Triaxial Compression Test - Soil Properties: Testing, Measurement, and Evaluation - page 345

[B] Triaxial Compression Data

Chamber pressure on test specimen,

σ 3 (psi)

Rate of axial strain (in./min)
Deformation dial readings H and proving ring dial readings (in.)

Δ

Note —These data are obtained for each of three or more specimens
tested at different chamber pressures.

CALCULATIONS [A] Specimen Parameters

The initial area, volume, height-to-diameter ratio, wet unit weight,
water content, dry unit weight, and degree of saturation of the specimen
are all calculated by methods described in previous chapters.

[B] Triaxial Compression

For each applied load, the axial strain, , can be computed by dividing

ε

the specimen's change in height, H , as read from the deformation in-

dicator, by its initial height, H 0 . In equation form,

Δ

¢ H
H 0

(21-1)

ε

Each corresponding cross-sectional area A of the specimen can be
computed by the equation

A 0

A (21-2)

1

ε

is the axial strain for
the given axial load (expressed as a decimal). Each corresponding
applied axial load can be determined by multiplying the proving ring
dial reading by the proving ring calibration. Finally, each unit axial load
(deviator stress) can be computed by dividing each applied axial load
by the corresponding cross-sectional area. These computations must be
repeated for each specimen tested.

where A 0 is the initial area of the specimen and

ε

Note —In the event that the application of the chamber pressure results
in a change in the specimen length, A 0 should be corrected to reflect this
change in volume. Frequently, this is done by assuming that lateral
strains are equal to vertical strains. The diameter after volume change
would be given by D D 0 (1 - Δ H/H ). [3]