Saurab Ppt.pptx

GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS

Submitted to Prof .D.K Bansal Submitted by Saurav Thakur 1

INTRODUCTION 

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Transportation - needed for the development o f the country. The main mode of transportation is by road or highways. In the process of road development, the alignm ent of road may have to be fixed through the s oils which may not bear the traffic loads . There are various techniques of ground improv ement. 2

METHODS FOR GROUND IMPROVEMENT 1. 2. 3. 4.

5. 6. 7. 8.

Soil stabilization Vertical drains Stabilization trenches Capillary cut-off Soil nailing Stone columns Vibro compaction Dynamic compaction 3

SOIL STABILIZATION 

Improvement of stability or bearing capacity of soil by use of controlled compaction or by the addition of suitable admixtu res or stabilizers .

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There are various methods of soil stabilization .

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The methods of soil stabilizati on are:

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Mechanical Stabilization Soil-cement Stabilization Soil-lime Stabilization Soil-bitumen Stabilization Chemical Stabilization Electrical Stabilization Stabilization by grouting Stabilization by geo textile and fabrics Reinforced earth

2. 3. 4. 5. 6. 7. 8. 9.

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Mechanical Stabilization  Process of improving the properties of soil by changing its gra dation.  Two or more natural soils are mixed to obtain a composite m aterial. Cement Stabilization  Done by mixing soil and cement with water and ng the mix to attain a strong material.

compacti

Lime Stabilization  Lime stabilization is done by adding lime (2%-10%) to soil. 6

Bituminous Stabilization  Bituminous stabilization provide water proofing and binding. Chemical Stabilization  Stabilization by adding different chemicals. Electrical Stabilization  Done by a process known as electro-osmosis. Stabilization by Grouting  In this method grouting is done under pressure the stabilizers with high viscosity are suitable only for soils with high perme ability. 7

Stabilization by Geotextiles and Fabrics  Geo textile which have very high tensile strength can be used as reinforcement for strengthening soil. Reinforced Earth  Soil can be stabilized by introducing thin strips in to it .

Stabilization using Bio-Enzymes  Bio-enzyme stabilization is a newer technique for strengtheni ng of sub grade soil.  Terra Zyme is one of the largely used bioenzymes.

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VERTICAL DRAINS 

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Act as free draining water channel. surrounded by a thi n filter jacket which prevents the surrounding soil from entering the core. A vertical sand drain accelerates the rate of consolidati on. Installation of vertical sand drains is a convenient techn ique for stabilization of soft and compressible soil . There are two types of vertical drains - sand drains and sand wicks. 9

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Fig : vertical drains

Sand drains  Typically 200-500 mm in dia.  Formed by infilling sand in to a hole in the ground.  Hole formed by driving ,jetting or augering.  Typical spacing 1.5 - 6.0 . Sand wicks  Sand wicks are improved technique of sand drains.  A small diameter hole is made by driving mandrel or by borin g.  Then cylindrical bag with sand is lowered into this. 11

STABILIZING TRENCHES 

Excavation which has a blanket of filter material between 0.5 m and 1.00 m thick against its upstream slope and at the bott om of system for collecting and eliminating water.

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Improves the stability of embankment by providing drainage and replacing weaker material with better material .

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Fig : Stabilizing trench

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CAPILLARY CUT-OFF 

In some cases capillary water accumulates and saturates the subsurface layers which results in failures.

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To arrest this capillary rise, capillary cut-off has to be provide d.

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Capillary cutoff is of two types. Permeable Capillary Cut-off Impermeable Capillary Cut-off

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Permeable Capillary Cut-off A layer of granular material is provided which has a thickness higher than the capillary rise so tha t water cannot rise above the cut-off layer

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Fig:-Cross-Section of pavement showing Permeable capillary cut-off

Impermeable Capillary Cut-off An impermeable capillary cut-off is prepared by inserting bit uminous layer in place of permeable blanket.

Fig: Cross-Section of pavement showing impermeable capillary cut-off

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SOIL NAILING 

Earth retention structure that combines reinforcements and s hortcrete to support excavations , hillside , embankment stee ping etc…

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The nails must have bending stress. The tension developed in nails provides resisting forces which stabilize the soil mass.

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Fig: Soil nail

STONE COLUMNS 

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Done to provide adequate support for relatively light foundat ion. The method consists of forming vertical holes in ground whic h are filled with compacted crushed stone, gravel and sand or a mixture.

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Fig : stone columns

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VIBRO COMPACTION 

For loose sand deposits, the density index can be increased b y vibro compaction.

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This process employs a depth vibrator suspended from crane

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Compaction of sand can be achieved up to distance of 2.5m fr om axis of vibrator.

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Compaction can be carried out to significant depths up to 12 m. 21

Fig : vibro-compaction

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DYNAMIC COMPACTION 

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This involves in increasing the density of soil near the s urface by tamping. Density improvement up to 10m is feasible. This method consists of dropping heavy mass of 8 to 40 tonnes known as pounder on the surface from a height 5 to 30m

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Fig :Dynamic compaction Equipment

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CONCLUSIONS

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While constructing highways different ground condition s are encountered. Considering all factors a suitable ground i mprovement technique has to be done. Ground improvemen t techniques have been extensively used by developed countr ies. Lime stabilization is suitable for expansive soil like black cott on soils. In bitumen stabilization optimum content of bitumen vanes f rom 4 to 6 % soil. Electrical and Chemical stabilization are expensive compared to others. Stabilization by grouting is suitable only for soils with high pe rmeability. Stabilization by Terra Zyme is most effective for fine grained s oil. 25

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Provision of capillary cut-off is effective for expansive s oils. For soft and compressible soils provision of sand drains and sand wicks are found to be effective. Dynamic compaction is found suitable for soft, loose co hesionless soil layers.. Stone column has also been found useful for soft soils.

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REFERENCES 

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Sanjay Kr Singh & Par-deep Kr Gupta, (2002), "Critic al review of ground improvement techniques for hig hways ", Volume 30, No: 8, Indian Highways, New D elhi, pp. 5-13. Gaul-kar M.P, (1999), "Construction of roads III blac k cotton soils", Volume 27, No: 3, Indian Highways, New Delhi, pp. 37-43. Sharma . S.C, (1994), "Ground Improvement Techniq ues", Vol. 22, No: 12, Indian Highways, New Delhi, p p. 3-4. (1994), "Application of Geo-grids in Highway Engine ering", Special report: 12, Indian Road Congress, Ne w Delhi, pp. 59-61.

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