Characterization of Bridge Foundations Workshop Report

SUMMARY OF THE FIRST PLENARY SESSION: FEDERAL RESEARCH PROGRAMS—NATIONAL PERSPECTIVE

INTRODUCTION TO THE PLENARY SESSION

The workshop began with a series of presentations that were designed to focus the participants on key issues relevant to characterization of bridge foundations. Specifically, the participants were tasked to identify and define the key factors and actions related to unknown foundations, foundation characterization, and reuse of bridge foundations. The presentations are available on the TRB Committee on Soil and Rock Properties (AFP30) Web site.⁽²⁾ It is accessible at https://sites.google.com/site/trbcommitteeafp30/characterization-of-bridge-foundations/May-2013-workshop-fhwa---presentations.¹

WELCOME, OBJECTIVE OF WORKSHOP, FHWA PERSPECTIVE

Welcoming remarks were provided by Mr. Louis Triandafilou, Acting Assistant Director, on behalf of Mr. Jorge E. Pagán-Ortiz, Director of the FHWA Office of Infrastructure R&D. Mr. Triandafilou highlighted the following:

• The Unknown Foundation Program has been many years in the making, based on a summit held in Lakewood, CO.⁽³⁾
• The scour program has high priority within FHWA.
• Bridges flagged with unknown foundations in the NBI should have a risked-based plan of action until a suitable countermeasure is implemented. Countermeasures include structural, hydraulic, and, in some instances, long term monitoring.
• Workshop attendees are challenged to revisit current nondestructive evaluation (NDE) methods and identify what needs to be revisited or updated.
• FHWA looks forward to the input from the participants in order to develop a roadmap with objectives, strategies, activities, measures, etc.
• The program should include bridges over roadways as well as over waterways.
• The program should develop guidelines for owners to make better data-driven decisions.
• Although the scour program and the unknown foundation issue are vitally important, FHWA have decided to expand the scope of this research to other hazards and concerns. Frank Jalinoos will cover this in his presentation.

OVERVIEW OF FHWA´S CHARACTERIZATION OF BRIDGE FOUNDATION PROGRAM

Frank Jalinoos, Research Engineer at the FHWA Office of Infrastructure R&D, provided a comprehensive overview of the draft CBF program. The Schoharie Creek Bridge failure in April 1987 started the national bridge scour program; the failure also involved an unknown foundation. What was started as a program for pre-event vulnerability assessment for scour has expanded to include other hazards with unknown foundations, changes in service loads and foundation reuse, and available tools and technology for the characterization of bridge foundations.

As of December 2011, the NBI includes over 600,000 structures with a span greater than 20 ft (6 m).⁽¹⁾ FHWA provided guidance in January 2008 and June 2009 to eliminate bridges with unknown foundations, with a target date of November 2010.⁽⁴⁾ The number of bridges in the NBI database coded as unknown foundation has steadily decreased over the years, from 104,000 in 1996 to approximately 36,000 as of December 2012.⁽¹⁾ FHWA guidance on unknown foundations can be found on the FHWA Web site.⁽⁴⁾

The engineering risk associated with bridge foundations can be summarized as:

• Geo/Hydraulic Hazards.
  — Pre-event vulnerability assessment (scour, seismic, others).
  — Post-event evaluation (flooding, seismic, barge impact, blast, fire, explosion, etc.).
• Changes in Service Loads, Foundation Reuse.
  — Use of heavy loads (military, industrial, mining, truck size and weight (TS&W), including proposed use of higher truck loads by the trucking industries and changes in truck route).
  — Foundation reuse: rehab, widening, and replacement.
• Foundation Inspection (Condition assessment and performance monitoring).

Examples of each risk were shown.

The engineering problems associated with foundation characterization include foundation type, pile type, embedment depth, geometry and material, foundation integrity, and load carrying capacity. Figure 1 illustrates the complexity in evaluating unknown foundation conditions. Available geophysical and NDE techniques are a common means of identifying these characteristics and were briefly reviewed. Although initially the emphasis has been on identifying unknown foundation characteristics for scour issues, recent efforts have also focused on identification for reuse of foundations.

A number of tools and technology exist for identification and characterization of bridge foundations including geophysical tools, NDE, destructive material sampling, load testing, numerical modeling, site investigation, and risk-based analysis. A tentative research plan was proposed that included testing of existing bridges from State agencies and the Long-Term Bridge Performance (LTBP) Program, load testing of decommissioned bridges, and integrity testing of a small testbed constructed with defective foundation types.

Research deliverables will include reports and technical briefs, guidance documents, and tools and technologies.

Figure 1. Diagram. Typical foundation conditions.⁽⁵⁾

HYDRAULICS RESEARCH

Dr. Kornel Kerenyi, Hydraulics Laboratory Manager at the FHWA Office of Infrastructure Research and Development at Turner Fairbank Highway Research Center (TFHRC), presented an overview of the physical modeling experiments conducted at the TFHRC Hydraulics Laboratory, and the high performance computing simulation conducted at Argonne National Laboratory (ANL). Presently, physical experiments are used to calibrate numerical models, and the vision for the future is to move away from physical modeling towards computational modeling. Dr. Kerenyi showed the current bridge scour research conducted utilizing the hydraulic loading-bridge pier turbulence and soil erosion testing devices.⁽⁶⁾ See figure 2 and figure 3. Videos were shown of the Computational Fluid Dynamics model calibration experiments and validation/comparisons, illustrating the importance of matching loading with soil type and the sour associated with fluctuating flow stresses.

Figure 2. Diagram. Hydraulic Loading—Soil Resistance Approach.⁽⁶⁾

Figure 3. Diagram. In-situ scour testing device for a 10-ft-deep erosion test.

Dr. Steven Lottes of ANL provided an overview of their Transportation Research and Analysis Computing Center (TRACC). The TRACC cluster computing capabilities are available to all transportation researchers and analysts, with universities and government making up the bulk of the cluster user groups. Example uses include traffic modeling, bridge hydraulics, bridge structural analysis, and vehicle occupant safety and crashworthiness. Dr. Lottes reported on modeling soil-structure interaction with large deformations using the Oat Ditch bridge failure (figure 4) as well as simulation of soil penetration tests and bridge pier failure. A model of fluid structure interaction for the onset of motion for riprap was presented.

Figure 4. Photo. Failure of Oat Ditch Bridge on I-15 in California.

OVERVIEW OF PAST, CURRENT, AND PLANNED GEOTECHNICAL RESEARCH AT TFHRC

Dr. Jennifer Nicks, Research Geotechnical Engineer at the FHWA Office of Infrastructure R&D, presented an overview of the Geotechnical Research Program at TFHRC, beginning with background information on bridge foundations, including type, cost, and common State concerns. She then described the FHWA Foundation Engineering Research Program (FERP) initiated in the late 1970s. Five FERP projects were detailed: structural consequences of foundation movements, predicting behavior of piles and foundation soils under structural loads (see figure 5 and figure 6), improved design and construction techniques for drilled shafts, innovative load test methods, and improved design for shallow foundations. Past research projects related to bridges were also described. Dr. Nicks indicated that current research efforts are focused on deformation analysis of shallow foundations, performance of Geosynthetic Reinforced Soil (GRS) as a bridge foundation system, steel corrosion in Mechanically Stabilized Earth (MSE) structures, long-term GRS dead load tests, retaining wall asset management, and design and load testing of large diameter driven pipe piles. Important topics for future research include geophysics for reliable determination of soil and rock design parameters, risk analysis for geotechnical structures, and reuse of geotechnical features.

Figure 5. Photo. Laboratory instrumentation of a pipe pile for field load testing.⁽⁷⁾

Figure 6. Photo. Predicting the behavior of micropiles and foundation soils under structural loads.⁽⁷⁾

FHWA LTBP PROGRAM – REPORT ON THE WORKSHOP ON BRIDGE SUBSTRUCTURE ISSUES AND OVERVIEW OF THE GEOTECH TOOLS

Professor Vern Schaefer of Iowa State University provided an overview of the LTBP Workshop and the GeoTechTools system. In March 2010, approximately 60 participants from State transportation departments, FHWA, domestic universities, and industry, met in Orlando, FL, to identify bridge substructure performance issues.⁽⁸⁾ The bridge performance issues were grouped into three areas: geotechnical bridge performance issues, data needs and gaps, and tools, technology development and monitoring. The participants were divided into three groups to discuss each of these areas and then reconvened to further discuss them. The geotechnical bridge performance issues included abutment/approach settlement; foundations in terms of measuring loads, unknown foundations, and tolerable movements; hydraulic issues of scour and drainage; materials, in particular corrosion/deterioration; and construction quality control, see table 1. The key data needs and gaps identified included existing capacity and integrity of foundation elements; and design scour and measured scour, see table 2. Less emphasis was placed on the tools, technology development, and monitoring, with a simple delineation of what is currently available, what will be available in the near future and what is needed in the long term, see table 3.

Dr. Schaefer also provided a brief overview of the GeoTechTools system, which is a comprehensive web-based information and guidance system for embankment, ground improvement and pavement applications that was developed through the Strategic Highway Research Program (SHRP 2). The system provides guidance on the use of 46 technologies for ground improvement and geoconstruction in transportation infrastructure. For each technology, there are eight products available including technology fact sheets, photographs, case histories, design procedures, quality control/quality assurance procedures, cost estimating, specifications, and a bibliography. A live demonstration of the system was made.

Table 1. FHWA LTBP Workshop Breakout Session 1: Summary of priority geotechnical performance issues identified by each group.⁽⁸⁾

Table 2. FHWA LTBP Workshop Breakout Session 2: Data needs and gaps related to performance issues for bridges.⁽⁸⁾

Table 3. FHWA LTBP Workshop Breakout Session 3: Needed tools, technology development, and monitoring.⁽⁸⁾

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