富水砂卵石地层大直径盾构施工过程中，易出现掌子面坍塌、喷涌、卵石沉舱以及螺旋出土器卡死等现象，同时，盾构转矩大，渣温高，一次性渣土改良体积大，使得对渣土改良的要求更加苛刻。为保证富水砂卵石地层土压平衡盾构的顺利进行，通过大量的室内试验对膨润土及泡沫剂最佳配比进行研究，并提出渣土改良剂的掺入体积分数及评价指标。研究发现： 1）膨润土的漏斗黏度随钠基膨润土掺入体积分数的增加而增加； 2）泡沫溶液发泡倍数和半衰期均随着泡沫剂体积分数的增加而增加； 3）改良渣土流动性随着膨润土和泡沫剂掺入体积分数的增加而显著提高，渗透性随着膨润土掺入体积分数的增加而降低，随着泡沫剂掺入体积分数的增加而提高。建议： 膨润土漏斗黏度不低于35 s，按照渣土体积的10%~12%掺入； 泡沫剂发泡倍数控制在15倍，按照渣土体积的20%掺入。通过现场实际渣土取样以及掘进参数分析验证了渣土改良的效果。

During the construction of largediameter shield tunnels in waterrich sandy pebble strata, the following difficulties are often encountered: collapsing tunnel faces, water gushing, rock falls, and jamming of screw cutters. Meanwhile, due to the high shield torque, high muck temperatures, and large volumes of slag, soil conditioning becomes essential. Accordingly,  many laboratory experiments are conducted to explore the optimal mixing proportion of bentonite and foaming agent, and according to analysis, proportion and evaluation indices for soil conditioning  are proposed. The following conclusions are drawn: (1) The viscosity of bentonite increases with increasing sodium bentonite ratios. (2) The foaming multiples and halflife period of the foam solution increases with increasing foaming agent concentration. (3) The fluidity of the conditioned soil significantly increases with increasing proportions of bentonite and foaming agent; the permeability of the conditioned soil decreases with increasing proportions of bentonite and increases with increasing foaming agent proportion. Finally, it is recommended that the bentonite viscosity should not be less than 35 s, bentonite volume should be 10%~12% of the soil volume, foaming multiple of the foaming agent should be less than 15, and volume of foam should be limited to approximately 20% of the soil volume. The soil conditioning effect is verified by actual soil sampling and excavation parameter analysis.