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

2. Flow Rock Chute Filters, Bedding, and Geotextiles

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

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

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

6.  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 Filters, Bedding, and Geotextiles

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

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

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

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

11. Filters vs. Bedding

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

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

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

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

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

17. Granular Filter Design  Filter Design begins with:  Base soil gradation. #4#2003” (fines) (gravel) (sand) Percent Passing 0 100 Particle Size

18. Granular Filter Design  Filter Design Procedure: 1.Regrade on #4, if applicable. #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size

19. Granular Filter Design  Filter Design Procedure: 2.Determine category of regraded soil. #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size Category % Fines 1 >85 2 40-85 3 15-39 4 <15

20. Granular Filter Design  Filter Design Procedure: 3.Determine d 85 of soil. #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size 85

21. Granular Filter Design  Filter Design Procedure: 4.Determine max D 15 of filter (retention). #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size 85 15 D 15-max = n*d 85 Category D 15-max 1 9*d 85 2 0.7 mm 3 equation 4 4*d 85

22. Granular Filter Design  Filter Design Procedure: 5.Determine min D 15 of filter (permeability). #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size 85 15 D 15-min = 4*d 15 (>0.1 mm)

23. Granular Filter Design  Filter Design Procedure: 6.Plot max. & min sizes of filter. #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size 85 15 D 100-max = 3” D 5-min = #200

24. Granular Filter Design  Filter Design Procedure: 7.Determine design envelope of filter. #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size 85 15 Segregation Gap-graded Uniformity

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

27. Bedding Design  Bedding Criteria  Ref.: MN-TR-3 1.% fines < 5% 2.Thickness of bedding = 6” – 12” 3.Increase thickness by 50% for underwater placement.

28. Bedding Design  Bedding Design Procedure: #4#2003” (fines)(gravel)(sand) Percent Passing 0 100 Particle Size 85 15 (cobbles/ boulders) 36” (2) Permeability d 15b < D 15R /4 (1) Retention d 85b > D 15R /4 riprap (1) (2) bedding (3) Max. fines d 5b > #200 (3)

29. Geotextile Filter Design  Theoretical Design Criteria for Geotextile Filters (Giroud) 1.Retention – O GT < d 85-soil 2.Permeability – K GT > K soil 3.Porosity – n GT > 0.55 4.Thickness - # constrictions > 25 5.Shape of openings - woven GT’s only

30. Geotextile Filter Design  Industry-Standard Geotextile Design Criteria for Filtration 1.AASHTO – Std. M288 2.FHWA – Refinements based on research 3.NRCS – Design Note 24 (1991, 2011 revision awaiting distribution)

31. M288 Specification - AASHTO

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

33. FWHA Procedure

34. Based on Giroud criteria and other research. Based on Giroud criteria and other research. Differentiates between: Differentiates between: Steady & dynamic flow Steady & dynamic flow “less critical” & “critical” applications “less critical” & “critical” applications “less severe” & “severe” conditions “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 M288 FHWA FHWA

37. Sugar Creek, OK Soil Gradation Size% 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 Gradation Size% 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 C u =8.1

42. FWHA Procedure Retention Criteria AOS or O 95-GT < B * D 85-soil Since C u = 8.1 > 8, B = 1 So, AOS or O 95-GT < (1) * (0.17 mm) < 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 AASHTOFHWA PropertyM288WovenNonwoven Max. AOS (O 95 ) (mm)0.250.17 (sieve size)#60#100 Min. Permeability (cm/s)---0.004 Min. Permittivity (s -1 )0.2 Min. POA (%)---4 Min. Porosity (%)--- 50

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.” Leave no “unfiltered exits.” Soil will pipe into riprap. 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). 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). 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). Recommend using granular filters with silty soils (SM, non-plastic ML).

51. Other Design Considerations  Precautions with silty base soil Sand layer under GT

52. Construction Considerations  Cutoffs with geotextiles Possible flow path between soil and GT No confinement Especially critical with highly erosive soils (SP, SM, etc.)

53. Construction Considerations  Cutoffs with geotextiles Cutoff GT

54. Construction Considerations  Subgrade preparation  Cushion layer – installation damage  Minimum cover for equipment

55. Construction Considerations  Subgrade preparation (see C.S. 95) Reasonably smooth surface. Reasonably smooth surface. Free of: loose rock and clods, holes, depressions, projections, muddy conditions, and standing or flowing water. Free of: loose rock and clods, holes, depressions, projections, muddy conditions, and standing or flowing water. Intimate contact between soil and geotextile. Intimate contact between soil and geotextile.

56. Construction Considerations Subgrade preparation?

57. Construction Considerations Subgrade preparation?

58. Construction Considerations  Cushion layer – to protect GT No cushion – Class I GT required With 6” cushion – Class II GT allowed 3’ max. drop GT Cushion mtl., 6” min. thickness 220 lb. max. (1’ max. drop w/ sharp, angular rock)

59. Construction Considerations  Minimum cover for equipment 12” min. cover

60. Filters, Bedding, and Geotextiles Summary

61. SM Base Soil Riprap (angular) NW Geotextile  Critical Installation – silty base soil Installation damage Loss of soil

62. Filters, Bedding, and Geotextiles SM Base Soil Riprap (angular) Cushion/beddingFilter NW Geotextile  Critical Installation – silty base soil

63. Filters, Bedding, and Geotextiles Questions?