1. Steps in Foundation Engineering Understand project and site Develop design criteria Identify possible foundation alternatives Conduct soil investigation Characterize site Engineering analysis to evaluate alternatives Develop recommendations and write report Monitor design, construction and performance

2. Project and Site Project intent (from owner) Assess general soil and site conditions – Previous borings, maps, reports, aerial photography Previous experience in area – Adjacent structures (How were they constructed? how did they perform?) Constraints – Local building codes, neighboring facilities, ` access issues, economic limitations

3. Develop Design Criteria Allowable settlement and tilt Acceptable factors of safety Identify constructability issues Obtain design loads (provided by structural firm) Building codes (UBC, IBC, ACI, AISC, etc)

4. Develop Design Criteria Allowable Settlement? Total settlement Tilt Differential Settlement

5. Allowable Settlements

6. Settlement issues Connections with existing structures and utility lines Surface drainage Access by vehicles and pedestrians Aesthetics

7. Tilting and Differential Settlement Non-uniform site conditions Ratio of actual-to-design load differs over structure Ratio of dead load to live load differs over structure As-built dimensions differ from plan dimensions

8. Tilting Lack of stability  /H<1/500 (text) Differential Settlement Stresses in structure – Cracking δ/L<1/500 (C B C) δ/L<1/150 (text) FS=1.5-2

9. Factors of Safety FS = capacity/demand FS = 2-3 for foundations (typical) FS = 1.5 for slopes and walls (typical)

10. Factors of Safety – why? Required reliability Uncertainties in soil properties and applied loads Construction tolerances (design vs. as-built) Cost-benefit ratio of additional conservatism in design

11. Factors of Safety Foundation failures are typically more costly than failures in the superstructure Construction tolerances in foundations are wider than those in the superstructure. Thus, as-built dimensions may differ from the design. Extra weight on the superstructure increases foundation loads.

12. Design Loads Types of structural loads Normal, P Shear, V X, V Y Moment, M X, M Y Torsion, T

13. Design Loads Dead Loads, D Live Loads, L Wind Loads, W Earthquake, E Earth Pressure Loads, H Snow, rain, fluid, impact, stream, etc.

14. Soil Investigation In-situ testing: Identify materials (geology) Clays (CPT, DMT, vane) Sands (CPT, DMT, SPT) Borings (get samples – GSD) Laboratory Engineering properties from soil samples Engineering properties (e.g. w, γ, LL, GSD) Strength Consolidation

15. Identify Possible Foundation Alternatives Consider types of foundations Assess benefits and potential problems

16. Site Characterization Geology Soil and effective stress profiles Identify and estimate key soil properties Monitor Design, Construction, and Performance

17. Final Comments Soil mechanics is the basis that allows for the selection, design and construction of foundations. Foundation design = assessment and optimization of options through analysis. Requires the ability to consider what might go wrong. “Failure” is an unacceptable difference between expected and observed behavior. Key goal as foundation engineer: build economical foundation that works. Use rules of thumb when possible to check for reasonableness.

18. Your Job Understand physics and soil behavior Develop understanding Develop engineering judgment Lifelong Learning