Abstract: To comprehensively analyze the muck cake risk of shield tunneling and plastic flow characteristics of muck, a series of tests on rotational shear, triaxial, and slump are conducted to explore the adhesion characteristics and shear strength parameters of moderately-weathered mudstone in Changchun, China. Based on muck strength, reasonable improvements for the slump of the mudstone are proposed, and their rationality is validated in actual engineering. The main conclusions drawn include the following: (1) With the increase in the water content, the (interfacial adhesion) cohesion of the moderately-weathered mudstone increases first and then decreases, and the (interfacial) friction angle gradually decreases. At the water content of 22.58%－27.36%, soil and metal exhibit a greater interfacial adhesion than cohesion. Moreover, when the water content is 15.99%－24%, the interfacial friction angle is greater than the internal friction angle. (2) The slump value is closely related to muck strength. With the increase in the slump value, the adhesion and shear strengths of the muck exhibit a rapid decrease. When the slump value is greater than 4 cm, adhesion and shear strengths show relatively small changes. In addition, at the slump value between 0.5 and 1 cm, the muck attains a greater adhesion strength than shear strength. Therefore, the slump value of moderately-weathered mudstone during shield tunneling should not be less than 1 cm, and that of muck should be as large as possible that is, more than 4 cm, to reduce the muck′s strength and increase its fluidity sufficiently.

Key words: moderately-weathered mudstone, shield, adhesion strength, shear strength, slump value, soil conditioning