1. Geotechnical Investigation Report
July 2008
Hadi J. Yap, PhD, PE, GE

2. Table of Contents 1.0 Introduction 2.0 Scope of Services
Field Investigation
Laboratory Testing
Geology and Seismicity
regional geology
regional seismicity and faulting
geologic hazards
Site Conditions
site conditions
subsurface conditions
Discussions and Conclusions
foundation support
groundwater
excavation
dewatering
shoring and underpinning
Recommendations
mat foundation
pile foundation
below-grade walls
basement floors
seismic design
site preparation
excavation
dewatering
shoring
8.10 earthwork
8.11 utilities
8.12 construction monitoring
8.13 site drainage
Additional Geotechnical
Services
10.0 Limitations

3. Introduction Present our understanding of the project:
Site: location, size, conditions
building type, number of stories and basements, column loads
Site grading/fill to be placed
additional elements of the project (retaining walls, parking areas, etc.)

4. Scope of Services Field exploration Laboratory testing
Engineering analysis
Develop conclusions and recommendations regarding:
soil and groundwater conditions at the site
the most appropriate foundation type(s) for the structure
estimates of foundation settlement
lateral earth pressures for the design of permanent and temporary below-grade walls
site seismicity and seismic hazards, including ground rupture, liquefaction, lateral spreading and differential compaction
San Francisco Building Code seismic design parameters
subgrade preparation
criteria for fill, quality, placement and compaction
pavement design
construction considerations

5. Field Investigation Evaluate existing data Perform site reconnaissance
T&R database
city records
geologic maps
historic maps
Perform site reconnaissance
Develop field investigation program:
test pits
dynamic cone penetrometer tests
test borings
Cone Penetration Tests (CPTs)

6. United States Coast Survey Map - February 1852

8. Laboratory Testing Geotechnical parameters Corrosivity
index testing for classification
shear strength
compressibility
R-value (for pavement design)
Corrosivity

9. Site Conditions Describe site history, if known
reclamation history
past development
previous grading
Describe existing conditions
surface conditions
existing site use
known obstructions

10. Subsurface Conditions
Describe soil encountered
thickness
density/strength
compressibility
Groundwater conditions

11. Typical Stratigraphic Layers
Fill
Dune Sand
Bay Mud
Colma Formation
Old Bay Clay
Franciscan Complex Bedrock

13. Typical Stratigraphic Layers
Fill
Heterogeneous soil consisting of: sands, clays, silts, gravels, construction debris
Engineered fill or not?
If not-engineered fill, can not be relied upon for foundation support

14. Typical Stratigraphic Layers
Dune Sand
clean fine-grained sand, wind-blown deposit
covers the majority of San Francisco
Typically loose in upper 10’
Typically medium dense, 10’ to 30’
Typically dense below 30’

15. Typical Stratigraphic Layers
Bay Mud
consists of clay and silt with occasional sand lenses and organic material
relatively low strength material
relatively compressible material
If underlain by new fill, it could settle, causing downdrag on piles

16. Typical Stratigraphic Layers
Colma Formation
consists predominantly of sands with occasional clay lenses
typically contains between 0 to 20% silt/clay
relatively strong material
relatively incompressible material
excellent foundation support

17. Typical Stratigraphic Layers
Old Bay Clay
consists of stiff to hard overconsolidated clay
may contain sand and gravel lenses
relatively strong
moderately compressible

18. Typical Stratigraphic Layers
Franciscan Complex bedrock
deformed bedding planes and shear zones due to seismic activity
highly variable hardness & strength
moderately to highly weathered
Relatively strong and incompressible
excellent foundation support

19. Geology and Seismicity
Regional Geology
Seismicity & Faulting
distance to faults
Geologic Hazards
ground shaking
liquefaction
lateral spreading
landsliding
tsunami

20. Discussion, Conclusions & Recommendations
discuss issues, alternatives, implications
conclude foundations type and settlement, shoring, soil improvement
Recommendations
provide recommendations regarding the geotechnical aspects of the project

21. Settlement Consolidation Liquefaction Seismic Densification
A slow process of squeezing water out in soft clay, resulting in denser packing of soil particles, when overlain by new fill
Liquefaction
Temporary loss of shear strength in loose sand due to a rise in excess pore water pressure generated by strong seismic shaking
Seismic Densification
Densification of loose sand above the water table due to ground shaking
Foundation Settlement

22. Groundwater
Depth groundwater encountered
Likely fluctuations
Design

23. Ground Improvement Stone columns Compaction grouting Chemical grouting
Jet grouting
Dynamic compaction

24. Foundations The most appropriate foundation type depends on:
Subsurface conditions
Building type and size
loading conditions
basement levels
Site constraints
noise
vibrations
proximity to existing improvements
proximity to bay, channel
Economics

25. Shallow Foundations
Footings
isolated
continuous
grid (waffle)
Mat

26. Shallow Foundations
suitable where competent material is encountered at subgrade elevation
can be used in fill where it is improved and building is small and light
mat can be used to span localized areas of non-support
mat can be used on softer soil in excavation where weight of structure is equal to or less than weight of soil removed

27. Deep Foundations
Piers
Piles

28. Piers
Efficient – can use one large diameter pier in lieu of several piles
Lengths can be adjusted in the field – reduce waste
Derive capacity mainly from friction
Use casing and/or drilling fluid if groundwater and/or loose soil is present

29. Driven Pile Concrete piles are economical in Bay Area
Use where soft soil or un-documented fill is present
Can be used at sites with high groundwater table or thick Bay Mud
Fabricated at yard (concrete) – good quality control
Moderately high capacity

30. Retaining Walls Restrained vs. Unrestrained Walls
Design wall pressure is higher for restrained walls
Drained vs. Undrained Walls
undrained walls are designed to resist hydrostatic pressure
Drainage
drainage panels
gravel drain
weep holes/pipes
Waterproofing
where moisture transmission is unacceptable

31. Floor Slabs Slab-on-grade Structural slab supported on ground
less expensive
will lose support and settle/crack if settlement occurs beneath slab
Structural slab
supported on foundations
more expensive
can span areas of non-support due to liquefaction and/or settlement

32. Floor Slabs Vapor Barrier
typically included beneath floor slabs above the water table
consists of:
4” crushed rock
10+ mil visqueen
2” sand
alternatives include Griffolyn T65-G
easier to install
takes less space
more expensive
perform moisture emission testing prior to placement of floor covering

33. Seismic Design Provide site class (A through F)
Provide spectral acceleration values for Maximum Considered Earthquake (MCE) and Design Earthquake (DE)

34. Seismic Design Site Class A hard rock B rock
C very dense soil and soft rock
D stiff soil profile
E soft soil profile F
liquefiable
more than 10 feet of peat
more than 25 feet of very high plasticity clays (PI>75)
more than 120 feet of soft/medium stiff clay (Bay Mud)

35. Excavation
Allowable slopes
Shoring
Dewatering

36. Site Preparation & Earthwork
remove pavements, organics
abandon utilities
abandon/remove old foundations
overexcavation
Earthwork
compaction requirements
acceptable fill materials

37. Utilities
Settlement
hangers
flexible connections
sleeved connections

38. Pavements
Flexible
Rigid
Pavers
pedestrian
vehicular

39. Site Drainage Keep water away from building
Collect all downspouts and surface water
All water should be directed to storm drain

40. Additional Geotechnical Services
Review geotechnical aspects of plans and specifications
Observation geotechnical aspects of construction
confirm subsurface conditions are as expected
contractor performs work in accordance with plans and specifications

41. Limitations
Conclusions and recommendations are based on limited subsurface exploration
We should provide observation services to check work is completed per plans, specs, and our recommendations