Field and Laboratory Tests in Rock Mechanics by L. G. Alexander
Fig. 6.—Stress Test Sites in Eucumbene-Tumut Tunnel.
The use of 12-in. jacks facilitates site selection, and permits of more rapid site work and drilling than for larger jacks. Tincelin claims that tests with small jacks are subject to essential errors which prohibit their use. The error, however, appears to lie in Tincelin’s theory, in which the Boussinesq theory for a loaded area on the surface of a semi-infinite solid is used to compute the strains caused by the jack.
Theory :
Tincelin has given the theory for strain on the faces
adjacent to the slot, considered as an elliptical hole in a two-
dimensional plate, but for the present tests, formulae for
displacements are required. The available reference books
do not give the required displacement for points near an
elliptical hole cut in a stressed plate, but a method is
available
The result is given here as the sum of three terms:
(a) The displacement at points along the axis normal to the slot (at first taken as an infinitely thin slot), due to slot cutting is:
S = rock stress normal to the plane of the slot,
y = distance of point from the major axis of the slot,
2c = length of slot, and
E,μ = elastic modulus and Poisson’s ratio (Fig. 7).
Fig. 7.—Displacement of Rock Adjacent to Elliptical Slot.
Fig. 8.—Flat Jack Tests—Theoretical Displacements.
