Search

The paper shows how eigenanalysis may be used to reduce data to principal components in problems concerning fracture orientation, stress measurements and rock mass permeability. Each application is described by an example.

An analysis of some 200 tunnel case records has revealed a useful correlation between the amount and type of permanent support and the rock mass qualityQ, with respect to tunnel stability. The numerical value ofQ ranges from 0.001 (for exceptionally poor quality squeezing-ground) up to 1000 (for exceptionally good quality rock which is practically unjointed). The rock mass qualityQ is a function of six parameters, each of which has a rating of importance, which can be estimated from surface mapping and can be updated during subsequent excavation. The six parameters are as follows; theRQD index, the number of joint sets, the roughness of the weakest joints, the degree of alteration or filling along the weakest joints, and two further parameters which account for the rock load and water inflow. In combination these parameters represent the rock block-size, the interblock shear strength, and the active stress. The proposed classification is illustrated by means of field examples and selected case records. Detailed analysis of the rock mass quality and corresponding support practice has shown that suitable permanent support can be estimated for the whole spectrum of rock qualities. This estimate is based on the rock mass quality Q, the support pressure, and the dimensions and purpose of the excavation. The support pressure appears to be a function ofQ, the joint roughness, and the number of joint sets. The latter two determine the dilatency and the degree of freedom of the rock mass. Detailed recommendations for support measures include various combinations of shotcrete, bolting, and cast concrete arches together with the appropriate bolt spacings and lengths, and the requisite thickness of shotcrete or concrete. The boundary between self supporting tunnels and those requiring some form of permanent support can be determined from the rock mass qualityQ.

In a transversely electrically anisotropic rock mass of arbitrary dip, the potential distribution about an electrode at arbitrary depth is the sum of the whole-space potential about that electrode, plus the whole-space potential about a postulated image electrode displaced up-dip from the source position. Equipotential lines on the rock-air surface are ellipses, elongated parallel to strike, and with centers displaced up-dip from the surface projection of the electrode position. In metamorphosed rocks frequently encountered in mining geophysics, anisotropy is such that elongation is most marked in steeply dipping rocks, with displacement most evident in low to moderate dip. Graphs relating the anisotropy coefficient to displacement and elongation assist in separation of the anisotropy-related effects from those of a significant subsurface conductive body, particularly if surface resistivity sounding establishes the coefficient of anisotropy.

1. By taking account of the delay in support setting behind drivage, we can calculate the internal stresses and displacements in a support lining: the results are close to the observed values. 2. Complete contact between a monolithic lining and the creeping rocks leads to an increase in the internal stresses in the lining over those in a lining which does not cohere with the rocks. 3. The suggested method enables us to calculate the strength of a monolithic liningin terms of its elastic characteristics and the creep characteristics of the rocks, the time of onset of action of the lining, and the conditions of contact.

1. It is shown, on the basis of an analysis of experimental data and of the derived design method, that highpressure grouting of the rock mass surrounding the tunnel can definitely prestress the lining. Howerver, creep effects in the rock and the lining concrete cause a marked diminution (by one-half or two-thirds) of the stresses with time. 2. For reliable and economic design of the linings of high-pressure tunnels, it is necessary to conduct a series of laboratory and field investigations aimed at establishing the rheological parameters of the concrete and the rock mass, which will enable the effect of prestressing due to grouting under different geotechnical conditions to be computed on a sufficiently well-founded basis. 3. It follows from the experimental data [3], which can be demonstrated analytically, that the prestressing effect of grouting can be, substantially increased by prolonging the time of grout injection.

This paper deals with the results of studies on the theoretical analysis of the deformation behavior of rocks, and the actual measurements made during the underground cavity excavation at Okutataragi Pumped-Storage Hydro Project.To initiate the studies, the material properties of rock were obtained by repeated in-situ tests at the proposed location for the projects to define the initial ground stress, rock shear strength, modulus of elasticity, creep deformation ratio, retardation ratio, Poisson's ratio, and rock compressive strength. The material properties thus obtained were used to analyze the extent of rock loose zone, the rock displacement and other fundamental factors for each step of the excavation work by means of a two- or three-dimensional elastic finite element method.To compare the measured data with the analytical calculations, the rock deformeters were installed in such an arrangement as to observe changes with the time of the rock displacement at the cavity arch and side walls, and several concrete strain gauges and reinforcing bar strain meters were also buried in the arch concrete to measure the loads on the arch concrete.The comparison of the calculations and these measurements disclosed the followings;(1) The results or calculations of the analysis could be adequately utilized for designing the rock walls anchored by prestressed steel bars and for maintaining the safety or security control during the construction.(2) The three-dimensional analysis and the results of measurements confirmed that the rock strut or rock mass support method could confine the displacement to about 70 percent of the estimated values of displacement for the construction method without rock strut support. As proposed and adopted at Okutataragi Project, the rock strut was arranged to come in the center of the cavity to house the underground power station and to provide the space for assembling the power equipment, machinery and tools.(3) The horizontal displacement, which was most carefully studied, was 12 to 14mm at the measurement as against 11mm arrived at by the analysis. It follows that the analysis calculation proved to be fairly precise.(4) It is understood that the loads on the arch concrete comes primarily from the horizontal forced displacement arising out of the loose side walls, but not from the ground pressure in the upper direction as has otherwise been assumed. This was proved by the measurement of the maximum concrete compressive stress of 120 to 130kg/cm2 and the calculated estimate of 140kg/cm2 maximum.The estimations and the measurements carried out for this project have proved quite satisfactory. However, several problems have been raised for further reviews and analyses to improve the safety or security of large underground power station structures, such as;(1) Decrease of the rock strength in the loose zones.(2) A method or methods to estimate the effects of rock bolts of prestressed steel bars.(3) Development of more accurate and efficient devices or methods for measuring the initial ground pressure.(4) Improved excavation methods to prevent the rock loose zone from developing or expanding.

In the first part, concerning case histories, further activity at Lake Kariba twelve years after filling is described. Studies of seismicity have been initiated at the following sites, including the monitoring of micro-seisms on magnetic tape. Some preliminary findings are stated: Murchison Falls, Uganda; Lar Dam and Diversion Works, Iran; Tendaho Dam, Ethiopia. In the second part effective reservoir loading and rock stresses are discussed. The effective loading on the rock due to different rates of movement of water in zones of the rock mass can sometimes greatly exceed the direct loading of the weight of water in the reservoir. The stress distribution in the rock is affected not only where this effective loading occurs, but at great distances from it. Site investigations should take account of this. Lines for further research are suggested.

UDC 627.842.034.92.04 This article presents the results of analyses carried out to determine the stresses in arched tunnel linings due to the combined action of the internal pressure, the rock pressure, and the external uniform pressure exerted by ground water, as well as basic concepts for an investigation of the relation between the stiess state of such a lining and the quantitative correlation of these loads. The analyses were performed on a Nairi electronic computer, using a program developed at the Scienti~c-Research Institute for Foundations and underground Structures for solving the corresponding two-dimensional contact problems of the theory of elasticity [1-3]. A previous article [4] presented the stress diagrams in an arched Lining having an arch angle ~ = 120 ~ a ratio between the linear dimensions of the internal contour h/2b = 1.2 (in which h is the height between the bottom and the crown, and 2b is the span), and a relative thickness 6/2b = 0.15 (in which 6 is the thickness at the crown of the arch), for a ratio between the moduli of deformation of the lining and the surrounding rock mass Et/E 0 = 1.25 and values of Poisson's ratio v, = 0.3 and v0 = 0.3 in the case of action of an internal pressure p. Figures 1 and 2 show the stress diagrams in a lining acted upon by the rock pressure and the uniform pressure p, exerted by the ground water. In Fig. 1, the values of the stresses are referred to the quantity 7H(1-/9, in which 7 is the unit weight of the rock, H is the depth at which the excavation is made; and f is a coefficient which takes into account the lag between the time of excavation and installation of the supporting elements, and which is determined from the solution of a three-dimensional axisymmetrical problem of the theory of elasticity [fi].

An air gun repeatedly shot in a water-filled hole every 6 or 10 s was used to measure the in situ seismic velocity over a distance of 200 m in a granite quarry. We found a peak-to-peak half-percent variation of velocity, which correlates well with the variation in tidal stress. The inferred high stress sensitivity of velocity change (0.2 bar−1) may be attributed to the presence of extremely thin cracks (aspect ratio 10−5) by which the rock mass near the surface is broken into blocks. Such cracks should close at a depth of about 15 m. When the present results for detecting the tidal effect on velocity are extrapolated for waves penetrating to depths of a few kilometers, the velocity must be measured with a precision of better than one part in 105.

Instrumentation placed ahead of three model tunnels in the laboratory and ahead of a crosscut driven in a metamorphic rock mass detected stress changes several tunnel diameters ahead of the tunnel face. Stress changes were detected 4 diameters ahead of a model tunnel drilled into nearly elastic acrylic, 2·50 diameters ahead of a model tunnel drilled into concrete, and 2 diameters ahead of a model tunnel drilled into Silver Plume Granite. Stress changes were detected 7·50 diameters ahead of a crosscut driven in jointed, closely foliated gneisses and gneissic granites in an experimental mine at Idaho Springs, Colorado. These results contrast markedly with a theoretical elastic estimate of the onset of detectable stress changes at 1 tunnel diameter ahead of the tunnel face. A small compressive stress concentration was detected 2 diameters ahead of the model tunnel in acrylic, 1.25 diameters ahead of the model tunnel in concrete, and 1 diameter ahead of the model tunnel in granite. A similar stress peak was detected about 6 diameters ahead of the crosscut. No such stress peak is predicted from elastic theory. The 3-dimensional in situ stress determined in the field demonstrate that geologic structure controls stress orientations in the metamorphic rock mass. Two of the computed principal stresses are parallel to the foliation and the other principal stress is normal to it. The principal stress orientations vary approximately as the foliation attitude varies. The average horizontal stress components and the average vertical stress component are three times and twice as large, respectively, as those predicted from the overburden load. An understanding of the measured stress field appears to require the application of either tectonic or residual stress components, or both. Laboratory studies indicate the presence of proportionately large residual stresses. Mining may have triggered the release of strain energy, which is controlled by geologic structure.

1. The constructed plasticity curves BCD and EFG (see Fig. 1) enable one to assess the type of stress-strain state of a core as a result of its relief, on the basis of the instrumentally measured deformation parameters (−u) and a. Thus the presence of plastic deformations of inverse sign leads to residual tensile stresses σϕ0 > 0, σz0 > 0, Fig. 3); depending on the strength characteristics of the rock, this may entail cracking of the core in a radial direction or scabbing in planes perpendicular to the core axis [8]. 2. After the type of state of the core has been established, formulas (3.7), (3.16), and (3.20) enable one to determine the load q and stress σz (along the borehole axis) in the rock mass before relief. If the loads q and σz are known, these formulas may also be used to determine the elastic constants of the rock mass. 3. The appearance of regions of platic deformations of inverse sign in the core leads to considerable errors in the determination of the load q from formulas (3.7) of elasticity theory. This is readily seen by the example of the determination of stresses in a coal mass with the following characteristics:E=2·104 kg/cm2, v=0.3, 2Te=150 kg/cm2, β=0.1 when R0=2,5 cm and R1=15 cm. Let the change in the diameter of a measuring borehole Δd be 600 μ and leta=0. Compare (−u)=300 μ anda=0 with the plasticity curve EFG and make certain that plastic deformation of inverse sign occurred during relief. According to (3.16), q=112 kg/cm2, whereas by (3.7), q=89 kg/cm2. 4. Incorporation of the parametera (deformations along the borehole axis) in the calculation scheme enables one to obtain information on the direction of the measuring borehole. Thus, if boreholes are driven in different directions, one of the principal directions of the state of stress in the rock mass must correspond to the maximum value of the parametera.

A water pressure higher than 50 kp/cm2 and an air pressure higher than 40 kp/cm2 have been used in the unlined tunnel and closed surge chamber of a hydroelectric power plant in Precambrian rock. The rock conditions demanded are discussed. In particular the resistance to hydraulic fracturing, but also the leakage problem through the rock mass, is mentioned. Some practical advice for the design is put forward.

The Mratinje bridge in Montenegro, now under construction, will carry a road across the river Piva and the lake which will be created by the Mratinje dam, 220 m high. The principal engineering-geological problem was posed by the 100 m high pier No. 3 whose footing is founded in flysch (limestone and shale) overlain by a thick blanket of limestone talus up to 22 m thick. Immediately after completion the bridge will be submerged up to its steel superstructure. A slope stability analysis was made of the talus whose bottom part is clayey and which is likely to slump during filling of the reservoir and especially during rapid drawdown (level amplitude up to 80 m), thereby endangering pier No. 3. Slope stabilization works were therefore proposed.

Summary A continuum description of a rock mass containing one or more sets of regularly spaced parallel joints is adopted for length scales large compared with joint spacing. It is also supposed that relative displacements across joints are small compared with joint spacing. An elastic joint assumption is considered; namely, that relative displacements across joints are functions of the tractions on the joint plane. The overall anisotropic elasticity of a rock mass containing one or more joint sets is determined, assuming that the intact rock blocks are isotropic elastic. Effects of joint orientation are illustrated by simple loading responses with one and two joint sets.

1. The dynamic methods for investigating the deformability of a fissured rock mass permit obtaining information on considerably larger volumes of rock and at greater depths than with the use of the static methods currently used. For this reason they may be recommended for the extension of the “point” data obtained by means of tests using separate plates, as applying to the average characteristics of portions of the foundations of hydraulic structures. 2. Until it is further improved the correlation proposed here (curve 1, Fig. 4) may be utilized in the investigation of the deformation indexes of fissured rock masses by fulfilling the condition of standardization of the methods for carrying out the static tests (loading rate, time of loading for each stage, dimensions, and rigidity of the plates, etc.). 3. When carrying out static tests on rock it is convenient to determine simultaneously the dynamic moduli of elasticity, according to the methods explained; this permits collecting additional material which will serve for improving the correlation proposed here.

1. Complex compressive and tensile deformations occur in the foundations of high dams, caused both by the loads from the installations and (to a greater extent) by the weight of water in the reservoirs. These have to be taken into account in the static calculations and model investigations into stability and stress of dams and their foundations. 2. In the relief and deconsolidation zones, the properties and behaviour of the rock masses differ substantially from those in the rock masses loaded and compressed from all sides outside these zones. In the first case, the rock mass must be considered as a system of blocks of different shape and size, interacting along the boundary surfaces and contacts. In the second case the rock mass is considered as an elastic medium, characterized by relatively high values of C, and capable of resisting the total and tensile stresses; fissuring, with the exception of individual breaks in continuity, is largely reduced to a minimum. 3. The detection and plotting of the deconsolidation zones of rock masses is one of the most important problems of prospecting and investigation of the foundations of high dams. 4. The principles governing the behaviour of rock foundations of high dams under the action of external loads, depending on a number of factors, have so far been little studied. Theoretical and experimental forecasts frequently diverge substantially from the actual.

This paper is a translation of a summarizing report, which has been presented at the above mentioned Symposium, where the following four themes were discussed: 1. Fundamentals and in situ determination of permeability 2. Mechanical behaviour of fissured rock due to percolation; Man-made earthquakes 3. Water supply and water pollution 4. Influence of joint water on the stability of structures; drainage measures.

1. Natural segregation of stone material inevitably occurs when dumping dry rock in layers, even of small thickness (4–5 m). 2. When the broken rock contains small fractions, including sand and fines, and the height of the dumped layer is appreciable, the small fractions accumulate in the upper part of the embankment and along with the stone components of the rock mass from the skeleton; in the lower part of the embankment are many cavities. 3. The small fraction pressed into the upper part under the effect of water or vibrations can migrate in time into the pores of the lower part of the stone embankment, as result of which settlement and deformation of the embankment occur. 4. The accumulation of the small fraction in the upper part of an embankment in quantities greater than 20–25% is not permitted for essential structures; for this purpose the height of the dumped layer is reduced or the voids in the lower part of the embankment are filled by washing in sand. 5. When dumping with washing (the water is delivered simultaneously with dumping) the height of the layer depends on the quantity of the small fraction in the original material. Washing of the dumped layer with the small fraction pressed into the upper zone does not yield results even at a quite appreciable water delivery rate.

1. Investigations of the acoustic and strength properties of Karaganda sandstones have enabled the authors to derive empirical equations for the interrelationship of these parameters. 2. The experimental data justify the recommendation of the ultrasonic pulse method for assessing the strengths of sandstones, because it is less laborious and enables investigations to be performed on the rock mass in situ.

The representation of discontinuities in analysis of blocky rock is discussed. A linkage type element is developed for addition of rock joint stiffness to the structural stiffness matrix describing the behavior of a system of rock blocks and joints. Several basic problems of jointed rock are studied. These examples demonstrate the marked influence joints may have on the stress distribution, displacements, and failure pattern of an underground opening or other structures in jointed rock. A new classification of joints is introduced, based on the application of the joint element to finite element analysis of structures in jointed rock. Normal stiffness, tangential stiffness, and shear strength are used as parameters in the classification system. The methods discussed in this paper allow a jointed rock mass to be treated as a system of blocks and links. Just as analysis of a reinforced concrete building requires detailed knowledge of the behavior of concrete alone and steel alone, the joint stiffness approach calls for and uses detailed description of the behavior of rock blocks and rock joints independently.

Shear Strength Anisotropy in a Bedded Pyritic Shale and a Siliceous Dolomite The orientation, frequency and extent of joint and bedding plane fractures were measured in bedded pyritic shale and siliceous dolomite, host rocks of the lead-zinc and copper orebodies at Mount Isa, Queensland, Australia. The measurements, carried out in openings 10 by 10 feet, bring out the marked difference between the two rock types in regard to frequency and extent of the geologie discontinuities. Friction tests on joint and bedding planes, together with the continuity measurements, provide information on the shear strength anisotropy in the rock mass. It was found that an increase of the fracture frequency parallel to bedding planes is related to an increase in joint frequency, although not a proportional one, and that fractures of higher frequency show a tendency to have greater continuity.

The geological features of the immediate neighbourhood of the Santa Fé Mine, which is situated about nine leagues nearly due east of the departmental town of Pichucalco, have been partially described by the author in a paper recently read before the Institution of Mining and Metallurgy. The key to the position, from the point of view alike of mineralogical and of economic interest, is found in a dome-shaped mass of wollastonite in a nearly pure condition, the horizontal section of which, at the lowest level where it has been sufficiently explored to determine its shape, takes the form of an irregular ellipse about 400 yards long by 160 yards wide. With the exception of the ore-bodies, which are developed on the outskirts of this mass and close to the contacts with other rocks, the whole mass is of nearly uniform composition, consisting of the mineral wollastonite in a nearly pure condition and very coarsely crystallized.

A series of minor folds developed in the Moine rocks of Monar, Scotland, have been studied in detail using various geometrical methods of analysis and are interpreted as having formed by a process involving both buckling and uniform “shortening”. The rocks, highly metamorphosed sediments, are well-banded psammitic to pelitic granulites with interlayered quartzo-feldspathic pegmatitic veins. Studies of thickness variation with apparent dip and isogon patterns within the folded layers show that the overall fold geometry is close to that of a similar fold. Together with the results of harmonic analysis these studies also indicate that the fold geometries of both layers and single surfaces show considerable variation, and that there are slight but systematic differences in fold shape that can be related to differences in composition of the layers. These differences are related to differences in competence of the layer material. Most competent are the quartzo-feldspathic pegmatitic veins that often form ptygmatic structures with an average layer geometry least removed from that of a parallel fold. Competence decreases with increasing biotite content in the granulitic layers and is least for the pelitic layers whose mean geometry is furthest removed from that of a parallel fold. Where competence contrast is least across single folded surfaces their shapes are near sinusoidal, and with increasing competence contrast they become progressively non-sinusoidal and more variable. Interpretation of the fold geometry in terms of folding processes has been made by analogy with theory and the results of experiments. All geometric features are consistent with a process of fold development involving both buckling and uniform shortening (flattening) normal to the axial surfaces of the folds and to the schistosity. During deformation the rock mass behaved as a complex multilayer in which the more competent layers controlled fold initiation and development by buckling. Some of the pegmatitic veins buckled to form ptygmatic folds for which there is an approximately linear relationship between wavelength and thickness. These folds have developed as if the veins were single competent layers embedded in a uniform incompetent medium, and their geometry shows the effects of a modifying flattening deformation. Some folds also show features to indicate that buckling and flattening have proceeded simultaneously. Where pegmatitic veins are absent in the layered granulites and competence contrast is low, effects of buckling are slight and almost homogeneous strain has produced nearly perfect similar folds with sinusoidal form. The strongest effects of buckling and least effects of flattening are seen in the ptygmatic folds. Applying single-layer buckling theory to the ptygmatic folds in the pegmatitic veins suggests that the maximum viscosity (competence) ratio, between the quartzo-feldspathic layers and the pelitic granulites, that existed at the time of fold development was about 10 1 , and that the total strain in the profile plane of the folds is given by a value for √ λ 1 λ 2 of 11 1 . Studies of early linear structures deformed around the folds show that the fold axes are nearly parallel to the maximum extension axis of the finite bulk strain ellipsoid.

1. Introduction The rock slope engineer is faced with two types of design problem: (a) General stability analyses which apply to the overall design of highway or opencast mine slopes and where the quality of the geological data available does not justify a detailed stability calculation. (b) Particular stability analyses which are required for critical slopes identified by the general analysis or for slopes which act as foundations for arch dams, large buildings and similar projects in which a high financial investment is concentrated on a relatively small volume of rock. These two types of design problem are linked in the flow chart presented in Fig. 1 which shows that any slope design study should proceed from a general to a particular form of analysis. Details of the methods which may be used for the stability analysis of critical slopes (step 8 in Fig. 1) have been published by Hoek, Bray & Boyd (1973). The present paper will deal with the general methods of slope analysis which may be used for step 2 in Fig. 1. 2. Recognition of failure mechanism Good rock slope engineering starts with good geological data collection and any attempt to carry out a stability analysis without first having defined the geology of the slope is a total waste of time. Rock slope failure is generally controlled by structural discontinuities such as faults, bedding planes and joints in the rock mass and hence the definition of these features is the most important part of the preliminary

INTRODUCTION MANY experts, including Stini, Oberti, Mtiller, Jahns, Kastner and Haupt, have pointed out, not only that the mechanical properties of a rock mass differ from the mechanical properties of a rock specimen, but also that there is a relationship between them which depends on the jointing. Various investigations have also been carried out in an endeavour to determine a so-called rock modulus. Efforts in this direction are, of course, very expensive and results are not easy to achieve. It is well known that the rock and rock pressure conditions in Kiruna are good. No major difficulties arise during the development work in rock or ore and roof supports in the stopes are almost unheard of. The hanging wall and the foot wall of the massive magnetite orebody consists of quartz or syenite porphyry. These rocks are quite homogeneous in outer appearance, yet there are considerable differences in the strength of the rock mass of the various mine sections. These 'anomalies' in the strength of the rock mass compelled us in Kiruna to study in greater detail the mechanical properties of the rock mass, and not only to test the rock in the form of rock specimens. The object of these investigations was the estaolishment of numerical relations between the strength of the rock and of the rock mass. The strength of the rock or more accurately the strength of the rock sample depends inter alia on the mineral composition and on the compactness of the rock. Quite a low strength of the rock mass may be found to exist when the jointing is poor in spite of the fact that the strength of the rock is fairly high. The visible and invisible fissures are responsible for the separation of rock particles of varying size during development work, and in the worst cases the strength of the rock mass is found to be nil.

Mine shafts have traditionally been protected by leaving the ore in the immediate surroundings of the shafts in place as a pillar. Empirical rules are used to determine the dimensions of these protective pillars. The face element principle introduced by Salamon has been used to compute functions which express the influence of mining in a horizontal seam on the rock mass above it. Values have been calculated for the tilt, distortion, horizontal and vertical strain, curvature, and vertical stress along a shaft for various values of Poisson's ratio, seam depth, pillar radius, mining geometry, and closure over the mined area. The results are compared with those obtained using empirical ideas, particularly the angle of draw concept in determining pillar size. It appears that the depth of the seam is of major significance and that no pillar is needed for the protection of a shaft when the mined seam is beyond a certain depth. On the other hand it is possible, at all depths, to replace the protective action of a shaft pillar by other mining schemes. A significant amount of information which has been published on experience gained during the mining of shaft pillars tends to indicate that in many mines shaft pillars are excessively large.

The following paper presents the concept that the terrestrial globe has hot spots where melting follows upon gradual heating by radioactive energy, and that in connection with such spots orogenic disturbances may develop: it is suggested that the growth of a molten body produces uplift; uplift results in unbalanced load; unbalanced load tends to cause lateral creep; heat from the molten body initiates expansion in the cover and also reduces strength of rock; creep becomes plastic flow by intimate, low-angle shearing; when shearing progresses to displacements on structure planes of crystal lattices atoms are forced out of balanced positions and jump into new ones; crystals are thus elongated and the crystalline rock mass is expanded accordingly; a very powerful thrust is thus set up and the opposing rock mass is sheared on a level at or near the top of the molten body; the magma transmits hydrostatically the pressure exerted upon it by the wall at the deep level of its bottom; that relatively great pressure causes it to intrude the major shear at the base of the expanding segment and to lubricate it; the dynamic elongation of the cover and the lifting power of the magma combine to thrust the segment forward and upward and it appears at the surface as a mountain uplift, characterized by sheared and folded rocks in association with intrusives. Emphasis is laid upon the fact that the rate of heat generation is extremely slow and the cycle of an orogeny should comprise the stages of initiation, gestation, upthrust, and decadence, i.e. , the time lapse of millions of years from peneplain to peneplain, but not the succeeding period of stability.

The study of metamorphic rocks is on the whole a difficult matter. Dam engineering geologists attempt to cast light on the structural data on a microscopic scale. Many methods are used to detect microfissuration, but generally the microscopic field below 100 μ is neglected. It is possible to detect, with a standard microscope which enlarges up to 2,000 times, the anomalies of crystalline structures: primary cavities, secondary fluid inclusions and their alignment which may give information on the engineering properties and on the geological history of the rock mass. Rocks from several dam sites have been examined. In the Malpasset rock, a very dense network of microfissuration was detected, very rich in secondary fluid inclusions, with a great number of alignments.

A numerical method for the determination of the stresses associated with the fracture processes of a brittle rock material is proposed. It is shown that the various zones of fracture around an underground opening can be predicted and a stability analysis of the rock structure can be performed, while taking the complete physical behavior of the rock material into account. The method is based upon the finite-element analysis and a process of successive approximations. An example of application for a norite rock mass containing a circular opening, under the conditions of plane strain and a uniaxial stress field, is given for illustration.

1. The criterion of fracturability C is a reliable numerical characteristic of the yield of a rock mass to the crushing action of an explosion. 2. The criterion of fracturability can greatly increase the efficiency of intelligent control of the main blasting parameters during the working of fissured rock. 3. This method of assessing the fissurability of rock provides a reliable quantitative characteristic of the rock’s structure in the in situ state and can be used for improving drilling and blasting in quarries and for solving other problems associated with the mining of fissured rock.

The author collected intrusive rocks in Nose district in Kinki Province and measured their natural remanent magnetization. Results of measurements of rocks collected from one rock body are as follows: the natural remanent magnetization of the intrusive rocks collected at the contact zone with country rocks was normal, while that of the intrusive rocks collected at places a little far from the contact zone was reverse. The directions of remanent magnetization were neither typical normal nor reverse. The normal direction deviated easterly relative to the present field direction, and the reverse one westerly.A fact that the rocks from a single mass possess both the normal and reverse magnetization can be explained, considering that the rock mass had been formed at the times when a transition of the geomagnetic field occurred, and the intermediate direction of magnetization seems to indicate the transition of the dipole of the geomagnetic field. The pole positions obtained from the intermediate direction of natural remanent magnetization lie in the same zone as those obtained from the Mio-Pliocene rocks in southwestern Japan.

1. The factors influencing the angle of internal friction of a rock mass (determined on a plane shear instrument) include, as well as the initial density and normal stress, the fraction sizes and the ratio of the minimum dimension of the instrument to the weighted mean diameter of the fractions in the mixture. 2. Our experiments confirmed that the angle of internal friction of a rock mass is reduced by increasing its content of dust—clay particles.

Abu Zaabal doleritic basalt, a volcanic extrusion present in the form of an extensive sheet, is a coarse holocrystalline rock exhibiting an ophitic texture. Petrofabric techniques were used in order to reveal the flow pattern of this rock using the (010) composition plane of the albite and carlsbad twins in the plagioclase crystals as the fabric element. The results of the fabric analysis on two basalt samples showed the tendency of the poles of this planar fabric element to describe a girdle pattern of orientation. It was also found that the plagioclase crystals tend to be oriented with their longest dimension parallel to the girdle axis. The motion was found to have been accomplished through the rotation of the plagioclase crystals about an axis normal to the direction of flow. Field studies showed the presence of two groups of joints; primary highly dipping joints and secondary nearly horizontal joints. Correlation between the orientation of the primary joints and the results of the fabric analysis showed that they are tension fractures developed parallel to the (ac) plane of the fabric. The mechanism of development of these tensile fractures are discussed in terms of the possible thermal anisotropy of the plagioclase crystals in such an anisotropic rock mass.

A continuum-Mechanical Approach to the Mechanics of Rock Masses A quasihomogeneous region of a discontinuous rock mass is approximated by a generalized Cosserat continuum. Blocks of the rock mass are represented by mass points, and to each point a number of vectors — the directors — is assigned. These directors determine the size and shape of the individual blocks. For this continuum are derived the basic equations of motion and the thermodynamic relations. The stress state is represented by a non-symmetric stress tensor.

1. The construction plans for hydraulic tunnels and underground structures for hydroelectric stations require designing on the basis of scientific investigations of the physicomechanical characteristics of rocks, carried out during excavation. 2. For hydraulic tunnels and underground structures of all classes the calculation of rock pressure must be carried out on the basis of scientific investigations. However, when carrying out calculations in stages of the project development rock pressure can be calculated also by well-founded equations and analogies. 3. When determining the wall pressure and elastic characteristics of the rock it is necessary widely to introduce contemporary leading geophysical methods of surveying, including seismic surveying. 4. The value of the rock pressure for spalling rocks depends on the fracturing and the dip of the strata and not on the coefficient of stability. 5. It is necessary to refine the coefficient a for significantly fractured rocks.

1. Microseismic prospecting on slopes can prove effective in the solution of the following hydraulic engineering construction problems: a) determination of the thickness of the weathered rock zone at the abutment of installations in the banks, and in arriving at the depth of insertion; b) clarification of the effect of slope degradation and nature of the stress in the rock mass; c) carrying out systematic observations on slip slopes on the abutment sections and in the reservoir zone. During these investigations it is possible to determine the boundaries between the slipping rocks (or those susceptible to slips) and the stable rock, to determine the morphology of the slip bed, to clarify the geometry of slip blocks in the plane, and sometimes the slip stage, the nature of fissuring of the slip mass, and sometimes the preferred direction of slip cracks. The setting up of long-term periodic observations employing microseismic prospecting on potentially dangerous sections in respect of slip may provide material necessary for engineering geologists when assessing the dynamic nature of slips. 2. Microseismic prospecting data must be duly corrected on the basis of general geologic procedures.

Synopsis A new method is given for the complete determination of either the initial or the induced state of stress at a given point in a rock mass by means of measurements carried out in a single borehole. The hole need not be dry and the method can be applied at great depths. The method consists in cementing into a small diameter borehole a plastic cylinder in which an assembly of electrical strain gauges is embedded, and relieving the stresses by overcoring. Analytical expressions are deduced which enable the state of stress in the rock mass to be determined from the deformations undergone by the strain gauges, and laboratory and in situ tests are described to show the feasibility and accuracy of the proposed method. On presente une nouvelle methode pour etablir completement l'etat initial ou l'etat induit de contrainte a un point donne dans une masse de rocher au moyen de mesures effectuees dans un forage unique. Le trou de sondage n'a pas necessairement besoin d'etre creuse et l'on peut appliquer la m...