Dangerous Landslide Potential at Azusa Rock Quarry
AGI Geotechnical, Inc. performed a study on the geology of the Azusa Rock Quarry and found that the finished reclamation slopes described in the proposed reclamation plan did not have adequate factors of safety against landsliding. For example, the finished slope surface is to have a total height of 1,230 feet, with some gradients locally steeper than 1:1. A slope with a total height of 700 feet failed in 1997, resulting in a one million ton landslide on the east side of the quarry. Stability analyses showed that the slope would have a factor of safety of 1.059, although a factor of 1.5 is considered "safe" by the County of Los Angeles in areas near faults (the Sierra Madre Fault is 0.3 miles from the project site). The EIR assumes solid bedrock under the decomposed surface rock, although test borings have shown that the rock is fractured to at least 400 feet below the surface. Such fracturing would compromise the safety of a slope cut to 45°. Another problem is the planned buttress fill slope on the east side of the quarry. It has not been shown that the material used for the fill would have sufficient shear strength to be stable at the proposed 42° slope. The EIR says that the material would be supplemented "through the addition of geosynthetic fibers", although no tests have been run to insure that such treatment would produce a stable slope. This is of grave concern, since it has been proposed that the new Fish Canyon trail would pass directly underneath the filled slope, subjecting hikers to potentially dangerous conditions.
Vulcan Materials' current conditional use permit allows slopes to be as steep as 51°. However, because they are running out of rock on the west side, they have cut over-steepened slopes between the roads that lead to the top of the west quarry. This is an image of the west wall, showing such a slope, estimated to be ~70°:
Although the over-steepened slope on the west side of the Azusa Rock Quarry is not a threat to hikers or ordinary citizens, it is potentially dangerous to Vulcan's own workers, who drive vehicles both above and below the cut slope. If the slope should fail at a time when Vulcan personnel are on the road, the results might be tragic. Click here to see an aerial view of the slope's location.
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