Stabilization of Soils Using Geosynthetics
Published on Feb 27, 2019
A Large variety of reinforcing materials emerged and have been developed for construction purposes, including: metal strips ,bar mats, Geotextile sheets, Geo Grids etc. Reinforced soil technologies has been extensively used during the past few decades in the construction of (railway formation, highway embarkments, earth dams and retaining walls). As a reinforcing material the Geo synthetics are widely used in engineering practice to strengthen the foundation, slope, road, pavement, crushed-stone column etc. Pavement is a hard crust constructed over the natural soil for the purpose of providing and even surface for the vehicles. In pavement construction soil stabilization is also deals with the construction practice(Highways, dams, bridges, railway structures)it shows the various mean by which the stabilization responds of different soils can be identified.
This paper presents soil geostnthetic intraction properties for different types of soils, four types of soils were used with geocomposit reinforced materials for conducting CBR test to finding the density of soil samples and mechanical strength of sub grade soil.These geo synthetic products have helped desigeners and contractors to solve several types of engineering problems where the use of conventional construction materials would be restricted or considerably more expensive.
Keywords : Geotextiles,geogrids,soils,CBR test.
The main objective of the present work is to study the effect of the soil strength after the application of geosynthetics. In the present study the strength variations in different soil was observed. In the present thesis the analysis of soil has been carried out by application of geosynthetics in soils by using sieve analysis and CBR test.
The future scope appears to be more promising with stronger and more durable geosynthetics emerging into the market along with fibrous system to be mixed with soil for giving more hope as well as challenge to the geotechnical engineer in the years to come.
Applications of Reinforcements for Soil Stabilization
The overall behavior of the strengthened mass depends on the reinforcement material properties, the soil characteristics, and therefore the nature of the interaction between the soil and therefore the reinforcement. The interaction mechanism is stricken by factors such as: state of stress inside the strengthened mass; nature of loading; direction of reinforcement; boundary conditions; and material and interface properties. within the case of monotonic loading, 3 mechanisms of interaction are identified: passive anchorage; increased confinement; and tensile membrane action.
Types of Reinforcement
Reinforced Soil Structures square measure classified loosely, into three classes:
Mechanically-Stabilized Earth (MSE) Walls
Reinforced Slopes and Embankments
Soil Reinforcement is also created with variety of materials:
Polymer Geogrids of synthetic resin (usually uniaxial) & plastic (usually biaxial)
Polyester and covering material Geogrids (often unwoven or sewn at junctions) and frequently coated with a chemical compound like synthetic resin or PVC or with hydrocarbon.
Welded wire mesh
Geosynthetics with high tensile strength used in combination with soil of high compressive strength have been found to be effective in the design of many civil engineering applications. The application of Geosynthetics in the field of geotechnical, transportation, hydraulics, and geo-environmental engineering has been explained by many researchers.
The materials employed in the manufacture of geosynthetics square measure primarily artificial materials, generally, derived from crude oil oils, though rubber, fiberglass. Geosynthetics could be a generic name representing a broad vary of plane merchandise factory-made from compound materials. the foremost common ones square measure geotextiles, geogrids, geonets, geomembranes and geocomposites, that square measure employed in contact with soil, rock Associate in Nursingd/or the other material as an integral a part of a artificial project, structure or system. The term ‘geosynthetics’ has 2 parts:
‘GEO’ touching on Associate in Nursing finish use related to rising the performance of applied science works involving earth/ground/soil.
‘SYNTHETICS’ touching on the very fact that the materials square measure virtually solely from artificial merchandise
The various types of geosynthetics that are available in the market are named below:
Geosynthetic clay liners (GCL)
Geotextiles type one among the 2 largest teams of geosynthetics. Their rise in growth throughout the past 35years has been nothing wanting extraordinary. they're so textiles within the ancient sense, however they comprises artificial fibers instead of natural ones like cotton, wool, or silk. Thus, biodegradation and resultant short life isn't a drag. These artificial fibers ar created into versatile, porous materials by normal weaving machinery or ar matted along during a random non-woven manner. Some also are unwoven. There ar at-least a hundred specific application areas for geotextiles that are developed, however, the material invariably performs a minimum of one among four distinct functions: separation, reinforcement, filtration and/or drain.
Geotextiles are classified based on manufacturing process into the following:
A geotextile made by interwoven, sometimes at right angles, 2 or a lot of sets of yarns or
Other parts employing a typical weaving method with a weaving loom.
A geotextile made from directionally or willy-nilly oriented fibres into a loose internet by bonding with partial melting, needle punching or chemical binding agents.
Knitted GT A geotextile made by inter-looping one or a lot of yarns beside a textile machine rather than a weaving loom
A geotextile within which fibres or yarns or each ar interlocked by handicraft or stitching.
Some major kinds of soils that are encountered are:
(i) Black cotton soil – marshy regions, dried up river or lake beds, etc.
(ii) Marine clay – river delta, high rainfall zones, d/s of erosion prone areas.
(iii) Granular soil– Desert regions, coastal areas, etc.
(iv) Red laterite soil – Plateaus, boulder regions.
Black cotton soils are expansive in nature and tend to shrink in dry seasons while in wet seasons they expand highly depending on the mineral present in it. It has weak strength
Properties like the load bearing capacity. This is an adverse property for the construction of pavement and so the soil needs to be assessed for the various engineering properties including the depth of the layer to compensate the amount of expansion and shrinkage.
Marine clay also belongs to the family of pure clays but has fine sand embedded into it. This might have happened due to the exposure of clayey soils to desert winds and eroded soils. These sand grains have acted as coarse aggregate as in concrete and strengthened the soil to some extent but are still not good enough for engineering applications. Expansion behavior is reduced as compared to that of clays.
Red laterite soils possess good strength properties but when exposed to high moisture, these also behave like clay and may cause the failure of pavements and so need the assessment for strength behavior. From literature survey we found that expansive nature is not as extreme as in clays.
Collection and storing of samples
Red laterite soil:
Red soil is collected from the laboratory premises where a work for gardening was undergoing. The soil was broken down to make it free from lumps and all the non-required waste was carefully picked out and cleaned.
This soil was collected from Maisammaguda
Black cotton soil:
Black cotton soil was also collected from the Narsapur Medak.
Granular soil was also collected from the Bahadhurpally.
Application of geosynthetics
The procedure for testing remains a similar for each the cases except the addition of geosynthetic layers into the soil whereas compacting at totally different heights of the soil within the mould. The geotextile and therefore the geogrid were take circular items that will match specifically into the mould while not. Layers were placed higher than of the primary and therefore the third layer whereas compacting the soil which might grow to be top of second layer and fourth layer when inverting the mould for cosmic microwave background testing and CBR test was conducted.
Granular soil had shown improvement in the CBR values for Geogrids and had nearly doubled for the penetrations of 2.5mm and 5mm for geogrids, this implies the applications of Geogrids for pavements in case of Granular soil can reduce the thickness of the layer by almost half of the original depth.
The Granular soil have shown higher CBR values. This had happened due to the fact that sands consisted of high amount of coarse grains as compared to that of soils which had higher fines and were clayey.Black cotton soil had tripled its strength when the Geogrids 40x40 were used for reinforcing this soil. We can use these formats of Geogrids for Black cotton soils for construction of low volume roads at a cheaper cost for the same amount of traffic.
All the three clayey soils i.e. the red laterite, Marine clay and the black cotton soil have positively responded to the Geotextile in contradiction with the Sandy soils. The Geotextile being the non-woven type was being compressed when the load was being imposed on soils.
The clayey soils when consisted high moisture in them, Geotextile can be a remedy as well as reinforcement. This is stated as the Geotextile was absorbing water from the soils and also the soils were high in clay content which turned them stiff, thereby improving the load bearing capacity of the soil.
Marine clay had shown good improvement i.e. the load bearing capacity had doubled when the 40x40 Geogrid was used for reinforcing it. In all other cases of Geogrids the strength improvement was not so high as compared to the 40x40 Geogrid.
Geogrids when no other economically feasible soils are available in the nearby areas. Also care is to be taken that the boundaries of the sand stratum had stiffer soils with high fines to prevent the flowing of sand particles when high moisture is induced. This will form our basis for the further research for economically constructing pavements on a weaker subgrade, sub-base and base soils in combinations with various reinforcing methods.
Some of our future research ideas include the use of Geocells for holding the sands in place and also trying to prevent the expansion of clayey soil. Also woven Geotextiles will be implied to check for CBR value improvement and the cost feasibility in comparison with the Geogrids and the non-woven type of Geotextile.
Future scope of the work
It is expected that the use of geosynthetics will become increasingly routine, and that geosynthetics will be the standard material of choice for several applications. It can be used in environmental engineering for landfill projects. It can also be applied in railway construction which includes antifiltration, anti-seepage,drainage,protection and reinforcement needle punched staple fiber nonwovens were used as filtration for subgrades.
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Project Done By S.Sugandini, Dr.M.Madhuri