Investigation into net cutting rate of a slurry microtunneling machine

This study is about a waste water collection and treatment project to prevent pollution of sea water in Bosporus. The study includes 3 different microtunneling projects on which the same slurry type Herrenknecht AVN1800C microtunneling machine was used in Istanbul. Daily advance rates, net cutting rates, machine utilization ratios are investigated based on daily shift records, machine data logging records and visual in situ observations in different project sites. Lithological units and their properties are summarized based on the borehole reports and project documents. An empirical model is developed for predicting net cutting rate of the microtunneling machine. The dominant lithology is clay in all project sites investigated. Total driving length of the projects is 1000 m. The achieved best daily advance rate is 27.07 m/day. Average of the net cutting rates in all project sites is obtained as 1.96 m/h for these 3 projects. The highest average net excavation rate is achieved as 4.24 m/h in Kurbagalidere site and it varies between 1.1 m/h (Cirpici site) and 1.34 m/h (Nakkasdere site). Statistical analysis is performed to investigate the effects of some ground related parameters (natural water content, plastic limits, liquid limits, plasticity index, SPT-standard penetration values, and TCR-total core recovery) on net cutting rates. The best relationship is obtained with SPT values being lower than 15. Net cutting rate decreases with increasing SPT value. The model is valid for slurry microtunnel boring machines with 2.5 m of excavation diameter and clay-silt lithology with SPT values lower than 15.