Fiji Technical Workshop Geotextiles May 2019 Agenda • Overview • Classification • Polymers • Stress Strain • Design • Specification 1
Overview - Why do we need them? Overview - Why do we need them? 2
Overview - Why do we need them? Classification » Nonwoven • Continuous Filament • Needle punched • Heat bonded • Staple Fibre • Needle punched • Needle punched & Heat set » Woven • Slit Film • Flat • Fibrillated • Multi-filament • Mono-filament » Knitted 3
Polymers » Polyester • Bidim • Texcel R » Polypropylene • Texcel P • Polyfelt TS • Mirafi N Short term strength Long term strength Polymers 4
Stress/Strain Behavior W : Woven CNW-HB : Continuous Filament Non Woven – Heat Bonded CNW-NP : Continuous Filament Non Woven – Needle Punched SNW-NP : Staple Fibre Non Woven – Needle Punched Design – By Function » Filtration • Pore Size • Through Flow • Permeability • Abrasion resistance • CBR Burst • Grab Strength • Tear Strength 5
Design – By Function » Separation • Tensile Strength • Trapezoidal tear • CBR Burst Design – By Function » Drainage • Through flow • Permeability • Pore size 6
Design – By Function » Liner Protection • Mass • Density • Fibre thickness • CBR Burst Design - Importance of Separation » Loss of aggregate 7
Design - Importance of Separation » Pavement performance Reduction in Flexible Pavement Load Carrying Capacity Due to the Loss of Aggregate Base Course (%) over Time 100% Pavement Load Carrying Capacity (%) of Original Design: AASHTO 80% 1993 Flexible Pavement Design Method 60% 40% 20% 0% 0.0% 2.5% 5.0% 7.5% 10.0% 12.5% 15.0% 17.5% 20.0% 22.5% Aggregate Base Course Loss over Time (%) Design - Importance of Separation » Full scale fields trials using different geogrids and geotextiles 8
Design - Importance of Separation » Pavement performance Nonwoven Geotextile maintains the boundaries geotextile between adjacent soil layers Intermixing of granular layer with soft subgrade SOFT SUBGRADE SOFT SUBGRADE Design - Properties » Drainage • Geotextile permeability 10 times subgrade » Filtration • Geotextile must retain subgrade material • d 50 < Geotextile pore size < d 90 » Survivability • Geotextile must not be damaged during installation to such an extent that points above are rendered irrelevant • Geotextile life must exceed design life 9
Design - Cover material » Size/Weight • Greater mass = greater damage potential » Drop Height • Greater height = greater damage potential » Angularity • Sharp stone = greater damage potential » Depth of cover • Thin = greater damage potential Never overestimate the products’ ability to withstand mechanical impact! Design - Foundation » Density • Soft = geotextile bursting (CBR) • Hard = geotextile splitting (Grab) » Presence of Stones • Stones are likely to increase damage due to pinching/cutting (Mass) » Slope • Steeper = greater force on geotextile (Tear or Tensile strength) 10
Design – Field Trials » Construction methodology • Conduct field trials for site specific design to eliminate uncertainty. • Consider the following: • Different drop heights i.e. 1.5 & 3m • Excavator tracking Design – Full Scale Testing » Research & Development • Conduct full scale rock drop tests • Consider the following: • Different drop heights i.e. 0.5, 1.0, 1.5 & 2.0m • Different rock mass i.e. 250, 500 & 1000kg 11
Design – Full Scale Testing » Research & Development • Develop Design curves Design - When things go wrong » Construction • Despite extensive testing the construction methodology was changed 12
Design - When things go wrong » Construction • Use of a non specified woven geotextile Specification » Methods for specifying geotextiles Independent Suppliers - Guidelines Technical Publications Past Experience Trial and Error 13
Specification » Parsons Brinckerhoff Independent Report – 2010 • The variation in test results was found to be significant, with one product failing to meet the typical published data by 76% • Typical data does not give an accurate platform on which to base engineering design • In some instances weaker direction results were not presented • Design certainty can be achieved through the use of MARVs presented in both the machine and cross machine direction Regulatory Body Specifications 14
Independent Specification » Mechanical Properties • AS 2001.2.3 Grab Tensile Strength Independent Specification » Mechanical Properties • AS 3706.3 Trapezoidal Tear Strength 15
Independent Specification » Mechanical Properties • AS 3706.4 CBR Puncture Independent Specification » Mechanical Properties • AS 3706.5 Drop Cone Impact (h ) 50 16
Independent Specification » Hydraulic Properties • AS 3706.9 Flow Rate and Permittivity Independent Specification » Hydraulic Properties • AS 3706.7 EOS (Dry Sieving) - O 95 Filtration Blinding Clogging 17
Independent Specification » Geotextile Application Categories Application Material Requirement Filtration Class G1: Separation under / Strength requirement in Class 4 within Embankments Table 2 & Table 6 G2: Filtration/Separation Strength requirement in Class 2 under Embankments inc. Table 2 & Table 6 Drainage Blankets G3: Trench Drains / Strength requirement in Class 1 Highway Edge Drains Table 3 & Table 6 G4: Drainage/Separation Strength requirement in Class 1 Retaining Structures Table 4 & Table 6 G5: Under Rock Armour Strength requirement for Class 3 Revetment layer in Class D and E in Table 6 Embankments Independent Specification » Geotextile Application Separation The use of geosynthetic material between two dissimilar materials to prevent the intermixing of materials Granular layer Geotextile separator Soft subgrade 18
Independent Specification » Geotextile Application Separation Embankment fill Aggregate drainage blanket Soft subgrade Geotextile separator Independent Specification » Selection of Geotextiles for Mechanical Separation (Table 2) Nominal Max Stone Geotextile Strength Class Particle Size D (mm) 1 ≤ CBR ≤ 3 CBR > 3 ≤ 37.5 C (A29) A (A14) ≤ 75 C (A29) B (A19) ≤ 200 D (A39) C (A29) ≤ 400 E (A49) D (A39) ≤ 600 n/a E (A49) 19
Independent Specification » Geotextile Application Trench Drains Trench Depth < 3m Geotextile Independent Specification » Selection of Geotextiles for Trench Drain (Table 5) Nominal Max Stone Geotextile Strength Class Particle Size D (mm) Trench Depth Trench Depth <2m <3m ≤ 37.5 A (A14) B (A19) ≤ 75 B(A19) C (A29) ≤ 200 C (A29) D (A39) 20
Independent Specification » Geotextile Application Gabion walls / Mattresses Gabion Retaining Geotextile Wall Reno Mattress Independent Specification » Selection of Geotextiles for Gabion Walls and Mattresses (Table 6) Type of Structure Geotextile Strength Class Conventional concrete retaining walls B (A19) Segmental block walls Reinforced soil panel walls Gabion walls C (A29) Crib walls Rock filled mattresses 21
Independent Specification » Geotextile Application Rock Armour Revetments/Breakwaters Rock armour Geotextile Independent Specification » Selection of Geotextiles under Rock Armour (See Table 7) Nominal Max. Stone Particle Size D 85 Geotextile Strength Class (mm) <200 D (A39) <400 E (A49) 22
Independent Specification » Independent Specification Example – TNZ F7 Independent Specification » Independent Specification Example – TNZ F7 23
Independent Specification Specification 24
Questions? 25
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