Despite several months of initial stabilization and slide removal efforts, a new slide enveloped the Regent’s Slide repair site in August 2024, with movement calculated at more than 1 ft per day. 

In March, Caltrans District 5 began using two remote-controlled bulldozers and two remote-controlled excavators to increase productivity while protecting workers from challenges associated with the height, steepness and instability of the slide area. The remotely operated equipment was used in tandem with traditionally operated bulldozers and excavators.

The remote controlled machines are being run by an operator seated in a control center located above the slide. Equipment with onboard operators push material to the remote-controlled machines, which perform the dangerous task of pushing material over the edge.

The month-long effort was initially successful, but regular monitoring identified new movement—likely in response to excavation activities and environmental effects—and new surface cracking immediately above the project area. Crews paused the heavy equipment work to focus on slope stabilization above the area by installing additional shear dowels. 

As of mid-June, about 750 shear dowels have been installed. Caltrans reports that measurements indicate that where these dowels have been installed, they are having their intended effect by providing shear resistance and halting the advance of slide activity.

Kevin Drabinski, a Caltrans spokesperson, says “there is an incredible array of monitoring” on the slide area with crews using a variety of equipment. “We absolutely have to understand how it’s moving and where, how deep, and at what angle for the safety of our crew,” says Drabinski. Daily geologic assessments also are performed. There have been no injuries since work began, the agency reports.

Surface-mounted prisms are used to monitor slide movement, incorporating newer technology such as shape accelerometer arrays, slope inclinometers, three-dimensional drone surface comparisons, and vibrating wire piezometers. According to Caltrans, the data collected by the monitoring instruments are used with visual observations of site conditions and surface measurements to make informed decisions and to adjust design assessments. 

When slide movement on the north end of the site occurred, the team had to constantly readjust strategy. Workers “do this dance of loading and then backing off as cracking accelerates,” Drabinski explains. “We’re now looking at installing shear dowels as we move down the slope as we continue with excavation activity and clearing slide material and bringing the bench down and continuing to install shear dowels as needed."

The number of dowels installed will depend on the area created with this new slope. Dowel installation is expected to continue for another couple of weeks before the remote-controlled excavation resumes. 

A section of Highway 1 has been closed for over a year due to slide activity.

Photo courtesy of Caltrans

Caltrans crews are working with Caterpillar Inc. and other contracting partners to incorporate the innovative technology. Geoff Pirro, a senior product consultant and application specialist for Caterpillar, notes this is the first time that its remote-controlled equipment has been used for a landslide.

Every slide has different geological formations, and the operators need to understand the particular slide application, says Pirro. One benefit of the remote-controlled equipment is to keep the operators safe. By working the remote controls from a distant facility, they reduce risk of soft tissue damage or other, more severe injuries, he explains. 

Virtual Training

Caterpillar conducts the remote control training either at one of its own facilities or on a project site. The equipment features “screen mirroring” meaning that many onboard features can be used "off board" via remote controls. 

The equipment operators who work the Cat D8 bulldozers and excavators under traditional conditions are trained to operate their same equipment via remote control, notes Drabinski. 

A C-Train trailer, typically used in the mining industry, was airlifted up to the site. It serves as a mobile office building where the operators sit in specially-equipped chairs that resemble gaming-like seats approximately 1,000 ft from the equipment. The operators have controls on their arms, a shoulder harness and controls on their feet. They receive information from screens and four cameras that show the front, back and both sides. External microphones are mounted on the heavy equipment. 

There is a joystick and a foot pedal; it’s like being in a virtual cab. The operators gain familiarity with the set-up generally within 24 to 48 hours, Pirro adds.  

The remote-controlled equipment works off an encrypted Wi-Fi network. Each machine has an encrypted IP address and runs off of a machine network that can handle several pieces of equipment, explains Pirro. 

Once the site is excavated, crews will install a metal drapery on the slope, which will help keep people safe from falling rocks. Workers will drill in and make points where they can attach the metal drapery, which acts similar to a netting system. Also, spotters are stationed at the bottom, middle and top of the slope to visually monitor any slide activity. The spotters are in constant communication.

“We’re really throwing everything at Regent’s Slide,” says Drabinski. 

Caltrans' concern for the area is long term due to inherent landslides in the Santa Lucia Mountains—a natural occurrence evident even before the highway was built in the 1930s. The mountain range is never more than 11 miles from the coastline and forms the steepest coastal slope in the contiguous United States. In a geological survey that mapped the 75 miles south from the Carmel River, 1,500 slides were identified.  

A range of engineering options has been suggested to preserve thruway traffic. The state has explored some, including building a tunnel. That would be a delicate operation, complicated by the fact that the land doesn’t belong to the state, notes the Caltrans spokesman. Another concern is where the tunnel would end—possibly at another location that is prone to slide activity. Preventative measures are performed year-round.        

But that doesn’t mean there is a timeline for when the remediation work at Regent’s Slide will be completed. At very least, the Regent’s Slide area of Highway 1 will be closed through this summer, Caltrans states. An updated estimate will come at a later date.