Page 255 - Analysis and Design of Energy Geostructures

230 Analysis and Design of Energy Geostructures

Figure 5.16 Relation between the plasticity index and the thermal collapse observed per unit tem-
perature change.

attractive forces and the electrostatic repulsive forces (Laloui, 2001). All of these phe-
nomena are associated with a decrease in the shearing strength of inter-particle con-
tacts (governed by physicochemical interactions). This decrease in interparticle strength
leads to an increase in the probability of particle slippage. The maximum probability
of particle slippage occurs when the mobilised force producing such slippage is highest
(i.e. under NC conditions). Under NC conditions, heating produces a partial collapse
of the soil structure and a decrease in void ratio until a sufficient number of additional
particle contacts are formed to allow the soil carrying stress at the higher temperature
(Campanella and Mitchell, 1968). The reason why the thermal collapse is not observed
in highly OC conditions is related to the stable soil structure and lower mobilised
force. Such a reversible mechanical behaviour is typical for most materials and leaves
valid the micromechanical processes associated with the thermoplasticity of NC soils
observed upon heating.

5.4.7 Considerations for analysis and design of energy geostructures

Based on the results considered thus far, the temperature sensitivity of the volumetric
behaviour of fine-grained soils may generally be considered more significant than
coarse-grained soils. This sensitivity may preferably be considered in the analysis and
design of energy geostructures. Nevertheless, the use of simplified analysis approaches
(e.g. analytical models) may justify to neglect the temperature sensitivity of the volu-
metric behaviour of soils in situations wherein these materials have a thermal