ABSTRACT
LA Effluent Outfall Tunnel is currently under construction for the Sanitation District of Los Angeles County. The tunnel has a 11.26 km long with a 5.5 m internal diameter it is designed to evacuate peak flows of treated water, with the possibility of becoming pressurized when combined with large in-tunnel flows. The first tunnel section is excavated in soil materials with relatively low overburden. The second tunnel section is excavated in rock materials with overburden up to 145 m and with expected groundwater pressures up to 9 bar. For the first section, the design conditions necessitate the execution of a post-tensioned system within the tunnel segments to guarantee there is enough hoop forces in the segments to remain compressed under peak flows. For the second section, the rock conditions are variable and may experience moderate to extreme squeezing ground during construction.
