Concept
Description and Procedure
The direct shear test is a laboratory testing methods used to determine the shear strength parameters of soil. The test can be carried out at different moisture contents; however, it is common to saturated the sample before running the test.
To achieve reliable results, the test is often carried out on three or four samples of undisturbed soil. The soil sample is placed in a cubic shear box composed of a upper and lower box. The limit between the two parts of the box is approximately at the mid height of the sample. The sample is subjected to a controlled normal stress and the upper part of the sample is pulled laterally at a controlled strain rate or until the sample fails. The applied lateral load and the induced strain are recorded at given internals. These measurements are then used to plot the stress-strain curve of the sample during the loading for the given normal stress.
Results of different tests for the same soil are presented in a chart with peak stress on vertical axis and normal (confining) stress on the horizontal axis. A linear curve fitting is often made on the test result points. The intercept of this line wit the vertical axis gives the cohesion and its slope gives the peak friction angle .
Standards
- BS 1377-7:1990
- ASTM D3080 - 04 Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions Go
References - External Links
- Principles of Direct Shear Test , Chap 7.4 of Experimental Soil Mechanic Bardet, J. P., Experimental Soil Mechanics, 1997, Prentice-Hall, Upper Saddle River, New Jersey.
- Detailed description of Direct Shear Test , Chap 7.5 of Experimental Soil Mechanic Bardet, J. P., Experimental Soil Mechanics, 1997, Prentice-Hall, Upper Saddle River, New Jersey.
- Detailed description of Direct Shear Test with photos and an example data Engineering Properties of Soils Based on Laboratory Testing, Experiment 11: Consolidation, Prof. Krishna Reddy, UIC
- Direct Shear Test on Wikipedia
- A Simple Technique for Determining the Shear Strength of Fine-Grained Unsaturated Soils using the Conventional Direct Shear Apparatus, J.J. Lane, S.K. Vanapalli. 2002. 2nd Canadian Specialty Conference on Computer Applications in Geotechnique, Winnipeg, pp. 245-253.
- Continuous Failure State Direct Shear Tests,A. Tisa,1984. Swiss Federal Institute of Technology, Zurich, Switzerland. Rock Mechanics and Rock Engineering 17, 83-95. Springer-Verlag.