Showing papers on "Fracture (geology) published in 1969"

Fundamentals of rock mechanics

Abstract: Keywords: Mecanique des roches ; Analyse des contraintes ; Elasticite Reference Record created on 2004-09-07, modified on 2016-08-08

The relation between fault plane solutions for earthquakes and the directions of the principal stresses

Abstract: The stresses involved in shallow earthquakes and their occurrence along fault planes suggest that they occur by failure on weak planes, rather than by brittle fracture of a homogeneous material. Possible orientations of the stress tensor are examined to determine what limits fault plane solutions can place on the orientation of the greatest principal stress. For the general case of a triaxial stress, the only restriction is that this stress direction must lie in the quadrant containing P , but may be at right angles to the P direction. Thus shallow earthquakes impose a few limitations on the orientation of the stress tensor. In contrast the fault plane solutions from deep earthquakes are best explained by fracture of a homogeneous material, with the greatest principal stress directed down the dip of the earthquake zone.

Stress-induced velocity anisotropy in rock: An experimental study

Abstract: Application of uniaxial stress to a sample of granite causes elastic wave velocity anisotropy. Compressional waves travel fastest in the direction of the applied stress. Two shear waves travel with generally different speeds in any direction, exhibiting acoustic double refraction which increases with increasing stress.

In-situ stress determination at great depth by means of hydraulic fracturing

Abstract: One of the main functions of rock mechanics research has been to find ways of determining in situ stresses. Most methods usually employ some instrumentation for the purpose of measuring hole deformation. The method of hydraulic fracturing has been suggested, because it has been shown that the recorded pressures can be theoretically related to magnitudes of the principal in situ stresses; the orientation of the fracture can often be used to determine the direction of the principal stresses. The advantage of hydraulic fracturing over the present in situ stress determination methods is simplicity: no sophisticated instrumentation is required inside the borehole; hence, the stresses can be measured at any depth. If the formation is impermeable to the fracturing fluid, no elastic constants of the rock are required in calculating the stresses, a factor that not only simplifies the problem, but renders the results more reliable. The theoretical considerations are discussed. A laboratory experimental program was undertaken to verify some of the assumptions and results stated in the theoretical section. The equipment is described. (19 refs.)

In-Situ Stress Determination At Great Depth By Means Of Hydraulic Fracturing

Abstract: One of the main functions of rock mechanics research has been to find ways of determining in situ stresses. Most methods usually employ some instrumentation for the purpose of measuring hole deformation. The method of hydraulic fracturing has been suggested, because it has been shown that the recorded pressures can be theoretically related to magnitudes of the principal in situ stresses; the orientation of the fracture can often be used to determine the direction of the principal stresses. The advantage of hydraulic fracturing over the present in situ stress determination methods is simplicity: no sophisticated instrumentation is required inside the borehole; hence, the stresses can be measured at any depth. If the formation is impermeable to the fracturing fluid, no elastic constants of the rock are required in calculating the stresses, a factor that not only simplifies the problem, but renders the results more reliable. The theoretical considerations are discussed. A laboratory experimental program was undertaken to verify some of the assumptions and results stated in the theoretical section. The equipment is described. (19 refs.)

Fracture of Sapphire

Abstract: The fracture of sapphire was studied using the double-canti-lever-cleavage technique. Fracture surface energies were 7.3 and 6.0 J/m2 for the (100) and (012) type planes, respectively. Attempts to measure the fracture surface energy on the (0001) plane were unsuccessful. The failure of sapphire to fracture along the basal plane was attributed to the fact that these planes lack electrostatic charge neutrality. The possibility of fracture-induced dislocation motion in sapphire at room temperature was investigated using etch-pit techniques, but no evidence for dislocation motion could be found. Fracture behavior on (012) planes was erratic, varying from boule to boule. The topology of surfaces formed by crack propagation along this plane is described, but no explanation for the erratic behavior or the observed fracture features is given.

Theoretical size of hydraulically induced horizontal fractures and corresponding surface uplift in an idealized medium

Abstract: For the disposal of radioactive wastes by hydraulic fracturing and grout injection, it is considered essential that the induced fractures be nearly horizontal. Bottom-hole injection pressure in excess of overburden pressure has been recognized as one indication that fracturing is horizontal. The amount of uplift of the ground surface caused by the injection can be used as another indicator. For an impervious, homogeneous, isotropic medium, a mathematical model for calculating the amount of uplift of the ground surface, the maximum separation of the horizontally induced fracture at the injection well site, and the radius of extension of the fracture was developed from the basic formulas derived by I.N. Sneddon (1946) and A.E. Green (1949). If the bottom-hole injection pressure is greater than the overburden pressure, and the observed uplift is nearly the same as the calculated uplift, the fracture orientation probably is nearly horizontal. Uplifts from 9 injections made at the Oak Ridge National Laboratory, Tennessee, from 1960 through 1965, have been used to test the validity of the mathematical model. The calculations agree reasonably well with the observed data. (31 refs.)

Mechanical Properties of Metal Oxide Films

Abstract: A brief review is given of mechanical property measurements on oxide films. This review is followed by a detailed discussion of the mechanical and fracture properties of anodic aluminum oxide films as observed in the author's laboratory. Extensive measurement of Young's modulus, ,and fracture strain, , for separated films 3000Aa thick is reported as a function of environmental water vapor pressure. The fracture of these unsupported films is shown to occur by a brittle mechanism. Mechanical properties of adhering aluminum oxide films are given as a function of their thickness. These oxides were observed to fracture either at slip steps, or at right angles to the tensile axis in a regularly spaced fashion. A theory of adhering oxide fracture is discussed which accounts well for the observations. An equation which describes the spacing of regular oxide fracture cracks as a function of substrate strain e is given in the form , where () are the initial conditions for regular fracture, is the oxide thickness, and is a constant.

Limiting equilibrium of brittle solids with fractures

Abstract: : The monograph analyzes the theoretical principles of a quasistationary equilibrium of brittle solids with fractures The results of investigations which were carried out by the author on the theory of propagation of fractures in a deformable solid are generalized and calculated model diagrams for such problems are given Solutions of new plane and three-dimensional problems on a limiting equilibrium of brittle solids with fracture are shown An attempt is made to formulate the elements of the theory of brittle destruction of deformable solids with fracture defects

Fracture zones and magnetic anomalies south of the Aleutian Trench

Abstract: Magnetic anomalies south of the Aleutian trench between 164° and 180°W trend east-west. The magnetic pattern is disrupted at 173°W and 177°30′W by north-south-trending fracture zones named Amlia and Adak fracture zones, respectively. Correlation of magnetic anomaly profiles shows apparent left-lateral offsets of 220 km across the Amlia fracture zone and 30 km across the Adak fracture zone. The amplitudes of the anomalies are sharply reduced where they intersect the trench, resulting in a magnetically ‘quiet zone’ over most of the Aleutian trench and terrace. Although there are suggestions that the fracture zones extend north of the trench, the evidence is inconclusive.

Role of Cohesive Strength in the Mechanics of Overthrust Faulting and of Landsliding

Abstract: The Mohr-Coulomb criterion for failure, modified in light of the concept of effective stress, is where τ c is the critical shear stress at failure, S the normal pressure, and p the pore pressure across the plane of internal slippage at failure , ϕ i the internal friction angle, and τ 0 an empirical constant, commonly referred to as the cohesive strength. Experiments showed that the τ 0 for sedimentary rocks is about 200 bars. Hubbert and Rubey (1959) assumed that once a fracture is started, TO is eliminated and further movement results when They proceed, however, to use this formula for the frictional sliding of cohesionless block as the criterion of failure of large thrusts, after they assumed that τ 0 could be eliminated through a concentration of stress. This assumption led to their conclusions that very long overthrust blocks are possible and that such blocks may have moved by gravitational sliding along very gentle slopes. I present arguments to show that their assumption of zero τ 0 was based upon a faulty argument and to point out that the τ 0 term should not be omitted unless it could be proved the moving block slid along an already existing fracture plane. The first part of this paper consists mainly of conclusions based on computations. Clearly, an unjustified omission of a 200-bar cohesive strength would lead to erroneous and misleading results; particularly, gravitational sliding cannot be an important mechanism if such a cohesive strength has not been eliminated during overthrust faulting. The second part presents evidence to distinguish between movements of cohesively bound blocks and cohesionless blocks. The Glarus overthrust, characterized by presence of a ductilely deformed limestone layer within the thrust zone, is considered a typical example of thrusting of cohesively bound blocks. The Heart Mountain thrust, characterized by a shattering of the “upper plate” and absence of a weak layer above the thrust contact, is interpreted as an example of thrusting of cohesionless blocks. The former is compared to slowly creeping slides moving at rates of centimeters or less per year, and the latter with catastrophic landslides (such as the Flims, Goldau, and Vaiont slides) moving at speeds of many meters per second. Third, the conclusion of Raleigh and Griggs (1963) that large thrusts can only form when a toe of the thrust is continually eroded is also traced to the assumption of zero cohesive strength along thrust plane. Otherwise, the toe effect would produce a zone of imbrication at the front of overthrust blocks, particularly those sliding downslope under their own weight.

Fracture Toughness of Portland Cement Concretes

Abstract: FRACTURE TOUGHNESS IS A MATERIAL PROPERTY DETERMINED BY EVALUATING THE STRESS INTENSITY FACTOR AT THE ONSET OF RAPID, UNSTABLE CRACK PROPAGATION. THE STRESS INTENSITY FACTOR DENOTES THE ELASTIC STRESS AND DISPLACEMENT FIELDS IN THE REGION OF THE CRACK TIP OF A HOMOGENEOUS MATERIAL. WHEN THE CONCRETE IS ANALYZED AS A HOMOGENEOUS MATERIAL AN EFFECTIVE FRACTURE TOUGHNESS IS OBTAINED. AN EXPERIMENTAL INVESTIGATION WAS CONDUCTED TO DETERMINE THE EFFECTS OF SEVERAL CONCRETE PARAMETERS ON THE FRACTURE TOUGHNESS OF CONCRETE. /A/RRL/

Method of fracturing formations in wells

Abstract: The present invention is directed to a method for fracturing a subterranean formation penetrated by a well bore, the fracturing being accomplished by alternately injecting into said formation a high-viscosity non-Newtonian fluid and a low-viscosity Newtonian fluid. The low-viscosity fluid carries propping agents into the fracture if a wide fracture having a relatively small radius and a layered proppant configuration is desired, and the highviscosity fluid carries propping agents into the formation if narrow fractures having a relatively large radius and a high permeability are desired.

Fracture and secondary flow of elastic liquids

Abstract: In the absence of disturbances at the free surfaces, secondary flow due to elastic forces occurs in elastic liquids sheared in cone-and-plate rheometers but not in parallel-plate rheometers. In both types of apparatus an instability is observed. Using a theory based on a fracture mechanism, the critical normal stress differences for the onset of the instability can be correctly predicted for both types of apparatus. It is concluded that the fracture instability is a distinctly different effect from the secondary flow considered.

Structural Analysis of Fractures in Cores from Saticoy Field, Ventura County, California

Abstract: The orientation and relative positions of subsurface faults are inferred from analysis of macro- and microfractures in cores from the Saticoy field, Ventura County, California. The conclusions are reached from study of 1,044 macrofractures (joints) in 4,168 ft of core from 28 wells and from the orientations and relative abundances of microfractures (unhealed fractures in quartz grains) studied in thin sections from cores at several depths in each of six wells. The conclusions are checked by comparison with the known structure of the Saticoy field. In the main, four macrofracture sets exist along the length of the field. Their "real" rather than observed relative development is assessed upon consideration of the problems of determining the orientation of macrofractures in core samples. In the absence of offset criteria, an interpretation of the fracture data is made solely on geometric grounds and with the geologic knowledge available before the field discovery well was drilled. It is concluded that two of the fracture sets parallel, and therefore define, the orientations of two reverse faults. The microfractures are shown statistically to be parallel with the macrofractures. In addition, information on the abundance of microfractures is presented for 31 sample locations in six holes that are deviated both toward and away from known faults. The abundance of microfractures increases with proximity to the faults and is essentially independent of the depth of burial. The strike, dip, and position relative to drill holes of the faults predicted from the fracture data agree with the known subsurface structure.

Fracture of Fibre Reinforced Materials

Abstract: A SIMPLE experiment has been carried out which shows the importance of the rate of loading on the fracture characteristics of a unidirectional composite. Three specimens of flexibilized epoxy resin, 12.7 mm × 6.4 mm in cross-section and 50 mm test length reinforced with 3 volumes per cent continuous silica fibres in unidirectional array, were loaded to fracture at 0.051 mm/min, 5.1 mm/min, 510 mm/min respectively, at room temperature. Fracture was deliberately encouraged by forming a small notch at one side of each specimen and a tensile crack then spread in the resin to the opposite side. Fibre fracture did not coincide with resin fracture but was spread over a region on either side of the resin crack.

The brittle fracture of alumina below 1000°C

Abstract: Alumina is normally regarded as truly brittle below ∼ 1000°C. Contrary to this view, it is argued that plastic deformation at the crack tip plays a necessary part in the fracture. This is used to explain the minimum observed at 250°C in the fracture stress of polycrystalline plates containing drilled cracks and in the stress intensity required for crack-branching. Other details of the fracture of single crystal and polycrystalline alumina, including changes in the proportion of intergranular and transgranular fracture with temperature, crack length and crack-branching, are also explained by the involvement of plastic deformation.

Theory of rate of growth of fatigue cracks under combined static and cyclic stresses

Abstract: An equation is derived that describes the rate of growth of fatigue cracks under combined static and cyclic stresses. The equation predicts that a static tensile stress has very little influence on the rate of growth of fatigue cracks, even if the static stress is very much larger than the amplitude of the cyclic stress, unless the maximum total applied stress is comparable to the (static) fracture stress.