Examples of Testing and Monitoring Programs - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 609

The strength of the Lias is determined by the low shear strength parallel to the hori-

zontal bedding-parallel discontinuities B and the vertical joints of sets J1 and J2.

α

Figure 19.2 Results of LFJ tests in claystone of Lias α (Wittke 1990)

The in-situ stress measurements in claystone using triaxial cells of the CSRI type (Sec-
tion 16.2.1) were not successful. No results could be obtained due to core disking par-
allel to bedding planes during overcoring. The increased horizontal in-situ stresses

Δσ H

in the order of 1 to 2 MPa acting in the Lias were realized first during excavation of

the Hasenberg tunnel and the excavation of the construction pit at Station University
(Section 16.7.2).

α

The LFJ tests carried out in the Knollenmergel yielded moduli of 1000 - 4000 MPa for
initial loading and 2000 - 6000 MPa for unloading and reloading (Wittke 1990).
The strength of the Knollenmergel is mainly determined by the slickensides S. The
evaluation of two multiple failure state in-situ shear tests on shear planes with slick-
ensides resulted in a friction angle of

φ S = 15°. The shear strength with no slickensides
on the shear plane is considerably higher. The results of these tests are represented in
Fig. 15.23 (Section 15.7).

Figure 19.3 shows the structural model and the characteristic rock mechanical param-
eters of the Lias

, the Rhaetian and the Knollenmergel derived from the results of
mapping, testing, monitoring and back analyses. As mentioned in Section 16.7.2, for
the purpose of stability analyses the transversely isotropic deformability of the Lias
α

α

formation, including single sandy limestone layers, was described according to the
homogeneous model by means of equivalent elastic constants. The deformability of
the Knollenmergel was found to be similar to that of the Lias

but isotropic. The tests
carried out in the Rhaetian and the weathered Knollenmergel (reduction zone) yielded
considerably lower moduli. The shear strength parallel to the discontinuities can gener-
ally be assumed very low in all formations.

α