Direct Shear Test - Soil Properties: Testing, Measurement, and Evaluation - page 374

use in calculating the initial water content and unit weight of the
specimen.

(2) The minimum specimen diameter for circular specimens, or
width for square specimens, shall be 2.0 in. (50 mm), or not less
than 10 times the maximum particle size diameter, whichever is
larger, and conform to the width to thickness ratio specified in (4).

(3) The minimum initial specimen thickness shall be 0.5 in.
(12 mm), but not less than six times the maximum particle diameter.

(4) The minimum specimen diameter to thickness or width to
thickness ratio shall be 2:1.

Note 1 —If large soil particles are found in the soil after test-
ing, a particle size analysis should be performed in accordance
with ASTM Method D 422 (Chapter 10) to confirm the visual
observations, and the result should be provided with the test
report.

(1.1) Undisturbed Specimens —Prepare undisturbed specimens
from large undisturbed samples or from samples secured in accor-
dance with ASTM Practice D 1587 or other undisturbed tube sam-
pling procedures. Undisturbed samples shall be preserved and
transported as outlined for Group C or D samples in Practice D 4220.
Handle specimens carefully to minimize disturbance, changes in
cross section, or loss of water content. If compression or any type of
noticeable disturbance would be caused by the extrusion device, split
the sample tube lengthwise or cut it off in small sections to facilitate
removal of the specimen with minimum disturbance. Prepare
trimmed specimens, whenever possible, in an environment which will
minimize the gain or loss of specimen moisture.

SPECIMEN
PREPARATION [1]

Note 2 —A controlled high-humidity room is desirable for this
purpose.

(1.2) Compacted Specimens —Specimens shall be prepared using
the compaction method, water content, and unit weight prescribed
by the individual assigning the test. Assemble and secure the shear
box. Place a moist porous insert in the bottom of the shear box. Spec-
imens may be molded by either kneading or tamping each layer
until the accumulative mass of the soil placed in the shear box is
compacted to a known volume, or by adjusting the number of layers,
the number of tamps per layer, and the force per tamp. The top of
each layer shall be scarified prior to the addition of material for the
next layer. The compacted layer boundaries should be positioned so
they are not coincident with the shear plane defined by the shear
box halves, unless this is the stated purpose for a particular test.
The tamper used to compact the material shall have an area in con-
tact with the soil equal to or less than half the area of the mold.
Determine the mass of wet soil required for a single compacted lift