Geotextile Filter Background

Transcription

1 Geotextile Filter Background GT filters used in dams since 1974 U. S. COE initiated design in 1980 s based on soil filtration principles basic difference is the thinness of GT s some clogging (aka, tuning) will occur dangers are over excessive clogging or continuing soil loss

2 Design Criteria (as with Soil Filters) 1. Adequate open area (permittivity) 2. Sufficiently closed structure (retention) 3. Long-term equilibrium (flow stability)

3 Approach to this Presentation 382 published papers on GT filters I have ~ 25 of them (with presentations) however, dam personnel don t buy it so, let s take a different approach here are 82-GT filter failures if your project doesn t fit any, then go for it (or write the 83 rd paper)

4 Geotextile Filter Failures by Bob and George Koerner Geosynthetic Institute 1.0 GT Design Failures 2.0 Failures Involving Atypical Soils 3.0 Failures Involving Atypical Permeants 4.0 GT Installation Failures

5 Preliminary Comments presentation taken from an internal GRI Report #26 in 2008 includes 82 GT filter failures where no citation is given the case history is from authors files let s see what s out there

6 Types of Geotextiles Used as Filter Fabrics Woven Slit (Spilt) Film Woven Monofilament Nonwoven Heat Bonded Nonwoven Needle Punched

7 1.0 GT Design Failures 1.1 Lots and lots (tons!) of design literature geotextile-filtration-design: 80 citations geotextile-filtration-theory: 35 citations geotextile-filtration-laboratory-clogging: 71 citations geotextile-filtration-laboratory-general: 108 citations geotextile-filtration-laboratory-opening size: 48 citations geotextile-filtration-laboratory-permeability: 40 citations Total = 382!

8 (a) Upstream particles blocking geotextile openings (b) Soil particles blocking geotextile structure (c) Depth filtration concept using thick geotextiles (an extension of the concept in sketch b ) (d) Upstream particles arching over geotextile openings (d) Formation of an upstream soil filter Various mechanisms involved in long term flow; McGown (1978) and Heerten (1992) Note: Most agree that the fabric is the catalyst in stimulating the upstream soil to do its own filtration.

9 1.2 Commonly Used Design Methods (a) Carroll (1986) is easiest O 95 < (2 or 3) d 85 where O 95 = AOS of fabric d 85 = 85% finer particle size (b) AASHTO (1991) For soil with 50% passing the No. 200 sieve: O 95 < 0.60 mm; ( No. 30 sieve) For soil with > 50% passing the No. 200 sieve: O 95 < 0.30 mm; ( No. 50 sieve) (c) AASHTO (2005) Filtration Requirements, (strength is a different table) Percent in Situ Soil Passing mm Units < to 50 > 50 Geotextile class Class 2 from Survivability Table Permittivity sec Apparent opening size (Max MARV) Ultraviolet stability (retained strength) mm e % 50% after 500 hours of exposure (d) Luettich (1992) et al. charts

10 Steady-state flow conditions, after Luettich, et al. (1992)

11 1.3 Various Design Field Problems Poor Filtration Fabric Selection Woven Slit Films Woven Silt Film ( no voids) Woven Slit Film Fabric Caused This It s so bad, they are used as silt fences!

12 The other extreme is huge voids created by subgrade or cover soil stones pushing aside the filaments since they are not bonded together. What is the AOS now????? Message: Don t use woven slit films as filters

13 1.3.2 Excessive Coverage of Fabric Typical cross-section of slope armoring including a geotextile filter. As-constructed system Shortly after construction Design procedures is to include a RF for amount of fabric covered by the hard armor system.

14 Most Recent (2010) Case History extremely large water storage reservoir 2.5-to-1 side slope, i.e., 23.6 deg. silty sand placed above geomembrane GT placed on the silty sand, then stepped soil-cement armoring clogging of the geotextile filter helped cause erosion of the silty sand during drawdown and subsequent failure of the armoring

15 1.3.3 GT Wrapped Drainage Pipe Geotextile wrapped perforated solid wall drainage pipe excessively clogged at each inlet opening. FS k k reqd allow DCF where FS = flow rate factor-of-safety k allow = allowable permeability (or permittivity) k reqd = required permeability (or permittivity) DCF = drain correction factor = (footprint area/available flow area)

16 GT GT Gravel Perforated Perforated Gravel pipe GT pipe GT GM Gravel GM Perforated Perforated Gravel pipe pipe (a) (a) Full Entire footprint cell filter filter (DCF (DCF = 1) = 1) (b) GT wrapped drain (DCF = 10 to 40) (b) GT wrapped drain (DCF = ) to GM GM - GOOD - - ACCEPTABLE - (a) Entire cell filter (DCF = 1) GT (b) GT wrapped drain (DCF = = ) to GT Slotted GT pipe Slotted pipe GM (c) Socked corrugated pipe (DCF = = ) to GM (c) Socked (c) Socked corrugated pipe (DCF (DCF = 60 = = 60 to ) to 260) Perforated GT pipe Perforated GM pipe (d) Socked smooth perforated pipe (DCF = = 7,500-24,000) to GM (d) Socked smooth perforated pipe pipe (DCF (DCF = = 7,500-24,000) = to to 24,000) - DICEY - - HOPELESS - Typical design-related drainage correction factors (DCFs).

17 1.3.4 Reversing Flow Conditions difficult situation due to cyclic breakdown of upstream soil structure; recall previous sketches both sides of fabric are alternatively upstream! numerous literature case histories Application Author Date tidal weirs railroad ballast highway drain sea wall filter* * Case history follows. Miller Saxena & Hsu Mlynarek Maisner & Myles

18 Sydney s Airport with runway extensions supported by seawalls.

19 *Sea Wall Failure in Australia airport runway extensions into harbor side-by-side concrete retaining wall panels with GT strips covering the open spaces fine sand backfill was lost through the fabric soil loss eventually undermined airport runways $5M judgment against the designer!

20 2.0 Failures Involving Atypical Soils 2.1 Typical, or Standard, Soil Types soil characteristics are well established typical soils are covered by USCS following are troublesome to filters; both soils and GTs (SP, SM, ML, OL, CH-disp.) particularly for GTs due to their thinness

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22 2.2 Atypical Soils and GT Filter Failures Cohesionless fine grained soils fines can move through filter (high AOS) fines can get trapped in filter (low AOS) requires a careful design balance between soil loss and excessive clogging many failures reported in the literature

23 Soil Type Failure Author Date rock flour sandy loam fine silt fly ash fine sand fine sand soil loss soil loss soil loss soil loss clogging soil loss Koerner Lennoz-Gratin Mlynarek Gabr, et al. Gardoni & Palmeria Khan & Kitazune

24 2.2.2 Gap graded cohesionless soils Haliburton and Wood (1982) Soil Loss =? Lennoz-Gratin (1987) in French farm-drains; fine soil loss into encapsulated drainage pipes Mlynarek (1998); soil loss and collapse of overlying rip-rap at a protected sea wall

25 2.2.3 Dispersive clay soils fugitive clay particles from the cohesive soil matrix ASTM D4647 for identification ASTM D4751 for Pinhole Test Hoare (1982) clogging of NW-GTs Crum (2008) clogging of GT Filter

26 2.2.4 Ferrous iron soils leading to Ochre Ochre is an orange substance rich in organic matter and high in iron oxides Fe 2+ content (mg/l) Ford (1982) < 0.5 > 2.5 Kuntze (1982) < > 6.0 Maslov, et al. (1975) Ochre Clogging Hazard Ranking Fe 2+ content (mg/l) ph < 7 ph > 7 Fe 2+ content (mg/l) > 14 < > 90 Clogging Hazard Slight Moderate Great Very Great Clogging Hazard None Severe Clogging Hazard None Slight Moderate Great Very Great

27 Ochre deposition on geotextile filters Ochre deposits in a highway underdrain pipe

28 Process of Ochre Formation Ref. VanGulek and Novy, University of Manitoba

29 Ochre clogging of GT filters Application Author Date horizontal drain filter Ford 1982 dam drainage filter earth dike filter drain pipe filter land drain filter erosion control filter Scheurenberg Van Zanten & Thabet Puig, et al. Stuyt & Oosten Abromet

30 Possible (?) Strategies Preventing surface or trench lining aerating subsurface soil addition of iron complex material addition of bactericide, reduce the drain spacing submerge the drainage outlets Remediation* flushing of drainage pipes high pressure cleaning chemical (biocide) cleaning *only addresses the pipe and localized fabric adjacent to holes or slits

31 3.0 Failures Involving Atypical Permeants 3.1 Water; The Usual Permeant properties are well known standard testing uses tap water temperature at 20 C (68 F) with D.O. < 6 ppm soil permeability is well established

32 Typical gradations and Darcy permeabilities of several aggregate and graded filter materials (U.S. Navy, 1982).

33 3.2 Atypical Permeants and Filter Failures Oily water and related sludge permeants In Holland (1980) permeation of oil water through filter mattress clogging the filter points In Texas (1988) sludge clogging of pipe outlets

34 3.2.2 Turbid waters with high TSS Suits and Minnitti (1989) used three fabrics as turbidity curtains to contain dredged soils; all excessively clogged Harney and Holtz (2005) report on a turbidity curtain that clogged such that built-up hydraulic pressures caused fabric strength failure

35 3.2.3 High alkalinity waters Water Salinity Based on Dissolved Salts in Parts Per Thousand (ppt) Freshwater Brackish water Saline water Brine < > 50 Los Angeles highway underdrain fabric clogged by passing groundwater of ph ~ 10.5 Florida (1999) failure of sea wall filter by high alkalinity (Ca and Mg) groundwater Crum (2008) reports that fabrics in toe drains of dams have clogged from chemical precipitation

36 3.2.4 Landfill leachate beneath the waste mass Schematic of a typical landfill leachate collection and removal system.

37 Major Literature Studies Bass (1984) reports on 20 cases of biological growth in all components of the LCRS G. Koerner (1993, 94) reports on three excessively clogged GT filters) Landfill Type ph COD (mg/l) TSS (mg/l) BOD 5 (mg/l) municipal ,000 28,000 27,000 industrial 9.9 3,000 12,000 1,000 municipal ,000 9,000 11,000

38 Woven monofilament fabric as manufactured and after permeation with landfill leachate Nonwoven, needle-punched fabric after permeation with landfill leachate

39 Additional Landfill Leachate Case Histories with GT Problems Hamilton and Dylinggowski (1989) Brune, et al. (1991) Cuzzuffi (1991) Mitchell, et al. (1993) Corcoran and Bhatia (1996) All cases of excessive GT filter clogging! General Comments 1. TSS > 2500 mg/l and BOD 5 > 2500 mg/l concern should be expressed 2. Concern with all MSW leachates; particularly bioreactors 3. Consdier a no filter strategy 4. Use select waste directly on the LCRS

40 The No-Filter Strategy It Works!

41 3.2.5 Wastewaters and agriculture waste liquids Davis, et al. (1977); bacteria was too numerous to count in sewage wastewater filter clogging Martel, et al. (1999); focused on BOD and TSS Barrington, et al. (1998); three GTs decreased in permittivity by an average of 50,000 times Liquid waste from animal operations, e.g., CAFO s, will generally be disastrous!

42 4.0 Geotextile Installation Failures 4.1 Basics of GT filter installation; Holtz, et al. (1995) provide a smooth graded surface free of debris and large cavities GT pre-cut to fit situation use clean GT; no mud caking fabric MD follows flow direction adequate overlaps on bottom and sides limit exposure to sunlight, dirt, damage, etc. provide adequate overlap on top take adequate care in backfilling

43 (a) Initial trench excavation (b) Placement of geotextile (c) Crushed stone bedding layer (d) Installation of drainage pipe (e) Backfilling of drainage pipe (f) Closure of fabric and final backfill Construction of highway drainage systems using a geotextile filter.

44 4.2 GT Filter field installation problems Lack of intimate contact (GT-to-soil) generally occurs with fabric vertical or inclined can also occur by uplifted horizontal fabric wrinkles and folds generally not problematic many reported problems from the field

45 Field Problems from the Literature Jubien (1985); uplifted fabric into large rip-rap voids with loss of soil subgrade Seagirt, MD (1987); fabric fixed to concrete and uplifted by backfilling with subsoil erosion and the failure of the parapet Faure, et al. (1994); water flow parallel to vertical oriented fabric which caused erosion and scouring Crum (2008); unconfined filters in dams have been susceptible to excessive clogging G. Koerner (1996); NCHRP field exhuming project with fourteen GT filter problems (over)

46 Summary of Exhumed Field Sites, G. Koerner, et al. (1996) Type of Drainage System No. of Sites Acceptable Performance (A,B, or C)** Nonacceptable Performance (D or F)** Const./Maint. Component Drain Component Geotextile Component PGED GWUD PPUD n/a GSPP GWDF GECF Totals *where PGED = prefabricated geocomposite edge drain GWUD = geotextile wrapped underdrain (stone and perforated pipe) PPUC = perforated pipe underdrain (no geotextile filter) GSPP = geotextile socked perforated pipe GWDF = geotextile wall drain filter GECF = geotextile erosion control filter

47 Installation Method Installation of Prefabricated Geocomposite Edge Drains (PGED)

48 Lack of Intimate Contact Problem Using PGED s Remediation of Above Situation

49 4.2.2 Glued or blocked fabric surfaces (case history in Pennsylvania in 1989) Filter Fabric Placed Over Openings Between Hexagonal Panels Abutment Failure (Blow-Out) Due to Built-Up Hydrostatic Pressure

50 The Exhumed, and Completely Glued, Fabric (Duh!)

51 Summary Comments Design Concerns woven slit film fabrics are verboten excessive surface blockage of fabric by armoring systems GT wrapped drainage pipe reversing flow situations Atypical Soils Concerns cohesionless fine grained silts cohesionless gap-graded sandy silts; to a lesser extent dispersive clays beware of ochre forming soils Atypical Permeant Concerns oily water and sludges turbid waters (high TSS) high alkalinity (Ca & Mg) permeants landfill leachates (high TSS and/or BoD) wastewater and ag-waste (extremely high BoD) Installation Concerns lack of intimate contact glued or blocked surfaces

52 Parting Commentary we have many long term laboratory tests long-term flow test, per GRI-GT1 gradient ratio test, per ASTM D5101 hydraulic gradient ratio test, per ASTM D5084 biological clogging test, per ASTM D1987 it s time we start using them!

53 Thanks for the Invitation and Any Questions?