Analysis of Jacking Force of Small Diameter Micro-Tunnel-Boring Machine by Slurry Pressure Balance Method in Short Distance

Using micro-tunnel-boring machine (MTBM) in the trenchless operation has been widely used in the underground pipeline construction. To prevent damage of pushing pipe and neighboring construction, most important point in the jacking process is controlling the thrust force. Formulae for predicting jacking force have been proposed for decades. Whether these formulae are suitable for project, data collected from the worksite needs to be evaluated and analyzed. Most literature is focusing on projects with pipes of long distance and large diameter. Streets in developed urban area in Taiwan are narrow and zigzag, which is different from the most cases mentioned in the literature. Distance is short and excavation diameter is small are the feature of the Taiwan pipeline construction project. This research focused on data collected from few jacking sections in a project which located in Jhonghe district, New Taipei city, Taiwan. The research verified the suitability of the predicting formulae in Taiwan. In the process of collecting data in the worksite, the condition of MTBM (RASA DH-FsT400), the condition of worksite equipment and work details in the working process were recorded as well. The soil layer in Jhonghe district is rich in pebble gravel. From data collected from the worksite, following conclusions can be drawn. -Excavation face is not stable, the soil in the crown will collapse in the jacking process. The collapse of excavation hole develops huge frictional force. -Terzaghi’s silo model is well applied in the calculating frictional force.