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Page 103
Suggested Citation:"Endnotes." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27536.
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Suggested Citation:"Endnotes." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27536.
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Page 105
Suggested Citation:"Endnotes." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27536.
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Suggested Citation:"Endnotes." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27536.
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Page 107
Suggested Citation:"Endnotes." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27536.
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Suggested Citation:"Endnotes." National Academies of Sciences, Engineering, and Medicine. 2024. Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27536.
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103   1. Term “analytical” is used herein in a broader sense and to refer to other options available to evaluate the effects of local site conditions on design ground motion. Numerical modeling has been used to perform computations in this study. 2. The uncertainty results from differences in input ground motions, soil property representations, model-to- model variations, and so forth. Some of these uncertainties might be handled by running various models for the same input ground motions and soil properties. However, uncertainty cannot be eliminated, even under the best of circumstances. As guidance for modelers and users of model results, the uncertainties are discussed and quantified herein to the extent practicable. 3. DesignSafe is comprehensive cyberinfrastructure that is part of the Natural Hazard Engineering Research Infrastructure (NHERI) and provides cloud-based tools to manage, analyze, understand, and publish critical data for research. Information posted on DesignSafe is available to the public. 4. Past terminology includes “attenuation equation” and ground motion prediction equation (GMPE). 5. Because site terms in GMMs are derived from global ground motion databases and are based on incomplete information on the site condition, their predictions represent average levels of site response observed at sites conditional on VS30. Such predictions are referred to as “ergodic.” 6. Calibration mostly refers to development of viscous damping parameters in a trial-and-error process. This process is explained in detail in Chapter 7. 7. Various errors related to the application of ground motions at the model base, boundary conditions, selec- tion of numerical solver type, inadequate selection of nonlinear CM total stress parameters, and so forth, are possible. Most of these errors can be identified and corrected at this stage of modeling. 8. The input ground motion is converted into a series of harmonic (sinusoidal) motions using the FFT algo- rithm. The site response calculations are performed with sinusoidal motions. On completion of calcula- tions, the process is reversed to obtain conventional histories for further processing, such as the calculation of acceleration response spectra. 9. Technically, modulus reduction curves can also be developed from static shear stress–strain curves and knowledge of shear wave velocity. Damping curves can then be calculated by assuming that the Masing rules are valid for a given soil and strain range. 10. The explanation of the FDM is beyond the scope of this document. However, the key principles are analo- gous to its counterpart, the FEM. 11. Soil dilation is an increase in soil volume when soil is being sheared. It is common for dense sands to increase in volume when sheared due to particle interlocking. 12. Undrained conditions mainly occur for saturated soils with relatively low hydraulic conductivity, when the soils are excited with seismic motions. The rate of the dissipation of PWP in soils with low hydraulic con- ductivity is relatively low; hence, the PWP dissipation occurs during a relatively long period, and therefore the effect of PWP dissipation in such soils may be neglected. 13. In simple words, mechanical and fluid calculations are performed sequentially at each timestep. First, the CM is invoked, and the excess PWP increment is calculated. Second, the flow calculation is invoked, and excess PWP is redistributed. For example, in the program FLAC, both calculations use FLAC’s mixed dis- cretization scheme (i.e., each quadrilateral element is decomposed into two sets of two triangles formed by drawing the diagonals of the quadrilateral) and both are solved using FLAC’s explicit, time-marching algorithm. Calculation is quasi-static: timestep is selected such that a wave cannot propagate from one node to another within the duration of the timestep. 14. In this study, the term “constitutive model” is used loosely and hence includes modulus reduction curves and elastic-ideal plastic models that would not qualify otherwise. Endnotes

104 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines 15. All UDMs are available free of charge. None of the UDM developers provide technical support at the profes- sional level. Software developers charge an extra fee for use of an option for use of independently developed CMs, but provide no technical support related to the use of these CMs. 16. Such a study was performed on the re-instrumented portion of the WLA site. 17. Excess PWP histories from the 1987 M 6.2 Elmore Ranch event are missing; the validity of records of excess PWP from the 1987 M 6.6 Superstition Hills event is questioned by several researchers, while some also question whether the WLA site responded in a true 1D manner. 18. Case histories of response in three earthquakes share the same site characterization information. 19. PWP time history was recorded within the profile, and normalized PWP (normalization with the initial vertical effective stress) is in excess of ru = 0.95. 20. Soils with indirect evidence of soil liquefaction, such as observed sand boils and settlement. The extent affected by soil liquefaction was assessed by means of the Seed–Idriss simplified method. 21. Damping curves are not available. 22. Note that different discretization is required for the purposes of site response modeling and for modeling of excess PWP dissipation. A finer mesh is sometimes required to adequately capture dissipation. 23. Encompasses broad range of physical modeling, including centrifuge testing, shake table (1 g) testing, blast- ing, and Vibroseis truck-induced deformation/porewater pressure. 24. It is very unlikely that occurrence of a strong earthquake will coincide with presence of historic high groundwater conditions. Relatively short occurrences of historic high groundwater conditions may not be sufficient to fully saturate sandy soil. Partially saturated sandy soils are less likely to liquefy and should not be modeled as liquefiable soils in effective-stress SRA. 25. This iteration is performed in a very low strain range, typically between 0.001% (sands) and 0.01% (clays of high plasticity). One may assess the appropriate strain from bending in modulus reduction curves presented in Figure 3-1. 26. Refer to references cited in Appendix B-1 for location of the borings, CPTs, Vibroseis setups, and other investigations conducted at the site. 27. An attempt was made to consolidate lean clay by spinning it in the centrifuge (prototype scale of 105 years, which is consistent with the material deposition history); however, even after spinning, the soil was too soft, so material was prepared by means of wet tamping. 28. The PI of the WLA site clay changes with depth and across investigated Units A and C. Depending on the sample recovery location, it was classified as lean clay (CL), sandy silt (ML), or fat clay (CH) in the past. CH appears to be the dominant material in the profile and was used for the centrifuge experiment. 29. In a dynamic centrifuge test on saturated cohesionless soils, since the soil specimen is rapidly excited with seismic loads, the time during application of seismic motion is so short that the excess pore water pressure does not have enough time to dissipate completely. Therefore, the excess pore water pressure accumulates. When the seismic loading stops, the excess pore water pressure continues to dissipate. After some time, the excess pore water pressure reverts back to zero. The first part of the centrifuge test, when excess pore water pressure mainly accumulates, is considered a surrogate of an undrained CyDSS test. The excess pore water pressure in a centrifuge test mainly dissipates through the soil specimen from the bottom of the specimen toward the soil surface. 30. In laboratory testing, ru = 0.95 is adopted as the onset of soil liquefaction for a variety of reasons, including the fact that ru = 1.0 is not achievable with most laboratory testing. 31. Additional intact samples were not available to repeat this CyDSS test at a lower CSR and thus delay the onset of soil liquefaction to subsequent cycles. 32. The maximum shear strain that could be applied in a commercial laboratory that performed testing of intact samples was 1.0%. The maximum strain that could be applied in the university laboratory was only 0.5%. 33. Only triangular finite elements are available in the PLAXIS element library. Therefore, to create a rectan- gular domain for an element test, a minimum of two triangular finite elements is required. 34. Validation is the process of checking that a software achieves its goal (i.e., validation refers herein to a comparison of the user’s model against a well-known solution, such as a simple SRA model, case history, or the results of advanced laboratory testing, all provided in this study). 35. The behavior of an advanced CM (e.g., PM4SAND, UBCSAND, UCSDSAND) depends on its 3D state of stress. This includes its initial state of stress as well as the stress path during loading. It is common, particu- larly for 2D programs, that one or more static loading stages are required to establish the initial state of stress before dynamic loading is applied. Before proceeding to the dynamic loading stage (i.e., the SRA itself), the modeler should perform adequate quality control checks to assess whether the initial state of stress is reasonable. 36. It is common, particularly when using 2D programs, for the modeler to code subroutines to streamline various aspects of the model (e.g., property assignment, model variable tracking, post-processing). If not coded and checked carefully, subroutines can contain coding errors, potentially resulting in erroneous

Endnotes 105   model input or output. Examples of coding errors include (i) use of an incorrect variable name, (ii) incorrect sign convention (e.g., values should be added but are subtracted instead), and (iii) incorrect order of opera- tions (e.g., missing parentheses). 37. Particularly when using a transmitting boundary at the model base, the actual horizontal ground motion applied can diverge significantly from the target motion. This may occur even when the modeler has speci- fied the ground motion in accordance with published procedures (e.g., Mejia and Dawson, 2006), as the relationship between outcrop motion and its upward-propagating component depends on various model- specific factors (i.e., the upward-propagating component is not necessarily equal to one-half of the outcrop motion). 38. The modeler should perform adequate quality control checks to ensure that the actual input ground motion matches the target motion. These checks may be performed using a low-intensity motion (e.g., ground motion scaled down to a PGA on the order of 0.05 g) in the selected modeling software and with an equiva- lent model in SHAKE. The output motion at the ground surface with the selected modeling software should match well with the corresponding output motion in SHAKE. 39. Input (half-space) PHGA on the order of 0.05 g. 40. Besides the comparison of spectral ordinates, checks may be performed on the acceleration, strain, and shear stress profiles to confirm similarity. 41. Calibration herein typically boils down to evaluation of the Rayleigh damping model parameters that allow for a better match to the target spectrum. Usually, just two to three iterations will suffice. 42. Shear waves cannot pass through a Newtonian fluid and are diminished when passing through a material that has residual shear strength, such as liquefied soil. 43. From a structural design perspective, accurate spectral acceleration (or displacement) predictions between about 0.2 s and 3.0 s are of greatest benefit. 44. Stress-controlled testing. Dilation is easier to visualize on the results of stress-controlled testing than on the results of its strain-controlled counterpart. 45. Plotting of acceleration response spectra in a format that is common in geotechnical earthquake engineer- ing (i.e., abscissa plotted in a logarithmic scale) is recommended.

Abbreviations and acronyms used without de nitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration GHSA Governors Highway Safety Association HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 ADDRESS SERVICE REQUESTED ISBN 978-0-309-70941-5 9 7 8 0 3 0 9 7 0 9 4 1 5 9 0 0 0 0

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One-dimensional (1D) equivalent-linear total-stress site response analysis (SRA) is the de facto standard for state department of transportation (DOT) highway facilities at locations where site-specific ground response analyses are conducted. However, many users and various DOTs have concerns about the applicability of equivalent-linear analyses for the cases where site-specific SRA is most relevant.

NCHRP Research Report 1092: Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines, from TRB's National Cooperative Highway Research Program, presents guidelines for the selection and use of methods for 1D nonlinear seismic SRA with excess pore water pressure generation and dissipation.

Supplemental to the report is NCHRP Web-Only Document 383: Seismic Site Response Analysis with Pore Water Pressure Generation: Resources for Evaluation.

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