PLASTIC LIMIT en Atterberg Limits

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

INTRODUCTION.

Soil mechanics is defined as the application of laws and a nd 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 and construction management. It’s 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 +256771806065

[email protected]

1


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.


+256771806065

[email protected]

2


1. Determination of the plastic limit using Cone Penetrometer.

Apparatus. o

 Oven (maintain temperature between 105 and 100 c)  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 un til 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. ©jonah-sem 1-MUK-CEM 2010/2011

+256771806065

[email protected]

3


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 wasn’t consistent hence remix sample and repeat).

Test

Penetration 1

Penetration 2

Penetration 3

Average

no. I II III IV V

(mm) 15.7 18.4 21.4 23.4 25.7

(mm) 16.2 18.9 21.4 24.9 25.7

(mm) 16.4 18.2 26.1 24.4 26.1

(mm) 16.1 18.5 23.0 36.4 25.8

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

Test 1


+256771806065

[email protected]

4


Tin no. Tin + wet(g) Tin + dry(g) I 32.5 27.5 II 33.0 27.0 III 33.0 27.0 Average moisture content (%)

Tin (g) 14.5 15.0 15.0

Wet(g) 18.0 18.0 18.0

Dry(g) 13.0 12.0 12.0

Moisture(g) 5.0 6.0 6.0

Moisture (%) 27.8 33.3 33.3 31.5

The 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


Tin (g) 15.0 15.0 14.5

Wet(g) 22.0 21.5 23.0

Dry(g) 14.5 14.0 6.5

Moisture(g) 7.5 7.4 6.5

Moisture (%) 34.1 34.4 28.3 32.3

Tin (g) 15.0 15.0 15.0

Wet(g) 24.5 23.0 23.5

Dry(g) 16.0 15.0 13.5

Moisture(g) 8.5 8.0 10.0

Moisture (%) 34.7 34.8 42.6 37.4

Tin (g) 14.5 15.0 14.5

Wet(g) 29.5 27.0 27.5

Dry(g) 17.5 17.0 17.5

Moisture(g) 12.0 10.0 10.0

Moisture (%) 40.7 37.0 36.4 38.0

Test 3

Tin no. Tin + wet(g) Tin + dry(g) I 39.5 31.0 II 38.0 30.0 III 38.5 28.5 Average moisture content (%) Test 4



+256771806065

[email protected]

5


Test 5


Tin (g) 14.5 14.5 14.5

Wet(g) 34.5 26.0 24.5

Dry(g) 15.5 16.0 15.0

Moisture(g) 19.0 10.0 9.5

Moisture (%) 55.1 38.5 38.8 44.1

Final table of results.

Penetration (mm) 16.1 18.5 23.0 36.4 25.8

Moisture content (%) 31.5 32.3 37.4 38.0 44.1

A graph of penetration is plotted against moisture content.

A graph of penetration against moisture content. 60 n o i ) t 40 a r m t m20 e ( n e 0 P 0

10

20

30

40

Moisture content (%)

From the graph, plastic limit =11.0 mm


+256771806065

[email protected]

6


Note.  The moisture content corresponding to the cone penetration of 20mm is taken as

the liquid limit of the soil.



During air drying of the soil, the soil is spread on a tray and kept at room temperature.

 In determination of water content,  Measure and record the weight, W1 of an empty tin.  Place the wet sample in the tin, and then measure and record the weight

W2 of the tin + wet sample.  Place the tin containing the wet sample in the oven for 24 hours.  Measure and record the weight, W3 of the tin + dry sample.  Treatment of results.  Weight of wet sample,Ww = W2 – W1  Weight of dry sample, Wd =W3 – W1  Therefore, weight of moisture, Wm =Ww - Wd

Moisture content (%) = (Wm /Ww) × 100%

2. determination of liquid limit using casagrande.

Apparatus.

 Flat glass  Palette (mixing knife)  Grooving tool and gauge  Evaporating dish


+256771806065

[email protected]

7


 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 un til 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.


+256771806065

[email protected]

8

PLASTIC LIMIT en Atterberg Limits

Recommend Documents