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Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines (2024)

Chapter: Chapter 4 - Basis for Development of Guidelines

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Suggested Citation:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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:"Chapter 4 - Basis for Development of Guidelines." 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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19   4.1 General The basis for the development of the guidelines documented herein is the experience of the research team, their in-house resources, and the resources of two subcontracted institutions and a commercial testing facility (see Author Acknowledgments). Additional input came from the NCHRP Project 12-114A Panel, which included practitioners, researchers, and DOT representa- tives. Additionally, indirect input was gained through a literature review, while direct input was generated by performing research to fill in data gaps and support statements that were based on common knowledge. This effort is documented in detail in the appendices. The literature search included a review of software (computer programs); constitutive models incorporated into the software or available as user-defined modules (UDMs) that can be used with the software; and field, centrifuge, and shake-table case histories. The literature search was conducted based on study-specific criteria explained in the balance of this chapter. The literature search was followed by a synthesis of available data. The synthesis of available data served as a basis for identifying data gaps in selected case histories. The research portion of this effort is documented in Chapter 6 (Field and Experimental Programs) and Chapter 7 (Numerical Model- ing Program). 4.2 Computer Programs 4.2.1 General There are many site response analysis computer programs that operate in either the time domain or the frequency domain. These programs are available as public domain software, com- mercial products, or through direct contact with the developers. The research team gathered available information about these programs, processed it, and critically reviewed it. Sources of information included technical papers, reports, information posted online, information obtained by interviewing authors and modelers, benchmarking studies (e.g., Kwok et al., 2007; Kramer, 2009), and miscellaneous digital information provided by others. 4.2.2 Required Attributes of Software Table 4-1 shows the software attributes for 1D nonlinear effective-stress site response analysis required to meet the project objectives (see Section 1.4) while considering study limitations (see Section 1.3). As explained in Chapter 1, this study is limited to the evaluation of vertical propagation of horizontally polarized shear waves (i.e., to 1D analysis). However, this limitation does not mean C H A P T E R 4 Basis for Development of Guidelines

20 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines that the study is limited to 1D software. This is because 2D and 3D programs can be run in 1D mode (i.e., in technical terms, they can be used to simulate vertical propagation of horizontally polarized shear waves). Key information about screened software (65 programs, including 1D, 2D, and 3D software) is presented in Appendix A-1. There is a variety of SRA software available; a handful of this soft- ware is in use in engineering practice and satisfies the required attributes identified in Table 4-1. This is because, in general, only relatively large commercial software companies have developed user-friendly graphical interfaces for 2D and 3D software, offer a provision for the use of UDMs, offer maintenance and updates for their software, and offer technical support and training. In turn, other developers generally place priority on writing and maintaining constitutive models for incorporation into such software as UDMs. 4.2.3 Selected Software The software was selected based on a study-specific screening process. The general steps in the process were as follows: (i) establish required attributes (i.e., screening criteria; see Table 4-1), (ii) compile a master list of the software of interest and corresponding relevant information (i.e., references and key attributes), (iii) apply preliminary screening to eliminate incompatible soft- ware and retain candidate software (i.e., items that, by inspection, might realistically be of value for this study), and (iv) apply detailed screening to select software for the numerical modeling program portion of this study. Software that passed step iii (preliminary screening) is listed in Appendix A-1. The selected programs that passed step iv (detailed screening) are presented in greater detail in the following and are outlined in Table 4-2. Information presented in Appendix A-1 shows that there are several other programs that passed step iv (detailed screening). However, this study is limited to the five programs listed in Table 4-2, including two 1D programs and three 2D/3D programs that can be used in 1D mode. Consider- ation was given to the mode of operation (time domain and frequency domain; SHAKE2000 and D-MOD2000, respectively), formulation of the FEM method (lumped mass and distributed mass; D-MOD2000 and OpenSeesPL), dimension (2D and 3D; FLAC, PLAXIS, and OpenSees), and method of analysis (FEM and finite difference; PLAXIS and FLAC). Brief descriptions of selected software, as well as URLs, are presented in Table 4-2. Required Attribute Note 1. The software should be able to simulate a horizontally layered soil deposit. 2. The software should be able to perform both TSA and ESA within the same computational framework. 3. In addition to generation of excess PWP, the software should be able to account for its dissipation. 4. The software should have a provision for including soils other than clean sand. 5. The software should be commercially available with technical support included in the purchase price or provided as a subscription option. 6. Detailed documentation and technical support should be available. 1. The software must be able to run in 1D mode. 2. It is impractical to use different programs for TSA and ESA. 3. PWP dissipation occurs simultaneously with PWP generation and continues after shaking has stopped. 4. Even though PWP is a phenomenon mostly associated with sand and this study is limited to sand, software should have a provision to model the cyclic response of other soil types, including silty sands, silts, clays, and gravels. 5. By terms of the NAS contract with Geo-Logic Associates, Inc. (GLA), this study is limited to commercially available software with technical support included. 6. Since nonlinear effective-stress SRA is not a standard analysis, technical support is likely to be required. Technical support is often fee-based. Table 4-1. Required attributes for 1D nonlinear effective-stress SRA software.

Basis for Development of Guidelines 21   The 2D/3D programs FLAC, PLAXIS, and OpenSees can simulate vertical propagation of horizontally polarized shear waves (i.e., can be run in 1D mode) can be run in the total-stress and effective-stress modes, and can model sand, clay, and silt in the same profile. Finally, all three programs have a UDM option (i.e., an option to incorporate constitutive models developed independently of the software packages). These UDMs can be easily added to these programs by software developers. They act as dynamic link libraries (DLLs). Once implemented, numeri- cal modelers can use UDMs (i.e., DLLs) as other CMs embedded in the software (i.e., without extensive knowledge of programming). The use of SRA programs like FLAC, PLAXIS, and OpenSees is not a trivial task, especially in effective-stress mode. For example, FLAC requires static initialization of normal and shear stresses and offers seven ways to model damping, three ways to assign ground motion, and a choice of a dozen or so constitutive models, each of which comes with its own documentation. Therefore, in engineering practice, reviewers typically require calibration of advanced SRA 2D site response models based on 1D analyses. The calibration of an advanced SRA 2D site response model is an effort to replicate the response of a simpler case [i.e., of a simpler model developed using a well-established 1D program such as SHAKE (TSA) and D-MOD (ESA)]. These 1D models are easy to understand and run, are well-calibrated against case histories, and do not require as many input parameters as their 2D counterparts. When subject to a low-intensity motion, 2D or 3D site response models (FLAC, PLAXIS, or OpenSees) should match their 1D counterpart(s) in the free-field. A five-step cali- bration procedure is described in detail in Section 7.2. SHAKE2000 is one of several commercially available pre- and post-processors for SHAKE (frequency domain equivalent-linear analysis). The SHAKE program is a de facto standard for No. Program Name Brief Description 1 SHAKE/ SHAKE2000 http://www.geom otions.com/modul es.php?name=Con tent&pa=showpag e&pid=8 SHAKE (Schnabel et al., 1972) is equivalent-linear analysis program. SHAKE2000 is a commercially available pre- and post-processor for SHAKE. Sections 3.2 and 7.2.3.2 explain the role of equivalent-linear analysis in this study. 2 D-MOD/ D-MOD2000 http://www.geom otions.com/modul es.php?name=Con tent&pa=showpag e&pid=4 D-MOD (Matasovic, 1993) is a lumped-mass formulation of an FEM program. LE, KZ, and MKZ constitutive models are implemented. D-MOD2000 is a commercially available pre- and post-processor for D-MOD. Widely used in practice and research. 3 FLAC https://www.itasc acg.com/software/ flac2d FLAC (Itasca, 2019) is an FDM program. Widely used both in practice and in research. Has many UDMs available as FLAC. 4 OpenSees/ OpenSeesPL https://opensees. berkeley.edu/ OpenSees (McKenna and Fenves, 2001) is an object-oriented, open-source software framework based on FEM. OpenSeesPL is a commercially available 1D pre- and post-processor for OpenSees. UCSDSAND3 and PM4SAND CMs have been implemented to date. 5 PLAXIS https://www.seeq uent.com/product s-solutions/plaxis- 2d/ PLAXIS is an FEM program. UBCSAND and PM4SAND CMs have been implemented. Widely used in practice. Notes: UDM is the terminology used by Itasca/option in FLAC; similar options are available in other software. UCSD = University of California, San Diego. Table 4-2. Software selected for use in this study.

22 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines 1D TSA and requires no formal introduction. SHAKE2000 was used in this study solely for practical reasons because it comes in the same package as D-MOD2000 (another software pro- gram used in this study), and therefore data input and output processing are connected and uniform. OpenSees is available at no charge; however, there is a charge for its pre- and post- processor OpenSeesPL. Other non-commercially available software for frequency-domain analysis (e.g., STRATA), or software that has a provision for frequency-domain analysis (e.g., DEEPSOIL), may be used for this application. 4.3 Constitutive Models 4.3.1 General In site response analysis software, including nonlinear effective-stress SRA software, nonlinear material behavior is simulated by means of CMs.14 These can be built into the software or made available for use with certain software as UDMs. In this project, a review of CMs that accom- modate PWP buildup was performed concurrently with the software review. This allowed the research team to develop a reduced list of CMs for sand and silty sand (i.e., a list of candidate CMs), develop project-specific attributes of candidate models, and further reduce the list by secondary screening and evaluation, as explained in the following. 4.3.2 Required Attributes of Constitutive Models The required attributes of CMs implemented in 1D, 2D, and 3D effective-stress SRA software are outlined in Table 4-3. In defining these attributes, the research team considered both CM ability to accurately model the nonlinear and undrained response of silty sand (e.g., items 1 through 4 in Table 4-3) and the availability of generic curve fitting and other model parameters. An important attribute considered herein is the availability of clear guidance for calibration of CMs against results of cyclic testing. This calibration of CMs is referred to herein as “element testing” and is further explained in Chapter 5. 4.3.3 Selected Constitutive Models This discussion of the selection of CMs or UDMs is similar to that of the selection of soft- ware. While many UDMs are available,15 few are regularly supported, updated, or routinely used in engineering practice. To exercise a reasonable effort during this study, only four CMs were employed to model the undrained response of silty sand, including three models that are based on the theory of plasticity and one semi-empirical model. Models based on the theory Requirement Note 1. Can be used in both total and effective-stress modes. 2. Can be calibrated against advanced laboratory test results (e.g., CyDSS and CyTX). 3. Has been implemented in at least one effective- stress SRA program. 4. Can simulate dilation. (This is a requirement only for advanced CMs.) 5. Other (number of parameters, ease of use, etc.). 1. One does not want to change a CM to perform ESA. 2. Both stress–strain and PWP response test results. 3. A must for ESA and assessment of soil liquefaction. 4. Dilation is a fundamental aspect of soil behavior that affects ground motions and should be used whenever justifiable. 5. The number of total/default model parameters and ease of development of model parameters matters for practical application of the model. Table 4-3. Required attributes for CMs.

Basis for Development of Guidelines 23   of plasticity include UBCSAND (Beaty and Byrne, 1998; 2011), PM4SAND (Boulanger and Ziotopoulou, 2013a; 2013b), and UCSDSAND3 (Khosravifar, 2018). With one exception, these models are implemented by software developers in the selected commercially available software. All of the selected CMs have been calibrated against results of advanced laboratory testing (i.e., an element test successfully replicated the results of undrained testing of clean sand in CyDSS or CyTX), can be run in total- and effective-stress modes, and with one exception (MKZ; Matasovic 1993; Matasovic and Vucetic, 1993), can simulate the effects of soil dilation. The semi-empirical MKZ constitutive model is the simplest selected model. It is representative of a class of semi- empirical models commonly used in 1D software and of a model that comes with an extensive database of generic total-stress and effective-stress parameters. The selected CMs are listed in Table 4-4, along with information relevant for their use in prac- tice. URLs lead to detailed information. These effective-stress models are capable of matching the results of advanced laboratory tests (i.e., element tests; see Chapter 5). However, as explained before, the MKZ model, like other semi-empirical models (see Section 3.4.2.2), cannot simulate dilation. This ability is reserved for models based on the theory of plasticity, such as PM4SAND, UBCSAND, and UCSDSAND3. None of the selected models can capture void ratio redistribution. (The void ratio redistribution is an important effect in some soil profiles but has not been identified as one of the required attributes in Table 4-3 because it is still in the domain of research.) 4.3.4 Other Constitutive Models Used in This Study Very rarely, if ever, does the entire soil profile consist only of saturated sand. Because CMs such as UBCSAND, PM4SAND, and UCSDSAND3 were developed for and are primarily used to simulate the cyclic response of saturated sand, additional models are required to simulate the response of silt, clay, and other soils. Case histories evaluated in this study include soils other than saturated silty sands (see, e.g., case history profiles shown in Figure 7-1, where saturated sand is shown in pink). Therefore, other models are used for their appropriateness for modeling cyclic behavior of non-liquefiable sandy soil. These models include the PM4SILT, the S-I model described in detail in Section 3.2, the model referred to in FLAC as the LE-MC model, and a No. Model Name Relevant Information 1 MKZ https://doi.org/10.1061 /(ASCE)0733- 9410(1993)119:11(1805) Total number of model parameters: 9 Required/default parameters: 9/0 Generic parameters available: yes (for many soils) 2 PM4SAND https://pm4sand.engr.u cdavis.edu/ Two-yield surface model; bounding surface model Total number of model parameters: 21 Required/default parameters: 3/18 Generic parameters available: yes [directly for clean sand; indirectly by converting (N1)60 to (N1)60–CS for simulation of silty sand] 3 UBCSAND https://www.itascacg.co m/software/udm- library/ubcsand Two-yield surface model Total number of model parameters: 15 Required/default parameters: 6/9 Generic parameters available: yes (only for clean sand) 4 UCSDSAND3 http://soilquake.net/ucs dsoilmodels/ Multi-yield surface model; bounding surface model Total number of model parameters: 22 Required/default parameters: 21/1 Generic parameters available: yes (only for clean sand) Note: The number of parameters listed refers to the effective-stress mode of listed CMs. Table 4-4. Advanced CMs selected for modeling of response of silty sand.

24 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines similar model incorporated in PLAXIS and referred to as the HSsmall model. Other models used in this study are listed in Table 4-5. The LE-MC model is a pressure-dependent linear-elastic perfectly plastic constitutive model that uses the Mohr–Coulomb failure criteria to describe the yield stress and an elastic modulus. In FLAC, this model is coupled with the Masing rules (Masing, 1926; see Pyke, 1979, for a sum- mary in English) to form a model that includes hysteretic damping. A detailed description of this model is presented in Itasca (2016). In general, the default behavior of the LE-MC CM is linear-elastic pre-yield (i.e., stress state remaining within the Mohr–Coulomb failure envelope) and perfectly plastic thereafter. Pre- and post-yield behavior can be modified by the user through parameter inputs or by writing a program-specific script (or one can formulate the CM as UDM and import it into the program FLAC as a DLL). For dynamic problems, the built-in hysteretic damping feature can be used to change the pre-yield behavior from linear to nonlinear elastic based on a modulus reduction curve. In PLAXIS, the hardening soil with small strain stiffness (HSsmall) constitutive model is used for most soils. A detailed discussion of the HSsmall, and an example of its application, is provided in Laera and Brinkgreve (2015). In general, the function of the HSsmall CM in PLAXIS is analo- gous to that of the LE-MC in FLAC when used with hysteretic damping. Inputs include the initial tangent shear modulus and one parameter for the shear modulus reduction curve. This allows for a very basic representation of modulus reduction and damping. The only input for this rep- resentation is the strain level “at which the shear modulus degrades to 70 percent of its initial value” (Laera and Brinkgreve 2015). PM4SILT (Boulanger and Ziotopoulou, 2018) is an advanced constitutive model based on the PM4SAND model. It can be used to model the undrained monotonic and cyclic loading response of low-plasticity silts and clays. The primary input parameters are the undrained shear strength ratio (or undrained shear strength), the shear modulus coefficient, the contraction rate parameter, and an optional post–strong-shaking shear strength reduction factor. All second- ary input parameters are assigned default values based on a generalized calibration. Secondary parameters that warrant adjustment based on site-specific advanced laboratory test data include the shear modulus exponent, plastic modulus coefficient (adjusts modulus reduction with shear strain), bounding stress ratio parameters (affect the peak friction angles and undrained stress paths), fabric-related parameters (affect the rate of shear strain accumulation at larger strains and No. Model Name Relevant Information 1 S-I Total number of model parameters: N/A (Curves are input at 6–10 strain levels.) Required/default parameters: N/A Generic parameters available: yes (for most soils) 2 LE-MC Total number of model parameters: 8 Required/default parameters: 8/0 Generic parameters available: no 3 HSsmall Total number of model parameters: 19 Required/default parameters: 19/0 Generic parameters available: no 4 PM4SILT Total number of model parameters: 26 Required/default parameters: 3/23 Generic parameters available: no 5 UCSDCLAY Total number of model parameters: 13 Required/default parameters: 13/0 Generic parameters available: yes Note: N/A = not applicable. Table 4-5. Other CMs used in this study.

Basis for Development of Guidelines 25   shape of stress–strain hysteresis loops), maximum excess pore pressure ratio, initial void ratio, and compressibility index. The PM4SILT CM is incorporated into FLAC and OpenSees. The UCSDCLAY model (Elgamal et al. 2008) is an elastoplastic CM that reproduces nonlinear hysteretic shear behavior of soil and accounts for accumulation of permanent shear deformation. Soil plasticity is exhibited in the deviatoric stress–strain response. Nonlinear response of soil is formulated based on the multi-surface (nested surfaces) concept with an associative flow rule. The yield surfaces are of the Von Mises type. The primary input parameters include shear modu- lus and the yield strain and strength (the shear stress–strain curve). The UCSDCLAY model is incorporated into FLAC, OpenSees, FLAC-3D, and LS-DYNA. 4.4 Case Histories 4.4.1 General The priority of this study, as a whole, is to highlight ground motions from sites that liquefied in events spanning a range of moment magnitudes (Ms) of interest to design engineers (Typi- cally M 5 to M 9+). However, the corresponding set of field case histories of soil liquefaction is small. Therefore, at the planning stage of this study, the database of candidate case histories was expanded to include the results of physical modeling, including centrifuge tests and shake- table tests. Case histories generated by blasting or by means of University of Texas at Austin Vibroseis shakers16 were initially considered for inclusion in this study as well. However, these case his- tories do not represent free-field (F-F) 1D ground shaking and were therefore eliminated from further consideration. The Vibroseis-generated data, however, were considered indirectly (i.e., as a supplement to a dataset used for the development of modulus reduction curves for the WLA site case history; see Chapter 5). Presented in the following are required attributes for case histories and for screening of gath- ered information. A brief summary of each case history that was considered, including refer- ences and URLs, is provided as well. 4.4.2 Required Attributes of Case Histories Table 4-6 shows the attributes required for case histories to meet the project objectives (see Section 1.4) considering the study limitations (see Section 1.3). They include requirements on geometry, instrumentation, and site and material characterization, as well as observational data that may supplement other information. 4.4.3 Selected Case Histories – Summary of Relevant Information The review of over 30 field case histories (i.e., field case histories with acceleration and PWP records; see Appendix A-3) showed that there is no field case history that meets all of the required attributes listed in Table 4-6. In other words, it appears that there is no ideal case history to study the effects of liquefiable soil conditions on site response. Therefore, selected case histories meet several required attributes, but not all. Selected case histories are listed in Table 4-7. Summary information is provided in the Relevant Information column. Relevant information for the first six cases in Table 4-7 was initially compiled from technical literature. Citations are provided in the appendices, and URLs are provided in the leftmost column of the table. Gathered information includes in-hole or outcropping, in-profile, and ground sur- face acceleration records (six cases) and PWP histories (three cases).

26 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines Case History Image Relevant Information Wildlife Liquefaction Array http://www.soilquake. net/Downholearray/Wil dlife/ 1987 Elmore Ranch earthquake 1. M 6.2/shallow crustal event (strike-slip fault) 2. R = 23 km 3. Outcrop record: NO 4. In-hole record (PGA): YES (0.078 g at 7.5 m b.g.s.) 5. Ground surface record (PGA): YES (0.13 g) 6. PWP records: NO 7. Liquefaction: NO 8. Lateral spreading: NO 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES(1) 12. Advanced-level material properties: NO Wildlife Liquefaction Array http://www.soilquake. net/Downholearray/Wil dlife/ 1987 Superstition Hills earthquake 1. M 6.6/shallow crustal event (strike-slip fault) 2. R = 31 km 3. Outcrop record: NO 4. In-hole record (PGA): YES (0.17 g at 7.5 m b.g.s.) 5. Ground surface record (PGA): YES (0.21 g) 6. PWP records: YES (@ 4 depths)(2) 7. Liquefaction: YES 8. Lateral spreading: YES 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES(1) 12. Advanced-level material properties: NO Wildlife Liquefaction Array http://nees.ucsb.edu/d ata-portal Re-instrumented at a site nearby, 2012 Hovley(3) earthquake 1. M 4.9/shallow crustal events 2. R = 8 km 3. Outcrop record: NO 4. In-hole record (PGA): YES (0.25 g at 30 m b.g.s.) 5. Ground surface record (PGA): YES (0.30 g max.) 6. PWP records: YES (complete record) 7. Liquefaction: NO 8. Lateral spreading: NO 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES(1) 12. Advanced-level material properties: NO Table 4-7. Case histories selected for use in this study – summary of relevant information. Attribute Note/Explanation 1. F-F case history of site response. 2. Recorded in-hole (i.e., within) or outcropping input motions. 3. Recorded F-F ground surface motion(s) is/are available. 4. Recorded history(ies) of excess PWP (exceptions will be justified for some cases). 5. Site (i.e., soil profile) characterization data are available (see Table 5-1). 6. Advanced soil testing data required for the development of CM parameters are available (if empirical relations or default parameters are not sufficient). 7. Relevant observational data are available (e.g., sand boils, large settlements, and recorded settlement profiles). 8. Preference is given to liquefiable soils found in- situ (silty sands). 1. F-F assumes level ground conditions with no structures or structural inclusions within the profile. 2. This refers to the recorded motion or centrifuge model (laminar box) excitation. 3. Calculated response should match this motion in the time domain (F-F response spectrum). 4. Reliable records of excess PWP are available and usable. 5. Shear wave velocity, unit weight, shear strength profiles, and saturated hydraulic conductivity profile. 6. CyDSS or CyTX test results. However, for some case histories, these may not be available; nevertheless, the cases remain quite useful. 7. This information may compensate for the lack of PWP records (e.g., one may assume that ru in given event was ≥ 0.95). 8. Most of the physical modeling (centrifuge and shake- table tests) was performed on clean sands. Note: F-F: level surface; no embankments higher than 5 m; structure or structural inclusions; no lateral spreading. Table 4-6. Required attributes for case histories.

Basis for Development of Guidelines 27   Case History Image Relevant Information Treasure Island/ Yerba Buena Island https://en.wikipedia.or g/wiki/Treasure_Island, _San_Francisco 1989 Loma Prieta earthquake 1. M 6.9/shallow crustal event (strike-slip fault) 2. R = 70–75 km 3. Outcrop record: YES (well characterized) 4. Outcrop record (PGA): YES (0.067 g) 5. Ground surface record (PGA): YES (0.159 g) 6. PWP records: NO 7. Liquefaction: YES 8. Lateral spreading: unknown 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES 12. Advanced-level material properties: NO 35 g centrifuge experiment (this study) 1. M 7.1/shallow crustal event (strike-slip fault) 2. R = 68 km 3. Outcrop record: NO 4. Base of laminar box (PGA): YES (0.57 g) 5. Ground surface record (PGA): YES (0.35 g) 6. PWP records: YES (@ 4 depths) 7. Liquefaction: YES 8. Lateral spreading: NO 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES 12. Advanced-level material properties: YES Notes: (1) RT performed a significant site characterization and laboratory testing program at this site to supplement existing data. (2) There is a controversy associated with these PWP records (see Section 4.4.6). (3) Event referenced herein as the Hovley earthquake is a part of the 2012 Brawley Swarm (see Steidl, 2014). R = approximate site-to-source distance; b.g.s. = below ground surface. Owi Island https://www.jstage.jst.g o.jp/article/sandf1972/2 1/4/21_4_85/_article/- char/en Tokyo Bay, Japan, 1985 Chiba-Ibaragi earthquake 1. M 6.2 (subduction event) 2. R = 50 km 3. Outcrop record: NO 4. In-hole record (PGA): YES (0.04 g at 10 m b.g.s.) 5. Ground surface record (PGA): YES (0.07 g) 6. PWP records: YES 7. Liquefaction: NO, ru = 3% 8. Lateral spreading: NO 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES 12. Advanced-level material properties: NO Port Island https://en.wikipedia.org /wiki/Port_Island Kobe, Japan, 1995 Hyogo-Ken Nanbu (Kobe) earthquake 1. M 6.9/shallow crustal event (thrust fault) 2. R = 18 km 3. Outcrop record: NO 4. In-hole record (PGA): YES (0.58 g at 16 m b.g.s.) 5. Ground surface record (PGA): YES (0.30 g) 6. PWP records: NO 7. Liquefaction: YES 8. Lateral spreading: unknown 9. Intrusions (pile foundations): NO 10. Layering/sand only: YES/NO 11. Design-level site characterization info. available: YES 12. Advanced-level material properties: NO Table 4-7. (Continued). The seventh case history was created for this study. It was designed as a project-specific centri- fuge experiment with an intent to compensate for the fact that none of the available case histories fully meets the required attributes as listed in Table 4-6, including the three cases at the WLA site17 subject to relatively strong events. 4.4.4 Selected Case Histories – Ground Motions Basic seismological parameters for each case history, including event moment magnitude and estimated site-to-source distance R, are provided in Table 4-7. Information presented in

28 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines Table 4-7 (see item 2 in the Relevant Information column) reveals that, out of seven case histories considered, one is representative of a near-field seismic event (R: 0–15 km), five are representa- tive of intermediate-field events (R: 16–50 km), and two of far-field events (R: 51+ km). Engineering seismology parameters of ground motions from these events, as recorded at the respective sites, are provided in Table 4-8. These parameters, created by seismological processing of input motions, include PGA, significant duration of strong ground shaking (Ds), Arias inten- sity (AI), and predominant period of input motion (Tp), that corresponds to a peak in response spectrum (see Figure 4-1). The acceleration response spectra of input motions listed in Table 4-8 and the corresponding recorded ground surface spectra are shown in Figure 4-1. Noted in the individual captions for Figure 4-1 are the quasi-predominant periods of soil deposits. With the exception of the Treasure Island (TI) site, these periods were calculated as Ts = 4 × H / (Vs)avg, where H correspond to the distance between in-hole strong-motion (SM) instrument and ground surface, and (Vs)avg is a weighted-average shear wave velocity in the profile. Values of H used in calculations are pro- vided in the legends of Figure 4-1. For the TI site, given that H equals the depth to bedrock, the calculated period is the predominant period of the entire soil deposit. Review of Figure 4-1 reveals a variety in site response characteristics for the case histories, including (i) input motions were amplified over a broad range of frequencies in five out of seven case histories considered; (ii) only recorded responses of the Port Island site and in the project- specific centrifuge experiment reveal attenuation with respect to the input motion, including at sites that are known to have liquefied in these events; and (iii) shift of ground surface spectral ordinates toward longer periods is clearly observable for the Port Island site that liquefied and for the WLA site in the Hovley event (no liquefaction). By inspection, this shift to the right may be, however, inferred for the WLA site in the Elmore Ranch event, for the WLA site in the Superstition Hills event (liquefaction), and for the Treasure Island site in the Loma Prieta event (liquefaction). 4.4.5 Selected Case Histories – Site Conditions Detailed information about selected case histories, including site characterization, and infor- mation about recorded acceleration and PWP histories is provided in the appendices. Site char- acterization information about three WLA case histories18 is provided in Appendix B-1. With few exceptions, this information was also used to develop the case history from a centrifuge Record (Component)(1),(2) Record Type (Depth) PGA DS AI Tp Elmore Ranch (NS) In hole (7.5 m) 0.078 g 16.08 s 0.098 m/s 0.14 s Superstition Hills (NS) In hole (7.5 m) 0.171 g 28.96 s 0.560 m/s 0.34 s Hovley (EW) In hole (30 m) 0.252 g 5.17 s 0.062 m/s 0.10 s Chiba-Ibaragi (NS) In hole (10 m) 0.044 g 24.16 s 0.031 m/s 0.44 s Hyogo-Ken Nabu (NS) In hole (16 m) 0.576 g 9.54 s 3.353 m/s 0.36 s Loma Prieta (EW) Outcropping 0.067 g 8.20 s 0.043 m/s 0.64 s Western Washington (NS) Ground surface(3) 0.569 g 16.41 s 7.511 m/s 0.32 s Notes: (1) The record name corresponds to a seismic event as recorded at the case history site in-hole, except for the Treasure Island site, where it refers to a bedrock outcrop, and for the centrifuge experiment, where a ground surface record was applied at the base of the laminar box. (2) The larger of the two orthogonal components was selected. NS = north–south (component); EW = east–west (component); and Ds = 5%–95%. (3) Centrifuge experiment reported values refer to the record as modified by a hydraulic actuator and applied at the base of the laminar box. Table 4-8. Characteristics of input ground motions for evaluation of selected case histories.

(a) WLA Site - Elmore Ranch Earthquake (Ts = 0.29 s) (b Site Superstition ills E (Ts = 0.29 s) (c Site o ley Earth ua e (Ts = 0.63 s) (d) Owi Island, Japan - Chiba-Ibaragi Eq. (Ts = 0.25 s) (e ort sland pn yogo en anbu E (Ts = 0.38 s) (f) Treasure Island - Loma Prieta Eq. (Ts = 1.38 s) (g entri uge e peri ent (this study estern Washington Eq. (Ts = 0.22 s) Figure 4-1. Acceleration response spectra of input and ground surface motions (Ts 5 period of soil prole above in-hole strong-motion instrument; NS 5 north–south; EW 5 east–west; b.g.s. 5 below ground surface).

30 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines experiment (see Section 6.3). Appendices B-2, B-3, and B-4 contain site characterization infor- mation for the Owi Island site, Japan, the Port Island site, Japan, and the TI site case histories, respectively. Figure 4-2 aggregates information from these appendices. It schematically presents site condi- tions for the selected sites (case histories 1 through 7; see Table 4-7). For clarity of presentation, soils are grouped into generic categories such as “clay,” “sand,” “silt,” and “bedrock.” Additional description of soils, such as “fill,” “silty clay,” “silty sand,” and so forth, is also presented using the same color-coding scheme. Other relevant information, such as location of critical layers within the profile, is also schemat- ically presented in Figure 4-2. The critical layers include (i) layers with confirmed19 liquefaction, which are highlighted with diagonal hatching (the original WLA site and WLA site as modeled in the centrifuge experiment); (ii) layers with inferred liquefaction,20 which are highlighted with horizontal hatching [Port Island site in the 1995 M 6.9 Hyogo-Ken Nanbu (Kobe) earthquake and Treasure Island site in the 1989 M 6.9 Loma Prieta earthquake; maximum depth of liquefied soil is not actually known]; and (iii) layers assessed as potentially liquefiable by screening, which are highlighted with dotted hatching (Owi Island site and re-instrumented WLA site). Groundwater elevations and bedrock outcrops are indicated by special symbols in the figure. For field case histories, groundwater elevations correspond to the best estimates during or immediately after cessation of shaking. Geotechnical instrumentation (SM instruments and PWP transducers) are also indicated by special symbols. Installed depth is noted adjacent to the symbols. The capabilities of geotechnical centrifuges and shaking tables currently in use in the United States are also included in the figure. The green arrows on the far left are representative of the equivalent thickness of a soil column that can be simulated by a given device. Figure 4-3 provides supplemental information about the field case histories outlined in Table 4-7 and schematically presented in Figure 4-2. It compares the grain size distributions of soils within critical layers that are identified in Figure 4-2 by hatching. The acronyms WSA, WSB, PB, and CF refer to sands from the broader WLA site. WLA site Sand A is also representative of remolded soil used in the centrifuge experiment (see Section 6.3). In Figure 4-3, Owi sand and Owi silt refer to liquefiable soils from the Owi Island site, Tokyo Bay, Japan. The grain size distribution curve for decomposed granite soil (“mesa soil”) recovered from the Port Island site is from Yamaguchi et al. (2002). The bounds of the most liquefiable (silty) sands shown in Figures 4-3 and 4-4 are commonly cited as Tsuchida (1970). They are reproduced from Ishihara (1996) and serve as a reference and for rapid screening of liquefiable soils. Dr. Onder Cetin reports a narrower range for liquefiable sands, as identified from the SPT-based liquefaction triggering case histories (Stewart, 2022a). Figure 4-4 shows grain size distribution curves for commercially available, industrially pro- cessed sands, such as Ottawa Sands F-55, 65, and 75 and Monterey sands 0 and 0/30, that were used in almost all centrifuge experiments identified in Appendix A-3. Tests by Ramirez et al. (2018) and Dobry et al. (2018) were identified as candidate tests and were considered as an alter- native to the study-specific centrifuge experiment presented in Section 6.3. Information processed, including the material presented in Figure 4-3, reveals that the suite of selected case histories represents a reasonably broad range of site conditions, both in terms of geometry (including stratification and layer thickness) and soil properties (including grain size distribution and soil density). Soils are representative of a fairly broad range of silty fine sand and include one well-graded sandy gravel. As explained in Chapter 7, ground motions associated with selected case histories were, with one exception, sufficient to induce significant nonlinear effects, and with two exceptions, sufficient to cause soil liquefaction.

Figure 4-2. Capabilities of physical modeling in the United States compared to case histories evaluated in this study.

32 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines Figure 4-4. Grain size distribution curves of liquefiable clean sands from past centrifuge experiments. Note: MDS = medium dense sand. Figure 4-3. Grain size distribution curves of liquefiable silty sands from field case histories.

Basis for Development of Guidelines 33   4.4.6 Selected Case Histories – PWP Records PWP records are available for only three out of six field case histories evaluated in this study (the WLA site in the 1987 M 6.6 Superstition Hills and 2012 M 4.9 Hovley events and the Owi Island site in the 1985 Chiba-Ibaragi event). For the remaining three field case histories, the PWP response was either inferred from the observational data (sand boils and large settlement documented for the Port Island and Treasure Island sites), or the PWP record was reconstructed in a centrifuge experiment (see Section 6.3 and Appendix C-1; simulation of the WLA site in the M 6.2 Elmore Ranch earthquake). PWPs recorded in field case histories are shown in Figures 4-5 through 4-7 and are discussed in the following. Figure 4-5(a) presents the normalized PWP response of the WLA site silty sand layer (Unit B) in the M 6.6 Superstition Hills earthquake. The normalization is with the initial vertical effec- tive stress, and these normalized values are referred to as the PWP ratio (ru). This layer is known to have liquefied, as evidenced by documented observation of sand boils and recorded lateral spreading. The closest acceleration record [i.e., acceleration history recorded just below Unit B at a depth of 7.5 m below ground surface (b.g.s.)] is shown in Figure 4-5(b). Figure 4-5 reveals the following: (i) the onset of notable PWP buildup coincides with the largest recorded acceleration response; (ii) the largest PWP response is delayed, relative to the occurrence of the peak in acceleration record, by at least 60 s; (iii) the effects of PWP redistribution (through cracks associated with sand boiling) are observable in the shallow piezometer P5 (e.g., sudden drops in excess PWP at approximately 55 and 80 s); (iv) the range of recorded PWP response in a 4 m thick layer of silty sand is relatively small; (v) the recorded response of piezometers embedded (a) (b) Figure 4-5. Recorded at the WLA site in the M 6.6 Superstition Hills earthquake: (a) normalized excess PWP; (b) acceleration (D 5 depth of record; P 5 piezometer designation).

34 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines at the same depth (e.g., P2 and P5) notably varies; and (vi) values of ru > 1.0 are not possible, and therefore the P5 record should be disregarded. Likely causes of ru > 1.0 in P5 include (i) under- estimate of in-situ unit weight, and (ii) improper saturation of P5 at the time of installation. Figure 4-6(a) presents the normalized PWP response of the WLA site silty sand layer (Unit B) in the M 4.9 Hovley earthquake. The closest acceleration record (i.e., acceleration history recorded just below Unit B at a depth of 7.7 m b.g.s.) is shown in Figure 4-6(b). Figure 4-6 reveals the follow- ing: (i) as at the WLA site in the M 6.6. Superstition Hills earthquake, the onset of PWP buildup coincides with the largest recorded acceleration response; (ii) the largest PWP response is delayed, relative to the occurrence of the peak in acceleration record, by 5 s (P60) to approximately 45 s (P66); (iii) the effects of PWP dissipation are more pronounced in shallow piezometers (P60–P63) and are very small in deeper piezometers; (iv) the range of recorded PWP response in a 4 m thick layer of silty sand is relatively large—at approximately 20 s, the range of recorded ru varies from 0.05 to 0.65; and (v) the recorded response of piezometers embedded at the same depth (e.g., P60-NP and P61) or at relatively close depths (e.g., P63 and P62) varies. Figure 4-7(a) presents the normalized PWP response of the silty fine sand layer of the Owi Island site in the M 6.2 Chiba-Ibaragi earthquake. The closest acceleration record (i.e., accelera- tion history recorded just below the silty fine sand layer at a depth of 10 m b.g.s.) is shown in Figure 4-7(b). The peak of the excess PWP record is very small (ru = 0.03) and occurs just a few seconds after the peak in the acceleration record. The PWP response indicated by the red line in Figures 4-5(a) through 4-7(a) was set herein as the target responses for numerical modeling (see Section 7.3.3 and Figure 7-9). (a) (b) Figure 4-6. Recorded at the WLA site in the M 4.9 Hovley earthquake: (a) normalized excess PWP (600 s recorded; 220 s shown); (b) acceleration (D 5 depth of record; P 5 piezometer designation).

Basis for Development of Guidelines 35   4.4.7 Selected Case Histories – Discussion For the purposes of this study, the WLA site, with two instrumented areas (i.e., arrays) and multiple recorded events, arguably yields the best set of case histories. The originally instrumented area was strongly shaken in 1987 by the successive M 6.2 Elmore Ranch and M 6.6 Superstition Hills events, but liquefied only during the second one. Acceleration was recorded in the first event [Figure 4-1(a)], and both acceleration and PWP records were recorded in the second event [Figures 4-1(b) and 4-5, respectively]. Lateral spreading was reported after the 1987 M 6.6 Super- stition Hills event. Given the relative success of the original instrumentation program at the WLA site, a re-instrumentation program was implemented. Supplemental sensors were installed nearby. Critiques of the original instrumentation program (e.g., PWP sensors were not fully saturated at the time of installation) were addressed, and a supplemental site characterization effort was undertaken. This effort included advancement of a 100 m deep borehole to confirm the deep allu- vial soil conditions. Presently, the acceleration records from the 33 M ≥ 5.0 events and 1 M 7.2 event (El Mayor-Cucapah earthquake) are available. Acceleration records and PWP records from a near-field earthquake swarm known as the Brawley Swarm are available for the WLA site (see Steidl, 2014, and updates at the University of California, Santa Barbara, website). One of the largest events from the Brawley Swarm is selected for this study and is named herein the M 4.9 Hovley earthquake. The corresponding records are shown in Figures 4-1(c) (response spectra) and 4-6 (PWP and acceleration records). This event was selected for further evaluation due to the relatively large excess PWP record (max recorded ru ≈ 0.65). Owi Island is a hydraulic fill site in Tokyo Bay, Japan. The site was well instrumented at the time it was shaken by a M 6.2 event. Histories of both PWP and acceleration have been recorded (a) (b) Figure 4-7. Recorded at the Owi Island site in the M 6.2 Chiba- Ibaragi earthquake.

36 Seismic Site Response Analysis with Pore Water Pressure Generation: Guidelines and have been converted herein to a format usable by modern software. However, in the recorded seismic event, the site did not liquefy. Basic soil properties, including modulus reduction curves21 for sand and silt, are available. The results of undrained laboratory testing are not available for this site. Thus, this site provides an opportunity to evaluate how well one can develop parameters of simple and advanced constitutive models based on available relevant site characterization information and observational information on the cyclic response of soil. This site can further reveal how well selected software can replicate the recorded acceleration and PWP response. Port Island, Kobe, Japan, is another relatively well-instrumented site known to have lique- fied in the past, although no PWP transducers were installed before this liquefaction event. The instrumentation triggered during the 1995 M 6.9 Hyogo-ken Nanbu (Kobe) earthquake included SM instruments on the ground surface and at depths of 16, 32, and 83 meters. Evidence of soil liquefaction (lengthened periods of the ground motion recorded above a layer known to have liquefied) can be seen on the ground surface SM records. Thick deposits of ejecta (sand boils) observed near the SM instrument array and large surface settlements also provide corroborating evidence that the site liquefied. Yamaguchi et al. (2002) performed a centrifuge test replicating the Port Island case history. The SM records required to evaluate this site are available. Informa- tion from the Yamaguchi et al. (2002) centrifuge testing program is sufficient to develop param- eters of semi-empirical models and, with some engineering judgment, of the advanced CMs. The Treasure Island–Yerba Buena Island pair of recording sites is in the San Francisco Bay (SFB), which was shaken in the 1989 M 6.9 Loma Prieta earthquake. Numerous observed sand boils at Treasure Island demonstrated that the site liquefied in this 1989 event. This site is repre- sentative of a far-field, low-intensity but long-duration seismic event as well as of soft soil ampli- fication of weak input ground motion. This is also an example of a nearby bedrock outcrop–deep soil profile site, which is a site condition commonly assumed in engineering practice develop- ment of design ground motions. SM records are available for both bedrock outcrop (Yerba Buena Island) and deep soil deposit (Treasure Island). The site geology is typical of the SFB. It consists of, from top to bottom: (i) fill and young alluvium, (ii) young bay mud (YBM), (iii) medium- dense sand (MDS), and (iii) old bay mud (OBM). Modulus reduction and damping curves of these materials have been developed by Hwang and Stokoe (1993) by testing of intact samples in an RC device. The results of undrained testing of the MDS, including results of CyDSS, are available for a site nearby. The physical modeling experiment was designed to (i) replicate and further supplement the WLA site case histories, and (ii) generate a new case history of strong ground shaking using the same soil profile. Capabilities of geotechnical centrifuges and shaking tables currently in use in the United States are schematically presented in Figure 4-2. Green arrows to the left of schematic soil profiles indicate the equivalent thickness of a soil column that can be shaken at its base in a given device. Information presented in Figure 4-2 indicates that (i) shake tables at the University of California, San Diego (UCSD), are not suitable for simulation of the WLA site response, and (ii) both a small centrifuge at the University of California, Davis (UCD), and a centrifuge at the University of New Hampshire (UNH) can do the job.

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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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