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Design of a given component shall limit permanent displacement to the following: 1. Less than 10 cm for a Level 1 earthquake (10% probability of exceedance in 50 years). 2. Less than 30 cm for a Level 2 earthquake (5% probability of exceedance in 50 years). These standards are intended to insure that following a Level 1 earthquake (operating level event for structures of normal importance), the damages will be negligible, non-structural, and the bridge will remain serviceable. Following a larger, Level 2 earthquake (operating level event for structures of high importance and/or collapse prevention), the damage will be non-catastrophic and repairable in a reasonable amount of time. The deformation limits are bridge and component specific, and reflect the sensitivity of the structure and appurtenant components to deformation. Several transportation departments are developing programs to mitigate liquefaction hazards at major bridge sites. Common ground treatment methods include soil densification, increasing the strength and stiffness of the soil by grouting, and/or improved soil drainage. These improvements are accomplished using many methods such as deep dynamic compaction, vibrocompaction, stone columns, soil mixing, and many others. Although the use of soil improvement methods is increasing, there are very few tools currently available for establishing the extent of ground treatment necessary to minimize earthquake damage. The most comprehensive reference has been prepared by the Japanese Port and Harbour Research Institute (PHRI 1997). Although this reference is based on experience gained in the port environment, most of the recommendations are transferable to the highway transportation field. The recommendations are largely based on limit state analysis and model testing. Additionally, the guidelines do not address permanent deformations as a function of design-level ground motions, a primary concern in performance-based design. Current “standard of practice” seismic design for embankments and bridge abutments involves using pseudo-static, limit equilibrium mechanics. The design utilizes empirically determined seismic coefficients, which are functions of the maximum ground accelerations. The coefficients are used to estimate the seismic inertial body forces. These limit equilibrium methods can be used to account for the presence of potentially liquefiable soils, but only in a simplistic manner by decreasing the soil strength. Additionally, the output of these methods is usually the factor of safety against the exceedance of a given limit state, and therefore, are not directly applicable for deformation-based analysis. There have been several recent enhancements to pseudo-static design methods for evaluating seismic deformations of the earth structures (the term “embankment” will be used for the remainder of this report to cover the types of earth structures encountered adjacent to bridges). These methods include the well-known rigid body, sliding block methods for both nonliquefiable and liquefiable soils, and numerical modeling procedures for evaluating the patterns of deformations resulting from strong ground motion. In summary, the prevalent issues for the deformation-based, seismic analysis of highway embankments include the need to estimate lateral deformations for non-liquefiable soils, potentially liquefiable soils, varying design-level ground motions, and sites with remedial soil improvement. 2
1.2 STATEMENT OF OBJECTIVES AND SCOPE OF WORK 1.2.1 Objectives The Geo-Hydro Section of the <strong>Oregon</strong> Department of Transportation (ODOT) is responsible for assessing liquefaction hazards and estimating potential bridge damage for projects in the state. Given this responsibility a Liquefaction Mitigation Policy has been developed (ODOT 1996), which states that the following factors will be considered when determining whether to mitigate potential liquefaction damage. 1. The risk to public safety. 2. The importance of the structure (lifeline, economic recovery, military). 3. The cost of the structure (capital investment and future replacement costs). 4. The cost of mitigation measures. The policy further specifies that, “All bridges should be evaluated for liquefaction and lateral spread potential and the possible effects of these conditions on the structure.” Consideration is given to the magnitude of the anticipated lateral soil deformation, the influence of piles on embankment deformations, and tolerable deformation limits of the structures under consideration. Close coordination between the geotechnical engineer and the bridge design engineer is required. A flow chart for the mitigation procedure is provided in Figure 1.1. A key element for implementing the ODOT liquefaction mitigation procedure is the estimation of seismically-induced ground deformations (with or without liquefaction hazards). Current methods for evaluating deformations of embankments include simplified design charts based on sliding-block methods of analysis, site-specific slope stability analysis combined with slidingblock analysis, and numerical modeling. The level of effort required for these techniques varies significantly, as does the uncertainty in the computed deformation. In order to optimize the resources for seismic and liquefaction hazard assessments, simplified, straightforward screening tools are needed. In <strong>Oregon</strong>, there are over 5,400 bridges greater than 6 m in length that span waterways. These bridges may require preliminary evaluations for liquefaction hazards. ODOT is charged with managing approximately 2,640 bridges, of which about 65% are over water (foundations on or in saturated soils). Of this subset, only 16% are supported on non-liquefiable, dense soil or rock; the remaining bridges are founded on potentially liquefiable deposits. It also is important to note that 44% of the bridge foundations in saturated soils are supported by piles. There is a demonstrated need for improved predictive methods for evaluating liquefaction damage to highway structures. When considering the seismic retrofit of bridge foundations and embankments, however, it is desirable to reduce conservatism in assessing the magnitude of post-liquefaction deformations, prior to developing specifications for ground remediation. The primary purpose of this report is to provide specific guidance on the evaluation of postliquefaction deformations and the possible effects of these deformations on bridges. This is intended not only to assist engineers with the methods of evaluating the liquefaction susceptibility of soils, but also to develop strategies for mitigating the liquefaction susceptibility of foundation soils at existing bridge sites. 3
Page 1: ASSESSMENT AND MITIGATION OF LIQUEF
Page 5 and 6: ACKNOWLEDGMENTS The authors would l
Page 7 and 8: ASSESSMENT AND MITIGATION OF LIQUEF
Page 9 and 10: 8.0 HAZARD EVALUATION AND DEVELOPME
Page 11 and 12: LIST OF FIGURES Figure 1.1: ODOT’
Page 13: Figure 8.8: Long Valley Dam and Lak
Page 18 and 19: Liquefaction Mitigation Procedure G
Page 20 and 21: Pacific Northwest also are summariz
Page 23 and 24: 2.0 OVERVIEW OF LIQUEFACTION-INDUCE
Page 25 and 26: oughly 50 centimeters, with numerou
Page 27 and 28: supported bridges along the Seward
Page 29 and 30: Another area of extensive bridge da
Page 31 and 32: Nineteen bridges were also damaged
Page 33 and 34: 1. No foundation failures were obse
Page 35 and 36: piles supporting the fourth pier, l
Page 37 and 38: Figure 2.17: Observed Pile Deformat
Page 39 and 40: Figure 2.19: Damage from the 1906 S
Page 41 and 42: Figure 2.22: Ground Deformations Ne
Page 43 and 44: induced ground displacement was the
Page 45 and 46: Well-documented case histories of t
Page 47 and 48: Similar damage to pile foundations
Page 49 and 50: Examples of acceptable bridge found
Page 51 and 52: Numerous investigations of liquefac
Page 53 and 54: 3.0 EVALUATION OF LIQUEFACTION SUSC
Page 55 and 56: The evaluation of liquefaction haza
Page 57 and 58: Table 3.1: Estimated Susceptibility
Page 59 and 60: movements, or localized ground disp
Page 61 and 62: Shear wave velocities can now be ob
Page 63 and 64: 3.4 LIQUEFACTION RESISTANCE: EMPIRI
Page 65 and 66: Figure 3.1: Range of r d Values for
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The earthquake-induced shearing str
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drill rod during hammer impact. In
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Figure 3.5: Minimum Values for K σ
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3.4.2.2.1 CPT Method Developed by R
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1. Sensitive, fine grained 6. Sands
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Figure 3.9: CPT-Based Curves for Va
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CRR where: q c 2 3 0.00128 0.0
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Tacoma, Washington (Dickenson and B
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Table 3.8: Influence of OCR on the
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Figure 3.13: Influence of Fines Con
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Gravel Sand Figure 3.16: Relationsh
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FS L > 1.4: Excess pore pressure ge
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The post-liquefaction strength of s
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Figure 4.3: Undrained Critical Stre
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4.3 INTRODUCTION TO MODES OF FAILUR
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Figure 4.5: (a) Relationship betwee
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not available for many case studies
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provided to give the recommended ra
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Figure 4.8: Overview of EPOLLS Mode
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Figure 4.10: Model of Hypothetical
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4.5.2 Advanced Numerical Modeling o
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Figure 4.12: Post Volumetric Shear
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The relationship shown in Figure 4.
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A third type of failure is shown in
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Table 5.1: Liquefaction Remediation
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5.3 DESIGN OF SOIL MITIGATION The d
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soil improvement guidelines state t
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The models were instrumented with a
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The model uses an explicit method,
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A simplification was made in the mo
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permanent earthquake displacements)
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7.0 DEFORMATION ANALYSIS OF EMBANKM
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engineers; (2) requisite input incl
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π g 2 a t I a 2 dt (7-1) The A
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10 1 Bracketed Intensity (m/s) 0.1
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7.3 PARAMETRIC STUDY A well-validat
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the rigid body methods. The point a
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0.4 Acceleration (g) 0.2 0 -0.2 -0.
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Embankment Height (m) Depth of Liqu
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10 1 DISPLACEMENT (m) 0.1 Morgan Hi
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2.0 Embankment Toe Embankment Mid-S
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suitably reliable estimates of perm
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interest. Specifically, the peak be
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Flow Chart for Evaluation and Mitig
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The deformation evaluations were pe
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Portland (a) (b) Figure 8.2: Illust
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Figure 8.4: Contours of PGA on Rock
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Borehole 4E CPT Hole 4E 26.0' NGVD
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8.4.2 Subduction Zone Bedrock Motio
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154 Table 8.5: Selected Acceleratio
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Spectral Acceleration (g) 1.50 1.40
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with the calculated equivalent unif
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n ( M 10 1) (8-1) where M is the
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0.20 0.15 0.10 Acceleration (g) 0.0
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15.0 12.5 10.0 Long Valley Dam Lake
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CSR should be modified for the pres
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8.7 EVALUATION OF INITIATION OF LIQ
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crest stage Marine Drive 42.5 ft NG
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Table 8.9: Fines Content Values Est
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large sliding and long-term disrupt
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Table 8.12: Deformation Results fro
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The earthquake time histories used
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North (river) South (land) North To
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Table 8.20: Riverward Deformation R
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applications (DDC, closely spaced v
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Table 8.21: Comparison of Predicted
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9.0 SUMMARY AND CONCLUSIONS Recent
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dewatering may be warranted. Additi
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Bardet, J.P. (1990). “LINOS - A N
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California Division of Mines and Ge
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Fujii, S., M. Cubrinovski, K. Tokim
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Ishihara, K. and M. Cubrinovski. (1
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Liu, A.H. and J.P. Stewart. (1999).
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Oregon Department of Transportation
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Schnabel, P., J. Lysmer, and H.B. S
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Sun, I.H. and I.M. Idriss. (1992).
Page 223:
Youd, T.L. and C.F. Jones. (1993).
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