Erosion Control March/April 2017 : Page 37

Johnny Cash Pedestrian Bridge was fraught with challenges. In particular, the 25-foot-high and adjoining concrete bridge walls being spaced only 15 feet apart made stability a major concern. Dokken Engineering worked with the city of Folsom to design the paths that connect the East Lake Natoma and Folsom Lake Crossing trails. Tony Powers of Dokken explains that usually, the Ultrablock components wouldn’t necessarily require the use of geogrid. On the other hand, Chuck Kull with H&K notes that the design had a bit of a paradox, in that a wall as tall as this one would require geogrid for stabilization. These walls, however, were too close together to allow the required lengths of geogrid. Therefore, the geogrid layers would overlap and compromise the effectiveness. Powers explains that in a typical situation, the length of the geogrid is based on 80% of the height of the wall. In effect, the team resolved to shorten the wall. By backfilling the lower 10 feet of the wall with a cement-soil mixture, they reduced the amount of geogrid required. “The challenge of this project was to design the reinforcing fabric in such a way so that fabric from both sides of the bridge did not interfere with the internal stability of the walls. This was performed by offsetting the height of blocks on each side so that the fabric had sufficient soil between the rein-forced layers,” says Kull. By staggering the blocks on the oppos-ing walls, they were able to have more than a foot of soil fill material between layers of Strata geogrid. At the 25-foot wall, they began placing geogrid at blocks three and four and continued to blocks nine and 10, overlapping the geofabric from the opposite side as necessary. Finally, concrete leveling pads minimized the potential for dispro-portionate settling. The deck slab and copings were constructed as one unit, and essentially “pinned” into the top of the Ultrablock units “to provide a level of redundancy for seismic loads.” At the extreme top layer of the wall, Westcon constructed cone-shaped copings with precast concrete. These cones are one of the primary features that stand out to people approaching the bridge. They have made the site as inimitable as its MARCH/APRIL 2017 namesake is infamous. Cash’s fam-ily made many comments at ribbon cutting about how much joy he would have taken from the entire trail and the legendary bridge. Additional retaining walls and trails are planned for the second phase of the project that’s scheduled to be com-pleted in 2017. Beginning at Cimmar-ron Circle, the 1.25-mile trail includes an undercrossing at Prison Road and a 190-foot-long wooden bridge that will provide views of the American River and Lake Natoma. The “Man in Black” would appreciate the planned park, including the faux guard towers, 7-foot guitar picks, and a prison-cell-like sculpture made of giant guitar necks. The winding paths and rolling hills of oak trees offer views of the 1,200 acres that surround the 136-year old prison. Just so there are no misun-derstandings, large yellow signs are posted throughout the park that read “California State Prison Property. No Trespassing.” Reliable. Durable. Proven. Trusted by Engineers. It makes the difference. Keystone Compac ® Design with Confidence. Keystone Fiberglass Pin Beyond stunning aesthetics, it is what you don’t see that makes a Keystone wall remarkable. Our interlocking pin connection system improves design versatility while maximizing the strength and durability of your project. To view Keystone’s complete line of innovative products and project ideas, visit us online at www.keystonewalls.com or call 1-800-747-8971 . Keystone is proud to be a subsidiary of Contech Engineered Solutions LLC EROSION CONTROL 37

Keystone Retaining Wall Systems

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