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1.1 1. INTRODUCTION AND RESEARCH APPROACH 1.1 Scope and Research Objectives 1.1.1 Background The importance of the filter component of a countermeasure for stream instability or bridge scour installation should not be underestimated. Filters are essential to the successful long- term performance of countermeasures, especially armoring countermeasures. There are two basic types of filters: granular filters and geotextile filters. Some situations call for a composite filter consisting of both a granular layer and a geotextile. The specific characteristics of the base soil determine the design considerations for the filter layer. The filter must retain the coarser particles of the subgrade while remaining permeable enough to allow infiltration and exfiltration to occur freely. It is not necessary to retain all the particle sizes in the subgrade; in fact, it is beneficial to allow the smaller particles to pass through the filter, leaving a coarser substrate behind. The filter prevents excessive migration of the base soil particles through the voids in the armor layer, permits relief of hydrostatic pressure beneath the armor, and distributes the weight of the armor to provide more uniform settlement. Guidance for the design of both granular and geotextile filters is provided in National Cooperative Highway Research Program (NCHRP) Report 568, "Riprap Design Criteria, Recommended Specifications, and Quality Control" (Lagasse et al. 2006), and is found in Volume 2 of Hydraulic Engineering Circular (HEC) â 23 as Design Guide 16 (Lagasse et al. 2009). HEC-23 Volume 1 also provides some limited guidance on placing filters underwater. However, experience and a survey of practitioners indicate that few countermeasure installations in water actually include a filter as shown on the design plans and as recommended in the technical guidance publications cited above. The most common reasons given for the omission of a filter have been related to constructability issues or environmental concerns. Consequently, research on filter selection, design, and installation techniques for scour and erosion countermeasure systems in various underwater conditions is a high priority requirement if the most recent design guidance on armoring countermeasures (e.g., HEC-23) is to be implemented effectively. Moreover, an effective implementation plan will be necessary so that DOT design, construction, and maintenance personnel (along with their consultants and contractors) receive training on how countermeasures function and the overriding importance of the underlying filter. 1.1.2 Objectives The objectives of this research are to develop specific guidance for design, construction, and maintenance personnel on the function of filters and their installation. The research considered various depths and velocities of stream flow for placing geotextiles and granular filters under countermeasures with emphasis on underwater installation. The project deliverables address: â¢ Education â¢ Selection â¢ Design â¢ Construction â¢ Maintenance â¢ Specifications â¢ Quality Control/Quality Assurance â¢ Implementation Plan
1.2 1.2 Research Approach During Phase I of this research a review of the technical literature was combined with a survey of practitioners to produce a detailed synthesis of the current state of practice. Phase II included development of selection criteria for granular and geotextile filters in relation to requirements and constraints for underwater placement. Prototype scale laboratory testing was implemented to document underwater installation procedures. Findings from these activities supported development of design, construction, maintenance, testing, recommended specifications, and quality control guidance for underwater placement. To support implementation of the findings of this research, educational materials, including videos and case studies were developed and a stand-alone implementation document was prepared to supplement the final report for this research. The following specific tasks were completed to accomplish project objectives. These tasks incorporate Panel guidance and parallel, with some modifications, the tasks established in the original Research Work Plan. PHASE I Task 1 - Review Technical Literature Task 2 - Survey for Current State of Practice Task 3 - Synthesize Current State of Practice Task 4 - Interim Report and Panel Meeting PHASE II Task 5 - Develop Selection Criteria Task 6 - Documentation of Underwater Filter Installation Procedures Task 7 - Develop Design, Construction, Maintenance, Testing, Specifications, and Quality Control Guidance Task 8 - Prepare Educational Materials, Videos, and Case Histories Task 9 - Develop Stand-Alone Implementation Document for Installation Guidance Task 10 - Submit Final Report 1.3 Research Tasks PHASE I 1.3.1 Task 1 - Review the Technical Literature The Research Team conducted a thorough review of the technical literature from foreign and domestic sources to assess the adequacy and extent of existing information on the functions, design, installation, inspection, and quality assurance for granular and geosynthetic filters for armoring and other erosion control countermeasures. Specifically, the search sought guidance and experience with placing filters underwater in riverine environments with various depths and velocities of flow. The literature review identified research in progress as well as completed work. Under Task 1 of the Research Work Plan, a literature search of domestic and foreign sources concentrating on underwater installation of filter systems was conducted. The search began with the search source Google Scholar which includes GeoRef and TRB's TRID. Secondary searches were conducted using reference search engines provided by the American Society
1.3 of Civil Engineers (ASCE), International Association of Hydrological Sciences, United States Geological Survey, Geological Society of America, America Geophysical Union, and the Institute of Civil Engineers in the United Kingdom. The key words used in the search included: â¢ Granular filter â¢ Stream bank â¢ Abutment scour countermeasures â¢ Geotextile filter â¢ Stream bank armor â¢ Filter design case studies â¢ Geocomposite filter â¢ Stream bank protection â¢ Filter installation case studies â¢ Filter design â¢ Scour countermeasures â¢ Filter failure case studies â¢ Filter installation â¢ Pier scour countermeasures â¢ Underwater filter Combinations of these key words with the search term "underwater" also helped refine the search. The advantages of using Google Scholar include: â¢ It is a freely accessible web search engine that indexes the full text of scholarly literature across an array of publishing formats and disciplines. â¢ Google Scholar index includes most peer-reviewed online journals of Europe and America's largest scholarly publishers, plus scholarly books and other non-peer reviewed journals. â¢ Google Scholar allows users to search for digital or physical copies of articles, whether online or in libraries. â¢ Google Scholar indexes "full-text journal articles, technical reports, preprints, theses, books, and other documents, including selected Web pages that are deemed to be 'scholarly'." The preponderance of the literature available did not specifically cover how to install filters at depth and in river currents. Instead, much of the literature identified in this initial search discussed only very general design and installation criteria for the filter and standard methods of construction on the bed or banks of a waterway. The initial literature review under Task 1 provided 41 abstracted references. Review by the Panel of an annotated bibliography resulted in a number of suggestions on specific references or general search areas that would add to the bibliography. The search for relevant references and design guidance continued as the Task 3 synthesis of the current state of practice for underwater filter installation was prepared. This subsequent search produced a total of 94 citations, several of which do provide specific guidance for installation of filters underwater. 1.3.2 Task 2 - Survey for Current State of Practice The objective under Task 2 was to survey federal agencies, state departments of transportation, contractors, consultants, geosynthetic manufacturers and suppliers, to determine practices used to select, design, specify, install, maintain, and inspect filters for armoring and erosion control countermeasures. The survey collected data on granular and geotextile filter selection, design, installation, specifications, standard plans, and construction guidance.
1.4 The survey was prepared in consultation with the NCHRP Panel. Concurrently, a mailing list was developed which included all state DOT hydraulic engineers and FHWA Resource Center and Division/District engineers. Contacts with the Army Corps of Engineers, the Bureau of Reclamation, and the Natural Resources Conservation Service (NRCS) and resource/permit agencies were also used to develop the survey mailing list for those agencies. The final mailing list included: â¢ All Panel members â¢ Selected authors of key documents identified in the annotated bibliography from Task 1 â¢ All state DOT hydraulic engineers â¢ All members of appropriate ASTM committees â¢ Selected FHWA personnel from the Resource Center and Federal Lands Divisions â¢ Other Federal agencies with hydraulic engineering construction responsibilities (e.g., U.S. Army Corps of Engineers, U.S. Bureau of Reclamation, NRCS, etc.) â¢ Contractors, consultants and professional colleagues of Research Team members 1.3.3 Task 3 - Synthesize Current State of Practice Based on the findings of Task 1 and subsequent literature search (as described under Task 1, above) a detailed synthesis of the current state of practice for underwater installation of granular and geotextile filters was developed for Panel review. This synthesis included design, installation, inspection, and quality assurance of granular and geosynthetic filters for armoring and other erosion control countermeasures at stream and river banks, bridge piers, bridge abutments, and other locations requiring scour countermeasures. The focus was on the availability of guidance for placing filters underwater in riverine settings with various depths and velocities of flow. However, as noted in the Research Problem Statement for this project, DOT construction and maintenance personnel along with general contractors who perform countermeasure installations have not been educated on how countermeasures function and the value of the underlying filter. Consequently, the synthesis started with an overview of the purpose, need, and function of the filter component of countermeasure armor systems for scour and other erosion control requirements. Using this synthesis of the literature and the results of the Task 2 survey of practitioners, a critical evaluation of all commonly used selection criteria, design guidance, material specifications, test methods, and construction/installation practices was conducted. Based on this critical evaluation, the need for and methods to develop full and complete guidance for the placement of filters underwater under the proposed Phase II tasks were identified with reference to the eight critical factors established by the Panel for the design guidance. 1.3.4 Task 4 - Interim Report The Research Team prepared and submitted an Interim Report documenting the information developed in Tasks 1 through 3. The Interim Report included recommendations for selection criteria, the form and format of the guidance document, and development of educational materials to implement the findings and guidance resulting from this research. The Interim Report meeting with the Panel was crucial to the refinement of a Phase II work plan that would accomplish all project objectives.
1.5 PHASE II 1.3.5 Task 5 - Develop Selection Criteria Selection criteria were developed for granular, geotextile, and geocomposite filter systems considering the relative advantages and limitations of various approaches to underwater installation, including equipment type and capability. Site hydraulic, geotechnical, and geomorphic conditions were considered, as will site restrictions, extreme conditions, and site- specific permitting and environmental issues. The selection criteria also considered the availability of specialized filter systems that facilitate underwater placement such as the sand-filled geotextile container or the sandmat approaches discussed under the Task 3 Synthesis of Current State of Practice (see Section 2.2); however, the proprietary nature of such systems, and the equipment necessary for placement, may affect selection. 1.3.6 Task 6 - Documentation of Underwater Filter Installation Procedures For more than 18 months from Notice to Proceed the Research Team attempted to identify and coordinate field test sites to document filter installation procedures. Concerns with integrating research objectives into construction activities on the part of both bridge owners and contractors, as well as scheduling conflicts proved to be significant issues. Because of this lack of progress at proposed field test sites, the Research Team proposed and the Panel approved the use of prototype scale laboratory facilities at CSU to implement a laboratory test program to provide definitive information to support developing installation guidance for both granular and geotextile filters underwater. Laboratory and the installation testing was conducted in the outdoor flume using instrumentation readily available at CSU. The tests included the use of divers in the flume to conduct various installation experiments and record the procedures and equipment employed in support of developing more definitive underwater installation guidance for both granular and geotextile filters. The laboratory testing sequence, results, and documentation are presented in detail in Chapter 3. 1.3.7 Task 7 - Develop Design, Construction, Maintenance, Testing, Specifications and Quality Control Guidance Under this task the Research Team developed design, construction, and maintenance/ inspection guidance for granular, geotextile, and geocomposite filter systems. Design criteria include hydraulic and scour characteristics, durability and longevity of the filter, and details such as anchoring, seams, and edge protection and considered existing design guidance for the associated armoring system. Installation guidance includes options and best practices, as well as safety and construction sequencing requirements. Maintenance guidance relates to identification of critical issues/conditions and considers means and methods for repair. Under this task material testing specifications, and quality control guidance that will ensure the durability and longevity of filter materials installed underwater were also developed.
1.6 For this task standard test methods were also reviewed (where available) or developed for underwater placement of the various types of filter materials. AASHTO guide specifications are subdivided into five main sections: 1) Description; 2) Materials; 3) Construction Requirements; 4) Method of Measurement; and 5) Basis of Payment. In many instances, the Materials section will reference ASTM or other relevant standard test methods, while the Construction Requirements section often references ASTM standards of practice, as appropriate. As related to granular filters, test methods are typically concerned with the quality of the aggregate as determined by specific measures of durability (i.e., resistance to deterioration by physical and chemical weathering), unit weight (indexed by specific gravity), and size gradation (distribution of equivalent particle diameters of the mix). Subgrade particle retention and filter permeability are both related to the size gradation of the granular filter. With respect to geotextile filters, test methods consider durability (trapezoid tear strength, grab strength, elongation, and puncture resistance), Apparent Opening Size (AOS), open area (for woven monofilament fabrics), thickness (for nonwoven needle-punched fabrics), permeability, clogging, and uplift. 1.3.8 Task 8 - Prepare Educational Materials, Videos, and Case Histories Based on data acquired from the Task 1 literature review, Task 2 survey, and documentation available to Research Team members from past (or ongoing) projects and educational activities, a variety of educational materials to include photographs, videos, and case histories were developed to support the implementation of the findings of this research. Task 6 activities also supported Task 8 objectives. 1.3.9 Task 9 - Develop Stand-Alone Implementation Document for Installation Guidance As a stand-alone deliverable, the Research Team prepared a companion Training Manual for Implementation in the form of a modular workshop that incorporates photographs, videos, and case histories obtained during Tasks 6 and 8 to provide training on the underwater placement of filters. This deliverable meets all current ISD standards established by the FHWA NHI. This underwater filter workshop in the form of an NHI Instructor's Guide provides the basic instructional components for a range of training engagements to implement the results of this research project and for the development of a distance learning (web based) presentation at some time in the future. 1.3.10 Task 10 - Submit Final Report A final report that documents the entire research effort was submitted. The Final Report provides a companion executive summary that outlines the research results. The Task 9 stand-alone training document is designed to support implementation of the findings of this research.