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MATERIAL CHARACTERSTICSDEPARTMENT :CIVIL ENGINEERING

CBRCalifornia bearing ratio is defined as the ratio (expressed as percentage) between the load sustained by the soil sample at a specified penetration of a standard plunger (50 mm diameter) and the load sustained by the standard crushed stones at the same penetration.

CBR test procedureNormally 3 specimens each of about 7 kg must be compacted so that their compacted densities range from 95% to 100% generally with 10, 30 and 65 blows.Weigh of empty mouldAdd water to the first specimen (compact it in five layer by giving 10 blows per layer)After compaction, remove the collar and level the surface.Take sample for determination of moisture content.Weight of mould + compacted specimen.Place the mold in the soaking tank for four days (ignore this step in case of unsoakedCBR.Take other samples and apply different blows and repeat the whole process.After four days, measure the swell reading and find %age swell.Remove the mould from the tank and allow water to drain.Then place the specimen under the penetration piston and place surcharge load of 10lb.Apply the load and note the penetration load values.Draw the graphs between the penetration (in) and penetration load (in) and find the value ofCBR.Draw the graph between the %ageCBRand Dry Density, and findCBRat required degree of compaction.

Points regarding CBRThe stronger the subgrade (the higher the CBR reading ) the less thick it is necessary to design and construct the road pavement, this gives a considerable cost saving.

Presence of coarse grained material gives poor results . Material passing through 20 mm sieve only is used in the test

Conversely if CBR testing indicates the subgrade is weak (a low CBR reading) we must construct a suitable thicker road pavement to spread the wheel load over a greater area of the weak subgrade in order that the weak subgrade material is not deformed, causing the road pavement to fail.Modulus of Subgrade reaction of soilModulus of subgrade reaction is the reaction pressure sustained by the soil sample under a rigid plate of standard diameter per unit settlement measured at a specified pressure or settlement.P=K

Procedure to find modulus of subgrade reactionPrepare the test site and remove the loose material so that 75 cm diameter plate rests horizontally in full contact with the soil sub-grade.

Place the plate accurately and then apply a seating load equivalent to a pressure of 0.07 kg/cm 2 and release it after few seconds.

The settlement dial readings are adjusted to zero for zero load.

A load is applied by means of the jack, sufficient to cause an average settlement of about 0.25 mm. When there is no perceptible increase in settlement or when the rate of settlement is less than 0.025 mm per minute, the load dial reading and the settlement dial readings are noted.

Procedure to find modulus of subgrade reaction The average of the three or four settlement dial readings is taken as the average settlement of the plate corresponding to the applied load. The load is increased till the average settlement increased to a further amount of about 0.25 mm and the load and the average settlement readings are noted as before. The procedure is repeated until the settlement is about 1.75 mm

IS 9214 1979Blending of aggregatesA "blend" is a mixture of two or more different things or substancesGrading:The process that determine the particle-size distribution of a representative sample of the aggregateBleanding:The process of combining aggregates of various sizes to obtain a specified gradationReasons for blending:Obtain desirable gradationWhere single natural or quarried material not enoughEconomical to combine natural and process materials Increase / Decrease permeability

Soil stabilizationSoil stabilization is the process which is used to improve the engineering properties of the soil and thus making it more stable. Soil stabilization is required when the soil available for construction is not suitable for the intended purpose. It includes compaction, preconsolidation, drainage and many other such processes.WHY to stabilize soilIt is used to increase the bearing capacity of foundation soils.It helps to decrease the void ratio of the soil.Stabilization of soil increases the shear strength of soil.METHODS OF SOIL STABILIZATIONCement stabilizationLime stabilizationChemical stabilizationBituminous stabilizationGrouting concrete stabilizationGeotextile stabilizationReinforced earth stabilization

CEMENT STABILIZATIONAdvantagesIt is widely available.It is highly durableSoil cement reduces the swelling characteristics of the soil.It is commonly used for stabilizing sandy and other low plasticity soils.DisadvantagesCracks may form in soil cement.It is harmful for environment.It requires extra labor.The quantity of water must be sufficient for hydration of cement and making the mixture workable.Cement stabilizationof soil is done by mixing pulverized soil and Portland cement with water and compacting the mix to attain a strong material. The material obtained by mixing soil and cement is known as soil-cement. The soil cement becomes a hard and durable structural material as the cement hydrates and develops strength.Cement stabilization is done while the compaction process is continuing.LIME STABILIZATIONAdvantagesSoil becomes more workable.Strength is generally improved.Lime stabilization increases the compressive strength sometimes as high as 60 times.It is effective for soils.DisadvantagesLime is produced by burning of lime stone in kilns, so that it is harmful for environment.It needs more cost to burnt lime stone.It is not effective for sandy soils.Lime stabilization is not effective for sandy soils. However these soils can be stabilized with clay, fly ash etc which serve as hydraulically reactive ingredients. The ratio of fly ash to lime generally varies in between 3 to 5. The fly ash is used is about 10 to 20% of the soil weight.

chemical stabilizationIn this soil is stabilized by adding different chemicals. The main advantage of chemical stabilization is that setting time and curing time can be controlled. Chemical stabilization is however generally more expensive than other types of stabilization.

Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextilesgeogrids geonets geomembranes geosynthetic clay liners geofoam geocells and geocomposites

List of Indian codes for practice on GEOSYNTHETICSIS 13321 (part-1)-92 :Glossary of terms for geosynthetics : materials & properties.

IS 13325-92: Test method for determination of tensile properties of extruded polymer grids using wide strip methods.

IS 13326 (part-1)-92 :Method of test for evaluation of interference friction between geosynthetics and soil by modified direct shear method.

Functions of geosynthetics as stabilizersAs a stabilizer

The natural soil on which thegeotextile is placed is usually a wet, soft, compressible material, exhibiting very little strength.

By acting asa separator, the geotextile allows water from the soft natural soil to pass from this soil into a free-drainingconstruction soil, which in turn allows consolidation of the natural soil to take place.

As a result of the consolidation process, there is a strength gain in the natural soil, which then provides an adequate foundationfor construction to take place.

As a reinforcing agent

Reinforcement the strength characteristics (stressstrain) of the geotextile provide added strength to the whole system.

Geocells (also known as Cellular Confinement Systems) are three-dimensional honeycombed cellular structures that form a confinement system when infilled with compacted soil.Geotextiles form one of the two largest groups of geosynthetics. They are textiles consisting of synthetic fibers rather than natural ones such as cotton, wool, or silk.

AdvantagesThe manufactured quality control of geosynthetics in a controlled factory environment is a great advantage over outdoor soil and rock construction. Most factories are ISO 9000 certified and have their own in-house quality programs as well.The low thickness of geosynthetics, as compared to their natural soil counterparts, is an advantage insofar as light weight on the subgrade, less airspace used, and avoidance of quarried sand, gravel, and clay soil materials.The ease of geosynthetic installation is significant in comparison to thick soil layers (sands, gravels, or clays) requiring large earthmoving equipment.Design methods are currently available from many publication sources as well as universities which teach stand-alone courses in geosynthetics or have integrated geosynthetics in traditional geotechnical, geoenvironmental, and hydraulic engineering courses.When comparing geosynthetic designs to alternative natural soil designs there are usually cost advantages and invariably sustainability (lower CO2 footprint) advantagesDisadvantagesLong-term performance of the particular formulated resin being used to make the geosynthetic must be assured by using proper additives including antioxidants, ultraviolet screeners, and fillers.The exposed lifetime of geosynthetics, being polymeric, is less than unexposed as when they are soil backfilled.Clogging of geotextiles, geonets, geopipe and/or geocomposites is a challenging design for certain soil types or unusual situations. For example, loess soils, fine cohesionless silts, highly turbid liquids, and microorganism laden liquids (farm runoff) are troublesome and generally require specialized testing evaluations.Handling, storage, and installation must be assured by careful quality control and quality assurance about which much has been written.

Polymer and Rubber modified bitumenBitumen is an oil based substance. It is a semi-solid hydrocarbon product produced by removing the lighter fractions (such as liquid petroleum gas, petrol and diesel) from heavy crude oil during the refining process. As such, it is correctly known as refined bitumen.

Resilient Modulus Ratio (MRR)

Resilient Modulus, MR is a ratio of applied stress to recoverable resultant (horizontal) strain. The resilient modulus test is basically a repetitive load test using the stress distribution principles of the indirect tensile test. Resilient modulus is close to conditions that prevail in the field since a loading pulse is followed by a rest period. The loading time and rest period can be varied to represent different vehicle speed and traffic intensity. The values of resilient modulus can be used to evaluate the relative quality of materials as well as to generate input for pavement design or pavement evaluation and analysis. The repeated load indirect tensile test for determining resilient modulus of bituminous mixtures was conducted by applying compressive loads with a haversine waveform.Resilient Modulus Ratio (MRR)The load was applied vertically on the vertical diametral plane of cylindrical specimen of bituminous concrete. The resulting horizontal deformation of the specimen was measured. The loading frequency of 2 Hz inducing 0.25 s loading period and the rest period of 0.45 s were used. From the instantaneous resilient horizontal deformations the resilient moduli of PMBC and BC mixes were calculated at test temperature of 250C using the equation

Dynamic modulusDynamic modulus :The absolute value of the complex modulus that defines the elastic properties of a linear viscoelastic material subjected to a sinusoidal loading, | E*| Dynamic modulus is Calculated as follows: Dynamic modulus = o/ocomplex modulus : It is a complex number that defines the relationship between stress and strain for a linear viscoelastic material, E*. Linear material :It is a material whose stress to strain ratio is independent of the loading stress applied.