Field Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 466

plied load, the diameter of the plates and the measuring accuracy. According to Serafim
& Guerreiro (1968) and Palmström & Singh (2001), beyond three times the plate diam-
eter only very small or no displacements are measurable if a pressure of 5 to 6 MPa is
applied. Figure 15.9 shows a uniaxial jacking test, oriented horizontally, carried out in
a fully excavated tunnel cross-section (GIF 2004).
Figure 15.8 Double-plate loading test in isotropic rock mass, calculation of Young's modulus
In addition to instrumentation holes equipped with extensometers, the loading plates
may be equipped with gauges to record the displacements of the rock surface at differ-
ent positions directly underneath the plate (DGEG 1985a, Ünal 1997). Also, testing
devices with more than one instrumentation hole in each plate have been used (Oberti
et al. 1986, Ünal 1997).
In other test layouts, only one horizontal rock surface (Ünal 1997) or the flattened end
of a large diameter borehole is loaded by a single plate (ISRM 1979c). Then an an-
chored beam or an anchor (cable-jacking test) serves as an abutment for the plate. In
these testing devices only displacements of the rock surface are measured.