State-of-the-Art on the Applications of Geosynthetics for Dam Repair and Rehabilitation

Transcription

1 State-of-the-Art on the Applications of Geosynthetics for Dam Repair and Rehabilitation K. Rajagopal and D. N. Arnepalli Department of Civil Engineering Indian Institute of Technology Madras

2 According to ASTM (D 4439): Introduction to Geosynthetics A planar/three dimensional product manufactured from polymeric material used with geomaterials or other civil engineering related material as an integral part of a structure (Natural materials : Jute and Coir are considered to be geonaturals) Wide Array of Applications: Geotechnical Engineering Geoenvironmental Engineering Transportation Engineering Hydraulic Engineering Reasons for Explosion: Quality-control manufactured in factory environment Can be installed very rapidly Generally replace raw material resources Generally replace difficult designs using soil/construction material Use is required to meet stringent regulations in some cases (Eg: sub title-d, PCB) Cost competitive

3 Types of Geosynthetics Geomembrane (Barrier) Geosyn. Clay Liner (Barrier) Geosynthtic composite liner (Barrier) Uniaxial / biaxial Geogrid (Reinforcement) Woven Geotextiles (Reinforcement) nonwoven Geotex. (Filter/protection) Geonet (Drain) Geocomposite Drain Pictures adapted from Shukla, 2010 and Koerner, 2005 Geocell (Reinforcement) Geocell (Erosion control)

4 Geosynthetics-Primary Function Type of Geosynthetic Primary Function Separation Reinforcement Filtration Drainage Barrier Geotextile (GT) Geogrid (GG) Geonet (GN) Geomembrane (GM) Geosynthetic Clay Liner (GCL) Geopipe (GP) Geofoam (GF) (Low BC) Geocomposite (GC)

5 Growth of Geosynthetics in North America (Koerner, 2000)

6 Geosynthetics in Dam Application as Barrier Contrada Sabetta Rockfill Dam, Italy (Cazzuffi, 1987 and ICOLD, 19919)

7 Geosynthetics in Dam Application as Barrier 1. Concrete slab of 200 mm thick 2. One sheet of bituminous paper-felt and two sheets of polyisobutylene geomembrane (2 mm thick) and bituminous adhesive 3. Porous concrete of 2 m thick 4. Reinforced concrete slabs of 250 mm thick 5. Dry masonry of 2 to 3 m thick 6. Joint between plinth and upstream facing 7. Concrete diaphragm wall 8. Concrete plinth 9. Gallery Contrada Sabetta Rockfill Dam, Italy (Cazzuffi, 1987 and ICOLD, 19919)

8 Geosynthetics in Dam Application as Barrier Contrada Sabetta Rockfill Dam, Italy (Cazzuffi, 1987 and ICOLD, 19919)

9 1. Clayey silt core 2. Filters 3. Transitions 4. Rockfill 5. Rip rap Geosynthetics in Dam Application as Barrier 6. Cofferdam (with upstream face 1:2 and downstream face 1:1.5) 7. PVC geomembrane (t GM = 1.2 mm) and PP geotextile (μ = 350 g/m2) Bilancino Zoned Embankment Dam, Italy (Baldovin, 1993)

10 Geosynthetics in Dam Application as Filter/Drain First compacted layer Second compacted layer La Parade Homogeneous Earthfill Dam, France (Navassartian, 1993)

11 Geosynthetics in Dam Application as Filter/Drain The Hans Strijdom Zoned Rockfill Dam, South Africa (Hollingwarth and Druyts, 1982)

12 Geosynthetics in Dam Application as Reinforce./ Barrier The Maraval Earth Dam, France (Kern, 1977)

13 Geosynthetics in Dam Application as Reinforce./ Barrier The Maraval Earth Dam, France (Kern, 1977)

14 Role of Geosynthetics in Dam Application A Typical Failure Mechanism Induced by Overtopping (A) First Phase, (B) Second Phase And (C) Third Phase (Croce, 1989)

15 Geosynthetics in Dam Application as Reinforce./ Barrier The Moochalabra Zoned Rockfill Dam, Australia (Johnson, 1973)

16 Ageing Mechanisms & Impact on Longterm Performance Deterioration and dissolution of polymers when exposed to aggressive Chemicals Physical ageing (change in crystallinity with no breaking of covalent bonds) Chemical ageing (leads to covalent bond breaking) Swelling PHOTO DEGRADATION (to impede carbon black is added) OXIDATION (to retard/delay antioxidants added)

17 Photo Degradation Mechanism Prolonged exposure of geomembrane to sunlight can cause Chain scission Discoloration, surface stress cracking and brittleness Results in loss of physical and mechanical properties To understand photo degradation mechanism Field natural/accelerated test (Fresnel solar concentrator) Laboratory accelerated test (Xenon arc & Fluorescent lamp)

18 Field Natural or Accelerated Test Exposure Rack for Field Natural Weathering of Material

19 Weather Station Pyranometer Total solar UV radiometer A Typical Field Natural Weather Site may have.

20 Irradiance (W/m 2 /nm) Sun light UVA-340 Wave length (nm) Spectral distribution of UVA- 340 Fluorescent lamp and sunlight (ASTM D154, 2006)

21 Sample Racks Spray Nozzles for Rain Effect Booster Pump and Supply Tank Touch Screen Control Panel Calibration Unit Features of UV Weatherometer

22 Polymer Oxidation Cycle O 2 ROH+H 2 O RH I I RH II R A ROO RO + OH B I II ROOH RH RH R Polymer chain Free radical ROO Hydroperoxy radical ROOH Hydroperoxide I Primary antioxidants (Hsuan et al., 1995) II Secondary antioxidants

23 Conceptual Three Stage Chemical Ageing of HDPE GM Percent Property Retained (%) T 2 T 1 Service Life= T 1 +T 2 +T 3 T T 1 = Time to deplete antioxidants T 2 = Induction time to the onset of polymer degradation T 3 = Time for degradation of polymer (to decrease physical property) Temperature ( o C) Service Life (Rowe, 2005) to 1830 Y to 370 Y to 90 Y Log time

24 Summary and Concluding Remarks Geosynthetics successfully used in rehabilitation and new construction of dams Geosynthetics have allowed reductions in volumes of natural materials used in the dams The long term performance of dam depends on durability of the geosynthetic materials Photo degradation and Oxidation seems to be the major degradation mechanisms by which HDPE geosynthetic material ages Three stage conceptual model can be employed to predict the service life of the geosynthetic material under realistic simulated conditions

25 State-of-the-Art on the Applications of Geosynthetics for Dam Repair and Rehabilitation K. Rajagopal and D. N. Arnepalli Department of Civil Engineering Indian Institute of Technology Madras

26 Geosynthetics in Dam Application as Reinforce./ Barrier The Davis Creek earth dam, USA (Hensley, 1989)

27 Geosynthetics in Dam Application as Barrier 1. Rockfill (up to 1 m size) 2. Inspection and drainage gallery 3. Sand and gravel layer (2 m thick, mm grain size) 4. Gravel layer (0.15 m thick, mm grain size) 5. Cold premix layer (50 mm thick, 6 12 mm grain size) 6. Geotextile (μ = 400 g/m 2 ) bonded to geomembrane 7. PVC geomembrane (t GM = 2.0 mm) 8. Geotextile (μ = 400 g/m 2 ) 9. Concrete slabs (0.14 m thick, m 2 size) The Codole Rockfill Dam, France (ICOLD, 1991)