subsurface conditions mission bay san francisco, california presented by hadi j. yap, phd, pe, ge...
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Subsurface Conditions Mission Bay
San Francisco, California
Presented by Hadi J. Yap, PhD, PE, GE
DTX Project Meeting San Francisco County Transportation Authority
11 October 2011
Typical Stratigraphic Layers
• Fill
• Bay Mud
• Colma Sand
• Old Bay Clay
• Colluvium/Alluvium
• Franciscan Complex Bedrock
Typical Stratigraphic Layers
• Fill
– Non-engineered, generally loose to medium dense
– Heterogeneous material consisting of sand, clay, silt, gravel, bedrock fragments, abandoned structures, construction debris, and organics
Typical Stratigraphic Layers
• Bay Mud
– Soft clay and silt with occasional sand lenses and organic material
– Low strength and high compressibility
Typical Stratigraphic Layers
• Colma Formation– Dense to very dense sand with occasional
clay lenses
– Generally contains up to 20% fines (silt and clay)
– High strength and low compressibility
Typical Stratigraphic Layers
• Old Bay Clay
– Stiff to hard clay and silt
– Occasionally contains sand and gravel lenses
– Moderate strength and moderate compressibility
Typical Stratigraphic Layers
• Colluvium
– Dense sands and gravels and stiff to hard clays
– High strength and low compressibility
Typical Stratigraphic Layers
• Franciscan Complex bedrock– Deformed bedding planes and shear zones
due to seismic activity
– Highly variable in hardness & strength
– Deeply to moderately weathered
– High strength and low compressibility
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