Otira Viaduct
Upon first glance one may think this large bridge is spoiling the natural beauty of this spectacular, steep-sloped valley, but it undoubtedly demonstrates some of the difficulties faced while living in a geologically active area such as New Zealand. The Otira viaduct is a 440 metre stretch of road that connects two highpoints and spans both a river and a high frequency landslide path. The old road (located higher up the hill to the right) was constantly prone to rockfall, snow avalanches and landslides but was the only option until 1923 when the Otira train tunnel was completed as a way to accommodate heavy gold traffic. The road was also becoming increasingly unstable from the constant erosion of the base of the hill by the river at the bottom of the valley. This Otira Viaduct was the best solution that road engineers could come up with for this problem, but required a huge investment of time and money to build. The first foundations were poured in January 1998 and the first cars drove over the new viaduct in November 1999; costing New Zealanders a total of 25 million New Zealand dollars, the viaduct was deemed an engineering success! Many special features on this bridge were added due to the high geologic activity of this area. The combined high relief of this terrain with some of the highest uplift and erosion rates in the world caused engineers unimaginable grief while designing this viaduct. Besides the overall bend required of the bridge to traverse the topography, engineers also made this bridge forty percent more resistant to seismic activity than other comparable viaduct’s seismic maximums. They did so by incorporating 25 metre deep basal foundations for each pier, and adding triangular supports uphill of the two outer supports to help protect their integrity during landslide events (the middle pier didn’t receive one since it didn’t appear to be in a high frequency landslide zone). The difficulty of engineering design was also exasperated by the fact it is located within a national park, so the well-being of local wildlife such as the Kea (an endemic alpine parrot) was also placed at the forefront of importance when selecting bridge design methods. As part of the planning for this viaduct (which began in 1986) geologists obtained 14C dates of wood buried in landslide debris in the valley that suggests one large event occurred around 1900 years BP, that may correspond to the large eruption of Taupo during this time periof- though this has not yet been proven. One can only wonder how long this huge investment will last before being inevitably destroyed by the awesome powers of nature at work in this dynamic landscape.
Upon first glance one may think this large bridge is spoiling the natural beauty of this spectacular, steep-sloped valley, but it undoubtedly demonstrates some of the difficulties faced while living in a geologically active area such as New Zealand. The Otira viaduct is a 440 metre stretch of road that connects two highpoints and spans both a river and a high frequency landslide path. The old road (located higher up the hill to the right) was constantly prone to rockfall, snow avalanches and landslides but was the only option until 1923 when the Otira train tunnel was completed as a way to accommodate heavy gold traffic. The road was also becoming increasingly unstable from the constant erosion of the base of the hill by the river at the bottom of the valley. This Otira Viaduct was the best solution that road engineers could come up with for this problem, but required a huge investment of time and money to build. The first foundations were poured in January 1998 and the first cars drove over the new viaduct in November 1999; costing New Zealanders a total of 25 million New Zealand dollars, the viaduct was deemed an engineering success! Many special features on this bridge were added due to the high geologic activity of this area. The combined high relief of this terrain with some of the highest uplift and erosion rates in the world caused engineers unimaginable grief while designing this viaduct. Besides the overall bend required of the bridge to traverse the topography, engineers also made this bridge forty percent more resistant to seismic activity than other comparable viaduct’s seismic maximums. They did so by incorporating 25 metre deep basal foundations for each pier, and adding triangular supports uphill of the two outer supports to help protect their integrity during landslide events (the middle pier didn’t receive one since it didn’t appear to be in a high frequency landslide zone). The difficulty of engineering design was also exasperated by the fact it is located within a national park, so the well-being of local wildlife such as the Kea (an endemic alpine parrot) was also placed at the forefront of importance when selecting bridge design methods. As part of the planning for this viaduct (which began in 1986) geologists obtained 14C dates of wood buried in landslide debris in the valley that suggests one large event occurred around 1900 years BP, that may correspond to the large eruption of Taupo during this time periof- though this has not yet been proven. One can only wonder how long this huge investment will last before being inevitably destroyed by the awesome powers of nature at work in this dynamic landscape.
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