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Direct Shear Apparatus

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Direct Shear Apparatus is a soil testing equipment which is used for testing direct shear of cohesive soils. Direct Shear Apparatuses are widely used in construction industry.

Direct Shear Test

Direct shear test is a laboratory test, mostly conducted by geotechnical engineers to find the shear strength parameters of soil. Soil shear strength parameters are essential for stability because every physical structure imposes some load on the soil that supports the foundations. In a direct shear test, the failure of the soil sample in shear is caused along a pre-determined plane. In this test, the normal load, strain and shearing force are measured directly. The U.S. and U.K. standards defining how the test should be performed are ASTM D 3080 and BS 1377-7:1990 respectively. In India these standards are defined by IS 2720 part XIII

Direct Shear Test Apparatus

Direct shear test apparatus uses a square box which is divided horizontally into two halves. This box containing the soil sample is placed in a water jacket and subjected to constant normal load. Meanwhile, a horizontal force is applied till the specimen fails along the plane of juncture of the two halves. A number of soil specimens are tested under various loads. The angle of internal friction and shearing strength of the soil is then evaluated from the data thus obtained. There are two major types of direct shear test apparatuses- hand operated apparatus and motorized apparatus. Digital direct shear apparatus with digital displays have also become popular in the recent times.

Direct Shear Apparatus Specification

For determining the direct shear strength of soil or specimen size 60 mm x 60 mm x 25 mm, the direct shear apparatus consists of the following components

Loading Unit

This unit is provided with load yoke with direct and lever system for attaching balanced and detachable lever. There is provision for applying the load either through steel balls recessed in the loading pad or directly on the pre calibrated loading yoke. The loading unit is also provided with V strip and roller strip for frictionless movement of shear box cover.

Direct Shear Apparatus Accessories

Besides loading unit, there are some other essential accessories and optional accessories supplied with direct shear apparatus.

Essential accessories

The essential accessories for a direct shear apparatus include:

High sensitivity compression proving ring cap 200 kg
One consolidation dial gauge 0.01 mm x 25 mm
One strain dial gauge 0.01 x 25mm.

Optional accessories

The optional accessories for a direct shear apparatus include:

Additional set of weights to give a normal stress 5kg/sq cm.
Soil sampler for 60 mm x 60 mm specimen
Test form pad of 50.

Spare accessories include a porous stone for 60 mm x 60 mm size sample and is available in pairs.

Direct Shear Apparatus Applications

The basic application of the direct shear test apparatus includes determining the shear strength of soil. Some areas, including industries, where this soil testing apparatus finds application are :

Construction (Buildings, Bridges, Dams, etc.)
Testing of Rock Samples
Testing of Minerals
Mining

Tags:- Direct Shear Test, Direct Shear Test Apparatus, Soil Apparatus

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