Application of soil nail wall to roadway widening using GFRP rebars as per Australian design guidelines

This paper presents the application of soil nail wall technology to roadway widening. An arterial road upgrade project in Melbourne consists of widening the freeway in the northern part of Melbourne, including massive cuts into a hillside on the southern side of the existing freeway. Cuts up to 12 meters necessitated the use of retaining walls at 1H:10V batter to stay within the right of way. A soil nail retaining wall was adopted to facilitate reduced excavation, less impact on the existing slope, and improved construction speed with a top-down process. The soil nail retaining wall is 520 m long with a maximum height of approximately 12 meters, including the undercut for pavement and drainage. The ground comprises clay fill overlying residual clay and subsequent weathering profiles of basalt from Newer Volcanics group, partly overlying Brighton Group sediments. Eleven boreholes were drilled sufficiently below the bottom of the wall. Laboratory tests were conducted to estimate the soil and rock strength, including triaxial compression tests with pore pressure measurement to determine effective strength parameters for Brighton group clayey soil. The design employed Glass Fibre Reinforced Polymer (GFRP) bars to enhance the work efficiency by removing encapsulation of steel bars, the durability of which was reviewed for the 100 year design life with the proven data provided by the manufacturer. The soil nail retaining wall was designed as per AS5100.3 and AS4678 guidelines selectively depending on the importance of the wall with reference to VicRoads Specification Section 683 and FHWA-NHI-14-007.