Finite Element Modeling of Swelling Soil Pressures Using Joint/Interface Elements

There could be some discontinuities in a soil media such as layers, earth structures, cracks, and fissures so that estimation of stresses and deformations in these types of soil masses are somewhat different from continuous masses. The discontinuities in a soil mass could be considered as a special link between two blocks. Transmitted swelling pressures affected by the soil properties of the backfill especially at the interface between the backfill and retaining wall. In order to estimate the transmitted swelling pressure distribution behind a retaining wall, using with interface element, a new finite element model and a code (SWELPRES) have been developed. To evaluate the effect of backfill characteristics and interface element from the transmitted lateral swelling pressures, four cases of thickness of backfills with or without interface elements are investigated.     

Monitoring Large-Scale Tests for Nuclear Waste Disposal

Two large-scale “in situ” demonstration experiments and their instrumentation are described. The first test (FEBEX Experiment) involves the hydration of a compacted bentonite barrier under the combined effect of an inner source of heat and an outer water flow from the confining saturated granite rock. In the second case, the progressive de-saturation of Opalinus clay induced by maintained ventilation of an unlined tunnel is analyzed. The paper shows the performance of different sensors (capacitive cells, psychrometers, TDR’s) and a comparison of fill behaviour with modelling results. The long term performance of some instruments could also be evaluated specially in the case of FEBEX test. Capacitive sensors provide relative humidity data during long transient periods characterised by very large variations of suction within the bentonite.     

Cyclotron amplification of geomagnetic micropulsations Pc1 in the magnetosphere

A numerical analysis of cyclotron instabilities is carried out by computing the dispersion relation for a three component cold plasma-beam system. Rates of growth and damping for various values of the stream density are calculated from the dispersion relation. The rates of growth and damping increase monotonically as the number density of the proton stream increases. It is found that the frequencies at the rates of maximum growth and the damping decrease slightly to lower frequencies and a sharp peak at these frequencies becomes blunt. The minimum e-folding times of an ion cyclotron wave for (a) σ_s = 10⁻⁴, σ_i = 10⁻² and (b) σ_s = 10⁻¹, σ_i = 10⁻² are about 3·84 and 0·16 sec respectively in the vicinity of the equatorial plane at 6 Re, where σ_s and σ_i are the ratios of the beam density N_s and the helium ion (H₆⁺) density N_i to the total positive ions in the plasma-beam system.     

SOME EXPERIMENTS CONCERNING THE PRIMARY SEISMIC PULSE*

Recordings were made with three types of detector of the primary compressional (P) and shear (S) wave pulses generated by explosions in boreholes. Charge weights varied from 0.08 kg to 9.5 kg and detector distances varied from about 3 m to about 80 m. Scaling by the simple factor W^1/3 where W is the charge weight, enabled observations from different sized charges to be fitted to a single expression. Experiments were carried out in the Bunter sandstone and the London clay and both fluid and solid tamping were used. This variation in tamping had no significant effect on the P-waves but it may have affected the generation of SV-waves. In both media the P-wave energy carried at 30 m from the shot by frequencies less than 100 Hz decreased rapidly with depth and was usually 1–2 % of the available chemical energy for a shot depth of 15 m. The S-wave energy was much less than this, but was highly directional. The P-wave pulse had the appearance of a damped sinusoid in very good agreement with the predictions of the ‘equivalent radiator’ hypothesis. However, the surface of this radiator should be identified not with the blown cavity but with the surface at which the tensile stresses associated with the stress wave become less than the tensile strength of the rock. The predominant frequency for a 1 kg charge at a depth of 15 m was 24 Hz in the clay and 52 Hz in the sandstone. In these and similar media, therefore, an effort should be made to keep individual charges less than 1 kg in reflection shooting and less than 10 kg in refraction shooting. The value of Q was about 50 in clay and about 25 in the sandstone. These estimates are rather uncertain because of the small distances over which the pulses were observed. The Z-transforms of the sampled pulses indicated that they were all of minimum phase, or very near to it.     

THE ELECTRICAL CURRENT PATTERN INDUCED BY AN OSCILLATING MAGNETIC DIPOLE IN A SEMI INFINITE CONDUCTIVE THIN PLATE*

In a paper by Koefoed and Kegge (1968), which was based on previous work of Wesley (1958), the electrical current pattern has been derived that is induced by an oscillating magnetic dipole in a semi-infinite thin plate of infinitesimal resistivity. In the present paper, the range of validity of the assumptions, on which the work of Wesley is based, is subjected to a theoretical analysis. It is found that the decisive factor for the validity of Wesley's derivation is the quotient of the square of the penetration depth of the electrical current over the product of the thickness of the plate and a distance that is indicative of the size of the current loops in the plate. Wesley's derivation is shown to be valid only when this factor is negligible. It is also shown that in this condition the imaginary component of the anomaly must be negligible. Model experiments are described in which the electrical current pattern is studied also in the range in which the derivation of Wesley is not valid. The procedure used in these model experiments was to measure the tangential component of the magnetic field strength very close to the metal plate that simulated the conductive dyke. In order to express the results of the measurements in terms of the imaginary to real ratio, these results are compared with an interpretation graph for field measurements that was published by Hedström and Parasnis (1958). It is found that the current pattern in the plate is essentially the same as that which follows from Wesley's derivation, provided that the imaginary to real ratio is less than one third. The measurements do not permit to draw conclusions regarding the current pattern in the plate in conditions that correspond to larger values of the imaginary to real ratio.     

Pole-to-pole moisture conditions for the IGY

Summary A study of the mean atmospheric humidity conditions on a planetary scale during the IGY covering the calendar year 1958 is presented. The fields of mean precipitable water content and of the zonal and meridional transports of water vapor are analyzed for the entire globe. Zonally averaged values of the various quantities at several levels are presented in tabular form and compared whenever possible with previous results or indirectly are analyzed on the basis of information obtained from different sources. The structure of these fields is studied and the corresponding implications for the general circulations of the atmosphere are discussed. Finally the zonal water balance for all the globe is discussed and its implications analyzed.     

THE AIR PHOTOGRAPH REQUIREMENTS OF GEOLOGISTS

The geologist's use of air photographs and the characteristics studied by photogeologists are briefly described. The influence of photographic factors such as scale, season, time of day, film type, processing, overlap and dimensional accuracy are considered from the geologist's viewpoint.     

PHOTOGRAMMETRIC MEASUREMENTS OF GLACIAL LANDFORMS

Photogrammetric methods using sequential aerial photography can provide the geomorphologist with comparative measurements of rapidly changing glacial landforms. Examples are given of eskers, kame and kettle areas, an ice-dammed lake and coastal features in south-east Iceland.