7. Give English equivalents of the following:

еластично крихкі, подрібнювати, поздовжній, поперечний, модуль пружності, співпадати, підтримувати, залишкова деформація, агломерація, закон Тука, прояв, крива, наслідок.

7. Make a written translation off the following:

A number of other features specific for rocks are also related to the abovefactor. In rocks, for example, manifestations of elastic hysteresis are observed. In compression the stress-strain curves fail to coincide in applying and relieving the stress. In the case of porous rocks (sandstone, for instance), the relief curve fails to come to the origin of the coordinates, since there is observed a certain residual deformation owing to the creep of the rock. If a rock is exposed to a certain quickly applied pressure, this pressure being subsequently maintained at the same level, the deformation (strain) will then continue increasing for some lime. If the pressure is then quickly relieved the rock will show a certain residual strain that disappears completely only after a definite time interval. This phenomenon is designated as elastic lag or aftereffect.

7. Make a plan to Text 4 and retell it.

8. Learn the meaning of the following words, word-combinatiions and word groups: plastic deformation, strain hardening, mineral composition of rocks, creep, a long-term action of pressure on the rock, running quality, mastic limit, period of relaxation, plastic properties, peak value, long- term strength point, rock strength, short-term loading.

16 Read Text 5:

Text 5 Plasticity. Creep. Stress Relaxation

Plasticity. As stated earlier, the disintegration of some rocks is preceded by their plastic deformation. It begins as soon as stresses in the rock exceed the elastic limit. In the case of an ideally plastic body such a deformation develops with a constant stress. The real rocks undergo strain hardening: i.e. to increase their plastic deformation it is necessary to build up some additional stress.

Plasticity depends on the mineral composition of rocks and declines with a higher level of quartz, feldspar and other hard minerals. High plastic properties are common to moist clays and to some chernogenic rocks.

The plasticity of solid rocks (granites, crystalline schists, sandstones) becomes manifest, in the main, at high temperatures.

Creep (running quality) becomes manifest with a continually growing deformation under a constant stress. Creep can develop consequent upon a protracted action of pressure on the rock, even when the stress is below the elastic limit. A high degree of creep is characteristic of sedimentary rocks, such as clays, clay shales, argillites and some varieties of limestones. Creep deformations are seen to be severest under pressures applied normal to bedding.

Stress relaxation is a gradual diminution of stresses in a body undergoing continuous deformation. It becomes manifest under a long-term action of pressure on the rock. If the load acting on the rock be brought to a point at which the stresses in it would not exceed the elastic limit, the first to appear will be the elastic flow. With a prolonged action of such a load the elastic deformation will gradually change into plastic one and the stress in the rock will start declining with the growth of plastic deformation. Once the pressure is relieved the rock sample fails to regain its initial shape, though the stress did not go up beyond the initial Mastic limit.

The time it takes for the stress in the rock to decrease e times is termed the period of relaxation. For most of the rocks this period of relaxation extremely long. Therefore, if a stress that does not transcend the elastic limit acts on the rock for a relatively short period of time, the rock behaves like an elastic body. On the other hand, when the action of such a stress continues to be effective over a time interval comparable to the period of relaxation, the rock then acquires plastic properties. As the action of pressure continues with time the strength of the rock gradually decreases, asymptotically approaching the peak value, known as the long-term strength point. The latter usually comprises 50 to 80 per cent of the rock strength under short- term loading.

17. Put 10 questions to Text 5.

18. Give definitions of plasticity, creep and stress relaxation of rocks using Text 5.

19. Find, read and translate the sentences in Text 5 in which we learn about creep.

20. Working in pairs test each other's ability to describe physical and mechanical properties of rocks.

Unit 2

The Effect of Three-Dimensional Compression and Temperature on the Mechanical Properties of Rocks

2 Read Text 1. Try to understand its contents.

Text 1 The Effect of Three-Dimensional Compression and

Temperature on the Mechanical Properties of Rocks

When exposed to three-dimensional (triaxial) compression mechanical properties of rocks beco me subject to material changes.

A uniform triaxial compression of minerals and monolithic rocks is attended, essentially, by elastic deformations, but in the case of porous rocks such a compression can be followed by the development of residual strain or permanent set. The compressibility of minerals and rocks is habitually expressed by the volumetric contraction coefficient 3c, by which is understood a relative contraction of the volume with an increase of three-dimensional compression by 1 Pa. The compressibility is minimal in the strongest minerals. Thus, for diamond (5c ^:::: 0.18 • 10-" Pa-¹. With increasing three-dimensional compression the volumetric contraction coefficient decreases somewhat for nearly all minerals.

The compressibility of rocks, especially porous ones, is greater than that of minerals, and then., with increasing three-dimensional compression, the value of the contraction coefficient for rocks drops more sharply than this is the case with minerals. This is due to the fact that under the effect of three-dimensional compression subject to contraction are not minerals alone, but the whole of the rock's structure; the distances between mineral particles along the contact boundaries become s horter, arid in porous rocks the volume of voids diminishes. The recuction in porosity is paralleled by dwindling permeability of rocks.

Changes of porosity, permeability and, especially, of the contraction coefficient are also affected by the lithological- petrographic properties of the rocks.

Three-dimensional compression of rocks results in an increase of their volume mass. For instance, the volume mass of sandstones in the Canada submontane region deposits, occurring at a depth of around 3000 m, is roughly 30-35 per cent and that of argillaceous rocks 45-50 per cent greater than the volume mass of analogous rocks lying at the surface.

With growing triaxial compression the Poisson ratio and modulus of elasticity for rocks go up somewhat. But it is the strength and plastic properties that are affected most tangibly by the three- dimensional compression.

Intensification of three-dimensional compression tells above all, on the plasticity of the rock, for many types of rocks, which under atmospheric pressure crumble like brittle bodies, acquire plastic properties when subjected to three-dimensional compression. Under ordinary pressure marble behaves like a brittle body. However, already under a three-dimensional pressure of 23 MPa in evidence is plastic deformation that proceeds with continually diminishing stresses. Under a greater three-dimensional compression (>80MPa) plastic deformation of this marble is attended by its strengthening.

The magnitudes of triaxial compression at which plastic deformation sets out are dissimilar for different rocks. Thus, plastic deformation of uniform medium- and coarse-grained limestones and also of little metamorphosed argil lites sets in under a three- dimensional compression of 50-100 MPa; of fine-grained and pelitomorphic limestones, compact argillites, anhydrites and aleurolites - at 80 -100 MPa and more; of fine-grained dolomites and heavily metamorphosed argillaceous rocks - only at 200-350 MPa. Under a pressure of up to 1000 MPa quartzites behave like brittle bodies, and sandstones with siliceous cement behave almost in the same manner.

For most rocks the yield point, goes up as the three-dimensional compression gains in intensity and the more so the less plastic the rock. In salt rock the yield point is almost unaffected by the three- dimensional compression.

The degree of plastic deformation up to disintegration augments as the three-dimensional compression becomes more intensive, this being most marked in limestones and insignificant in quartzites, with dolomites and sandstones occupying an intermediate position.

The strength of all rocks increases as the three-dimensional compression gains in intensity. The strength of rocks of the same name rise^^nore sharply with a decrease in the size of grains therein.

^fhree-dimensional Compression causes shifting of rock grains with respect to one another and their convergence. The greater compression, the tighter the grains press against one another, and the higher the interaction forces between them the fewer the possibilities for their relative movement. In rocks plastic deformations occur basically due to a relative movement of grains (in-tercrystal gliding). In a more fine-grained rock there are more intergranular boundaries and, consequently, the possibilities for intergranular gliding are broader and, therefore, the rock has greater plasticity. With an extremely great three-dimensional compression the displacement of grains becomes virtually impossible and plastic deformation sets in owing to gliding inside the grains proper, which is usually accompanied by strengthening of the rock.

Reduced porosity of the rock following an intensified three- dimensional compression, convergence of the grains and subsequent enhancement of the interaction forces between them are factors contributing to an added strength of the rock. Deformation strengthening or strain hardening due to intercrystal gliding causes an increase in the strength of rocks as the three-dimensional compression rises. Intensification of three-dimensional compression leads to "healing" of internal defects in the crystal lattice of the rock and, as a result of this, to a higher strength and a greater degree of plastic deformation prior to breaking.

Let us segregate mentally inside the earth a certain volume of rock. This volume is subjected to the action of a vertically directed force caused by the weight of superjacent rocks. Under the effect of this force the segregated volume of rock undergoes compression (contraction) along the vertical axis, but tends to expand radially (in the horizontal plane). Its radial expansion is resisted by the surrounding rocks. Consequently, the segregated volume becomes subject to the action of a lateral compressive force exerted by the ambient massif.

In mining the pressure originating from the weight of overlying rock strata is commonly referred to as geostatic or rock pressure. The magnitude of rock pressure depends upon the volume mass of this rock and on the depth at which the volume under consideration occurs.

The pressure produced as a result of resistance of the surrounding rocks to radial deformation of the segregated volume is called lateral pressure. Its magnitude is a function of rock pressure. Since both rock and lateral pressure increase with depth, the strength of a rock of the given mineralogical composition accrucs as well. As the temperature rises so does also the ability of rocks to undergo plastic deformation, but at the same time the yield point and the strength of the rock decline. At times the influence exerted by the temperature is so considerable that the effect of the strength increment due to an elevated three-dimensional compression is cancelled out altogether. Thus, the strength of some argillaceous rocks, limestones and even dolomites at a temperature of 300°C and under three-dimensional compression of 200 MPa proves lower than at a temperature of 24°C and under a pressure of 100 MPa. A temperature rise adversely affects most particularly the strength of a number of chemogenic rocks (bishofite carnallite, halite).

With rising temperature the elastic properties of rocks experience but an insignificant change. The modulus of elasticity goes up slightly, while Poisson's ratio remains practically almost unchanged.

3. Read Text 1 again. Find, read and translate the sentences in Text 1 in which we learn about shifting of rock grains, changes in the crystal lattice of the rock, rock pressure, plastic deformation.

4. Look through Text 1 again. Give the main points of each passage of the text. Use: "deals with".

5. Give English equivalents of the following:

залишкова деформація, стискуваність, коефіцієнт ГІуассона, кремнистий, межа текучості, переміщення, посилення, решітка, пласт, верхній пласт, піднімати, сатурований.

3. Make a written translation of the following:

Reduccd porosity of the rock following an intensified three- dimensional compression, convergence of the grains and subsequent enhancement of the interaction forces between them are factors contributing to an added strength of the rock. Deformation strengthening or strain hardening due to intercrystal gliding causes an increase in the strength of rocks as the three-dimensional compression rises. Intensification of three-dimensional compression leads to "healing" of internal defects in the crystal lattice of the rock and, as a result of this, to a higher strength and a greater degree of plastic deformation prior to breaking.

Unit 3

The Effect of Saturating Fluid on the M echanical Properties of Rocks