Experimental study on shield machine cutting steel-reinforced concrete diaphragm wall

Shield tunneling during metro construction frequently hits steel reinforced concrete diaphragm walls. A high risk is involved in using a shield machine to cut through a diaphragm wall owing to limited theoretical research and engineering experience. To evaluate the performance of the shield machine and obtain feasible operation parameters, this study conducts a full-scale field test using a shield machine to cut through a diaphragm wall in Suzhou, China. The machine has a diameter of 6.84 m, equipped with 38 disc cutters and 48 scrapers. The wall has a width of 8.8 m, height of 9.7 m, and thickness of 0.6 m, reinforced with 25 mm and 28 mm diameter main steel rebars. The study finds: 1) the shield machine has adequate capacity to cut the diaphragm wall with small wear (maximum amplitude of 0.7 mm) to disc cutters and light damage to scrapers; 2) the concrete is mainly damaged under compression shear and peel-off with 95 % of particle size smaller than 10 cm, whereas the steel rebars are broken under the combined effects of compression shear and pull-apart with five damage modes identified based on different damage mechanism; and 3) a low advance rate (1-2 mm/min) and medium rotational speed (0.6 rpm) are recommended such that the machine can cut the wall smoothly with wall acceleration below 0.15 g and maintains its thrust and toque close to 10 % and 15 % of rated thrust and torque, respectively. The findings prove the feasibility of using a shield machine to cut through a diaphragm wall, and provide guidance for project implementation.