Performance of Station Excavations for LA Metro K (Crenshaw/LAX) Line

This paper presents the effects of excavations in Los Angeles on the surrounding ground surface. Three large excavations with varied support systems for stations constructed as part of the K (Crenshaw/LAX) Line Transit Project provide an opportunity to acquire data through an extensive geotechnical investigation and field monitoring program to further our understanding of soil-structure interaction and excavation-induced ground deformations. The ground conditions encountered on site include alluvial deposits of silts, clays, and sands. The data acquired illustrates that ground displacement and wall deflection largely depend on the stiffness of the excavation support system. Support systems with relatively high stiffness are able to successfully limit surface settlement behind excavations. The data shows that heaving caused by unloading governs the soil response given the relatively small lateral support wall deformations. Current empirical models are unable to capture this ground behavior. An update of these empirical relations is needed to represent this behavior in support of the design of future excavations.