Rufi Hydropower Plant - Latest Technology Enables Large Diameter Curved Microtunnel Below Railways

Abstract

Using a recently completed penstock of a hydropower project in Switzerland as an example, this paper shows the capabilities of today's technologies regarding curved microtunneling. In highly permeable coarse gravel with boulders, a 1770 ft long, 126 inch inner diameter / 150 inch outer diameter pipe had to be pushed in a 3D compound S-curve alignment with radii as small as 920 ft. The pipe line had to cross under existing infrastructure like a sewer line, railway line and an old arch channel with an overburden of partly as low as 2 ft. As the railway line remained operational throughout the under passing of the TBM, a geodetic monitoring system was installed providing continuous information about induced deformation as well as horizontal and vertical displacement. On the last part of the drive the machine was steered steeply upwards to minimize the depth of the receiving pit and therefore the dewatering systems resulting in significant cost savings. VMT's "SLS-Microtunneling LT" navigation system ensured the proper alignment. The 920 ft radius was done using 9.8 ft long pipes. This was accomplished by the application of the Jackcontrol® Hydraulic Joint (Jackcontrol® System), which allows large joint rotation angles without reduction of jacking forces. On this drive, the gap between the pipes on the inside of the smallest radius was half an inch wide while on the outside it was 3 inches. Thanks to the Jackcontrol® real-time monitoring system, the pipes remained without any damage and the Jackcontrol® joint design ensured the water tightness of the pipe coupling successfully.

Techniques