中文摘要：

盾构机在卵石含量高、粒径大的砂卵石地层中掘进时，由于土体塑流性差，土体在土舱内无法及时排出，时常出现盾构推力、刀盘扭矩异常增大，推进速度极其缓慢等现象；由于土舱内土体颗粒间力的传递是点对点，使支护压力不能有效施加到开挖面上，极易出现地表沉降超限、塌方等事故。为此，以北京地铁9号线盾构隧道工程为背景，进行砂卵石地层土压平衡盾构隧道施工土体改良试验研究。试验结果表明：采用泡沫＋膨润土作为土体改良剂对砂卵石地层土体进行改良是可行的；在土体改良过程中应根据出土量、土压力、盾构推力及刀盘扭矩等参数的控制情况，及时调整土体改良剂的注入时间、注入量等参数；在确保盾构出土量可控的前提下，采用满舱欠压掘进模式可以提高砂卵石地层盾构掘进的效率。

英文摘要：

During the tunneling of shield machine in sand gravel strata containing high content and large diameter gravels, the soil mass cannot be timely discharged from earth chamber due to poor plasticity and fluidity, which often results in such phenomena as the abnormal increase of shield thrust and cutterhead torque as well as extremely slow advancement speed. Since the force transfer among soil particles in earth chamber is point-to-point, the support pressure in earth chamber cannot be effectively applied to excavation face, which may easily result in the overrun of ground settlement and collapse, etc. Therefore, with the shield tunneling engineering of Beijing Metro Line 9 as background, soil conditioning tests are carried out in the process of EPB shield tunneling in sand gravel strata. Results show that it is feasible to adopt foam plus bentonite as soil conditioner for sand gravel strata. During soil conditioning, such parameters as the injection time and volume of soil. conditioner should be adjusted in time with the varying of these parameters, such as the volume of excavated earth, earth pressure, shield thrust and cutterhead torque, etc. Under the premise that the volume of excavated earth is controllable, the advancing mode in lower pressure can be used for improving the efficiency of shield advancing in sand gravel strata when earth chamber is full.