Showing papers on "Discontinuity (geotechnical engineering) published in 1979"

Electron flow and visual aurora at the Harang discontinuity

Abstract: We present several examples of the ionospheric electron drift patterns and of the aurora near the Harang discontinuity. The drift patterns were detected with the Scandinavian Twin Auroral Radar Experiment, and the auroral features were determined by using all-sky camera data. We find the behavior of the discontinuity to be strongly dependent on the level of magnetic activity as measured by the Kp index. During low activity the discontinuity remains at a fairly constant latitude for a considerable length of time. Usually, one to two auroral arcs are observed within the discontinuity. With increasing magnetic activity the Harang discontinuity tends to surge rapidly equatorward with mean speeds ranging from 150 to 600 m/s. This equatorward surge is observed at earlier local times as magnetic activity increases. We have found two cases in which an arc appears in the discontinuity at some point during its equatorward surge. The equatorward surge of the essentially east-west-aligned discontinuity appears to be associated with a limited region of strong equatorward electron flow which splits up into eastward and westward flow. This region may form the eastward termination of the discontinuity. The eastward termination of the Harang discontinuity during times of low magnetic activity appears to consist of an equatorward extension of the region of eastward electron flow within a spatially limited region near local magnetic midnight. We find the equatorward surges to be terminated by the sudden activation of an arc in the discontinuity, followed by a poleward expansion. Following these substorms the Harang discontinuity disappears from the field of view. At times, we have observed arcs to brighten and surge poleward in the region equatorward of the discontinuity. The discontinuity did not appear to be strongly affected by these substorms. We find in general that auroral arcs are located in or poleward of the discontinuity, even though active arcs at times appear south of the discontinuity. Diffuse aurora have been observed only equatorward of the discontinuity.

Computer simulation of mining in faulted ground.

Abstract: This paper descriptionbes a numerical procedure for the computation of the displacements and stresses induced by the mining of a tabular ore deposit in faulted ground. The numerical procedure is based on the displacement discontinuity method, which can be regarded as an application of Salamon's 'face element principle' to cases in which the reef plane is faulted into several sections, or even folded in an arbitrary way. An element of a fault is modelled in the same manner as an element of the reef, except that a fault element is allowed to undergo permanent inelastic deformation (i.e., slip) if the stresses transmitted through the fault-filling material satisfy a Mohr-Coulomb yield condition. An iterative technique for the incorporation of a Mohr-Coulomb yield condition in the general displacement discontinuity method is explained. This technique is illustrated by means of a simple example involving the mining of a flat-lying reef intersected by a fault. The displacements and stresses at selected locations along the fault are examined as the reef is mined, element by element. A consideration of the energy changes reveals that the occurrence of slip along a fault leads to a sudden increase in the energy release rate due to mining as the excavation intersects the fault. The energy release rate then falls off abruptly to a value less than that which would occur in the absence of any slip, and gradually builds up to re-establish the conditions that would exist in unfaulted ground.

Static strike-slip faulting in a horizontally varying crust

Abstract: A simple and accurate method is shown for a static two-dimensional model of a long strike-slip fault in a crust with horizontally varying rigidity. The rigidity variation is approximated by a series of vertical laminated layers. The layer model has an exact solution represented by zero-frequency Thompson-Haskell layer matrices. The slip regime is modeled by a planar displacement discontinuity (i.e., screw dislocations) within one layer. The method was used to calculate the surface displacement and strain fields for a number of slip regimes and crustal rigidity profiles. In general, it was found that large modifications and/or excursions to the conventionally expected deformation fields resulted using physically reasonable crustal rigidity models. For example, very large local amplification spikes in the strain field were found in crustal low-rigidity zones. The results further showed that not adequately considering crustal strength variations can be a cause of misinterpreting field data. A possible source of “noise” in field observations was also linked to crustal nonuniformity. The demonstrated sensitivity of static data to both large scale and local rigidity variations points up the potential use of dense field observation nets for delineating heterogeneous regions in the crust.

Discontinuity surface in a fluid system: Local equilibrium

Abstract: The balance equation of the specific area of a discontinuity surface is derived and the effect of this balance on the formulation of the hypothesis of local equilibrium is discussed.

Magnetic head sliding detecting system

Abstract: PURPOSE:To readily and positively prevent troubles by sliding by detecting the sliding of a magnetic head by combining the conductive patterns mounted to the floating face of the head and a continuity or discontinuity detection circuit.

Unsteady flow of incompressible fluids in deformable tubes

Abstract: We investigate the unsteady axially symmetric flow of an incompressible fluid in a deformable tube including the effects of leakage and wall friction. In particular, we consider the general conditions whereby a discontinuity in the fluid pressure rate may develop into a pressure discontinuity, a situation which may be interpreted as an abrupt shear of the tube wall and which could be damaging. The problem is inherently non-linear even for the simplest situation of a linearly elastic tube undergoing infinitesimal deformation. The problem of initial steady flow in a circular tube with axially varying cross section is also considered.

Heat Flow, Crustal Thickness and Recent Vertical Movements

Abstract: The relationship between heat flow and/or the depth of the Moho discontinuity and recent vertical movements based on repeated leveling is tentatively discussed. Studies were made in central and east European regions with the help of data supplied by the International Center on Recent Crustal Movements. For analytical purposes the area under study was divided into suitable subareas displaying tectonic features as uniform as possible. As may be inferred from the obtained results, areas of young orogenic belts are characterized by increased vertical movements with increasing heat flow. There is an inverse relationship in the areas of platform nature: subsidences increase as heat flow increases. A less distinct relationship exists between the depth of the Moho discontinuity and the vertical movements.

Strength of reinforced-concrete hydraulic structures having block joints

Abstract: 1. The proposed method of calculating the strength of reinforced-concrete structures permits taking into account the actual discontinuity of a massive structure (presence of block joints). 2. On the basis of a multiple-factor analysis of the state of stress obtained by the method of elasticity theory with the use of the theory of the strength of concrete, methods were proposed for calculating the crack resistance and predicting the failure of structures having block joints, which permit taking into account the nonlinearity of the distribution of stresses, combined stresses, and resistance of the principal longitudinal reinforcement to the effect of cleaving forces. 3. The results of the experimental investigations and the actual character of cracking of certain structures agree with the calculation results, which indicates the correctness of the initial assumptions of the proposed method.

Correlation of Structural Steel Fractures Involving Massive Plasticity

Abstract: A three-dimensional, elastic-plastic fracture strength correlation for A36 and HSLA structural steel connections containing discontinuities was determined. The fracture specimens comprised beam-column connections in whichone column flange contained a mid-thickness plane of discontinuity. Beam loading or direct tension applied normal to the column face imposed tensile load transfer around the boundaries of the discontinuity. Fracture extension was mixed mode (crack opening and edge sliding), and inclined toward the free surface on the web side of the column flange containing the discontinuity. Successful correlation for these specimens was accomplished with a plastic stress singularity strength model, if the discontinuity was sufficiently large. The average singularity strengths at ultimate load were 64.6 MNm - 3 / 2 (58.7 ksi in. 1 / 2 ) for HSLA steels, and 53.7 MNm - 3 / 2 (48.8 ksi in. 1 / 2 ) for A36 steel. The percent coefficient of variation was 6.4 percent for HSLA steels and 8.4 percent for A36 steel.

Development of two-dimensional perturbations on the surface of a tangential discontinuity

Abstract: A study is made of the asymptotic behavior at long times of initially localized small two-dimensional perturbations of the interface of two fluids in the presence of a tangential discontinuity of the velocity; surface tension is taken into account. The development of one-dimensional perturbations was considered earlier in [1]. The asymptotic behavior of the perturbed region is found, i.e., in the xyt space there is found a cone with apex at the origin such that perturbations tend to infinity with increasing t along rays within the cone, while perturbations tend to zero along the remaining rays. Conditions are found under which the instability of the tangential discontinuity is not absolute, i.e., when these conditions are satisfied, flows with tangential discontinuity of the velocity can take place. These conditions, like the shape of the cone, do not depend on the magnitude of the surface tension.

Influence of physico-mechanical properties and geological discontinuities on rock blasting

Abstract: It is now an established fact that rock properties and presence of geological discontinuities affect rock blasting to a great extent. An attempt has been made in this paper to discuss the influence of various physical and mechanical properties of rock and geological planes of weakness on blasting. Strong elastic rocks require explosives capable of developing higher peak strains whereas explosives of lower energy perform better in softer rocks. Suitable orientations of blast patterns with respect to major planes of weakness are described. Various methods of determining the blastability of rocks are discussed. (a) (TRRL)

A Variational Approach to Compute the Equivalent Capacitance of Coaxial Line Discontinuities

Abstract: A variational approach is presented which enables both to compute the discontinuity capacitance in coaxial structures and to state its frequency behaviour. The results compare favorably with the ones previously given in literature. Moreover, the method enables to consider structures having different dielectric permittivities at the sides of the discontinuity.

An analogical verification of the discontinuity of matter based on the Law of Definite Proportions

Abstract: Demonstrates the discontinuity of matter and the law of definite proportions using Play-Dough, nuts and bolts.