Experimental study on adhesion reduction at the clay-metal interface through chemical conditioners and electro-osmosis synergetic conditioning in EPB shield tunneling

Abstract

When Earth Pressure Balance shield tunneling passes through cohesive strata, excavation efficiency is often significantly reduced due to issues such as cutter head adhesion, mud cake formation and chamber clogging. Traditional mechanical methods have proven ineffective in mitigating cutterhead adhesion. This study proposes a synergistic adhesion-reduction method combining anti-clay agents and electro-osmosis. The adhesion reduction and desorption mechanisms were systematically investigated through tilted plate test, Atterberg limits measurements, zeta potential test and microstructural analysis. The efficacy and intrinsic mechanisms of adhesion reduction and desorption under single chemical conditioning, single electro-osmosis and their synergistic conditioning were evaluated across varying bentonite contents, water contents, and voltage levels. The results showed that when using single anti-clay agent conditioning, although soil aggregation can be effectively reduced, adhesion at the clay-metal interface cannot be adequately addressed. With single electro-osmosis conditioning, when the threshold conditions of water content > 35 % and voltage > 5 V are met, effective adhesion reduction and desorption at the interface can be achieved. Moreover, higher bentonite content leads to longer mud cake slip-off time. Under chemical-electric synergetic conditioning, the water content threshold decreases to 30 % and the voltage threshold to 3 V, with slip-off time shortened to one-fifth of that under single electro-osmosis, greatly improving efficiency. For soil samples with varying bentonite contents, the patterns of single electro-osmosis and chemical-electric synergetic conditioning are generally consistent: mud cake slip-off time significantly decreases with increasing voltage and water content, exhibiting a distinct three-stage variation. Compared to single anti-clay agent or electro-osmosis conditioning, chemical-electric synergetic conditioning achieves superior adhesion reduction. These findings provide novel insights for resolving adhesion and clogging issues in cohesive strata.