Water reacting with silica causes the generation of hydroxyl SiOH accompanied by a volume or swelling expansion. The principle of LeChatelier ensures that the hydroxyl concentration increases with increasing externally applied stresses. From the analysis in  it becomes obvious that
a) the hydroxyl concentration must depend on the multi-axiality of the applied stresses, and
b) that the swelling effect is anisotropic.
On the basis of the results in  it will be shown that under torsion loading the strongest effects should occur.