Core cutter: Types, uses and safety tips

Core cutters allow one to determine the soil’s density quickly. First, a calculation of void percentage is computed. A high void percentage indicates poor compaction of the soil. It is a rapid method for the field and helps find the field density of cohesive soils such as clay.

 

Why is it needed?

The occurrence of soil and its distribution varies from one location to another. The soil type depends on the rock type, the mineral constituents, and the region’s climatic conditions. The usage of soils is common in construction. The properties of soil can influence the stability of the structures built. For the stability of structures, such as bridges, tunnels, buildings, highways, and dams, there is a requirement for suitable foundation soil. Testing the ground is a requirement before using it as a material in construction. The soil properties need to be understood for designing and constructing proposed structures. 

Geotechnical properties of soil have different influences on the construction of civil engineering structures.  

 

• Specific Gravity

Specific Gravity entails the ratio of the mass of the soil solids to the group of an equal volume of water. This property is linked closely with the chemical composition of water. Therefore, specific gravity is a vital indicator of the quality of the soil and is applicable in the classification of the minerals in the soil. 

• Density Index

The degree of compaction of the fine-grained soils is measured concerning the maximum dry density for a particular compactive effort. It measures the degree of compactness and stability of the soil stratum. 

• Consistency

Water largely influences the consistency of fine-grained soils. A gradual loss of water hifts the soil from a slurry state to a plastic state, semi-solid state, and then to a solid form. Consistency is an important measurement. The plasticity and cohesion of soils explain their workability. 

• Particle Size Analysis

Particle size analysis allows for the classification of soils. The data obtained from grain size curves allow for the development of filters and determine the suitability of a particular soil. Furthermore, this analysis can help predict soil-water movement, and one can speculate a proper gradation of filter material.  

• Compaction

Soil compaction is a key in ground improvement techniques. By compacting the soil, there is a close arrangement of soil grains. Compaction increases the strength of the soil and reduces the soil’s permeability and compressibility. 

• Consolidation

Soil goes under compression when bearing the weight of construction activities. Compression is the re-arrangement, crushing of particles, and elastic distortions. The consolidation test allows for obtaining soil data, which helps to understand the rate and amount of settlement in structure. 

• Permeability

The movement of water has a prime role in the behavior of soil. Data from permeability tests in the field help civil design structures. The permeability of the soil has a direct effect on the stability of a structure.

• Shear Strength

The resistance of soil is due to the friction and interlocking of particles. The shear strength is based on the cohesion and friction angle. This strength is affected by the materials used, mineralogy of the soil, grain particle size, and construction features such as layers, joints, fissures, and cementation. 

Such properties in soil have different effects on structures built. The interactions between these geotechnical properties help with the construction of the foundations for the building of new structures.  

 

What is a core cutter method?

A core cutter method allows for determining the dry density for the cohesiveness of soil. It is a test that checks the soil whether it has achieved a dried condition. The determined dry density helps with the construction of pavements and highways. This method is used only for cohesive, fine-grained soils without stones. When the moisture content of the soil is determined, this allows for calculating the dry density and void percentage. 

See also about: Consistency

Types of core cutters

 

Core cutter manufacturers provide custom-desired sizes and length of the machine, which can be

Fully automatic core cutting

Automatic core cutter

Manual core cutter

 

 

Apparatus and preparation of core cutter method

Specifications about the apparatus are detailed below:

• A cylindrical, steel core cutter 
• A steel dolly of 25mm high and 100mm in diameter
• Steel Rammer
• Weighing balance
• Knife
• Steel Ruler
• Spade or pickaxe
• Straightedge or steel strip. 
• Apparatus to determine the moisture content
• Device to extract core sample. 

Calculate the internal volume of the core in cubic centimeters. The cutter should be weighted to the nearest 1 gram. In addition, the mold factor of each cutter should be measured, which helps calculate the soil’s bulk density. 

 

Procedure of a core cutter method

There is a five-step procedure for using a core cutter method. 

• Preparation

Firstly, the core cutter is set up at the experimental location. Then, the area test is leveled, and all loose material is removed.

• Place

A cylindrical mold is greased and fitted into the dolly.

• Rammer

The mold is driven into the soil with a rammer until about 10mm of the dolly remains above the soil surface. The use of a jack is preferred as it least disturbs the soil. If the dolly is driven down entirely, the soil compresses, and there are inaccurate results. 

• Extract

The cylinder is removed by excavating the sides without creating any disturbance to the sample. Next, a spade removes the cylinder, dolly, and soil. 

• Trim

Extra soil at both ends is trimmed, and the weight of the soil is determined. 

From the known dimension of the cutter, the volume is determined. The usage of an oven-drying method determines the moisture content of the soil. The use of a formula computes the dry density of the soil. The calculation has the following chief parameters:  

• Soil Weight
• Bulk Density
• Moisture content or Water Content
• Dry density 
• The volume of Core Cutter
• Weight of Core Cutter
• Weight of Core Cutter + Weight of Soil
• Maximum dry Density

 

Using a core cutter for sampling concrete

Concrete cores are usually cut using a rotary core cutting tool with diamond bits.

Advantages of using core cutter 

There are several advantages of using the core cutter method.

• It is relatively fast and straightforward.
• Also, it can be carried out in a natural environment without sampling disturbance. 
• This method is highly suitable for determining dry density for fine-grained soils. 

 

Disadvantages of core cutter method

There are some disadvantages to note of. 

• This method is only practical where the soil is exposed, and the cutter can easily be driven down. 
• It is not suitable with soils that are not cohesive. 

 

Precautions for using the core cutter method

There are some helpful precautions to take care of when using the core cutter method. Before lifting out the core cutter, the soil should be removed around the core cutter. This helps to minimize any disturbances. The test should only be performed on fine-grained cohesive soils. The core cutter apparatus should be driven into the ground until the dolly is only halfway in to avoid the compaction of the soil. Frequent checks should be made on the apparatus for any damage as that may lead to inaccuracies in measurement. Any repair for the cutter will require the mold to be determined again. 

 

Maintaining and cleaning your core cutter

A heavy-duty machinery of this scale requires professional cleaning and maintenance services. Most manufacturers these days provide regular cleaning and maintenance services.

FAQs

What is the core cutter apparatus?

A core cutter of a known volume is driven into the soil via a rammer.

Which is more accurate for determining the field density of the soil, the core cutter or sand replacement method?

The core cutter method is more accurate for determining the field density of soil.

Why are only fine-grained soils used for this method?

There is no use for the core cutter in soils with stones or large particles. This leads to inaccuracies in the measurements.

What is the difference between the core cutter and the sand replacement method?

The core cutter method determines the density, such as clay soil or other cohesive soils. In the sand replacement method, a small pit is made, and the soil excavated is weighed.

Why is 95% compaction needed?

The layer is fully compacted when the soil compaction is at 95%. A well-compacted soil ensures the soil under various constructions can take the load.