Showing papers on "Discontinuity (geotechnical engineering) published in 1978"

Trajectory Discontinuity and Morphogenesis: The Implications of Catastrophe Theory for Archaeology

Abstract: The problem of discontinuity in the behavior of culture systems-the last stronghold of the anti-processualists-is discussed. Abrupt change in behavior can now be described in terms of smooth changes in the underlying causative factors by means of Rene Thom's Theory of Elementary Catastrophes. The theory suggests insights not only into discontinuities with respect to time ("sudden" changes) but into the differentiation offorms as the result of bifurcations (morphogenesis). Although existing applications of the Theory in the social sciences lack quantitative precision, they offer a deeper understanding of crucial mechanisms of social evolution and, it is suggested, go far toward solving the discontinuity problem in archaeology.

Geomechanical Model for Rock Foundation Settlement

Abstract: A geomechanical model is proposed for estimating the settlement of foundations on rock masses. Included is a rock mass model for reducing rock material properties to rock mass properties and an RQD model to correlate RQD with discontinuity frequency. The models are used with anisotropic elastic solutions to evaluate settlements on isotropic, transversely isotropic, and orthogonally jointed rock masses. An extensive material property summary is included for initial estimations, and design examples are included.

Local Magnetic Field Variations and Stress Changes Near a Slip Discontinuity on the San Andreas Fault

Abstract: Data from an array of proton magnetometers in central California indicate that a systematic decrease in magnetic field of about 2 γ in 5 years has occurred in a localized region near Anzar, California, just north of the creeping section of the San Andreas fault. This field change has most likely resulted from changes in crustal stress in this region, although an unknown second-order effect of secular variation cannot be excluded as a alternate explanation. Tectonomagnetic models have been developed using dislocation modeling of slip on a finite section of fault. Assuming a fault geometry and rock magnetization, these models relate changes in stress, fault slip, and fault geometry to surface magnetic field anomalies. A large-scale anomaly, opposite in sense to that observed but of similar amplitude, would be expected to have accumulated in this area during the past 70 years. A localized 5-bar decrease in shear strain on the fault resulting from about 2 cm of slip on a 0.25-km square patch at a depth of 1 km beneath the surface trace of the fault opposite the magnetometer could explain the observed data and still be compatible with the geodetic strain measurements in the area. Other models of limited local slip are equally possible. The occurrence of a moderate magnitude earthquake in this region will allow comparison of stress changes estimated by different techniques.

Non-equilibrium thermodynamics of a discontinuity surface

Abstract: A comprehensive axiomatic system of the non-equilibrium thermodynamics of a surface of discontinuity is formulated. The general formulation of the axioms is applied to the problem of an n -component visco-elastic isotropic non-polar mixture. The effect of mass currents from one phase to the other on the formulation of the hypothesis of local equilibrium is discussed.

Comprehensive Model for Rock Discontinuities

Abstract: The full understanding and analytical modeling of rock discontinuity behavior requires a comprehensive model that can describe the entire history leading to the present state of the discontinuity as well as subsequent changes of this state. The comprehensive model presented in this paper is based on a general purpose elastic viscoplastic critical state model that can be applied to most materials used in civil engineering. In a newly developed stress-strain-time space, the entire stress-strain history, including time-related effects like creep and consolidation, can be represented. The concept of the critical state makes a complete description of post-yield behavior possible which is of particular importance for rock discontinuities. The powerful capabilities of the comprehensive model are demonstrated by performing the required full description of rock discontinuity behavior. A comparison with the best known rock discontinuity models shows both the versatility of the comprehensive model and the possible inadequacies of these previous models.

Interaction of water molecules with the surface of tin(IV) oxide

Abstract: Water vapour adsorption was investigated on SnO2 surfaces prepared by oxidizing metallic tin with nitric acid. The adsorption isotherms reveal a discontinuity, i.e., a sharp increase in the amount of adsorbed water in the range of relative pressure 0.02–0.03; this is the second example of metal oxide + water systems exhibiting a discontinuity in the adsorption isotherm after the system ZnO + H2O. The height of the discontinuity decreased gradually by successive evacuation of the sample at higher temperatures in the order of 313, 573 and 773 K (series 1) or of 1073, 573 and 773 K (series 2), and finally the discontinuity disappeared. Plots of isosteric heat of physisorption of water show a plateau in the same range of coverage as that corresponding to the discontinuity. The plateau also decreased by successive heating of the sample, in parallel with the decay of the discontiniuity. The adsorption data show a good fit to the Hill–de Boer equation in the range of the discontinuity. The structure of the adsorbed water layer on SnO2 is discussed, by evaluating the ratio of the number of physisorbed molecules in the monolayer to that of underlying surface hydroxyls.

Primary factors governing hydraulic fractures in heterogeneous stratified porous formations

Abstract: Some primary material, macrostructural and tectonic features of typical geological formations are identified, insofar as they affect the hydraulic fracturing operation whereby suitably treated fluid is pumped into massive crack(s) underground: the retardation or channeling due to strata interfaces, discontinuities and other heterogeneities is roughly characterized, in the context of fully three-dimensional crack shape evolution, and the initiation from oriented boreholes is discussed in detail. A general-purpose numerical scheme is described, efficiently based on a physically transparent distribution of discontinuity multipoles (or dislocations) and the solution of resulting singular integral equations, which permits precise quantification of these effects: in particular, the barriers provided by adjacent stiffer and tougher strata are properly rationalized and the roles of inelastic slippage, blunting, branching, arrest, and re-initiation are placed in more transparent perspective. Stabilization effects due to alterations of pore-fluid pressure (and hence effective decohering stress), or the flux of formation fluid into the open region near to the crack tip, are described as potentially unfavorable for hydrofrac containment. However, the dominant time-dependent mechanism of frac fluid penetration into the narrow crack aperture attracts most attention: this process is very naturally and tractably incorporated in our comprehensive numerical formulation so that realistic simulation ofmore » actual field operations should be feasible in the near future.« less

The influence of obliquely dipping discontinuities on the use of rayleigh channel waves for the in‐seam seismic reflection method *

Abstract: The geological sequence rock-coal-rock represents a seismic low-velocity channel. Channel waves generated in a coal seam and their reflections from discontinuities can be used for proving the minability of the seam. To investigate the process of reflection, two-dimensional models of the sequence rock-coal-rock have been investigated by means of the ultrasonic transducer technique. Two-dimensional models have the advantage that the wave field can be observed at an arbitrarily chosen point of the model plate. Thus, by means of these models the direct and the reflected Rayleigh channel wave can be observed along their path of propagation. From the geophysical point of view the various types of discontinuities of a coal seam can be divided into two basic types: one is restricted to the seam, the other includes in addition a fractured zone in the adjoining rock. The investigation of the symmetrical Rayleigh channel wave reflected by a discontinuity yields the following results: For dip angles γ between approximately 90° and approximately 60° the reflectivity is virtually independent of the type of discontinuity. This does not hold for the limiting case of γ= 90° (vertical dip) for which the reflectivity increases with increasing influence of the fractured zone. For dip angles γ between approximately 60° and approximately 40° the reflectivity is still independent of the fractured zone but the shape of the reflected wave deteriorates with increasing influence of the fractured zone. For dip angles γ below approximately 40° the reflected wave deteriorates such that the application of the in-seam seismic reflection method will be difficult or even impossible. The conversion of the direct wave of the symmetrical fundamental mode into a reflected wave of the antisymmetrical fundamental mode has been observed.

The Compensation of Step Discontinuities in TEM-Mode Transmission Lines

Abstract: A method for the compensation of the effects due to discontinuities that arise when transmission lines of different characteristic impedance are joined is presented. The proposed method is not based calculating the equivalent circuit of the discontinuity but makes use of simple taper on the wider line at an impedance step to remove the effects of the discontinuity.

Neutron wave propagation across an absorption discontinuity

Abstract: Two-group calculations of the propagation of neutron waves across an absorption discontinuity in beryllium are reported. The first slab is assumed to be of finite width, while the second is taken to be of infinite dimensions. It is found that in the first slab, the effect of the interface is felt earlier for lower frequencies.

Development of perturbations at the interface between two liquids

Abstract: The asymptotic behavior is studied in the case of large times of initially localized, one-dimensional, small perturbations of the interface between two liquids in the presence of a tangential velocity discontinuity, taking account of surface tension and the force of gravity. The asymptotic behavior of the perturbed region is found; i.e., on the plane x, t a sector is shown with vertex at the origin of the coordinates, inside of which the perturbations tend to infinity with increase of t, and outside of which the perturbations tend to zero, and the velocities of motion of the boundaries of the perturbed region are calculated. The conditions are shown for which the instability of the tangential discontinuity will not be absolute; i.e., when they are fulfilled, flows with a tangential velocity discontinuity can occur. For the case where the effect of the force of gravity can be neglected, these conditions are independent of the magnitude of the surface tension.

A preliminary study based on gravity data of the crustal structure of the peking-tientsin area and its neighboring regions

Abstract: In this paper, the method of "Compressed Mass Plane'' is used to study on the basis of gravity data the crustal structure of the Peking-Tientsin area and its neighboring regions. The depth contours of the Mohorovicic Discontinuity and that of the "Second Crustal Discontinuity" are drawn. A preliminary study of the relation between the crustal structure thus obtained and the seismieity of the various regions has been made. It can be shown that within the seismic active regions, the two sides of an upper mantle uplift and the places of abrupt changes of crustal discontinuity, especially at the junction of two different trends of crustal structures are locations and tectonic background for the occurrence of strong earthquakes. Ithas been pointed out that within the belt from Qinghuangdao (秦皇岛) to Suizhong (绥中) and Jinxi (锦西) and the region from Changping (昌平) to Yanqing (延庆) and Fangshan (房山), such tectonic backer, und exists which deserves of our attention and of strengthening of observations.

Determination of the dip and strike of the Moho from array analysis

Abstract: A new method, using only available array data, is developed to determine the dip and the strike of a major velocity discontinuity such as the Mohorovicic discontinuity. The method employs the coherencies of body waves in the P coda from both the vertical and horizontal detectors to obtain the slowness and azimuth of the direct and the converted wave from a major discontinuity. An example is given from array measurements in southern Alberta.

The propagation of weak discontinuities in quasi-linear hyperbolic systems when a characteristic shock occurs †

Abstract: In this paper we study the propagation of weak discontinuities in quasi-linear hyperbolic systems of equations with discontinuous coefficients when one or more speeds of propagation of the discontinuity wavw is coincident with the speed of propagation of the strong discontinuity

Quantitative Characterization of Distribution Parameters of Joints in Rock Masses

Abstract: Highly simulated description of the joint system in rock masses can be performed by utilizing new parameter of discontinuity ratio besides the orientation and the spacing of joints. The discontinuity ratio is derived mathematically using field measurements of the spacing of joints.The general parameters obtained are illustrated on some projects.

Some singular aspects of three-dimensional transonic flow

Abstract: a series of elastic concentration- factor values from 1.05 to 10 and for values of the Ramberg- Osgood .exponent from 5 to 200. The data for Figs. 1 and 2 were obtained from the tabular output of the program. Conclusions 1) Design relations have been developed for plastic discontinuity stresses using Neuber's equation and the Ramberg-Osgood analytic approximation of stress-strain properties. 2) The limiting value of the discontinuity stress in the developed relations is the Ramberg-Osgood end-value. The latter is the maximum value of stress for which the Ramberg- Osgood equation provides a satisfactory fit of experimental stress-strain data. The end-point of the equation has been identified using a non-dimensional strain parameter. The end- stress is obtained by computation. 3) The relative reduction of the stress concentration factor associated with plastic discontinuity stresses is independent of the elastic concentration factor. The reduction is mainly dependent on the maximum discontinuity stress and the Ramberg-Osgood exponent value. 4) Limiting values of the stress-concentration reduction factor occur when the discontinuity stress is at the Ramberg- Osgood end-value and the reference stress is elastic: a) If the end-value is the secant-yield stress, the plastic concentration factor is 83.7% of the elastic concentration factor for all values of the Ramberg-Osgood exponent and for all elastic values of the reference stress; or b) If the end value is greater than the secant-yield stress, the reduction value is a function of both the exponent and the end-stress. However, for given values of the two parameters, the limiting value of the reduction factor is constant for all elastic values of the reference stress.

Formation of shock waves in dissociating gases

Abstract: Using singular surface theory the phenomena associating with the non-uniform propagation of weak discontinuities through dissociating gases are studied. The fundamental differential equations governing the growth and decay of these discontinuities are formulated and these equations are solved completely. The criteria for decay or “blow up” of these discontinuities are obtained. It turns out that the dissociating character of the gas allows the existence of a singular surface carrying a weak discontinuity into a non-uniform medium, this weak discontinuity may grow into a shock, and the role of mass-fraction variable is to contribute to possible damping in the formation of the shock.

On the Interaction of a Weak-R Type Ionization Front and a Contact Discontinuity

Abstract: A numerical solution is given to the problem of a weak R type ionization front approaching a contact discontinuity across which the density increases. During the interaction it is found that there are three possible configurations produced; the weak-R type ionization front becomes (a) weak-R type but slower for ρ1/ρ0 < 1.15, (b) strong-D type for 1.15 < ρ1/ρ0 < 3.4 or (c) weak-D type for ρ1/ρ0 > 3.4, where the original ionization front travels through a region of initial density go and across the contact discontinuity the density becomes ρ1. A fine spacial mesh length is chosen so that the structures of the resulting ionization fronts and shock waves may be identified clearly at any time.