- Emerald Bay Service District
- Geotechnical Project of the Year
- Additional Files
- Additional Information
Emerald Bay Entrance Widening
- Project Location:
he project is located at the main entrance to the Emerald Bay Community - aka Shamrock Road in the County of Orange, Laguna Beach area. The project is bounded on the south by North Coast Highway, on the west by residential homes with the Emerald Bay Community, on the north by Belview road and on the east by Swanson Park.
- Project Description:
The project involves the widening of the existing entrance roadway (Shamrock Road) eastward into the community of Emerald Bay. The widened entrance extends over Swanson Park which exists approximately 21 feet below the roadway. Because of the elevation differential between the roadway and the park, a new slope was required founded on alluvial soils existing beneath Swanson Park. The alluvial soils beneath the new slope consist of soft, weak and highly compressible silts and clays interlayered with loose silty sand and sand deposits. Groundwater exists approximately 11 feet below ground surface in the park area further complicating the subsurface conditions. Because of the soil and groundwater characteristics and the load induced by the new slope, geotechnical engineering analyses indicated that the slope would be impacted by significant amounts of seismic settlement, lateral spreading, and static consolidation settlement. In addition, the new slope needed to blend into the existing slopes which range in steepness from approximately 2:1 to greater than 1 1/2: 1.
- Project Justification:
This project involved numerous geotechnical engineering challenges that had to be overcome, required the use of unique, innovative and cost effective solutions to meet the geotechnical challenges and economics of the project as well the development of a close working relationship with the County of Orange with regard to acceptance of a relatively new ground improvement technique – Drilled Displacement Columns (DDC’s). Prior investigators had recommended solutions which were either too costly or unviable. GMU’s innovative design enabled the project to move forward, thereby creating a new entrance witch improved traffic safety and traffic circulation. In addition, the selection of the DDC mitigation measure also significantly reduced drilling spoil haul-off which in turn significantly reduced the carbon footprint of the project.
- Special Circumstances:
Numerous geotechnical challenges were encountered and special regulatory approval was required from a geotechnical perspective. These include the following:
1. Geotechnical Construction Constraints
The site is highly constrained and difficult to access. In addition, the project area is in the immediate vicinity of existing multi-million dollar homes. Consequently solutions to the geotechnical issues had to consider these constraints.
2. Large lateral spreading magnitudes due to strain softening of fine grained soils during the design earthquake event.
Lateral spreading due to clay softening of soft clays and silts resulted in lateral spreading magnitudes in excess of 100 inches (>8 feet) potentially resulting in slope failure during dynamic loading. Consequently a cost effective ground remediation strategy had to be developed. Standard corrective grading solutions were ruled out given the shallow groundwater depth. Consequently, several ground remediation options were developed and analyzed. After additional geotechnical engineering analyses, Drilled Displacement Columns (DDC) were selected to mitigate the lateral spreading and potential slope failure.
DDC involves drilling the alluvial soils in the park below the slope using a displacement drill and heavy equipment crowd. Then the displacement drill is slowly raised and the created cavity is filled with grout under pressure to form the DDC with relatively low construction noise and with no significant vibrations. The procedure not only creates high strength grout columns but also densifies the surrounding soil while creating virtually no drilling spoil. Consequently, the selection of the DDC ground improvement option simultaneously solves the issue of construction vibration and noise, reduces consolidation and seismic settlements and does not involve significant haul-off which is critical for the tightly constricted site. This ground remediation technique was spear-headed by GMU for this project and it was the first time the technique had been submitted and approved in the County of Orange for this purpose.
3. Static/Consolidation Settlements Due to the Loading of the New Slope on Saturated, Fine Grained Soils.
Although the DDC methodology densifies the soils surrounding the piles, significant time-delayed settlements (i.e. on the order of 5 inches) had to be addressed. This was addressed by carefully monitoring settlements during construction to ensure settlements were occurring during construction. Settlements also had to be monitored to: 1) ensure that fill loading did not occur too quickly so as to induce potentially unstable high pore pressures, and 2) that new utilities could be safely installed (i.e. without being exposed to significant adverse settlements). Static consolidation settlements also required the removal of an old sewer line that existed within the slope.
4. Creation of New Slopes that are Significantly Steeper than the County Mandated 2:1 Ratio
Because the new slope had to be blended into the existing slopes which are significantly steeper than the County maximum 2:1 slope special design considerations were required. To address this problem the entire face of slope needed to be reinforced with geogrid. In addition, because of the significant planting requirements, special, project specific geogrid details needed to be developed.
REGULATORY CHALLENGES AND SPECIAL RELATIONSHIPS
Because DDC’s are a relatively new ground improvement strategy, the County of Orange Building and Safety Staff had to be convinced that the design and construction methodologies were adequate and met County Standards. This resulted in a close working relationship with the County and development of special design requirements that were acceptable to the County.
- Project Attachments:
This project is being submitted as a small geotechnical/community improvement project. The project was deemed by us to be too small to be submitted under the Geotechnical Project category, but due to its complexity and uniqueness, it is in our opinion worthy of its own category. The submittal thus emphasizes the geotechnical aspects, geotechnical team members, etc. of the project as opposed to the project as a whole.
- Award Citation::
The Emerald Bay Entry Widening project had to overcome numerous geotechnical engineering challenges which included the mitigation of lateral spreading, static consolidation settlements and the construction of over-steepened slopes. Mitigation measures had to be selected so as to be compatible with construction noise and vibration and tight construction access requirements. The selected main mitigation measure consisted of a ground improvement strategy (Drilled Displacement Columns).
- Suggested Award Summary:
The Emerald Bay Entry Widening project which improved traffic safety and circulation at the intersection of Shamrock Road and PCH had to overcome numerous geotechnical engineering challenges which included the mitigation of seismically induced lateral spreading, static consolidation settlements and the construction of over-steepened slopes. Lateral spreading was mitigated with the implementation of Drilled Displacement Columns or DDC’s. DDC’s involve the drilling of the alluvial soils in the park below the widened slope using a displacement drill and heavy equipment crowd. Then the displacement drill is slowly raised and the created cavity is filled with grout under pressure to form the DDC with relatively low construction noise and with no significant vibrations. The procedure not only creates high strength concrete columns but also densifies the surrounding soil while creating virtually no drilling spoil. The use of DDC’s also reduced the static consolidation potential. In addition, the DDC’s addressed the general construction constraints consisting of the utilization of low noise and vibration equipment as well as working within tight working conditions. The DDC mitigation measure consisted of a “relatively new” and sustainable ground improvement strategy that required the development of a close working relationship with the County to insure that the design methodologies were consistent with County requirements.