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Table 8.6: Summary of PGA values LOCATION EARTHQUAKE SCENARIOS M w = 6.2 M w = 7.0 M w = 8.5 M w = 9.0 Soil (Crest of Levee) 0.16g 0.18g 0.11g 0.12g Bedrock (Sandy River Sandstone) 0.29g 0.38g 0.12g 0.14g 8.6 LIQUEFACTION ANALYSIS The liquefaction analyses performed in this study consisted of: (1) computing the cyclic shear stresses in the soil deposits for each scenario earthquake (CSR EQ ), (2) calculating the cyclic shear stress required to initiate liquefaction in the cohesionless soils (CRR), (3) comparing the results of steps 1 and 2 to assess the liquefaction susceptibility of the soil, and (4) utilizing the results of step 3 to estimate the cyclic shear strength of the soil. 8.6.1 Determination of the Cyclic Stress Ratio The determination of earthquake induced cyclic shear stresses can be estimated in two ways: (1) by performing a simple empirical analysis developed by Seed and Idriss (1971, 1982, updated summary by Youd and Idriss, 1997), or (2) by performing a more in-depth, site-specific dynamic ground response analysis (SHAKE91). The cyclic shear stresses computed from the SHAKE91 analyses were used for this example problem. The computed cyclic shear stresses used in the liquefaction analyses are the “equivalent uniform” ( eq. uniform ) shear stresses. The maximum shear stress ( max ) is reduced by the reduction factor (n given in Equation 8-1) using Equation 8-2 to account for the irregular and transient nature of the shear stress time history. The eq. uniform is then normalized by the effective overburden stress ( vo ′) to produce the CSR induced by the earthquake as given in Equation 8-3. Figure 8.17 shows the CSR versus depth for the magnitude 6.2 earthquake motions employed in this study. τ n * eq.uniform τ max (8-2) CSR τ eq.uniform σ vo ' (8-3) 8.6.2 Determination of the Cyclic Resistance Ratio As defined in Chapter 3, the CRR describes the ability of the soil to resist the cyclic loading induced by the earthquake. The CRR can be determined through empirical relationships based largely on SPT and/or CPT penetration resistance, or laboratory tests. Both methods were used in this project and they are discussed in the following sections. 163
15.0 12.5 10.0 Long Valley Dam Lake Hughes #4 7.5 5.0 Elevation (m) 2.5 0.0 -2.5 -5.0 -7.5 -10.0 -12.5 -15.0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Cyclic Stress Ratio, CSR Figure 8.17: Cyclic Stress Ratio Profile for the Magnitude 6.2 Earthquakes 8.6.2.1 Laboratory Tests Cyclic triaxial tests were performed to determine the cyclic behavior of the silty and fine sandy soils at the site. Undrained, stress-controlled tests consisting of uniform sinusoidal loading were carried out at a frequency of 1 Hz. The cyclic loads were applied to the specimens until: (1) a single amplitude axial strain of 5% was reached, or (2) 100 loading cycles, whichever occurred first. The limiting axial strain of 5% was selected in order to preserve the shape of the specimen for the post-cyclic load tests. The CRR values obtained from the laboratory tests was corrected to field CRR values through the use of correction factors (Chapter 3). The results of the cyclic triaxial tests on silty soils are presented in Table 3.8 and Figure 3.11. Cyclic triaxial tests conducted on soils from the Columbia River levee adjacent to PDX and from Hayden Island are presented to further illustrate the expected shape of the cyclic resistance curves. The laboratory results demonstrated an increase in the cyclic resistance ratio with increasing overconsolidation ratio (OCR). However, the silts were 164
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ASSESSMENT AND MITIGATION OF LIQUEF
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ACKNOWLEDGMENTS The authors would l
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ASSESSMENT AND MITIGATION OF LIQUEF
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8.0 HAZARD EVALUATION AND DEVELOPME
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LIST OF FIGURES Figure 1.1: ODOT’
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Figure 8.8: Long Valley Dam and Lak
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Design of a given component shall l
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Liquefaction Mitigation Procedure G
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Pacific Northwest also are summariz
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2.0 OVERVIEW OF LIQUEFACTION-INDUCE
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oughly 50 centimeters, with numerou
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supported bridges along the Seward
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Another area of extensive bridge da
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Nineteen bridges were also damaged
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1. No foundation failures were obse
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piles supporting the fourth pier, l
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Figure 2.17: Observed Pile Deformat
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Figure 2.19: Damage from the 1906 S
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Figure 2.22: Ground Deformations Ne
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induced ground displacement was the
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Well-documented case histories of t
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Similar damage to pile foundations
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Examples of acceptable bridge found
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Numerous investigations of liquefac
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3.0 EVALUATION OF LIQUEFACTION SUSC
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The evaluation of liquefaction haza
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Table 3.1: Estimated Susceptibility
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movements, or localized ground disp
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Shear wave velocities can now be ob
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3.4 LIQUEFACTION RESISTANCE: EMPIRI
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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,
Page 126 and 127: A simplification was made in the mo
Page 128 and 129: permanent earthquake displacements)
Page 130 and 131: 7.0 DEFORMATION ANALYSIS OF EMBANKM
Page 132 and 133: engineers; (2) requisite input incl
Page 134 and 135: π g 2 a t I a 2 dt (7-1) The A
Page 136 and 137: 10 1 Bracketed Intensity (m/s) 0.1
Page 138 and 139: 7.3 PARAMETRIC STUDY A well-validat
Page 140 and 141: the rigid body methods. The point a
Page 142 and 143: 0.4 Acceleration (g) 0.2 0 -0.2 -0.
Page 144 and 145: Embankment Height (m) Depth of Liqu
Page 146 and 147: 10 1 DISPLACEMENT (m) 0.1 Morgan Hi
Page 148 and 149: 2.0 Embankment Toe Embankment Mid-S
Page 150: suitably reliable estimates of perm
Page 153 and 154: interest. Specifically, the peak be
Page 155 and 156: Flow Chart for Evaluation and Mitig
Page 157 and 158: The deformation evaluations were pe
Page 159 and 160: Portland (a) (b) Figure 8.2: Illust
Page 161 and 162: Figure 8.4: Contours of PGA on Rock
Page 163 and 164: Borehole 4E CPT Hole 4E 26.0' NGVD
Page 165 and 166: 8.4.2 Subduction Zone Bedrock Motio
Page 167 and 168: 154 Table 8.5: Selected Acceleratio
Page 169 and 170: Spectral Acceleration (g) 1.50 1.40
Page 171 and 172: with the calculated equivalent unif
Page 173 and 174: n ( M 10 1) (8-1) where M is the
Page 175: 0.20 0.15 0.10 Acceleration (g) 0.0
Page 179 and 180: CSR should be modified for the pres
Page 181 and 182: 8.7 EVALUATION OF INITIATION OF LIQ
Page 183 and 184: crest stage Marine Drive 42.5 ft NG
Page 185 and 186: Table 8.9: Fines Content Values Est
Page 187 and 188: large sliding and long-term disrupt
Page 189 and 190: Table 8.12: Deformation Results fro
Page 191 and 192: The earthquake time histories used
Page 193 and 194: North (river) South (land) North To
Page 195 and 196: Table 8.20: Riverward Deformation R
Page 197 and 198: applications (DDC, closely spaced v
Page 199 and 200: Table 8.21: Comparison of Predicted
Page 202 and 203: 9.0 SUMMARY AND CONCLUSIONS Recent
Page 204: dewatering may be warranted. Additi
Page 207 and 208: Bardet, J.P. (1990). “LINOS - A N
Page 209 and 210: California Division of Mines and Ge
Page 211 and 212: Fujii, S., M. Cubrinovski, K. Tokim
Page 213 and 214: Ishihara, K. and M. Cubrinovski. (1
Page 215 and 216: Liu, A.H. and J.P. Stewart. (1999).
Page 217 and 218: Oregon Department of Transportation
Page 219 and 220: Schnabel, P., J. Lysmer, and H.B. S
Page 221 and 222: Sun, I.H. and I.M. Idriss. (1992).
Page 223: Youd, T.L. and C.F. Jones. (1993).
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