Guidance for Underwater Installation of Filter Systems (2018) / Chapter Skim
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Pages 66-74
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From page 66... ...
66 3.1 Overview A variety of means and methods are available for placing filter materials underwater and in flowing water. The selection of any particular technique depends on the materials to be used and the flow conditions at the time of placement (e.g., flow depth and velocity)
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From page 67... ...
Documentation of Underwater Filter Installation Techniques 67 For geotextile filters, the selected materials were the following: • Nonwoven, needle-punched geotextile sheets (buoyant) unrolled in the direction of flow adjacent to and downstream of the pier.
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From page 68... ...
68 Guidance for Underwater Installation of Filter Systems The first flow rate was held steady at 50 ft3/s, resulting in a modest approach velocity of about 0.6 ft/s along the flume centerline. The second flow rate was established at 200 ft3/s, which resulted in a centerline approach velocity in excess of 3.5 ft/s upstream of the pier.
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From page 69... ...
Documentation of Underwater Filter Installation Techniques 69 where Vc = Critical velocity above which particles of size d50 or smaller will be transported, ft/s (m/s) y = Flow depth, ft (m)
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From page 70... ...
70 Guidance for Underwater Installation of Filter Systems 0 2 4 6 8 10 12 14 1 10 100 Cr iti ca l v el oc ity , ft /s Particle size, mm 8 ft 20 ft Particle S.G. = 2.65 depth = 4 ft Figure 3.4.
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From page 71... ...
Documentation of Underwater Filter Installation Techniques 71 tremie hose was also tested. Figure 3.6 shows the geobag with fill port (a)
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From page 72... ...
72 Guidance for Underwater Installation of Filter Systems A 6 mm thick double-sided drainage composite (CETCO Aquadrain G25) with high density poly ethylene geonet core was used as the self-sinking fabric; it was made negatively buoyant by affixing metal strips at 4 ft intervals along its length to achieve a handling capability comparable to a sandmat commonly used in Europe (see Figures 2.9 and 2.10)
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From page 73... ...
Documentation of Underwater Filter Installation Techniques 73 3.5 Appraisal of Underwater Installation Testing Results Placement of granular and geotextile filters at a prototype-scale bridge pier was successful during all tests conducted at 50 ft3/s, with an approach velocity of about 0.6 ft/s. The tests at 200 ft3/s were conducted with a centerline approach velocity somewhat in excess of 3.5 ft/s.
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From page 74... ...
74 Guidance for Underwater Installation of Filter Systems The divers noted that with this approach, "the bags almost filled themselves," even during the high-flow test. Given the rate of gravel delivery from the solids-handling pump, each bag could be filled in about 3 minutes.
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