1. Geotechnical Aspects of ODOT Seismic Bridge Design
Jan Six P.E.
ODOT Bridge Section

2. Seismic Design Standards
ODOT Geotechnical Manual
AASHTO Guide Specifications for LRFD Seismic Bridge Design
ODOT Bridge Design & Drafting Manual

3. Topics When is a Site Specific Response Analysis Needed?
What does a Ground Response Analysis consist of?
How is liquefaction and lateral spread quantified?
How are these results used in design?
When is liquefaction mitigation needed?

4. Hazard Analysis vs. Ground Response Analysis
When is a Site Specific Response Analysis Needed?
Site Specific Analysis ?????
Hazard Analysis
vs.
Ground Response
Analysis

5. When is a Site Specific Response Analysis Needed?
Seismic Hazard Analysis
Probabilistic seismic hazard analysis (PSHA) or
Deterministic seismic hazard analysis
A deterministic hazard analysis (DSHA) involves evaluating the seismic hazard at a site for an earthquake of a specific magnitude occurring at a specific location, considering the attenuation of the ground motions with distance. The DSHA is usually conducted without regard for the likelihood of occurrence.

6. When is a Site Specific Response Analysis Needed?
Probabilistic Seismic Hazard Analysis (PSHA)
Focuses on the spatial and temporal occurrence of earthquakes, and evaluates all of the possible earthquake sources contributing to the seismic hazard at a site with the purpose of developing ground motion data consistent with a specified uniform hazard level.
Quantifies the uncertainties associated with the seismic hazard, including the location of the source, extent and geometry, maximum earthquake magnitudes, rate of seismicity, and estimated ground-motion parameters.
Produces a uniform hazard acceleration response spectrum based on a specified uniform hazard level or probability of exceedance within a specified time period (i.e., 7% probability of exceedance in 75 years).

7. When is a Site Specific Response Analysis Needed?
Seismic Hazard Analysis
Site specific hazard analysis are typically not performed on routine ODOT projects. Only if new information on new or existing sources was uncovered and documented.
The 2002 USGS Probabilistic Seismic Hazard Maps are typically used.

8. When is a Site Specific Response Analysis Needed?
Ground Response Analysis
Usually done to either:
Develop acceleration response spectra (ARS) or
For liquefaction analysis

9. When is a Site Specific Response Analysis Needed?
AASHTO “General Procedure” usually adequate
Use 2002 USGS Seismic Hazard Maps to obtain bedrock PGA, S0.2 and S1 for 500 and 1000 yr return periods
Determine soil site class designation (A – F)
Develop Response Spectra

10. When is a Site Specific Response Analysis Needed?
General Procedure for determining Response Spectrum
Use the program:
SeismicDesignUtility_2002.mde

11. When is a Site Specific Response Analysis Needed?
A site-specific ground motion response analyses should be performed if any of the following apply (AASHTO):
The site consists of Site Class F soils, as defined in Article
The bridge is considered critical or essential according to Article 4.2.2, for which a higher degree of confidence of meeting the seismic performance objectives of Article 3.2 is desired.

12. When is a Site Specific Response Analysis Needed?
Near–Fault Effects
AASHTO 3.4:
If the site is located within 6 mi of a known active fault capable of producing a magnitude 5 earthquake and near fault effects are not modeled in the development of national ground motion maps, directivity and directionality effects should be considered as described in Article and its commentary.
AASHTO
For sites located within 6 mi of an active surface or shallow fault, as depicted in the USGS Active Fault Map, near-fault effects on ground motions should be considered to determine if these could significantly influence the bridge response.

13. When is a Site Specific Response Analysis Needed?
Near–Fault Effects
AASHTO 3.4 definition:
An active fault is defined as a near surface or shallow fault whose location is known or can reasonably be inferred and which has exhibited evidence of displacement in Holocene (or recent) time (in the past 11,000 yr, approximately).
Use USGS Quaternary Fault database to determine if fault is considered “active” (<15ka) and for description of fault characteristics.

14. When is a Site Specific Response Analysis Needed?
Near–Fault Effects
• Directivity effects that increase ground motions for periods greater than 0.5 sec if the fault rupture propagates toward the site, and
• Directionality effects that increase ground motions for periods greater than 0.5 sec in the direction normal (perpendicular) to the strike of the fault.
AASHTO :
These effects are significant only for periods longer than 0.5 sec and normally would be evaluated only for essential or critical bridges having natural periods of vibration longer than 0.5 sec.

15. When is a Site Specific Response Analysis Needed?
Near–Fault Effects
• Currently no ODOT classification of “essential” or “critical” bridges.
All bridges considered subject to near fault effects if criteria is met.
Ground Response Analysis typically not required. Currently researching procedures to use for modifying general response spectrum.

16. When is a Site Specific Response Analysis Needed?
Site Class F soils, as defined in Article :
Peat or highly organic clays, greater than 10 ft in thickness,
Very high plasticity clays (H > 25 ft with PI > 75)
Very thick soft/medium stiff clays (H >120 ft),

17. When is a Site Specific Response Analysis Needed?
A site-specific ground motion response analyses should be considered if any of the following apply:
Evaluation of Liquefiable Soil Conditions
(vs. Simplified Methods, when FOSliq ≈ 1.0)
Very deep soil deposits or thin (<40 – 50 feet) soil layers over bedrock.
Obtain better information for evaluating lateral deformations, near surface soil shear strain levels or deep foundation performance.
Obtain ground surface PGA values for abutment wall or other design.

18. When is a Site Specific Response Analysis Needed?
Ground Response Analysis
Primary uses:
Developing Site Specific Design Acceleration Response Spectra (ARS)
Developing ground motion data for use in liquefaction evaluation

19. What does a Ground Response study consist of?
Evaluates the response of a layered soil deposit subjected to earthquake motions.
One-dimensional, equivalent-linear models are commonly utilized in practice.

20. What does a Ground Response study consist of?
This model uses an iterative total stress approach to estimate the nonlinear elastic behavior of soils.
Modified versions of the numerical model SHAKE (e.g., SHAKE2000, ProSHAKE, SHAKE91) are routinely used to simulate the propagation of seismic waves through the soil column

21. What does a Ground Response study consist of?
Output consists of:
acceleration response spectra at ground surface or at depths of interest,
time histories at selected depths in the soil profile,
plots of ground motion parameters with depth (e.g., PGA, maximum shear stress and shear strain),
induced cyclic shear stresses in individual soil layers, which may be used in liquefaction analysis.

22. What does a Ground Response study consist of?
Acceleration Response Spectra
Development Steps
Earthquake Source Characterization (deaggregation of uniform seismic hazard)
Develop input ground motions (time-histories)
Develop soil profile and dynamic properties for soil model
Run program and develop response spectrum from output

23. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
Develop Uniform Hazard Spectrum from 2002 USGS Seismic Hazard maps (“target bedrock spectrum”)
Use the deaggregation information from the 2002 USGS Seismic Hazard database to obtain information on the primary sources that affect the site.
Review USGS deaggregation data to:
Determine and characterize primary seismic sources
Determine magnitude (M) and distance (R) of each source

24. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
All seismic sources (M-R pairs) that contribute more than about 5% to the hazard in the period range of interest should be considered.
Scale (or spectrally match) earthquake time histories to the “target” spectrum

25. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
2002 USGS PSHA maps

26. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
USGS Web Site:
Custom Mapping Analysis Tools

27. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization (Deaggregation)

28. Design Response Spectra from Ground Response Analysis

29. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
2475 year
Period = 0 sec
Period = 0.1 sec
Period = 0.2 sec
Period = 0.3 sec
Period = 0.5 sec
Period = 1 sec
Period = 2 sec
PGA =
SA = 0.784
SA =
SA =
SA =
SA =
SA =
SUMMARY STATISTICS
Cont. (%)
R (km) M e
Mean Values --
29.7
6.76
0.82
24.7
6.51
0.87
30.7
6.78
0.92
37.2
7.03
0.95
55.6
7.57
1.05
61.3
7.73
1.07
70.5
7.9
1.18
Modal Values
7.5
6.63
-0.24
7.7
-0.05
88.5 9
1.42
1.29
1.03
0.94
Gridded Modal
6.408
1 - 2
5.543
7.6
0 - 1
6.909
9.497
16.13
16.9
16.96
Principle Sources (contributions >10%)
WUS shallow gridded
54.17
9.5
5.96
0.79
62.58
9.8
5.85
0.84
54.08 10
5.97
0.9
46.51
10.1
6.08
0.91
30.52
6.24
0.96
26.41
11.7
6.35 1
21.5
14.1
6.46
1.14
Wash-Oreg faults
22.55
6.74
-0.07
19.84
9.6
6.72
0.12
21.92
9.7
0.1
22.57
6.73
0.11
19.04
6.75
0.24
17.82
9.9
0.32
15.46
10.9
0.53
M 9.0 Subduction
13.03 98
1.54
13.82
98.2
1.52
17.95
98.9
1.4
28.7
100
32.82
101
1.06
34.9
102
1.04
M 8.3 Subduction
12.38
99.3
8.3
1.94
21.12
1.75
22.34
103
27.23
108
1.72
Individual fault hazard details (contributions >1%)
Grant Butte Fault
1.34
17.8
6.2
1.49
17.9
1.9
17.7
1.88
1.69
17.6
1.87
1.16
1.96
1.21
18.1
1.38
16.8
Helvetia Fault
15.7
6.38
0.72
15.5
0.78
15.3
6.39
0.86
Portland Hills Fault Char.
6.56
6.96
-0.42
8.2
-0.27
Portland Hills Fault 13
8.4
-0.23
11.31
6.71
-0.08
12.29
-0.1
12.31
10.65
0.13
9.61
0.2
7.76
0.4
877 Portland Hills Fault
5.51
8.1
6.95
-0.21
6.43
-0.29
5.82
-0.14
5.57
6.97
4.84
0.06

30. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
Period = 0.1 sec
SA = 0.784
Cont. (%)
R (km) M e --
24.7
6.51
0.87
7.7
6.63
-0.05
5.543
7.6
0 - 1
62.58
9.8
5.85
0.84
19.84
9.6
6.72
0.12
1.49
17.9
6.2
1.9
11.31
8.2
6.71
-0.08
5.51
8.1
6.95
-0.21
Period = 2 sec
SA =
Cont. (%)
R (km) M e --
70.5
7.9
1.18
88.5 9
0.94
16.96
1 - 2
21.5
14.1
6.46
1.14
15.46
10.9
6.75
0.53
34.9
102
1.04
27.23
108
8.3
1.72
1.38
16.8
6.2
1.9
7.76
6.74
0.4
4.84
6.97
0.06
2475 year
Period = 0 sec
Period = 0.1 sec
Period = 0.2 sec
Period = 0.3 sec
Period = 0.5 sec
Period = 1 sec
Period = 2 sec
PGA =
SA = 0.784
SA =
SA =
SA =
SA =
SA =
SUMMARY STATISTICS
Cont. (%)
R (km) M e
Mean Values --
29.7
6.76
0.82
24.7
6.51
0.87
30.7
6.78
0.92
37.2
7.03
0.95
55.6
7.57
1.05
61.3
7.73
1.07
70.5
7.9
1.18
Modal Values
7.5
6.63
-0.24
7.7
-0.05
88.5 9
1.42
1.29
1.03
0.94
Gridded Modal
6.408
1 - 2
5.543
7.6
0 - 1
6.909
9.497
16.13
16.9
16.96
Principle Sources (contributions >10%)
WUS shallow gridded
54.17
9.5
5.96
0.79
62.58
9.8
5.85
0.84
54.08 10
5.97
0.9
46.51
10.1
6.08
0.91
30.52
6.24
0.96
26.41
11.7
6.35 1
21.5
14.1
6.46
1.14
Wash-Oreg faults
22.55
6.74
-0.07
19.84
9.6
6.72
0.12
21.92
9.7
0.1
22.57
6.73
0.11
19.04
6.75
0.24
17.82
9.9
0.32
15.46
10.9
0.53
M 9.0 Subduction
13.03 98
1.54
13.82
98.2
1.52
17.95
98.9
1.4
28.7
100
32.82
101
1.06
34.9
102
1.04
M 8.3 Subduction
12.38
99.3
8.3
1.94
21.12
1.75
22.34
103
27.23
108
1.72
Individual fault hazard details (contributions >1%)
Grant Butte Fault
1.34
17.8
6.2
1.49
17.9
1.9
17.7
1.88
1.69
17.6
1.87
1.16
1.96
1.21
18.1
1.38
16.8
Helvetia Fault
15.7
6.38
0.72
15.5
0.78
15.3
6.39
0.86
Portland Hills Fault Char.
6.56
6.96
-0.42
8.2
-0.27
Portland Hills Fault 13
8.4
-0.23
11.31
6.71
-0.08
12.29
-0.1
12.31
10.65
0.13
9.61
0.2
7.76
0.4
877 Portland Hills Fault
5.51
8.1
6.95
-0.21
6.43
-0.29
5.82
-0.14
5.57
6.97
4.84
0.06

31. Design Response Spectra from Ground Response Analysis
Earthquake Source Characterization
Most Significant Contributors to Seismic
Ground Motion Hazard
0 – 0.5s period: Shallow Crustal
0.5 – 2s period: Subduction Zone Mega-Thrust
In areas where the hazard has a significant contribution from both the Cascadia Subduction Zone (CSZ) and from crustal sources, both earthquake sources need to be included in the analysis and development of a site specific response spectra.

32. Design Response Spectra from Ground Response Analysis
Selection of Time Histories
considering tectonic environment and style of faulting (subduction zone, Benioff zone, or shallow crustal faults),
seismic source-to-site-distance,
earthquake magnitude,
duration of strong shaking,
peak acceleration,
site subsurface characteristics,
predominant period,
spectral shape

33. Design Response Spectra from Ground Response Analysis
Selection and Scaling of Time Histories
AASHTO (2009) allows two options for the selection of time histories to use in ground response analysis. The two options are:
a) Use a suite of 3 response-spectrum-compatible time histories with the design response spectrum developed enveloping the maximum response, or
b) Use of at least 7 time histories and develop the design spectrum as the mean of the computed response spectra.

34. Design Response Spectra from Ground Response Analysis
Selection and Scaling of Time Histories
Use at least three (3) spectrum-compatible time histories, representing the seismic source characteristics.
Used for single primary source sites
Match the selected time-histories to the “target” spectrum using response spectrum matching techniques.
Develop the design response spectrum by enveloping the caps of the resulting response spectra.

35. Design Response Spectra from Ground Response Analysis
Selection and Scaling of Time Histories:
Sites with multiple primary sources
Difficult to match time histories from every source to the entire target spectrum (gives unrealistic results)
Use a collection of time histories that include at least three (3) ground motion records representative each primary source (typically subduction zone events and shallow crustal earthquakes)
Scale the records associated with each primary source so that the average of the records closely matches the target spectrum in the period range of significance.
Develop the mean spectrum for each primary source
Design response spectrum is developed as an envelope with minor reductions in the spectral peaks (mean + one standard deviation).

36. Design Response Spectra from Ground Response Analysis
Scaling of Time Histories
Four earthquake records based on PSHA deaggregation, deterministic specta
Two Shallow Crustal (SC-1, SC-2)
Two Subduction Zone (CSZ-1, CSZ-2)
Earthquake
Station
Direction
Magnitude
Distance
SC-1
Northridge, CA
Santa Monica City Hall
360 deg.
6.7
18 km
SC-2
90 deg.
CSZ-1
Michoacán, MEX
La Union
8.1
83.9 km
CSZ-2
Zihuatenejo
132.6 km

37. Design Response Spectra from Ground Response Analysis
Scaling of Time Histories
Scaling to get the geometric mean matched to period range of predominate hazard contribution

38. Design Response Spectra from Ground Response Analysis
Scaling of Time Histories
Once the time histories have been scaled or spectrally matched, they can be used directly as input into the ground response analysis programs to develop response spectra and other seismic design parameters.
Five percent (5%) damping is typically used in all site response analysis.

39. Design Response Spectra from Ground Response Analysis
Site Characterization
Select bent location
Develop input parameters
dependent on type of analysis, total or effective stress (nonlinear)
Shear wave velocity profile
static and dynamic soil properties

40. Design Response Spectra from Ground Response Analysis
Total Stress Analysis
SHAKE91 Computer Program (Shake2000, Proshake)
One Dimensional Wave Propagation Theory
Vertical Propagation of Shear Waves
Equivalent Linear Analysis
Effective Stress, Nonlinear Analysis
D-MOD, DESRA Computer Program
One Dimensional Wave Propagation Theory
Vertical Propagation of Shear Waves
Models pore water pressure generation
Models nonlinear soil degradation

41. Design Response Spectra from Ground Response Analysis

42. Design Response Spectra from Ground Response Analysis

43. Design Response Spectra from Ground Response Analysis

44. Design Response Spectra from Ground Response Analysis

45. Liquefaction Assessment from Ground Response Analysis
Liquefaction Assessment Procedures
(AASHTO 6.8 and GDM Section )
Preliminary Screening
Liquefaction Assessment not required if:
The bedrock PGA (or Acceleration Coefficient, As) is less than 0.10g,
The ground water table is more than 75 feet below the ground surface,
The soils in the upper 75 feet of the profile have a minimum SPT resistance, corrected for overburden depth and hammer energy (N’60), of 25 blows/ft, or a cone tip resistance qc of 150 tsf.

46. Liquefaction Assessment from Ground Response Analysis
Liquefaction Assessment Procedures
(AASHTO 6.8 and GDM Section )
Preliminary Screening (cont.)
Liquefaction Assessment not required if:
All soils in the upper 75 feet are classified as “cohesive”, and
Have a PI ≥ 18.
Note that cohesive soils with PI ≥ 18 may still be very soft or exhibit sensitive behavior and could therefore undergo significant strength loss under earthquake shaking. This criterion should be used with care and good engineering judgment.

47. Liquefaction Assessment from Ground Response Analysis
Liquefaction Assessment Procedures (AASHTO 6.8)
Simplified (empirical-based) Procedures (Seed & Idriss and others)
Limited to depths of about 50 feet
Total stress ground response analysis methods, used to obtain parameters for use in simplified procedures
Limited to low to moderate cyclic strain and moderate peak accelerations
Effective stress, nonlinear ground response analysis methods are used to obtain pore pressure ratio to assess liquefaction potential
More sophisticated analysis, requires peer review

48. Liquefaction Assessment from Ground Response Analysis
Liquefaction Assessment Procedures
Simplified Procedures (Seed & Idriss and others)
Limited to depths of about 50 feet
Stress reduction factor (rd), becomes
highly variable and uncertain with depth

49. Liquefaction Assessment from Ground Response Analysis
Liquefaction Assessment Procedures
Simplified Procedures
(Seed & Idriss and others)
Cyclic Resistance Ratio (CRR)

50. Liquefaction Assessment from Ground Response Analysis
Ground Response Analysis for Liquefaction Assessment
Earthquake Source Characterization
Identify primary sources contributing to the hazard
Attenuate PGA from primary source(s) to site (given M-R pairs)
Develop soil profile and dynamic properties for soil model
Apply soil amplification factors to obtain surface PGA for use with simplified procedures OR
Perform ground response analysis
total stress or
effective stress, nonlinear analysis

51. Liquefaction Assessment from Ground Response Analysis
Earthquake Source Characterization
Period = 0 sec
PGA =
Cont. (%)
R (km) M e --
29.7
6.76
0.82
7.5
6.63
-0.24
6.408
88.5 9
1 - 2
54.17
9.5
5.96
0.79
22.55
9.8
6.74
-0.07
13.03 98
1.54
1.34
17.8
6.2
1.94
1.03
15.7
6.38
0.72
6.56
8.3
6.96
-0.42 13
8.4
6.72
-0.23
2475 year
Period = 0 sec
Period = 0.1 sec
Period = 0.2 sec
Period = 0.3 sec
Period = 0.5 sec
Period = 1 sec
Period = 2 sec
PGA =
SA = 0.784
SA =
SA =
SA =
SA =
SA =
SUMMARY STATISTICS
Cont. (%)
R (km) M e
Mean Values --
29.7
6.76
0.82
24.7
6.51
0.87
30.7
6.78
0.92
37.2
7.03
0.95
55.6
7.57
1.05
61.3
7.73
1.07
70.5
7.9
1.18
Modal Values
7.5
6.63
-0.24
7.7
-0.05
88.5 9
1.42
1.29
1.03
0.94
Gridded Modal
6.408
1 - 2
5.543
7.6
0 - 1
6.909
9.497
16.13
16.9
16.96
Principle Sources (contributions >10%)
WUS shallow gridded
54.17
9.5
5.96
0.79
62.58
9.8
5.85
0.84
54.08 10
5.97
0.9
46.51
10.1
6.08
0.91
30.52
6.24
0.96
26.41
11.7
6.35 1
21.5
14.1
6.46
1.14
Wash-Oreg faults
22.55
6.74
-0.07
19.84
9.6
6.72
0.12
21.92
9.7
0.1
22.57
6.73
0.11
19.04
6.75
0.24
17.82
9.9
0.32
15.46
10.9
0.53
M 9.0 Subduction
13.03 98
1.54
13.82
98.2
1.52
17.95
98.9
1.4
28.7
100
32.82
101
1.06
34.9
102
1.04
M 8.3 Subduction
12.38
99.3
8.3
1.94
21.12
1.75
22.34
103
27.23
108
1.72
Individual fault hazard details (contributions >1%)
Grant Butte Fault
1.34
17.8
6.2
1.49
17.9
1.9
17.7
1.88
1.69
17.6
1.87
1.16
1.96
1.21
18.1
1.38
16.8
Helvetia Fault
15.7
6.38
0.72
15.5
0.78
15.3
6.39
0.86
Portland Hills Fault Char.
6.56
6.96
-0.42
8.2
-0.27
Portland Hills Fault 13
8.4
-0.23
11.31
6.71
-0.08
12.29
-0.1
12.31
10.65
0.13
9.61
0.2
7.76
0.4
877 Portland Hills Fault
5.51
8.1
6.95
-0.21
6.43
-0.29
5.82
-0.14
5.57
6.97
4.84
0.06

52. Liquefaction Assessment from Ground Response Analysis
Earthquake Source Characterization
Three Primary Sources for consideration
Shallow Crustal
Gridded (random)
Subduction Zone
For the crustal and “gridded” sources, review the individual fault details to select fault characteristics (M, R, fault mechanism, etc.) most relevant to the hazard.

53. Liquefaction Assessment from Ground Response Analysis
Attenuate PGA from Source to Site
Summary of Magnitude, Distance and PGA (1000-yr return period)
Source
Magnitude
Distance, (km)
Depth, (km)
Crustal
6.72
8.4
10.5
Subduction
9.0 98 20
Magnitude and Distance pairs represent weighted averages of
the individual sources

54. Liquefaction Assessment from Ground Response Analysis
Ground motion attenuation relationships used in 2002 USGS PHSA
Shallow Crustal:
Boore et al. (1997)
Abrahamson and Silva (1997)
Sadigh et al. (1997)
Spudich et al., 1999,
Campbell and Bozorgnia (2003).
Cascadia Subduction Zone:
Youngs et. al. (1997)

55. Liquefaction Assessment from Ground Response Analysis
Attenuate PGA from Source to Site

56. Liquefaction Assessment from Ground Response Analysis
Attenuate PGA from Source to Site

57. Liquefaction Assessment from Ground Response Analysis
Attenuate PGA from Source to Site
Summary of Magnitude, Distance and PGA (1000-yr return period)
Source
Magnitude
Distance, (km)
Depth, (km)
PGA rock
Crustal
6.72
8.4
10.5
0.38
Subduction
9.0 98 20
0.09
Magnitude and Distance pairs represent weighted averages of
the individual sources

58. Liquefaction Assessment from Ground Response Analysis
Site Characterization
Select bent location
Develop input parameters
dependent on type of analysis, total or effective stress (nonlinear)
shear wave velocity profile
static and dynamic soil properties

59. Liquefaction Assessment from Ground Response Analysis
Total Stress Analysis
SHAKE91 Computer Program (Shake2000, Proshake)
Calculate cyclic shear stress ratio (CSR) with depth
Calculate cyclic resistance ratio (CRR) with depth
FOS against liquefaction equals (CRR/CSR)
Effective Stress, Nonlinear Analysis
Used in areas of high accelerations and high cyclic shear strains
D-MOD, DESRA or other computer Program
Calculates pore pressure ratio, Ru, with depth in soil profile
Determine where Ru ≥ 0.80 – 0.90 for liquefaction

60. Liquefaction Assessment from Ground Response Analysis
Selection of Time Histories use at least:
3 motions representative of subduction zone events and
3 motions appropriate for shallow crustal earthquakes
Scaled to the bedrock PGA determined from attenuation relationships

61. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; Peak Acceleration

62. Liquefaction Assessment from Ground Response Analysis
CSR(Shake) vs. CSR Simplified Procedure

63. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; FOS Against Liquefaction
Subduction Zone

64. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; FOS Against Liquefaction
Subduction Zone

65. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; FOS Against Liquefaction
Subduction Zone

66. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; FOS Against Liquefaction
Crustal EQs

67. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; FOS Against Liquefaction
Crustal EQs

68. Liquefaction Assessment from Ground Response Analysis
Shake Analysis; FOS Against Liquefaction
Crustal EQs

69. Liquefaction Assessment from Ground Response Analysis
FOS Against Liquefaction
FOS < 1.1 » Liquefaction (also indicates the potential for liquefaction-induced ground movement (lateral spread and settlement).
FOS between 1.1 and 1.4 » reduced soil shear strengths due to excess pore pressure generation.
FOS > 1.4 » excess pore pressure generation is considered negligible and the soil does not experience appreciable reduction in shear strength.

70. Liquefaction Assessment from Ground Response Analysis
DMOD Analysis; Liquefaction Assessment
Crustal and
Subduction Zone EQs

71. Recommendations
Use deepest liquefaction depth with UHS Design Response Spectra (from either AASHTO General Procedure or Ground Response Analysis)
Design Response Spectrum cannot be lower than 2/3rd of spectrum from the AASHTO General Procedure

72. Lateral Spread Assessment
Use conventional limit equilibrium analysis to assess slope failure potential
• Residual shear strengths are used in liquefiable layers,
• Typically don’t use Kh or Kv (de-coupled analysis),
• If FOS < 1.0; Flow failure
If FOS ≥ 1.0; Deformation Analysis

73. Lateral Spread Assessment
Methods to estimate the magnitude of seismically induced lateral slope deformation include:
• Empirically-based displacement estimates for lateral spreading
(Youd et al. (2002),
• Newmark-type analyses using acceleration time histories generated from site-specific soil response modeling.
• Simplified charts based on Newmark-type analyses (Makdisi and Seed, 1978)

74. Lateral Spread Assessment
Methods to estimate the magnitude of seismically induced lateral slope deformation include:
• Simplified procedures based on refined Newmark-type analyses (Bray and Travasarou 2007, Saygili and Rathje 2008)
• Simplified charts based on nonlinear, effective stress modeling (Dickenson et al, 2002)
• Two-dimensional numerical modeling of dynamic slope deformation.

75. Lateral Spread Assessment
Several of these methods should be used as appropriate, and engineering judgment applied to the results, to determine the most reasonable range of predicted displacements

76. How are these results used in design?
Liquefaction effects include:
reduced axial and lateral capacities and stiffness in deep foundations,
ground settlement and possible downdrag effects
lateral spread, global instabilities and displacements of slopes and embankments,
loads transferred to foundation piles and shafts from lateral displacements

77. How are these results used in design?
Bridge Approach Fills:
Assess performance requirements (no-collapse & serviceability)
Global stability
Settlement
Allowable
deformation and
foundation damage

78. Abutment Resistance for Seismic Loads
Designer has two options:
Use passive resistance
Don’t use passive resistance
If using presumptive values in AASHTO the longitudinal passive soil pressure shall be less than 0.70 of the value obtained using the procedure given in Article 5.2.3

79. Abutment Resistance for Seismic Loads
Presumptive Pp (AASHTO 5.2.3)

80. Abutment Resistance for Seismic Loads
Presumptive Pp

81. Abutment Resistance for Seismic Loads
Passive soil pressure less than 0.70 of the value obtained using presumptive method = no Agency Approval Required
Passive soil pressure greater than 0.70 of the value obtained using presumptive method = Agency Approval Required

82. How are these results used in design?
Bridge Foundations
(Extreme Limit State I):
Loss of strength due to liquefaction generally assumed to be concurrent with the peak loads in the structure
Unless nonlinear effective stress analysis is performed.

83. How are these results used in design?
Bridge Foundations
(Extreme Limit State I):
For bridge sites where liquefaction occurs bridges should be analyzed and designed in two configurations as follows:
• Nonliquefied Configuration: no liquefaction occurs, using the ground response spectrum appropriate for the site soil conditions in a nonliquefied state.
• Liquefied Configuration: The structure as designed in the nonliquefied configuration should be reanalyzed assuming that the layer has liquefied and the liquefied soil provides the appropriate residual resistance for lateral and axial deep foundation response analyses consistent with liquefied soil conditions The design spectrum should be the same as that used in a nonliquefied configuration.

84. How are these results used in design?
Bridge Foundations
Spread Footings:
Not recommended over liquefiable soils unless ground improvement provided
Piles & Drilled Shafts:
Tips located below deepest liquefiable layer
Friction resistance in liquefiable layer not included in Extreme Event I state loading case
Provide modified soil parameters for modeling p-y curves in liquefied soil layers (don’t use built-in DFSAP program option for estimating liquefied lateral stiffness parameters)
Provide estimates of downdrag loads due to liquefaction settlement

85. How are these results used in design?
Bridge Foundations
Piles & Drilled Shafts (cont.):
Assess effects of lateral spread deformations on deep foundations and the ability of the pile/shaft foundation to resist these loads
ATC/MCEER reports: Recommended LRFD Guidelines for the seismic design of bridges (Design Examples & Liquefaction Study Report); MCEER/ATC 49-1/49-2.
Determine if mitigation is necessary

86. Earthquake Resisting Elements not permitted
Full plastic hinging of pile foundations under seismic loads is not permitted (BDDM)

87. When is liquefaction mitigation needed?
Mitigation is required when the bridge performance requirements cannot otherwise be met.
Design deviations can be considered by the Bridge Section
All mitigation designs are to be reviewed by the Bridge Section

88. When is liquefaction mitigation needed?
Performance Requirements (New Bridges)
1000-year “No-Collapse” Criteria
Under this level of shaking, the bridge and approach structures, bridge foundation and approach fills must be able to withstand the forces and displacements without collapse of any portion of the structure.
If large embankment displacements (lateral spread) or overall slope failure of the end fills are predicted, the impacts on the bridge end bent, abutment walls and interior piers should be evaluated to see if the impacts could potentially result in collapse of any part of the structure.
Slopes adjacent to a bridge or tunnel should be evaluated if their failure could result in collapse of a portion or all of the structure.

89. When is liquefaction mitigation needed?
Performance Requirements (New Bridges)
500-year “Serviceability” Criteria
Under this level of shaking, the bridge and approach fills, are designed to remain in service shortly after the event (after the bridge has been properly inspected) to provide access for emergency vehicles.
In order to do so, the bridge is designed to respond semi-elastically under seismic loads with minimal damage. Some structural damage is anticipated but the damage should be repairable and the bridge should be able to carry emergency vehicles immediately following the earthquake. This holds true for the approach fills leading up to the bridge.

90. When is liquefaction mitigation needed?
Performance Requirements (New Bridges)
500-year “Serviceability” Criteria (cont.)
Approach fill settlement and lateral displacements should be minimal to provide for immediate emergency vehicle access for at least one travel lane.
For mitigation purposes approach fills are defined as shown on Figure 6-12.
As a general rule of thumb, an estimated lateral embankment displacement of up to 1 foot is considered acceptable in many cases as long as the “serviceable” performance criteria described above can be met. Vertical settlements on the order of 6” to 12” may be acceptable depending on the roadway geometry and anticipated performance of the bridge end panels.

91. When is liquefaction mitigation needed?
Performance Requirements (New Bridges)
500-year “Serviceability” Criteria (cont.)
These displacement criteria are to serve as general guidelines only and engineering judgment is required to determine the final amounts of acceptable displacement that will meet the desired criteria. It should be noted that these estimated displacements are not at all precise values and may easily vary by factors of 2 to 3 depending on the analysis method(s) used. The amounts of allowable vertical and horizontal displacements should be decided on a case-by-case basis, based on discussions and consensus between the bridge designer and the geotechnical designer and perhaps other project personnel.

92. When is liquefaction mitigation needed?
BDDM Section & GDM Appendix 6C

93. When is liquefaction mitigation needed?
Mitigation Zone at Bridge Approaches

94. Thank You For Your Attention