Deformation of RocksThe factors that influence the deformation characteris-tics and the failure of rock can be divided into two categories: internal and external.. The internal category
Trang 1Deformation of Rocks
The factors that influence the deformation
characteris-tics and the failure of rock can be divided into two
categories: internal and external The internal category
includes the inherent properties of the rock itself, whilst
the external category is that of its environment at a
particular point in time As far as the internal factors
are concerned, the mineralogical composition and
tex-ture are obviously important, but fractex-tures within a
rock and the degree of mineral alteration are frequently
more important The temperature-pressure conditions
under which a rock exists, significantly affect its
mech-anical behaviour, as does its pore water content
Importantly, the length of time that a rock experiences
a change in stress, and the rate at which this is imposed,
significantly affects its deformation characteristics
The composition and texture of a rock are gover-ned by its origin and geological history Few rocks are composed of only one mineral species and even when they are the properties of that species vary slightly from mineral to mineral Such variations within min-erals may be due to cleavage, twinning, inclusions, cracking, and alteration, as well as to slight differ-ences in composition This, in turn, is reflected in the mechanical behaviour of the resultant rocks As a consequence, few rocks can be regarded as homoge-neous isotropic substances The size and shape rela-tionships of the component minerals/grains are also significant in this respect, generally the smaller the size, the stronger the rock One of the most important features of texture as far as mechanical behaviour, particularly strength, is concerned, is the degree of
Figure 5 Correlation chart for Schmidt hardness, relating unit weight, unconfined compressive strength and hardness value (After Deere DU and Miller RP (1966) Engineering Classification of Engineering Properties for Intact Rock Technical Report AFWL TR 65 116, Air Force Weapons Laboratory, Kirkland Air Base, New Mexico).
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