Pressurized Slot Testing
pressurized slot testing provides in situ mechanical properties
of the rock. At the selected test locations, the rib surface
is instrumented to monitor deformations, and two vertical
slots will be cut in the rib to create a "tendon"
of rock between them. Flatjacks and bearing plates are placed
in the slots, which are instrumented to measure displacement
across the slot.
the initial flatjack pressurization, the pressure at which
the deformation of the rock cancels the deformation due to
slot cutting can be used to estimate the in situ stress acting
normal to the slots. Subsequent loading-unloading cycles provide
a pressure/deformation history that is evaluated to determine
the rock mass deformation modulus.
information can be obtained by including a borehole in the
center of the tendon between the slots and measuring the deformation
across the borehole diameter as the slots are loaded. As the
pressures in the flatjacks increase, the stress around the
borehole will also increase, possibly resulting in failure
of the rock. The failure stress of the rock can then be determined
from the borehole observations.
the rock mass strength can be evaluated by increasing the
flatjack pressure until gross failure of the tendon of rock
between the flatjacks occurs. Because this test is conducted
in a complex configuration, numerical modeling of the test
is required during both test design and for post-test analyses
of the results.
Commission on Testing Method, Suggested Method for
Deformability Determination Using a Large Flat Jack
Technique, Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. Vol. 23, No. 2, pp. 131-140, 1986.
Zimmerman, R.M. et. al., G-Tunnel Pressurized Slot-Testing
Evaluations, SAND87-2778, Sandia National Laboratories,
Zimmerman, R.M. Et Al., G-Tunnel Pressurized Slot-Testing
Data Summary, SAND88-0586, Sandia National Laboratories,
M. et. Al, A New Technique for Applying the Method
of the Flat Jack in the Determination of Stresses
Inside Rock Mass, Proc. 1st Cong. ISRM (Lisbon), Vol.
2, pp. 57-65, 1966.