扬州瘦西湖隧道采用泥水盾构穿越全断面硬塑性黏土地层，施工停机后多次出现地表塌陷事故。利用室内试验研究硬塑性黏土浸水条件下的崩解、软化特性，结合现场实测数据分析该工程地表塌陷的原因，进一步讨论此类破坏发生的过程，据此提出泥水盾构在全断面硬塑性黏土地层施工时地表塌陷的预防措施。研究表明：泥水盾构停机使开挖面硬塑性黏土在泥水浸润下发生崩解、软化，使开挖面上方形成局部孔洞；随着时间延长，局部孔洞逐渐向上发展直至地表，最终形成地面局部塌陷。泥水盾构在硬塑性黏土地层施工时，应当避免停机；当必须停机时，应尽量缩短停机时间，避开建筑地段，同时加强地面监测，必要时应在开挖面上方地层进行注浆加固，防止坍塌破坏。

The Yangzhou Slender West Lake tunnel passes through the hard plastic clay stratum by slurry shield machine in full section. During the construction process, surface subsidence accidents occurred many times after halting the slurry shield machine. The disintegration and softening of hard plastic clay in soaking condition are investigated by experimental study. The analysis of reason of surface collapsing by combining with field data, and the discussion about the procedure of surface collapsing propose corresponding preventive measures on collapsing in slurry shield construction in the hard plastic clay stratum. This study concludes: disintegration and softening of hard plastic clay occur when the slurry shield shutdown in slurry soaking condition, which generates the local cavity above the excavation face. With the time prolonging, the local cavity gradually develops to the surface, and ultimately forms the ground collapse. It is suggested to avoid halting machine when slurry shield go through full section hard plastic clay stratum. When halting machine is inevitable, reducing the halting time, avoiding the building region, meanwhile strengthening the monitoring and grouting reinforcement in the stratum above the excavation face are suggested to prevent collapsing.