Effect of Foam Parameters on Cohesionless Soil Permeability and Its Application to Prevent the Water Spewing

Water spewing from the screw conveyor often occurs in cohesionless soil strata below the groundwater level during tunnel excavation with earth pressure balanced (EPB) tunnel boring machines (TBM). Foaming agents have been extensively employed as soil conditioner during the use of EPB TBMs to change the properties of soil, and the conditioned soil, with its low permeability, was the key to reduce the frequency of water spewing. To determine effect of foam parameters on cohesionless soil permeability, the conditioned sand permeability under different foam liquid half-lives ( T hl ) foam expansion rates (FERs), and foam injection rates (FIRs) was tested. To verify the permeability test results, a case study was carried out to optimize the foam parameters for preventing water spewing. Based on these results, this paper suggests that high-stability foaming agents with a medium FER and FIR represent an effective way to reduce cohesionless soil permeability and to prevent water spewing.