CBR Test on Subgrade Soil – Procedure and Observation


The CBR Test is a measure of the resistance of a material to penetration of standard plunger under controlled moisture conditions and density. The California Division of Highways developed it as a method of evaluating and classifying soil-subgrade and base course materials for flexible pavements.
The test might be conducted in the undisturbed or remoulded sample. A cylindrical plunger of 50 mm diameter is used to penetrate a pavement component material at 1.25 mm/minute.
Loads of 5 mm and 2.5 mm are recorded. It is expressed as a percentage of standard load value at a respective deformation level to obtain the value of CBR.
California Bearing Ratio Test on Subgrade Soil
The primary aim of this test is to determine the California Bearing Ratio value of the subgrade soil.
Apparatus for CBR Test
Any compression machine that can operate at a constant rate of 1.25 mm per minute can be used. It consists of a moulds of 150 mm and 175 mm height offer a collar of about 50 mm length and detachable perforated base.
The procedure of CBR Test
Sieve the sample through 20 mm IS sieve. Take a sample of 5 kg of soil specimen. Add water to the soil in the quantity such that field moisture content or optimum moisture content is reached. After this, the water and soil are mixed thoroughly. Spacer disk is placed over the plate of the base at the bottom of the mould. And a coarse filter paper is placed over the spacer disc in the CBR test.
The prepared mixture of soil water is divided into five parts. The mould is cleaned, and oil is applied. Then fill one-fifth of the mould with the soil prepared. The layer is compacted by giving 56 evenly distributed blows using a hammer of weight 4.89 kg.
The top layer of the compacted soil is scratched. Again the second layer is filled, and the procedure is repeated. After the third layer, the collar also gets attached to the mould, and the process is continued. After the fifth layer, the collar is removed, and excess oil is struck off. The base plate is removed and the mould is inverted. Then it is clamped to the base plate.
The CBR test is one of the most commonly used methods to evaluate the strength of a sub-base, subgrade oil, and base course material for the design of thickness for airfield pavement and highways.

Comments

Post a Comment

Popular posts from this blog

Advantages of Universal Testing Machine

The main advantage of investing in a universal testing machine is that the device can be used to test the strength, durability, and suitability for most any material. A universal testing machine has the capability to pull, compress, bend, or stretch material to its breaking point. It is primarily used by laboratories that manufacture and or mould different types of plastics. A universal testing device features one or two vertical columns mounted on a base. A second horizontal plate contains attachments that are used to hold the sample and slides up and down during stress testing samples. Dual vertical column machines are preferred by most laboratories as they can handle larger samples in terms of size and weight. Determining tensile strength is the most common test performed in a universal testing machine. This is done by holding one end of a sample in place while the other is pulled away until two sides are torn apart. The same process is used for testing flexural str
Read more

Uses for Universal Testing Machine

Universal testing machine or UTM is aptly named as it can perform various types of tensile and compression tests on different materials. There are also many different terms used to refer to a UTM that you will commonly hear in the industry, among the most popular of which are a tensile tester, bend tester, and compression tester. Some types of UTMs are stripped of some capabilities and/or are marketed to specific sectors, like texture analyzers for food, peel tester for adhesives, labels, and tapes, and top load compression tester for pipes and packaging. True UTMs can perform all of these and more. They are great multi-purpose instruments for any QC or R&D laboratory. The following are only a few common uses for UTMs: Tensile testing – One of the most common applications for UTM, a tensile test measure how strong a material is, how long it can stretch, and how stiff it is as the material is pulled apart until breaking point. Compression testing – Compr
Read more

Precautions to Be Taken While Using a Piezometer

The piezometer is a measuring device that determines pore pressures underground and liquid pressure. By determining pore pressure, you can understand the behaviour of the ground before, during, and after a construction project. Certain precautions must be taken when using a piezometer to ensure proper usage and the accuracy of results. Here are some of them: Have the right equipment – Invest in a state-of-the-art piezometer that uses a proven method of converting fluid pressures on the sensitive diaphragm into frequency signals which are ideal in the demanding environment common with civil engineering applications. Modern piezometers are capable of long distance signal transmission without degradation. They can tolerate wet wiring conditions and resist external electrical noise, too. Some manufacturers make piezometers specific for different applications, for instance, you should be able to find one with a heavy-duty body that can be b
Read more