UFC 3-260-02

30 June 2001

APPENDIX L

PROCEDURE FOR DETERMINING RESILIENT

MODULUS OF SUBGRADE MATERIAL

L-1. GENERAL. The objective of this test procedure is to determine a modulus value for subgrade

soils by means of resilient triaxial techniques. The test is similar to a standard triaxial compression

test, the primary exception being that the deviator stress is applied repetitively and at several stress

levels. This procedure allows testing of soil specimens in a repetitive stress state similar to that

encountered by a soil in a pavement under a moving wheel load.

L-2. DEFINITIONS. The following symbols and terms are used in the description of this procedure:

F1 = total axial stress

F3 = total radial stress; i.e., confining pressure in the triaxial test chamber

Fd = F1-F3 = deviator strain; i.e, the repeated axial stress in this procedure

,1 = total axial strain due to Fd

,R = resilient or recoverable axial strain due to Fd

,R1 = resilient or recoverable axial strain due to Fd in the direction perpendicular to ,R

MR = Fd/,RI = resilient modulus

2 = F1 + 2F3 = Fd + 3F3 = sum of the principal stresses in the triaxial state of stress

F1/F3 = principal stress ratio

Load duration = time interval over which the specimen is subject to a deviator stress

Cycle duration = time interval between successive applications of a deviator stress

L-3. SPECIMENS. Various diameter soil specimens may be used in this test with the specimen

height at least twice the diameter. Undisturbed or laboratory molded specimens can be used.

Methods for laboratory preparation of molded specimens and for backpressure saturation of

specimens are given in the following paragraphs.

L-4. PREPARATION OF SPECIMENS. Specimens shall have an initial height of not less than 2.1

times the initial diameter, though the minimum initial height of a specimen must be 2.25 times the

diameter if the soil contains particles retained on the No. 4 sieve. The maximum particle size

permitted in any specimen shall be no greater than one-sixth of the specimen diameter. Triaxial

specimens 35.5, 71, 102, 152, 305, and 381 millimeters (1.4, 2.8, 4, 6, 12, and 15 inches) in

diameter are most commonly used.

L-1

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