盾构砂性渣土-泡沫混合物渗透性影响因素研究

Study of Influencing Factors of Permeability of Sand-Foam Mixture for Shield Tunneling

渣土改良是确保土压平衡盾构在砂性地层中安全高效掘进的重要措施。目前盾构渣土常用的改良剂是泡沫剂,泡沫与砂性渣土混合后能有效降低刀盘扭矩、提高渣土的抗渗性。为研究盾构砂性渣土-泡沫混合物渗透性的影响因素,通过常水头渗透试验,从砂土级配、泡沫剂体积分数以及泡沫注入体积比3个方面分析混合物渗透系数的变化规律。结果显示:1)混合物的渗透系数与等效粒径d20呈正相关变化;2)随着时间的增加,混合物的渗透系数K20逐渐增加;3)随着泡沫剂体积分数的增大,混合物的渗透系数先减小后增大;4)当泡沫的注入体积比达到一定值时,混合物的渗透系数趋于稳定。

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 d20.（ 2） With the increase of time,the permeability coefficient K20 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.