The role of the engineer in controlling the excavation phase at the iSangoyana Rail tunnel

Abstract

Abstract The iSangoyana double-track rail tunnel is an 11 -m span × 8-m-high opening 2.4 km long, driven using drill-and-blast through sandstone/siltstones and carbonaceous shale. The maximum cover of the tunnel is 173 m. Because of the nature of the rock, support was required immediately following excavation in order to stabilize the excavation and to prevent rockfalls. An unreinforced 250-mm-thick concrete lining was placed after the excavation was completed. In order to prevent short-term loads from being applied to the lining at the time of placing the lining, and in order to limit the magnitude of long-term loads on the lining, it was necessary to ensure that controlled blasting was used during the excavation; and that tensioned rockbolts of the correct spacing and length, commensurate with the encountered rock conditions, were installed to minimize rock loosening. The paper describes the techniques used by the Engineer to ensure adequate control of the excavation and initial support procedures.