Experimental assessment of Soil/metal interface adhesion behaviours of EPB shield Machines

In order to effectively diminish clogging of EPB shield machines, it is an urgent need to systematically understand the soil/metal interface adhesion behaviours. Here, a series of piston pull-out tests are proposed to systematically understand the soil/metal interface adhesion behaviour by the optimal selection of clayey soils such as kaolinite, montmorillonite, bentonite and completely decomposed granite. For all of these clayey soils, the adhesion stress first increases and then decreases with an increase of water content, while it increases linearly with the increase of compression pressure. Besides, plating chrome as a hydrophobic layer could effectively decrease the adhesion stress of the clay. The influence of metal surface structure and compression time is limited. Based on the test results, we proposed a modified clogging potential assessment diagram with water content, adhesion stress, and compression pressure as reference indexes. Adhesion stress can be used as a reference index to evaluate the risk of shield clogging. The diagram is validated by four clayey soils. This work systematically reveals the soil/metal interface adhesion behaviours and evidently provides a reference index for reducing clogging of EPB shield machines.