A contribution to the measurement of frequency dependence of electrical conductivity of rocks

Summary Some errors of method occurring in A. C. measurements of the electrical conductivity of rocks are discussed. It is demonstrated that the difference between A.C. and D.C. conductivities, at given frequency, depends mostly on the magnitude of the D.C. conductivity and magnitude of the dielectric constant.     

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.     

The intensity of the earth's magnetic field in the past derived from the archaeomagnetic data

a n¶rt;u¶rt; amuu amua uuu anmuaum n a n¶rt;u 8500 m nm um au aam m uuu m naama. ¶rt;u u ¶rt;a ¶rt; u ¶rt; m¶rt; mumu auu nau nuu aau mama [1–3] (Puc. 1.B). nma aau auau (Puc.2) mnaua m m m¶rt;a, ¶rt; au n¶rt; amu u, m n¶rt;u 2- ma m, mmu naa auu nu¶rt; n¶rt;a 1000 m u 350 m, au a aumu, mmm 80%- mmu. am au ¶rt;a u anmu ¶rt; m¶rt; mumu (mum) naa auu u¶rt; ma u ¶rt; m naama[5] (Puc. 3). uma a mam nma aaua naaa auu nu¶rt; n¶rt;a 750 m, 200 m u a — 300 m. (Puc. 4.) nmu u ¶rt;a nma amua an¶rt;u n¶rt;u n u ma m (au) auumu m ¶rt;m m (Puc. 5). aa a m¶rt;m nu naamaum n aam ¶rt;uu mu au, anum¶rt;a m uua nm m¶rt;a.

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Dedicated to Academician Alois Zátopek on His 65th Birthday     

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).