GEOSYNTHETICS AND REINFORCED SOIL STRUCTURES Different Types of Geosynthetics and Their Applications K. Rajagopal, Professor Department of Civil Engineering IIT Madras, Chennai e-mail: gopalkr@iitm.ac.inac in
RECAP OF PREVIOUS LECTURE Introduction Historical background Early applications Functions of geosynthetics Types of geosynthetics 2/52
OUTLINE OF 2 nd LECTURE TYPES of geosynthetics ----CONTINUED TYPICAL APPLICATIONS 3/52
TYPES OF GEOSYNTHETICS Geotextiles Geogrids Geonets Geomembranes Pre-fabricated vertical drains (PVD) Geosynthetic Clay Liner (GCL) Geocells (3-d confinement) Geocomposites & Geo-others 4/52
GEONETS Geonets are also planar products Consists of ribs in two directions Apertures are of diamond shape Ribs in the two directions are at different planes Thickness of geonets is larger than that of geogrids Geonets are also referred to as geospacers 5/52
TYPICAL GEONETS Ribs at two horizontal planes 6/52
GEONET APPLICATIONS Erosion control ribs act as small check dams to slow down the surface runoff decreases erosion potential of water Drainage layers water flows along the geonet because of large thickness 7/52
Boulder net laid on Konkan railway line in Western ghats functions as guide for loose boulders and vegetation support 8/52
Laying of boulder net Vegetation growth after two seasons Courtesy: M/s Garware Wall Ropes Ltd., Pune 9/52
Anchor trench at the top of the slope, 1m deep, 0.5m wide, filled with soil 10/52
GEOMEMBRANES Thick impervious plastic sheets Thickness.5 mm to 3 mm approximately To contain liquids and gases Rough surface texture t Smooth double sided membrane 11/52
Landfill lining Canal lining Tunnel lining APPLICATIONS OF GEOMEMBRANES 12/52
Geomembrane in a landfill 13/52
Canal lining using geomembranes Concrete lining of surface geomembrane Anchor trench 14/52
Tunnel lining for moisture protection ti 15/52
Pre-fabricated vertical drains to accelerate the pre-consolidation T c d v 2 T d cv t T v of soft clay soils t T v f (U %) v 2 T v = time factor t = time c v = coefficient of consolidation d = drainage path length U% = degree of consolidation 16/52
Reducing the flow path length to accelerate rate of consolidation surcharge fill Highly permeable drainage medium 17/52
PVDs for pre-consolidation L Corrugated plastic core for drainage t Geotextile filter 18/52
Pore water flows laterally to the wick drains and is carried through the core Connection arrangements for wick drain installation 19/52
Installation of PVDs at a construction site notice the connection of PVD with the anchor plate 20/52
PVD being pushed into the ground 21/52
General view after installation of PVD s at a site 22/52
Geosynthetic Clay Liners Consist of a core of bentonite clay sandwiched between layers of thick nonwoven geotextile Applied below and above geomembrane layers in landfills Self-repair mechanism Bentonite expands when flid leaks through punctured geomembrane closes the gap 23/52
Geosynthetic Clay Liner Geotextile layers dry bentonite powder 24/52
GEOCELL 3d confinement product Plan view showing the mechanism of confinement Iso-metric view of a geocell layer 25/52
Photograph of an expanded geocell 26/52
Advantages Easy to transport Any fill material can be used All round confinement to soil Semi-rigid layer (very stiff support) Spreads loads over a large area Excellent support even under cyclic loads. 27/52
APPLICATIONS Erosion control Steep slopes and retaining walls Sub-base b support Road bases Railway tracks Container yards 28/52
Use of geocells for construction of unpaved road Factory Preparation of ground Stapling Sap to ojoin different geocells Stretching of the geocell layer Stone aggregate filled in geocell pockets Compaction by a 10 tonne roller 29/52
Geocells used for construction of a steep slope 30/52
Vegetation taking root through geocell pockets 31/52
IITM students standing on a geocell supported soil 32/52
Typical Container yard heavy loads, usually constructed on soft marine clays near the shore 33/52
Typical mud wave formation in container yards due to heavy loads and extremely soft subgrade soil 34/52
Geotextile separator being laid on the ground surface at a container yard 35/52
Geocell layer laid on the geotextile separator and filled with stone aggregate 36/52
Container yard 3 years after geocell treatment 37/52
Some more pictures of the same yard Perfectly level surface minor damage in paver blocks 38/52
Polymeric erosion control mats 39/52
Geocomposites Combination of two different types of geosynthetics to take advantage of each 40/52
Geo-others Geodrains Lightweight fills Geopipes Geotextile til bags & soil encapsulation Gabions Geosynthetic Encased Stone Columns Many others left to the imagination of engineers 41/52
Drainage boards for use in Retaining Walls 42/52
Light-weight fill cum drainage medium Thick medium made of polystyrene beads 43/52
Gabions filled with stones 44/52
Gabions filled with sand bags SAND FILLED GEOBAGS PLACEMENT OF GEOBAGS TYING OF ROPE GABIONS FINAL VIEW 45/52
Light-weight drainage medium Made of used rubber tyres and other industrial wastes 46/52
Encased Stone Column Bearing capacity enhanced by Passive pressure + Geosynthetic Additional encasement confinement Stone column Sectional plan 47/52
Construction of Encased Stone Column Alexiew et al. (2005) 48/52
Courtesy: Dipl.-Ing. Holger Pohlmann Naue Fasertechnik GmbH & Co. KG Present study 49/52
Load settlement curve for stone columns encased in non-woven geotextile t (mm) Se ettlemen 0 10 20 30 40 50 Pressure (kpa) 0 100 200 300 400 ESC - 50 mm ESC - 75 mm ESC - 100 mm OSC - 50 mm OSC - 75 mm OSC - 100 mm Clay 50/52
Latest Trends Vacuum consolidation Encased stone columns Electro Kinetic geosynthetics 51/52
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