Underwater Installation of Filter Systems for Scour and Erosion Countermeasures, Volume 1: Research Report (2018) / Chapter Skim
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2.1 2. FINDINGS 2.1 Survey for Current State of Practice The approved Task 2 survey was programmed into Survey Monkey format and submitted to NCHRP for distribution to the Panel.
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2.2 • The design guidance document most often cited is FHWA Hydraulic Engineering Circular No. 23 (74% of respondents)
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2.3 The comments received included the following: - I'm not sure we use granular material. - Not a typical usage.
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2.4 2.1.4 Summary of Survey Results Despite the disappointing rate of return, some valuable information can be derived from the responses received: 1. Given the fact that almost 90% of respondents indicated that a filter is "Always" or "Usually" required for installations placed under water, only 16% of respondents indicated that the filter installation is inspected prior to the armor being placed on top.
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2.5 countermeasure installations may not be aware of how countermeasures function and may not appreciate the value of the underlying filter. Consequently, this synthesis also includes an overview of the purpose, need, and function of the filter component of countermeasure armor systems for scour and other erosion control requirements.
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2.6 • A historical survey and the current state of practice for placing filter systems underwater in the U.S. are presented.
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2.7 Service life for a countermeasure installation can be considered a measure of the durability of the total, integrated bank, pier, abutment or countermeasure protection system. The durability of system components and how they function in the context of the overall design will determine the service life of an installation.
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2.8 Figure 2.1. Examples of soil and filter compatibility processes.
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2.9 In Figure 2.1d, an unstable soil is covered by a filter with large pores. Suffusion of the fine particles will continue unabated, since there are no particles of intermediate size to prevent their movement by the forces of seepage flow and turbulence at the interface.
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2.10 Figure 2.2. Changes in water levels and seepage patterns during a flood.
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2.11 Hydraulic conductivity. Hydraulic conductivity (sometimes referred to as permeability)
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2.12 Thickness. Practical issues of placing a granular filter indicate that a typical minimum thickness of 6 to 8 inches should be specified.
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2.13 Porosity. Porosity is a comparison of the total volume of voids to the total volume of geotextile.
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2.14 Table 2.2. Recommended Tests and Allowable Values for Geotextile Properties.
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2.15 Step 3. Determine Key Indices for Granular Filter.
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2.16 Figure 2.3. Granular filter design chart according to Cistin and Ziems (Heibaum 2004a)
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2.17 Figure 2.4. Geotextile selection for soil retention (modified from NCHRP Report 593)
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2.18 Note: If the required AOS is smaller than that of available geotextiles, then a granular transition layer is required, even if the base soil is not clay. However, this requirement can be waived if the base soil exhibits the following conditions for hydraulic conductivity (K)
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2.19 Note: Alternative Filter Design Procedures from U.S. Practice (1)
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2.20 The results of more than 30 years' experience with research, testing, construction observation, field installation, monitoring and maintenance on Germany's extensive inland waterway system are summarized in a series of papers by M.A. Heibaum of the BAW Institute: Heibaum (1999, 2000, 2002a, 2002b, 2004a, 2004b, 2008)
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2.21 based on the tests conducted by Bertram (1940)
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2.22 layers may require more effort and cost than an impermeable one. A filter is always needed for a permeable system and placement of the top layer material has to be done much more accurately, but in the end such a system is, in most cases, more successful (Heibaum 2008)
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2.23 Figure 2.6. Preparing a fascine mattress (including additional brushwood layer)
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2.24 Figure 2.7. Roller for placing geotextiles onto the subgrade.
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2.25 In the 1970s - 1980s time frame countries in Europe (in addition to Germany) were developing procedures for and encountering problems with incorporating geotextiles in revetment construction, including Yugoslavia (Bozinovic et al.
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2.26 Figure 2.8. Flexible revetment with integrated geotextile filter ready to be placed under water.
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2.27 CUR Report 169 (CUR 1995) includes a detailed section on construction methods for bed and bank protection.
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2.28 Bank protection works are carried out on underwater slopes and usually extend to the water level. Therefore, waterborne operations close to the structure are limited by the draft of the equipment.
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2.29 The following paragraphs provide an overview of current practice in Germany for placing filters underwater based on the 2001 field visits. This overview is followed by examples and specific citations that further document current technology in Europe for placing filters underwater.
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2.30 Figure 2.9. Close-up photo of a geocomposite blanket (photo from NCHRP Project 24-07(2)
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2.31 Figure 2.11. Sand-filled geotextile containers (Lagasse et al.
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2.32 Figure 2.13. Handling a 1.0 metric tonne sand-filled geotextile container (photo from NCHRP Project 24-07(2)
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2.33 addition, coarse aggregate (stones) may get beneath the geotextile leading to risk of perforation, reduction of mechanical stability of the top layer on slopes, and increased risk of abrasion damages.
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2.34 Granular filters may be designed for almost any purpose according to one of the well-tried filter rules. However, in rivers granular filters can be used only if there is no current or low current.
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2.35 To provide a flawless filter layer with geocontainers, it is essential that there are no gaps between the elements, so two layers usually are required. As with geotextile filters, nonwoven fabrics cover a larger spectrum of grain size distributions than woven fabrics.
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2.36 Figure 2.14. Placing geosynthetic containers (sketch courtesy of Colcrete/von Essen-Bau (Heibaum 2000, 2000a)
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2.37 Documentation From Other Sources. In addition to the detailed guidance on underwater placement of filter systems provided by the BAW experience in Germany, several other sources of documentation of European practice are available.
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2.38 • Prototype experiments indicate that geocontainers with a volume of more than 200 m3 (260 yd3) and dumped in water of which the depth exceeds 10 m (33 ft)
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2.39 The installation continues on site with: (5) use suitable methods to locate the exact position of the previous geotextile length to be placed.
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2.40 Typically, geotextile products do not contain: - Chlorofluoro carbons (CFC) - Pentachloro phenols (PC)
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2.41 Emergency Action Fire: Toxic fumes are not produced but breathing apparatus may be required to combat smoke and carbon monoxide particularly in confined spaces. Molten burning droplets require resistant clothing and footwear.
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2.42 The findings of the study indicated that although there was wide and varied use of filter fabrics by Corps Districts, a test program was needed to define the engineering properties of the fabrics when used for filter and drainage applications. As part of this program (1967-1972)
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2.43 An International Conference in London on flexible armored revetments incorporating geotextiles (Institution of Civil Engineers 1984) provides a "snap shot" (circa 1984)
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2.45 • The porosity of the geotextile filter should be sufficient to allow release of pore pressures without causing uplift of the fabric under flood conditions. The selection of a relatively open fabric may be advantageous.
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2.46 pier face to the periphery of the riprap (Figure 2.19b)
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2.47 Figure 2.20. Schematic layout for sand filled geotextile containers and riprap tests (dimensions approximate)
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2.48 Figure 2.22. Installation of geotextile containers, pier is on the left.
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2.49 Figure 2.24. Installation of riprap around pier.
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2.50 Geotextile sand containers are strongly recommended as a practical, proven, and effective technique for placing a filter under water for riprap or partially grouted riprap, and gabion and grout-filled mattresses. For the partially grouted riprap/geotextile container filter system described above, the flume was reconfigured to achieve a maximum velocity at the pier with the flow discharge available (Figure 2.26)
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2.51 A bridge scour countermeasure was investigated during this study. A non-proprietary concrete hammer head prefabricated block called a Toskane was developed and tested as a hydraulic model (Figure 2.27)
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2.52 furthest downstream section to be covered. The upstream frame and cloth should overlap the downstream frame and cloth at least 0.5 m.
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2.53 Guidance" - Third Edition (http://www.fhwa.dot.gov/engineering/ hydraulics/ pubs/ 09111/091216.cfm)
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2.54 Figure 2.30. Erosion control installations: (a)
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2.55 Figure 2.31. Construction of hard armor erosion control systems (a, b, after Keown and Dardeau 1980; c after Dunham and Barrett 1974)
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2.56 Figure 2.32. Special construction requirements related to specific hard armor erosion control applications (Holtz et al.
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2.57 For streambank protection, selecting a geotextile with appropriate clogging resistance to protect the natural soil and meet the expected hydraulic conditions is extremely important. Should clogging occur, excess hydrostatic pressures in the streambank could result in slope stability problems.
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2.58 Scour caused by high flows around or adjacent to structures in rivers or coastal areas generally requires scour protection for structures. Scour protection systems generally fall under the critical and/or severe design criteria (see Appendix B)
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2.59 • Thickness of layers should be monitored to ensure designed discharge capacity and continuity of the filter. • Quality control/assurance is very important during filter construction because of the critical function of this relatively small part of the embankment An Army/Air Force Technical Manual on "Engineering Use of Geotextiles" was released in July 1995 (Departments of the Army and the Air Force 1995)
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2.60 Figure 2.33. Geotextile placement for currents acting parallel to bank or for wave attack on the bank (Departments of the Army and Air Force 1995)
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2.61 dumping from barges, pumping through tremies or diffusers, and placement from landbased equipment (see schematics in Figure 2.35)
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2.62 Figure 2.35. Techniques for placing sand caps on contaminated sediments underwater (Palermo et al.
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2.63 2.2.7 Coastal and Offshore Applications There are additional applications of geotextiles for a variety of purposes (e.g., geotubes used as a construction element) , particularly in the coastal environment.
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2.64 Bezuijen and Pilarczyk (2012) provide the following observations: • Geosynthetics and geosystems constitute potential alternatives for more conventional materials and systems.
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2.65 Restall et al.
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2.66 In a series of case studies of applications in Australia Restall et al.
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2.67 Offshore Applications Two publications from the International Conference on Scour and Erosion (ICSE6) in Paris, France in 2012 provide insights on scour and erosion problems with offshore structures and filter design and installation approaches in a deep water environment.
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2.68 Schurenkamp et al.
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2.69 • If installed in two layers and properly designed there is no need for any additional granular filter or cover layers. The complete scour protection is given by two layers of GSC (Figure 2.37)
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2.70 Figure 2.37. Scour protection solutions for OWT foundations.
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2.71 Figure 2.39. Installation of scour stabilization by the use of a stone dumping barge/vessel at the Eidersperrwerk (Peters and Werth 2012)
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2.72 Figure 2.41. Geotextile tube and fill ports (courtesy Maccaferri)
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2.73 I Figure 2.42. Equipment and filling process for geotextile tubes (courtesy Maccaferri)
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2.74 • Discharge Pressures - Discharge pressures at the tube fill port shall not exceed 5 psi (35 kPa)
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2.75 2.2.9 Permitting of Filter Installations In general, permitting requirements for underwater installation of filter systems for scour and other erosion control measures will be subject to the same restrictions and requirements as the installation of the overlying armor system. Where required, permitting should consider the total proposed countermeasure, armor and filter, where the granular or geotextile filter is an essential component of the system.
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2.76 additional insights, observations, and guidance on several topics. The following paragraphs are extracted from Heibaum (2004b)
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2.77 Thin elements like sheets containing a fill material in between two geotextiles also belong to the container family even though they are rather thin. Examples are the sandmat and the geosynthetic clay liner.
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2.78 To overcome the problems related to geotextile filters, stability can be increased by attaching heavy iron chains at the edges of the filter cloth; however, such a measure is rather time and cost intensive. To facilitate placement of a filter underwater, the "sandmat" was invented (see Figures 2.9 and 2.10)
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2.79 Figure 2.43. Large fascine mattress being floated into place.
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2.80 Seams. Special care has to be taken concerning the seams of the container.
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2.81 The placement of numerous containers is generally not done element by element. Small containers can be placed using a belt conveyor.
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2.82 Figure 2.44. Scour-hole at Eider storm surge barrier-cross section of scour and barrier (top)
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