I-680 Red Top Road Interchange Project, Solano County, CA


  • Construct a new partial interchange at I-680 and Red Top Road as construction Package 2 of the seven construction packages of Phase 1 of the STA overall Interstate 80/Interstate 680/State Route 12 Interchange Project.
  • Reduce congestion, accommodate anticipated increase in traffic demand and address safety concern.
  • Northbound I-680 off-ramp to Red Top Road will consist of two embankments, which is separated by the “Red Top Off-Ramp Separation” in the middle and over the I-680. The two embankments will be supported by a total of four retaining walls.

Project Elements

PARIKH provided geotechnical investigation, engineering analyses, geotechnical/foundation recommendations for the following:

  • Pavement widening along I-680 and Red Top Road on-Ramp to Southbound I-680.
  • The “Red Top Off-Ramp Separation” will be s six-span structure with a total length of approximately 825 feet.
  • Four retaining walls with the maximum design heights between 19.2 feet and 21.7 feet to support the embankment of the embankments of the Northbound I-680 off-ramp. The retaining wall will be the Mechanical Stabilized Embankment (MSE) wall.


  • Field exploration
  • Laboratory testing
  • Engineering analyses and geotechnical/foundation recommendation.


  • Geotechnical Design and Materials Report
  • Foundation Report for the “Red Top Off-Ramp Separation”.
  • Foundation Report for the four MSE retaining walls for the Northbound I-680 off-ramp to Red Top Road.

Results and Highlights

  • Driven pile was selected as the pile type for the bridge structure. There is an existing 36-inch water pipeline within a short distance from the pile cap footing. Predrilling was recommended to minimize impact on the existing utility due to vibration from the pile driving.
  • There are some drainage pipes and utility pipes (either existing or new) will be located underneath or in the vicinity of the proposed south embankments of the Northbound I-680 off-ramp. The total settlement and loading stress at these utility locations were estimated using the Settle 3D to provide the designer and utility owners information for utility protection, relocation, and sequence of construction.
  • Downdrag has been considered in the pile capacity analyses due to the post-liquefaction settlement. Pile drivability analyses was performed to verify the driving stressed due to the relatively high nominal driving resistance.

Project Details




Solano Transportation Authority


BKF Engineers


Gary Parikh
Alston Lam

Project Gallery

I-680 Red Top Road Interchange 1
I-680 Red Top Road Interchange 2