Abstract: The traditional underground excavation method can hardly be applied to the saturated soft soil with high water content and low bearing capacity, while the piperoof undercutting method provides a new way for soft soil excavation construction. At present, the design and construction experience of piperoof undercutting method are not mature, which leads to great difficulty. The risk control is particularly important during construction. Hence, based on the engineering practice of the piperoof section of Guiqiao Road Station on Shanghai Metro Line No. 14, some risk factors such as advancing precision of piperoof, MJS reinforced underground pressure control, lining wall overturning, melting and grouting, collapse and water gushing during excavation are discussed from the perspective of risk control, and the corresponding countermeasures are put forward. The analytical results show that: (1) It is feasible to construct large crosssection underground space by piperoof undercutting method in soft soil, and the construction risk is generally controllable. (2) The jacking process is the basis for the implementation of piperoof undercutting method, the process of excavation and support is the key process for the construction risk control and also the main factor causing ground subsidence.

Key words: tunneling engineering, piperoof undercutting method, construction risks, countermeasures, saturated soft soil