NEW Shallow Foundation - Settlement

Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 1 of 25
Figures after Crawford, 1972 (CBD-148)
TYPES OF SETTLEMENT
L L
L
Uniform
Settlement
Tilt Non-Uniform
Settlement
!
!
Where:
S
t
= Total Settlement
(Typically limited to 1 inch)
! = Maximum Differential Settlement
L = Building (or Span) Length
Deflection Ratio = !/L
Table 2-1. Maximum Allowable S
t
(EM1110-1-1904)
S
t
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 2 of 25
Figures after Crawford, 1972 (CBD-148)
TYPES OF SETTLEMENT
L L
L
Uniform
Settlement
Tilt Non-Uniform
Settlement
!
!
Where:
S
t
= Total Settlement
! = Maximum Differential Settlement
L = Building (or Span) Length
Deflection Ratio = !/L
Table 2-2. Limiting !/L (EM1110-1-1904)
S
t
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 3 of 25
Figure 2-1. EM1110-1-1904
DIFFERENTIAL SETTLEMENT
Where:
! = Max. Differential Settlement
# = Differential Settlement between 2 Pts
L = Building (or Span) Length
l = Length between 2 Points
Angular Distortion $ = #/l
Differential Settlement
Interference w/ Adjacent Structures
Disruption of Machinery & People
Cracking
Jammed Floors & Windows
Uneven Floors
Reduction of waterstop efficiency
Structural Failure
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 4 of 25
Figure 2-1. EM1110-1-1904
DIFFERENTIAL SETTLEMENT
Table 2-3. Limiting $/l to Avoid Damage
(EM1110-1-1904)
*Based on field surveys of damage
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 5 of 25
Figure 2-1. EM1110-1-1904
DIFFERENTIAL SETTLEMENT
Table 2-3. Empirical Correlations between ! and $ (EM1110-1-1904)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 6 of 25 Figure 1-3. EM1110-1-1904
FOUNDATION CONTACT PRESSURES
RIGID FOUNDATIONS
Typically Experience
Uniform Settlement
FLEXIBLE FOUNDATIONS
Typically Experience
Differential Settlement
Figure 12-14. Das FGE (2005)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 7 of 25
WHAT DO YOU NEED TO CALCULATE SETTLEMENT?
FOUNDATION SETTLEMENT COMPONENTS
Total Foundation Settlement = Elastic Settlement + Consolidation Settlement
a.k.a. Immediate.
Primary Settlement Component
of Sands but also occurs in
Cohesive Soils.
a.k.a. Long-Term.
Primary Settlement Component
of Cohesive Soils.
Covered in CIVL409
S
t
= S
e
+ S
c
Foundation Loads/Pressures
Changes in Vertical Soil Stress (!%)
Foundation Size and Location
Soil Profile
Soil Properties:
Elastic Settlement: E
s
, µ
Consolidation Settlement: 1D Consolidation Test Data
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 8 of 25
Boussinesq Distributions
Figure 1-2. EM 1110-1-1904
STRIP
VERTICAL STRESS INCREASE (!%) IN SOILS (REVIEW)
SQUARE
Westergaard Distributions
Figure 11. NAVFAC DM7.01
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 9 of 25
APPROXIMATE 2V:1H DISTRIBUTION METHOD
Figure C-1. EM1110-1-1904
Where:
!% = Change in Total Vertical
Stress
Q = Applied Foundation Load
B = Foundation Width
L = Foundation Length
VERTICAL STRESS INCREASE (!%) IN SOILS (REVIEW)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 10 of 25
Table C-1. Boussinesq Solutions (EM 1110-1-1904).
VERTICAL STRESS INCREASE (!%) IN SOILS (REVIEW)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 11 of 25
Table C-1. Boussinesq Solutions (EM 1110-1-1904).
VERTICAL STRESS INCREASE (!%) IN SOILS (REVIEW)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 12 of 25
VERTICAL STRESS INCREASE (!%) IN SOILS (REVIEW)
Table C-1. Boussinesq Solutions (EM 1110-1-1904).
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 13 of 25 Figures courtesy of http://www.taunton.com
VERTICAL STRESS INCREASE (!%) IN SOILS
Depth of Influence of !% for Settlement Calculations
SQUARE: Depth = 2B
STRIP: Depth = 4B
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 14 of 25
VERTICAL STRESS INCREASE (!%) IN SOILS
Depth of Influence of !% for Settlement Calculations
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 15 of 25
Where:
S
e
= Elastic Settlement
q
o
= Contact Stress
& = Foundation Location Factor
for Settlement under Center
& = 1, m’ = L/B, n’ = H/(B/2)
For Settlement under Corner
& = 1, M’ = L/B, n’ = H/B
B’ = Width
use B for Settlement @ Corner
use B/2 for Settlement @ Center
General Elastic Relation
(Flexible Foundation):
µ
s
= Soil Poisson’s Ratio
E
s
= Soil Elastic Modulus
I
s
= Shape Factor
f(µ
s
, F
1
, F
2
) – Table 12.3 Das FGE (2005)
I
f
= Depth Factor
f(D
f
/B, µ
s
, L/B) – Table 12.4 Das FGE (2005)
General Elastic Relation
(Rigid Foundation):
ELASTIC SETTLEMENT OF SOIL
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 16 of 25
ELASTIC SETTLEMENT OF SOIL – TABLE 12.3 Das (2005)
Center of
Footing:
Corner of
Footing:
H = Depth to rigid layer
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 17 of 25
ELASTIC SETTLEMENT OF SOIL – TABLE 12.4 Das (2005)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 18 of 25
ELASTIC SETTLEMENT OF SOIL – TABLE 12.4 Das (2005)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 19 of 25
ELASTIC PARAMETERS OF SOIL
Table 12.5. Typical Elastic Parameters of Soils
(Das FGE (2005)
Table D-3. Typical Soil Elastic Moduli
(EM1110-1-1904)
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 20 of 25
Figure courtesy of Marchetti (1999) - The Flat Dilatometer (DMT) and
It's Applications to Geotechnical Design
ELASTIC SETTLEMENT OF SOIL - DMT
Uses Direct
Measurement of Soil to
Calculate Settlement
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 21 of 25
ELASTIC SETTLEMENT OF SOIL - DMT
Stress Distribution
Figure courtesy of Marchetti (1999) - The Flat Dilatometer (DMT) and
It's Applications to Geotechnical Design
Where:
S
e
= Elastic Settlement
!% = Change in Stress
M
DMT
= Constrained Modulus
Z = Depth
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 22 of 25
ELASTIC SETTLEMENT OF SOIL - DMT
Marchetti (1999) - The Flat Dilatometer (DMT) and
It's Applications to Geotechnical Design
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 23 of 25
Figure from Hayes (1990)
ELASTIC SETTLEMENT OF SOIL - DMT
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 24 of 25
DMT SETTLEMENT EXAMPLE (NTS)
Depth
(ft)
0
10.2
GWT 10 ft
Silty Sand (SM)
'
t
= 115 pcf, (' = 34°
3ft Sq. Column
Q = 27 kips
D
f
= 1ft D
f
= 1ft
2ft x 4.5 ft Column Footing
Q = 27 kips
Determine Settlement of Both
Footings using the provided
DMT Data
Revised 2/2010
CIVL410 Geotechnical Engineering II
Shallow Foundations
Slide 25 of 25
DMT
SETTLEMENT
EXAMPLE
DMT Data