Experimental study on polyurethane ring in the replacement of shield tail brush in water-rich sand strata at the coast

Abstract:

In shield tunneling， the method of replacing the shield tail brushes with grouting needs to forma closed and stable water stop ring， including a polyurethane ring and a slurry ring. This paper combines the example of shield tunneling construction in a water-rich sand strata at the coast， collects the in-situ groundwater to conduct indoor test about the polyurethane including the initial setting time， foaming rate， solid strength， etc. The results show that hydrophilic polyurethane reacts rapidly with groundwater， forming a compact and uniform consolidated body with low foaming rate and low strength， while the hydrophobic polyurethane is in the opposite state. Both can be considered to use on site actual injection at the same time， first injecting hydrophilic polyurethane， then injecting hydrophobic polyurethane with the dosage of 5∶1.The on-site application proves that the formed inclusions are stable and of good quality.

Key words:replacement of shield tail brush;water-rich sand strata;polyurethane ring;hydrophilic polyurethane;hydrophobic polyurethane