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

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.