Engineers Australia

Recent experiences with soil nailing in deep cuts as part of level crossing removal works in Melbourne

J. Gniel, C. Lenthall and D. Paul

Abstract

The adoption of prudent soil-structure design parameters is a critical component of the design of soil and rock retention systems. Designs must also account for the influence of construction practices on performance. This paper discusses the adopted design soil parameters, construction practices and the measured response of soil nail retention systems at four sites in Melbourne as part of the Furlong Road, Main Road, Blackburn Road and Heatherdale Road level crossing removal project (FMBH LCRP). The project involved retention of near vertical cut faces up to 15 m high such that existing rail lines could be lowered to pass under local roadways. In the case of Furlong and Main Roads, the geological setting comprised Pleistocene age residual basaltic clay overlying basalt rock. At these two sites, a greater than expected degree of soil fissuring was observed. This paper presents a theory on the origin of the fissuring and construction methodologies that were used to reduce the risk of instability posed by the fissured soils. The geological setting at the Blackburn and Heatherdale Road sites comprised Silurian age residual siltstone clay overlying variably weathered siltstone rock. This paper describes some of the challenges involved in constructing soil nail retention systems in the two different geological settings, including the varying influence of drilling practices in both settings.