TBM tunnelling on the Upper Diamond Fork tunnel in Utah, US, by the Obayashi/WW Clyde & Co JV is more than 50% into the 6.9km long drive. The JV launched its 3.8m Robbins TBM refurbished by Herrenknecht Tunnelling Systems in October 2000 and by late April 2001 had reached the 3.9km mark.
The rock in each of the tunnel’s three geological reaches is hard and competent and support requirements comprise Split Set rockbolts and with steel sets in the faulted zones.
Meanwhile, the JV has started work on other elements on the $53M design and build contract for the Central Utah Water Conservancy District (CUWCD) irrigation program. Work is progressing on installation of 2,000m of 2.4m diameter pipeline and there is a large underground flow chamber to be excavated on the tunnel line, once the TBM has holed through. There are two 215m deep shafts to be raise bored onto the chamber. One is to connect water inflow to the new tunnel from the Sixth Water outlet at the end of the Syar Tunnel in the Bonneville Unit of the CUWCD’s Central Utah irrigation project.The other is to provide access for maintenance into the valve chamber.
The single tunnel drive of the design-build option submitted by Obayashi/WW Clyde & Co JV and its contract designers, Jacobs Associates of San Francisco (in association with Camp Dresser McKee and Golder Associates) replaces the two tunnels and the pipelines of the original base design. This eliminates the impact of heavy construction in the river valley canyon. Hole through is scheduled for the end of July 2001 and completion for late 2003.