Presentation contents 1. Role of geosynthetic veneer reinforcement - - PowerPoint PPT Presentation

Peter er Assinde der

HUESKER Synthetic GmbH, Manager AFRICA

Laura a Ca Carbone ne

HUESKER Synthetic GmbH, Engineering department

Morne ne Breyten ytenbach bach

HUESKER Synthetic GmbH, Manager MINING

Landfill2015

Geogrid reinforcement in harsh environments

September 2015 Conference & Exhibition Landfill2015

Presentation contents

• 1. Role of geosynthetic veneer reinforcement in barrier

systems

• 2. Reinforcement performance in elevated temperatures

September 2015 Conference & Exhibition Landfill2015

Why do we need veneer reinforcement? 1989 test section on German landfill 100m x 20m section 1 in 4 (14°) slope

• Clay foundation
• HDPE geomembrane (“semi-textured”)
• 2000g/m2 nonwoven protection geotextile
• 110 kN/m (ultimate) uniaxial geogrid reinforcement
• 0.5m thick gravel drainage layer

Design worst case interface friction angle = 17.1° (15.4 °)

September 2015 Conference & Exhibition Landfill2015

°

Why do we need veneer reinforcement?

September 2015 Conference & Exhibition Landfill2015

b =13 ° t

Smooth (solution A) Textured (solution B)

Geogrid (solution A and B2)

Veneer cover example layout

September 2015 Conference & Exhibition Landfill2015

Liu & Gilbert methodology

• Simple analytical model to estimate geosynthetic loads

during the placement of cover soils and/or waste

• Graphical method based on an accurate and test validated

mathematical model

• Considers strain compatibility between the layers
• Models tensile stress distribution between individual layers
• For each layer any induced load is proportional to it’s

stiffness (relative to the total stiffness) Veneer reinforcement

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Material Solution A – Smooth gmb lining system Solution B – Textured gmb lining system

Properties Interface friction angles Properties Interface friction angles Granular soil gsoil= 18 kN/m fsoil = 32° tsoil = 0.5m Kc= 485 kN/m fsoil/GTX = 29° gsoil= 18 kN/m fsoil = 32° tsoil = 0.5m Kc= 485 kN/m fsoil/GTX = 29° Geotextile (GTX) Kt,GTX= 50 kN/m fGTX/GMB = 12° Kt,GTX= 50 kN/m fGTX/GMB = 31° Geomembrane (GMB) Kt,GMB= 308.3 kN/m fGMBs/clay = 11° (lab test value) fGMBs/clay = 9° (design value) Kt,GMBt= 308.3 kN/m fGMBt/clay = 14° (lab test value) fGMBt/clay = 9° (design value) Geogrid (PET) (GR) Kt,GR= 1100 kN/m / Kt,GR= 350 kN/m (for Solution B2) /

Model properties

September 2015 Conference & Exhibition Landfill2015

b = 13°, t = 0.5m, g = 18 kN/m3, fsec = 9°, Kt = 708.3 kN/m, Kc = 485 kN/m Les = 30m, Leg = 0m Kt/Kc = 0.74, Leg/Les = 0, Lt/les = 0.475 fnet = 1 –

𝑢𝑏𝑜𝜒 (𝑢𝑏𝑜9) tan 𝛾 (tan 13) = 0.314

∆𝜐𝑕𝑡 = 𝜒𝑜𝑓𝑢

𝑀𝑢/ 𝑀𝑓𝑡 = 0.15

∆𝑈𝑕𝑡 = ∆𝜐𝑕𝑡 (𝛿𝑢𝑀𝑓𝑡𝑡𝑗𝑜𝛾) = 9.1 kN/m

Estimation of tension load in geosynthetic layers – Example Solution B1

X

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Solution Tension load in geosynthetic layers (kN/m) A 12.1 B1 9.1 B2 10

Estimation of tension load in geosynthetic layers

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Distribution of tensile forces

• 1. Smooth GMB with geogrid reinforcement

% carried by GTX =

𝐿𝑢𝑕𝑢𝑦 𝐿𝑢𝑢𝑝𝑢 = 50 1458.3 = 3%

% carried by GMB =

𝐿𝑢𝑕𝑛𝑐 𝐿𝑢𝑢𝑝𝑢 = 308.3 1458.3 = 21%

% carried by GR =

𝐿𝑢𝑕𝑠 𝐿𝑢𝑢𝑝𝑢 = 350 1458.3 = 76%

• 2. Textured GMB no reinforcement

% carried by GTX =

𝐿𝑢𝑕𝑢𝑦 𝐿𝑢𝑢𝑝𝑢 = 50 358.3 = 14%

% carried by GMB =

𝐿𝑢𝑕𝑛𝑐 𝐿𝑢𝑢𝑝𝑢 = 308.3 358.3 = 86%

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Distribution of tensile forces continued

• 3. Textured GMB with geogrid reinforcement

% carried by GTX =

𝐿𝑢𝑕𝑢𝑦 𝐿𝑢𝑢𝑝𝑢 = 50 708.3 = 7%

% carried by GMB =

𝐿𝑢𝑕𝑛𝑐 𝐿𝑢𝑢𝑝𝑢 = 308.3 708.3 = 43%

% carried by GR =

𝐿𝑢𝑕𝑠 𝐿𝑢𝑢𝑝𝑢 = 350 708.3 = 50%

• 4. Textured GMB with stiffer geogrid reinforcement (same UTS)

% carried by GTX =

𝐿𝑢𝑕𝑢𝑦 𝐿𝑢𝑢𝑝𝑢 = 50 941.6 = 5%

% carried by GMB =

𝐿𝑢𝑕𝑛𝑐 𝐿𝑢𝑢𝑝𝑢 = 308.3 941.6 = 33%

% carried by GR =

𝐿𝑢𝑕𝑠 𝐿𝑢𝑢𝑝𝑢 = 583 941.6 = 62%

September 2015 Conference & Exhibition Landfill2015

What happens to the reinforcement if we change the in-situ temperature?

Temperature plays a major role in all degradation mechanisms and in mechanical behaviour (creep and rupture) The temperature of the soil is constant (to within ± 0.5ºC) only at a depth of 10 m or more. Its value is then equal to the annual average atmospheric temperature at the surface. Daily and seasonal variations occur with decreasing intensity as the distance from the surface increases. Since higher temperatures increase the rates of ageing and creep of polymers disproportionally, their effect on geotextile behaviour may need to be considered…

Source: ISO 13434 – Guidelines on durability

September 2015 Conference & Exhibition Landfill2015

What happens to the reinforcement if we change the in-situ temperature?

Effective design soil temperature - In the absence of other information the effective design temperature can be taken conservatively as the average of the mean annual air temperature and the mean air temperature for the hottest month of the year

Source: ISO 20432 Guide to the derivation of reduction factors for soil reinforcement materials

Source: worldweatheronline.com

= 19.5°c = 23.25°c

September 2015 Conference & Exhibition Landfill2015

Long term strength as a function of conditions [kN/m] R and [kN/m] A * A * A * A * A R R

, d B, 5 4 3 2 1 k B, k B, M k B

R g = = Characteristic Value of the Long Term Reinforcement Strength

RB,d Design value of the tensile strength of geosynthetic reinforcement RB,k Characteristic value of the long-term tensile strength RB,k0 Characteristic value of the short-term tensile strength A1 Reduction factor for creep strain and creep rupture behaviour (depending on the load duration) A2 Reduction factor for damage caused during installation, transportation and compaction A3 Reduction factor for processing (seams, connections, joints) if applicable A4 Reduction factor for environmental impacts (resistance to weathering, chemicals, microorganisms, animals) A5 Reduction factor for the impact of dynamic action ɣM Partial safety factor for the structural resistance of flexible reinforcement elements

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Influence of temperature on creep rupture behaviour, A1

65.0 67.0 69.0 71.0 73.0 75.0 77.0 79.0 0.00 0.01 0.10 1.00 10.00 100.00 1000.00

Tensile load [%] Design life tD [years] Creep-Rupture Behavior PET- 50 °C PET- 20 °C PET- 10 °C PVA- 50 °C PVA- 20 °C PVA- 10 °C

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Effect of temperature on reduction factor for a given design life for PET and PVA reinforcement Influence of temperature on creep rupture behaviour, A1

Design life [years] Design temperature [°C] Retained strength [%] A1 PET PVA PET PVA 100 10 68.8 72.7 1.45 1.38 100 20 66.2 71.6 1.51 1.40 100 35 62.3 69.7 1.61 1.43 100 50 58.5 67.8 1.71 1.48

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Temperature (°C) Time required to reach % residual strength (days) – PET reinforcement 95% strength 90% strength 85% strength 60 273.1 546.2 819.3 70 99 198 296.9 80 33.8 67.5 101.3 90 10 20.1 30.1

Influence of temperature on creep rupture behaviour, A1

September 2015 Conference & Exhibition Landfill2015

Influence of temperature on creep rupture behaviour, A1 for HDPE

Source: Kasozi et al, 2015

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95.0 95.5 96.0 96.5 97.0 97.5 98.0 98.5 99.0 99.5 100.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 Retained strength T [%] Design life [years]

Hydrolytic Degradation Curve for PET Products

50 °C 20 °C 10 °C

Influence of temperature on chemical degradation, A4

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Effect of temperature on reduction factor for a given design life for PET reinforcement

Design life [years] Design temperature [°C] Retained strength [%] R4/RFCH 100 10 99.5 1.01 100 20 97,3 1.03 100 35 75.5 1.32 100 50 Fail

Influence of temperature on chemical degradation, A4

September 2015 Conference & Exhibition Landfill2015

What happens to the reinforcement design strength if we change the in-situ temperature?

Example B2 (textured gmb with geogrid) Based on a PET geogrid with UTS of 35 kN/m Assume 100 year design life at 35°C in-situ temperature Total load carried by geosynthetics = 10 kN/m 50% load carried by geogrid = 5 kN/m 35 1.61 𝑦 1.2 𝑦 1.0 𝑦 1.32 𝑦 1.0 = 13.7 𝑙𝑂/𝑛 13.7 1.2 = 11.4 𝑙𝑂/𝑛 Increase in-situ temperature from 35°C to 50°C 35 1.71 𝑦 1.2 𝑦 1.0 𝑦 𝐺𝑏𝑗𝑚 𝑦 1.0 = 0 𝑙𝑂/𝑛 Note: Assumes environment for internal hydrolysis

September 2015 Conference & Exhibition Landfill2015

What happens to the reinforcement if we change the in-situ temperature?

Source – ISO 13434 – guidelines on durability

September 2015 Conference & Exhibition Landfill2015

• PVA reinforcement with a higher stiffness modulus (but same ultimate

strength) reduces the relative tensile load acting on the gmb

• PVA is less sensitive to temperature increase than PET in relation to

creep rupture

• PVA appears to be less sensitive to temperature increase than PET in

relation to chemical degradation (research ongoing)

• Simple data acquisition systems to monitor temperature and moisture

conditions in Southern Africa will increase confidence in design

• Accommodations should be made when selecting design tensile

strength to address the corresponding A1 and A4 reduction in strength in relation to an increased temperature. This would help to ensure satisfactory mechanical performance of polymeric reinforcement subjected to elevated temperature conditions

Summary

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Thank you for your attention. Any questions?

Peter er Assinde der

HUESKER Synthetic GmbH, Manager AFRICA

Laura a Ca Carbone ne

HUESKER Synthetic GmbH, Engineering department

Morne ne Breyten ytenbach bach

HUESKER Synthetic GmbH, Manager MINING