SFT construction method

A safe and economical tunnel construction method that does not excavate at the working face

Outline of construction method

The SFT (Simple and Face-Less Construction of Tunnel) method is a construction method of simply constructing a tunnel without working face excavation. Square pipe loop member (section steel loop 1,000 x 1,000) is used as the earth retaining ball of the construction section.

At vertical apertures installed on both sides of the crossing point, square pipe loop is installed through the whole cross section and all the extension according to the structure of the target structure.

Square pipe loop is designed to reduce the frictional resistance and to separate it from the surrounding ground during propulsion or traction by redundantly arranging steel plate called Friction cut plate.
Next, the structure is built on the departure base, and square pipe loop, ground soil and structure are integrally excavated in the tunnel and extruded to the arrival side and replaced with the structure. Square pipe extruded from the reach base is recovered and earth and sand are discharged.

The internal spoil of the construction section extrudes the top, bottom, left and right of square pipe loop in a state where the member of vertical aperture temporary facility at both ends of departure and reach is constrained. If there is no site restriction that can be used on the arrival side, work efficiency will be good when the whole square pipe loop is moved horizontally to arrival side.

Features of construction method

1) Construction method of tunnels to propel structure without excavation

- Excavation is not performed at the working face because square pipe and spoil surrounded by square pipes are extruded in one piece and ridged on the arrival side.
- The ground improvement cost for working face stabilization is greatly reduced because excavation is not performed at the working face.
- The working face does not collapse and is safe because excavation is not performed at the working face.

2) It is a simple method because the main structure is extruded after square pipe loop is installed.

- It is a simple and safe construction method because it does not require the work such as working face excavation, working face earthflow facilities, working face stability in the structure (ground improvement) generally performed in the propulsion method.

- A pipe loop around the outside of the structure built in the conventional trenchless construction method is used to install the protection form. In this construction method, square pipe loop is used around the outside of the structure, enabling construction with the minimum cover soil.

- Since square pipe loop is recovered and reused, buried temporary materials are minimized, so it is environmentally friendly construction method.

4) Compared with the conventional method, the construction time can be shortened and the construction cost can be reduced.

- Since the ground improvement is minimized by simple structure and simple construction method, construction period and construction cost can be reduced compared with the conventional construction method.

5) The structure to be constructed is a simple structure.

- Old Raman Structure of Reinforced Concrete
- Quality is good because structures are built on the departure stand.
- Maintenance is unnecessary.

STF method conceptual diagram