plastic limit en atterberg limits

7/29/2019 PLASTIC LIMIT en Atterberg Limits

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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT

INTRODUCTION.

Soil mechanics is defined as the application of laws and principles of mechanics and

hydraulics to engineering problems dealing with soil as an engineering material.

Soil has many different meanings, depending on the field of study. To a geotechnical

engineer, soil has a much broader meaning and can include not only agronomic material,

but also broken-up fragments of rock, volcanic ash, alluvium, Aeolian sand, glacial

material, and any other residual or transported product of rock weathering.

Along with rock mechanics, soil mechanics provides the theoretical basis for analysis andconstruction management. Its used to analyze the deformation of the flow of fluid with

in natural and man made structures that are supported on or made of soil for example

building and bridge foundation, retaining walls, dams etc.

Under soil mechanics, the following are studied:-

Atterberg limits

Grading or particle size

Specific gravity

Linear shrinkage or cylindrical.

Atterberg limits. Is the measure of the nature of a fine-grained soil.

Liquid limit -water content where a soil changes from plastic to

liquid behavior. i.e begins to behave like a viscous mud and flow

under its own weight.

Plastic limit- water content where soil starts to exhibit plastic

behavior. i.e when it is about to change from a plastic to a crumbly

semi solid.

Shrinkage limit- is the water content at which further loss of water

in the soil will not cause further reduction in the volume of the soil.

jonah-sem 1-MUK-CEM 2010/2011 +256771806065 [email protected] 1
mailto:[email protected]:[email protected]


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i.e water content required just to fill the voids of a sample which

has been dried.

Finding liquid limits

Cone Penetrometer- moisture content which corresponds

with a cone penetration of 20mm.

Casagrande apparatus- moisture content corresponding

with 25 taps.

Finding plastic limits

Found by rolling a ball of wet soil between the palm of

the hand and a glass plate to produce a thread 3mm

thick before the soil begins to crumble.

The water content of the soil is in this state taken to be

as the plastic limit

Finding shrinkage limit

Found by measuring the weight and volume of the soil

at intervals as it is allowed to air dry until no further

volume changes takes place.

The volume is found by using a mercury displacement

vessel.



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1. Determination of the plastic limit using Cone Penetrometer.

Apparatus.

Oven (maintain temperature between 105 and 100oc)

Penetrometer

Sieve (0.425mm)

Flat glass plate

Palette knife (mixing knife)

Cone

Wash bottle

Metal cup

Evaporating dish

Moisture content tins

Deskator (air tight container)

How to obtain material from the field.

Sampling

Reconnaissance survey- this involves going to the field carrying out

reconnaissance survey depending on what type of construction (horizontal e.g.

roads or vertical e.g. buildings)

Procedure.

A sample of air dried soil of atleast 200g that passes through 0.425mm sieve is mixed

thoroughly with distilled water using a mixing knife until it forms a paste which is

homogeneous.

The paste is allowed to stand for 24 hours in an air tight container. This is to allow water

permeate thoroughly through the soil mass.



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The sample is then removed from the air tight container and remixed for atleast 10

minutes (without adding any more water).

The sample is then pushed into a metal cup using a mixing knife taking care to remove

the voids. This can be done effectively by taping the cup.

Place the cup on the Penetrometer. Attach the cone to the Penetrometer (it becomes a

cone Penetrometer). Lower the cone so that it just touches the surface of the soil (make

an arc on the surface of the soil)

The cone is the released for 5 seconds from the timer. Lock the cone in this position, then

lower the dial gauge and take a reading.

The cone is then lifted, cleaned and some wet soil is added and the process is repeated

atleast twice. If the difference between the first and second penetration reading is less

than 0.5mm, the average is calculated and recorded (if the difference is greater than

0.5mm, it means the remixing wasnt consistent hence remix sample and repeat).

Test

no.

Penetration 1

(mm)

Penetration 2

(mm)

Penetration 3

(mm)

Average

(mm)

I 15.7 16.2 16.4 16.1

II 18.4 18.9 18.2 18.5

III 21.4 21.4 26.1 23.0

IV 23.4 24.9 24.4 36.4

V 25.7 25.7 26.1 25.8

A sample of about 10g is removed from penetrating area and its moisture content

determined.

Test 1



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Tin no. Tin + wet(g) Tin + dry(g) Tin (g) Wet(g) Dry(g) Moisture(g) Moisture (%

I 32.5 27.5 14.5 18.0 13.0 5.0 27.8

II 33.0 27.0 15.0 18.0 12.0 6.0 33.3

III 33.0 27.0 15.0 18.0 12.0 6.0 33.3

Average moisture content (%) 31.5The whole procedure is repeated for atleast four with successive additions of distilled

water to the same sample. The amount of water added is chosen such that the range of

penetration values is approximately.

Test 2


I 37.0 29.5 15.0 22.0 14.5 7.5 34.1II 36.5 29.0 15.0 21.5 14.0 7.4 34.4

III 37.5 29.5 14.5 23.0 6.5 6.5 28.3

Average moisture content (%) 32.3

Test 3


I 39.5 31.0 15.0 24.5 16.0 8.5 34.7

II 38.0 30.0 15.0 23.0 15.0 8.0 34.8III 38.5 28.5 15.0 23.5 13.5 10.0 42.6


Test 4


I 44.0 32.0 14.5 29.5 17.5 12.0 40.7

II 42.0 32.0 15.0 27.0 17.0 10.0 37.0

III 42.0 32.0 14.5 27.5 17.5 10.0 36.4Average moisture content (%) 38.0



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Test 5


I 49.0 30.0 14.5 34.5 15.5 19.0 55.1II 40.5 30.5 14.5 26.0 16.0 10.0 38.5

III 39.0 29.5 14.5 24.5 15.0 9.5 38.8


Final table of results.

Penetration (mm) Moisture content (%)

16.1 31.518.5 32.3

23.0 37.4

36.4 38.0

25.8 44.1

A graph of penetration is plotted against moisture content.

A graph of penetration against

moisture content.

0

20

40

60

0 10 20 30 40

Moisture content (%)

Penetration

(mm)

From the graph, plastic limit =11.0 mm



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Metal cup /tin

Wash bottle

Air tight container

Casagrande

Procedure.

A sample of air dried soil of atleast 200g that passes through 0.425mm sieve is mixed

thoroughly with distilled water using a mixing knife until it forms a paste which is

homogeneous.

The paste is allowed to stand for 24 hours in an air tight container. This is to allow water

permeate thoroughly through the soil mass.

The sample is then removed from the air tight container and remixed for atleast 10

minutes (without adding any more water).

A portion of the sample is placed in the cup and leveled off parallel to the base of the cup.

The sample is then divided using a grooving tool along the diameter through the center.

The crank is then turned at a rate of 2 revolutions per second and the number of blows

required to bring the two portions together along the distance of 13mm is recorded.


plastic limit en atterberg limits

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