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

Abstract

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 < 0.75). The results proved that water content is a key parameter in adhesion stress variation and clogging behavior of clayey materials. The results of the direct shear test on clay/clay and clay/steel interface indicate that with increasing water content, the cohesion of soil decreases and tangential adhesion to the steel surface tends to increase. Based on piston pullout test, the normal adhesion stress of samples increased to a peak value at IC = 0.65 to 0.75. The results obtained in this study indicate a moderate to high risk of clogging in the mechanized excavation of subway lines in the study area while encountering clayey layers.