Foam plays a crucial role in conditioning the mechanical properties of coarse-grained soil during earth pressure balance shield tunneling.Experimental findings have shown that an appropriate foam injection ratio impro...Foam plays a crucial role in conditioning the mechanical properties of coarse-grained soil during earth pressure balance shield tunneling.Experimental findings have shown that an appropriate foam injection ratio improves the workability and compressibility of conditioned soil,while reducing its shear strength under undrained conditions.Understanding how foam operates in soil pores is essential for interpreting these phenomena.This study utilized a theoretical two-dimensional(2D)model to analyze the effects of gas saturation,gas-liquid interface,and gas dissolution on the undrained mechanical properties of foamconditioned soil.Based on these analyses,a constitutive equation was developed,using the transition void ratio,compression index and contact coefficient as key parameters to describe the relationships among vertical stress σ_(v),void ratio e_(c),and shear strengthτ.The undrained mechanical properties calculated by the 2D model align well with experimental observations,indicating that while foam enhances the bonding force between soil particles,both excessive and insufficient gas saturation,along with larger contact angles,notably undermine this enhancement,resulting in unsuitable workability.A gas saturation of 0.5-0.8 is recommended for soil conditioning.Under typical chamber pressures,the effects of gas-liquid interface and gas dissolution on compressibility and shear strength are negligible.The constitutive equation demonstrates excellent agreement with experimental data,and can well predict the variations in σ_(v)-e_(c)-τ.This study contributes to understanding the role of foam in soil pores,and the developed constitutive equation serves as a valuable reference for describing the undrained mechanical behavior of foam-conditioned coarse-grained soil.展开更多
Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this ...Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this study,a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed.In contrast to conventional foam-conditioned sands,the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam,and the initial permeability coefficient decreases by approximately two orders of magnitude.It also exhibits a suitable workability,which is attributed to the enhanced capability of the thickened foam to condition sandy soils.In addition,the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect,and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.展开更多
基金financial support from the National Natural Science Foundation of China(Grant No.51979144)the State Key Laboratory of Hydroscience and Engineering(Grant No.SKLHSE-2024-B-02).
文摘Foam plays a crucial role in conditioning the mechanical properties of coarse-grained soil during earth pressure balance shield tunneling.Experimental findings have shown that an appropriate foam injection ratio improves the workability and compressibility of conditioned soil,while reducing its shear strength under undrained conditions.Understanding how foam operates in soil pores is essential for interpreting these phenomena.This study utilized a theoretical two-dimensional(2D)model to analyze the effects of gas saturation,gas-liquid interface,and gas dissolution on the undrained mechanical properties of foamconditioned soil.Based on these analyses,a constitutive equation was developed,using the transition void ratio,compression index and contact coefficient as key parameters to describe the relationships among vertical stress σ_(v),void ratio e_(c),and shear strengthτ.The undrained mechanical properties calculated by the 2D model align well with experimental observations,indicating that while foam enhances the bonding force between soil particles,both excessive and insufficient gas saturation,along with larger contact angles,notably undermine this enhancement,resulting in unsuitable workability.A gas saturation of 0.5-0.8 is recommended for soil conditioning.Under typical chamber pressures,the effects of gas-liquid interface and gas dissolution on compressibility and shear strength are negligible.The constitutive equation demonstrates excellent agreement with experimental data,and can well predict the variations in σ_(v)-e_(c)-τ.This study contributes to understanding the role of foam in soil pores,and the developed constitutive equation serves as a valuable reference for describing the undrained mechanical behavior of foam-conditioned coarse-grained soil.
基金The financial support from the National Natural Science Foundation of China(Grant No.52022112)the Fundamental Research Funds for the Central South University(Grant No.2023ZZTS0366)are acknowledged and appreciated.The authors are also grateful for the help from Dr.Ji Zhao of China University of Mining and Technology.
文摘Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this study,a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed.In contrast to conventional foam-conditioned sands,the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam,and the initial permeability coefficient decreases by approximately two orders of magnitude.It also exhibits a suitable workability,which is attributed to the enhanced capability of the thickened foam to condition sandy soils.In addition,the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect,and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.
