Having a blast

In a bulk earthmoving or construction contract, rock can sometimes be the great unknown. How do you break and move it? How much will this cost? How much will it add to construction time? In fact, despite the wondrous properties of rock, the construction contractor often considers its very presence an unwelcome complication, but there is a safe, fast and cost-effective solution.

Failing to properly assess and manage the presence of rock in a construction project can put a contracting company between ‘a rock and a hard place’, however, it doesn’t have to be all that bad. Rather, with an open mind for alternative and innovative methods, it is entirely possible to be productive and profitable when excavating and working with rock.

Driven by booming infrastructure development and an insatiable global demand for mineral resources, commercial explosives technology has evolved rapidly. The focus is on safe, controlled and low cost rock breakage. As the world’s largest commercial explosives manufacturer and with explosives related research centres on four continents, Orica remains at the forefront of this development.

So what does this really mean for a construction contractor? It means that whether excavating a million cubic metres of rock for building a motorway or driving precision tunnels under a major CBD, solutions exist to make work faster, safer and more profitable.

Rock to specification – Northern Gateway Project

One of the difficulties with rock is that it is not necessarily found in the specification required. For example, the Northern Gateway Alliance was carving a wide expanse of free flowing modern motorway between Albany and Puhoi north of Auckland. As would be expected, the rock was found as a solid mass in the hillsides and did not meet the size specification for use as fill.

The original approach was to rip and excavate the material, mechanically crush it, and then re-handle it into the required areas. However, during blasting elsewhere on site, co-operation between contractors led to an innovative approach being adopted that would end up being very profitable for the Northern Gateway Alliance.

“We proposed a ‘rock to specification’ offer to eliminate the need for crushing the rock and associated re-handling processes,” explains Orica New Zealand’s construction manager Peter Johnston.

“The tailored blasting solution was, at face value, a considerably more expensive option than traditional blasting practices or ripping and free digging. However, the increased upfront costs more than paid for themselves by removing an entire crushing process and, just as importantly, this solution allowed the works to be completed well ahead of the budgeted timeline.

“As the saying goes ‘time is money’, and nowhere is this more so than in construction project works.”

The rock to specification offer was a combination of Centra Gold bulk emulsion explosive and Orica’s electronic blasting system. Extensive technical planning and design allowed the once solid rock mass to be reduced to the required specification in a single step.

Northern Gateway Alliance’s master blaster Mark Blanchard has worked alongside Orica for the past 15 years, and for the past three years on the NGA project.

“It’s definitely not your regular quarry or mining project,” he says. “It’s been challenging to get the rock fragmentation size down to 300mm. Having the experience and backup of Orica and their design team has been brilliant on this project.”

Ultimately a few short months ago, when the ribbon was cut, the construction contractors had spent less money and completed the work more quickly than planned. This is why, on every job, Orica is working together with its customers to identify opportunities and develop successful blasting solutions.

Blasting beneath their feet in Newmarket

As cities expand, the infrastructure that carries their lifeblood of people, power, water and sewage must grow with them. And this means construction must share space with homes and schools, hospitals and parks. So, how do you complete the work that must be done when you are restricted by the needs of those around you? You evolve, you work together and you innovate.

The DART 2 project to electrify and increase the capacity of metro rail on Auckland’s western line requires this approach. Bridges must be widened, tracks need to be installed and essential services must be relocated. In the Auckland suburb of Newmarket Orica is blasting six metres directly below Khyber Pass Road into a compacted mix of clay and hard rock. These exceptional tunnelling conditions are met in close proximity to the southern motorway, a major school and busy urban streets. The purpose of this tunnel is to rapidly advance 80 metres of 1.2 metre diameter concrete pipe for a stormwater and sewer diversion.

Blasting in this environment was an unexpected challenge for those in charge of approving this project. There are a lot of new risks and processes to understand and manage. These risks included blasting in a confined space and in a dense urban area, vibration and air-blast management, fly-rock management, and safety of site personnel.

Orica’s Blast Based Service technical group was well equipped to assess and manage these risks and develop the processes and plans required to achieve an efficient result. They were able to provide to the principal contractor a customised solution that simplified the whole process.

“We developed the technical design and work methodology for the project locally, we visited the site several times to discuss the requirements of our customer and stakeholders, assess the surroundings and make judgements about the nature of the rock,” says Orica New Zealand’s technical services engineer, Austin Turner.

“After we had developed a design we judged to be safe, productive and efficient, we sent the plans, along with a 3D simulation and site photos to our specialised underground design team in Australia to review and provide feedback.”

The blasting tools used include some of the latest technology in this field, such as the electronic blasting system that allows Orica engineers to design blasts, that were once thought not possible, specific to site conditions. Reduction of construction delays, minimised vibration and increased safety of those on site are some of the typical benefits of this system. Specifically developed vibration modelling software was used to predict the level of vibration that could be expected for each individual blast design before work even began. Orica prides itself as having an experienced team of professionals capable of delivering such technically challenging project

The work at DART 2 will soon be complete, the majority of the rock has already been broken and blasting has been without incident, and soon commuters will travel on the new electrified rail lines without a thought to the work that made it possible.

The growth of cities and the building of infrastructure won’t stop. And while the challenges will not become easier, Orica will continue to innovate and work together with its construction customers to meet the challenges and find safe, efficient solutions.

• Article supplied by Orica.