SAN MATEO COUNTY, CA

Alpine Road Trail Stitch Pier Repair Evaluation

The Alpine Trail Improvements Project consisted of several miles of trail improvements adjacent to Alpine Road in Portola Valley, CA. The trail improvements consisted of repaving of the existing asphalt pedestrian walking trail, addition of trail drainage swale and storm drain inlets to adequately drain the trail, construction of new retaining structures to support the trail and Alpine Road, and the realignment and scour countermeasures of the existing creek adjacent to Alpine road. In two locations along the trail, new soldier pile wall structures were designed by Cornerstone to help support the trail and existing road and to act as an emergency repair for scour protection along the creek. The two soldier pile walls were roughly 100 feet long and up to 17 feet in total height from the creek bottom to the top of wall. A precast concrete lagging system was provided as a long term protective measure and openings in the lagging were detailed to allow for existing storm drains to flow through the wall and down to the creek.

 

As part of the wall locations scour countermeasures, the existing creek was rerouted and vegetated log crib wall was installed in front of the soldier pile wall to mimic the original condition of the creek, including planting of willows as part of the vegetated crib wall. The project also included several challenges during construction such as dealing with a nearby existing gas line, existing guy wire for an overhead utility, and an existing storm drain penetrating through the lagging. At this location, a modified panel was designed to allow for the utility to remain. This “super panel” was cast in the field and lifted into place around the existing utility. Caltrans OSFP provide construction oversight for the design of the project. Construction of the Alpine Trail Improvements was completed in spring 2018 by Graniterock Construction. The Alpine Trail Improvement Project won the ASCE Award for Bikeways and Trail Projects in Spring 2018.