Abstract:

Soil conditioning is an essential measure to enable the earth pressure balance shield to bore safely and efficiently in sandy ground. At present, the foam is the most commonly used as soil conditioner. The mixture of foam and sand can effectively reduce the torque of cutter and improve the impermeability of the soil. In order to study the influencing factors of permeability of the mixtures of sand and foam, the variation of the permeability of sand and foam mixture is studied by the constant head penetration tests in terms of gradation of sand, concentration of foam agent and volume injection ratio of the foam. The experimental results show that: (1) The permeability coefficient of the mixture has a positively linear relation with the value of equivalent particle size d20. (2) With the increase of time, the permeability coefficient K20 of the mixture gradually increases. (3) With the concentration of the foam increase, the permeability coefficient of the mixture decreases firstly and then increases. (4) When the volume fraction of the foam reaches a certain value, the permeability coefficient of the mixture trends to be stable.

Key words: earth pressure balance shield, sandy soil, foam, permeability, influencing factors