Ground Improvement Using Geotextile and Reinforced Earth.pptx
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Geosynthetics; Types of geosynthetics; Geotextiles; Functions of the geotextiles; Design Considerations; Geonets; Geosynthetic clay liners; Mechanical Properties; Mechanisms of reinforced soil structures; Load Carrying Mechanism; RE Wall;
Ground Improvement Using Geotextile and Reinforced Earth.pptx
- 1. Ground Improvement Using Geotextiles and Reinforced Earth Prof. Samirsinh P Parmar Mail: [email protected] Asst. Prof. Department of Civil Engineering, Faculty of Technology, Dharmasinh Desai University, Nadiad, Gujarat, INDIA
- 2. Content of the presentation: • Geosynthetics • Types of geosynthetics • Geotextiles • Functions of the geotextiles • Design Considerations • Geonets • Geosynthetic clay liners • Mechanical Properties • Mechanisms of reinforced soil structures • Load Carrying Mechanism 2
- 3. 3 A planar product manufactured from earth, polymeric or other material used with soil, geotechnical engineering rock, related materials as an or integral part of a man-made project, structure, system Geosynthetics ?
- 4. Types of Geosynthetics Geotextiles Geogrids Geonets Geomembranes Geosynthetic clay liners Geopipes Geocomposites
- 5. They are indeed textiles in the traditional sense, but consist of synthetic fibers rather than natural ones such as cotton, wool or silk. Thus biodegradation is not a problem They are made into a flexible, porous fabric by standard weaving machinery or are matted together in a random, or nonwoven, manner Geotextile ?
- 6. Woven Geotextiles: high tensile strength, modulus and low elongation Non-woven Geotextiles: high permeability because of their high elongation
- 7. Separation Reinforcement Filtration Functions of geotextile Drainage Liquid barrier
- 8. Separation
- 11. Determine critical function Filtration, Reinforcement, Separation or Drainage If Filtration → FOS If Reinforcement → Tensile strength and Modulus If Separation → Survivability Consider long-term performance Design Considerations
- 12. 12 Geogrids are plastics formed into a very open, gridlike configuration i.e. they have large apertures Used primarily as reinforcement of unstable soil and waste masses It is differ from geotextile, as geogrid facilitate interlocking of soil/aggregate particle within their opening. Geogrids ? Biaxial Geogrid Uniaxial Geogrid Woven or Welded Geogrid
- 14. Design Considerations Consider tensile modulus and strength Mechanical interlock with granular fills Damage during construction
- 17. Their design function is completely within the drainage area where they have been used to convey fluids of all types Though they are used for the drainage function but they have high tensile strength Generally used along with one or two geotextile matter one at the top and other at the bottom to prevent soil intrusion Design Considerations: flow rate (whichis preferred to transmissivity), Normal stress, Hydraulic gradient Geonets ? 17 NIT Jamshedpur
- 18. Geomembranes ? The materials themselves are "impervious" thin sheets of rubber or plastic material used primarily for linings and covers of liquid- or solid- storage or disposal facilities Thus the primary function is always as a liquid or vapor barrier Design Considerations: Leakage rates, potential slip-surface on slopes, exposure to long-term environmental agents of weathering (sunlight, air, burrowing rodents
- 19. Seepage barrier
- 20. Geosynthetic Clay Liners (GCLs) ? Geosynthetic Clay Liners (or GCLs) are the newest subset within Geosynthetic materials They are rolls of factory fabricated thin layers of bentonite clay sandwiched between two Geotextiles or bonded to a Geomembrane The engineering function of a GCL is containment as a hydraulic barrier to water, leachate or other liquids and sometimes gases
- 21. Cross-section sketches of GCL
- 22. A Geocomposite consists Geogrid; of a combination of or Geogrid and Geogrid, and Geotextile and Geomembrane; or Geotextile, Geomembrane; or any one of these three materials with another material (e.g., various soils, deformed plastic sheets, steel cables, or steel anchors) The major functions encompass the entire range of drainage, and liquid/vapor barrier Geocomposite ? functions listed for Geosynthetics discussed previously: separation, reinforcement, filtration,
- 23. Geocomposite
- 24. Applications
- 25. Determine the function of the Geosynthetic component in question Determine the required properties (filtration size, in- plane or cross-plane hydraulic flow capacity, required tensile strength and modulus) In specifications, reference required material properties to the standard “INDEX” tests such as Strength (tensile, burst, tear), Filtration Permeability and Drainage capacity (FOS), Summary
- 26. Geosynthetic properties and test methods specific project. Properties of geosynthetics: Physical properties Mechanical properties Hydraulic properties Endurance properties Firstly for any project the design engineers must check the required specifications of geosynthetic materials. Without knowing proper specifications, it difficult to select the correct geosynthetic is very for any
- 27. Mass per unit area (Weight) Thickness Specific gravity Stiffness or flexural rigidity or flexural stiffness Physical Properties:
- 28. Mass per unit area (ASTM D5261) Five test specimens are to be machine (accuracy of 0.01 recorded. weighed in a weighing g) and average value is Test samples are of size 100 mm × 100 mm Unit is expressed as g/m2 The cost of geotextile is directly related to the geotextile . weight of
- 29. Thickness (ASTM D5199) Geotextile s pressures. exhibit different thickness different The thickness is measured to an accuracy of 0.02 mm under a specified pressure of 2.0 kPa. Sample size is 200 mm × 200 mm. The thickness is generally in the range of 0.25 to 8.5 mm. The thickness of geogrids and geomembranes are measured under a normal stress of 20 kPa.
- 31. 31 Specific gravity (ASTM D 792 or D1505) Specific gravity can be defined as ratio of the unit weight of material to the unit weight of distilled water at 4°C. Specific gravity of different geosynthetic materials Materials Sp. Gravity Polypropylene (PP) 0.91 Polyethylene (PE) 0.9 to 0.96 Polyester (PET) 1.22 to 1.38 Polyvinyl chloride (PVC) 1.69 Nylon 1.05 to 1.14
- 32. Stiffness or flexural rigidity or flexural stiffness (ASTM D1388) The geotextile specimen is a 25 mm wide strip. The geotextile is placed along the length of a horizontal plane and bends gravitationally under its own weight on a inclined plane making an angle of 41.5 degree with the horizontal.
- 33. Stiffness of the geotextile = (l/2)3 x w l = length of overhang geotextile and bending length = l/2 (cm), w = mass per unit area (mg/cm2) The unit of stiffness is mg-cm. The minimum stiffness of geotextile depends on the various degree of required workability (Haliburton et al., 1980) The property is important in field workability requirements for installation of geotextile. If the soil is very poor or California bearing ratio value is very less, the stiffness of geotextile required is very high.
- 34. Mechanical Properties Compressibility Tensile strength test of geosynthetics Burst strength test Puncture Resistance Test Penetration resistance test (drop test)/ drop cone (impact strength)/ tear (impact) resistance Tensile behavior of geogrid Tensile strength of Gabions Direct shear test Pullout or anchorage resistance Tensile strength of geomembrane Tear resistance of Geomembrane
- 35. Compressibility Compressibility indicates the reduction in thickness under applied pressure. Compressibility of geotextile depends on its thickness and mass per unit area. As the pressure increases, thickness of non-woven needle- punched (NW-NP) and resin bonded geotextiles gets reduced significantly and accordingly, the transmissivity gets reduced. Compressibility of woven and non-woven heat bonded geotextile (NW-HB) is low. Compressibility of nonwoven needle-punched geotextile plays a very important role as most of the time we use these type of geotextiles to pass the liquid along their plane.
- 36. Variation in thickness of geosynthetics with change in pressur e It is clearly observed that nonwoven needle punched geosynthetics are more compressible.
- 37. Tensile strength Wide width tensile strength (ASTM D4595 and ISO 10319) Very wide width tensile strength test Narrow strip tensile strength (ASTM D4751) Sewn seam strength of geotextile (ASTM D4884 and ISO 13426) Grab tensile strength (ASTM D4632) Trapezoidal tear strength test
- 38. Wide width tensile strength (ASTM D4595)
- 39. The machine strain rate is 10 ± 3 %. The reason for the necessity of wide-width specimens is that geotextiles (particularly non-woven) achieve high poison’s ratio value from narrow strip test. Tensile strength of geotextile (Tgeotextile) can be expressed as force per unit width of geotextile. Fb/ W (kN/m) Fb = Observed
- 40. Size of sample for very wide width test Very wide width tensile strength test For design purpose, the very wide width tensile test is not recommended.
- 41. Narrow strip tensile strength (ASTM D 1682) Tensile strength appears low compared to wide width tensile strength test. Not recommended as design value. Size of test sample with the test assembly
- 42. Tensile modulus: Different tensile modulus from typical stress-strain curves
- 43. Tensile strength vs. strain curves for different geotextiles
- 44. Sewn seam strength of geotextile (ASTM D4884 and ISO 13426) (After Diaz, 1985) Size of test sample for sewn seam strength Strain rate =10 ± 3 %/ min, Unit in kN/m Butterfly seam is recommended for 44
- 45. Main strong reasons for exploring this exciting new engineering construction material in civil engineering are as follows: Excellent stress-strain behavior Good flexibility Excellent filtration characteristics High water permeability Excellent mechanical properties Can be welded together Does not form by-products High resistance to climate condition High resistance to chemical and biological attack Chemically ultraviolet stabilized Time, cost, rapid construction, environment friendly, sustainability and durability
- 46. Mechanisms of reinforced soil structures Region A & C,direct shear tests canbe employed to quantify bond. soil–reinforcement Region B, plane strain test similar to the in-soil tensile test can be used. Region D, pull-out tests would be applicable. Interaction mechanisms in a geosynthetic reinforced soil wall (Marques and Palmeira 2009)