Cutterhead and Cutting Tools Configurations in Coarse Grain Soils

Abstract

Background:Many subway/metro tunnels were constructed using close face shield machines in coarse grain soils in last decades. Configurations of the shield cutterhead and cutting tools are critical in terms of cost and project duration. There are currently no recognized methodologies available for the configurations due to the various geological and technical influencing factors. Several aspects have been considered in many single case studies. Objective and Method:To aid a better understanding for the involved design and operational aspects in a system way, main physical and mechanical characteristics of the coarse grain soils encountered in China are briefly summarized; advantages and disadvantages of the spoke type and plate type cutterhead equipped with corresponding cutting tools are outlined; performances of the different shield cutterheads used in the typical subway construction cases are introduced. Results:Based on the jobsite experiences, discussed are the options with respect to design of the cutterhead and cutting tools in the coarse grain soils, including opening ratio of the cutterhead, configuration of the cutting tools, use of the single disc cutters with inserts, reasonable movement of shield machine, robust shield machines against wears and interventions for changing tools. Conclusion:According to the discussions, the rule-of-thumb suggestions are presented to provide references for later similar projects.

Wear mechanism and life prediction of the ripper in a 9‐m‐diameter shield machine tunneling project of the Beijing new airport line in a sand‐pebble stratum

“…The cutterhead has a total of 104 rippers and 156 scrapers arranged on the main spokes and auxiliary spokes. The multiconfiguration tools loosen the ground in front of the cutterhead with the center fish‐tail cutter and the precut bits, crush the oversized stones of the soil matrix with rippers and shave off weak materials with scrapers (Li et al, 2018). The two multidimensional rippers with a height of 300 mm in the center and a total of 102 rippers with a height of 190 and 155 mm are arranged on the spokes, which effectively improves the advancing speed.…”

“…The diameter‐preserving gauge cutters with a height of 220 mm and the scraper on the shell ensure that the diameter of the excavated tunnel meets the construction requirements. The shell bits also protect the cutterhead and reduce the friction between the cutterhead and the soils (Li et al, 2018). The 190‐ripper can cut and break large pebbles in the sand‐pebble stratum, and the 155‐ripper can cut the broken pebbles again.…”