Laboratory tests on conditioning the sandy cobble soil for EPB shield tunnelling and its field application: Fid-Bau Portal

Laboratory tests on conditioning the sandy cobble soil for EPB shield tunnelling and its field application

Xu, Qianwei / Zhang, Lianyang / Zhu, Hehua / Gong, Zhengyu / Liu, Jianguo / Zhu, Yaohong

Highlights • According to the slump value and its water contents, the natural sandy pebble soil in Beijing area can be divided into three groups of dry, lower water content, high water content. • The flow plasticity of sandy pebble soil is highly sensitive to water content. Therefore, it is necessary to develop the corresponding optimization soil conditioning scheme according to the water content of different soil groups before the shield tunneling. • For the dry sandy pebble soil (W < 5%), the ideal addition ratio of bentonite slurry is 7%, while that of foam is 40–50%. For the low water content sandy pebble soil (5% < W < 9%), the ideal addition ratio of bentonite slurry is 7%, while that of foam is 5% to 15%. For the high water content sandy pebble soil (W > 9%), it is necessary to first add appropriate amount of polymer solution to reduce water, and then inject a certain amount of foam to improve the soil flow plasticity.

Abstract During the construction of the interconnection tunnel from Tianqiao Station to Yongdingmen Station of Metro Line 8 in Beijing, the Earth Pressure Balance (EPB) shield machine had to excavate in sandy cobble soil. Because the sandy cobble soil has varying moisture content along the tunnel route and shows the characteristics of loose particle structure, large pores and no cohesion between the cobble particles, it is difficult to stabilize the support pressure acting on the cutting face and transport the muck. To effectively and efficiently use the EPB tunnelling in such situations, a series of laboratory tests on conditioning the sandy cobble soil to a reasonable quality were conducted, and the influence of water content and additive amount on the conditioning effectiveness was studied. Based on the test results, the optimal soil conditioning schemes corresponding to the water content of different soil groups were proposed. Finally, the laboratory test results were used to guide the soil conditioning in the field and the measured field data showed that the conditioned material fulfills the required standard for an EPB application.