In-situ measurements of shield machine receiving in foamed concrete

The foamed concrete can be used in the shield machine receiving to stabilize the ground near the soft eye and to prevent water inrush. One of the critical points of this method is to control the shield tunneling parameters. Based on the shield machine receiving in the foamed concrete at Yunshan Road Station of Shanghai metro line No. 14, the critical parameters, change of pressures on end and side walls, deep displacements of the foamed concrete and their correlation during the tunneling process in the foamed concrete are studied through in-situ measurements. According to the analysis, the main findings are as follows: (1) The magnitude and fluctuation of thrust, torque and pressure in the earth cabin all experience a "down then up" process. (2) When the shield advances in the foamed concrete, the pressure increment on the end wall is more significant than that on the side wall. The change of pressure on the side wall is 20~30 kPa, while the maximum pressure increment on the end wall is up to 120 kPa, which is 6~7 times the initial value. (3) The pressure on the end wall accumulates in a "zigzag" pattern with the starting and stopping of the advance cycle of shield construction. (4) As the cutter head is closer to the end wall, the pressure increment generated by the unit advance distance increases accordingly. (5) The foamed concrete in front of the shield presents a "convex distribution" along the advancing direction. The pressure increment on the vault of the end wall is the minimum, with an increase of about 60 kPa in the middle and about 120 kPa in the bottom. These results can provide an essential reference for shaft design, material optimization and parameter control. The successful implementation of this project also lays a foundation for the further popularization and application of the proposed method.