土压平衡盾构在不同的地层进行渣土改良的关键是选择合适的改良剂，纯砂层施工中最常用的改良剂就是膨润土泥浆，目前已开始尝试使用聚合物进行改良。本文选取3种典型的聚合物，研究聚合物溶液特性与聚合物浓度、搅拌时间和静置时间的关系，并选择合适的聚合物对粗砂试样进行塌落度试验、渗透试验和直剪试验的室内试验研究。研究结果表明，针对粗砂地层（含水率10%左右），0.3%的PAM聚合物溶液注入率为20%~25%时，能有效增强粗砂的流动性和黏聚性，降低渗透系数和摩擦因数，满足土压平衡盾构施工要求。

The modifying agent is very important in ground conditioning of different strata during EPB shield tunneling. The bentonite slurry is a common ground conditioning agent in pure sand stratum, and the polymer is still under experiment. The relationships between characteristics of 3 kinds of polymers and concentration, mixing time and setting time are studied, and then indoor experimental study of slump, permeation and direct shear of coarse sand samples by polymer. The study results show that the fluidity and cohesiveness of coarse sand can be strengthened and the permeability coefficient and friction coefficient of coarse sand can be minimized when injecting 0.3 % PAM polymer for about 20%-25% in coarse sand with water content rate of 10%.