Revitalization of the 42-acre Martin Luther King, Jr. Medical Campus in the Willowbrook/Compton area of South Los Angeles County began in 2011 and includes the MLK Community Hospital, Outpatient Center, Recuperative Care Center, and the Center for Public Health. This growth demanded new parking to serve the growth at the hospital and specifically a 1,430-space, 6-story parking structure. In 2016, Los Angeles County Department of Public Works (LACPW) contracted with McCarthy to design-build this much needed addition. McCarthy and its engineering team looked to Farrell Design-Build to provide foundation support for the parking structure addition to the MLK hospital campus. Farrell responded by delivering a highly resilient ground improvement system consisting of Type 2 and Type 3 Drill Displacement Column™ (DDC) for foundation support and seismic settlement control.
In August 2016, McCarthy, Jessen-Wright, AECOM, and Farrell prepared a plan to support conventional shallow footings with DDC improved ground for LACPW review and approval. The engineers for LACPW requested additional geotechnical and structural calculations to substantiate the performance and reliability of the DDC ground improvement system. Farrell demonstrated reliable static and dynamic performance of the DDC system using a Finite Element Analysis with Plaxis 3D®.
Based on AECOM soil borings and testing, the site was underlain by 15-feet of soft/compressible undocumented fill, primarily silty sand and sandy clay mixed with chunks of asphalt and concrete, bricks, and crushed rock. The fill was underlain by 30 to 35 feet of soft to medium stiff, and loose to medium dense, fine-grained clayey, silty, and sandy alluvial soil and then medium dense to dense alluvium to depths of 100 feet. The compressible soil coupled with a historic high groundwater level at around 8-feet plus the new structural loads had the potential for static settlement greater than 2-inches and seismic settlement due to liquefaction greater than 2.5-inches with a possible differential settlement of more than 2-inches.
AECOM recommended common “cast-in-drilled-hole” Concrete Piers or ground improvement using 10-feet of Excavation/Replace plus “Compacted Aggregate Pier” (CAP) beneath shallow footings. But Farrell set out to make a case for ground improvement using fully grouted, DDC rigid inclusions. With the collaboration from AECOM and Static models and Dynamic Time History models using Plaxis 3D®, Farrell Engineers proved that an unreinforced, Type 1 DDC would provide the ground improvement strength needed and reduce settlement to less than 1-inch after a major earthquake. The LACPW engineers, AECOM, and Farrell agreed to reinforce the DDC with rebar (Type 2 DDC) to add a higher level of resiliency for multiple seismic events. LACPW also approved Type 3 DDC as a ground anchor to resist seismic upfit loads in the parking structure. In early 2017, Los Angeles County approved the innovative DDC ground improvement system for shallow footing support at the new MLK Parking Structure East project, a first for the County.
In March of 2017, Farrell installed over 580 DDC in less than 4 weeks. The Type 2 DDC were 16-inches in diameter with rebar reinforcement and drilled to depths of 28 to 35 feet. Each DDC was topped with 12-inches of crushed rock aggregate cushion. Full-scale load tests were loaded to over 300% of design capacity, with tested deflections less than estimated. Once again, the Drill Displacement Column™ demonstrated its strength as an effective ground improvement solution in high seismic areas.
“A Nod to History. The “center green” is north of the parking structure and features colorful accent pavement embedded with recycled glass. The color of the glass gradates along the timeline, from red in 1965 to blue representing the current commitment to the hospital. The historic past and significance of Dr. Martin Luther King Jr. are captured through themes of reflection and inspirational quotes moving along the walkway,” (International Parking Design, Inc. 2019). The inspirational MLK East Parking Strucutre will reliably serve many generations of Los Angeles residents for years to come. Farrell is happy to have been part of the McCarthy team and to help MLK East Parking Structure Go Verical with Confidence®.
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