Environmental Engineering Reference
In-Depth Information
FIGURE 6.63
ERTS image of the San Francisco Bay area showing the lineaments of (1) the San Andreas fault, (2) the Calaveras
fault, and (3) the Hayward fault. (Original image by NASA; reproduction by USGS, EROS Data Center.)
6.6
Residual Stresses
6.6.1
General
Residual stresses are high, generally horizontal compressive stresses stored in a rock mass
similar to force stored in a spring, in excess of overburden stresses. They have their origin
in folding deformation, metamorphism, the slow cooling of magma at great depths, and
the erosion of overburden causing stress relief.
Relatively common, they can be in the range of 3 to 10 times, or more, greater than over-
burden stresses, causing heaving of excavation bottoms, slabbing of rock walls in river
gorges and rock cuts, and rock bursts in deep mines and tunnels.
During investigation they are measured
in situ
in shallow-depth excavations with strain
meters, strain rosettes, and flat jacks; at greater depths in boreholes, they are measured
with deformation gages, inclusion stress meters, and strain-gage devices as described in
Section 4.4.4.
