The Arrowhead Tunnels project forms part of California's Inland Feeder project, which is a critical component of a water transfer and storage system enabling the delivery of an additional 2.4 million cubic meters of water a day.

The segmental linings for the Arrowhead east and west tunnels are to be constructed behind pressure balance tunnel boring machines to form 4.88m internal diameter tunnels, within which steel and concrete pipes will be constructed to form the permanent works.

key factors:

	bolted and gasketed segmental tunnel lining
	over 300m design external water pressure
	high load on radial joints
	testing regimes for gaskets and radial joints
	design and build

Halcrow undertook the detailed design of the segmental lining for the tunnel sub-contractor, Traylor-Shea-Ghazi, who worked for main contractor Shea-Kenny.

The bolted and gasketed lining consisted of 5 segments plus a key and had a structural thickness of 330mm, with straight "spear" bolts through both radial and circumferential joints.

The design was developed using two different concrete strengths to suit the varying loads within the tunnel drives (approximately 50MPa and 65MPa cube strength). The segments were reinforced and particular attention was given to the radial joints where high stresses meant an onerous design situation had to be economically accommodated.

A special lining was also developed that allowed the use of a grout bag on the outside of the lining, to form an external seal between the lining and the rock in areas of high water flow.