LDE provided comprehensive geological assessments and analyses of the significant landslide and sections of the affected road.
The road traverses across the top of a narrow section of the ridge which drops away steeply for several tens of metres on either side. The southern side of the ridge was subject to land slippage resulting in the complete evacuation of a section of hillside, measuring approx. 32m wide x 35m long with an estimated depth of 3m. The slip also left a fence hanging some 3m out from the road. Previous stabilisation attempts included willow baskets and appeared ineffective.
Saturation of soils and fill from discharge surface water were the likely cause of the slippage and ongoing localised collapse was likely to occur.
Our collected investigation and testing data were used to determine the engineering design options for the sites, and the best remedial option posed was to construct timber pole retaining walls to inhibit regression into the carriageway and to widen the shoulder along the affected section of the road.
Location: Tauwhareparae Road, Gisborne
Client: Tairawhiti Roads (Waka Kotahi/Gisborne District Council)