Third Revolution In Civil Engineering Materials: Geosynthetics In Infrastructure Projects

Third Revolution In Civil Engineering Materials: Geosynthetics In Infrastructure Projects

Madhav Madhira1 & Akshay Jha2
1IIT & JNT Univ., Hyderabad 2Chief Engineer, SC Railway

Indian Infrastructure sector is poised to grow very fast in the coming days. A number of initiatives have been initiated for expediting the same. One of the impetus areas of infrastructure sector development is expediting construction and/or widening of highways. Ministry of Road Transport is likely to set daily target of 30 km of National Highway Construction from 2015-16 onwards. The other area being Indian Railways which is planning for large scale expansion of its network for catering to increased traffic demand. Great emphasis is being given to big ticket projects like ports, airports, power plants, High Speed Rail, Smart Cities, Haul roads, Power plants, etc., that require development of areas which are difficult for construction. In addition, construction techniques which require lesser parcel of land for the same engineering structure are most preferred. Use of Geosynthetics in Civil Engineering could be the ideal solution for reducing land requirement and preservation of precious and limited natural resources.

Revolutions in Civil Engineering Materials

Our ancestors relied on stone, soil, bricks, lime and wood for all constructions for ages. The Appian Way discernable even now has stone paving. Mesopotamians are pioneers in visualization of reinforced soil as a construction alternative and used the concept for the construction of Ziggurats. But for this very unique experiment in developing new construction methodology, no other alternative seemed to have come about. The first major revolution in Civil Engineering materials followed the Industrial Revolution in late 17th and early 18th century. Iron and steel could be manufactured and found ready application in practically all Civil Infrastructure projects, especially for bridges, roofs, towers, and tall buildings.

The second major revolution in Civil Engineering materials is because of manufacture of cement starting from late 19th and early 20th century. Concrete has become a versatile product in innumerable forms, viz., reinforced cement concrete, prestressed reinforced concrete, fibre reinforced concrete, high performance concrete, etc.

Advent of geosynthetics heralded the third and the most recent revolution in Civil Engineering materials. Finally Civil Engineers have found a very versatile material that can be used for a variety of applications and in practically all sub-disciplines of civil engineering, viz., highways, pavements, retaining structures, slopes, shore or coastal protection, irrigation projects, environmental engineering, pollution control, building elements, etc. In particular, a material is available to reinforce soil and impart lateral strain restraint. Use of geosynthetics also entails smaller volume of earthwork, faster rate of construction, sustainable development and lesser carbon footprint.

Geosynthetics

Geosynthetics are a class of materials that are used in conjunction with soil to improve the overall performance in a specific context. They include Geotextiles, Geomembranes, Geogrids, Geonets, Geocomposites, Geosynthetic Clay Liners, Geopipes, Geobags, etc. Geosynthetics find application in Road and Highway Construction, Slope Stabilisation, Building over soft soils, Retaining Walls, Airport Runways, Costal Protection, Drainage of Structure, Groundwater Protection, Landfill Engineering, etc.

Geosynthetics in general are planar product manufactured from polymeric material used with soil, rock, earth or other geotechnical engineering related material, e.g. flyash/pond ash, as an integral part of human made project structure or system. Geosynthetics are used in a wide variety of Civil Engineering Applications such as Transportation, Geotechnical, Geoenvironmental, Hydraulics, and other Infrastructure Developments like even real estate projects. The reason for extensive use of geosynthetic material in to Civil Engineering projects are (i) Better Quality Control (as they are manufactured in a factory environment), (ii) Rapid Installation, (iii) Difficult site restrictions, (iv) Cost Competitiveness  against other construction material and lower carbon footprint, requirement of smaller parcel of land for the same engineering structure, etc.

The concept of Reinforced Earth developed in Europe in 1960s was adopted by almost 30 countries of the world by 1970s. The use of Mechanically Stabilised Earth increased dramatically in the last two decades of 20th Century and continues to grow to present time. First reinforced soil retaining wall was constructed in India in1986 at Ludhiana. Geosynthetics are being manufactured in India since 2006.

Geosynthetics in Highway Construction

Geosynthetics are used in highways in two ways, first one being in construction of road itself and other one being in retaining soils of steep embankment slopes in areas where right of way is restricted and as reinforced soil walls for bridge approaches.

Geosynthetics in Pavements: Use of geosynthetics in infrastructure projects involving roads results in significant savings, improved performance and very good serviceability on both short term and long term basis. Geosynthetics have made it possible to construct roads and pavements in seemingly difficult locations such as marshy stretches, soft /organic deposits and in expansive soil areas.

Geosynthetics placed at the interface between the aggregate and subgrade functions as a separator to prevent two dissimilar materials (subgrade and aggregate) from intermixing. Geotextile and geogrid perform this function by preventing penetration of the aggregate in to subgrade. In addition Geotextiles prevent intrusion of subgrade soil up in to the base course aggregate. The overall performance of road even if it is designed based on the separation criteria is influenced by secondary functions of filtration, drainage and reinforcement.

Geosynthetics finds application both in temporary and permanent roads. Temporary roads include detours, haul and access roads, construction platforms, stabilised working area required for construction of permanent roads as well as over soft foundations. Geosynthetics allow access for construction equipment to site where soil is normally too weak to support initial construction work. This is one of the important uses of geosynthetics.

In paved roads, geotextile is used at the interface between the granular sub-base and the subgrade soil to avoid possibility of rutting and to some extent to reduce the thickness of sub-base apart from controlling the contamination of the sub-base by fines from the subgrade soil. The use of geotextile within a wearing course helps in restricting reflection cracking, in reducing rutting, restricting the fatigue cracking.

Geosynthetics can be used for controlling moisture infiltration and retardation of reflection cracks in pavement overlays beneath surface overlays. Properly installed asphalt saturated geotextiles function as moisture barrier that protects the underlying pavement structure and provides cushioning for overlays thus functioning as stress relieving interlayer.
By including separation and reinforcement functions of geosynthetic products in technical specifications, an equivalent and superior design can be achieved by reducing expensive mineral base course material thickness. If the subsoil of the intended road construction does not have sufficient bearing capacity, geosynthetic reinforcement can also be used in stabilisation of the subsoil.

Geosynthetics for Earth Structures – Retaining Walls and Embankments

In conventional reinforced earth structure, metal strips extending from the facing panels back into soil being reinforced serve the dual role of anchoring the facing units and restraining the soil through frictional stresses mobilized between the strips and the backfill soil. Walls called MSE or Reinforced Soil walls with geosynthetic reinforcement are very flexible compared to conventional gravity structures and can absorb significantly higher dynamic loads.  In addition the cost per square meter of exposed surface for reinforced soil walls is significantly lower.

Just as vertical walls are built using geosynthetics, steep slopes and embankments can be constructed using geosynthetics. As the slope angle with the horizontal decreases from near 900 a wall translates in to a slope or embankment. In embankments the exposed surface should be covered with erosion control measure or vegetation. Geotextiles or georgids are laid in horizontal layers with no facing unit. Wrap around geosynthetic reinforced slopes are a very good alternative.

The design methodology translates from that of a retaining structure to resist lateral earth pressure to slope stability analysis. The use of geosynthetics in slopes facilitates construction of steep embankment slopes or a flatter slope with higher factor of safety. Another advantage of geosynthetic reinforced slope is that the slope facing merges with green surroundings.

Gabion walls along with geosynthetics are used in hilly terrain for slopes which experience heavy precipitation. This concept has been used in Mumbai – Pune Expressway.

Geosynthetics in Railways

The concept of use of geosynthetics in Railways is almost similar to that of Roads so far as retaining of earth is concerned although not being practised on large scale in India. MSE Walls and slopes are used extensively in all developed countries especially in Japan.

Geosynthetics are used for separation and reinforcement in order to arrest pumping of fines from sub-base in to ballast to prevent contamination of ballast and minimize settlement of railway track. Geogrids provided below ballast acts as reinforcement and help in reducing settlement.  Geotextiles used below ballast bed prevent pumping of fines in to ballast and also minimizes ingress of moisture in to formation thus reducing problems in case of bad formation consisting of black cotton soil, etc.

Geosynthetics in Airports

Geosynthetics are used in airport construction for creating space for runways, and reinforcing the pavements. Steep reinforced embankment or gabion walls provide flat area for runway and other infrastructure.

Geogrid Reinforced slope 74 m high with 1H:1V slopes has been used for construction of runway in Charleston, West Virginia. The slope surface has been turfed (Fig. 10).

Bridge, Concrete Retaining Wall and Reinforced Earth Slope were considered for runway extension. Geosynthetic reinforced green faced slope provided the most economical and aesthetically pleasing alternative which blended well with the surrounding hills. Woven polypropylene geogrid mesh (Fig. 11) was used as facing material for the slope.

Geosynthetics have also been used for the construction of airport at Pakyong in Sikkim. The runway was constructed from huge cutting of earth from the hill and filling it on the valley side to get a level platform. Composite soil reinforcement system has been employed to retain and stabilize this fill of height varying from 30 m to 74m. This flexible and draining type of retaining structure is said to be the tallest reinforced soil structure in the world.

Reinforced Steep Slope for building project

The attention to environment has been increasingly spreading throughout the world including the building industry. Pinzani and Paolicelli (3) have dealt with case of reinforced slope design for a building in Matera, Italy. This case study covers a building complex requiring planar area of approximately 10 hectares along the slope of a hill which was partially affected by pluvium fed by two seasonal springs.

A road and some buildings were planned to be built over the reinforced steepened slope. The total and post constructional deformations were to be controlled. Polyster welded geogrid with high modulus was used as the silty clay layer on which reinforced slope was to be founded posed the risk of large total and differential settlements. To reduce environmental impact to a minimum and to improve visual aesthetics, autochthonous species seedlings were planted for rich and flourishing vegetation on the frontage (Fig. 13).

Geosynthetics and Geosystems in Coastal Engineering

Geobags (Fig. 14) filled with sand or concrete are usually used as a temporary measure/structure for revetment, groynes, artificial reefs, slope buttressing, and protection dykes, etc. Large geobags are also used for construction of underwater dams. These large geobags are filled with lean concrete. Geotubes (Fig. 15) are popular structure for shore protection and are sued for revetment, offshore breakwaters, protection dykes, containment dykes and groynes.

Geocontaniners are recent additions that are used as breakwaters, containment dykes, artificial reef or slope buttressing.

Conclusions

Use of Geosynthetics in Infrastructure Sector is bound to grow exponentially in India. Geosynthetics are a boon for Engineering Construction as its use reduces land requirement and in many cases leads to safer design with a lower carbon footprint.  Many of these structures have aesthetically pleasing appearance and blend well with surrounding. Greenery can be developed easily on them using proper type of geosynthetics facia on slopes and earth retaining structures.

References

1.     Gharpure, A.D., Kumar, S., Scotto, M. (2012). Composite soil reinforcement system for retention of very high and steep fills – A case study. 5th European Geosynthetics Congress, Vol. 5, Topic: Soil Improvement and Geosynthetics.
2.      Lostumbo, J. M. (2010). The Yeager Airport Runway Extension: Tallest 1H: 1V Slope in US – Case Study. In Advances in Analysis, Modelling and Design, GSP No.199 ASCE, GeoFlorida.
3.     Pinzani, G.P. and Paolicelli, A. (2010).  Reinforced Steep Slope Design for a building area in Matera, Italy. 9th International Conference on Geosynthetics, Brazil, pp.1735-1738.

About Author:

I am Thomas Britto here to share my experiences in the civil engineering field to all my readers.Today many students are struggling to buy books at high prices. So I decided to start a blog and share my experience and knowledge with all my readers.

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