Blu Harbor Residential Community Project- Redwood City, California

Project Highlights

  • DMM along 3000 feet of the shoreline and under the buildings.
  • A total of 121,000  CY of the ground was improved by deep mixing including 57,000 CY for shoreline stabilization and 64,000 CY under buildings and utilities.
  • The depth of the DMM elements varied between 28 feet to 37 feet.
  • The DMM system along the shoreline consisted of interlocking DMM columns and panels in a longitudinal and transverse direction. This system acted as a below-grade gravity retaining structure resisting both static and seismic loads.
  • DMM elements under the building and utilities acted as foundation support.

Sub-Surface Profile

  • The project site was capped with 5 to 7 feet of fill (SC to CH) over 13 to 20 feet of Young Bay Mud (CH).
  • Clay with gravels, concrete debris, and brick fragments were encountered within the surficial fill layer.
  • Below the Young Bay Mud, potentially liquefiable loose to medium dense sand (SM/SP) deposits approximately 5 to 8 feet thick were encountered.
  • below the sand, stiff to very stiff alluvial deposits (CL to MH) was encountered.

Stability Analysis of DMM Buttress

                                                                                                                                                                                                                     (Source: Rockridge Geotechnical)

A limit equilibrium slope stability analysis was performed by ENGEO and verified by  Rockridge Geotechnical using SLIDE to model potential failures under seismic conditions. A peak horizontal ground acceleration of 0.24g was applied to the pseudo-static models. Loading from proposed buildings was applied onto the top of the DMM Buttress.