Product feature: Boss Attachments' alternatives to breaking and blasting

Date: 04.06.2021

Antraquip Milling Heads provide a safer and more robust short- and long-term solution

Trimming batters at Puhoi

During the last 30 years, Antraquip says they have been involved with some of the most impressive, challenging, and rewarding rock-cutting projects on the planet. It comes as no surprise then that since their arrival to New Zealand, they have made their mark across a number of landmark New Zealand projects, including the NCTIR Kaikoura Rail and Road Rebuild, the NAL North Auckland Rail Rebuild, and the Ara Tuhono—Puhoi to Warkworth Motorway.

With the shift in emphasis to long-term operational safety, utilising different construction methods to achieve this is becoming increasingly important. 

"Antraquip Milling Heads operate with little or no micro-cracking of the area outside of the excavation line, and as shown in the two examples, they are a proven alternative to blasting or breakers and provide a safer and more robust short- and long-term solution," says Paul Herbison of Boss Attachments.

This low impact benefit was particularly relevant at the Kaikoura and North Auckland rail projects. In both cases, it was important to avoid any vibration that could further compromise the existing structural integrity of the tunnels.

NCTIR Kaikoura Rail and Road Rebuild

Milling earthquake-damaged tunnel Linings at Kaikoura

The Kaikoura earthquake caused substantial damage to the 100-year-old tunnels. This included cracking, rock falls, and general weakening. Some sections also had vertical and traverse movement in excess of 500mm, caused by traverse faults running through the tunnels.

Because cracking from breakers and blasting have been shown to reach up to two metres, Antraquip Milling heads were the ideal option for this remediation project. During a two-year period, two of the range’s smallest units—a 120kg AQ-1s and AQ-1—were utilised to gently mill back the concrete tunnel linings and the raw blue greywacke walls.

NAL North Auckland Railway Line Lowering

The historically significant Northern Line between Auckland and Whangarei, parts of which date back to 1876, requires a major rebuild to enable it to handle the demands of modern heavy rail freight and hi-cube container traffic.

As was the case at Kaikoura, minimal vibration of existing structures was paramount, and at various times, Boss Attachments have had up to eight Antraquip milling heads operating on the widening and track lowering on the line’s 13 tunnels. Being able to use a single unit to carry out both lowering and detailed soffit milling operations was a significant project benefit.

Other benefits included the following:

Ability to work right up to existing tunnel foundations when lowering without any compromise to the structural integrity. Ability to trench in rock not able to be ripped with a 40-tonne excavator single pick.

Ara Tuhono—Puhoi to Warkworth Motorway

On completion, the Ara Tuhono—Puhoi to Warkworth project will extend the four-lane section of the Northern Motorway by 18.5km. The extension traverses a steep section of topography with cuts of up to 70 metres through varying soil types and weak to moderate sandstone and mudstone.

This material is too hard to rip and required production blasting to excavate, some of which is best described as tortured in its geological formation. This material is highly variable from solid four- to five-metre hard sandstone lay ers to 50mm interbedded sandstone/mudstone.

This variability presents real challenges for blasting. As a result, Antraquip Milling Heads have been used and have delivered the following benefits to a range of tasks, including scaling, shaping, and detailed trimming of batters.

Some other benefits include:

• Ability to stand the blast radius of the batters by two metres, which dramatically reduces any structural damage to the face from blasting
• Long-term benefits of reduced maintenance due to rockfall
• Much safer slope to work under
• Scaling of all rock faces to remove any loose material at the same time
• Accurate trimming of a Mono slope with excavators guided by GPS

"Throughout these projects, the support and industry knowledge transfer that we have received from Antraquip in the US has been tremendous," says Paul. "They have had decades of experience in wide ranging projects all around the globe and provide us with 24/7 support."

The Antraquip range includes models suitable for materials with uniaxial compressive strength (UCS) ranging from one to 200+ mpa for small- to mid-sized cutters. The AQ-5 (200kW for 50+ tonne carrier) and AQ-6 (400kW for 65+ tonne carrier) models can be utilized in rock substantially harder than this. Antraquip also have a range of Soft Soil mixing attachments that have used in New Zealand and around the world for soil remediation and Mud-Crete.

Key features

• Little or no micro-cracking of the ground outside the excavation line. (cracking from hammers has been shown to reach up to two metres, depending on rock type). This can cause issues with existing infrastructure.
• Minimised overbreak of milled face
• Minimal disturbance of Cut face making for a safer more intact slope or trench
• Significantly less noise
• Significantly less vibration
• Ability to reuse the material onsite as hard fill, thus reducing waste and cost
• Extremely reliable tools

"Antraquip is a fantastic brand to be associated with," says Paul. "Their product quality, durability, and performance is exceptional, on top of which, their unparalleled level of hands-on international construction and tunnelling experience helps us add real value to our New Zealand client’s projects."

For more information, contact Paul Herbison 027 290 8306 or visit bossattachments.co.nz

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