Excavation failure during micro-tunneling in fine sands: A case study

Partly funded by the World Bank, a new gravity sewer line is currently being constructed in Anzali, Iran using micro-tunneling methods. The project includes the installation of 2551 m reinforced concrete pipes with diameter ranging from 600 to 1000 mm at an average depth of 5 m below surface. Micro-tunnel Boring Machine (MTBM) and hydraulic pipejacking have been used to install the sewer line. Pipejacking in saturated highly porous sandy soil poses various challenges during construction including the risk of face failure, possibility of shaft collapse, massive rush of groundwater (in this case from the Caspian Sea) and surface subsidence. This paper provides an overview of the project and summarizes the challenges faced and the techniques used to handle the difficulties encountered during construction.