Engineering Rock Mechanics

Methods of stress determination 43

Figure 4.2 In situ stress determination in the Carmenellis granite.

a fuller description of the indirect methods, the reader is referred to Dyke
(1988). The key reference for the ISM methods is Suggested Methodsfor Rock
Stress Determination, produced by Kim and Franklin (1987). Here, we now
go on to explain these methods in the context of their ability to determine
the components of the stress tensor.
In Fig. 4.3, we have shown four stress tensors and indicated the ability
of each method to determine the six components of the stress tensor in one
application. For the flatjack and with the x-axis aligned perpendicular to
the flatjack, one normal component-in this case oxx-can be determined.
It immediately follows that, to determine the complete state of stress, six

1. Flatjack

xy T~~ One normal stress

component

I \‘yy Tyz determined, say

, parallel to x-axis.

3. USBM overcoring torpedo

Three components

change.

2. Hydraulic fracturing
   Principal stresses
   axes i.e. plane of the
   fracture, two deter-
   mined, say u, and
   u3, one estimated,
   say isz.


3. CSIRO overcoring gauge

R- \ --

All six components

determined from six

(or more) measurements

Figure 4.3 The four ISRM suggested methods for rock stress determination and
their ability to determine the components of the stress tensor with one application of
the particular method.