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75 4.1 Overview This chapter presents a summary of information, observations, and recommended guidance for the installation of filters underwater. Guidance for selecting filter types and placement techniques are presented in flowchart fashion. The selection criteria are based on site-specific conditions including (1) access for construction equipment; (2) overhead clearance constraints; and (3) antici- pated hydraulic conditions during the construction season, including depth and flow velocity. Guidance for placing both geotextile filters and granular filters is provided. Standard rolled geotextiles as well as self-sinking fabrics (e.g., sandmat) are considered. It should be noted that a geocontainer filled with granular material may be considered a âhybridâ filter and can be installed either as a pre-filled geobag that is dropped through the water column or filled under- water by divers using a flexible hose-type tremie. In addition to the diver-assisted filter placement trials at CSU (see Chapter 3), a well- documented case study of underwater filter placement using construction equipment at a bridge over the Snake River in Idaho was provided by the Idaho Transportation Department. A com- panion case study of underwater filter installation by North Carolina DOT (NCDOT) is also presented in this chapter. This case study of filter placement at a coastal bridge reinforces many of the lessons learned from the Snake River installation in Idaho. 4.2 General Considerations In general, the intent of the guidance in this chapter is to provide information and recom- mendations 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 final result of the placement must meet the intent of the design in order to achieve successful long-term performance. 4.3 Selection Criteria for Underwater Filter Installation The selection guidance presented here considers seven filter types and their suitability for placement underwater. The selection guidance considers placement environment (velocity and depth) and construction considerations (site access and overhead clearance conditions beneath, for example, a bridge deck). Filter types presented in this section are the following: â¢ Loose granular filter (placed either by clamshell or tremie, not dumped) â¢ Geotextile fabric by itself (typically placed by divers and temporarily secured by sandbags, steel frame, or pins) C H A P T E R 4 Guidance for Installation of Filter Systems
76 Guidance for Underwater Installation of Filter Systems â¢ Self-sinking mat (machine-placed) â¢ Self-sinking mat (diver-placed) â¢ Pre-filled geocontainers â¢ Diver-filled geocontainers â¢ Geotextile affixed to armor 4.3.1 Construction Constraints: Filter Selection Based on Site Access and Overhead Clearance Construction constraints take into account the different needs and challenges required for placing a filter underwater and/or in flowing water. Construction constraints for filter placement are primarily concerned with site access issues in general, and, particularly when working in and around bridges, the overhead clearance between the water surface during construction and the low chord of the bridge deck section. The requirements for specialized equipment are addressed. For example, the equipment requirements, placement techniques, and construction QA/QC procedures for placing a geo- textile fabric underwater (typically using divers and temporary weights, pins, or frames) is rela- tively straightforward in situations where velocity and depth permit divers to work unhindered. In contrast, placing a sandmat (for example) requires specialized bulky and heavy construction equipment. Subgrade preparation requirements and placement tolerances also vary among filter types. A granular filter cannot simply be dumped through water because of particle segregation and transport by the flow; therefore, controlled placement using a flexible tremie pipe or a clamshell bucket is required. However, working beneath a bridge deck that affords little headroom will preclude the use of a clamshell and will dictate the type of equipment that can be used for instal- lation of any kind of filter. Figure 4.1 presents the recommended filter selection guidance when considering site access and overhead clearance. Access conditions that are considered âremote or restrictedâ indicate that large or heavy construction equipment cannot be used to place the filter material (or the overlying armor layer, for that matter). In these cases, materials must be handled and placed in individual installments small enough to be handled by smaller equipment or by divers. 4.3.2 Placement Environment: Filter Selection Based on Velocity and Depth Water velocity and depth during the construction period, including velocities during slack tide vs. flood and ebb tides in tidal environments, must be considered when placing a filter underwater. Typically, riverine construction will occur during the low-flow season when veloci- ties and depths are at a minimum; however, it is obvious that a granular filter cannot be placed if the local velocity during construction is greater than the critical velocity of the particles. We consider the 15% finer particle size (d15) as the limiting criterion for placement in flowing water; higher velocities will require a granular filter with a larger d15 particle size, as long as it meets the filter design criteria. Similarly, a geotextile fabric cannot be placed in a controlled fashion, even using divers, if velocities are greater than about 2.5 ft/s. Therefore, a different type of filter must be selected when placement must be conducted in higher velocity flow. Figure 4.2 presents the recommended filter selection guidance when considering velocity and depth.
Legend: = Well suited P = Possible use = Unsuitable Figure 4.1. Selection based on access and clearance.
Figure 4.2. Selection based on velocity and depth.
Guidance for Installation of Filter Systems 79 4.3.3 Additional Considerations There are additional issues to consider when selecting a filter to be placed underwater. For granular filters, issues to consider are the following: â¢ Availability of filter material of the required size and gradation â¢ Haul distance For all filter types, issues to consider are the following: â¢ Site access â¢ Equipment requirements, including barge if necessary â¢ Environmental and water quality issues and permitting requirements â¢ Habitat and/or migration issues for threatened and endangered species â¢ Traffic control during construction activities Lastly, materials and installation costs will be a factor in the selection of a filter when more than one filter type and/or construction technique is viable at a particular site: 1. Initial construction materials and delivery costs 2. Initial construction installation costs associated with labor and equipment 3. Use of in-house forces vs. outside contract Each of the above components is composed of multiple elements, which differ among the var- ious filter types. For example, quantities and unit costs of alternative materials will vary depend- ing on the specific project conditions, as well as local and regional factors. Experience with these factors, as well as project-specific knowledge of the project site, are required in order to be as practicable as possible when using the selection guidance presented in this section. It should be noted that current FHWA guidance as promulgated in HEC-23 (Lagasse et al. 2009) tends to discourage (but not preclude) the use of granular filters alone when placement underwater (flowing water) is required. This is based, primarily, on the findings of NCHRP Report 593 (Lagasse et al. 2007), which were based on extensive laboratory testing of both granu- lar and geotextile filter systems. HEC-23 cautions that in a riverine setting where dune-type bedforms may be present, it is strongly recommended that only a geotextile filter be considered. 4.4 Guidance for Underwater Installation of Granular Filters 4.4.1 Design The recommended design method for granular filters is that of Cistin and Ziems, as presented in HEC-23 (Lagasse et al. 2009). The Cistin-Ziems method is presented in detail in Section 2.2.3 of this document. An alternative method for granular filter design, developed by USACE, is presented in NCHRP Web-Only Document 254, Volume 1, Appendix B. 4.4.2 Installation Underwater installation of granular filters should only 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.
80 Guidance for Underwater Installation of Filter Systems A successful demonstration of the flexible tremie hose technique is summarized in Sec- tion 3.3.2. That demonstration used a standard contractor solids-handling pump (âtrash pumpâ) with 2 inch diameter suction and discharge hoses to pump 3/8 inch pea gravel as the granular filter. The pea gravel stockpile was submerged such that a consistent slurry of pea gravel and water was delivered to divers at a bridge pier when they called for it. 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 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. The critical velocity can be estimated using Equation 3.1, presented previously. 4.4.3 Inspection and Maintenance Immediately after placing the granular filter, and before the armor layer is installed on top of it, the filter should be inspected for adequate thickness and areal coverage. Underwater inspec- tion is best accomplished by divers. In situations where the water clarity is good, the filter may be inspected using underwater cameras on poles or remotely operated vehicles. If the granular filter layer is not thick enough, or is spotty in places, additional material must be added before placing the armor. Once the armor layer is placed on top of the filter, there is no maintenance required unless the armor layer is damaged (for example during a flood event). Subsequent inspection of the armor may reveal that it has been displaced and is missing in areas; if so, the underlying granular filter is likely gone as well. The filter material must be replaced prior to repairing and restoring the armor layer. In the United States, when bridge inspections require diver support, regular underwater inspections must be made at intervals not to exceed 5 years. At many bridges, more frequent underwater inspections may be required in a bridge-specific plan of action; for example, inspec- tion of underwater bridge components and scour countermeasures may be required after sig- nificant flood events. 4.4.4 Testing Mineral aggregates used for granular filters should be hard, dense, durable, and generally of good quality. The recommended tests and frequency of testing for granular filter material are similar to those for rock used as riprap. Detailed guidance is provided in HEC-23 (Lagasse et al. 2009). Table 4.1 provides a summary of the recommended test methods and testing frequency. 4.4.5 Specifications Specifications are the following: â¢ Gradation. Standard gradations of aggregate are preferred over custom gradations because of cost. ASTM C33/C33M, âStandard Specification for Concrete Aggregates,â provides 15 stan- dard size classes of aggregates. The standard gradations have maximum particle sizes ranging from 4 inches (Size No. 1) to 3/8 inch (Size No. 9). This range covers most of the applications for which granular filters might be specified. As standard materials, these aggregate classes should be relatively easy to obtain across the United States. The gradations shown in Table 4.2 will typically result in a relatively uniformly sized material with a uniformity coefficient
Guidance for Installation of Filter Systems 81 Cu = d60/d10 ranging from 1.5 to 2.5. Table 4.2 is from ASTM C33/C33M, which identifies the particle size limits for each of the 15 standard classes. â¢ Aggregate quality. Aggregate for granular filters should be hard, dense, durable, and should conform to the allowable values for the standard tests shown in Table 4.1. â¢ Filter layer thickness. For practicality of placement, the nominal filter layer thickness when placed underwater should be no less than 6 inches. Upon inspection, the minimum allowable thickness should be no less than 2/3 of the nominal thickness. â¢ Method of measurement. The granular filter shall be measured by the number of square yards computed from the payment lines shown on the plans or from payment lines established in writing by the engineer. This shall include granular filter material used in crest and toe of slope treatments. Slope preparation, excavation and backfill, bedding, and cover material are separate pay items. â¢ Basis of payment. The accepted quantities of granular filter shall be paid for per square yard in place. Payment will be made under: Pay Item Pay Unit Granular Filter Square Yard Test Designation Property Allowable Value Frequency (1) Comments AASHTO TP 61 Percentage of Fracture < 5% 1 per 20,000 tons Percentage of pieces that have fewer than 50% fractured surfaces AASHTO T 85 Specific Gravity (Sg) and Water Absorption Average of 10 pieces: Sg > 2.5 Absorption < 1.0% 1 per year If any individual piece exhibits an Sg less than 2.3 or water absorption greater than 3.0%, an additional 10 pieces shall be tested. If the second series of tests also exhibits pieces that do not pass, the riprap shall be rejected. AASHTO T 103 Soundness by Freezing and Thawing Maximum of 10 pieces after 25 cycles: < 0.5% 1 per 2 years Recommended only if water absorption is greater than 0.5% and the freeze-thaw severity index is greater than 15, per ASTM D 5312. AASHTO T 104 Soundness by Use of Sodium Sulfate or Magnesium Sulfate Average of 10 pieces: < 17.5% 1 per year If any individual piece exhibits a value greater than 25%, an additional 10 pieces shall be tested. If the second series of tests also exhibits pieces that do not pass, the material shall be rejected. AASHTO TP 58 Durability Index Using the Micro- Deval Apparatus Value > 90 > 80 > 70 Application Severe Moderate Mild 1 per year Most riverine applications are considered mild or moderate (Holtz et al. 2008). ASTM D 3967 Splitting Tensile Strength of Intact Rock Core Specimens Average of 10 pieces: > 6 MPa 1 per year If any individual piece exhibits a value less than 4MPa, an additional 10 pieces shall be tested. If the second series of tests also exhibits pieces that do not pass, the material shall be rejected. ASTM D 5873 Rock Hardness by Rebound Hammer See Note (2) 1 per 20,000 tons See Note (2) ASTM C 136 Standard Test Method for Sieve Analysis of Fine and Coarse Aggregate Per design gradation 1 per year See Note (1) (1) Testing frequency for acceptance of riprap from certified pits or quarries, unless otherwise noted. Project-specific tests exceeding quarry certification requirements, either in performance value or frequency of testing, must be specified by the Engineer. (2) Test results from D 5873 should be calibrated to D 3967 results before specifying quarry-specific minimum allowable values. Table 4.1. Recommended tests and allowable values for aggregate quality (modified from FHWA HEC-23, Lagasse et al. 2009).
Table 4.2. Standard coarse aggregate gradations from ASTM C33.
Guidance for Installation of Filter Systems 83 4.4.6 Quality Assurance/Quality Control In construction, the quality assurance program focuses on the procedures used to ensure that the design meets quality standards. This includes design calculations, construction plans and detail drawings, and specifications for required material properties. In contrast, quality control procedures ensure that the materials at the job site meet the design standards, includ- ing material testing requirements, and that they have been installed in accordance with the design intent. Quality Assurance Quality assurance measures for the design and installation of granular filters underwater include the following checklist items: 1. Filter design per methods identified in Section 4.4.1. 2. Filter extent, thickness, and termination details per FHWA HEC-23 (Lagasse et al. 2009). These design parameters vary depending on the project-specific application (e.g., pier protec- tion vs. abutment protection). 3. Material properties specified in accordance with test methods and allowable values from Table 4.1. Allowable values may be revised by the design engineer as necessary for project- specific conditions. 4. Aggregate gradation specified in accordance with standard classes defined in Table 4.2. Cus- tom gradations may be specified by the design engineer as necessary for project-specific conditions. Quality Control Quality control procedures for the underwater placement of granular filters include the following checklist items: 1. Checking contractorâs submittals for material quality testing and size gradation in confor- mance with project specifications. 2. Spot-checking random truckloads for proper gradation of granular material delivered to the job site. Checks may be made by random sampling and sieve analysis or by a visual examina- tion and comparison with a control sample in a bag or jar. 3. Determining local velocity of flow at the job site. Placement of loose granular filter material must be made on or near the bed; in flowing water, loose granular material must not be placed when the local velocities exceed 0.5 Vcrit, where Vcrit is the velocity for the threshold of motion for the d50 (median) size particle as determined by Equation 3.1. Underwater installation may proceed in accordance with Section 4.4.2. 4. Inspecting filter placement extent, thickness, and termination details to determine confor- mance with the design plans and detail drawings. In underwater situations, this will usually be best accomplished by divers, as described in Section 4.4.3. 5. Using divers in accordance with all applicable dive safety precautions, including tethers, under- water and topside communications, and buffer distance from equipment and machinery. 4.4.7 Environmental and Permitting Considerations In a discussion of aquatic and habitat issues, NCHRP Report 822 (Lagasse et al. 2016) notes that in using the term âenvironmentâ it is generally implied that this represents the sum of all influences within the living space of a plant or animal. For aquatic organisms, habitat includes the stream, its boundaries (bed and banks), and existing vegetation. Physical factors such as water depth, velocity, cover, and bed material are referred to as physical habitat. Streams tend to provide complex, dynamic physical habitat but, in relation to placing a granular filter
84 Guidance for Underwater Installation of Filter Systems under water in a stream, the only likely change in the physical habitat would be to the bed material factor. The design and installation of an erosion protection countermeasure might require placing a granular filter component prior to placing much larger material, such as riprap, as an armor layer. The design of such countermeasures typically focuses on the hydraulic and structural properties of a relatively short reach of the stream habitat during higher flow periods when boundary shear stresses are at a maximum. The installation of such a countermeasure, how- ever, will typically be accomplished during a low-flow period. Fish (and most other organisms that are specialized for life in aquatic systems) are highly mobile creatures that live out their lives in a series of habitats, such as feeding, resting, spawning, and nursery habitats, which can be separated by substantial distances along the stream corridor. It is unlikely that a fish population, for example, would ever be entirely dependent on the relatively small areas typi- cally affected by the installation of a single erosion countermeasure (McCullah and Gray 2005, Lagasse et al. 2016). In considering environmental impacts and permitting of a countermeasure that includes a granular filter placed in flowing water, issues that could be of concern would likely be limited to potential short-term increases in turbidity and changes in the characteristics of the stream substrate. Here, a concern for the physical habitat would be infilling of interstices in the exist- ing substrate (e.g., impacts on spawning habitat) by the addition of finer material. However, to perform its intended function, the granular filter material will by design be coarser than the substrate on which it is placed. This will minimize the primary concern of impacts on the bed material, even if a fraction of the granular material is displaced downstream during installation. In addition, at the installation site, the granular filter material would, by design and installation practice, be exposed to stream flow only for a limited period prior to placement of the overlying armoring component. Also, by design and specification, the granular filter will consist of clean washed material, which should limit any concerns regarding turbidity effects on the physical habitat to a local area and a short time period. One must recognize that in some cases, in relation to the physical habitat, regulatory agencies will permit the use of only ânaturalâ (in some cases described as 100% virgin) material. Permit- ting of the use of a granular filter for a countermeasure will then hinge on the interpretation of the term ânatural.â If, however, the armoring component of a countermeasure system can be permitted, the granular filter component should not present any additional permitting issues. 4.5 Guidance for Underwater Installation of Geotextile Filters 4.5.1 Design The recommended design procedure for geotextile filters is that provided in HEC-23 (Lagasse et al. 2009). This geotextile filter design method is presented in detail in Section 2.2.3 of this document. Two alternative methods for geotextile filter design, one developed by FHWA and NHI, and the other by USACE, are presented in NCHRP Web-Only Document 254, Volume 1, Appendix B. 4.5.2 Installation Many methods have been developed for installing geotextiles underwater, as described in Section 2.2.6 (European practice) and Section 2.2.7 (U.S. practice). In general, the geotextiles should be placed so that they are free of folds and wrinkles and lie in intimate contact with the
Guidance for Installation of Filter Systems 85 subgrade. Individual sheets should be overlapped a minimum of 12 inches and temporarily weighed down before the armor is placed (see Figure 2.32). Section 3.4 of this document describes the placement of geotextiles in flowing water by divers. Buoyant geotextile fabrics can be placed in currents of up to about 2.5 ft/s; self-sinking geo textiles such as sandmats are both stiffer and heavier and can be placed by divers in flows up to 3.5 ft/s. Under conditions of flowing water, divers should be tethered at all times. It was found that unrolling the geotextile in the direction of flow facilitated 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 (see Fig- ures 2.21â2.26 and associated text). Alternatively, empty geobags can be placed by divers and filled in place with a flexible tremie hose (see Figures 3.5â3.8 and associated text). 4.5.3 Inspection and Maintenance Immediately after placing the geotextile filter and before the armor layer is installed on top of it, the filter should be inspected for sufficient areal coverage and overlaps. Underwater inspec- tion is best accomplished by divers. In situations where the water clarity is good, the filter may be inspected using underwater cameras on poles or remotely operated vehicles. When geobags are used, they must be inspected to ensure that appropriate overlap has been achieved, and no voids or bare spots exist in the filter layer. Once the armor layer is placed on top of the filter, there is no maintenance required unless the armor layer is damaged, for example, during a flood event. Subsequent inspection of the armor may reveal that it has been displaced and is missing in areas; if the underlying geotextile filter is exposed, the armor layer must be repaired and restored. In the United States, when bridge inspections require diver support, regular underwater inspections must be made at intervals not to exceed 5 years. At many bridges, more frequent underwater inspections may be required by a bridge-specific plan of action; for example, inspec- tion of underwater bridge components and scour countermeasures may be required after sig- nificant flood events. 4.5.4 Testing Recommended standard tests and the allowable values for geotextile properties are provided in Table 4.3 (see AASHTO 2006). 4.5.5 Specifications The recommended specification for geotextiles is AASHTO M288. It covers six geotextile applications: Subsurface Drainage, Separation, Stabilization, Permanent Erosion Control, Tem- porary Silt Fence, and Paving Fabrics. AASHTO M288 provides materials specifications and construction/installation guidance for geotextiles in highway applications; it is not a design guideline. It is the engineerâs responsibility to choose a geotextile for the application that takes into consideration site-specific soil and water conditions. When site conditions are unknown, engineers can refer to AASHTO M288 Survivability Default Classes for guidance. Survivability is divided into three classes: Class (1) being the most severe and Class (3) being the least severe. Each class is then subdivided according to elongation. This offers a choice of non- woven geotextiles or woven geotextiles for each class. For certain applications, hydraulic properties are included in AASHTO M288.
86 Guidance for Underwater Installation of Filter Systems Example specification language for geotextiles used in permanent erosion control applica- tions is provided in Holtz et al. (2008). 4.5.6 Quality Assurance/Quality Control In construction, the quality assurance program focuses on the procedures to ensure that the design meets quality standards. This includes design calculations, construction plans and detail drawings, and specifications for required material properties. In contrast, quality control pro- cedures ensure that the materials at the job site meet the design standards, including testing requirements, and that they have been installed in accordance with the design intent. Test Designation Property Allowable value (1) Comments Elongation < 50%(2) Elongation > 50%(2) ASTM D 4632 Grab Strength > 315 lbs (Class 1) > 250 lbs (Class 2) > 180 lbs (Class 3) > 200 lbs (Class 1) > 160 lbs (Class 2) > 110 lbs (Class 3) From AASHTO M 288 ASTM D 4632 Sewn Seam Strength (3) > 270 lbs (Class 1) > 220 lbs (Class 2) > 160 lbs (Class 3) > 180 lbs (Class 1) > 140 lbs (Class 2) > 100 lbs (Class 3) From AASHTO M 288 ASTM D 4533 Tear Strength (4) > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) From AASHTO M 288 ASTM D 4833 Puncture Strength > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) From AASHTO M 288 ASTM D 4751 Apparent Opening Size Per design criteria Maximum allowable value ASTM D 4491 Permittivity and Hydraulic Conductivity Per design criteria Minimum allowable value ASTM D 4355 Degradation by Ultraviolet Light > 50% strength retained after 500 hours of exposure Minimum allowable value ASTM D 4873 Guide for Identification, Storage, and Handling Provides information on identification, storage, and handling of geotextiles. ASTM D 4759 Practice for the Specification Conformance of Geosynthetics Provides information on procedures for ensuring that geotextiles at the job site meet the design specifications. ASTM D 5101 Gradient Ratio Test GR < 3.0 Values less than 1.0 may indicate a potential for piping. (1) Required geotextile class for permanent erosion control design is designated below for the indicated application. The severity of installation conditions generally dictates the required geotextile class. The following descriptions have been modified from AASHTO M 288: Class 1 is recommended for harsh or severe installation conditions where there is a greater potential for geotextile damage, including placement of riprap that must occur in multiple lifts, drop heights that may exceed 1 foot (0.3m), or when repeated vehicular traffic on the installation is anticipated. Class 2 is recommended for installation conditions where placement in regular, single lifts is expected and little or no vehicular traffic on the installation will occur, or when placing individual rocks by clamshell, orange peel grapple, or specially equipped hydraulic excavator with drop heights less than 1 foot. Class 3 is specified for the least severe installation environments, with drop heights less than 1 foot onto a bedding layer of select sand, gravel, or other select imported material. (2) As measured in accordance with ASTM D 4632. (3) When seams are required. (4) The required MARV tear strength for woven monofilament geotextiles is 55 pounds. The MARV corresponds to a statistical measure whereby 2.5% of the tested values are less than the mean value minus two standard deviations (Koerner 1998). Table 4.3. Recommended tests and allowable values for geotextile properties.
Guidance for Installation of Filter Systems 87 Quality Assurance Quality assurance measures for the design and installation of geotextile filters under water include the following checklist items: 1. Filter design per methods identified in Section 4.5.1. 2. Filter extent and termination details per HEC-23 (Lagasse et al. 2009). These design param- eters vary depending on the project-specific application. 3. Material properties specified in accordance with test methods and allowable values from Table 4.3. Allowable values may be revised by the design engineer as necessary for project- specific conditions. 4. Geotextile specified in accordance with AASHTO M288 for permanent erosion control appli- cations. Recommended specification language is provided in âStandard Specifications for Transportation Materials and Methods of Sampling and Testing and AASHTO Provisional Standards.â Quality Control 1. Checking contractorâs submittals for material quality testing in conformance with project specifications. 2. Checking product labels on rolls of geotextile delivered to the job site. 3. Determining local velocity of flow at the job site. Placement of standard geotextiles can be performed by divers in flow velocities up to 2.5 ft/s; self-sinking geotextiles can be placed in velocities up to 3.5 ft/s, as described in Section 4.5.2. Large pre-filled geocontainers of 1 m3 in volume (1.3 yd3) have been successfully placed in Germany in flow velocities up to 2 m/s (6.5 ft/s). 4. Inspecting filter placement extent, overlap, and termination details to determine confor- mance with the design plans and detail drawings. In underwater situations, this will usually be best accomplished by divers, as described in Section 4.5.3. 5. Using divers in accordance with applicable dive safety precautions, including tethers, under- water and topside communications, and buffer distance from equipment and machinery. With geotextile filters, the fabric should be unrolled in the downstream direction to facilitate placement and to avoid divers becoming entangled in the fabric. 4.5.7 Environmental and Permitting Considerations As noted in Section 4.4.7, for aquatic organisms, habitat includes the stream, its boundaries (bed and banks), and existing vegetation. Physical factors such as water depth, velocity, cover, and bed material are referred to as physical habitat. Streams tend to provide complex, dynamic physical habitat, but, in relation to placing a geotextile filter underwater in a stream, it is not likely that there would be any change in these factors of the physical habitat. However, if water quality is considered a component of the physical habitat, the use of geotextiles as a ânon-naturalâ or âman-madeâ material could be an issue that needs to be addressed. The design and installation of an erosion countermeasure might require placing a geotextile filter component prior to placing much larger material, such as riprap, as an armor layer. The design of such countermeasures typically focuses on the hydraulic and structural properties of a relatively short reach of the stream habitat during higher flow periods when boundary shear stresses are at a maximum. The installation of such a countermeasure, however, will typically be accomplished during a low-flow period. As noted in Section 4.4.7 it is unlikely that a fish population, for example, would ever be entirely dependent on the relatively small areas typi- cally affected by the installation of a single erosion countermeasure (McCullah and Gray 2005, Lagasse et al. 2016).
88 Guidance for Underwater Installation of Filter Systems If water quality is a primary concern with the use of geotextiles in the aquatic environment, a closer look at the chemical and biological characteristics of these materials is justified. Geotextile producers and suppliers indicate that geotextiles are manufactured from fibers, filaments, and yarns, formed by the extrusion of polypropylene or polyethylene, individually or in combination (see Section 2.2.6). The handling and storage of these products present little or no health hazard. Furthermore, the polymers used to manufacture these products are polyolefins derived from oil and are regarded as chemically and biologically inert. For needle-punched fabrics, a lubricant is applied to the fibers during their manufacture; however, it is not required for woven fabrics. This lubricant is added in extremely small quantities (less than 0.4% by weight). The ecologi- cal data from the lubricant supplier refer to lubricant in concentrated form and, even then, it is considered to be only moderately toxic to aquatic organisms. Manufacturers report that in some situations a foaming effect may appear on the surface of a geotextile. They note that this is a physical interaction between water and the lubricant, and they claim that it is a transient effect and has no harmful effects on the environment. In reporting the converse, i.e., environmental effects on geotextiles, USACE notes that geo- textiles are generally not considered biodegradable and that they are relatively unaffected by chemicals found in normal concentrations in the aquatic environment, including the coastal zone. USACE reports that, although geotextiles are impervious to biological attack, marine growth on exposed plastics or bacterial activity in the interstices of geotextiles can clog the fab- ric and increase piping resistance. USACE also points out that unless stabilizers have been added during manufacture, geotextiles will deteriorate when exposed to ultraviolet radiation. Because of this, it is standard practice to quickly place armoring overlayers and sequence construction to minimize exposure of the geotextile fabrics to sunlight when using them as a filter for an erosion countermeasure. Thus, at the installation site, the geotextile filter material would, by design and installation practice, be exposed to stream flow only for a limited period prior to placement of the overlying armoring component. One must recognize, however, that in some cases, in relation to the physi- cal habitat, regulatory agencies will permit the use of only ânatural, not man-madeâ material. Permitting of the use of a geotextile filter for a countermeasure will then hinge on the interpreta- tion 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. 4.6 Applications In the following sections, two projects involving underwater placement of geotextile filters are used to illustrate and supplement the discussion of the current state of practice in the United States: (1) a project by Idaho DOT on the Snake River in 2002 to install pier scour protection and (2) a project by NCDOT at the Bonner Bridge crossing in 2014 for emergency installation of pier scour protection. Both projects use A-JacksÂ® as the primary armor element. A summary of the characteristics and design requirements of the proprietary A-JacksÂ® system can be found in HEC-23, Volume 2, Design Guideline 19 (Lagasse et al. 2009). 4.6.1 Underwater Installation of a Filter for Scour Protection at a Riverine Bridge From November 2002 through January 2003, the A-JacksÂ® armor system with an under- lying geotextile filter was installed by Idaho DOT on two bridges on the Snake River in eastern Idaho. The following descriptive information and photographs are taken from an Idaho DOT PowerPoint presentation (Reese 2014) and supplementary notes provided by Mr. Lotwick
Guidance for Installation of Filter Systems 89 Reese, State Hydraulic Engineer, Idaho DOT. Installation of the A-JacksÂ® system took place on two bridgesâthe Ferry Butte Bridge and the West Shelley Bridge on the Snake River between Idaho Falls and Pocatello, Idaho. The following overview of Idaho DOTâs approach to placing a filter underwater for the A-JacksÂ® armor system will concentrate on pier protection at the Ferry Butte Bridge; however, the same approach was used for the West Shelley Bridge. The DOTâs first objective on arriving at the Ferry Butte site was to investigate conditions of the riverbed in the vicinity of pier structures using divers. The dive equipment included an underwater video camera. The DOTâs specifications required that â¢ Woody debris be removed from scour protection zones. â¢ Boulders projecting 400 mm (16 inches) above the streambed be removed from scour protec- tion zones. â¢ Scour holes be filled with clean gravel. â¢ All A-JacksÂ® modules be connected together and secured to the pier structure to prevent modules from being displaced. Underwater video was used to provide verification of the A-JacksÂ® and filter placement and connectivity of the A-JacksÂ® units. The DOT further specified that each module would be placed on geotextile fabric, per HEC-23, directly on the riverbed as no excavation would be allowed in the river for this project. The fabric would be secured to each A-JacksÂ® module individually prior to placement. Although the DOT intended that the scour holes would be filled with clean gravel, an envi- ronmental resource agency prohibited this, even though the intent was to use a washed gravel. As a result, the A-JacksÂ® modules were placed on the streambed. In some cases, where the scour holes were extremely deep, the A-JacksÂ® modules were placed in tiers. Skids were used to fabricate the 6 Ã 6 A-JacksÂ® modules to provide easy transport of each module assembly (see Figure 4.3). Following assembly of the A-JacksÂ® into modules, they were tightly secured using 0.25 inch corrosion-resistant steel cables and copper clamps. The modules were then ready for delivery to the bridge site. At the bridge site, placement depths at the piers ranged from 2 ft to about 9 ft, and river velocity was low. Figure 4.4 provides a sketch of the handling device designed by the contractor to place the A-JacksÂ® modules. Figure 4.3. Assembly of 6 Ã« 6 A-JacksÂ® module on skids (courtesy Idaho DOT).
90 Guidance for Underwater Installation of Filter Systems Idaho DOT required that the contractor: â¢ Fit modules as close as possible to each other and to the pier structure. â¢ Meet the manufacturerâs recommendation of Â± 6 inches except that one fit-up in four place- ments could exceed the 6-inch fit-up tolerance by 3 inches. â¢ Meet the manufacturerâs request that geotextile be applied to modules prior to placement. â¢ Provide divers to verify fit-ups and the acceptability of placed modules and report directly to Idaho DOT inspector. â¢ Remove any broken A-JacksÂ® from the river. â¢ Provide connections between all modules. â¢ Provide direct evidence to Idaho DOT for final acceptance of all A-JacksÂ® modules placed. Figure 4.5 shows the lifting frame designed by the contractor to place the cabled 6 Ã 6 A-JacksÂ® modules. Figure 4.6 shows the use of the lifting frame to apply geotextile to the base of each 6 Ã 6 A-JacksÂ® module, and Figure 4.7 shows the crane and assembled module at the bridge site. As shown in Figure 4.8, assembly at the pier started downstream and progressed upstream to facilitate handling of the modules and ensure good fit-ups between modules. Finally, it was found essential to support the installation with divers and a pontoon boat for proper and safe Figure 4.4. Handling device designed by contractor to place the A-JacksÂ® modules (courtesy Idaho DOT). Figure 4.5. Lifting frame to place the A-JacksÂ® modules (courtesy Idaho DOT).
Guidance for Installation of Filter Systems 91 Figure 4.6. Applying the geotextile filter to an A-JacksÂ® module (courtesy Idaho DOT). Figure 4.7. Crane and assembled A-JacksÂ® module (with geotextile filter) at the bridge site (courtesy Idaho DOT). placement of the modules (see Figure 4.9). Figure 4.10 shows a diver inspecting and providing video documentation of the installed A-JacksÂ® modules at the Ferry Butte Bridge (Reese 2014). On the West Shelley Bridge, A-JacksÂ® modules were installed at three piers underlain with a geotextile filter. In addition, A-JacksÂ® modules were installed at the north abutment, where there had been a concrete slope paving failure. Installation was in the dry except at the abutment toe. The A-JacksÂ® pier scour placements were identical on both bridges, except that higher flow velocities (approximately 6 ft/s) and deeper water (up to 15 ft) were encountered at the West
92 Guidance for Underwater Installation of Filter Systems Figure 4.8. Installation at the bridge started downstream and proceeded upstream (courtesy Idaho DOT). Figure 4.9. Divers and pontoon boat used to assist module placement (courtesy Idaho DOT). Figure 4.10. Diver inspecting in-place A-JacksÂ® module at Ferry Butte Bridge (courtesy Idaho DOT).
Guidance for Installation of Filter Systems 93 Shelley Bridge. In 2013, site inspection at the Ferry Butte Bridge indicated that the streambed had aggraded to approximately 1.5 ft above the top of the A-JacksÂ® modules (Lotwick Reese, personal communication). 4.6.2 Underwater Installation of a Filter for Scour Protection at a Coastal Bridge Emergency repair work by NCDOT on the Herbert C. Bonner Bridge (NC 12) provides a very recent example of the state of practice at a DOT for placing a filter in a deep water inlet subject to high-velocity tidal flows. As with the Snake River project (described above), A-JacksÂ® were selected as the armoring element. Both a geotextile wrap on A-JacksÂ® modules and geotextile containers (sand bags) were used as a filter and for scour protection. The discussion in this section (4.6.2) is adapted from âScour and the Test of Time: Herbert C. Bonner Bridge Cross- ing Oregon Inlet, North Carolina,â an article prepared by Mr. Dave Henderson, Senior Scour Engineer, FHWA Office of Bridges and Structures (Henderson 2014). Mr. Henderson and the NCHRP Project 24-42 research team collaborated in reworking the material from the article for presentation herein. Overview On Tuesday, December 3, 2013, a public news release announced North Carolina Depart- ment of Transportationâs (NCDOTâs) closure of NC 12 Herbert C. Bonner Bridge crossing of Oregon Inlet. Inlet dynamics and movement of the 65 ft deep channel coupled with bridge scour jeopardized stability of an interior bent between the navigation span and the southern terminus. A second element of danger loomed over the only highway connection to the North Carolina Outer Banks. A major low pressure system centered over the Midwest would race east, stall offshore, and set up a major norâeaster in just four days. Rapid response by NCDOT, with collaboration and cooperation of other agencies and private contractors, stabilized the scour condition, allowing the bridge to be reopened on Sunday, December 15, 2014. Restoring traffic to the Outer Banks was crucial in advance of the holiday influx of tourists headed south to the 60 miles of barrier islands, seven historic villages, and gateway to Ocracoke Island. In addition, the route is the critical link in public safety, emergency services, and hurricane evacuation and recovery. The 2.5 mile long Bonner Bridge was constructed in 1963 replacing ferry service to Hatteras Island. The coastal geology of the site required the bridge to be founded on friction piles in deep sand. The north terminus is anchored on National Park Service property and the south end touches down on U.S. Fish & Wildlifeâs Pea Island Refuge. Design life for the bridge was 30 years. NCDOTâs 1992 replacement project was challenged by environmental advocates and continues to be held up by legal appeals in federal court. Structural decay and scour have long plagued the bridge. Bonner Bridge has been identified as scour critical with a comprehensive and aggressive monitoring plan. Hydrographic surveys and underwater inspection performed monthly and after storm events have been conducted for more than two decades. In 2012, NCDOT initiated monthly side scan sonar monitoring. The October 2013 survey identified a change in conditions south of the navigation span and monitoring was stepped up to weekly inspection. The November 29th inspection revealed that the bed elevation approached a scour critical condition at Bent #166. Daily monitoring was implemented. On Tuesday, December 3, the sonar survey and underwater dive team inspection revealed that the 10-pile cluster at Bent 166 had 9 piles with embedment below scour critical elevation. Three of the piles had less than 4 ft embedment. NCDOT immediately implemented bridge closure in accordance with its monitoring plan of action.
94 Guidance for Underwater Installation of Filter Systems Countermeasure Strategy The weather forecast added an additional factor of urgency to the situation. High winds, heavy seas and extreme tidal exchange from a three day norâeaster is always a concern for Oregon Inlet and the coastal highway, which parallels the shoreline along most of the Outer Banks. Although the bridge was closed to traffic, the immediate concern was potential loss of two spans during storm tides created by the norâeaster. NCDOT formulated a three phase strategy for structural countermeasure response. The strat- egy addressed immediate action to stabilize the scour, intermediate countermeasure installation, and long-term integrity of Bent 166. Long-term stability involved construction of a crutch bent with installation of longer piles to provide required embedment. The crutch bent required lead time for pile fabrication, precast pile/bent cap, and geotechnical investigation. The intermedi- ate action would stack three tiers of A-JacksÂ® to form a perimeter around Bent 166. Geotextile containers (sandbags) 3 ft cube and 4 ft cube, would be placed inside the battered pile cluster to avoid damage to the existing concrete piles. The configuration would also trap sand available in the high sediment transport regime of diurnal tidal exchange. NCDOT contacted suppliers and manufactures for availability and delivery. Geotextiles would require 5â7 days to be delivered. The A-JacksÂ® components would require 12â14 days to arrive at the site. The immediate need was a large volume of sand and a delivery system (within 72 hours). Action and Response Effort Timeline Actions and responses listed by date are the following: â¢ December 4th: Carolina Bridge Company of Orangeburg, SC, was awarded emergency con- tract. The contractor begins mobilization to drive test piles and install A-JacksÂ® and sandbags. â¢ December 5th: NC Governor issues Emergency Declaration, which will facilitate negotiations with other agencies and contractors. USACE has a contract maintenance dredging project of the navigation channel through the inlet bar. Great Lakes Dredge & Dock is finishing Corps work and agrees to contract with NCDOT before moving to their next contract obligation. â¢ December 6th: Great Lakes Dredge & Dock begins relocating 2,000 ft of 36 inch diameter discharge line from the beach disposal site to the vicinity of Bent 166. The ALASKA will be working around the clock, weather permitting. â¢ December 7th: Dredging operation begins. Carolina Bridge successfully negotiated with National Park Service and their vendor at Oregon Inlet Fishing Center for a staging area for A-JacksÂ® assembly and sand bag (geocontainer) filling operation. â¢ December 8th: Sonar survey indicates dredge material has filled the scour hole above scour critical elevation. â¢ December 9th: NCDOT Bridge Maintenance delivers 24 inch diameter test piles to site in record time. Bridge Maintenance forces fabricated the test piles at nearby Manns Harbor Ferry Rework Facility to take advantage of environmentally controlled work area. â¢ December 10th: Geotextile containers (Figure 4.11) begin arriving and are filled. Contractorâs crane and pile hammer are moved to work off the bridge deck at Bent 164. â¢ December 12th: Divers confirm consolidation of dredge placed sand at Bent 166. First ship- ment of A-JacksÂ® elements (Figure 4.12) arrive at staging area. â¢ December 13th: Carolina Bridge performed restrike hammer test. Strain gage and pile driver analyzer results confirmed pile capacity. â¢ December 15th: NCDOT opens Bonner Bridge to traffic! Access to the Outer Banks and his- toric villages is open for holiday season destination travel. â¢ December 15thâFebruary 10th: The contractor continues A-JacksÂ® and geotextile container installation. Weather conditions were favorable immediately after passage of the norâeaster. However, diver safety protocol limited placement of A-JacksÂ® modules and geotextile
Guidance for Installation of Filter Systems 95 containers to periods of slack tide twice a day (Figures 4.13, 4.14, 4.15, and 4.16). Water tem- perature, visibility, and tidal flow velocity allow for a dive window of only 75 to 90 minutes at slack tide. Weather conditions would soon change. Although contractor work continued over the holiday, high winds and heavy seas impacted work in the inlet. Unusually cold temperatures interrupted epoxy application in the A-JacksÂ® assembly process. Upon establishing A-JacksÂ® perimeter, the area around and between the battered 10 pile group of Bent 166 was protected with geotextile containers (Figures 4.17 and 4.18). â¢ February 10th: The last A-JacksÂ® module was installed and emergency contract for Bonner Bridge was completed. The emergency contract had a 90 day completion clause. The project was completed ahead of schedule even though weather conditions were not the most accommodating. The final numbers for work performed were: 78â3 ft Ã 3 ft Ã 3 ft geotextile bags 158â4 ft Ã 4 ft Ã 4 ft geotextile bags 980âA-JacksÂ® elements Cost = $1.79 million (excluding dredge activity estimated at +/â $1 million) Figure 4.11. Geotextile container stockpile (4 ft Ã« 4 ft Ã« 4 ft cubes) at Bonner Bridge (Henderson 2014). Figure 4.12. Pallets of 4 ft A-JacksÂ® (three jacks per pallet) at Bonner Bridge (Henderson 2014).
96 Guidance for Underwater Installation of Filter Systems (a) Assembly area (b) Stockpile of assembled A-JacksÂ® Figure 4.13. A-JacksÂ® assembly area and stockpile at Bonner Bridge (Henderson 2014). Figure 4.14. Stainless steel cable and hardware binding A-JacksÂ® elements into modules (Henderson 2014).
Guidance for Installation of Filter Systems 97 Summary Observations The Emergency Declaration by the Governor of North Carolina minimized many potential obstacles in immediate contract negotiation and established a dialogue with a host of state agen- cies including Marine Fisheries, Division of Water Quality, and Coastal Area Management Com- mission. Collaboration with USACE, U.S. Fish & Wildlife Pea Island Refuge, and National Park Service Hatteras National Seashore was effective and responsive. One of the key components of timely response action was NCDOT internal coordination and chains of command communica- tions. During the spring and summer of 2013, the North Carolina FHWA Division promoted and facilitated a Table Top Exercise for implementation of an emergency plan of action for Bonner Bridge closure. Bonner Bridge has experienced four decades of emergency crisis from tropical storms to vessel impacts. NCDOTâs Executive Leadership, Operational Management, Ferry Division, and various Design Units have always responded to the call for recovery efforts and restoring access to the otherwise isolated Outer Banks communities with the highest level of professionalism. However, areas of responsibility and authority often become clouded by public and political pressures, which can be brought to bear in crisis situations. As result of the recent Table Top Exercise, predicated on valuable experiences, open dialogue, and outside observa- tions, there was a clear and concise determination of authority, decision making, and cross lines Figure 4.15. Contractor apparatus for A-JacksÂ® module placement (Henderson 2014). Figure 4.16. Geotextile filter applied to A-JacksÂ® modules (Henderson 2014).
98 Guidance for Underwater Installation of Filter Systems of communication, which created a positive climate for managing internal roles and external influences of social, media, and political pressures. 4.7 Description of Stand-Alone Training Document A training manual for implementation of research results was developed as a stand-alone doc- ument (see NCHRP Web-Only Document 254, Volume 2). The training manual provides a com- panion workshop that incorporates photographs, videos, and case histories to provide training on the underwater placement of filters. The manual deliverable meets all current Instructional Systems Design standards established by FHWAâs NHI and, after review and approval by NHI, Figure 4.17. Placement of geotextile containers around Bent 166 at Bonner Bridge (Henderson 2014). Figure 4.18. Contractor lifting the geotextile containers to place at Bent 166 (Henderson 2014).
Guidance for Installation of Filter Systems 99 could be incorporated into several NHI course offerings as additional or optional workshops. Moreover, the underwater filter workshop provides the basic instructional components for the development of a distance learning (web-based) presentation at some time in the future. For this 240-minute workshop on underwater installation of filter systems, lesson develop- ment adheres to the guidance promulgated by NHI and the International Association of Con- tinuing Education and Training for adult learning. The workshop is organized in modular fashion to support presentations in various venues including a mini-workshop at conferences such as the TRB Annual Meeting, American Public Works Association, American Society of Civil Engineers, FHWAâs National Hydraulic Engineers Conferences, and others. TRB (via NCHRP) may also choose to make this material available on an expedited basis to state highway agencies and bridge owners who could use it not only for in-house training, but also as part of their contractor certification programs. In addition, the guidance developed under this research must reach well beyond bridge owners and their employees to include out- side designers, construction contractors, field inspectors, and resident engineers. The modular organization of the workshop would support presentations of 1, 2 or 3 hours, as well as the full 4-hour format. The five sessions of the workshop (presented in two parts) include the following topics and are designed to achieve the following user-oriented, performance-based learning outcomes. 4.7.1 Part I Topics covered in Part I are the following: â¢ Purpose and need for filters â¢ Current concepts and practice for underwater filter installation (U.S. and European practice) â¢ Case study: countermeasure installation by NCDOT at a scour critical tidal inlet bridge under emergency conditions Learning outcomes for Part I are listed below. At the end of Part I, participants will be able to â¢ Describe the purpose, need, and functions of geotextile and granular filters. â¢ Identify sources of design guidance for geotextile and granular filters. â¢ Discuss experience with, and local agency guidance for, installing filters underwater. â¢ Describe and list several techniques currently used to install filters underwater for typical armoring countermeasures (e.g., riprap, ACBs, etc.). â¢ List and discuss the lessons learned from a recent U.S. underwater installation project (Bonner Bridge case study). 4.7.2 Part II Topics covered in Part II are the following: â¢ Recommendations for underwater filter installation from NCHRP Project 24-42. â¢ Group workshop on installation techniques and solutions for a typical underwater filter installation project at a riverine bridge. Learning outcomes for Part II are listed below. At the end of Part II, participants will be able to â¢ Describe, evaluate, and list in order of priority (based on local conditions) the recommenda- tions for underwater filter installation from NCHRP Project 24-42. â¢ In a group workshop setting, develop installation techniques and discuss solutions for a typi- cal underwater filter installation project at a riverine bridge.