Caltrain declared an emergency on March 27 to repair damage to the embankment that supports the rail bridge between Palo Alto and Menlo Park, which was weakened by previous storms.
The Caltrain Finance Committee voted to authorize the emergency, allowing the rail agency to engage into a construction arrangement to rebuild the north embankment of the San Francisquito Bridge, a local news report said.
Caltrain staff assessed the bridge following the recent storms and discovered moderate scouring beneath the concrete wall that protects the bridge abutment and the historic El Palo Alto redwood on the Palo Alto side.
The bridge is located adjacent to El Palo Alto Park and the El Palo Alto redwood. The storm drain below the park, the embankment and the concrete bag slope protection for the drain’s outfall pipe have also undergone severe scour and embankment erosion. Rob Bernard, deputy chief of design and construction, said the loss of supporting soil has compromised the structural integrity of the outfall, according to the report.
Bernard said the pedestrian footbridge directly east of the rail bridge is in a similar state, with erosion to the embankment below and requires strengthening.
The Menlo Park part is on the north side, where the bridge was more threatened. According to Bernard, the dirt embankment rather than concrete supports that side of the structure.
The soil embankment beneath the railroad bridge experienced extensive scour, undermining the bridge’s eastern span. A large tree nearby has an exposed root mat as a result of extensive soil erosion and scour surrounding it.
The bank soil is unstable since it is now virtually vertical rather than sloping. As a result, if nothing is done, the soil will continue to deteriorate, according to Bernard.
The bridge is not in imminent danger, Bernard explained, but an emergency repair is necessary to prevent additional erosion.
Caltrain has proposed restoring or backfilling the slope on the Menlo Park side near the railroad bridge with soil to the right angle for stabilization, which would provide protection against additional erosion and scour.
According to Bernard, one proposed alternative would be to construct a concrete wall on the Menlo Park side similar to the existing one in Palo Alto, but that design could be harmful to the Central California Coast steelhead, a federally protected endangered fish species. He suggested that a less invasive way would be to place “riprap,” or large boulders, to protect the restored bank.
Any work would have to be completed within a four-month window, from June 1 to Oct. 15, to avoid interfering with fish migration, according to Bernard. Caltrain would need to prepare its designs and have them approved, as well as the permitting, within the next two months, he added. The design would then be reviewed by eight agencies.
Caltrain does not yet know how much the project will cost. Bernard expects staff to return with estimates in roughly a month.
The emergency declaration authorizes Caltrain to expedite the process by skipping the typical bidding procedure and awarding the contract to Walsh Construction, he said.