Experiment: Determination of Field Density Using Core Cutter Method
1. OBJECTIVE
The objective of this experiment is to determine the in-situ (field) bulk density and dry density of soil using the core cutter method.
2. APPARATUS REQUIRED
- Cylindrical core cutter (10 cm internal diameter, 13 cm height)
- Steel dolly (2.5 cm high)
- Steel rammer
- Balance (with an accuracy of 1 g)
- Spade or digging tool
- Straightedge or knife
- Moisture content containers (cans)
- Drying oven
3. THEORY
The core cutter method is a field-based test used to measure the in-situ density of fine-grained cohesive soils. It is not suitable for coarse-grained, gravelly, or very dry soils. The method involves driving a cylindrical cutter of a known internal volume into the soil to obtain a relatively undisturbed sample. By measuring the mass of the soil collected within the known volume of the cutter, the bulk density of the soil can be calculated. The dry density, a crucial parameter in geotechnical engineering for assessing the degree of compaction, is then determined by measuring the water content of the soil sample.
The bulk density (ρb) is the mass of the soil per unit volume, and the dry density (ρd) is calculated using the formula:
Dry Density Formula:
\[ \rho_d = \frac{\rho_b}{1+w} \]
where:
- ρd = Dry density of the soil
- ρb = Bulk density of the soil
- w = Water content (expressed as a decimal)
4. PROCEDURE
- The internal diameter and height of the core cutter were measured to calculate its internal volume.
- The mass of the empty, clean core cutter (M₁) was recorded.
- A small area of the ground was leveled and cleared of any loose material.
- The core cutter was placed on the prepared ground surface, and the dolly was placed on top of the cutter.
- The cutter was driven vertically into the soil using the rammer until approximately 1 cm of the dolly remained above the surface.
- The soil surrounding the cutter was excavated with a spade to facilitate its removal.
- The core cutter containing the soil sample was carefully lifted from the ground.
- The soil surfaces at the top and bottom ends of the cutter were trimmed flat using a straightedge.
- The core cutter filled with soil was cleaned on the outside and its mass (M₂) was recorded.
- A representative sample of soil was taken from the core and placed in a moisture can for the determination of water content using the oven-drying method.
5. OBSERVATION AND CALCULATION
1. Determination of Bulk Density
- Internal Diameter of cutter (D) = 10 cm
- Height of core cutter (H) = 13 cm
- Mass of Empty core cutter (M₁) = 0.915 kg = 915 g
- Mass of core cutter + soil (M₂) = 2.735 kg = 2735 g
Volume of cutter (V):
\[ V = \frac{\pi}{4} \times D^2 \times H = \frac{\pi}{4} \times (10)^2 \times 13 = 1021.02\ cm^3 \]
Mass of soil (M):
\[ M = M_2 – M_1 = 2735 – 915 = 1820\ g \]
Bulk Density (ρb):
\[ \rho_b = \frac{M}{V} = \frac{1820}{1021.02} = 1.782\ g/cm^3 \]
2. Determination of Water Content (w)
| Observation |
Can I |
Can II |
| Weight of empty can (w₁) |
10.433 g |
8.683 g |
| Weight of can + wet soil (w₂) |
21.288 g |
23.677 g |
| Weight of can + dry soil (w₃) |
20.440 g |
22.500 g |
| Mass of water (Mw = w₂ – w₃) |
0.848 g |
1.177 g |
| Mass of solids (Ms = w₃ – w₁) |
10.007 g |
13.817 g |
| Water Content (w = Mw/Ms) |
8.47% |
8.52% |
Average Water Content (w):
\[ w = \frac{8.47\% + 8.52\%}{2} = 8.50\%\ or\ 0.0850 \]
3. Determination of Dry Density (ρd)
Dry Density (ρd):
\[ \rho_d = \frac{\rho_b}{1+w} = \frac{1.782}{1+0.0850} = 1.642\ g/cm^3 \]
6. RESULT
The in-situ density of the soil sample was determined as follows:
- Bulk Density (ρb): 1.782 g/cm³
- Water Content (w): 8.50%
- Dry Density (ρd): 1.642 g/cm³
7. DISCUSSION AND CONCLUSION
The field density of the soil at the specific location was successfully determined using the core cutter method. The results show a bulk density of 1.782 g/cm³ and a dry density of 1.642 g/cm³. This method is relatively simple and provides a quick determination of soil density in the field, which is essential for evaluating the degree of compaction of soil layers in earthworks such as embankments and foundations.
Potential sources of error in this experiment include disturbance of the soil sample while driving the cutter, improper trimming of the soil, or errors in weighing. The method’s applicability is limited to cohesive, fine-grained soils that are free from large particles like gravel. The experiment was conducted with care to minimize these errors, and the results are considered a reliable representation of the in-situ soil conditions.
