Examples of Testing and Monitoring Programs - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 611

Figure 19.4 Urban railway Stuttgart, Hasenberg tunnel, construction lot 11, exploration shaft
and adit, testing and monitoring program

Before the excavation of the adit, two five-point rod extensometers were installed from
the ground surface to monitor the displacements of the ground due to excavation. After
excavation of the adit, in vertical and horizontal boreholes additional four-point rod
extensometers were installed in horizontal and vertical boreholes with their heads locat-
ed at the sidewalls and the invert of the adit (Fig. 19.4).
In the exploration adit four double plate loading tests and two in-situ shear tests were
carried out (Fig. 19.4). In two of the plate loading tests the roof and invert of the adit
were loaded vertically (Fig. 19.5). In the other two plate loading tests the sidewalls of
the adit were loaded horizontally. The two in-situ shear tests were carried out on cylin-
drical specimens with circular shear planes of 0.6 m2.
Furthermore, 10 undisturbed specimens were sampled from the invert of the adit for
laboratory direct shear tests (Fig. 19.6). The shear planes of these specimens were
0.15 m 0.3 m = 0.09 m2 (Fig. 19.7).

The plate loading tests yielded moduli of 17 - 46 MPa for initial loading and of about
300 MPa for unloading and reloading. The very low moduli for initial loading most
likely were the result of unavoidable rock loosening due to excavation of the adit
(Wittke & Rißler 1976). A distinct anisotropy of deformability could not be derived
from the test results.

⋅ 0.15 m = 0.02 m2 and 0.3 m ⋅

Figure 19.7 shows the results of the direct shear tests carried out in-situ and in the
laboratory, respectively. The tests yielded different shear strengths parallel and normal
to the bedding. It should be kept in mind, however, that the specimens on which the
laboratory shear tests were carried out had no discontinuities. For simplification, the
equivalent shear strength of the rock mass was assumed as isotropic and conservatively
set equal to the shear strengths parallel to the bedding.