TEST TITLE: DETERMINATION OF FIELD DENSITY OF SOILS BY THE CORE CUTTER METHOD
1.0
OBJECTIVE
To determine in-situ density of fine-Grained natural or compacted soils free form aggregate using a core cutter.
2.0
THEORY OF THE EXPERIMENT
Field density is defined as weight of unit volume of soil present i n site. That is :
Density or unit weight of soils may be determined by using the following method:
i. Core cutter method ii. Sand replacement test iii. Rubber balloon test iv. Water displacement method v. Gamma ray method
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Hear we use core cutter method, the equipment arrangement is shown as fallows,
a) Rammer
b) Dolly, c) Cutter
Core cutter method is used for finding field density of cohesive/clayey soils placed as fill. It is rapid method conducted on field. It cannot be applied to coarse grained soil as the penetration of core cutter becomes difficult due to increased resistance at the tip of core cutter leading to damage to core cutter. The cylindrical cores of standard volume, 13cms long and 10cms diameter, they have a sharpened edge at one end to improve penetration of the soil surface. These cores are driven fully into the surface to be tested; they are removed from the ground without disturbing the core contents. In the laboratory they are cut flush top and bottom and weighed.
Bulk density can be quickly calculated, and by determining the moisture content of the soil the dry density of the fill can be calculated and hence the voids percentage. A high percentage of voids indicating poor compaction. Unit weight is designed as the weight per unit volume. Here the weight and volume of soil comprise the whole soil mass. The voids in the soil may be filled with both water and air or only air or only water consequently the soil may be wet, dry or saturated. In soils the weight of air is considered negligible and therefore the saturated unit weight is maximum, dry unit weight is minimum and wet unit weight is in between the two.
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3.0
TEST EQUIPMENTS
1. Cylindrical core cutter seamless steep tube, 130mm long 10cm internal diameter with wall thickness of 3mm, bevelled at one end; giving a volume of 1000cm 3. 2. Steel dolly, 2.5cm high and 10cm internal diameter with wall thickness of 7.5mm with a lip to enable it to be fitted on top the core-cutter
3. Steel rammer with solid mild steel foot 14cm diameter and 7.5cm height with a concentrically screwed 2.5cm diameter solid mild steel staff 4. Balance.
5. Steel rule.
6. Container for determination of water content. 7. Soil sample = Fine grained soil where 90% of soil passes through 4.75mm I.S Sieve 3|Page
4.0
PREPARATION OF SAMPLE
1. Firstly, the internal volume of core cutter was calculated.
2. After that the weight of empty core cutter were recorded and labelled as in table. 3. The oil was applied on inner surface of core cutter, it functions to prevent soil sample stuck inside core cutter. 4. The core cutter were place vertically on a freshly prepared plain ground with dolly on it, and gently hammer it so that the cutter will get pushed in the soil completely.
Take out the soil sample from cylinder core cutter 5. Finally the field core cutter were take-out gently by removed the side material and the top and bottom surface were properly trim and it weight were recorded.
The soil core was removed from the cutter and a representative sample was placed in an air tight container to determine water content.
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5.0
OBSERVATION TABLE
a) Determination of bulk and dry density of soil
Determination No.
1
1
Mass of empty core-cutter (M1)
g
896
2
Mass of core – cutter + wet soil (M2)
g
2808
3
Mass of wet soil (M 2 - M1)
g
1912
4
Volume of core-cutter (V)
cm
997.5
g/cm
1.917
M
5
2
Bulk density b =
3
M 1
V
6
Dry density of soil
3
g/ cm
d
1
1.45
w
b) Determination of water content of soil
Container No.
1
2
3
Mass of empty container with lid
(M1)
g
18
18
16
Mass of container with lid and wet soil
(M2)
g
88
76
64
Mass of container with lid and dr y soil
(M3)
g
71
64
52
x100
%
32
26
33
Water content, w
w
M d
6.0
2
M
3
M 3
M 1
COMPUTATION AND RESULTS
Mass of wet soil (M2 – M1) = 2808g – 896g = 1912g H=12.7 cm
Volume of core-cutter (v) = πr 2h = π(5) 2(12.7)
D=10 cm
= 997.5 cm 3
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Bulk density, ρ b = (M2 – M1) / V = 1912g g 997.5 cm 3 = 1917 g/cm 3
Dry Density of soil, ρ b = ρ / (1+w) = 1.917/ ( 1+ 0.32) = 1.45 g/cm3
Water content, w = M w / Md = [(M2 – M3) / (M2 – M3) ] x 100
Sample 1 : W1 =
x 100 = 32 %
Sample 2 : W1 =
x 100 = 26 %
Sample 3 : W1 =
x 100 = 33 %
7.0
DISCUSSION
Based on our experiment we got mass of empty core cutter is 896g, mass of wet soil is 1912g and volume of core cutter is 997.5cm 3. For calculate the value of bulk density,ρ b we must use the mass of wet soil divide with the volume. So, we got 1.917g/ cm 3 for bulk density. For calculate the value of dry density, we must use the value of bulk density and water content. So, we got 1.45 g/cm 3.
For determine the water content of soil, we must have the value of the wet and dry soil. To get the mass of the dry soil, we put the three sample of soil and dry it into the oven. For mass of wet soil, we got 70g for sample one, 58g for sample two and 48g for sample three. After the sample was dry in oven, the sample was weight to get the mass of the dry soil. So, for sample one 53g, sample two 46g and the sample three is 36g. For calculate the water content, the mass of the wet soil must divide with mass of the dry soil. For sample one, we got 32%, sample two
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26% and sample three we got 33%. This result shows that the sample three has more percent of water content.
8.0
CONCLUSION
Field density is used in calculating the stress in the soil due to its overburden pressure it is needed in estimating the bearing capacity of soil foundation system, settlement of footing earth pressures behind the retaining walls and embankments. Stability of natural slopes, dams, embankments and cuts is checked with the help of density of those soils. It is the density that controls the field compaction of soils. Permeability of soils depends upon its density. Relative density of cohesion less soils is determined by knowing the dry density of soil in natural, loosest and densest states. Void ratio, porosity and degree of saturation need the help of density of soil.
If soils are below water table, submerged unit weight is also estimated. Unit weight of soil reflects the strength of soil against compression and shear. Unit weight of soil is used in calculating the stresses in the soil due to its overburden pressure. It is useful in estimating the bearing capacity and settlement of foundations. Earth pressure behind there retaining walls and in cuts is checked with the help of unit weight of the associated soils. It is the unit weight of the soil which controls the field compaction and it helps in the design of embankment slopes.
Permeability of soil depends on its unit weight .It may be noted here that , in the field the unit weight refers to dry unit weight only because the wet unit weight of soil at location varies from season to season and based on the fluctuations of the local water table level and surface water. Core cutter method in particular, is suitable for soft to medium cohesive soils, in which the cutter can be driven. It is not possible to drive the cutter into hard, boulder or murrumy soils. In such case other methods are adopted.
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9.0
REFERENCES
1. Fundamentals of Geotechnical Engineering, Fourth Edition, Braja M.Das,Christopher M.Shortt,2005. 2. Principles of Geotechnical Engineering seventh Edition, Braja M.Das, Chris Carson, 2010. 3. Determine The In-Situ Dry Density Of Soil By Core Cutter Method 4. www.engineeringcivil.com - Determine The In-Situ Dry Density Of Soil By Core Cutter Method 5. www.eieinstruments.com - Field Density Test Apparatus Core Cutter Method
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