Characterization of Bridge Foundations Workshop Report

BREAKOUT SESSION I: GEO/HYDRAULIC HAZARDS AND IMPACTS

BRAINSTORMING GEO HYDRAULIC HAZARDS AND IMPACTS

The first breakout session focused on identifying the geotechnical and hydraulic hazards and impacts associated with unknown foundations and characterization issues. The goal of this session was to solicit high priority input for new research and to prioritize listed high priority items. The workshop participants were divided into two groups to ensure a mix of disciplines and FHWA offices and discussed the session topic on the afternoon of April 30. Following the discussion, the participants reunited on Wednesday morning to summarize the group findings.

A list of preliminary topics for discussion at the breakout session was provided to attendees as a starting point for discussion topics. The topics included performance issues, engineering problems, tools and technology, proposed test plan, numerical modeling, research products, risk-based analysis, outreach and other funding mechanisms. An expanded list of topics is shown below.

Agenda Items for the Geo/Hydraulic Hazard and Impact Breakout Session.

1. Performance Issues—What are some of the main issues that required foundation characterization?
• Brainstorm performance issues and rank them.
• Pre-event vulnerability evaluations (scour, seismic, etc.)
• Post-event assessment (flooding, post-seismic, ship impact, etc.). Can the foundation still perform? Damage to the foundation? And so forth.
• Data needs and gaps.
2. Engineering Problems—What are the key engineering problems that need to be researched?
• Foundation type (shallow/deep).
• Foundation geometry (dimensions (L,W, D), pile tip elevation, pile distribution).
• Foundation material (concrete, steel, timber, masonry, stone).
• Foundation integrity (condition assessment).
• Load carrying capacity.
• Others.
3. Tools and Technology.
• Geophysics.
• NDT.
• Remote sensing.
• Destructive testing.
• Load testing.
• Numerical modeling.
• Risk-based analysis, statistical procedures.
• Others.
4. Proposed Test Plan.
• Existing bridges—geometry, type material.
• Decommissioned bridges—load testing.
• Test bed—with defects. Integrity testing. Baseline evaluation and technology validation.
• Other test sites—National Geotechnical Experimentation Sites (NGES), Reuse of Foundations for Urban Sites, German Federal Institute for Materials Research and Testing test site.
5. Numerical Modeling.
6. Research Products.
• Guidance documents.
• Reports and Tech Briefs.
• Web portal.
• Foundation database.
7. Risk-Based Analysis.
8. Outreach—Other events: TRB 2014 workshop, Geo-Institute.
9. Other Funding Mechanisms We Can Leverage—Pooled funds, NCHRP, Research and Innovative Technology Administration, National Science Foundation, etc.

The participants in Group 1 were as follows:

   Mohammed Mulla (NCDOT), Chair
   Jennifer Nicks (FHWA)
   Jerry Shen (FHWA/GENNEX)
   Dave Henderson (FHWA)
   Frank Jalinoos (FHWA)
   Khalid Mohamed (FHWA)
   Larry Jones (FDOT)
   William Kramer (IDOT)
   Benjamin Oltmann (FHWA)
   Sayed Sayed (GCI, Inc.)
   Emin Aktan (Drexel University)

The participants in Group 2 were as follows:

   Khamis Haramy (FHWA), Chair
   Vern Schaefer (Iowa State University)
   Kornel Kerenyi (FHWA)
   Ben Rivers (FHWA)
   Steven Lottes (TRACC/ANL)
   Jim Cuthbertson (WSDOT)
   Peter Connors (MassDOT)
   Hisham Sunna (Ayres Associates)
   Phil Yen (FHWA)
   Lubin Gao (FHWA)
   Ivan Bartoli (Drexel University)
   Silas Nichols (FHWA)

Each group approached the discussion in a different way. Below are summaries of their discussions.

GROUP 1

The following items were highlighted during the Geo/Hydraulic Hazard Impact breakout session.

Performance Issues—The key performance issues were super/substructure compatibility, strength and service limits, scour, load rating criteria, integrity, and environmental issues. Participants highlighted the importance of maintaining super/substructure compatibility as a key performance issue to prevent distress in either. It was pointed out that both strength and service limits should be considered in performance. The depth of embedment of the foundation must be defined in regards to scour performance. The load rating criteria based on the NBIS guidance must be further explored to better describe performance. Integrity after of the structure after extreme events is an important issue, with ship impact being raised as an example. Environmental issues, in particular corrosion, are also important to address.

Engineering Problem—The key engineering problems identified were load rating capacity in terms of risk-based criteria, the depth to satisfy stability, integrity of components, and corrosion or degradation of components.

Products—The key products identified as needed were guidelines for NDT selection, including cost information and rankings, and best practices for determination of foundation integrity and capacity.

Tools and Technology—Currently available tools and technologies are considered to be adequate and reliable. However, the integration or use of multiple tools to enhance their use should be explored, including risk-based decision making. Guidelines on the use of time and cost effective methods need to be developed. The use of tools from other fields (for example from medical, mining/oil exploration and aerospace industries) that could be utilized for foundation characterization should be explored. Continued and expanded use of finite element and other numerical modeling is encouraged, particularly when combined with field data.

Proposed Test Plan—Discussion on a proposed test plan focused on the possibility of testing decommissioned bridges in which an incentive is provided to the contractor to allow research tests to be conducted prior to removal. It was emphasized that both current and new technologies should be tested. Also discussed was the development of model tests at a Federal or academic facility.

GROUP 2

The following items were highlighted by Group 2 in the Geo/Hazard Impact breakout session.

Develop Guidelines for Evaluating/Characterizing Foundations—The development of guidelines for evaluating and characterizing foundations was deemed very important. The guidelines should include type, geometry, and materials of the foundation, as well as methods for determining the integrity of the foundation and the existing load capacity. Guidelines for reuse of foundations were deemed particularly important.

Develop Performance Indicators for Foundation Elements—In terms of performance indicators for foundation elements, the capacity of the foundation and its remaining service life were considered key performance indicators. Development of indicators quantifying reliability and post-extreme event capacity and integrity were also thought to be important.

Tools—The group felt that enhancement of existing tools through refinement in use and increasing resolution would be a particularly fruitful line of effort. Present numerical tools were considered to be in reasonably good state. New tools for determination of integrity and foundation life cycle analysis are needed.

Scour—There is a need for better prediction of the risk from scour hole development and for the risk placed on a bridge’s performance in general. Better delineation of countermeasures to reduce scour risk was also considered an important issue.

SUMMARY

Following the group discussions, the participants reconvened, and each group presented their findings (summarized above) with discussion following. There was agreement that we need performance/reliability indicators and guidelines to evaluate the performance of the foundation. Scour is a key hazard, but other hazards such as earthquakes also need to be considered. A focus should be on improving existing test methods to make them more reliable. It was noted that the transportation departments have developed unique ways to assess foundations.

The group felt that no one tool/instrument/product would answer all questions about foundation and scour issues. In general, the current equipment is regarded as good, but that methodologies and protocols need to be improved. The group felt that numerical codes can be of benefit to the bridge community but that additional development, calibration and verification is needed.

The lack of a load rating requirement for foundations was pointed out. There was discussion of the need to add/develop criteria of when a foundation load rating is required. Further, the means of obtaining this rating needs development work. This discussion raised the issue of risk and there was general agreement that risk needs to be assessed.

A possible test plan was discussed, with details about potential bridges that could be used for the program, bridges that are scheduled to be demolished, or construction of a scaled bridge system under more controlled conditions.