Lesson Learnt from Operating Three Different Soil Abrasion Testing Systems, A Pathway to Find New Index of Abrasivity in Soft Ground Tunneling

The use of mechanized excavation especially shielded tunnel boring machines (TBMs), has grown rapidly in various soft ground tunneling projects. One of the advantages of mechanized tunneling compared to conventional method is the ability of the machines in coping with various geological conditions. In recent years, Earth Pressure Balance (EPB) shields have been successfully used in many tunnels in urban areas while the range of soil types that it can handle has expanded. Estimation and assessment of the effects of abrasive ground on the primary and secondary wear of tools and machine components, costs, and schedule of a project has been a crucial issue due to the lack of a universally accepted measurement system for soil abrasion. In recent years some Universities and institutes have investigated and introduced various methods for measurement of abrasivity in soft ground. Each one of these methods have some deficiencies and mismatches in comparison with the actual working conditions at the tunnel face. This paper reviews some of the studies that have been conducted in three universities Pennsylvania state university, Ruhr-University Bochum, and Politecnico di Torino in this area and try to critique the initial steps towards the development of a new index for soil abrasivity. Furthermore, the results of some soil abrasion tests performed at Politecnico di Torino, Ruhr-University, and the soil abrasion index are compared.