In the area of Prague the bedrock is built up dominantly of Ordovician complexes showing different lithological character. Argillaceous shales alternate with arenaceous shales, greywackes and quartzites. This alternation of pelitic and psammitic rocks is interpreted in terms of the oscillation of the sea level during the Ordovician. The individual complexes differing in lithology repeat several times owing to the recurrence of analogous sedimentary conditions. The physico-mechanical properties of Ordovician rocks are controlled mainly by their lithological character and tectonic disturbance. In addition, the surface layers of the bedrock were disturbed by deep freezing during the Pleistocene, when the area under consideration was situated within the periglacial zone. The differing physicomechanical properties of the bedrock in the Prague area called forth the necessity of determining the deformational properties of rocks by in situ loading tests as early as in 1928. The results obtained by several tens of loading tests, which have been carried out on the Ordovician shales, make it possible to estimate the mechanical properties of rocks on the basis of their geological characteristics.
Le soubassement rocheux de la region de Prague est forme, pour la plupart, par des couches ordoviciennes d'un developpement lithologique different. Les schistes argileux et sableux, grauwackes et quartzites y sont deposes alternativement. Cette alternance de roches pelitiques et psammitiques s'explique par des fluctuations du niveau de la mer pendant l'Ordovicien. Les conditions de sedimentation se sont repetees à cette epoque plusieurs fois, si bien que plusieurs complexes d'un caractere lithologique different se sont formes. Les proprietes physico-mecaniques des roches ordoviciennes sont influencees surtout par le caractère lithologique et les accidents tectoniques. En outre, une alteration intense se manifestait à la surface du soubassement rocheux, alteration due à la gelification du sol pendant le Pleistocène, quand le territoire de Prague se trouvait dans la region periglaciaire. Cette alteration a aussi une influence considerable sur la deformabilite de la roche. A cause du caractère physico-mecanique different des roches dans Ie soubassement de Prague il etait necessaire d'en etudier les qualites de deformation par epreuve de charge dejà depuis 1928. Les resultats de plusieurs dizaines des epreuves de charge, executees depuis cette epoque jusqu'à present, permettent de prevoir les qualites de deformation à la base d'une appreciation geologique du type de roche respectif.
Der Felsuntergrund in Prager Raum besteht vorwiegend aus lithologisch bunt ausgebildeten Schichtenfolgen des Ordoviziums, die durch Wechsel von Ton- und Sandschiefer, Grauwacken und Quarziten gekennzeichnet sind. Dieser wird auf die Meeresschwankungen wahrend des Ordoviziums zurueckgefuehrt und kommt in der zyklischen Wiederholung von pelitischen und psamitischen Gesteinen zum Vorschein. Die physikalmechanische Eigenschaften dieser Gesteine sind hauptsachlich durch den lithologischen Charakter und die tektonische Störungen Beeinflusst. Daneben ist die Felsoberflache infolge der tiefen Frostwirkung im Pleistozan, als sich das Prager Gebiet in der periglazialen Zone befand, tief verwittert. Die Deformationseigenschaften gehen auch auf diese Verwitterung stark zurueck. Der verschiedene physikal-mechanische Charakter des Felsuntergrunds in Prag hat schon im Jahre 1928 die Notwendigkeit erfordert, die Deformationseigenschaften mit Hilfe von Belastungsversuchen in situ zu bestimmen. Aus den Ergebnissen von einigen Zehn Belastungsversuchen der ordovizischen Schiefer, die seit dieser Zeit durchgefuehrt worden sind, kann man auf deren Deformationseigenschaften aufgrund der geologischen Beurteilung des betreffenden Gesteinstypus schliessen.
The city of Prague is situated in a deep valley of the Vltava River, which is carved in the folded Early Paleozoic, prevalently Ordovician rocks. The ground is covered with superficial deposits, such as remnants of river terraces, slope debris, loess etc. of a small thickness. Therefore, all industrial plants and large buildings with deep basements reach down into the bedrock. The Ordovician shales provide a foundation soil of different properties which depend on their lithological composition, tectonic disturbance and weathering. These conditions called forth already in the 'thirties a need of fairly precise methods for the determination of the mechanical properties of rocks, their bearing capacity and compressibility in particular. Both these qualities were determined by in situ loading tests. These have been used up to the present for the establishment of elastic and deformational characteristics, so that the results of several tens of tests made at that time are now available for the preliminary evaluation of the rocks under consideration.
The Ordovician complexes of the Prague area consist of regularly alternating thick layers of clayey shales and arenaceous layers usually developed as quartzites. The alternation of pelitic and psammitic sediments suggests an oscillation of the sea bottom, i. e. an epeirogenic unrest at the time of their deposition. The recurrent sedimentary conditions are responsible for the recurrence of rocks analogous in lithological character and physico-technical properties throughout the Ordovician. From the biostratigraphical point of view, the rocks of the Prague area are ranged to the Middle Ordovician (Llanvirnian and Llandeilo) and the Upper Ordovician (Caradoc) and are further subdivided on paleontological evidence.
