The determination of dry density by the core cutter method generally involves the hammering or jacking of a steel cylinder ( with known mass and volume) into the soil thereby and determining the mass of the soil. This method of dry density determination is most desirable for the cohesive soil. Core cutter method is only used on fine-grained cohesive soils that do not contain stones. Core cutter method for dry density determination is commonly used for control of earthworks as well as the subgrade materials. This method is not desirable for coarse-grained soil or coarse-grained pavement materials.
OBJECTIVES OF CORE CUTTER METHOD
The primary objective of the sand replacement method is to determine the dry density of soil. It is used as a control test to check if the soil has acquired the designated dry density after compaction. The determined in situ dry density is necessary for the design of pavement and highway.
1. A steel rammer of mass 9kg and overall length including the foot and staff of about 900mm.
2. A cylindrical core cutter with 100mm internal diameter and 130mm long.
3. Weighing balance with an accuracy of 1 gram.
4. Steel dolly with 100mm internal diameter and 25mm high.
5. Palette knife.
6. Straight edge, ruler of steel etc.
The procedure for the dry density determination by the core cutter method involves the following series of steps:
i. The experimental setup of the cylindrical core cutter along with the dolly is first made.
ii. The steel dolly is then placed over the cutter to prevent the damage to the edges of the core cutter.
iii. The cylinder is then embedded into the ground up to its full height with the help of rammer and is taken out by excavating its sides without disturbing the sample.
iv. The surplus soil at both the ends is trimmed and the weight of the cylinder with soil is determined.
v. Then, from the known dimension of the cutter, the volume and the moisture content of the soil is determined.
vi. The dry density of the soil is then computed using the following formula:
Bulk Density (γ t ) = (W 2 – W 1 ) / V
Dry Density (γ d ) = γ t / ( 1 + W)
W 1 = Weight of cutter
W 2 = Weight of the soil + cutter
W 2 – W 1 = Weight of soil
V = Volume of the cutter
ADVANTAGES OF CORE CUTTER METHOD
1. The method is relatively fast and simple.
2. Core cutter test can be carried out in the natural environment without sampling disturbance.
3. Core cutter method is highly suitable for the dry density determination of cohesive soil as well as soft, fine-grained soils.
DISADVANTAGES OF CORE CUTTER METHOD
1. This method is only practicable at places where the surface of the soil is exposed and the cutter can be easily driven.
2. It is not suitable for cohesionless soil.