1. CIE 338 - Soil Mechanics and Foundations II
Soil Properties and Site Investigation
Shallow Foundation Design
Deep Foundation Design
Retaining Structures and Slope Stability

2. Building Codes Local and national codes guide practice.
Design must conform to code or
Departures require approval
Compliance does not assure safety or economy

3. Shallow Foundation Df < 4BP
Column
Ground Surface Df
Footing B
Shallow Foundation Df < 4B

4. A = total building foundation plan area
Af = Individual footing area
If  Af => 0.5 A then consider a mat foundation

5. Shallow (Mat) Foundation Df < 4B
Column Loads Df
Mat B
Shallow (Mat) Foundation Df < 4B

6. Deep Foundation - Piles
Friction Pile
End Bearing Pile
Hammer
Hammer
Hard Soil / Rock
Firm Soil

7. Pile
Shaft
Hammer
Poured in place fill
Pre bored hole
Deep Foundations

8. Foundation Shallow Deep Footing Pile Shaft Mat Df < 4B Df > 4B
Af < 0.5A
Af > 0.5A
Driven
Cast in Place
Footing
Pile
Shaft
Mat
Caisson
Pier
Bored Pile
Af =sum of footing areas
Df = depth of cover
A = plan area of structure
B = footing width

9. Earth Retaining Systems
Wall System
(external)
Stabilized Earth System
(internal)

10. Slope Stability How steep can the slope be?
What is the factor of safety (FS)?
How can we improve the FS?

11. Foundations transfer loads to subsurface
DL - dead loads consist of the structure load
usually well known
LL - live loads are service loads, wind, earthquake
usually involve large uncertainty

12. Types of Loads Normal Loads, P Shear Loads, V Moment Loads, M
Torsion Loads, T (usually negligible)

13. z y

14. Normal load
important for buildings P z y

15. Shear load
important for retaining walls z
Vy, Vx y Vy

16. Moment load
important for retaining walls
and buildings z Mx
Mx, My y

17. Torsion load
usually not significant z T y

18. Applied loads induce: Failure - (collapse/instability)
Design with a generous factor of safety
Movement - (settlement/deformation)
Design to a performance criteria

19. Factor of Safety (FS) against failure or for bearing capacity
FS = Resistance/Driving
FS for buildings ~ 3
FS for retaining structures and slopes ~1.5

20. Movement / Settlement / Deformation
Uniform settlement - least critical
Even tilting - can be critical
Distortion - potentially troublesome

21. Uniform settlement,  

22. Even tilting,  (limit < 1/250)

23. s s
As built foundation   D 

24.  = maximum total settlement
D= maximum differential settlement
S = column spacing
 = distortion = D/ S
Da = a * S
a, denotes allowable

25. a = allowable rotation (Table 2.2, Coduto)
Type of structure a
Frame warehouse 1/200
Steel and reinforced concrete buildings 1/600
Unreinforced masonry 1/2500

26. Consult Fig. 2.9 and 2.10 (Coduto)
Upper limit of D/  for foundations on sand = 1
Upper limit of D/  for foundations on clay ~ 0.3
The allowable total settlement is set to limit D

27. Example 2.1
A steel frame building without diagonal bracing
S = 20 ft on clay foundation, what are the
allowable total and differential settlements?
Da = a * S obtain a = 1/500 (Table 2.2)
Da = 0.5 in obtain D/ = 0.8 (Fig 2.9)
a = Da * ( /D) = 0.5 / 0.8 = 0.6 in

28. Frost Heave Ground swell due to water volume expansion on freezing
regular and < 50 mm (minor)
Water rise by capillary action and formation of ice lenses
irregular and of the order of 300 mm (major)
Surface down thawing leads to super saturation
foundation becomes very weak until drained

29. Conditions for Frost Heave
Freezing temperatures
usually natural, artificial also
Source of water
ground water table
Frost susceptible soil (Table 2.3, Coduto)
silts and fine sands - F4 soils

30. Measure to mitigate frost heave
Insulate - rare
Remove / replace - not common
Place foundation below depth of heave, Df
most common

31. Df is depth of frost penetration
Varies by geographic location (Fig. 2.12, Coduto)
Syracuse ~ 1.4 m
Minnesota ~ 2.5 m
California and Southern States < 0.3 m
Consult local practice, building codes

32. Other water related problems
Scour (armour, riprap)
Corrosion (coating, cathodic protection)
Sulfate attack (special cement, low w/c ratio)
Decay, insects and fire (creosote pressure treat)

33. Soils Coarse Fine #200 #200 Grain size vs plasticity and liquid limit
mm Gravel
Sand
< Silt and Clay
Coarse
#200
#200
Fine
Grain size vs plasticity and liquid limit

34. mass
volume Va Ma
air
voids Vw Mw
water
minerals Vs
solids Ms
Soil

35. = {(e-emin)/(emax-emin)}*100
Coarse grained soils
e = void ratio = Vv/Vs
emax and emin
Dr = relative density
= {(e-emin)/(emax-emin)}*100

36. Fine grained soils
Water content = w = (Mw / Ms)*100
SL = shrinkage limit
PL = plastic limit
LL = liquid limit
w = natural water content

37. Coarse grained soils e
emax
emin
Fine grained soils w PL LL

38. Gravel
Sand
Silt
Clay

39. Gravel
Sand
Silt
Clay
Gravity
G Wellpoint
V Wellpoint
Electro-osmosis?