Stabilization of a dangerous Landslide at California’s White Point Nature Preserve near Los Angeles
During the rainy month of November of 2011, a part of the Paseo del Mar Road at the White Point Nature Preserve suddenly collapsed, sliding down a 36.5m (120ft) cliff side into the Pacific Ocean. The owner of the road, the city of Los Angeles, hired the geotechnical consultant Shannon & Wilson to suggest a suitable stabilization measure.
The consultants found that an excess amount of water had accumulated beneath the surface due to poor drainage and the general slope setup had caused coastal erosion and the landslide. Furthermore, sensors placed in drilled shafts detected continuing ground movements in this area.
The city council was able to choose from different rehabilitation plans and decided to undertake the most economic solution, which was also the quickest alternative. The final design scheme included the horizontal drilling and installation of drainage pipes into the slope and the use of DYWIDAG Strand Anchors as tiebacks.
The engineer recommended slope stabilization with 18 Type 6-0.6" DYWIDAG Strand Anchors. At the beginning, two test anchors that were each fitted with seven DYNA Force® Sensors were used for realizing Shannon & Wilson’s proposal. Three of the sensors were placed at distances of 3m from each other in the bonded length of the test anchors, and four were placed at distances of 10m along the unbonded length.
The up to 55m long DYWIDAG Strand Anchors were placed in two levels of 9 anchors each. The anchorages are restressable so that loads can be adjusted after the stressing tails are cut. The anchor load is distributed to the soil through large, cast in place reinforced concrete pads.
The general contractor Hayward Baker Inc. selected DSI to supply the anchors and anchor stressing equipment as well as to provide technical assistance for the first anchors to be installed.
Testing went well with the DYNA Force® Readout Unit showing readings that were very close to those of the jack gauge. The cables of the DYNA Force® Sensors are connected to a waterproof NEMA box so that load monitoring can be carried out on a permanent basis.