Abstract: Example of a tunneling case with overburden less than tunnel width and the stratum mainly composed of mixed silt and gravel materials, and a local surface runoff passing tunnel route and water ponds neighboring the tunnel as well, this manuscript presents the effects of forepoling method and associated with chemical grouting, such as diminishing on excavation disturb zone, reinforcing on mixed silt and gravel stratum and groundwater sealing up for the potential water inflow. The piperoofing method enhances short term stability of excavating face and thus the swift excavating and supporting task can be achieved. The tunneling behavior is also reviewed and addressed in detail.

Key words: silty and gravel, shallow overburden, pipe-roofing method, chemical grouting, tunneling