Project Description

Diaz•Yourman & Associates (DYA) was the geotechnical and hazardous material subconsultant for preliminary design of a 8.6-mile-long segment of a proposed light rail transit (LRT) project from Downtown Los Angeles to Culver City.  The project alignment was generally within an abandoned rail right-of-way in the street median with several grade separations and 10 new stations, three (3) of which are aerial.  The grade separations consisted of aerial railroad bridges over La Cieñega Boulevard, Ballona Creek, and La Brea Avenue, and the trench structure near Flower Street, with vehicular bridges on top of the trench structure at Figueroa Boulevard and Padree Way.  The trench structure was adjacent to existing buildings and southbound I-110 ramps.  Retrofitting and replacement options were evaluated for the Adams Boulevard/Flower Street overcrossings at I-110.

Our scope of services included conducting a preliminary geotechnical investigation, preparing a Phase I Environmental Initial Site Assessment (ISA) Report, and performing a subsequent Phase II Hazardous Materials Investigation.  The geotechnical scope consisted of data review, site reconnaissance, a field investigation to collect subsurface data for the aerial structures, preliminary engineering analyses, including computer modeling to simulate trench structure construction, and a preliminary design report with recommendations for preliminary design.  Seismic design information was provided in accordance with Caltrans and AREMA formats.  The Phase I ISA was done in stages accommodating budget constraints.  In the initial stages, a drive-by site reconnaissance, limited environmental data review, and historical aerial photograph review were performed to recommend further tasks to complete a full ISA of the proposed LRT development.  We performed a full-scope Phase I later, and a Phase II Hazardous Material Investigation program was developed and performed based on those findings.  The Phase II investigation included testing for arsenic, lead, fuels, metals, pesticide/herbicide residues, and petroleum oil and lubricants.

We were requested to perform a subsequent investigation for the design-build contractor during the D-B phase of the project, evaluating the effects of the proposed La Brea and La Cieñega Aerial Structure approach embankment portions of the proposed project on an existing adjacent County of Los Angeles storm drain.  DYA’s tasks consisted of reviewing existing data and summarizing our engineering analyses, which provided estimates of additional lateral stresses on the storm drain using simplified methods, additional lateral stresses on the storm drain using finite element analyses, and evaluation of various ground improvement schemes to reduce the additional lateral stresses.  Our recommendations for ground improvement saved more than $1 million in construction costs compared to a structural option by avoiding the disposal of environmentally challenged soils.  DYA has also provided construction observation during the ground improvement.  Measurements during construction confirmed DYA's calculations.

V. R. (Nadesh) Nadeswaran, PE, GE – Geotechnical Manager

Allen M. Yourman, Jr., PE, GE – Geotechnical Principal

Gary K. Gilbert, PE, GE – Geotechnical Manager for Environmental Segments

Gary J. Halbert, RG, CEG – Geologist