Mechanized tunnelling under high pressure
In the U.S. state of Nevada, a machine from Herrenknecht has bored a tunnel for the Las Vegas water supply. In the process, new world records were set: the high-tech boring machine (Ø7.2 meter) had to withstand water pressure of 15 bar. Las Vegas draws 90% of its water from Lake Mead, the largest reservoir in the country. But its water level is dropping, the existing water intakes are at risk. In order to tap the water deep down in the lake in future, for three years the tunnel boring machine bored its way through extremely adverse ground conditions.
On December 10, 2014, with centimeter accuracy the Herrenknecht Multi-mode TBM reached its target at the bottom of Lake Mead. Within three years it has dug a 4.4 kilometer tunnel under the largest reservoir in the U.S.A
VMT has its share at this success by providing several products on the machine that cared for an advance as accurately and efficiently as possible. Thanks to our proven TUnIS TBMLaser the usually good breakthrough accuracy could be achieved here, too. During tunneling, our TUnIS Navigation Office and IRIS.tunnelviewer guaranteed uninterrupted provision of engineering and navigation data in real time.
The Las Vegas machine launched in late 2011 from a 180 meter deep shaft at the lakeside. For months it struggled through shattered rock and clay with full hydrostatic pressure caused by water from the lake. In doing so it had to withstand pressures of up to 15 bar, an absolute novelty in mechanized tunnelling. As a comparison: 15 bar is like diving at 150 meters or at a pressure of 15 kg per cm². With a diameter of over 7 meters and a length of 190 meters, immense forces were applied on the machine.
Work on Intake No.3 is due for completion in the summer of 2015. The new extraction tunnel will then take the lake water via Intake No.2 to a drinking water treatment plant, from where it will be supplied to households and businesses.
1.5km of pipe jacking under the Elbe River became with the good cooperation with A.Hak Drillcon from the Netherlands a great success with a precise breakthrough and with comprehensive navigation and safety technology delivered by VMT.
One of the world’s longest pipe-jacking jobs crossed under the Elbe River at Hetlingen west of Hamburg in complex geology for the construction of a casing tunnel for a gas pipeline. At a groundwater pressure of up to 4bar, sandy gravel soil with stones, layers of boulder clay featuring larger rocks as well as layers of clay which tend to be very sticky, challenged the tunnel boring machine’s cutterhead.
VMT joined the jobsite with a comprehensive range of navigation, survey and monitoring technology. Using IRIS.microtunnel – a web-based data management and monitoring system – it was, among other things, possible to permanently monitor all support pressures while comparing them in parallel with the fluctuating tides of the Elbe. Furthermore, the comprehensive HADES communication system featuring several modules such as video surveillance, fire alarm or RFID jobsite access control was used for the first time in Germany.
The Herrenknecht AVND machine (AVND2400AB , Ø 3,025mm) hit the target precisely and on time on December 4, 2015 on the Lühesand Island on the Elbe after 112 days of tunnelling only.
The VMT GmbH was supported by Check-Point Vermessung, which took over the basic surveying and control surveys.