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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.
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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT
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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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT
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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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT
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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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT
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
Tin no. Tin + wet(g) Tin + dry(g) Tin (g) Wet(g) Dry(g) Moisture(g) Moisture (%
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
Tin no. Tin + wet(g) Tin + dry(g) Tin (g) Wet(g) Dry(g) Moisture(g) Moisture (%
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
Average moisture content (%) 37.4
Test 4
Tin no. Tin + wet(g) Tin + dry(g) Tin (g) Wet(g) Dry(g) Moisture(g) Moisture (%
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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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT
Test 5
Tin no. Tin + wet(g) Tin + dry(g) Tin (g) Wet(g) Dry(g) Moisture(g) Moisture (%
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
Average moisture content (%) 44.1
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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CIV 1104 Elements of geotechnical engineering-coursework 1- LAB. REPORT
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.
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