为了解决土压平衡盾构在砾砂土地层掘进过程中，土体塑流性差、刀盘及螺旋输送机磨损严重和开挖面平衡不易保持等问题，通过自制泡沫发生器发泡，对砾砂土地层的泡沫改良技术进行室内试验研究，分析气液比、含水率和泡沫掺量对塑流性的影响和改良前后土样的渗透系数的变化规律，得出泡沫发生器气液比在30∶1～55∶1、含水率为5%～12.5%、泡沫掺量为20%～40%时，土体具有较好的塑流性，泡沫的“轴承效应”和泡沫剂中表面活性剂的亲水基团与水、砾砂土颗粒形成的氢键是塑流性提高的根本原因；使用泡沫剂改良砾砂土后，渗透系数大幅降低，掺泡沫后在280 min内渗透系数随时间变化较小，能达到10-5 cm/s，泡沫剂溶液中高分子化合物的联结和液桥力是土样具有堵水作用的原因。

The sandy gravel stratum is of unfavorable plasticity and fluidity, which is sure to induce serious wear of cutterhead and screw conveyor. Moreover, the earth pressure balance is not easily maintained and the face is easy to collapse. As a result, indoor experimental study of foaming technology for sandy gravel stratum is carried out with selfmade foam generator, the effects of foam expansion ratio（FER）, water content and foam injection ratio （FIR） on plastic flow state are analyzed, the variation law of permeability coefficient of soil before and after improvement are studied. The slump test results indicate that the optimal conditioning parameters to achieve required plastic behavior are FER of 30∶1 to 55∶1, water content of 5% to 12.5% and FIR of 20% to 40%, and the bearing effect and the hydrogen bond between hydrophilic group of surfactant with water and gravel sand particles are main causes. The permeability can reach 10-5 cm/s after using foam agent after 280 minutes; and the coupling and the liquid bridge force in the foam solution of the polymer can stop the water of soil.