Abstract: The particularity of sandypebble strata in Chengdu, China introduces problems to shield tunnels, such as cutterhead jamming, center mud cake, excessive wear of cutterhead, and broken screw conveyor shaft. Therefore, the discreteelement theory and analysis method are adopted to simulate the shieldtunneling process in sandypebble strata, and the law of soil movement and force characteristics of the shield are studied. It is concluded that (1) the moving speed of soil particles around the tunneling face of the cutterhead is higher than that of the center; (2) the soil moving speeds in the center of the soil chamber and at both sides of the screw shaft extending into the soil chamber are slow; and (3) the compressive force distribution of soil on tunneling face and soil chamber is related to the rotation direction of the cutterhead. Finite element analysis is conducted on the cutterhead and screw conveyor using EDEMANSYS coupling, and the results show that: (1) The maximum stress on the cutterhead is 123.27 MPa during shield tunneling, which is located at the junction of the cloud leg and the flange; the maximum deformation is 1.69 mm, which is located on the outermost ring beam of the cutterhead. (2) The maximum stress on the screw conveyor is 59.01 MPa, which is located at the connection between the rear partition of the soil chamber and the screw barrel, and the maximum deformation is 0.49 mm, which is located between the outer ring of the spiral blade near the junction of the soil chamber and the screw barrel.

Key words: shield, sandypebble strata, discrete element, tunneling process, EDEMANSYS coupling