Progress Report
June 9, 2010
Physical Description of Phase IV and V Repairs
Phases IV and V - Arrest Lower Portion of Active Landslide, will consist of a combination of a row of reinforced concrete shear pins with tieback anchors and a reinforced earth fill buttress to provide enough resistance to arrest the active landslide movement below the Phase VI repair area. Phase IV (arrest active landslide with a tiedback shear pin wall and shear cleats) will include a continuous row of 40, 48-inch diameter, 61.5- to 78.5-foot deep shear pins (drilled piers - cast in drilled hole, or CIDH) that will be installed at 7 to 8 feet on centers and located in a line across the slope - roughly 80 to 100 feet east of the intersection of Sycamore Canyon Road and Ranchito Vista Road. The tops of the shear pins will be connected with a massive reinforced concrete tiebeam and each shear pin will be equipped with between 2 and 7, 312,000 pound- resistance, post-tensioned tiebacks extending roughly 85 to 170 feet at an angle back and down into the hillside. Phase IV will also include a single row of 36, 48-inch diameter shear cleats (40-foot long reinforced concrete CIDH caissons extending 20 feet above and 20 feet below the basal landslide shear surface, plane) just down-slope of Phase VI Wall 1.
As part of Phase V (arrest active landslide with a reinforced earth fill buttress and associated under-drainage), two additional rows of 48-inch diameter shear pins will be installed along the northern limits of the Phase V construction area and oriented in two lines up and down the slope to protect the residence at 1750 Sycamore Canyon Road during the Phase V grading operations as well as to provide long-term resistance to movement of the small portion of the active landslide left in place above these shear pins. The northern row will consist of 17 shear pins with lengths of 37 to 61.5 feet, and 12 of these will be equipped with one row of 100,000-pound-resistance tiebacks extending roughly 70 to 100 feet back and down into the hillside beneath the residence at 1750 Sycamore Canyon Road. The southern row will consist of 7,42.5- to 62-foot long shear pins with no tiebacks.
The Phase V reinforced earth fill buttress will consist of engineered, geogrid-reinforced compacted fill and will extend from the row of 40 Phase IV shear pins 80 to 100 feet west to the approximate edge of Sycamore Canyon Road and Ranchito Vista Road. The buttress will be approximately 40 to 50 feet high and will have finished slope inclinations ranging from 2.6:1 (H:V), to 1.6:1 (H:V). Phase V will also include subdrainage and surface drainage, and a mid-slope modular block retaining wall to provide a drainage terrace with V-ditch.
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