Pressure infiltration characteristics of foam for EPB shield tunnelling in saturated sand – part 1: ‘clean’ foam

• DOI: 10.1680/jgeot.19.p.187
• Publication Date: 2020-12-04T17:29:45Z
• Authors: Tao Xu; Adam Bezuijen; Markus Thewes
• Keywords: Infiltration (HVAC); Capillary pressure

Infiltration of pressurised foam into saturated sand was investigated in a laboratory set-up that provided an hydraulic gradient comparable to real tunnels. Four different stages were identified the infiltration: ‘foam spurt’ (the infiltration pores sand); water flow with reduced permeability; increased and residual stage. It appears depth decreases increasing expansion ratio (FER) until limit FER (approximately 15 for foaming agent used this experiment). For higher FERs permeability remains more or less constant. also found ‘dry’ (FER = 20) is not essential formation low-permeability layer at surface; even ‘wet’ 5) can form layer. Furthermore, foam-infiltrated zone achieve In these tests, velocities lower than normal excavation velocity tunnel-boring machine. Thus there no consequently low during drilling. By comparing pore pressures measured using pressure transducers without hydrophilic filter papers, capillary found.