The SEM crossover cavern in the Regional Connector Transit Corridor project in downtown Los Angeles, once completed, will be the largest tunneled excavation in Los Angeles. The cavern was initially designed with a two-drift configuration with top heading and bench, but a project schedule optimisation led RCC and MM to select a three-drift configuration while also limiting risks and improving constructability. Design-build contracts promote close collaboration of contractors and designers, which was a key advantage in planning a SEM tunnel of this magnitude. The project exemplified its importance in large transportation projects, where design flexibility is crucial to accommodate global project changes.
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