A main highway in New Zealand has been undergoing a multi-year improvement and expansion project, and in winter 2019, a section with over-water bridges in New Zealand needed to be expanded. It was determined there was only one way to complete the job quickly and safely.Concrete cutting with diamond tools would allow for pre-planning of cut sections and a fast, clean removal of roadway sections. As this series of bridges and roads also spanned a tidal creek, it was imperative that no debris or slurry be allowed to fall into the creek, and also that no fly rock would strike vehicle traffic.
The SH1 Southern Motorway on the North Island of New Zealand is part of State Highway 1, the longest and most significant road in the country. SH1 runs for 2,033 km (1,263 miles) and is primarily a two-lane single carriageway. It is an essential part of Auckland’s transport network and is the primary route between Auckland, Hamilton and Tauranga. The Southern Corridor Improvements Project, which will cost $268 million (USD$183 million) and runs for over four years, covers the stretch of SH1 from the SH20/SH1 connection at Manukau down to Papakura in the south. CSDA member A1 Kiwi Cutters & Drillers Ltd. of Auckland was selected as the cutting contractor on the Southern Corridor Improvements project by the general contractor and the New Zealand Government. Roughly four months of planning took place before any work commenced, which contributed to the successful outcome of the project.
The entire project was to convert a two-lane section of motorway to a three-lane by constructing a temporary bridge, widening some existing bridges, removing other existing bridges and building a new wider bridge. The temporary bridge was constructed first to allow for southbound traffic to be diverted while the northbound traffic was diverted to the old southbound lanes. Then, the existing northbound bridge was removed, and a new wider bridge was constructed in its place.
Both north and southbound traffic was then diverted to the new bridge while the old southbound and temporary bridges were removed to allow for construction of the new, wider southbound bridge. A1 Kiwi Cutters was tasked with removing the existing southbound bridge and temporary bridge, including head stock and bridge beams. Concrete cutting was determined to be the best option for removing the old bridges primarily for environmental reasons. The bridge spanned a tidal creek, making it imperative that the creek be protected from any debris or concrete cutting slurry.
Additionally, the bridge was located within two meters (6.6 feet) of a heavily traveled section of motorway, with residents living within 50 meters (164 feet). Traditional demolition methods would have been noisy, presented an unacceptable risk of fly rock going into the live traffic lanes and would have resulted in significant amounts of rubble being dumped into a sensitive environmental area. “Concrete cutting is quick, significant amounts of concrete are moved intact and the Super Tee sections of the bridge were able to be used on other parts of the project,” said Sam Simons, General Manager for A1 Kiwi Cutters & Drillers Ltd. The first step of the project was to setup the slurry control system. All slurry was captured and disposed of off-site. Next, the bridge deck was pre-cut using Hilti DS WS 15 and DSW 3018-E wire saws, as well as some of the bridge abutments and head stock. There were three bridge sections to be cut, each weighing 45 tons (99,208 pounds). Two Super Tee units, each weighing 117 tons (257,940 pounds), were then cut so that they were resting on the bridge abutments and made ready for lifting out. This was done to minimize cutting when the 350- and 450-ton cranes were deployed. A1 Kiwi then installed lifting brackets that were rated to lift each bridge section. The motorway was closed from 22:00 to 5:00 the next morning to allow for the next phase of work. Because of the excessive weight of the cut sections, a double crane lift (using the 350- and 450-ton cranes) was used to rig the cut sections and lift them out. The two Hilti DS TS20-E and DST 10-CA wall saws were then used to cut along the edge of the head stock at an angle to aid in the removal of the bridge section. Once cut, the section was lifted onto the back of a transporter and removed from the site. In one shift, three bridge sections and two Super Tees had their final cuts and were lifted out for removal from the site. The second phase of the project involved removing the remaining two spans of bridge during normal working hours. Only one crane was needed because the spans were located
closer to the crane and loading out could be done on the closed roadways. Additional slab sawing was completed using a Corecut CC35 slab saw. In total, 100 feet of wire sawing, 335 feet of wall sawing 18 inches deep and 110 feet of slab sawing one foot deep was completed. This project produced many challenges for the contractors. Working close to a busy motorway, precautions had to be made to ensure there was no interaction between cars, the public and operations. Furthermore, most of the work took place during a three-day period of King Tides, the strongest tidal flows. This aspect required significant planning to ensure success and safety. Absolutely no slurry or debris was permitted to enter the creek due to environmental regulations. This was managed largely by the general contractor, with input and assistance from A1 Kiwi Cutters. Another concern was that this project took place during one of the hottest and most humid summers on record in the Southern Hemisphere. It was imperative that operators stayed hydrated and avoided risking heat illness.
It was very important that the project be completed on-time and according to plan due to the cost of using cranes and having to close the motorway. The three A1 Kiwi employees who were on site worked the hours required to keep the job on schedule, readily complied with standard health and safety protocols, kept a lookout for any environmental issues and communicated with the general contractor on issues as they arose. The contractor also kept backup wall and wire saws in close proximity on the job site in case they encountered any equipment issues, although this complication was not expected to be an issue. “A1 Kiwi invests heavily in new technology. Equipment is updated regularly which minimizes jobsite breakdowns. Part of the reason we were chosen for this job was that the general contractor realized our investment in the newest technology and latest equipment would help to guarantee the work would be completed on time,” Simons stated. The end result was 650 tons (over 1.43 million pounds) of concrete removed over the course of 12 work shifts. The project was completed according to plan and within budget. A1 Kiwi has done a number of significant concrete removal projects over the last decade. Each of the company’s employees has gone through, or are going through, the New Zealand Qualifications Authority unit standards for concrete cutting and drilling. “This gives our clients confidence that the people we send to site are competent to perform the work. The company has a structured training program so that every employee has the opportunity to get on these technical projects that test their capability. The clients also know that they can contact staff, some of whom have 45 plus years of experience, should they have any concerns,” said Simons.