PROJECT OVERVIEW
Project Name: Canyon Stabilization
Location: Orange County, CA
Job Type: Stabilization & Drainage Improvement
DESCRIPTION
This Southern California property located close to residential areas on a steep canyon hillside presented significant slope stability issues. Property development & associated grading was constructed without permits in the 1950s. In the 1980s, a fire destroyed residential structures and surrounding vegetation. A damage assessment with geotechnical investigation determined the housing pad and access roadway were constructed without proper compaction. In addition, spoils from the previous grading had been pushed down-slope and were left uncompacted. As a result, stormwater drainage created “piping” throughout the site. These adverse conditions presented the potential for slope failure and significant risks to adjoining and down-slope properties. E&E was contracted to implement a remedial grading plan, utilizing existing site material only, to mitigate the risk of slope failure & eliminate the transport of the un-compacted fill. The successful execution of the project returned the Property to its pre-development condition in terms of both topography and vegetation.
MAIN TASKS
- Install ingress/egress controls
- Clear and grub Property
- Locate and remove all subsurface utilities and structures
- Excavate overburden, build fill key
- Excavate and stockpile all undocumented fill
- Excavate any surficial failures
- Excavate, rip and re-compact all fill keys
- Prepare grade to receive the re-compacted fill
- Backfill/replace material including moisture conditioning
- Backfill and compact slope face consistent with the final grading plan and as necessary to establish pre-development contours
- Install and continuously maintain storm-water mitigation and Best Management Practices (BMP’s) throughout the Property
CHALLENGES
The Client was highly concerned about the potential impact on adjoining properties downslope of the construction area. Above-normal amounts of rainfall occurred during construction. Due to potential slope stability risks, the project required E&E to construct mitigation measures utilizing basic design plans in conjunction with a field engineering and construction process. The site was highly vulnerable to sheet flow of storm-waters across unconsolidated soils. Equipment that could be used was limited due to site access by a narrow private road.
INTERESTING POINTS
During the extraordinary rainfall that occurred, only minimal debris was seen to surface at the downslope properties. To mitigate surface water impacts, E&E built and maintained check dams, straw wattle, and silt fence that withstood the torrents. Access to the site required the delivery of heavy equipment on residential neighborhood roads. This was a very sensitive issue with closely located neighbors of the property. E&E actively participated in city meetings to help alleviate concerns and E&E staff walked all equipment up the road on plywood sheeting to avoid any damage to the existing road.
