泡沫稳定性对土压平衡盾构砂卵石渣土改良效果

为确保土压平衡盾构在砂卵石地层施工时切削的渣土具有良好的工程特性，以成都轨道17号线明九区间2号风井—九江北区间为背景，采用不同稳定性的泡沫剂分别掺入卵砾石含量为20%、40%和60%的砂卵石渣土中，开展室内坍落度试验、渗透试验和喷涌试验，研究各种泡沫土流动性、渗透性和时效性的变化规律，探讨泡沫剂稳定性与砂卵石渣土的适应性。结果表明：稳定性好的泡沫能够适应卵砾石含量低于60%的砂卵石土层，即泡沫稳定性的提高有利于扩大砂卵石地层的适用范围；稳定性好的泡沫剂能够保持改良砂卵石渣土掘削排渣全过程良好的流动性、抗渗性；过量的泡沫掺入改良的砂卵石渣土易发生离析，造成改良后的渣土难以达到良好的和易性；泡沫改良砂卵石渣土的喷涌压力可作为检验改良效果的重要指标。

Effect of foam stability on improvement of sandy pebble stratum in EPB shield tunneling

In order to ensure the engineering properties of sandy pebble soil during EPB shield tunneling through the sandy pebble stratum, foam agents of different stability were added to the sandy pebble stratum with 20%, 40% and 60% pebble content under the background of Mingjiu section No.2 air shaft to Jiujiangbei section of Chengdu rail line 17. Indoor slump test, seepage test and spewing test were carried out to study the changing laws of fluidity, permeability and time-dependent nature, which reflects the adaptability between the stability of foam agent sand and sandy pebble soil. The results show that: 1)The foam agent with good stability can adapt to sandy pebble soil with less than 60% pebble content, that is, foam stability is beneficial to enlarge the application scope of sand cobble soil; 2)The foam with good stability can keep the good fluidity and impermeability in the whole process of excavating and discharging the conditioned sandy pebble soil; 3)Excessive foam mixed into the improved sandy pebble soil is easy to disintegrate, which means that the improved soil is difficult to achieve good workability; 4)The gusher pressure of improved sandy pebble soil is an important index to test the improvement effect.