PCGE - 1. Basic Description, Function and Selection of Geosynthetics

Question 1

It combines ‘geo’, indicating use in earth-related civil engineering, and ‘synthetics’, referring to the materials being man-made, primarily from synthetic polymers derived from crude petroleum oils.

Answer 1

Geosynthetics

Question 2

It is a raw natural resource that is extracted from the earth and refined into products

Answer 2

Crude Oil

Question 3

are made from synthetic polymers, though materials like rubber, fiberglass, and bitumen.

Answer 3

Geosynthetics

Question 4

are planar, permeable, polymeric textile products that come in flexible sheet forms. They are essential in civil engineering applications for filtration, separation, and reinforcement.

Answer 4

Geotextiles

Question 5

It is produced by interlacing two or more sets of yarns, typically at right angles, using a conventional weaving loom. This method creates strong and durable fabrics.

Answer 5

Woven Geotextiles

Question 6

It is made from directionally or randomly oriented fibers bonded together through partial melting, needle-punching, or chemical binding agents like glue or latex. These geotextiles are typically used for filtration and separation due to their porous structure.

Answer 6

Nonwoven Geotextiles

Question 7

Formed by interlooping yarns using a knitting machine, providing flexibility and adaptability in various applications.

Answer 7

Knitted Geotextiles

Question 8

Created by interlocking or bonding fibers or yarns through stitching or sewing, offering a versatile solution for specific engineering needs.

Answer 8

Stitched Geotextiles

Question 9

These are planar, polymeric products characterized by a mesh or net-like structure composed of intersecting, tensile-resistant elements known as ribs. These ribs are connected at junctions through methods such as extrusion, bonding, or interlacing

Answer 9

Geogrids

Question 10

It involves forcing melted polymer through a die to create a continuous sheet or structure. For geogrids, the polymer sheet is then punched with a regular pattern of holes and stretched.

Answer 10

Extrusion Method for Extruded Geogrid

Question 11

It involves joining individual polymer strips or fibers to form a grid. This can be achieved through various techniques such as heat bonding, adhesive bonding, or ultrasonic welding.

Answer 11

Bonding Method for Bonded Geogrid

Question 12

It is similar to traditional textile weaving, where two or more sets of yarns (usually made from polymer fibers) are interlaced at right angles to form a grid. The woven structure provides strength and flexibility, with tensile properties depending on the type of polymer and the weaving pattern used.

Answer 12

Interlacing Method for Woven Geogrid

Question 13

Produced by stretching a polymer sheet longitudinally, resulting in much higher tensile strength in the longitudinal direction compared to the transverse direction.

Answer 13

Uniaxial Geogrid

Question 14

Created by stretching the polymer sheet in both the longitudinal and transverse directions, providing equal tensile strength in both directions.

Answer 14

Biaxial Geogrid

Question 15

Designed to offer equal tensile strength in multiple directions, achieving nearly 360° tensile properties.

Answer 15

Triaxial Geogrid

Question 16

These are planar, polymeric products consisting of a dense network of integrally connected parallel ribs, overlaid at various angles.

In-plane drainage of liquids or gases. Their structure is designed specifically to facilitate fluid movement within a project.

Answer 16

Geonets

Question 17

These are planar, synthetic sheets that are relatively impermeable and are used to control fluid migration by acting as barriers or liners.

They are manufactured from low-permeability materials.

used within an earth mass, the name for this geonsynthetic refers to as a “barrier”; when used as an interface or surface covering, it is termed a “liner.”

Answer 17

Geomembranes

Question 18

three-dimensional, permeable, polymeric structures with a honeycomb or web-like design.

They are produced using strips of needle-punched polyester or solid high-density polyethylene or assembled from geogrids and special connectors into triangular or square cells.

are used to provide structural support, erosion control, and soil stabilization.

Answer 18

Geocells

Question 19

are products made from the combination of two or more materials, with at least one being a geosynthetic such as geotextile, geogrid, geonet, or geomembrane.

These materials are assembled in laminated or composite form to perform specific functions more effectively than when used separately.

Answer 19

Geocomposites

Question 20

How does Geosynthetic help in Reinforcement

Answer 20

Geosynthetics are used to strengthen soil, creating a composite material called “reinforced soil” which has high compressive and tensile strengths, similar to reinforced concrete.

It resist applied stresses and prevent deformations in geotechnical structures by acting as tensioned members that stabilize the soil mass through friction, adhesion, interlocking, or confinement.

Question 20

is a lightweight, slab or block product with high void content. It is primarily used as lightweight fill, thermal insulation, and drainage channels.

is used as a lightweight fill material in embankments, bridge abutments, and retaining walls to reduce the load on underlying soils and prevent settlement. It is used in roadways to prevent settlement and to provide a stable base over soft or compressible soils.

Answer 20

Geofoam

Question 21

What are the Effects of Reinforcement in Geosynthetic

Answer 21

Shear Stress Reduction: Geosynthetics, when placed within soil, help to reduce the outward horizontal or shear stresses that can develop under loads. This reduction in shear stresses enhances the stability of the soil structure by preventing it from spreading outwards or failing under load.

Slab/Confinement Effect: Geosynthetics act like a slab, redistributing the loads applied on the surface across a wider area. This reduces the normal stress on the soil underneath, effectively confining the soil and preventing it from moving or deforming.

Membrane Effect: When a geosynthetic deforms under load, it creates a tensioned membrane that provides vertical support to the soil above it. This effect helps to distribute the load more evenly and reduces the potential for upward movement (heave) of the underlying soil.

Interlocking Effect: In geogrids, the grid structure allows for interlocking with the surrounding soil particles. This mechanical interlock enhances the transfer of stresses between the soil and the geosynthetic, leading to improved reinforcement.

Question 22

How does Geosynthetic help in Separation

Answer 22

The separation function of geosynthetics is crucial when preventing the intermixing of adjacent dissimilar soils or fill materials.

By placing a geosynthetic layer between soft soil and granular fill, it maintains the structural integrity and functionality of both materials, which is especially important in applications like pavements, railways, shallow foundations, and embankments.

Question 23

How does Geosynthetic help in Filtration

Answer 23

The filtration function of geosynthetics involves allowing fluid flow while restricting the migration of soil particles across its plane. This function is crucial in maintaining the stability of soil structures by preventing uncontrolled soil particle movement under seepage flows.

Often, filtration is used in conjunction with separation or reinforcement, rather than as a standalone function.

Question 24

How does Geosynthetic help in Drainage

Answer 24

Geosynthetics perform the drainage (or fluid transmission) function by allowing adequate fluid flow within their plane while limiting the migration of soil particles. This function is crucial for collecting and transporting water from the surrounding soil mass to various outlets, such as weep holes in retaining walls. Additionally, geosynthetics help dissipate excess pore water pressure by enabling water flow.

Question 25

How does Geosynthetic help in Fluid Barrier

Answer 25

Geosynthetics act as an almost impermeable membrane, performing the fluid barrier function by preventing the migration of liquids or gases. This is essential in applications such as lining the base of a pond, where the geosynthetic layer stops the infiltration of liquid waste into the natural soil.

Question 26

How does Geosynthetic help in Protection

Answer 26

Geosynthetics perform the protection function between two materials, thereby preventing or reducing damage to the underlying geotechnical or structural systems. Example: In landfills, geosynthetics are used to contain plastic waste and prevent leakage of microplastics and toxic substances, thereby protecting groundwater.