Experimental study on the influence mechanism of soil additives on scraper wear during EPB-TBM tunnelling in abrasive sandy ground

When earth pressure balance tunnel boring machines (EPB-TBMs) tunnelling in abrasive sandy ground, soil additives are critical for promoting excavation surface stability, reducing residual soil permeability, decreasing screw conveyor torque, avoiding mud cake siltation and preventing excessive tool wear. However, the existing studies mainly focus on the first four aspects. The influence mechanism of soil additives on cutting tool wear is still unclear due to the lack of reliable test methods. In the present study, a newly developed WHU-SAT tester (Soil Abrasion Tester developed by Wuhan University) was used to evaluate the influence of conditioning additives (foam additives and bentonite slurry) on soil abrasivity. Scraper wear in additive-conditioned sand has been compared with that in water-conditioned sand to reveal the mechanism of foam additive and bentonite slurry. The soil additive parameters (solution concentration and injection ratio) were optimized to reduce scraper wear in abrasive sandy ground. The results indicate that the mitigation effect of the foam additive on scraper wear is related to the lubrication of the active agent and the cushioning of the air bubbles. The optimized foam solution concentration and foam injection ratio for the quartz sand samples are FSC = [5%, 10%] and FIR = [22.5%, 25.0%], respectively. The aggravation in scraper wear caused by bentonite slurry is related to the improvement of particle gradation and the increase of sand cohesion. The bentonite slurry parameters should be selected to keep the water content of the conditioned sand away from the peak water content to decrease scraper wear.