Geosynthetics

A presentation on Geosynthetics, their properties and applications.

1. GEOSYNTHETICS 1 ANIRUDHAN K M LECTURER IN CIVIL ENGINEERING

2. Geosynthetics A planar product manufactured from polymeric material used with soil, rock, earth , or other geotechnical engineering related material as an integral part of a man-made project, structure, or system. 2

3. Types of Geosynthetics Geotextiles Geogrids Geonets Geomembranes Geosynthetic clay liners Geocells /geo web members GeoPipes Geofoam Geocomposites 3

4. Types of Geosynthetics 4

5. GeoTextiles Flexible, textile-like fabrics of controlled permeability Continuous sheets of woven, nonwoven, knitted or stitch-bonded fibres or yarns. The sheets are flexible and permeable and generally have the appearance of a fabric. Geotextiles are used for separation, filtration, drainage, reinforcement and erosion control applications. Used i n soil, rock and waste materials 5

6. GeoTextiles Woven geotextile : Produced by interlacing, usually at right angles, two or more sets of yarns (made of one or several fibres ) or other elements using a conventional weaving process with a weaving loom. Nonwoven geotextile A geotextile produced from directionally or randomly oriented fibres into a loose web by bonding with partial melting, needle-punching, or chemical binding agents (glue, rubber, latex, cellulose derivative, etc .). 6

7. GeoTextiles Knitted geotextile P roduced by inter-looping one or more yarns (or other elements ) together with a knitting machine, instead of a weaving loom. Stitched geotextile A geotextile in which fibres or yarns or both are interlocked/bonded by stitching or sewing. 7

8. GeoTextiles (L) woven monofilament (R) calendered woven monofilament (L) woven multifilament (R) woven slit film (L) nonwoven needle-punched (R) nonwoven heat-bonded 8

9. GeoTextiles 9

10. GeoGrids Stiff or flexible polymer grid-like sheets with large apertures Used primarily as reinforcement of unstable soil and waste masses Geogrids are either stretched in one or two directions or made on weaving machinery by unique methods . 10

11. GeoGrids extruded – (i) uniaxial (ii) biaxial; (b) Bonded (c) woven . 11

12. GeoGrids Uniaxial geogrid Produced by the longitudinal stretching of a regularlypunched polymer sheet Possesses a much higher tensile strength in the longitudinal direction than the tensile strength in the transverse direction. Biaxial geogrid Produced by stretching in both the longitudinal and the transverse directions of a regularly punched polymer sheet Possesses equal tensile strength in both the longitudinal and the transverse directions. 12

13. GeoNets Stiff polymer net-like sheets with in-plane openings Used primarily as a drainage material within landfills or in soil and rock masses Formed by two sets of coarse, parallel, extruded polymeric strands intersecting at a constant acute angle . Rhombus Shaped Apertures The network forms a sheet with in-plane porosity Functions to perform the in-plane drainage of liquids or gases 13

14. GeoNets 14

15. GeoNets 15

16. GeoMembranes Used as barriers for liquid or solid waste containment Planar - Relatively impermeable, synthetic sheet manufactured from materials of low permeability to control fluid migration in a project as a barrier or liner The materials may be polymeric or asphaltic or a combination thereof. The term barrier applies when the geomembrane is used inside an earth mass. The term liner is usually reserved for the cases where the geomembrane is used as an interface or a surface revetment . 16

17. GeoMembranes 17

18. GeoMembranes 18

19. Geosynthetic Clay Liners Prefabricated bentonite clay layers incorporated between geotextiles and/or geomembranes A geosynthetic clay liner is a manufactured hydraulic barrier Used as alternative material to substitute a conventional compacted soil layer For the low-permeability soil component of various environmental and hydraulic projects including landfill and remediation projects It consists of a thin layer of sodium or calcium bentonite (mass per unit area ≈ 5 kg/m 2 ) Bentonite sandwiched between two sheets of woven or nonwoven geotextiles or mixed with an adhesive and attached to a geomembrane . The sodium bentonite has a lower hydraulic conductivity. 19

20. Geosynthetic Clay Liners 20

21. GeoCells Relatively thick, three-dimensional networks constructed from strips of polymeric sheet . The strips are joined together to form interconnected cells that are infilled with In some cases 0.5 m to 1 m wide strips of polyolefin geogrids have been linked together with vertical polymeric rods used to form deep geocell layers called geomattresses . 21

22. GeoCells 22

23. GeoCells 23

24. GeoCells 24

25. GeoPipes Perforated or solid wall polymeric pipes Used for the drainage of various liquids Plastic pipe (smooth or corrugated with or without perforations) placed beneath the ground surface and subsequently backfilled 25

26. GeoFoams Geofoam blocks or slabs are created by expansion of polystyrene foam Low-density network of closed, gas-filled cells. Used for thermal insulation, as a lightweight fill or as a compressible vertical layer to reduce earth pressures against rigid walls. Manufactured by the application of the polymer in semi-liquid form through the use of a foaming agent Lightweight material in slab or block form with high void content Usage as lightweight fills, thermal insulators and drainage channels. 26

27. GeoComposites Hybrid systems of any of the different geosynthetic types Which can function as specifically designed for use in soil, rock, waste and liquid related problems 27

28. Classifications 28

29. Functions of Geosynthetics Separation - Prevent the mixing of two different soils or materials (using geotextiles, geocomposites ) Reinforcement - Provide tensile forces in the soil (using geogrids , and geotextiles) Confinement - Restrain the lateral movement of a soil mass geocells Filtration - Allow the passage of fluids preventing the migration of soil particles(geotextiles, geocomposites ) Drainage - Transport of fluids ( geonets , geocomposites ) Barrier or Containment - Fluid barrier (using Geomembranes , geocomposites ) Erosion Control - Avoid the detachment and transport of soil particles by rain , runoff and wind; root anchorage using geomats , geocells , biomats , bionets Protection - Avoid damages to a structure , a material or another geosynthetic (using nonwoven geotextiles, geonets , geocomposites ) 29

30. Functions of Geosynthetics Separation Prevention of intermixing of adjacent dissimilar soils and/or fill materials during construction and over a projected service lifetime Provided at the soil subgrade level in pavements or railway tracks to prevent pumping of soil fines into the granular subbase /base course and/or to prevent intrusion of granular particles into soil subgrade. Basic mechanism involved in the separation function: (a) granular fill–soft soil system without the geosynthetic separator; (b) granular fill–soft soil system with the geosynthetic separator . 30

31. Functions of Geosynthetics Reinforcement A geosynthetic performs the reinforcement function by improving the mechanical properties of a soil mass as a result of its inclusion . Reinforced soil posses high compressive and tensile strength (and similar, in principle, to the reinforced concrete ) 31

32. Functions of Geosynthetics Filtration A geosynthetic may function as a filter that allows for adequate fluid flow with limited migration of soil particles across its plane over a projected service lifetime. When a geosynthetic filter is placed adjacent to a base soil (the soil to be filtered), a discontinuity arises between the original soil structure and the structure of the geosynthetic . This discontinuity allows some soil particles, particularly particles closest to the geosynthetic filter and having diameters smaller than the filter opening size 32

33. Functions of Geosynthetics Drainage If a geosynthetic allows for adequate fluid flow with limited migration of soil particles within its plane from surrounding soil mass to various outlets 33

34. Functions of Geosynthetics Barrier A geosynthetic performs the fluid barrier function, if it acts like an almost impermeable membrane to prevent the migration of liquids or gases over a projected service lifetime 34

35. Functions of Geosynthetics Barrier 35

36. Functions of Geosynthetics Erosion Control A geosynthetic provides surface stabilization when it is placed on a soil surface to restrict movement and prevent dispersion of surface soil particles subjected to erosion actions of rain and wind, often while allowing or promoting growth of vegetation. A geosynthetic provides vegetative reinforcement and controls erosion of Soil 36

37. Functions of Geosynthetics Protection A geosynthetic , placed between two materials, performs the protection function when it alleviates or distributes stresses and strains transmitted to the material to be protected against any damage 37

38. Functions of Geosynthetics 38

39. Functions of Geosynthetics 39

40. Applications 40

41. Applications 41

42. Applications 42

43. Applications 43

44. Applications 44

45. Applications 45

46. Applications 46

47. Applications 47

48. Applications Geosynthetics in Walls 48

49. Applications Geosynthetics in Waste Water Treatment 49

50. Properties of Geosynthetics Physical Properties Specific gravity Unit mass (weight) Thickness Stiffness Some more physical properties which are important for geogrids and geonets Type of structure Junction type Aperture size and shape Rib dimensions Planar angles made by intersecting ribs and vertical angles made at the junction point . The physical properties are more dependent on temperature and humidity 50

51. Properties of Geosynthetics Physical Properties Specific gravity Determined by the displacement method. In case of geomembranes , a known mass is weighed in air and then in water. Given by the ratio of its weight in air to the difference between its weight in air and in water. Specific gravity is widely used in geomembrane identification and quality control 51

52. Properties of Geosynthetics Physical Properties Specific gravity 52

53. Properties of Geosynthetics Physical Properties Mass per Unit Area Usually given in units of gram per square metre (g/m 2 ) It is determined by weighing square or circular test specimens of known dimensions (generally area not less than 100 cm 2 ). Linear dimensions should be measured without any tension in the specimen. For commonly used geo-synthetics, it varies in order of 100 to 1000 g/m 2 . Unit weight of geo-textiles< Unit weight of geomembranes may have substantially larger values of mass per unit area, even up to several thousands grams per square metre . It should be measured to the accuracy nearest to 0.01 % of total specimen weight. Fabric cost is directly related to mass per unit area (Unit weight). Important for Economy of a project. Codes Used ASTM D5261-92 (Reapproved 1996) ASTM D5993-99 ASTM D6566-00 BS EN 965-1995 CAN/CGSB 148.1 No. 2-M85 IS 14716-1999 ISO 9864-1990 53

54. Properties of Geosynthetics Physical Properties Thickness The thickness of a geosynthetic is the distance between its upper and lower surfaces, measured normal to the surfaces at a specified normal compressive stress. Generally 2.0 kPa for geotextiles and 20 kPa for geogrids and geomembranes . Measured to the accuracy of 0.02mm Thickness varies in between 0.25mm to 7.5mm Thickness is important for permittivity (c/s plane)and Transmissivity (in-plane) Codes Used ASTM D5199-01 ASTM D5994-98 ASTM D6525-00 CAN/CGSB 148.1 No. 3-M85 BS EN 964 (Part 1)-1995 IS 13162 (Part 3)-1992 ISO 9863 (Part 2)-1996 54

55. Properties of Geosynthetics Physical Properties Stiffness It is ability to resist flexure (bending) under its own weight It can be measured by its capacity to form a cantilever beam without exceeding a certain amount of downward bending under its own weight. The stiffness of a geosynthetic indicates the feasibility of providing a suitable working surface for installation. Codes Used CAN/CGSB 148.1 No. 2-M85 IS 14716-1999 ISO 9864-1990 55

56. Properties of Geosynthetics Mechanical Properties Compressibility Tensile strength 56

57. Properties of Geosynthetics Mechanical Properties Compressibility Is very important for nonwoven geotextiles , because they are often used to convey liquid within the plane of their structure. Compressibility can be studied by applying compressive stress, by placing the geosynthetic between two plates and constant stress applied. 57

58. Properties of Geosynthetics Mechanical Properties Tensile strength Determination Tensile test on a 200-mm wide geosynthetic strip with a gauge length of 100 mm. Entire width of a 200-mm wide geosynthetic specimen is gripped in the jaws of a tensile strength testing machine and it is stretched in one direction at a prescribed constant rate of extension until the specimen ruptures (breaks). 58

59. Properties of Geosynthetics Endurance Properties Creep Durability Abrasion Long Term Flow Characteristics 59

60. Properties of Geosynthetics Endurance Properties Creep Creep is the time-dependent increase in accumulative strain or elongation in a geosynthetic resulting from an applied constant load. Test for determining the creep behaviour of a geosynthetic . 200 mm wide specimen. Load applied using weights, or mechanical, hydraulic or pneumatic systems. Test duration : 100 h. For a full analysis of creep properties, durations of 10,000 h will be necessary. 60

61. Properties of Geosynthetics Endurance Properties Durability The durability of a geosynthetic may be regarded as its ability to maintain requisite properties against environmental or other influences over the selected design life. 61

62. Properties of Geosynthetics Endurance Properties Abrasion Abrasion of a geosynthetic is defined as the wearing away of any part of it by rubbing against a stationary platform by an abradant with specified surface characteristics. The ability of a geosynthetic to resist wear due to friction or rubbing is called abrasion resistance. 62

63. Properties of Geosynthetics Endurance Properties Long Term Flow Characteristics The compatibility between the pore size openings of a geotextile and retained soil particles in filtration and/or drainage applications can be assessed by the gradient ratio test. This test is basically used to evaluate the clogging resistance of geotextiles with cohesionless soils (having a hydraulic conductivity/permeability greater than 5 x10-4 m/s) under unidirectional flow conditions. 63

64. Properties of Geosynthetics Survivability Properties Tearing strength Static puncture strength Impact strength (dynamic puncture strength) Bursting strength Fatigue strength Friction Behaviour 64

65. Properties of Geosynthetics Survivability Properties Tearing strength The ability of a geosynthetic to withstand stresses causing to continue or propagate a tear in it, often generated during their installation. The tearing strength of geotextiles under in-plane loading is determined by trapezoid tearing strength test. 65

66. Properties of Geosynthetics Survivability Properties Static puncture strength 66

67. Properties of Geosynthetics Survivability Properties Impact strength (dynamic puncture strength ) 67

68. Properties of Geosynthetics Survivability Properties Bursting strength Common test called as Mullen burst test. 68

69. Properties of Geosynthetics Survivability Properties Fatigue strength Specimen is stressed longitudinally at constant rate of extension to a predetermined load (less then failure load) and then back to lower zero load. This cycling is repeated until failure occurs. ower stress failure --- Larger number of cycles required. Examples: seismic load, rail road loadings, wave and tidal action. 69

70. Properties of Geosynthetics Survivability Properties Friction Behavior It is important that the bond developed between the soil and the geosynthetic is sufficient to stop the soil from sliding over the geosynthetic or the geosynthetic from pulling out of the soil when the tensile load is mobilized in the geosynthetic . Direct Shear Test Pull Out Test 70

71. Properties of Geosynthetics Hydraulic Properties Porosity Permittivity Transmissivity The voids (or holes) in a geosynthetic are called pores or openings. The measurement of sizes of pores and the study of their distribution is known as porometry . 71

72. Properties of Geosynthetics Hydraulic Properties Porosity 72

73. Properties of Geosynthetics Hydraulic Properties Permittivity Cross Plane Permeability Typical test arrangements of constant head in-plane water flow apparatus: (a) full width flow; (b) radial flow. 73

74. Properties of Geosynthetics Hydraulic Properties Transmissivity In Plane Permeability 74

75. Reinforced Earth 75

76. Reinforced Earth A geosynthetic performs the reinforcement function by improving the mechanical properties of a soil mass as a result of its inclusion . When soil and geosynthetic reinforcement are combined, a composite material, ‘ Reinforced Soil ’, possessing high compressive and tensile strength (and similar, in principle, to the reinforced concrete) is produced. In fact, any geosynthetic applied as reinforcement has the main task of resisting applied stresses or preventing inadmissible deformations in geotechnical structures. In this process, the geosynthetic acts as a tensioned member coupled to the soil/fill material by friction, adhesion, interlocking or confinement and thus maintains the stability of the soil mass 76

77. Reinforcing Elements 77

78. Reinforcing Elements The reinforcing elements (strip, grid or sheet, fabricated from metals or geosynthetics ) Facing units to prevent the soil from erosion (Pre-cast concrete panels, metal sheets and plates, gabions, welded wire mesh, shotcrete , wrapped sheets of geosynthetics ) Backfill materials (local soils, specified soils, marginal materials) 78

79. Reinforcing Elements 79

80. Applications 80

81. Applications 81

82. Structures with Vertical Faces 82

83. Structures with Vertical Faces 83

84. Structures with Vertical Faces 84

85. THANK YOU 85