UFC 3-260-02
30 June 2001
maximum value and is continuing to decrease at 15 percent strain, the test shall be continued to
20 percent.
(3) For brittle soils (i.e., those in which maximum deviator stress is reached at 6 percent
axial strain or less), tests should be performed at rates of strain sufficient to produce times to
failure as set forth above; however, when the maximum deviator stress has been clearly defined,
the rate may be increased such that the remainder of the test is completed in the same length of
time as that taken to reach maximum deviator stress. However, for each group of tests about
20 percent of the samples should be tested at the rates set forth above.
(4) Upon completion of axial loading, release the chamber pressure by shutting off the air
supply with the regulator and opening valve C. Open valve B and draw the pressure fluid back into
the pressure reservoir by applying a low vacuum at valve C. Dismantle the triaxial chamber. Make
a sketch of the specimen, showing the mode of failure.
(5) Remove the membrane from the specimen. For 35.5-millimeter- (1.4-inch-) diameter
specimens, carefully blot any excess moisture from the surface of the specimen and determine the
water content of the whole specimen. For 71-millimeter- (2.8-inch-) diameter or larger specimens,
it is permissible to use a representative portion of the specimen for the water content
determination. It is essential that the final water content be determined accurately, and weighings
should be verified, preferably by a different technician.
(6) Repeat the test on the two remaining specimens at different chamber pressures,
though using the same rate of strain.
L-6. EQUIPMENT.
a. Triaxial Test Cell.
(1) A triaxial cell suitable for use in resilience testing of soils is shown in Figure L-2. This
equipment is similar to most standard cells, except that it is somewhat larger so that it can
facilitate the internally mounted load and deformation measuring equipment and the equipment has
additional outlets for the electrical leads from the measuring devices. For the type of equipment
shown, air or nitrogen is used as the cell fluid.
(2) The external loading source may be any device capable of providing a variable load of
fixed cycle and load duration, ranging from a simple cam-and-switch control of static weights or air
pistons to a closed-loop electrohydraulic system. A load duration of 0.2 seconds and a cycle
duration of 3 seconds have been satisfactory for most applications. A square-wave load form is
recommended.
b. Deformation-Measuring Equipment.
(1) The deformation-measuring equipment consists of LVDTs attached to the soil
specimen by a pair of clamps. Two LVDTs are used for the measurement of axial deformation.
The clamps and LVDTs are shown in position on a soil specimen in Figure L-2. Details of the
clamps are shown in Figure L-3. Load is measured by placing a load cell between the specimen
cap and the loading piston as shown in Figure L-2.
(2) Use of the type of measuring equipment described above offers several advantages:
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