为探明隧道渗漏时聚氨酯的堵漏机制，设计并开展盾构隧道渗漏与聚氨酯注浆堵漏模型试验，通过试验分别对不同地层中隧道渗漏引发的外部地层侵蚀发展规律以及注浆堵漏的作用机制进行研究。研究表明： 1）隧道渗漏后砂土与粉土地层周围孔隙水压力迅速下降，水在压力差的作用下以渗流形式向渗漏点补给，造成周边地层侵蚀破坏，但2种地层侵蚀发展规律不同。 2）砂土与粉土地层中聚氨酯注浆堵漏机制相似，均可分为3个发展阶段，第1阶段聚氨酯反应释放大量气体，抵抗渗流水压；第2阶段聚氨酯固化，封堵渗漏通道，实现堵漏效果；第3阶段聚氨酯彻底固化，引起隧道结构外部荷载重分布。 3）由于砂土与粉土地层渗流侵蚀规律不同，聚氨酯注浆堵漏效果有所差异，粉土地层注浆堵漏效果更好。

To investigate the sealing mechanism of polyurethane for tunnel leakage, a model test of tunnel leakage and polyurethane sealing is designed and conducted. The development process of external stratum erosion triggered by tunnel leakage in different strata is discussed. The following conclusions are drawn: (1) The pore water pressure decreases rapidly after tunnel leakage both in sandy and silt soils, and the water is recharged to the leakage point in the form of seepage under the action of pressure difference, resulting in the seepage erosion of the surrounding strata. The two different strata show different erosion development patterns. (2) The leakage sealing mechanism by polyurethane grouting in the sandy and silt soils is similar, and it can be divided into three phases: the first phase, the polyurethane reacts with water and releases a lot of gas to resist seepage water pressure; the second phase, the polyurethane consolidates, thus seals the leakage channel and realizes the leakage plugging effect; the third phase, the polyurethane consolidates completely, resulting in the redistribution of the external load of the tunnel structure. (3) Due to the difference in seepage erosion patterns between sandy and silt soils, the sealing effect of polyurethane varies in different strata, and the effect of grouting and sealing in silt strata is relatively more obvious.