Abstract:  Engineering problems such as instability of excavation face, poor dumping, screw conveyor stuck, and pebble in chamber may arise when large diameter shield is driving in sandpebble layer. Meanwhile, excessive torque of shield cutterhead and screw conveyor may be caused in the sandpebble layer. Therefore, the requirements for conditioning of the fluidity of sandpebble soil are more stringent. In this paper, the reasonable conditioning parameters of sandpebble soil are obtained through laboratory experiments. Based on the experimental results, the flow characteristics of conditioned sandpebble soil are calibrated using discrete element method. The threedimensional 〖JP2〗model of soil chamber and screw conveyor is established by SolidWorks, and the conveying performance of conditioned sandpebble soil is simulated by EDEM. Conclusions are as follows: (1) When the 20% foam injection ratio is used for conditioning, the slump value is 14.8 cm, and the flowability and pressure maintaining capacity of soil are all ideal. (2) The soil velocity in soil chamber shows an inverted triangle distribution with the opening of the screw conveyor as the vertex, and the velocity in the inverted triangle area is faster, which is 2~8 cm/s, while the velocity on both sides of the soil chamber is slower, which is basically below 2 cm/s. (3) The particle pressure in the screw conveyor is far less than that in the soil chamber, which indicates that the fluidity of sandpebble soil is poor. (4) The particle velocity is slower than that of the screw blade, which leads to 44.5 %～47.7 % of the transportation efficiency of the screw conveyor.

Key words: earth pressure balance shield, sandpebble layer, soil conditioning, transportation performance, discrete element method