Closure Design and Construction of Contaminated Soft Sludge Lagoons: A Tale of Innovation, Poor Field Execution and Final Redemption

Transcription

1 West Lafayette, Indiana April, 2013 Closure Design and Construction of Contaminated Soft Sludge Lagoons: A Tale of Innovation, Poor Field Execution and Final Redemption PURDUE GEOTECHNICAL SOCIETY David Espinoza Washington DC, USA

2 Located in the Shenandoah valley (62 miles west of DC) AVTEX SUPERFUND SITE

3 A LITTLE HISTORY

4 Plant built in 1937 ONCE UPON A TIME

5 AVTEX FIBERS

6 SUPERFUND RECIPE Ingredients: Caustic soda Sulfuric acid Carbon disulfide 1950s

7 PRODUCE SOME MORE 1970s

8 ET VOILÀ (1990 s)

9 PROJECT BACKGROUND Fly Ash Stockpile (500,000m 3 ) Sludge Basins ( 21 Hectares) Fly ash was recommended to close the lagoon (260,000 m 3 )

10 REMEDIATION Leave in place and cap 5 sulfate sludge basins (~50 acres) Capping implied: 4 ft 10 ft surcharge Crust ( psf) ft Soft ( psf) 3-20 ft Natural Soil

11 CHARACTERIZATION Perm 10-7 to 10-8 cm/s Unit Weight: 10 pcf to 50 pcf Moisture Content: 90% to 800% Shear Strength: 10 psf to 100 psf

12 HOW SOFT IT IS PSF? An average person weighs 180 lb Average shoe size: 10 (~ 0.75 ft 2 ) 240 psf

13 Use fly ash as grading fill CLOSURE APPROACH Place soil-geomembrane cap on the top Soil-Geosynthetic Cover Fly Ash 1 m m Sulfate Sludge 1-7 m Surplus of fly ash available on site (240,000 m 3 )

14 THE $1M QUESTION IS: How to over build a 10 PSF soft sludge lagoon?

15 ANSWER: BROMS (1987) Stabilization of Very Soft Clay using Geofabric Geotextiles and Geomembranes Vol. 5, pp 17-28

16 HOW DOES IT WORK? LAGOON TO BE STABILIZED (SOFT SLUDGE) A. Lagoon Filled with Soft Sludge

17 CONSTRUCTION SEQUENCE GEOTEXTILE SEAM (TYP) A. Lagoon Filled with Soft Sludge STABILIZING BERM (TYP) B. Install Geotextile over Lagoon and Place Stabilizing Berms

18 CONSTRUCTION SEQUENCE A. Lagoon Filled with Soft Sludge B. Install Geotextile over Lagoon and Place Stabilizing Berm INTERMEDIATE BERM PERPENDICULAR TO SEAMS (TYP) C. Construct Intermediate Berms

19 CONSTRUCTION SEQUENCE A. Lagoon Filled with Soft Sludge B. Install Geotextile over Lagoon and Place Stabilizing Berm C. Construct Intermediate Berms D. Widen Intermediate Berms Construction involves a step-wise procedure to be followed in the field

20 CLOSURE METHOD STABILIZING BERM HIGH STRENGTH GEOTEXTILE SOFT SLUDGE LOCKING BERM SOFT SLUDGE INTERMEDIATE BERM SOFT SLUDGE

21 BROMS (1987) l h l h Hypothesis: h h l l For example: Excerpts from Page 23: 5ft 5(1ft) 1ft; 50ft 5(10ft) 10ft; h h l l

22 NEW APPROACH (2000)! CE68901 CE48300 MA161000

23 DESIGN ANALYSIS STABILIZING BERM HIGH STRENGTH GEOTEXTILE LOCKING BERM INTERMEDIATE BERM SOFT SLUDGE INITIAL SURFACE BERM SPACING INTERMEDIATE BERM DEFORMED SURFACE RUT DEPTH Bearing Capacity Analysis

24 DESIGN ANALYSIS Ultimate Reinforced Bearing Capacity of Soil, q ur (Membrane Effect from High Strength Geotextile) q ur = cn c +q gb +q gh BERM AREA L b HEAVED AREA L h BERM AREA L b ε h INTERMEDIATE BERM r h A h r b A b β h β b r b A b β b DEFORMED GROUND SURFACE, f(x) A b = Volume of soft sludge displaced under an intermediate berm A h = Volume occupied by soft Sludge heave between intermediate berms

25 DESIGN ANALYSIS q ur = c N c + q gb + q gh q gb = J L b L b L b / 2 / 2 ( x)1 f x 2 '( ) 1/ 2 f ''( x) dx q avg q gh = 2J L c L b / 2L L b h / 2 / 2 ( x)1 2 f '( x) 1/ 2 f ''( x) dx Data required: Modulus (J) and shape of deformation f(x) Reference: Espinoza and Sabatini (2008), Geosynthetics International

26 DESIGN ANALYSIS Deformed shape approximated by parabolas (Giroud and Noirey, 1981) q q avg ( 2J/L b ) = avg ln(tan + sec b b ) 1 ln(tan h + sec h) q avg q gb q gh avg gb 1 gh L L h b

27 Membrane Contribution λ=q ur /(2J/L b ) Membrane Contribution - q/(2j/lb ) Average Reinforcement Strain (%) Average Strain (%) GEOTEXTILE CONTRIBUTION Additional Bearing Capacity Provided by Reinforcement Additional Bearing Capacity Provided by Reinforcement % L h /L b Reinforcement Strain 5.0% % % Membrane Effect Contribution Rutting Factor - r b /L b Rutting Factor (r b /L b ) 20.0% Using this chart, the effect of geotextile contribution can be quantified

28 CALCULATION Unreinforced Case Sludge Thickness = 0.3m Undrained shear strength= 0.5 kpa Equipment CAT D3C-LGP-5II = 29.6 kpa qu = c N c kPa FS q q u equipment = Reinforced Case with Berms For Berm Deflection r b = 0.45m Berm spacing L h = 8.0 m Berm width L b = 2.7 m L L h b rb 3.0, L b 0.17 INITIAL SURFACE L b =2.7m L h =8.0m INTERMEDIATE BERM DEFORMED SURFACE r b =0.45m

29 Membrane Contribution λ=q r /(2J/L b ) Membrane Contribution - q/(2j/lb ) Average Reinforcement Strain (%) Average Strain (%) GEOTEXTILE CONTRIBUTION Additional Bearing Capacity Provided by Reinforcement Calculating factors using the proposed chart % ε=1.9% L h /L b Reinforcement Strain 5.0% L h /L b = % 5.00 λ= Membrane Effect Contribution Rutting Factor - r b /L b Rutting Factor (r b /L b ) r b /L b =0.17 Geosynthetic Contribution 15.0% 20.0% With = 1.9% and q r = 27.1 kn/m then J= 2540 kn/m Working tensile strength = (2,540 kn/m) 1.9% = kn/m For FS =2, u = 3.8%, T u = 96.5 kn/m

30 Develop construction details Specifications SPECIFICATIONS High strength geotextile (T u = 96.5 kn/m and u = 3.8%) Sequence of construction Equipment (D5G-LGP)

31 Fill Placement to slow and time consuming CLOSURE IMPLEMENTATION Specified Equipment (e.g., D5H-LGP) too small for production

32 Interesting but no, thanks Use large equipment to push fly ash over sludge to save the cost of geotextile and construction time ( )

33 After all it is just a dirt job Crust Displacement Mixing lots of fill with sludge

34 9 Years later (2009) Fly Ash Stockpile (500,000m 3 ) Remaining 100,000 m 3 Used 400,000 m 3 Sludge Basins (21 hectares) Remaining 9 hectares Closed 12 hectares Slow rate of closure and fly ash deficit for remaining work

35 FINAL REDEMPTION Maybe the consultant is not as dumb as he looks

36 SEAMS FOR GEOTEXTILES HAND SEAMING J SEAM Field panels seamed in accordion manner in the field

37 FIELD CONSTRUCTION Geotextile installed rapidly in the field Minimal slack following deployment of the seamed geotextiles

38 FIELD CONSTRUCTION Fly ash layer placement perpendicular to geotextile seams Ease of placement of fly ash material over sludge using equipment on site

39 FIELD CONSTRUCTION Parallel berms provided confinement to the sludge Increased bearing capacity due to membrane effect of geotextile

40 FIELD CONSTRUCTION Series of parallel berms were constructed Wave Propagation at Leading Edge of Berms Occurred Approximately 2 Weeks to Cover 2 Acre Area with Initial Lift of Fly Ash Grading Layer Reduced construction time to one month to cover one hectare of basin

41 FIELD CONSTRUCTION Problems occurred when the contractor tried to use oversized equipment Geotextile was torn and patched in place

42 FIELD CONSTRUCTION Intermediate space between berms was filled Fill thickness of 1-3 m was achieved with remaining fly ash

43 LESSONS LEARNED Printed correct

44 LESSONS LEARNED Developing good engineering solutions is not always sufficient Convey the risks associated with potential alternatives

45 TO BE A GOOD CONSULTANT We CANNOT focus in our mouse traps Remember, our clients don t care about our mouse traps They care about having less mice

46 THANKS Questions? Contact Information: David Espinoza Address: Old Columbia Road, Columbia, MD (Ph: )