Project Description

Diaz•Yourman & Associates (DYA) was the geotechnical consultant for a design-build team for a two-mile-long segment of a ten-mile-long railroad grade separation. The railroad tracks were depressed 33 feet to provide the grade separation. The trench walls were constructed using three-foot-diameter cast-in-drilled-hole piles, spaced at four feet on center. The walls were supported at the top by a strut and at the bottom by an invert slab. Dewatering was performed during construction. The project included five overhead crossings of the railroad tracks. The design recommendations were provided in accordance with Caltrans standards considering lateral deflections during construction and long-term loadings, including seismic conditions, effect of construction on adjacent structures, and soil structure interaction.

DYA also evaluated construction dewatering requirements, well types and depths, and dewatering volumes. Four large-scale, long-term pumping tests were performed at locations selected by DYA to evaluate the groundwater studies and to model dewatering systems. The results of the analysis indicated the dewatering volumes exceeded 1,000,000 gallons per day per 1,000 feet of open trench. These dewatering volumes were unexpected but were confirmed during construction. They confirmed DYA’s recommendation of seven wells per 1,000 feet of trench during construction also.

Our engineer’s approach to analysis of secant wall deflection for our initial 2-mile segment of the Alameda Corridor trench allowed optimization of the pile diameters and penetration resulting in substantial savings in costs and construction time throughout the 10-mile project. During construction, the approach was further confirmed by instrumentation. The Consulting Engineers and Land Surveyors of California (CELSOC) selected the Alameda Corridor as the 2001 Outstanding Project.

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

Gerald M. Diaz, PE, GE – Geotechnical Principal

Gary K. Gilbert, PE, GE – Geotechnical Engineer

Allen M. Yourman, Jr., PE, GE – QA/QC Reviewer