Engineering Rock Mechanics

Questions and answers: rock dynamics and time dependency 22 1

At t = 00 this reduces to

and so the difference between the long-term strain and the strain de-
veloped at time t is

Rearranging this leads to

GI
In (AE) = ---t +In
VI
which is the equation of a straight line, and shows how we can obtain
values for GI and vl.
The table below shows the data required to plot this straight line, and
the plot is given below.

t (s): 0 60 120 180 240 300 360 420

In (he) -25.33 -25.45 -25.58 -25.70 -25.83 -25.95 -26.08 -26.20

t (s): 480 540 600 660 720 780 840 900

In (As) -26.33 -26.45 -26.58 -26.70 -26.83 -26.95 -27.08 -27.20

time, seconds

-25.07 7- T-Vw-, -73

0 100 200 300 400 500 600 700 800 900

-27.54

At time t = 0 we have

from which we obtain GI = al/3A~ = 55.0 x 106/(3. 1.833 x =

100 GPa. The best-fit straight line through the data has a gradient of

-2.083 x

ql = G1/2.083 x

computed from

from which we obtain

= 100 x 109/2.083 x = 48000 MPas.

For small strains the volumetric strain in the uniaxial test may be

EV = E1 -k 2E3,