Project Title/ID Number Workshop on Uncertainties in Nonlinear Soil Properties and Impact on Modeling Response—2B03
Start/End Dates 9/1/03 – 6/30/04
Project Leader Michael Riemer (UCB/F)
Team Members Ellen Rathje (U.Texas/F), Donald Anderson (CH2Mhill/I), Cliff Roblee (Caltrans/I), Lawrence Chiu (CSUS/O)

F=faculty; GS=graduate student; US=undergraduate student; PD=post-doc; I=industrial collaborator; O=other

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1. Project Goals/Objectives:

This project supplements funding for an NSF Workshop focusing on identifying the key sources of uncertainty surrounding the non-linear dynamic properties of soils, and evaluating the role of this uncertainty in the context of other factors in performing Site Response Analysis (SRA).

The primary goals of the project are:

It is well established that uncertainties exist in nonlinear soil property determination. These uncertainties result from a number of sources, including inherent variations in nonlinear soil properties, soil sample disturbance, equipment testing effects, and in situ stress state/stress history. There are also a variety of soil models in use for predicting site effects, which can lead to substantial variation in predicted motions in some cases (see Figure 1).

Figure 1
Fig. 1 - Predicted spectra using different soil models at a deep soil site (after Silva, 1998)

2. Role of this project in supporting PEER’s mission (vision):

An improved understanding of the relative uncertainties in site response analyses is crucial to the PBEE methodology, since the variability of the seismic demand is a dominant sources of uncertainty in many hazard analyses.

3. Methodology Employed:

A key element to the Workshop is to bring together experts from different backgrounds that occupy different roles in the process of predicting seismic ground response. These include Testers, who measure the non-linear soil properties themselves (both in the lab and the field); Constitutive Modelers, who incorporate such properties into their models; Numerical Modelers, who develop the tools used to perform SRA; and Engineering Practitioners, who ultimately apply the tools developed by others to evaluate likely ground motions for specific projects. While there is some overlap among individuals in these groups, there is a clear lack of exchange among the different groups as a whole in terms of identifying common priorities, and insuring that research conducted in one area can be cleanly “handed off” to the others for direct application in reducing the uncertainties.

The structure of the Workshop was developed to both leverage the specific expertise within each group, and provide formal opportunities for individuals to interact through “cross-cutting” breakout sessions.

4. Brief Description of past year’s accomplishments (Year 6) & more detail on expected Year 7 accomplishments:

The organizing committee for the Workshop was active through frequent teleconference calls to identify appropriate speakers and other Workshop participants, develop and revise the agenda to best meet the goals of the Workshop, and prepare the participants through solicitation and posting of preliminary materials on the Project web site.

The Workshop itself was held on March 18 and 19, 2004, at the PEER Center in Richmond, and was attended by some 44 participants from around the world, include three from overseas.

5. Other Similar Work Being Conducted Within and Outside PEER and How This Project Differs:

PEER Lifelines Project 2B01/02 involved extensive testing of high quality soil samples obtained as part of the ROSRINE program in Southern California. As such, it provided direct comparisons of dynamic properties as determined through Resonant Column, Torsional Shear, and Double Specimen Direct Simple Shear testing methods. While this provided some measure of the variability in properties associated with different methods, the current Workshop establishes a framework for evaluating the importance of these variabilities, particularly in comparison with other sources of uncertainty (eg. the input ground motion, and the simplifications inherent in constitutive and numerical models for site response).

6. Plans for Year 8 if project is expected to be continued:

Not applicable.

7. Describe any actual instances where you are aware your results have been used in industry:

As the Workshop is primarily concerned with identifying key issues for quantifying sources of uncertainty and key areas for further research, there are not yet specific cases in practice that have been impacted. However, it is important to note that the inclusion of practicing engineers in the Workshop formed an important “reality check” on the ideas proposed by researchers at the workshop, while also establishing a direct path by which future developments can be incorporated by these individuals in industry.

8. Expected Milestones & Deliverables:

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