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Requirement

tunnelling project

Employment Water
Geology Granitic rock with mainly Quartz monzonite
Tunnel Length 12,892 m
Diameter 5,760 mm

Solution

machine data

  Machine Type Single Shield TBM
Support Techniques Segmental Lining
Cutterhead Power 2,000 kW
Torque 2,004 kNm

Providing drinking water for the population of Los Angeles, California, is without doubt one of the greatest challenges facing the municipal authorities and local government. The mountain overlooking San Bernardino, through which a tunnel is to be drilled to pipe the water, presents quite unique challenges of its own: the aqueous rock has been heavily fissured by the San Andreas fault, which is located very close to the mountain.

The two Single Shield TBMs S-233 and S-234, manufactured by Herrenknecht, were well able to meet this challenge: they were equipped with movable shields capable of withstanding water pressures of up to 10 bar. The powerful pumps that had been installed could, if required, pump over 550 liters of water. When the machines were not engaged in tunnelling through the rock, the construction site teams stabilized the brittle rock by injecting it with colloidal silica compounds. On May 2 (S-233, Lot Strawberry Creek) and on August 20, 2008 (S-234, Lot Waterman Canyon) the jobsite teams accomplished breakthrough.