钱塘江盾构越江隧道最小覆土厚度的确定

Determination of minimum thickness of overburden layer for shield tunnel through Qiantang River

钱塘江洪水冲刷河床与大潮回淤交替出现,必将影响盾构越江隧道安全。如何合理地确定越江隧道的埋深,既确保隧道安全,又降低工程造价,是一个迫切需要解决的问题。已有的研究成果认为,300年一遇的罕见洪水冲刷河床的最大深度可达16m,据此初步选择了河床冲刷后最小埋深分别为3.5m和4.0m两种隧道埋设方案,开展了隧道抗上浮研究。研究结果表明,考虑隧道周围土体和管片环间纵向螺栓的剪切抗浮效应时,两种方案均能够满足抗浮要求。但施工期刚脱出盾尾的管片环在未硬化注浆体的浮力作用下,大大增加隧道上浮的可能性,需要加强施工期的管理工作,减少对周围土体扰动。

It is of common occurrence that the flood scours the riverbed and the back-silting takes place immediately by turn, which inevitably influences the safety of shield tunnel through the Qiantang River. Hence, how to determine the thickness of covering layers reasonably is an urgent problem to be solved to ensure the safety of tunnel and the construction cost under control. According to the completed study that the riverbed thickness decreases extremely by nearly 16 m after the heaviest flood in 300 years, two embedding schemes of subway line are selected initially. That is, the minimum overburden layer thickness of tunnel is 3.5 m or 4.0 m. The results show that the two schemes are both safe for the tunnel considering the shearing effect of the soil around the tunnel and the one of the bolts between rings. However, in construction, the possibility of floating upward for shield tunnel increases greatly under the buoyant force action of back-filled grouting. More attention should be paid to construction management to minimize the disturbance of soil around the tunnel.