Study on Mud Fluid Properties in Sandy Cobble Stratum to Control the Risk of Cutting Face Instability of Slurry Shield

The construction of Beijing Underground Zhijing Line uses large-diameter slurry shield under the situation of sandy cobble stratum for the first time in Beijing. Since more than 95% of the soil stratum excavated by shield is cobble and circinal gravel, and the shield tunnel passes through long-distance water-rich zone with the largest permeability coefficient 1.74 x 10(-3)m/s and the largest water pressure 0.3Mpa, it is quite important to stability the cutting face. The main method to stability the cutting face of slurry shield is using high-quality mud and providing proper mud pressure. Mud with high-quality could form the mud membrane in a short time, which makes mud pressure perform on the cutting face effectively. Based on the analysis above, some tests on mud properties were done to study the adaptability of mud to ground by a home-made device to reduce the potential risk of cutting face instability, which could also provide important reference for future tests.