RESULTS AND DISCUSSION
SIEVE
ANALYSIS
The particle size analysis shows that the percentages passing number
200BS sieve are 22.18% and 13.02% for borrowpits 1 and 2 respectively.
These are shown in figure 1and 2
[CHART]
Figure 1: Particle size
distribution for borrowpit 1
[CHART]
Figure 2: Particle size distribution for borrowpit 2
ATTERBERG LIMIT
The results show that borrow pit 2 has sandy particle sizes
predominating. Hence the soil sample as a result of its particle size
composition happens to be a cohesionless soil with no plasticity while
pit 1 has liquid limit of 32.5%, plastic limit of 27.77%, plasticity
index of 5% and shrinkage limit of 5.8%. The result is shown in figure
3. Federal ministry of works general specification requirements for
roads and bridges (1997) recommend liquid limit not greater than 50%
for sub-grade and not greater than 35% for sub-base and base course.
Also, plasticity index not greater than 30% for sub-grade and not
greater than 12% for both sub-base and base. From the soil samples,
both borrowpits fall within this specification, thus making them
suitable for sub-grade, sub-base and base material.
[CHART]
Figure 3: Liquid limit for
borrowpit 1
4.3 NATURAL MOISTURE
CONTENT
The natural moisture content for the soil samples are 9.7% and 5%.
These values are suitable in accordance with Emesiobi (2000) which
states the classification for moisture content for different soil types
and indicate that natural moisture content in soil may range from below
5% to 50% in gravel and sand.
SPECIFIC
GRAVITY
The Specific gravity of the samples are 2.60 and 2.67, these values are
suitable in accordance with wright (1986) who states that the standard
range of values of Specific gravity of soils lies between 2.60 and 2.80.
CALIFORNIA BEARING
RATIO
The soaked CBR value for the soil samples are 70% and 66%. Federal
ministry (1997) recommended soaked CBR for sub-grade and sub-base soils
not less than 5% and 30% respectively. For the base (unsoaked and
soaked CBR) not less than 80%. The result for soil samples shows that
all the soils are suitable for sub-grade and sub-base course. The graphs
are shown in Figure 4 and 5
[CHART]
Figure 4: CBR graph for borrowpit
1
[CHART]
Figure 5: CBR graph for borrowpit
2
COMPACTION
The maximum dry density for the soil samples are
1.82Mg/m3 and 2.096Mg/m3 while that
of optimum moisture content are 16.24% and 13.5%. Figure 6 and 7 shows
the behavior of the soil for compaction.
[CHART]
Figure 6: Compaction graph for
borrowpit 1
[CHART]
Figure 7: Compaction graph for
borrowpit 2
UNCONFINED COMPRESSIVE STRENGTH
TEST
[CHART]Figure 8 shows the behavior of the soil samples for the
strength test. The unconfined compressive strength qufor borrowpit 1 is 91.5kPa. This shows that the shear strength of the
soil samples is adequate for use as either a foundation or sub-grade
material. Borrowpit 2 has no unconfined compressive strength value
because it is a sandy material and a cohesionless soil does not form an
unsupported cylindrical shape
Figure 8: Unconfined compressive
strength graph for borrowpit 1
CLASSIFICATION OF THE SOIL
SAMPLES
According to AASHTO soil classification borrowpit 1 can be classified as
A-2-4 material (silty or clayey gravel and sand). They are rated as good
materials for sub-grade material; it also satisfied condition for
construction materials while borrow pit 2 can be classified as A-3
material (fine sand) which is non-plastic. They are also rated as
excellent to good material for sub-grade.
CONCLUSION
From the tests carried out on the soil samples obtained from the two
borrow pits around Afe Babalola university, Ado-Ekiti, Ekiti State
Nigeria. The sieve analysis shows that the samples have less than 35%
passing 200BS sieve. Borrowpit 1 contains silty or clayey gravel and
sand while borrowpit 2 contains fine sand. The unconfined compressive
strength of borrowpit 2 could not be obtained as it is a sandy material.
Hence borrowpit 1 can be classified as A-2-4 material (silty or clayey
gravel and sand) while borrowpit 2 can be classified as A-3 material
(fine sand).
The samples are granular materials which can be used as a subgrade and
subbase materials.
RECOMMENDATION
Soil samples should be collected and taken to the laboratory for testing
before the commencement of earthworks on site. Further geotechnical
investigation can also be done on other borrowpits at Bank road, Ilawe
road, Iworoko road, and Ikere road, Ado-Ekiti, South Western Nigeria.