Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions

Importancia y uso:

5.1 The direct shear test is suited to the relatively rapid determination of the drained friction angle of soils under consolidated drained conditions because the drainage paths through the test specimen are short, allowing excess pore pressure to dissipate more rapidly than other drained strength tests. It is applicable for testing intact, or reconstituted specimens. There is, however, a limitation on the maximum particle size (see 6.2.1 and 6.2.2).

5.2 The testing protocols represent a field situation where complete consolidation has occurred under the existing normal stresses. Failure is reached slowly under drained conditions to allow excess pore pressure dissipation during shear. The shear rate must meet the requirements of 9.10. The results from several tests may be used to express the relationship between normal stress on the failure plane and drained shear strength.

Note 1: The equipment specified in this standard method is not appropriate for performing undrained shear tests. Using a fast displacement rate without proper control of the volume of the specimen will result in partial drainage and incorrect measurements of shear parameters.

5.3 During the direct shear test, there is rotation of principal stresses and failure may not occur on the weakest plane since failure is forced to occur on or near a plane through the middle of the specimen. The fixed location of the plane in the test can be an advantage in determining the shear resistance along recognizable weak planes within the soil material and for testing interfaces between dissimilar materials.

5.4 There are some limitations of the test, such as nonuniformity of shear stress on the failure plane and possibilities of nonuniformity of the failure plane due to nonuniformities within the soil and applied forces (moments caused by top half of shear box movement either up or down during shearing, and the like). Furthermore, when testing intact stiff clays, which are highly overconsolidated, there might be fissures or other discontinuities to cause excessive tilting, vertical movement (up or down) while shearing, and the like, and which, would nullify the use of the direct shear test.

5.5 The area of the shear surface decreases during the test. This area reduction creates uncertainty in the actual value of the shear and normal stress on the shear plane but should not affect the ratio of these stresses.

Note 2: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/and the like. Users of this test method are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.

Subcomité:

D18.05

Referida por:

D6270-20, D7499_D7499M-09R23, E2788_E2788M-24, A1115_A1115M-24, D6243_D6243M-20, D5321_D5321M-21

Volúmen:

04.08

Número ICS:

93.020 (Earthworks. Excavations. Foundation construction. Underground works)

Palabras clave:

compacted specimens; consolidated; direct-shear test; drained test conditions; intact; reconstituted specimens; shear strength;