Page 281 - Analysis and Design of Energy Geostructures

256 Analysis and Design of Energy Geostructures

Figure 5.43 Clay concrete interface (rough) failure envelope at 20 C and 50 C. Redrawn after Di

Donna, A., Ferrari, A., Laloui, L., 2015. Experimental investigations of the soil concrete interface: physi-
cal mechanisms, cyclic mobilisation and behaviour at different temperatures. Can. Geotech. J. 53 (4),
659 672.

appreciated in Fig. 5.43. The interface angle of shear strength reduces slightly at high
temperature but the most significant thermal effect is found to be an increase of the
adhesion (under constant volume conditions), c a;cv , between the two tested materials.
This is related to the thermal collapse of the clay, which results in an increase of the
contact surface between the two materials. The same effect is shown for both high
and medium rough interfaces, the second one having lower adhesion at both ambient
and high temperatures because of the smaller asperities. The observed behaviour is dif-
ferent from the one known for clay itself (whose strength under constant volume con-
ditions is recognised to be insensitive to temperature variations), as it is representative
of the clay concrete interface. The observed adhesion of the clay to the concrete
increases from approximately 7 kPa at 20 C to approximately 20 kPa at 50 C, while

the interface angle of shear strength decreases from 25 to 23 degrees for the same tem-
perature difference.
Complementary data that support the previous considerations are reported in
Fig. 5.44 with reference to data presented by Di Donna et al. (2015) for
clay concrete interfaces subjected to cyclic shearing under CNS conditions at the

temperature levels of 20 C and 50 C. The lower normal stiffness value (200 kPa/mm)
is responsible for the limited cyclic interface degradation that is likely to be encoun-
tered with geostructures installed in clays with respect to sands. While qualitatively
similar observation to those highlighted for sand concrete interfaces tested under
CNS can be made, a higher number of cycles is required to degrade the strength of