The geology of Houyenshan, Miaoli County, is Pleistocene Toukoshan formation, and major
gravel beds with thin layers of muddy sandstone. Landslides, detritus slides and debris flows are easily induced by
heavy rainfall. It has been officially declared a natural conservation area. From the satellite image, we can see a mass
of united alluvial fan on the north bank of the Da-an river impacting its water flow. Meanwhile, the gravel congeries
mainly induced by No.1 gully are reaching the east portal of the tunnel along No. 140 county road. However, using
the steel pipe-wall method to control the landslide and debris flow can be a good solution. This will prevent debris
flows from first occurring. This paper proposes the basic analysis and design steps of a steel pipe wall. Meanwhile,
some practical considerations for construction, such as the antirust arrangement of the steel pipe emersion, determination
of the casing driver, cost analysis of a single steel pipe etc., are explored.
Key Words : Debris flow, Landslides, Steel pipe-wall method, Arching effect.