The Turtmann cut-and-cover tunnel (1,350 m long) is on the A9 motorway between La Souste and Gampel.

The tunnel was built parallel to the main railway line to the Simplon Tunnel and a 132-kV HV transmission line. From west to east it crosses a 65-kV HV transmission line, the Turtmänna River, a sewage mains, an irrigation canal, an access road to Turtmann Station, and a road bridge. Due to difficult hydrogeological conditions, the excavation support consists of 31-m-deep sheetpiles (tied back with between 1 and 5 rows of anchors) and a jet-grouted preliminary invert (max. thickness of 1.5 m). During the construction phase this system was modified over a length of about 300 m, with a diaphragm wall (1000 mm thick) with either compression braces or tie-backs at the top. The two aquifers (one of which is artesian) were lowered by as much as 15 m by means of relief wells to depths of as much as 27 m.

The twin-cell structure has convex inverts and circular tunnels. Only the approach dives are of rectangular section. The entire structure is sealed with a bituminous waterproofing compound. Bypasses reinstating groundwater flow for the upper aquifer are located every 100 metres approximately.