为解决土压平衡盾构在富水砾砂地层中掘进土舱保压难度较大的问题，需对盾构渣土进行改良，减小其渗透性，提升土舱保压效果。依托昆明地铁4号线小—火区间盾构隧道工程，采用数值模拟手段，结合现场监测数据，对渣土改良下盾构掘进富水砾砂地层响应特征进行研究。研究结果表明： 1）随着改良渣土渗透性的降低，开挖面孔压逐渐增大，当土舱渣土渗透系数降至5×10-5 cm/s后，开挖面孔压接近原始孔压，表明改良渣土具有良好的止水性能；随着地下水位的升高，开挖面孔压逐渐增大，表明高水位对渣土止水效果的要求更高。2）小—火区间渣土渗透性较低，开挖面近似止水条件，盾构掘进过程中，开挖面附近会产生一定的超孔压，超孔压影响范围主要位于盾构前方1.5倍洞径，开挖面中心位移远小于失稳时的开挖面中心位移，开挖面稳定性较高。3）由于盾构渣土渗透性较低，盾构掘进会在周围形成较大的超孔压，同时渗透系数较小的渣土可以有效阻止开挖面前方地下水的自由渗流，提高开挖面的稳定性，减小地表沉降。4）随着地下水位的升高，地表沉降和地层超孔压有增大的趋势，维持开挖面所需支护应力迅速增加，水位高度对开挖面支护应力的影响十分明显。

It is difficult to maintain the pressure of the soil chamber when the earth pressure balance(EPB) shield tunnels in the waterrich gravel sandy strata. Therefore, it is necessary to improve the residual soil of the shield to reduce its permeability and improve the pressure holding effect of the soil chamber. A case study is conducted on the Xiaocaiyuan stationNorth Railway station section shield tunnel project of Kunming metro line 4, and the response characteristics of waterrich gravel sandy strata tunneled by shield under soil conditioning are examined using numerical simulation and field monitoring data. The results show the following: (1) With the declining permeability of conditioned soil, the pore water pressure on excavation face gradually increases, and when the permeability coefficient of conditioned soil in soil chamber decreases to 5×10-5 cm/s, the pore water pressure on excavation face will approach to the initial pore water pressure, which indicates that the conditioned soil with relatively low permeability has a good waterproof performance. With the rising groundwater level, the pore water pressure on excavation face gradually increases, indicating that the waterproof performance of conditioned soil is more important for the EPB shield tunneling in stratum with high groundwater level. (2) The permeability of conditioned soil in the Xiaocaiyuan stationNorth Railway station section is relatively low that the excavation face is of waterresisting condition to some extent. In the process of shield tunneling, a certain excess pore water pressure will be developed near the excavation face. The affected area of excess pore water pressure is mainly 1.5 times of the tunnel diameter in front of the shield. The soil displacement of the excavation face is far less than that of the excavation face when instability occurs, indicating that the stability of the excavation face is high. (3) Due to the low permeability of conditioned soil, a relatively high excess pore water pressure will be developed around the shield during tunneling. Meanwhile, the conditioned soil with low permeability can effectively limit the free seepage of groundwater in front of the excavation face, which can improve the stability of excavation face, and reduce the construction ground settlement. (4) With the rising groundwater level, the ground settlement and excess pore water pressure tend to increase, causing the support pressure required to maintain the stability of excavation face increases rapidly, which indicates the groundwater level has notable impact on the support pressure on excavation face.