Mount Soledad slid again Thursday, Jan. 17, causing major disagreements between geologists for the homeowners and those representing the city of San Diego.
“The story’s still coming,” said Kevin Rogers, an expert geologist with American Geotechnical, Inc. hired by the homeowners. “It’s at risk of additional movement.”
Rogers and other experts from American Geotechnical and the city waded Friday through the new slide area, which surveyors described as being about 3 to 5 feet vertically and 14 feet horizontally, to get a handle on the situation.
At about 3:30 p.m. the afternoon before, witnesses said the area, which was part of the original slide plane, began to move slowly onto Desert View Drive from above, essentially widening the original hole. The new slide area further damaged one home that officials red-tagged from the first slide, but missed another red-tagged home just at the toe that was left undamaged from the original slide.
The first slide’s toe encroached as far as one home’s porch on Desert View Drive, but left the home unscathed, said Steve Borron, a geologist with American Geotechnical, Inc.
Borron and other geologists agree the new slide was caused by grading done to the toe or bottom of the slide, similar to taking an orange from the bottom of a pile at the grocery store. But experts disagree about the level of responsibility regarding the incident.
“They [city crews] were doing removals on the toe down there at the bottom,” Borron said. “In our opinion, you never do that before fixing it.”
Rob Hawk, a city geologist, said that because this is a “catastrophic” slide, any movement could happen.
Borron said there are many options to fix or stabilize the toe of the plane, even temporarily. It is “standard stuff,” Borron said, to put in shorings before grading or removing dirt at the toe.
“Rob Hawk should’ve known better,” Borron said. “We never touch the toe of a slide.”
While geologists from American Geotechnical said the city is at fault for “playing the odds,” because they skipped a step in the process by not stabilizing the toe of the slide before grading the dirt, Hawk said the grading of the dirt was itself part of the stabilization.
Hawk exited a trailer at the top of Soledad Mountain early Friday morning fresh from a strategy meeting that included city workers, public information officers and other key players from the city. He reiterated the city’s position that they knew this could happen, but that no new homes were damaged. He said city officials are moving forward, adding that he thinks crews are “still on track.”
But according to Borron, as loose as the ground is at the toe, it should have been more simple to consider different options to temporarily stabilize the toe, including pounding steel pilings into the ground. Crews shouldn’t have just started moving dirt, he said. The crews had no problem stabilizing the top of the slide plane where they put in many caissons, Borron said.
“We didn’t damage any homes that weren’t already damaged,” said Rob Hawk, Geologist with the City of San Diego. “We just re-crushed the house that was already crushed.”
Hawk calls the new slide an “ingrading failure” that is part of the original Oct. 3 landslide that damaged about 20 homes at the 5700 block of Soledad Mountain Road and the alley of Desert View Drive.
“It gives us the opportunity to analyze more data now,” Hawk said. “We haven’t suffered any new damage.”
After they realized the ground slid again, crews rushed tons of dirt up to fill the toe of the slide plane to stop the sliding, Hawk said.
Crews demolished three homes on Soledad Mountain Road weeks ago, leaving a fourth as they worked to restore the roads. The city continues to stabilize the slope in anticipation of the upcoming rains. Hawk said a new forensic investigation will begin Monday.