Geosynthetics in Civil Engineering and Construction Works

There are various types of geosynthetics used in civil engineering and construction works. Properties, functions and uses of geosynthetics are discussed.

Depleting sources for granular and other elementary raw materials, combined with the limited availability of funds for projects, has been generating new opportunities for innovative engineering to achieve cost-effective solutions. One of those innovations is the introduction of geosynthetics into the field of civil engineering.

Geosynthetics are considered as bona fide engineering materials that not only are filling in for the scarce raw materials like cement and steel, but also are turning out to be a pretty sound and good alternative to the conventional designs.

The use of geosynthetics is, though, still novel in the construction industry, its use is nevertheless increasing every year in sectors such as reinforcement of fill, management of pore water pressure, foundations and pavements. Apart from being economical, they can be rapidly installed and help in quality control of factory manufactured products.

Geosynthetics are now considered necessary and indispensable for an economical solution in multiple functions, such as reinforcement, separation, filtration, drainage, barriers, erosion control, containment and protection.

Geosynthetics or geosynthetic materials are nothing but planar, polymeric (synthetic or natural) materials used in contact with soil/rock and/or any other geotechnical material, for Filtration, drainage, Separation, Reinforcement, Protection, Sealing and Packing.

Types of Geosynthetics in Civil Engineering and Construction Works

Following are the types of geosynthetics used in civil engineering:

1. Geotextiles
2. Geogrids
3. Geonets
4. Geomembranes
5. Pre-fabricated vertical drains
6. Geosynthetic clay liner
7. Geocells
8. Geocomposites

Functions of Geosynthetics in Civil Engineering and Construction Works

• Soil reinforcement structure
• Basal reinforcement to support the soil reinforcement structure
• Separation between the in-situ soil and the imported soil to avoid mixing and reducing mechanical performance
• Filtration behind all hydraulic structures
• Drainage control at the top 8 m to collect any seepage water coming from the other side of the embankment to avoid contamination on the structural fill
• Erosion control blanket to protect the slope at the top and avoid erosion.

Table: Types of Geosynthetics and their Uses

Type of geosynthetic	Separation	Reinforcement	Filtration	Drainage	Containment
Geotextile
Geogrid
Geonet
Geomembrane
Geosynthetic clay liner
Geopipe
Geofoam
Geocomposite

Uses of Geosynthetics in Civil Engineering and Construction Works

Separation of Soil Layers

In order to keep the imported material separated from the in-situ soil, a separating layer of geosynthetic is laid between the geotechnical entities. This is done to keep the properties of the imported material intact which otherwise could have altered under the action of applied loads.

Depending upon the surrounding conditions, nonwoven geotextile, geofoam and geocomposites can be laid in between the imported material and the in-situ soil.

They are usually applied at subgrade/sub-base interfaces in temporary and permanent roads, between rail-road blast and foundation soil, and between embankment fill and soft foundation soil.

Filtration of Water

The mismanagement of water on site is capable of causing extreme harm; erosion of soil in a particular area is one of the most harmful repercussions that carelessness could lead. It often results in the formation of irreparable gullies hence to help prevent that from happening, a geocomposite clay liner (GCL) is placed underneath all the hydraulic structures. This is a costly option therefore to remain within budget, it is also suggested to use nonwoven geotextile.

Drainage Works

If water isn’t contained properly on the sides of, say an embankment, an increase in the water table is observed that further brings pore pressure into the play. The increase in the pore pressure often requires a surplus amount of reinforcement of about 50%. To avoid this, geocomposite liner is installed usually at the back of the reinforced structure with a perforated pipe at the bottom to collect water. The pipe is then connected to the hydraulic structures.

Soil Reinforcement

1) Basal reinforcement

Basal reinforcement is provided at the foundation level of the reinforced structure. A standard penetration test is conducted to assess the soil’s bearing capacity. If the bearing capacity comes out between 10 and 60 Kpa, basal reinforcement is provided in the form of Geogrid reinforcement, which is laid out to counter for the failure that could have occurred due to the un-drained shear stress of the foundation.

2) Soil reinforcement

The technology of soil reinforcement, using geosynthetics, involves labor force to cut the geogrid to the required length, place it on site. Soil reinforcement is usually laid in one of the following scenarios: when either the soil bearing capacity is low or the layers are compressible; when in a landslide-prone zone; when there is excessive rutting and; when there are uneven settlements.

It allows the steepening of the slope, enabling to maintain the construction within the boundaries, as well as saving on earthmoving and importing of soil. The geogrids used are high-tensile polyester, encased in a LLDPE (linear low-density polyethylene) coating to prevent installation damage acting as primary reinforcement.

A secondary reinforcement in-between is given by a double-twisted mesh. Where hydraulic structures were required, a gabion face is used.

Soil Erosion Control

Usually, gabions, geotextiles and mattresses are used for erosion protection. Furthermore, geotextile filter and geotextile reinforcement ensure stability during saturation in the rainy season and sudden drawdown conditions.

Nonwoven geotextiles act as filter separator, drains and reinforcements. An economical pre-formed unit made of double-twisted mesh to provide primary reinforcement is used for erosion control.