Methods Adopted while Micro-tunnelling in Difficult Ground Conditions: A Review.

Abstract

In a congested area, installing a pipeline using an open excavation is not a feasible method. Hence, trenchless techniques are currently being used all over the world. Among different types of trenchless techniques, the most cost-effective method to lay pipes at deeper depths for long distances, is the micro-tunnelling method. Micro-tunnelling is the combination of using remotely controlled Micro Tunnel Boring Machine (MTBM) and pipe jacking technique. Many researchers have explored more on the procedure and the forces that act when driving an MTBM. However, only few research findings are focused regarding the problems encountered when driving an MTBM in difficult ground conditions. Among those, the most significant problem observed when driving a MTBM was the settlement of the MTBM. To overcome this obstacle, many findings suggest to modify the machines and some have utilized ground improvement techniques. Further, to maintain the stability of the tunnel face while driving in saturated cohesionless soil, bentonite slurry was utilized as a temporary support. Sinking of MTBM due to insufficient bearing capacity of soil was resolved through machine modification technique. Settlement of MTBM occurred in Hawaii was resolved by using cement grouting technique. However, driving an MTBM in very soft soil like peat is not a possible task as it possesses poor engineering properties. Although micro-tunnelling has been studied in different soil types, a detailed study on micro-tunnelling in peat has not been studied. Moreover, suitable ground improvement technique has not been found yet to drive MTBM successfully in very soft soil like peat. A case study presented in this study provides the measures required while driving micro-tunnel in soft soil. To overcome problematic nature of soft soil, deep mixing method has been successfully executed in many projects. Hence, this paper emphasizes the importance of ground improvement prior to micro-tunnelling in soft soil.