Tunnel Lining Design for a Strike Slip Fault Rupture on Westside Purple Line Extension Project–Section 2

Several underground projects in seismic areas are currently dealing with active fault crossings, in such locations the tunnel lining performance is a key element for the project’s success. The Westside Purple Line Extension Project–Section 2 (WPLE2) in Los Angeles is crossing a zone affected by Santa Monica Fault. Advanced three-dimensional numerical models were developed to capture the tunnel lining response to several fault rupture scenarios. A special precast concrete tunnel lining (PCTL) was designed to accommodate the imposed displacements on the tunnels due to the risk of a strike slip fault rupture. This innovative design was originated as a value engineering idea put forth by the Design Builder (Tutor Perini and Frontier Kemper) for an improved tunnel lining system that was more easily constructed and reduced long-term maintenance issues. The tunnel lining incorporates numerous special seismic provisions to safely accommodate the imposed fault displacements during a Maximum Design Earthquake (MDE) event. Finally, a physical testing program was developed in conjunction with the University of California San Diego (USCD) to physically test all key aspects of the special lining, document actual behavior, and allow for refinement of the structural design.