Geosynthetics

Geotechnical Engineering

Geosynthetics

Overview of Geosynthetics

1.1 Introduction
1.2 Historical Development
1.3 Types of Geosynthetics

1.1 Introduction

The application of geosynthetics in different civil engineering constructions like road construction, hydraulic construction, playgrounds, land fill and even in building construction is gradually increasing to solve different geotechnical problems as shown in Figure 1.1.




















Figure 1.1: Application of geosynthetics in civil engineering works

1.2 Historical Development

The application of different natural materials for the reinforcement of soft soil like tree trunks, branches, straw, grass etc has been started from prehistoric time. This technology was also used in the construction of Great Wall of China (see Figure 1.2). This technology is still using to stabilize soft soils.

Figure 1.2: Soil reinforcement technology used in Great Wall of China.

The major achievement in geotechnical engineering was taken place when the natural reinforcing materials could be replaced by similar quality and cost effective artificial synthetic material. The following graphs show the boom of market of geosynthetics immediately after its development.

Figure 1.3: Estimated geosynthetics market in North America

1.3 Types and functions of Geosynthetics

Geosynthetics are the flat synthetics structures developed with different properties as per the requirement of different geotechnical works. Basically there are five types of Geosynthetics:
a) Geotextiles b) Geomembranes c) Georids

  Figure 1.4: Types of Geosynthetics

d) Geonets e) Geocomposites
a) Geotextiles are basically textiles in traditional sense made from synthetic fibers. So this material is flexible, porous in nature and bio-undegradable. The main point is they are porous to water flow across their manufactured plane and also within their plane in wide variety. There are at least 80 specific application areas for geotextiles that have been developed to fulfill following major functions:
1. Separation
2. Reinforcement
3. Filtration
4. Drainage
5. Moisture barrier (when impregnated)
b) Geomembranes: This is an impervious thin sheet of rubber or plastic material used primarily for linings and covers of liquid or solid storage facilities. This is the second largest group of geosynthetics. The primary function of geomembranes is always as a liquid or vapour barrier. At least for 30 individual applications have been developed in civil engineering works.
c) Geogrids: These are plastic formed into a very open, grid like configuration with large apertures.
Often these are stretched into one or two directions for improved physical properties. By themselves, there are at least 25 application areas of geogrids, and they function in two ways: separation and reinforcement.
d) Geonets: Geonets are usually formed by continuous extrusion of polymeric ribs at acute angles to one another. When the ribs are opened, relatively large apertures are formed in a netlike configuration. The main function of this material is drainage in along the manufacturing direction.
e) Geocomposites: There are varieties of combinations of geotextiles and geogrids, geotextiles and geonets, geogrids and geomembrannes etc according to the special functions to be fulfilled in the site.

Functions of Geosynthetics: The primary and secondary functions of geosynthetics are presented in

Table 1.1.

Table 1.1: Functions of geosynthetics

Functions	Separation	Filtration	Drainage	Reinforcement	Protection	Sealing
Geotextiles	P	P	S	S	P	S
Geomembrannes	S			S		P
Geogrids				P
Geonets			P		S
Geocomposites			P		S	S
P-Primary S-Secondary

Geosynthetics Lecture Notes by S.P. Joshi (IOE, Nepal)