Tairāwhiti Roads Storm Damage: Determining factors for the best remediation solution to a mass number of slope failures

In 2017 and 2018 the Tairāwhiti Region was subject to multiple extreme rainfall events resulting in widespread damage to the regions roading network. Geotechnical assessment of the storm damage has found most failures were underslips resulting in loss of road width to the outside lane or road shoulder. The appropriate remedial solution for a site was determined by the following three fundamental engineering geology factors: geometry, geology, and water. Other varying factors included traffic volume/road importance level, expected level of resilience post repair, client budget, and construction material availability. Three geotechnical solutions were typically applied: bench and fill or mass stabilised earth walls (MSE), cantilever retaining wall (with or without anchors), and minor upslope road cut or full road retreats. Applying such fundamental engineering geological factors in a simple assessment template assisted the remediation of multiple sites in a rapid timeframe. This process highlighted the important role of an engineering geologist undertaking good geological observations, mapping, photography, record keeping, and understanding the wider context of the site. Including understanding the likely failure triggers such as leaking and blocked culverts, aging stormwater infrastructure, and forest harvesting.