Abstract:

The paper innovates the design and construction method of ultrashallow buried excavation by introducing an example of two ultrashallow buried excavation rectangular tunnels, including prereinforcement with lock pipe roof, fullface grouting, steel arch support and excavation of both big and small crosssection, etc. The example proves the advantages of ultrashallow buried excavation when open excavation is impossible in cities and offers the following suggestions: (1) As the use of lock pipe roof is the key to success, multioperation conditions should be considered in design, and flexibility fulcrum method should be used in design calculation. In the entrance 1H range, pipe roof internal force and support reaction changes greatly, to which special attention should be paid. Afterwards it is in a normal excavation stage, pipe roof internal force and support reaction tend to be stable. (2) It is particularly important to explore the underground pipeline in detail before construction. (3) As the construction of long lock pipe roof is difficult, the drilling technology has changed from steel pipe double line restraint to one line one point constraint to make pipe roof construction smooth and feasible.

Key words: ultrashallow buried excavation, underground passage, large crosssection rectangular tunnel, lock pipe roof, pipeline protection