The characterization of bridge foundations is complex. Bridges can be supported by shallow or deep foundations of varying footing geometries and materials. Footings can be square, circular, or rectangular. Foundations can be pedestal masonry stone footings or massive cofferdam footings. Piles can be present with or without pile caps and may be battered or vertical. Piles can be made of concrete (round, square, cylinder, or octagonal), steel (H-piles or round pipe sections), or timber. Deep foundations can be precast concrete piles, drilled shafts, or auger-cast concrete piles. The top of footings or pile caps can be buried underneath riprap, backfill mud, or channel soils. Additionally, design or as-built drawings of foundations are sometimes not available and technologies for determining foundation condition are expensive and sometimes unreliable. The goal of the Federal Highway Administration (FHWA) is to identify methods to quantify and clarify these unknowns. The Foundation Characterization Program (FCP) attempts to determine one or more of the following: Foundation type (shallow versus deep, or a combination).Elevation of the base of the foundation (e.g. pile tip elevation).Foundation geometry (width, length, and depth), which includes checking the accuracy of as-built plans.Material type (foundation materials, including concrete, masonry, stone, steel, or timber).Integrity (foundation condition, such as corroded steel, rotted wood, or cracked or defective concrete).Foundation load-bearing capacity. Pile distribution Target avoidance for foundation rehabilitation or underpinning.Remaining service life of the foundation.Subsurface characterization and imaging of soil and rock.
The objective of the Federal Highway Administration's (FHWA's) Foundation Characterization Program (FCP) is to develop and evaluate new and existing technologies and methodologies for characterizing existing bridge foundations for the determination of unknown geometry, material properties, integrity, and load-carrying capacity. The emphasis is on developing guidance and best practices for foundation reuse. Many foundation characterization decisions will likely be made in the framework of life-cycle cost and risk-management analysis.
The program will be executed through 5 main tasks and 23subtasks: Defining the Foundation Performance IssuesThe main issues that requires foundation characterization include:Formation of an Expert Task Group.Perform extensive literature review.Provide stakeholder outreach to refine issues and to research data gaps and needs.Conduct special projects to support this task as defined by Federal Highway Administration (FHWA). Analytical and Developmental Research ProgramThe Analytical and Development Research program includes the following subtasks:Technology Evaluation— Evaluation of new or existing methodologies, including:Ground imaging and characterizations (such as geophysical methods).Foundation testing and evaluation (such as destructive, nondestructive, and wireline logging).Geotechnical site investigation.Advanced methodologies from other fields.Technology Development — Development of system prototypes for field testing and instrumentations.Load Testing— Investigation of new ideas for static and dynamic load testing of existing bridge foundations, including rapid load testing methodologies.Numerical Modeling/Analysis (Two-dimensional (2D) and three-dimensional (3D))— Development of numerical simulations to model complex soil-structure interaction and to calibrate field test results.Risk-based Analysis and Statistical Methods Experimental ProgramA three-tiered field testing program will be conducted for the evaluation of technology:Inservice Bridges— Use of a selective group of in-service bridges mainly for the determination of foundation type, geometry, material, load, and integrity.Decommissioned Bridges— Use of decommissioned bridges mainly for the development of new load testing methodologies for existing bridge foundations.Small Testbed with Engineered Defects — Used mainly for the validation of technology under controlled conditions. Deliverables — Disseminate the Research FindingsDevelop guidance and synthesis documents.Federal Highway Administration publications, such as TechBriefs, TechNotes, and research reports.Journal articles.Web-based documents. Outreach ProgramCreate and maintain a project Web site.Outreach to communicate research findings at workshops, panel discussions, conferences, etc.Organize training and webinars in cooperation with FHWA headquarters, resource center, and field offices.