土压平衡盾构在砂性地层中施工时，土舱内的土体很难形成塑性流动状态，土舱压力平衡难以建立，易导致开挖面失稳崩塌、排土不顺畅、地表变形过大等影响盾构推进的问题。为确保盾构顺利推进，找出适应于该地层的改良剂及改良参数，对砂性地层土体改良进行研究。针对砂性地层采用添加泡沫剂和膨润土等方法进行改良，分析泡沫半衰期及发泡倍率随泡沫浓度变化的规律，膨润土泥浆黏度及相对密度随泥浆浓度变化规律，找出泡沫剂最优发泡浓度及膨润土最佳浓度，通过坍落度试验确定改良剂注入比，通过现场掘进试验分析改良效果，研究出适用于砂性地层的渣土改良方案。

The plastic flowability of soil in chamber during earth pressure balance (EPB) shield tunneling in sandy strata is bad, which would lead to collapse of excavation face, unsmooth mucking and large ground surface settlement. As a result, the soil should be improved so as to guarantee smooth advancing of the shield. The ground conditioning is carried out for sandy strata so as to find the applicable ground conditioning agent and conditioning parameters. The foaming agent and bentonite are used to improve the sandy strata. And then, the relationship between foam halflife period and foam concentration, that between foaming multiplying power and foam concentration, that between viscosity of bentonite slurry and slurry concentration, and that between specific gravity of bentonite slurry and slurry concentration are analyzed, so as to determine the best foam concentration and bentonite concentration. Meanwhile, the injection ratio of conditioning agent is determined by slump test. Finally, the soil conditioning effect is testified by field shield advancing, and a rational ground conditioning scheme for sandy strata is proposed.