analysis, the determination was made as to what depth the blast would be. In areas where hard basalt was present at the sub-grade level, a depth 500mm below sub-grade was adopted for drilling. Where hard basalt was overlying a more weathered or more densely fractured basalt, a depth of one to two metres below the base of the hard basalt was adopted to ensure good fracturing throughout the depth of the basalt being blasted. Another consideration was how to ensure good fracturing of the basalt at the top of the formation. As stemming was required in the top of the drill holes and was generally up to two metres in depth, an overlying layer of clay overburden with a depth of up to two metres was generally left in place to ensure the drill depth within the basalt itself was fully loaded with explosives.

The blast areas were always isolated from other project activities for safety reasons. This gave the drill rig operator the opportunity to operate clear of other heavy machinery and also minimised the number of activities that had to cease work during the blasts.

As of August 2010, one million cubic metres of material had been excavated from Anthonys Cutting. The project has made steady progress and celebrated its first completed section of works, with the Bulmans Road/High Street roundabout being opened to traffic. In July, urban design concepts were announced for the Bulmans Road and Hopetoun Park Road overpasses. These concepts represent ?gateways? between the urban and rural communities, highlighting the entries to Melton and Bacchus Marsh, and utilise colour schemes that reflect the existing rock formations.

The Bulmans Road overpass will feature 20m high weathered steel towers from the centre median. The patterned cladding design on the pylons will reference the surrounding environment and should be emphasised at night by lighting the pylons from within and below. Beams, crossheads and containment rails will be painted charcoal to contrast the off-white precast crash barrier and the weathered steel pylon cladding. Piling at Bulmans Road overpass was due to commence at the end of July 2010.

The Hopetoun Park Road overpass will feature weathered steel hexagonal patterns on both the bridge and on the cut rock face. These elements will be arranged in a snake-like fashion so that they start at each approach side and meander on and under the bridge to dissolve on the opposite rock face. They will be pinned off the cuttings and selected clusters will be lit to give them a different reading at night. The overpass will be a single span bridge. The crash rail with oval shaped section will be painted bright orange and will connect both sides of the rock face, emphasising the horizontal nature of the span over the vertical cut of the roads. In line with the other bridges, the beam, midrail and vertical rail supports will be painted charcoal to contrast the crash barrier. In order to allow for the pavement of the overpass and the construction of the bridge, a diversion road was to be implemented in the months after June 2010.

Earthworks will continue into the new year with a further 500,000 cubic metres of material to be excavated and placed. In addition, structural works at all four structures along the main alignment are progressing with the first structure, on Hopetoun Park Road, to be opened to traffic before the end of 2010.

The Western Highway ? Anthonys Cutting Realignment Project is expected to be completed by early 2012. However, Rod Jeffrey said that would depend very heavily on the weather.

?It really depends on how wet the winters are,? Rod cautioned. ?We are currently on track to meet the timeframes despite the very wet winter we are currently experiencing.?

For further information about the Western Highway ? Anthonys Cutting Realignment Project, visit

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