ABSTRACT
The main challenges related to TBM excavation under high water pressure are investigated on the example of the JWPCP Effluent Outfall Tunnel Project. The tunnel will transport secondary treated effluent from the Joint Water Pollution Control Plant in Carson, California. With a total length of approximatively 7 miles, a finished internal diameter of 18 feet, it will be excavated by using a TBM designed to cope with high water pressure up to 10 bar. The unicity of the project is due to the variety of subsurface conditions: over the first half of the alignment the tunnel runs in urban area at low overburden, while the second half of the alignment is characterized by higher overburden and water table along with extremely weak rock mass.
