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

Abstract

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.

Evaluation of foam application in providing required conditioning for EPB hard rock TBMs

“…In addition to conditioned material workability, it is critically important to evaluate the permeability and design the conditioning set to make the resulting mix impermeable. Considering that the available standard methods for measuring the permeability [55,56] are not applicable to the conditioned material, and in infrequent cases where the permeability of the conditioned material in soil has been measured by researchers in the laboratory [57][58][59][60][61], the process is not standardized and more importantly cannot be applied to the rock excavated conditioned material. Authors present an innovative laboratory method for evaluating the impermeability of the conditioned material, considering the significant differences of hydrological characteristics of the rock mass and soil.…”

Numerical investigation on the spewing mechanism of earth pressure balance shield in a high‐pressure water‐rich sand stratum

“…Through laboratory tests and numerical simulation, the mechanisms of soil improvement to regulate the soil characteristics have been analyzed. Zhou and Yang (2020) found that high‐stability foaming agents with an average foam expansion ratio (FER) and foam injection ratio (FIR) were effective in reducing the permeability of cohesion less soil and preventing water spewing. According to Langmaack and Lee (2016) and Zhao et al (2018), the reduction of permeability to prevent spewing at a relatively high underground water pressure required not only foaming additives but also bentonite and polymer compounds.…”

Effect of soil conditioning on the permeability of coarse-grained soil in mechanized tunnelling

“…Zhou and Yang (2020) studied the effect of foam parameters on the permeability of cohesionless soils and their application to prevent water seepage. The results of permeability experiments and field tests indicated highly stable foaming agents with a moderate FER (=10–20 %) and FIR (=50%–75 %) as an effective means to reduce the permeability of cohesionless soils and prevent water seepage from screw conveyors [ 25 ].…”