Inside Seven
Current Issue: September 2014
Wire mesh is attached to the slope above Route 14 to prevent loose rocks from falling on the roadway.

by  Judy Gish
Issue Date: 02/2007

Caltrans navigates a slippery slope to control falling rocks.

Looking like it’s wearing the cafeteria lady’s hairnet, the slope above the Antelope Valley Freeway (Route 14) in Santa Clarita is being made safer for motorists as a result of a slope stabilization project currently underway there.

The $8-million project, under the direction of Resident Engineer Kin Kwan, started on January 24, 2006. It involves cutting back the slope and installing cable net/wire mesh to prevent falling rocks.  Netting the hillside is greatly preferable, from a cost, time and convenience standpoint, to leveling it.

Before the project could even get off the ground, a lot of hard work and research was performed by Caltrans geologists Gustavo Ortega, Chi-Tseng Liu, Christopher Harris, John Ehsan and Jeremy Lancaster, who were instrumental in recommending the project, providing specifications, and reviewing final plans as well as providing support during construction. 

Slope stabilization might sound mundane but, on various Sunday mornings, when the mesh is fed to the hillside by helicopter and workers scramble up and down the slope to attach it, the project is pure adrenaline.  But first things first. Before the helicopter can take off, several weeks must be devoted to installing anchors on the slope and fabricating cable mesh in the construction yard.

There are two types of mesh used in this project: wire mesh, which is fabricated galvanized steel mesh coated with colorized polyvinyl chloride (PVC), and cable mesh, wire mesh fabric with heavy cable woven in. Wire mesh is similar to chain link fencing with larger holes but it is significantly stronger and is designed to allow small rocks to fall safely to the ground without bouncing out and away from the slope into the path of motorists.  Cable mesh is used to capture large rocks and boulders.

The first order of work in attaching the mesh to the slope is drilling anchor holes, inserting steel anchors and grouting them with concrete. Holes are drilled using pneumatic or hydraulic machines.  Concrete grout is pumped from the bottom of the slope to the anchor holes.  Cable, called "top cable," is attached to the anchors and is then ready for the attachment of steel mesh.

Next, tape is dropped down to measure the slope and those measurements will be used to fabricate the wire mesh fabric in the yard. The yard work, which can take up to two weeks at a time, is performed on weekdays. Part of the process is to join together two 13-ft.-wide rolls to make 25-ft.-wide rolls (with 1-ft. overlap). Wire mesh is used as is, but cable mesh has to be reinforced with cable. This process is called "spanexing," whereby connections are made with automatic pneumatic tools that squeeze "nose rings" to make the connections. 

After that, the labeled and numbered 25-ft. roles are delivered by trailer to the job site and placed behind K-rail for easy pickup by—(ta da) THE HELICOPTER!

The helicopter operation is performed on Sundays in order to minimize traffic disruptions. Route 14 is completely closed in both directions between the hours of 5 a.m. and 9 a.m., usually between Agua Dulce Canyon Road and Escondido Canyon Road.  As many as nine or more California Highway Patrol officers and cars are employed to ensure public safety.  Then, the helicopter lands on the freeway.

The size of the helicopter depends on the length and weight of the wire mesh to be carried and the density of the air.  A bar is connected to the helicopter that will attach to the wire mesh; the bar has an automatic disconnect so a load of mesh can be dropped with the push of a button.

Some workers stay on the ground to connect the mesh to the helicopter. Others climb the slope to attach the mesh to the pre-installed anchor/cable assembly, where they must be alert to the possibility of mesh literally falling from the sky.

The next day workers climb the slope to connect the mesh strips together to form one contiguous blanket, employing the same process ("spanexing") used to make cable mesh out of wire mesh. A large compressor sits at the bottom of the slope to provide pneumatic power for as many "spanexers" as are needed.

Most of the above is done by workers dangling from a rope.  “The workers are a hardy bunch,” says Assistant Resident Engineer Ed Christine.  “They climb the largest slopes using only a safety harness, moving up and down as they climb, and bouncing away from the slope to move around with tools in hand.” Christine says he has seen them do this carrying heavy loads in both 100-degree and windy, freezing weather. “As one of the workers told me, ‘This is a young man’s job.’"

The project is expected to finish by the end of this summer. It is yet another example of Caltrans’ ingenuity in the service of public safety.

A helicopter is used to feed the mesh onto the slope. Caltrans engineers Ali Sadat and Ed Christine have devoted many Sundays to monitoring the helicopter operation. Route 14 slope project Resident Engineer Kin Kwan is on site to ensure the job proceeds smoothly. A sheet of mesh dangles from the helicopter, ready to be fastened to the slope.