Krejčí O., Krejčí V. & Kašperáková D., 2020: Engineering geological limits of the urban development of the Brno city. Acta Geologica Slovaca, 12, 2, 107–119.

Engineering geological limits of the urban development of the Brno city

Oldřich Krejčí, Vladimíra Krejčí & Dagmar Kašperáková

Czech Geological Survey, Leitnerova 22, 658 69, Brno, Czech Republic; oldrich.krejci@geology.cz

Abstract

The area of the city of Brno was limited by natural conditions and from the 12th century also by human activity. The main geological structure here is north part of the Nesvačilka Graben in the surface area filled with Neogene clays of the Late Burdigalian and Langhian age. Neogene clays are fine-grained soils whose internal structure fundamentally affects their mechanical properties. These clays are significantly anisotropic, frost sensitive and susceptible to volume changes (shrinkage, swelling). In the surface parts they weather, crush and are prone to sliding. They are risky from the aspect of slope stability problems and when being exposed in construction pits. The surface of the Neogene clays on the raised blocks is located close to the surface and is mainly covered by anthropogenic fillings. Above the tectonically downslipped blocks, the surface of Neogene clays is usually below 10–15 m Quaternary sediments. At the areas of the elevated blocks and along the west edge of the Nesvačilka Graben, the clays crop out directly onto the surface or are covered by a thin layer of aeolian sediments. Human activity was proved mainly by the creation of numerous open pits for building materials, which were subsequently built up by continuous development. Many old built-up quarries are endangered until today by rockfalls. In the historical part of the city, the stability conditions were aggravated by a number of historical cellar systems and deposits up to 10 meters thick, which consist of the anthropogenic dump. The susceptibility to slope instabilities was modelled by a multivariate statistical method on the map sheet 1:25 000 Brno-sever 24-324, with an area of 115.45 km². The method combines input parameters (geology, land use, altitude, slope angle, aspect, relief curvature, presence of tectonic lines) and compares them with the occurrence of slope instabilities in the particular area. In addition, a layer of Neogene clays was used here, since this geological unit plays an important role in the Brno agglomeration.

Key words: Neogene clays, slope instabilities, multivariate statistical method, Czech Republic, Brno agglomeration

Manuscript received: 2020-05-27

Revised version accepted: 2020-11-13