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Florida Rock Chute Design and Construction Workshop

Florida Rock Chute Design and Construction Workshop. Filters , Bedding , and Geotextiles. Benjamin C. Doerge NDCSMC Ft. Worth, TX. Filters, Bedding, and Geotextiles. Rock Chute. Flow. Filters, Bedding, and Geotextiles. Filter?. Bedding?. Geotextile?. Filters, Bedding, and Geotextiles.

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Florida Rock Chute Design and Construction Workshop

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  1. Florida Rock Chute Design and Construction Workshop Filters, Bedding, and Geotextiles Benjamin C. DoergeNDCSMCFt. Worth, TX

  2. Filters, Bedding, and Geotextiles Rock Chute Flow

  3. Filters, Bedding, and Geotextiles Filter? Bedding? Geotextile?

  4. Filters, Bedding, and Geotextiles Overview: Filter functions and types Filters vs. bedding Design procedures Construction considerations (GT)

  5. Filters, Bedding, and Geotextiles Filter Functions and Types

  6. Filters, Bedding, and Geotextiles Filter Functions - Retention To prevent loss of soil particles due to flowing water at an “exit point.” Flow into slotted pipe Flow into voids between riprap

  7. Filters, Bedding, and Geotextiles Filter Functions - Permeability To not create a restriction or disturbance of the flow from the soil.

  8. Filters, Bedding, and Geotextiles Filter types: Granular filters (sand and/or gravel) Geotextiles (woven and nonwoven)

  9. Filters, Bedding, and Geotextiles Granular filters Advantages: • Excellent, proven performance • Thick section - less prone to clogging Disadvantages: • Multiple layers may be required • More effort to install • Higher cost

  10. Geotextiles Advantages: • Multiple layers not required • Ease of installation/lower cost Disadvantages: • Subgrade conditions critical • Subject to installation damage • Thin section - more prone to clogging Filters, Bedding, and Geotextiles

  11. Filters, Bedding, and Geotextiles Filters vs. Bedding

  12. Filters, Bedding, and Geotextiles Prevent loss of base soil through riprap due to flow exiting soil Filter Riprap Filters vs. Bedding Base soil Filter compatibility req’d between soil & riprap.

  13. Prevent loss of base soil through riprap due to eddying and surging Filters, Bedding, and Geotextiles Bedding Riprap Attack Filters vs. Bedding Base soil Filter compatibility req’d only between bedding & riprap.

  14. When to Use Filter or Bedding? Ok to usebeddingif: No significant seepage from base soil Steadyflow, low to moderate attack. Base soil is resistant to piping (cohesive soils, gravel, coarse sand). Use filter if: There is significant seepage from bank. Higher velocities with surging and reversal of flow possible. Base soil is susceptible to piping (SP, SM, non-plastic ML).

  15. Filters, Bedding, and Geotextiles Design Procedures Granular filter design Bedding design Geotextile filter design Example problem – GT design Other design considerations - GT

  16. Granular Filter Design Design criteria for granular filters: NEH, Part 633, Chapter 26Gradation Design of Sand and Gravel Filters.

  17. Granular Filter Design #200 #4 3” 100 Filter Design begins with: Base soil gradation. Percent Passing (gravel) (sand) (fines) 0 Particle Size

  18. Granular Filter Design #200 #4 3” 100 Filter Design Procedure: Regrade on #4, if applicable. Percent Passing (fines) (sand) (gravel) 0 Particle Size

  19. Granular Filter Design #200 #4 3” 100 Category% Fines 1 >85 2 40-85 3 15-39 4 <15 Filter Design Procedure: Determine category of regraded soil. Percent Passing (fines) (sand) (gravel) 0 Particle Size

  20. Granular Filter Design #200 #4 3” 100 85 Filter Design Procedure: Determine d85of soil. Percent Passing (fines) (sand) (gravel) 0 Particle Size

  21. Granular Filter Design #200 #4 3” 100 D15-max = n*d85 85 CategoryD15-max 1 9*d85 2 0.7 mm 3 equation 4 4*d85 Filter Design Procedure: Determine max D15of filter (retention). Percent Passing 15 (fines) (sand) (gravel) 0 Particle Size

  22. Granular Filter Design #200 #4 3” 100 85 Filter Design Procedure: Determine min D15of filter (permeability). D15-min = 4*d15 (>0.1 mm) Percent Passing 15 (fines) (sand) (gravel) 0 Particle Size

  23. Granular Filter Design #200 #4 3” 100 85 Filter Design Procedure: Plot max. & min sizes of filter. D100-max = 3” D5-min = #200 Percent Passing 15 (fines) (sand) (gravel) 0 Particle Size

  24. Granular Filter Design #200 #4 3” 100 • Segregation • Gap-graded • Uniformity 85 Filter Design Procedure: Determine design envelope of filter. Percent Passing 15 (fines) (sand) (gravel) 0 Particle Size

  25. Bedding Design Bedding Criteria Design bedding to be filter compatible with riprap (per NEH, Part 633, Chapter 26). and For information, refer to bedding criteria in MN-TR-3 (1989).

  26. Bedding Design No Bedding Needed Bedding Criteria Ref.: MN-TR-3 Riprap Base soil: < 20% fines > 40% gravel

  27. Bedding Design • % fines <5% • Thickness of bedding = 6” – 12” • Increase thickness by 50% for underwater placement. Bedding Criteria Ref.: MN-TR-3

  28. Bedding Design #200 #4 3” 36” 100 (1) (1) Retention d85b> D15R/4 85 riprap (2) Permeability d15b< D15R/4 Bedding Design Procedure: Percent Passing bedding (2) (3) Max. fines d5b>#200 15 (cobbles/boulders) (3) (fines) (sand) (gravel) 0 Particle Size

  29. Geotextile Filter Design Theoretical Design Criteria for Geotextile Filters (Giroud) Retention – OGT< d85-soil Permeability – KGT>Ksoil Porosity – nGT> 0.55 Thickness - # constrictions > 25 Shape of openings - woven GT’s only

  30. Geotextile Filter Design Industry-Standard Geotextile Design Criteria for Filtration AASHTO – Std. M288 FHWA – Refinements based on research NRCS – Design Note 24 (1991, 2011 revision awaiting distribution)

  31. M288 Specification - AASHTO

  32. M288 Specification - AASHTO • User friendly material specification that covers roughly 90 % of geotextile use in 5 major applications NRCS would consider: • Subsurface drainage • Separation and filtration • Stabilization • Erosion control (permanent) - riprap • Erosion control (temporary) - silt fence

  33. FWHA Procedure

  34. FWHA Procedure • Based on Giroud criteria and other research. • Differentiates between: • Steady & dynamic flow • “less critical” & “critical” applications • “less severe” & “severe” conditions

  35. FWHA Procedure

  36. Geotextile Filter Design Example Geotextile Design Problem Design GT for fine silty sand soil (SM) from Sugar Creek WS, Oklahoma Compare results from: • M288 • FHWA

  37. Sugar Creek, OK Soil • GradationSize% Finer #40 (0.42 mm) 100 #60 (0.25 mm) 98 #140 (0.105 mm) 60 #200 (0.074 mm) 25 0.005 mm 4 k = 0.004 cm/s

  38. Sugar Creek, OK Soil (Fine SM )

  39. M288 Specification - AASHTO 25% (nonwoven)

  40. M288 Specification - AASHTO woven nonwoven

  41. FWHA Procedure Retention Criteria Cu=8.1

  42. FWHA Procedure Retention Criteria AOS or O95-GT< B * D85-soil Since Cu = 8.1 > 8, B = 1 So, AOS or O95-GT< (1) * (0.17 mm) < 0.17 mm

  43. FWHA Procedure Permeability/Permittivity Criteria 25%

  44. FWHA Procedure Clogging Resistance Criteria

  45. FWHA Procedure Survivability and Endurance Criteria Refers to AASHTO M288 criteria.

  46. Example Problem - Comparison

  47. Other Design Considerations • Woven vs. nonwoven GT’s • Continuity of filter protection • Precautions with silty soils • Cutoffs

  48. Other Design Considerations • Woven vs. Nonwoven • Higher tensile strength • Lower elongation • Lower friction factor • Lower tensile strength • Higher elongation • Higher friction factor

  49. Other Design Considerations • Continuity of filter protection • Leave no “unfiltered exits.” • Soil will pipe into riprap. Filter element

  50. Other Design Considerations • Precautions with silty base soil • Geotextiles are subject to clogging when used to filter soil with mobile, non-plastic fines (silt). • ASTM tests available to determine clogging potential – Gradient Ratio Test (D5101), Hydraulic Conductivity Ratio Test (D5567). • Recommend using granular filters with silty soils (SM, non-plastic ML).

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