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Thermohydromechanical behaviour of soils and soil structure interfaces 255

Figure 5.42 Constant normal load sand concrete interface tests (rough) response subjected to

monotonic shearing at 20 C and 50 C under constant normal load conditions: (A) shear

stress horizontal displacement plane; (B) Mohr plane. redrawn after Di Donna, A., Ferrari, A., Laloui,
L., 2015. Experimental investigations of the soil concrete interface: physical mechanisms, cyclic mobili-
sation and behaviour at different temperatures. Can. Geotech. J. 53 (4), 659 672.

5.8.2 Strength of clay concrete interfaces
The strength of structural interfaces with fine-grained soils under nonisothermal con-
ditions exhibits a slight sensitivity to temperature variations. This evidence is related to
the more pronounced sensitivity of fine-grained soils to temperature variations com-
pared to coarse-grained soils, both in terms of volumetric and deviatoric behaviour.
The typical response to monotonic shearing under CNL conditions of a
clay concrete interface at 50 C (initially under NC conditions, heated at the desired

temperature and then sheared) and at the ambient temperature of 20 C is presented in
Fig. 5.42 with reference to the result of Di Donna et al. (2015). The results at high
temperature show an increase in the interface shear strength and a reduction in the
contraction during shearing with respect to the response at ambient temperature. This
response is attributed to the effect of the thermal collapse produced during the heating
phase prior to the shearing phase. The considered phenomenon indicates that a higher
force is necessary to shear a previously heated interface (as the material has a higher
preconsolidation stress) compared to an interface at constant temperature. Yet, this
phenomenon results in a peak strength (at small displacements) that is not present at
ambient temperature, while generally in a greater shear strength at constant volume
conditions (large displacements).
The increase of strength with increasing temperature for interfaces with fine-
grained soils initially under NC conditions, then heated and eventually sheared can be