Following a series of sub-tropical rainstorm events, Kawakawa and the wider Auckland region suffered extensive landslip issues. Many roads in the region developed both underslips and overslips, severely affecting the flow of traffic. On some roads, full closures were required. As a result of a long-standing relationship with our company, Broadspectrum contacted us to provide a competitive design/build solution.
With no geotechnical information available and working under an emergency timeframe, our in-house engineers conducted site investigations and mapping to determine the locations’ parameters and conditions. To provide a rapid turnaround, several assumptions were made during the design stage and confirmed with sacrificial soil nails tested to failure. A simple soil nail and shotcrete solution with micropile toe support was utilised to stabilise the slope and rebuild pavement width. The use of the company’s proprietary, low-carbon steel hollow bar soil nails provided the required durability, and this in-house design/build solution provided savings to the client in the order of 35% over traditional retaining systems. For the package of four slip sites, we developed solutions that minimised costs to the client through innovation and experience. Having four nearby sites meant a degree of symmetry could be established between the sites in regard to design and delivery.
First Gas owns and operates the 400 Line (Maui) which supplies natural gas from Taranaki to the Waikato while the Maui pipeline supplies gas to the Hamilton and Central North Island regions. Historic and more recent instability of the Maui pipeline easement fill occurred at two sites near Awakau Road.