Numerical model for rock bolts with consideration of rock joint movements

Summary The stability of any underground structure during and after excavation is the most important question for designers, because any kind of collapse may destroy large parts of a finished tunnel, causing major repairs and time loss. Preliminary calculations are therefore of great importance. A calculation is only useful, however, when the underlying numerical model correctly describes natural behaviour. The rock bolts used in tunnel excavations are mostly untensioned grouted bolts, and this type of bolt is the main focus of this work. From the model of the grouted bolt, other types of rock bolts can also be modelled by the theory presented herein. Bolt behaviour in intact rock mass is so different from behaviour when a bolt intersects a joint, that a model with two different elements is suggested for a numerical calculation; one element for the bolt in the rock mass and one as a bolt intersecting with a joint.The model for both elements is verified by the experimental results. The numerical results correspond favourably with the experimental work. A variation of the parameters important for the behaviour of the bolt in intersection with the joint is shown. As an implementation of the bolt model, the numerical simulation of excavation and stabilisation of one road tunnel is presented.     

On a new condition for directions of a spatial network

Zusammenfassung Es wird eine neue Bedingung, Gl. (6), angeführt, die von den bereits ausgeglichenen, z. B. durch den Stundenwinkel t und die Deklination δ definierten Richtungen der Seiten des Raumnetzes erfüllt werden muss. Zur Demonstration dieser Bedingung wird ein Modell des Raumnetzes in der Form eines Tetraeders benutzt (Abb. 1).

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Address: Karlovo nám. 13, Praha 2.     

Chemical composition and physical properties of lithium-iron micas from the Krušné hory Mts. (Erzgebirge)

Compositions of natural lithium-iron micas are approximated best by the sidero-phyllite-polylithionite join. These micas contain little or no magnesium and manganese. Their octahedral sheets contain close to two trivalent cations (mainly aluminum) in small crystallographic sites and a variable quantity of lithium and R⁺² (mainly iron) in large sites. Octahedral vacancies are situated mostly in large sites. Lithium and R⁺² approach a 44 replacement relationship in micas with octahedral occupancy close to six. Lithium and fluorine show a good positive correlation (small excess of fluorine over lithium), which indicates a crystallochemical association between them. There is a less distinct positive correlation between lithium and R⁺⁴.Based on simplifications, a calculation shows that about two-thirds of octahedral vacancies are caused by substitutions within the octahedral sheet, one-third, by tetrahedral substitutions. Different methods of calculating the crystallochemical formula yield slightly different numbers of octahedral vacancies, but do not affect the mica's position in plots of physical parameters against composition. If a crystallochemical formula is calculated from analysis of a mica contaminated with quartz, topaz, or feldspar, the apparent number of octahedral vacancies increases; such a formula exhibits unusual behavior in composition plots.     

Core waves recorded in central Europe

Summary The core waves recorded at four seismograph stations in Central Europe were investigated with the aim to find the most suitable set of travel-time curves and a fitting model of the core structure. Another travel-time curve was constructed by means of time differences between the core phases. The differences in the features of the travel-time curves were studied using records of shallow, intermediate and deep shocks from the same focal region (Tonga).     

Volles Gewicht einer im Refraktionsmilieu gemessenen Grösse (Teil I)

Summary As regards the concept of complete weight p with which an observed quantity (e.g., the direction of theA–G net) should enter the net adjustment, according to Eq.(1), apart from the fundamental weight p ₀ ), determined by the number of repetitions, it should also contain the time parameter p_t according to Eq.(11), where c>1 is a constant, and t is the number of days of observation, and also the refraction factor p_r according to Eqs(17, 18), where q is the structural weight of the direction. The condition for being able to determine p_r with the directions is observation by means of the three-directional vertex method[2], because it is not possible to localize lateral refraction by angular methods. The theory of complete weight is in favour of observations with a high fundamental weight p ₀ which automatically yield higher values of t, and also of p_t. The introduction of the complete weight into the experimental directional net in Fig. 2 caused the mean value of the uneliminated refraction error to decrease from 0.24 to 0.12, the mean square error of the adjusted direction being 0.17. The value of the constant c was investigated and the method of determining the parameter p_r was derived also for lengths measured electro-optically. Mention is made of the effect of complete weights on the length adjustment of a net in[6].     

Comment on some relations between the shape of streamlines and frontal interface in the proximity of a cyclonic vortex

Zusammenfassung Es wird ein einfaches Modell des zykolnalen Wirbels vorgeschlagen und die Beziehung zwischen seiner Intensität, der Form der Stromlinien und der Deformation der frontalen Grenzoberfläche in seiner Nähe diskutiert. Die Arbeit verfolgt das Ziel, die Kriterien der sogenannten dynamischen Klassifikation der aus den meteorologischen Satelliten photographierten Bewölkung zu finden.     

Die Steuerung des vertikalen Austauschkoeffizienten durch die Temperaturstruktur in der unteren Troposphäre

Zusammenfassung Zwei unabhängige Verfahren zur direkten Bestimmung des vertikalen Austauschkoeffizienten auf dem Wege über Aerosolmessungen werden über lange Zeiträume hinweg angewandt um gesicherte Beziehungen zwischen Austauschkoeffizient und meteorologischen Zustandsgrössen, vorallem des vertikalen Temperaturgrdienten, in der unteren Troposphäre zwischen 700 und 3000 m NN abzuleiten. Das eine Verfahren beruht auf der Messung der RaB-Konzentration in der Luft in 700, 1800 und 3000 m NN, das andere in der aerologischen Registrierung der totalen Luftleitfähigkeit zwischen 700 und 1800 m. Im ersten Falle können aus den mittleren Konzentrations gradienten die mittleren Austauschkoeffizienten direkt berechnet werden, im zweiten werden die Luftleitfähigkeitswerte zunächst in Partikelkonzentrationen umgerechnet. Diese gestatten die Be rechnung von differentiellen Austauschkoeffizienten über beliebig kleine Höhenintervalle. Die wichtigsten Ergebnisse sind: a) Der mittlere Austauschkoeffizient zwischen 700–800 und 1800–300 m lässt sich bei geringer statischer Streuung als Funktion des mittleren Temperaturgradienten in der jeweiligen Schicht angeben. Nebeneinflüsse: Luftkörperwechsel, Kondensationswärme, Windscherung. b) Der mittlere Austauschkoeffizient lässt sich als Funktion der Stabilitäenergie in der betrachteten Schicht darstellen, Nebeneinflüsse wie bei a). c) Der Austauschkoeffizient durch eine Inversionsschicht hindruch ist eine Funktion des grössten positiven Temperaturgradienten in der Inversion. d) Der vertikale Austausch durch eine beliebig dicke Schicht hindurch wird im wesentlichen durch den kleinsten differentiellen Austauschkoeffizienten innerhald dieser Schicht bestimmt. — Schliesslich werden Ergebnisse über Feinstrukturuntersuchungen im Bereich von Unstetigkeitsschichten mitgeteilt.

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Summary The vertical-mass-exchange coefficient was determined from aerosol measurements by two independent methods; the measurements were kept up for a considerable period of time. Thus, well-substantiated relationships between the exchange coefficient on the one hand and meteorological parameters — especially the lapse rate — on the other were found to exist in the lower troposphere between 700 and 1800 m.The first of the two methods is based on measurements of RaB concentration in air at 700, 1800 and 3000 m, the second on recordings of soundings of overall air conductivity between 700 and 1800 m a.s.l. In the first case, mean exchange coefficients were computed from RaB concentration gradients given as averages from RaB measurements at the above-specified levels; in the second, the air conductivity data were used to compute particle concentration profiles, from which incremental exchange coefficients can be computed for thin-layer increments. The latter may be made as thin as is consistent with the vertical resolution of the soundings. The major results obtained were the following: a) The mean exchange coefficient for the 700–1800 and the 1800–3000 m layer is found to be a function of the average temperature lapse rate in the respective layer; this relationship is subject only to some slight statistic alscatter, and is affected in some measure by air-mass changes, wind shear and heat of condensation. b) The mean exchange coefficient is a function of the stability energy of the layer concerned, subject to the influences listed in a). c) The exchange coefficient of an inversion layer is a function of the greatest inverse lapse rate existing in any part of the inversion. d) Vertical mass exchange in or through a layer of any thickness is primarily determined by the lowest incremental mass-exchange coefficient of any thinner layer contained therein. — The study is supplemented by results of fine-structure analyses of discontinuity layers and their surroundings.

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Die Beschaffung der Einrichtungen, die Durchführung und Auswertung der Messungen wurde durch Mittel der US Army, European Research Office (Verträge DA-91-591-EUC-3936, DAJA-37-67C-0254 und DAJA-37-68C-0331) und des Bundesministeriums der Verteidigung der Deutschen Bundesrepublik ermöglicht. Für die grosszügige Förderung der Arbeiten haben wir sehr zu danken.