Experimental assessment of clayey layers for clogging of TBM in Tabriz subway lines, Iran

[Display omitted] •Adhesion and clogging tendency of clay-rich soil and rocks were investigated using different test methods.•Correlation of normal adhesion to cohesion and tangential adhesion in various IC were investigated.•It was found that clayey material may encountered on the Tabriz subway lines have medium to high clogging risk. Clogging phenomenon is defined as the excessive adhesion of clayey particles to drilling equipment that adversely affect machine efficiency. This study involves the clogging potential of clayey soil and rock samples collected from Tabriz subway lines that were tested by laboratory experiments. In order to achieve the objectives of this study, a series of analyses were carried out including sieve analysis, hydrometer, Atterberg limit, slake durability, direct shear, modified direct shear test on the soil/steel interface, and piston pullout apparatus. According to USCS, the studied samples are classified as CL and CH. The clay minerals of the samples are mainly montmorillonite and illite. According to the exist diagrams and classifications based on Atterberg limits, consistency index and adhesion stress, samples are classified as medium to high risk for clogging. The maximum clogging occurrence is possible in the moisture content between 20 and 52% (IC