Direct Shear Test - Soil Properties: Testing, Measurement, and Evaluation - page 385

and cohe-
sion c for this soil are 17° and 1,340 lb/ft 2 , respectively. These values (the
shear strength parameters) are the major results of a direct shear test.

found to be 1,340 lb/ft 2 . Hence, the angle of internal friction

As indicated, values of the angle of internal friction and cohesion are the
major results of a direct shear test. In addition to these parameters,
however, reports should include values of the initial water content and
the specimen's size and initial thickness. The type of test performed
(UU, CU, CD) and the type (undisturbed, remolded) and shape (cylin-
drical, prismatic) of specimens should be reported as well. Of course, a
visual description of the soil and any unusual conditions should be
noted. Finally, graphs of shear stress versus shear (horizontal) dis-
placement for each specimen tested should be included, as well as a
graph of maximum shear stress versus normal stress.
For cohesionless soils, if the shearing rate is not extremely rapid, all
of the three direct shear tests (UU, CU, and CD) will give about the same
results whether the sample is saturated or unsaturated. For cohesive
soils, shear strength parameters are influenced significantly by the test
method, degree of saturation, and whether the soil is normally consoli-
dated or overconsolidated. Generally, two sets of shear strength parame-
ters are obtained for overconsolidated soils: one for tests using normal
loads less than the preconsolidation pressure and a second set for normal
loads greater than the preconsolidation pressure. Where an overconsoli-
dated soil is suspected, it may be necessary to perform six or more tests to
ensure that the appropriate shear strength parameters are obtained [2].

SUMMARY

REFERENCES

[1] ASTM, 2007 Annual Book of ASTM Standards , West Conshohocken,

PA, 2007. Copyright, American Society for Testing and Materials, 100
Barr Harbor Drive, West Conshohocken, PA 19428-2959. Reprinted with
permission.

[2] Joseph E. Bowles, Engineering Properties of Soils and Their Measurement ,

2d ed., McGraw-Hill Book Company, 1978.