We have developed a unique technique employing
optical holography to measure the static Young's modulus
(E) from a borehole. In the experiment, a known
point force induces micron scale displacements on the
borehole wall which are recorded by a double-exposure
hologram. Raw data consist of dark fringes superimposed
on the three-dimensional image whose pattern is
modeled to find E directly. In the laboratory, the holographic
technique determined E on rock and metal samples
to an uncertainty better than 10 percent. For example,
double exposure holograms of a saw-cut sample of
dolomitic marlstone gave an E of 16.8 ± 2.8 GPa in
agreement with 17.2 ± 2.0 GPa predicted by published
density-modulus relationships. Field tests of a holographic
tool in a horizontal mine pillar borehole gave
in-situ Es which range from 26.9 to 36.0 GPa. Although
these data could be interpreted as localized elastic heterogeneity
within the rock mass, elastic anisotropy of
the rock is a possible explanation for this variation
