Abstract: When tunnel excavation in the cohesive soil formations, the shielded tunnel excavation drill bits are prone to be clogged. To investigate the effectiveness of the antiadhesion coatings on the drill bits, largescale direct shear tests were conducted to evaluate the changes in the adhesive strength for different soil samples with varying consistency indices. A comparison was made between the adhesive strengths at the interface of metal blocks with and without antiadhesion coatings, and the mechanism of the effectiveness of the coatings was explained. The results showed that, with an increased shear displacement, the shear stress at the interface between the clay and the metal initially sharply increased, followed by a gradual increment. When the consistency index was less than 0.6, the adhesive strength at the claymetal interface showed minor variations. In the range of 0.6 to 1.2 consistency index, the adhesive strength at the claymetal interface experienced a rapid increase with an increasing consistency index. When the consistency index exceeded 1.2, the adhesive strength at the claymetal interface remained essentially constant. The antiadhesion coatings significantly increased the contact angle on the surface of the metal blocks, reducing their hydrophilicity. As a result, the adhesive strength at the interface between the metal blocks with the antiadhesion coatings and the cohesive soil was significantly lower than that between the metal blocks without the coatings and the cohesive soil, thereby reducing the risk of shield clogging in tunneling.

Key words: Cohesive Soil Formations, Mud Clogging Cakes in Shielded Excavation, Adhesion Strength, AntiAdhesion Coating