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NCHRP Web-Only Document 254: Underwater Installation of Filter Systems for Scour and Erosion Countermeasures, Volume 1: Research Report P.E. Clopper P.F. Lagasse Ayres Associates Inc. Fort Collins, Colorado Final Report for NCHRP Project 24-42 Submitted April 2018 ACKNOWLEDGMENT This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.
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C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP WEB-ONLY DOCUMENT 254 Christoper J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Megan Chamberlain, Program Associate Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Ellen Chafee, Senior Editor Jennifer Correro, Senior Editorial Assistant NCHRP PROJECT 24-42 PANEL AREA TWENTY-FOUR: SOILS AND GEOLOGY--MECHANICS AND FOUNDATIONS Steve Ng, Sacramento, CA (Chair) Larry J. Tolfa, New York State DOT, Albany, NY Barry R. Christopher, Christopher Consultants, Inc., Roswell, GA Nicolas P. Jadamec, Phoenix Marine Construction Co., Sayreville, NJ Blake E. Nelson, Minnesota DOT, Maplewood, MN Carlton D. Spirio, Jr., Florida DOT, Tallahassee, FL L. David Suits, North American Geosynthetics Society, Albany, NY Bart Bergendahl, FHWA Liaison
iv TABLE OF CONTENTS 1. Introduction and Research Approach ........................................................................... 1.1 1.1 Scope and Research Objectives ........................................................................... 1.1 1.1.1 Background .................................................................................................... 1.1 1.1.2 Objectives ...................................................................................................... 1.1 1.2 Research Approach .............................................................................................. 1.2 1.3 Research Tasks .................................................................................................... 1.2 1.3.1 Task 1 - Review the Technical Literature ....................................................... 1.2 1.3.2 Task 2 - Survey for Current State of Practice ................................................ 1.3 1.3.3 Task 3 - Synthesize Current State of Practice ............................................... 1.4 1.3.4 Task 4 - Interim Report .................................................................................. 1.4 1.3.5 Task 5 - Develop Selection Criteria ................................................................ 1.5 1.3.6 Task 6 - Documentation of Underwater Filter Installation .............................. 1.5 1.3.7 Task 7 - Develop Design, Construction, Maintenance, Testing, .................... 1.5 1.3.8 Task 8 - Prepare Educational Materials, Videos, and .................................... 1.6 1.3.9 Task 9 - Develop Stand-Alone Implementation Document for ....................... 1.6 1.3.10 Task 10 - Submit Final Report ....................................................................... 1.6 2. Findings ........................................................................................................................ 2.1 2.1 Survey for Current State of Practice...................................................................... 2.1 2.1.1 General Information ....................................................................................... 2.1 2.1.2 Design-Related Issues ................................................................................... 2.1 2.1.3 Underwater Installation Issues ....................................................................... 2.2 2.1.4 Summary of Survey Results ........................................................................... 2.4 2.2 Task 3 - Synthesis of Current State of Practice .................................................... 2.4 2.2.1 Overview ........................................................................................................ 2.4 2.2.2 Background and Approach ............................................................................ 2.5 2.2.3 Purpose, Need, Function and Design of the Filter Component of .................. 2.6 2.2.4 Documentation from European Practice for Filter Design ............................ 2.19 2.2.5 European Practice for Installation of Filter Systems Underwater ................. 2.22 2.2.6 U.S. Practice for Installation of Filter Systems Underwater ......................... 2.41 2.2.7 Coastal and Offshore Applications ............................................................... 2.63 2.2.8 Special Applications ..................................................................................... 2.69 2.2.9 Permitting of Filter Installations .................................................................... 2.75 2.2.10 Summary and Additional Observations ........................................................ 2.75 3. Laboratory Testing - Documentation of Underwater ..................................................... 3.1 3.1 Overview ............................................................................................................... 3.1
v 3.2 Laboratory Testing Plan ........................................................................................ 3.2 3.2.1 Preparation of Testing Facility........................................................................ 3.2 3.2.2 Testing Approach and Documentation ........................................................... 3.2 3.3 Underwater Installation of Granular Filters ............................................................ 3.7 3.3.1 Critical Velocity vs. Particle Size .................................................................... 3.7 3.3.2 Dispersion and Segregation Issues ............................................................... 3.8 3.3.3 Flexible Tremie-Type Approaches ............................................................... 3.10 3.4 Underwater Installation of Geotextile Filters ........................................................ 3.12 3.5 Appraisal of Underwater Installation Testing Results .......................................... 3.13 4. Installation Guidance and Appraisal of Research Results ............................................ 4.1 4.1 Overview ............................................................................................................... 4.1 4.2 General Considerations ........................................................................................ 4.1 4.3 Selection Criteria for Underwater Filter Installation ............................................... 4.1 4.3.1 Construction Constraints: Filter Selection Based on Site .............................. 4.2 4.3.2 Placement Environment: Filter Selection Based on Velocity ........................ 4.2 4.3.3 Additional Considerations .............................................................................. 4.5 4.4 Guidance for Underwater Installation of Granular Filters ...................................... 4.5 4.4.1 Design ............................................................................................................ 4.5 4.4.2 Installation ...................................................................................................... 4.6 4.4.3 Inspection and Maintenance .......................................................................... 4.6 4.4.4 Testing ........................................................................................................... 4.6 4.4.5 Specifications ................................................................................................. 4.7 4.4.6 Quality Control ............................................................................................... 4.9 4.4.7 Environmental and Permitting Considerations ............................................. 4.10 4.5 Guidance for Underwater Installation of Geotextile Filters .................................. 4.11 4.5.1 Design .......................................................................................................... 4.11 4.5.2 Installation .................................................................................................... 4.11 4.5.3 Inspection and Maintenance ........................................................................ 4.12 4.5.4 Testing ......................................................................................................... 4.12 4.5.5 Specifications ............................................................................................... 4.12 4.5.6 Quality Assurance / Quality Control ............................................................. 4.14 4.5.7 Environmental and Permitting Considerations ............................................. 4.15 4.6 Applications ......................................................................................................... 4.16 4.6.1 Case Study - Underwater Installation of a Filter for Scour ........................... 4.16 4.6.2 Case Study - Underwater Installation of a Filter for Scour ........................... 4.21
vi 4.7 Appraisal of Results ............................................................................................ 4.28 4.7.1 Advances in the State of Practice ................................................................ 4.28 4.7.2 Observations From the Survey of Practitioners ........................................... 4.29 4.7.3 Observations and Lessons Learned From the Laboratory ........................... 4.29 4.8 Implementation of Research Results .................................................................. 4.30 4.8.1 The Product ................................................................................................. 4.30 4.8.2 The Market ................................................................................................... 4.31 4.8.3 Impediments to Implementation ................................................................... 4.31 4.8.4 Leadership in Application ............................................................................. 4.31 4.8.5 Activities for Implementation ........................................................................ 4.32 4.8.6 Criteria for Success ...................................................................................... 4.32 4.9 Stand-Alone Training Document for Implementation of ...................................... 4.33 5. Conclusions and Suggested Research ........................................................................ 5.1 5.1 Conclusions and Applicability of Results ............................................................... 5.1 5.1.1 Conclusions ................................................................................................... 5.1 5.1.2 Applicability of Results to Highway Practice .................................................. 5.2 5.2 Suggested Research ............................................................................................. 5.2 6. References ................................................................................................................... 6.1 APPENDIX A â Survey Form .............................................................................................. A-1 APPENDIX B â Alternative Filter Design Procedures...........................................................B-1
vii LIST OF FIGURES Figure 2.1. Examples of soil and filter compatibility processes. ......................................... 2.8 Figure 2.2. Changes in water levels and seepage patterns during a flood. ...................... 2.10 Figure 2.3. Granular filter design chart according to Cistin and Ziems ............................. 2.16 Figure 2.4. Geotextile selection for soil retention.............................................................. 2.17 Figure 2.5. Use of a fascine mattress for placing a countermeasure with filter. ............... 2.22 Figure 2.6. Preparing a fascine mattress (including additional brushwood layer) ............ 2.23 Figure 2.7. Roller for placing geotextiles onto the subgrade. ........................................... 2.24 Figure 2.8. Flexible revetment with integrated geotextile filter ready to be ....................... 2.26 Figure 2.9. Close-up photo of a geocomposite blanket .................................................... 2.30 Figure 2.10. A geocomposite blanket being unrolled ........................................................ 2.30 Figure 2.11. Sand-filled geotextile containers................................................................... 2.31 Figure 2.12. Filling 1.0 metric tonne geotextile container with sand ................................. 2.31 Figure 2.13. Handling a 1.0 metric tonne sand-filled geotextile container ........................ 2.32 Figure 2.14. Placing geosynthetic containers ................................................................... 2.36 Figure 2.15. Eidersperrwerk on the Eiden estuary, Germany ......................................... 2.36 Figure 2.16. Cross section of a typical sandmat).............................................................. 2.37 Figure 2.17. GEOfabrics suggested underwater installation techniques .......................... 2.38 Figure 2.18. GEOfabrics installation techniques .............................................................. 2.39 Figure 2.19. Testing of granular and geotextile filters....................................................... 2.46 Figure 2.20. Schematic layout for sand filled geotextile containers and riprap tests ........ 2.47 Figure 2.21. Geotextile containers before installation around the pier. ............................ 2.47 Figure 2.22. Installation of geotextile containers, pier is on the left. ................................. 2.48 Figure 2.23. Geotextile containers after installation.......................................................... 2.48 Figure 2.24. Installation of riprap around pier. .................................................................. 2.49 Figure 2.25. Riprap armor over geotextile containers....................................................... 2.49 Figure 2.26. High velocity test of geotextile container filter with riprap armor. ................. 2.50 Figure 2.27. Colorado State University Toskane units ..................................................... 2.51 Figure 2.28. Rebar frame for placing geotextile filter underwater ..................................... 2.52 Figure 2.29. Typical filter detail beneath streambank armor ............................................. 2.53 Figure 2.30. Erosion control installations .......................................................................... 2.54 Figure 2.31. Construction of hard armor erosion control systems .................................... 2.55 Figure 2.32. Special construction requirements related to specific hard armor ................ 2.56 Figure 2.33. Geotextile placement for currents acting parallel to bank ............................. 2.60 Figure 2.34. Schematic of underwater mound of contaminated dredged material ........... 2.61 Figure 2.35. Techniques for placing sand caps on contaminated sediments ................... 2.62 Figure 2.36. Self-healing characteristic of high elongation containers ............................. 2.65 Figure 2.37. Scour protection solutions for OWT foundations .......................................... 2.70 Figure 2.38. Handling, filling and, closing of geotextile containers ................................... 2.70 Figure 2.39. Installation of scour stabilization by the use of a stone dumping barge ....... 2.71 Figure 2.40. Installation of scour stabilization by the use of a jib-crane ........................... 2.71
viii Figure 2.41. Geotextile tube and fill ports ......................................................................... 2.72 Figure 2.42. Equipment and filling process for geotextile tubes ....................................... 2.73 Figure 2.43. Large fascine mattress being floated into place. .......................................... 2.79 Figure 2.44. Scour-hole at Eider storm surge barrier-cross section of scour ................... 2.82 Figure 3.1. Sand-filled geocontainers placed as a filter around a bridge pier ..................... 3.1 Figure 3.2. Prototype-scale bridge pier in the River Engineering Flume ............................ 3.3 Figure 3.3. Prototype bridge pier in the River Engineering Flume. ..................................... 3.4 Figure 3.4. Plan view of flume showing point velocity contours at 60% depth. .................. 3.4 Figure 3.5. Point velocity contours (ft/s) at 50 ft3/s. ............................................................ 3.5 Figure 3.6. Point velocity contours (ft/s) at 200 ft3/s. .......................................................... 3.6 Figure 3.7. Critical velocity vs. particle size (particle specific gravity = 2.65). .................... 3.7 Figure 3.8. Granular filter dispersion tests. ......................................................................... 3.8 Figure 3.9. Grain size distribution curves for dispersion test at 50 ft3/s. ............................. 3.9 Figure 3.10. Grain size distribution curves for dispersion test at 80 ft3/s. ........................... 3.9 Figure 3.11. Test setup for granular filter placement. ....................................................... 3.11 Figure 3.12. (a) Geobag with fill port; (b) Divers filling geobag under water at the pier. .. 3.11 Figure 3.13. Tremie-placed granular filter during and after the 50 ft3/s demonstration. ... 3.12 Figure 3.14. Tremie-placed granular filter after the 200 ft3/s demonstration. ................... 3.12 Figure 3.15. Self-sinking geotextile filter. .......................................................................... 3.13 Figure 3.16. Geotextile filter placement after the 50 ft3/s demonstration. ......................... 3.13 Figure 3.17. Geotextile filter placement after the 200 ft3/s demonstration. ....................... 3.14 Figure 4.1. Selection based on access and clearance. ...................................................... 4.3 Figure 4.2. Selection based on velocity and depth. ............................................................ 4.4 Figure 4.3. Assembly of 6 x 6 A-Jacks® module on skids. ................................................ 4.17 Figure 4.4. Handling device designed by Contractor to place the A-Jacks® modules ...... 4.17 Figure 4.5. Lifting frame to place the A-Jacks® modules .................................................. 4.18 Figure 4.6. Applying the geotextile filter to an A-Jacks® module. ..................................... 4.19 Figure 4.7. Crane and assembled A-Jacks® module (with geotextile filter) ...................... 4.19 Figure 4.8. Installation at the bridge started downstream and proceeded upstream. ....... 4.20 Figure 4.9. Divers and pontoon boat used to assist module placement. .......................... 4.20 Figure 4.10. Diver inspecting in-place A-Jacks® module at Ferry Butte Bridge. ............... 4.21 Figure 4.11. Geotextile container stockpile (4'x4'x4' cubes) at Bonner Bridge ................. 4.23 Figure 4.12. Pallets of 4' A-Jacks® (3 jacks per pallet) at Bonner Bridge ......................... 4.24 Figure 4.13. A-Jacks® assembly area and stockpile at Bonner Bridge ............................. 4.25 Figure 4.14. Stainless steel cable and hardware binding A-Jacks® elements .................. 4.25 Figure 4.15. Contractor apparatus for A-Jacks® module placement ................................. 4.26 Figure 4.16. Geotextile filter applied to A-Jacks® modules ............................................... 4.26 Figure 4.17. Placement of geotextile containers around Bent 166 at Bonner Bridge ....... 4.27 Figure 4.18. Contractor lifting the geotextile containers to place at Bent 166 .................. 4.27
ix LIST OF TABLES Table 2.1. Typical Porosity and Hydraulic Conductivity of Alluvial Soils ........................... 2.11 Table 2.2. Recommended Tests and Allowable Values for Geotextile Properties. .......... 2.14 Table 2.3. Characteristics of Geotextile. ........................................................................... 2.47 Table 3.1. Results of Granular Filter Dispersion Tests. .................................................... 3.10 Table 4.1. Recommended Tests and Allowable Values for Aggregate Quality .................. 4.7 Table 4.2. Standard Coarse Aggregate Gradations From ASTM C33. .............................. 4.8 Table 4.3. Recommended Tests and Allowable Values for Geotextile Properties. .......... 4.13
x ACKNOWLEDGMENTS This work was sponsored by the American Association of State Highway and Transportation Officials, in cooperation with the Federal Highway Administration (FHWA), and was conducted under the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies. The research reported herein was performed under NCHRP Project 24-42 by Ayres Associates, Fort Collins, Colorado. Mr. Paul E. Clopper, Director-Applied Technology, Ayres Associates served as Principal Investigator (PI). Dr. Peter F. Lagasse, Senior Water Resources Engineer, Ayres Associates, served as Co-PI. The laboratory testing performed under this project (Task 6) was conducted at the Colorado State University (CSU) Engineering Research Center. The authors wish to acknowledge the efforts of Dr. Robert Ettema, Research Associate, and Mr. Jason Berg who supervised the CSU graduate students in hydraulic engineering. Mr. Dylan Armstrong and Scott Nesbitt of Ayres Associates participated in the implementation of the laboratory testing phase and compiled the results of the laboratory study for the Research Team. A special acknowledgment is due to the highly qualified certified divers who helped establish the limits and validated the requirements for underwater installation of filter systems. They included Mr. Jim Johnson of the High Plains Scuba Center in Fort Collins, Colorado, Mr. Gary Schranz, and Mr. Justin Fox. The assistance of Mr. Lotwick Reese, Senior Hydraulic Engineer, Idaho DOT, in providing data, design drawings and a PPT presentation to support the Snake River geotextile filter installation case study is gratefully acknowledged. Likewise, Mr. Dave Henderson, Senior Scour Engineer, FHWA Office of Bridges and Structures, Washington, D.C. provided valuable assistance in developing the case study of operations at the Bonner Bridge, NC (2013-2014) which is based on his article in FHWA's Hydrologic and Hydraulic News (Volume 2, Issue 1, April 2014). Finally, the participation, advice, support, and suggestions of NCHRP Panel members throughout this project are gratefully acknowledged. DISCLAIMER This is an uncorrected draft as submitted by the research agency. The opinions and conclusions expressed or implied in the report are those of the research agency. They are not necessarily those of the Transportation Research Board, the National Research Council, the FHWA, the American Association of State Highway and Transportation Officials, or the individual states participating in the National Cooperative Highway Research Program.
xi ABSTRACT This report documents and presents specific guidance for design, construction, and maintenance personnel on the function of filters as an essential component of bridge scour and other erosion control countermeasures. This research resulted in a synthesis of the state of practice, internationally, for installing filter systems underwater. For both granular and geotextile filters, recommended design procedures, specifications, material testing requirements, installation alternatives, and quality checklist items are provided. While the installation of granular filters in flowing water is problematic in most cases, the use of self-sinking geotextile composite fabrics is a common practice in Europe. Geotextile filters can also be installed as bags filled with sand or gravel. Geotextile containers can be filled prior to placement and dropped through the water column, or empty geobags can be placed underwater by divers and filled with a flexible tremie hose. These are commonly used in Europe, but are relatively unknown in the U.S. Wider use of the self-sinking geotextile mat or geobag approaches would constitute a significant advance in the state of practice for placing filters in flowing water in the U.S. Using innovative techniques such as these, there should be very few instances where a filter cannot be placed underwater as an integral part of a properly designed and installed scour or erosion control countermeasure.
xii UNDERWATER INSTALLATION OF FILTER SYSTEMS FOR SCOUR AND EROSION COUNTERMEASURES SUMMARY Overview The importance of the filter component of a countermeasure for stream instability or bridge scour 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. In practice, 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 applicable technical guidance publications. 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 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. The objectives of this research were 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: ⢠Education ⢠Selection ⢠Design ⢠Construction ⢠Maintenance ⢠Specifications ⢠Quality Control/Quality Assurance ⢠Implementation Plan 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 in the form of flow charts for granular and geotextile filters in relation to requirements and constraints for underwater placement. Prototype scale laboratory testing using certified divers was implemented to document underwater installation procedures and equipment requirements, to validate diver-supported installation techniques, and to establish limits on conditions where diver assistance could be employed safely. Findings from these activities supported development of design, construction, maintenance, testing, recommended specifications, and quality control guidance for underwater placement
xiii of filters as an essential component of bridge scour and other erosion control armoring systems. To support implementation of the findings of this research, educational materials were developed, including videos and case studies, and a stand-alone implementation document was prepared to supplement the final report for this research. Guidance for placing both geotextile filters and granular filters was developed. Standard rolled geotextiles as well as self-sinking fabrics (often referred to as a sandmat) are considered. It should be noted that geocontainers filled with granular material may be considered a "hybrid" filter, and can be installed either as pre-filled geobags that are dropped through the water column, or filled in place underwater by divers using a flexible hose-type tremie. In addition to the diver-assisted filter placement trials at Colorado State University, a well- documented case study of underwater filter placement using commonly available construction equipment at a bridge over the Snake River in Idaho was provided by the Idaho Transportation Department. A companion case study of underwater filter installation by North Carolina DOT is also presented. This case study of filter placement at a coastal bridge reinforces many of the lessons learned from the Idaho Snake River installation. The information from these case studies was used to support training modules and a detailed applications workshop for adult learning. The educational materials were developed to be compliant with Instructional Systems Design (ISD) guidance promulgated by FHWAâs National Highway Institute (NHI), and were designed as ready-made lessons that could be easily incorporated into existing training courses offered through the NHI. Appraisal of Research Results In general, the intent of the guidance in this report is to provide information and recommendations regarding the design and underwater installation of filter materials prior to placing an armor layer for erosion protection. Design and specification are within the purview of the engineer, whereas the means and methods of placement are up to the construction contractor. However, the end result of the placement must meet the intent of the design in order to achieve successful long-term performance. This report not only presents information and recommendations for placing filters underwater; it also provides filter selection and design guidance. Two methods for designing granular filters and three methods for designing geotextile filters are provided in this single document. The results of this research project provide practitioners with a variety of materials and methods for placing filters under water. Both granular and geotextile filter materials are considered. Filters can be placed underwater using construction equipment, or by hand using divers. The means and methods for the current state of practice regarding underwater filter placement in Europe, the U.S., and other countries are discussed in detail. Underwater installation of granular filters can be performed by clamshell bucket or tremie, with the filter material being released on or very near the bed. The tremie method of placement can be accomplished using either rigid pipe from the surface, or a flexible hose through which the filter material is pumped in a water slurry to divers at the end of the hose. Current practice and results of the laboratory studies indicate that loose granular filter aggregates should never be dumped into the water column and allowed to fall to the bed, as this will lead to segregation and dispersion of the filter particles, even in relatively quiescent water. The resulting dumped material will be coarser and more uniform than the original stockpile material. In flowing water, granular filters must be placed on or near the bed, and
xiv only when local flow velocities are less than about 0.5 times Vcrit, where Vcrit is the critical velocity for incipient motion of the d50 (median) particle size of the filter material. It was found that many methods have been developed for installing geotextiles under water for European practice and, to a lesser degree in U.S. practice. In general, geotextile sheets must be placed so that they are free of folds and wrinkles and lie in intimate contact with the subgrade. Individual sheets should be overlapped and when placed in flowing water must be temporarily weighed down before the overlying armor is placed. Current practice and results of the laboratory studies also indicate that buoyant geotextile sheets can be placed in currents of up to about 2.5 ft/s. Self-sinking geotextiles, for example a sandmat type product commonly available in Europe (consisting of layers of nonwoven, needle punched geotextiles with a filler of sand between upper and lower layers) are both stiffer and heavier, and can be placed by divers in flows up to 3.5 ft/s. Unrolling the geotextile in the direction of flow facilitates placement. Geotextile filters can also be installed as bags filled with sand or gravel. The geobags can be filled prior to placement, sewn shut, and dropped through the water column. Alternatively, empty geobags can be placed by divers and filled in place with a flexible tremie hose. Both approaches are commonly used in Europe, but are relatively unknown in the U.S. Widespread use of the geobag or geocontainer approaches would constitute a significant advance in the state of practice for placing filters in flowing water in the U.S. The report also considers environmental and permitting considerations for placing filters under water. At the installation site, both granular and geotextile filter material would, by design and installation practice, be exposed to stream flow for only a limited period prior to placement of the overlying armoring component. In general, it might be assumed that if the armoring component of a countermeasure system can be permitted, the granular or geotextile filter component should not present any additional permitting issues. One must recognize, however, that in some cases in relation to the physical habitat, regulatory agencies will permit the use of only ânatural, not man-madeâ material. Permitting of the use of a granular or geotextile filter for a countermeasure will then hinge on the interpretation of the term ânaturalâ and the flexibility of the permitting agency in enforcing a prohibition on the use of man-made materials in the aquatic environment. Conclusions 1. This research resulted in a synthesis of the state of the practice for installing filter systems underwater for bridge scour and other erosion control countermeasures. Materials, equipment, and placement techniques developed in Europe, the U.S., and other countries are presented. 2. A survey of practitioners across the U.S. revealed that some underwater installation practices in other countries are still new and largely untried in the U.S. The use of self- sinking geotextile composite fabrics (e.g., a sandmat) is one such practice. Another example is the use of a flexible tremie hose to deliver a slurry of coarse granular filter material to divers for placement underwater. When conditions allow divers to safely access the work area, they can, under moderate flow conditions, place granular material loosely on the bank or bed. 3. For both granular and geotextile filters, recommended design procedures, specifications, material testing requirements, installation alternatives, and QA/QC checklist items are
xv provided in this report. In addition, filter selection guidance (in the form of flow charts) is provided based on site-specific conditions which include flow depth, flow velocity, access for construction equipment, and overhead clearance. 4. Geotextile filters can also be installed as bags filled with sand or gravel. The geobags can be filled prior to placement, sewn shut, and dropped through the water column. Alternatively, empty geobags can be placed by divers and filled in place with a flexible tremie hose. Both approaches are commonly used in Europe, but are relatively unknown in the U.S. Wider use of the geobag or geocontainer approaches would constitute a significant advance in the state of practice for placing filters in flowing water in the U.S. 5. Practitioners in the U.S. indicate that underwater inspection of a filter installation is not usually required prior to placing the armor layer on top. This is an undesirable practice that must be rectified. Recommendations for filter inspection, as one component of a quality control program during construction, are provided in this report. 6. In summary, the current state of practice for filter installation provides a sufficient variety of filter material types and placement techniques to accommodate most underwater filter requirements including riverine as well as coastal and offshore applications. Indeed, there should be very few instances where a filter cannot be placed underwater as an integral part of a properly designed and installed scour or erosion control countermeasure.
