Design and construction of a cavern in Downtown Los Angeles

Overview

Los Angeles Metro is constructing a light rail corridor beneath Downtown Los Angeles - The Regional Connector Transit Corridor (RCTC). To provide operational flexibility, RCTC required a track crossover adjacent to one of the stations. Right of way constraints required the crossover be constructed at relatively shallow depth using Sequential Excavation Methods (SEM), resulting in what is believed to be the largest mined cross section in Los Angeles.

Challenges faced for the SEM cavern design and construction included strict limits for tunnelling induced displacements in surrounding structures and high seismic design loads with 2,500 year return periods. This presentation describes the design approach of the SEM cavern, with an emphasis on the seismic analysis, as well as the actual conditions faced during construction.