(SEM VII) THEORY EXAMINATION 2022-23 GEOSYNTHETICS AND REINFORCED SOIL STRUCTURE

SECTION A – Short Answers (2 Marks Each)

(a) Latest trends in geosynthetics

Recent trends include high-strength geogrids, smart geosynthetics with sensors, biodegradable geosynthetics, improved polymer blends, and use of geosynthetics in sustainable and green construction.

(b) Geomembrane

A geomembrane is a low-permeability geosynthetic liner used to control fluid or gas migration in engineering structures.

(c) Role of polymers in geosynthetics

Polymers provide strength, durability, chemical resistance, flexibility, and long service life to geosynthetic products.

(d) Functions of geosynthetics

Geosynthetics perform separation, reinforcement, filtration, drainage, barrier, and erosion control functions.

(e) Types of geosynthetics

Major types include geotextiles, geogrids, geomembranes, geonets, geocomposites, and geocells.

(f) Raw materials for soil reinforcement

Steel strips, polymeric strips, geogrids, geotextiles, fibers, and metallic meshes are commonly used.

(g) Surface treatment of slopes

Surface treatments include vegetation cover, stone pitching, shotcrete, erosion control mats, and turf reinforcement mats.

(h) Failure modes of soil-reinforcement system

Failure may occur due to pullout failure, tensile rupture of reinforcement, sliding, bearing capacity failure, or global slope failure.

(i) Earth pressure

Earth pressure is the lateral pressure exerted by soil on retaining structures due to its self-weight and surcharge.

(j) Erosion control products

Products include erosion control blankets, turf reinforcement mats, geotextiles, geocells, and biodegradable mats.

SECTION B – Long Answers (10 Marks Each)

(a) Basic functions of geosynthetics

Geosynthetics provide separation between soil layers, reinforcement to improve strength, filtration to allow water flow while retaining soil, drainage to carry water away, barrier function to prevent leakage, and erosion control to protect soil surfaces.

(b) Geotextiles best suited for drainage

Non-woven geotextiles are best suited for drainage applications due to their high permeability, thickness, and good water flow capacity.

(c) Mechanisms of soil reinforcement

Soil reinforcement works through frictional resistance, confinement effect, tension membrane action, and improvement of stress distribution within soil mass.

(d) Shear strength of reinforced soil

Reinforced soil exhibits higher shear strength than unreinforced soil due to interaction between soil and reinforcement. Actual strength is generally higher than theoretical predictions due to confinement and interlocking effects.

(e) Failure modes of retaining walls

Retaining walls may fail due to sliding, overturning, bearing capacity failure, structural failure, or global instability of the reinforced soil mass.

SECTION C – Long Answers (10 Marks Each)

(3a) Role of geosynthetics in landfills

Geosynthetics are used as liners, covers, drainage layers, and filters in landfills. They prevent leachate leakage, control gas movement, and enhance environmental protection.

(3b) Natural geosynthetics

Natural geosynthetics include jute, coir, bamboo, and other biodegradable fibers. They are eco-friendly, cost-effective, and suitable for temporary erosion control and slope stabilization.

(4a) Economic aspects of reinforced earth

Reinforced earth structures reduce construction cost, require less excavation, use locally available materials, reduce maintenance, and provide faster construction compared to conventional retaining structures.

(4b) Foundation stability and bearing capacity failure

During steep slope construction, failure may occur due to inadequate bearing capacity, excessive settlement, or shear failure. Proper reinforcement and foundation treatment improve stability.