Showing papers on "Discontinuity (geotechnical engineering) published in 1981"

Estimation discontinuity spacing and trace length using scanline surveys

Abstract: Abstract Knowledge of the spacing and size of discontinuities in a rock mass is of considerable importance for the prediction of rock behaviour. The characteristics of discontinuities can be estimated using scanline surveys but the precision of the estimates must be obtained and the bias caused by linear sampling must be eliminated before they can validly be used. Initially, an expression is presented which gives the degree of confidence that can be assigned to the measured mean discontinuity spacing. A reduced form of this expression is obtained for cases where the discontinuity spacings follow the negative exponential distribution. The precision of discontinuity frequency and RQD estimates is also explained. The distribution of trace lengths produced by the intersection of planar discontinuities with a planar rock face is used to determine the distribution of trace lengths, the distribution of semi-trace lengths and the distribution of censored semi-trace lengths intersected by a randomly located scanline. Comparison of the actual and sampled distributions demonstrates the bias introduced by scanline sampling of trace lengths. Relations between the distributions can be used to produce analytical or graphical methods of estimating mean trace length from censored measurements at exposures of limited extent.

Control of rupture by fault geometry during the 1966 parkfield earthquake

Abstract: A reanalysis of the available data for the 1966 Parkfleld, California, earthquake (Mr -- 5½) suggests that although the ground breakage and aftershocks extended about 40 km along the San Andreas Fault, the initial dynamic rupture was only 20 to 25 km in length. The foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault. Detailed analysis of the P-wave first motions from these events at the Gold Hill station, 20 km southeast, indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane. Other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at Parkfield. Analysis of the strong-motion records suggests that the rupture stopped at another discontinuity in the fault plane, an en-echeion offset near Gold Hill that lies at the boundary on the San Andreas Fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred. Foreshocks to the 1857 earthquake occurred in this area (Sieh, 1978), and the epicenter of the main shock may have coincided with the offset zone. If it did, a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do.

The excitation of long period seismic waves by a source spanning a structural discontinuity

Abstract: Simple theoretical results are obtained for the excitation of seismic waves by an indigenous seismic source in the case that the source volume is intersected by a structural discontinuity. In the long wavelength approximation the seismic radiation is identical to that of a point source placed on one side of the discontinuity or of a different point source placed on the other side. The moment tensors of these two equivalent sources are related by a specific linear transformation and may differ appreciably both in magnitude and geometry. Either of these sources could be obtained by linear inversion of seismic data but the physical interpretation is more complicated than in the usual case. A source which involved no volume change would, for example, yield an isotropic component if, during inversion, it were assumed to lie on the wrong side of the discontinuity. The problem of determining the true moment tensor of the source is indeterminate unless further assumptions are made about the stress glut distribution; one way to resolve this indeterminancy is to assume proportionality between the integrated stress glut on each side of the discontinuity.

The Contribution of Discontinuous Rock-Mass Failure to Glacier Erosion

Abstract: Geomechanical rock-mass properties control the response of bedrock to applied stresses and can be summarized in a linear Mohr-Coulomb equation, which defines the principal parameters determining failure. Nevertheless, in studying the erosion of bedrock by glacier ice, little attention has been paid to failure criteria though a coincidence of erosion all and forms with fracture systems at regional and local scales has been demonstrated. Few studies have analysed the precise nature of the fracture geometry, or proposed its mechanical impact in association with glacier ice. This investigation proposes that, since almost all bedrock possesses identifiable fracture systems, the properties of discontinuous rock mass (DRM) be regarded as defining primary conditions of stress and stability which are subsequently modified directly and indirectly by glacier ice. Consequent rock-mass failure modes are prescribed by discontinuity geometry and applied stresses, and evidence from North Wales confirms the validity of the theoretical treatment of rock-mass properties, and explains the accordance of landforms with structure.

Evening (Harang) and morning discontinuities in ionospheric electron drifts and their dependence on the interplanetary magnetic field

Abstract: Observations made with Scandinavian twin auroral radar experiment (Stare) have revealed the existence of a discontinuity in the electron drift pattern at high latitudes during the morning hours. The morning discontinuity appears to be equivalent to the evening (or Harang) discontinuity but has the region of westward drifting electrons located poleward of the eastward drifting electrons. The dependence of the discontinuity occurrence times on the sign of the azimuthal component, By, of the interplanetary magnetic field has been investigated. We find the evening discontinuity generally occurs earlier for By 0. A similar behavior was not found for the morning discontinuity, possibly due to the effects of the high level of magnetic activity (Kp ≥5−) associated with observations of this discontinuity. The average time separation between evening and morning discontinuities was 12 h 30 min. It is tentatively proposed that the morning discontinuity is the footprint of the polar cleft in the ionosphere. This would imply that the cleft, during very disturbed magnetic conditions, can extend down to ∼65° geomagnetic latitude.

Finite-element analysis of discontinuity problem of SH modes in an elastic plate waveguide

Abstract: A method for the solution of the discontinuity problem of SH modes in an elastic plate waveguide is described The approach is a combination of the finite-element and the analytical method. The results by this approach for the step discontinuity in a plate waveguide agree well with the results of the variational method.

Discontinuity and instability in early development: implications for assessment:

Abstract: Regina M. Rheingrover, M.A. Graduate Student Department of Special Education University of Maryland College Park, Maryland THE TERM development implies a high degree of continuity and stability in behavior change across time. Yet, in general, the preschool years are characterized by instabilities in development and lack of continuity in behavior change. In examining the implications of developmental discontinuities and instabilities for the assessment of infant and preschool-aged children, this article emphasizes the interpretation of assessment-related data. The term assessment will be used broadly to mean measurement activities whose goals and functions include screening, diagnosis, prognosis, and both qualitative and quantitative description of an individual's patterns and styles of performance—the purpose of these activities being to design interventions specific to the needs of the individual (Dunst, in press-a). The article examines several different types of stability-instability and continuity-discontinuity, and focuses on three categories of assessment procedures: psychometric intelli-

Intensity discontinuity location to subpixel precision

Abstract: Lateral inhibition processing of an image yields subpixel precision in the location of intensity discontinuity edges in a digitized image. The method is illustrated using a 512 × 512 × 8 bit image.

Crustal structure of south-western Honshu, Japan and the nature of the Mohorovičić discontinuity

Abstract: Summary. Two record sections have been prepared for a series of explosions near Lake Biwa, south-western Honshu, Japan. The record sections cover both the array stations and the network of microearthquake stations that are distributed throughout the area. This enabled us to detect for the first time in the Japanese islands the phase reflected at the Mohorovicic discontinuity. Until now the weakness and obscurity of the phase has made it difficult to detect. We were able to overcome this problem by processing the seismograms to enhance the phase. Our work leads us to propose that the surface of the Mohorovic discontinuity may be divided into pieces by a number of deep faults, while a thin layer of ultrabasic rock in the lower crust may account for the weakness of the signal.

System for detecting and locating surface discontinuity by a light beam

Abstract: The invention relates to a system for detecting and locating surface discontinuity by a light beam; it is more particularly intended for detecting any discontinuity forming a line on this surface, or any discontinuity forming two opposite lines on this surface. In the latter case, this discontinuity may, for example, be the join defined by the opposite edges of two metal sheets to be welded.

Scattering of the TE/sub 01/ and TM/sub 01/ Modes on Transverse Discontinuities in a Rod Dielectric Waveguide-Application to the Dielectric Resonators

Abstract: Our purpose is to determine the resonance frequency together with the radiation quality factor of dielectric resonators. To do that, the reflection and the scattering properties of the TE/sub 01/ and TM/sub 01/ modes, incident on an abruptly ended dielectric rod, are analyzed. After the building of the complete mode spectrum on each side of the discontinuity, the continuity relations in the discontinuity plane associated with the orthogonality properties lead to a coupled integral equation system. That one is solved by means of an iterative procedure, providing all the characteristics of the discontinuity (reflection or coupling coefficients, radiation losses). Then, these solutions are used to determine the resonant frequency and the radiation quality factor of cylindrical resonators which are considered as waveguide lengths between two interacting discontinuities.

Method of preparing semiconductor surfaces

Abstract: A method of treating semiconductor surfaces to produce an abrupt dielectric discontinuity between the semiconductor bulk and the ambient is described.

Method and apparatus for ultrasonic detection of near-surface discontinuities

Abstract: Near-surface discontinuities, or flaws, within a workpiece are determined by transmitting acoustic energy into the workpiece. If a discontinuity is present the acoustic energy will resonate in the section of the material between the discontinuity and the surface. Acoustic energy emerging from the section as a result of the resonating is detected and analyzed to determine this fundamental frequency, from which the half wavelength and depth of the discontinuity may be determined. The procedure is also applicable for determining the thickness of relatively thin sheets of material.

Guided Magnetostatic Waves of the YIG Plate Magnetized Nonuniformly

Abstract: It is shown that magnetostatic waves may propagate along a discontinuity of the internal dc magnetic field when its strength is made nonuniform such as a step. Backward waves may also propagate in this magnetic field configuration.

Stability of one-dimensional gas flows in expanding regions

Abstract: The stability of gas flows produced by the motion of a flat piston or the decay of an arbitrary discontinuity is considered. The boundaries of the region (or regions) in which the development of perturbations is considered are planes (shock wave, contact discontinuity, piston, etc.) which move away from each other.

On the Depositional Environment of the Nagthat Quartzite, Lesser Himalaya

Abstract: Nagthat quartzite shows well-developed sequences of a shallow tidal sea, and represents deposits of coastal sand bar/shoal complex and mixed flats. The sand bar deposits show large-scale cross-bedding of bar type, mega-ripple bedding and abundant planes of discontinuity. The mixed flat deposits show lenticular and flaser bedding, wavy bedding, tidal bedding, small ripple bedding, parallel bedding and laminated mud. Ripples showing characteristics of shallow-water and falling water-level environments are commonly present. In a typical Nagthat quartzite, sand bar deposits and mixed flat deposits alternate with each other in a cyclic manner. The Nagthat quartzite denotes deposit of a stable shelf association.

High frequency microstrip branch-line coupler design with T-junction discontinuity compensation

Abstract: A design procedure has been developed for high frequency microstrip branch-line couplers. The performance of these couplers is improved when T-junction discontinuity effects are compensated.

Seismic Plane Waves in a Layered Half-Space

Abstract: When seismic waves impinge on the earth’s surface or on an internal surface of discontinuity, the laws of reflection and refraction of a plane wave at a plane surface of discontinuity can be applied only approximately because both the wavefront and the surface are, in fact, curved. However, in many applications this approximation is quite satisfactory.

Rock Surface Roughness and Discontinuity Closure at Depth

Abstract: SUMMARY Preliminary consideration is given to two related matters: characterization of rock discontinuity surface roughness, and the normal pressure (as a depth-related parameter) necessary to achieve discontinuity wall closure through crushing of asperities in a type-rock. Experimental evidence is presented for effective acoustic fracture closure at normal stresses equivalent to about 15 percent of the intact unconfined compressive strength of the wall-rock. Fracture openings are implicitly predicted as a function of the combined rock surface roughness across the fissure and overburden pressure.