Geotechnical Engineering

DHARM

718 GEOTECHNICAL ENGINEERING

1. Fluid Transmission: A geosynthetic provides fluid transmission when it collects a
   liquid or a gas and conveys it towards an outlet within its own plane. Permeability is the key
   property of the geosynthetic here.


2. Filtration: A geosynthetic acts as a filter when it allows liquid to pass normal to its
   own plane, while preventing most soil particles from being away by the liquid current. Perme-
   ability and continuity are the key properties of the geosynthetic here.


3. Separation: A geosynthetic acts as a separator when placed between a fine soil and
   a coarse material. It prevents the fine soil and the coarse material from mixing under the
   action of repeated applied loads. ‘Continuity’ is the key property of the geosynthetic here.


4. Protection: A geosynthetic protects a material when it alleviates or distributes
   stresses and strains transmitted to the protected material. Two cases may be considered–

(a) Surface protection—a geotextile, placed on the soil prevents its surface being dam-
aged by weather, light traffic, etc.

(b) Interface protection—a geotextile, placed between two materials (such as asphalt
overlay/cracked pavement, or geomembrane/stony ground) from being damaged by the large
stresses or strains imposed by the other material. Continuity is the key property of the geotextile
here.

5. Reinforcement: A geosynthetic can provide tensile strength to a soil through inter-
   face shear strength (i.e., friction, cohesion/adhesion, and/or interlocking between geotextile
   and soil). It can also act as a tensioned membrane when it is placed between two materials, its
   tension balancing the pressure difference between them; this, in effect, is the reinforcement
   function of the geosynthetic, the key property being its tensile strength.


6. Wrapping: Specially fabricated geosynthetics, filled with sand, act as construction
   elements using the soil material at the site. This is the wrapping function, the key property
   being again the tensile strength.

Applications of geosynthetics

The following is a brief list of the broad fields of application

1. Hydraulic Words: Coastal works, bank and shore protection, canal and river works,
   and earth dams.


2. Earth Works: Dams on poor foundation, erosion control and retaining structures.


3. Traffic Structures: Paved and unpaved roads on poor subgrades, highway embank-
   ments, railway structures, and tunnels.


4. Pollution Control: Pond linings, and solid waste disposal; and,


5. Drainage: Agriculture, soil stabilization, and vertical drains.

IB.8 Illustrative Examples

Example 17.1: Following are the results obtained in a CBR test. Determine the CBR value:

Penetration (mm) 0.60 1.20 1.80 2.40 3.60 4.80 7.20

Load (kN) 3.2 5.0 6.4 7.3 8.5 9.4 10.6

(S.V.U—Four-year B.Tech.—Apr., 1983)