454 Questions 7 3.1- 13.10: rock dynamics and time dependency
zontal tectonic stress, OH. The tunnel deformations have been described
as follows:
"Directly after excavation, the sidewalls started to bulge,
horizontal cracks occurred which were growing in width
and length; bottom heave was obvious. These processes
increased in intensity with time. Void formation in the
dilatancy process increasing with time leads to serious over-
all weakening of the rock structure; in addition it is ag-
gravated by the suction and seepage of underground water.
The horizontal displacements... were in the order of 50 cm
within 90-150 days with an average rate of 5.4 mm/day.
Usually the inwards motion of the comer areas near the
bottom are largest, whereas the roof-top moved upwards
so gradually the tunnel cross-section is squeezed into the
'peach' form... Bottom upheavals at some locations were
about 40 cm within 131 days. Serious lateral motions of one
sidewall have been observed."Explain these observations in terms of the basic mechanisms involved.