Engineering Rock Mechanics

44 In situ rock stress

-10.0.

-5.0.

0.

5.0.

Shear stress, -7

I. , I , I , , , ,

5.0 10.0 15.0

-5.01

oX,rs= 14.52, -1.17

30.0

0

%7s = 20.48, -1.17 Norma' " tress, B

14.52 -1.17

-1.17 20.48

The stresses transformed to the xy axes are

Adding the two xy stress states gives

21.83 -1.83 14.52 -1.17 36.35 -3.00

[ -1.83 8.171 + [ -1.17 20.481 = [ -3.00 28.651

Plotting the Mohr circle for the combined stress state and reading

off the principal stresses and the principal directions gives the required

values.

Shear stress, -7

The principal stresses of the resultant stress state are 01 = 37.38 MPa

and 02 = 27.62 MPa, with 01 being rotated 18.9" clockwise from the

x-direction.

44.3 How many experimental set-ups are required to determine

the 3-0 state of stress in a rock mass, using each of the stand-

ard stress measurement methods of flatlack, hydraulic fracturing,

USBM gauge and CSlRO gauge? (Assume that the stress field is

constant in the vicinity of the test site.)

These stress measurement methods are described in Section 4.3 of EM 1.