1. GLE/CEE 330: Soil Mechanics Introduction to Foundation Engineering
Geological Engineering
University of Wisconsin-Madison

2. Learning Objectives Define key terms in foundation engineering
Discuss types of shallow and deep foundations
Describe basic foundation design philosophy

3. Key Terms
Foundation: structure that transmits loads to underlying soils.
(Coduto)
Shallow Foundations
(Df/B < )
Deep Foundations
(Df/B > 4.0)
Df = Embedment Depth
B = Characteristic Length

4. Key Terms
Bearing Capacity (q): Pressure that a soil can support (soil property)
Ultimate bearing capacity (qult): Max. pressure soil can support (determined by analysis)
Net bearing capacity (qnet): Max. pressure soil can support above current overburden pressure (account for embedment effect)
Allowable bearing capacity (qall): Design soil bearing pressure
F.S. = Factor of Safety (2.5 – 3.5) (Allowable Stress Design)

5. ASD vs. LRFD Allowable Stress Design (ASD)
Historical Approach in Geotechnical Engineering
“Blanket” factor of safety
More conservative
(More Cost)
Less conservative
(More Risk)

6. ASD vs. LRFD Load and Resistance Factor Design (LRFD)
Modern Approach in Geotechnical Engineering
Factored Load (Q) < Factored Resistance (R)
gi are “load factors” for different types of loads (g ≥ 1.0)
f are “resistance factor(s)” for nominal resistance (f ≤ 1.0)
Effectively accounts for uncertainty in a quantitative way
Structures may be designed for a specific amount of risk

7. Types of Foundation Loads
Normal Loads
Shear Loads
Moment Loads
Torsion Loads
Load Sources:
Dead Loads
Snow Loads
Earth Pressure
Fluid Loads
Earthquake Loads
Wind Loads
8) Impact Loads
9) Temperature Induced Loads
10) Stream/Ice Loads
11) Centrifugal/Braking
12) Shear Loads
(Coduto)

8. Shallow Foundation Types
Spread Footing (column loads)
(Alex Mead)

9. Shallow Foundation Types
Strip Footing (wall loads)

10. Shallow Foundation Types
Mat (Raft) Foundation
(floor loads)

11. Deep Foundations Insufficient soil “bearing capacity” near surface
Excessive settlements on shallow foundations
Differential settlements on shallow foundations
Constructability issues (e.g., shallow GWT)
Lateral loads, uplift forces
(wind, waves, earthquakes, earth pressure)

12. Deep Foundation Types Piles Timber Steel (H-piles, tubes, mandrels)
Reinforced Concrete
Cast-in-place concrete
Characteristics/Issues:
“Displacement” vs. “Non-displacement”
Driving stresses
Vibration/Noise
H-Pile
Concrete Pile

13. Deep Foundation Types Drilled Shafts B = 2-30 ft (0.6-9 m)
L < 300 ft (91 m)
Large Lateral Load Resistance
(Hayward Baker)

14. Pile Load Transfer (Single Pile)
Qf = “shaft friction” or “side shear”
Qb = “end bearing”
If Qf >0.8Qb then “friction pile”
If Qb = 0 (design assumption) then “floating pile”

15. Pile Groups

16. Foundation Design Philosophy
Limit State = “condition beyond which a component/member of a foundation or other structure ceases to satisfy the provisions for which the component/member was designed”
Strength Limit State (bearing capacity analysis)
Service Limit State (settlement analysis)
Extreme Event Limit State
Fatigue Limit State