Geological Factors and Stability Evaluation Affecting the Excavation Progress of A Tunnel Boring Machine for a Hydraulic Tunnel in Algeria: Case study

Abstract

The excavation of long tunnels has become one of the challenges of the tunnelling machines. Several types of machines exist in the tunnel market. The main factors controlling successful tunnel excavation include detailed geological and geotechnical studies. This paper focuses on the main geological and geotechnical problems affecting the tunnel excavating progress as well as tunnel design stability evaluation. Also this article studies the impact of geological conditions on the project schedule and cost. Tunnel design geotechnical parameters and Phase 2- RocLab Software programs are used to study tunnel stability. A case study of a 6 km long hydraulic tunnel with 4.3m outer diameter and 3.6m inner diameter is presented. The tunnel is excavated in mixed types of rock units with intensive geological deformation. This tunnel represents one part of a major project to transfer 23m³⁄s of water from Bin Haroun Dam at the North part of the project to Authmania dam at the South (Wilayet Mila –East Algeria). The geological units driven by the Tunnel Boring Machine (TBM) include calcareous claystone materials of Miocene age which represent a total of 1300 m of the tunnel length as well as dolomitic limestone of Cretaceous age representing a total of 4700 m of the tunnel length. Several major and intermediate-scale faults have been encountered in the excavated tunnel especially in the Cretaceous dolomitic limestone rocks. The geological complexity and the type of tunnelling mechanized machine used are considered the main factors causing delay in the work schedule and increase the project running cost.