SOIL STABILISATIOND P MajithiyaME Highway & Transport 1st semester

SOIL STABILIZATION Soil stabilization is a process of treating a soil

in such a manner as to maintain, alter or improve the performance of the soil as a road construction material. The changes in the soil properties are brought about either by the incorporation of additives or by mechanical blending of different soil types. OR simply

Soil stabilization refers to the process of changing soil properties to improve strength and durability. There are many techniques for soil stabilization, including compaction, dewatering and by adding material to the soil.

PURPOSE OF SOIL STABILIZATION1. To improve the strength of sub-bases, bases and

sometimes surface courses, in case of low cost roads 2. To bring about economy in the cost of road.3. To make use of inferior quality of locally available

soils/material. ( every time it is not possible to find required or specified strength in locally available material at that time we can go for soil stabilization methods)*

4. To improve certain undesirable properties of soils, such as excessive swelling or shrinkage, high plasticity, difficulty in compacting etc.

5. To facilitate compaction and increase load-bearing capacity

6. To reduce compressibility and thereby settlements.7. To improve permeability characteristics.

COMPONENTS OF STABILIZATION Soil Stabilizing agent

Cement Lime Fly ash Blast furnace slag

STAGES INVOLVED IN SOIL STABILIZATION PROCESS1. Evaluating the properties of given soil2. Deciding the lacking property of soil and choose

effective and economical method of soil stabilization

3. Designing the Stabilized soil mix for intended stability and durability values

DIFFERENT TECHNIQUES OF SOIL STABILIZATION

types of soil stabilization techniques

Mechanical stabilization chemical stabilization or stabilization by additives such as- soil-aggregate mixture -lime-soil- clay mixture -cement-sand-gravel mixture -sodium silicate- stabilization of soil with -Calcium chloride soft aggregates -bituminous material-resinous material

MECHANICAL SOIL STABILIZATION In this techniques the stability of soil is

increased by blending the available soil with imported soil or aggregate so as to obtain a desired particle-size distribution , and by compacting the mixture to the desired density. Compacting a soil at an appropriate moisture content is itself a form of mechanical stabilization

PRINCIPLE OF MECHANICAL STABILIZATION Mechanical stabilization is achieved by intelligently

blending locally occurring material so as to obtain a desired grading. compaction of soil is also a form of Mechanical stabilization. (It is well known as a dense, well graded mass offers high resistance to lateral displacement under a load).

If well graded material is compacted , densification of the mass takes place. The mechanical strength of mass is due to the internal friction and the cohesion. (internal friction is supplied by the coarser particles gravels, sand, silts where as cohesion is due to the clay friction.)

APPLICATION OF PRINCIPLE OF MECHANICAL STABILIZATION1. Soil-aggregate mixture.2. Sand-clay mixture.3. Sand-gravel mixture.4. Stabilization of soil with soft aggregate.

CHEMICAL STABILIZATION Under this category, soil stabilization

depends mainly on chemical reactions between stabilizer (cementitious material) and soil minerals (pozzolanic materials) to achieve the desired effect.

Different techniques of soil stabilization Soil-lime mixture Soil-cement mixture Chloride stabilization and Stabilization with other

chemicals

SOIL BITUMEN STABILIZATION The addition of a bitumen binder to a soil

improves its properties considerably.1. If the soil lacks cohesion, the bitumen coats

the soil particles, binds them together and supplies cohesion

2. Bitumen being a waterproof material , the mixture becomes less prone to the adverse effect caused by ingress of water

3. If bitumen binder sprayed on dry surface of low-cost road, it prevent dust and stop the entry of moisture into the road

SOIL BITUMEN STABILIZATION The following are various bituminous

stabilization techniques1. Sand-bitumen2. Soil-bitumen3. Soil-aggregate-bitumen4. Spraying bitumen on earth/gravel road

ADVANTAGES OF SOIL STABILIZATION It Improves The Strength Of The Soil, Thus, Increasing The Soil Bearing

Capacity. It Is More Economical Both In Terms Of Cost And Energy To Increase The

Bearing Capacity Of the Soil Rather Than Going For Deep Foundation Or Raft Foundation.

It Is Also Used To Provide More Stability To The Soil In Slopes Or Other Such Places.

Sometimes Soil Stabilization Is Also Used To Prevent Soil Erosion Or Formation Of Dust, Which is Very Useful Especially In Dry And Arid Weather.

Stabilization Is Also Done For Soil Water-proofing; This Prevents Water From Entering Into The soil And Hence Helps The Soil From Losing Its Strength.

It Helps In Reducing The Soil Volume Change Due To Change In Temperature Or Moisture content.

Stabilization Improves The Workability And The Durability Of The Soil.

REFERENCES http://www.industrialresourcescouncil.org/

applications/soilstabilization Youtube.com Principles and practices of highway

engineering by Dr. L. R. Kadyali

Thank you

SOIL-AGGREGATE MIXTURE. Soil-aggregate is a material in which soil and aggregate

particles are mixed in suitable proportion such that the resulting mixture conforms to a dense and stable mix when properly compacted.

This technique is used in countries abroad for the construction of base courses, and in the case of low traffic roads for the surface course as well

The particle-size distribution of the mixture is a major factor in determining the stability. The aggregate should be so graded that a grain to grain contact exists, producing internal friction.

SOIL-AGGREGATE MIXTURE. Specification for soil-aggregate sub-base

coursesSieve designation

Percent by weight passing the sieve for a nominal maximum size of80 mm 40 mm 20 mm

80 mm 100 - -40 mm 80-100 100 -20 mm 60-80 80-100 10010 mm 45-65 55-80 80-1004.75 mm 30-50 40-60 50-752.36 mm - 30-50 35-60600 micron 10-30 15-30 15-3575 micron 0-10 0-10 0-10

SAND-CLAY MIXTURE.

The sand-clay road is composed of a favorable mixture of clay, silt and sand. This blending can alter the undesirable properties of clay significantly. we can use this mixture to construct about 200 mm thickness road and as a surfacing course for low-traffic roads. When used as sub-base mix should have a minimum soaked CBR of 20, When used as base for heavily traffic road mix should have a minimum soaked CBR of 80

This mixture give good result only if proper equipments are used and quality control is done.

SAND-CLAY MIXTURE. Specification for sand-clay mixture

Sieve designatio

n

Percent by weight passing

25 mm 100 - -10mm - 100 -

4.75 mm 70-100 80-100 1002.36 mm - 50-80 80-1002.00 mm 55-100 - -1.18 mm - 40-65 50-80

600 micron - - 30-60425 micron 30-70 - -300 micron - 20-40 20-4575 micron 8-25 10-25 10-45

SAND-GRAVEL MIXTURE.

In tropical countries, the materials obtained from the disintegration of laterite are extensively found in a natural admixture of clay and coarse fractions and is known as lateritic gravel. In india, this material is locally known as moorum. Often the natural moorum contains to much of plastic material which lower its value as road pavement material. A suitable admixture of moorum with sand will not only result in a better gradation and increased strength but also will reduce the plasticity. Sand moorum mixture find ready application in sub-base and bases in india.

STABILIZATION OF SOIL WITH SOFT AGGREGATES

A method of stabilization of soil using soft aggregates is known as Mehra’s method

the principle behind this method is to embed in a soil mortar, coarse aggregates roughly one-third of the total volume. The aggregates are normally soft aggregates such as over-burnt brick ballast, kankar, moorum or laterite. Because of the larger proportion of the soil mortar, the resulting material has no grain to grain contact in the coarse aggregates, which merely float in the soil. Each aggregate is thus enveloped all round in the compacted soil and is thus protected from the crushing effect of traffic. This enables the soft aggregate to retain its strength and angular character for an indefinite period . About 10 percent of the coarse aggregates which are collected are not mixed with the soil but are saved and spread on the layer of the soil-aggregate mixture before rolling.

the soil-aggregates mixture is compacted to maximum dry density at optimum moisture content

SOIL-LIME STABILIZATION When lime is added to a fine-grained soil, a number of reactions

take place. Some of them occur immediately while others are slow to occur. One of the early reactions is base-exchange. Clay particles are usually negatively charged with exchangeable ions of sodium, magnesium, potassium or hydrogen adsorbed on the surface. The strong positively charged ions of calcium present in lime replace the weaker ions of sodium, magnesium, potassium or hydrogen resulting in a preponderance of positively charged calcium ions on the surface of the clay particles. This in turn reduces the plasticity of the soil. The clay particles tends to agglomerate into large sized particles (flocculation), imparting friability to the mixtureAfter above first reaction are complete, any additional quantity of lime will react chemically with the clay minerals. The aluminous and siliceous materials in the clayey soil will react with the lime in presence of water to form cementitious gels, which increase the strength and durability of the mixture. This pozzolanic reaction are slow and extend over a long period of time, several years in some instanceanother possible source of strength is the formation of calcium carbonate due to the absorption of carbon dioxide from air.

SOIL-CEMENT STABILIZATION Cement is a standard material whose quality is

tested and assured . Because of its very high flexural strength, it has a vary high load spreading property. Thus soil-cement is able to spread the load over a wider area and bridge over locally weak spots of the underlying sub-grade or sub-base.The main disadvantages are

1. The cost being higher than lime-soil 2. The need of high degree of quality control3. If volumetric change take place when cement

hydrates it results in early shrinkage cracks

CHLORIDE STABILIZATION calcium chloride has deliquescent and

hygroscopic properties. By the former is meant the ability of material to absorb moisture from the air and become liquid, the latter is meant the ability of material to absorb and retain moisture without necessarily becoming liquid.granular soils lack stability when they are too dry. By adding calcium chloride their moisture content can be stabilized and the soil can be used successfully in road construction.

We can also apply a number of other chemicals likesodium silicate, Resins , molasses, fly ash, etc.