Problemy budowlane na terenie miasta Bochni

Abstract

The town of Bochnia has been extended on the border of two physico-geographical units, i.e. the Carpathians and Sandomierz Valley. Between both units there is a distinct intermediate band which is called Bochnia Tectonic Foreland. It is constituted from plastic Miocene loams covered by Pleistocene deposits consisting from muds, clays, sands and loess. The Bochnia Foreland includes the flattened hummocks dismembered by Holocene valleys, the valley slopes being modelled by numerous landslides. The oldest relief components are hillplains which are arranged in two sharp levels. The higher level is 110 to 140 m above the Raba valley bottom and it is cixtting the Flysch deposits. It has been formed in lower Piocene period. The lower level is 60 to 80 m high and its surface cuts Miocene deposits. It has been formed in higher Pliocene period. This level drops into the Sandomierz Valley bottom forming a distinct step. The site within Sandomierz Valley is almost even and is constituted from the Raba silts. The Carpathian foreland within the town has a varied relief. The slope inclinations range from 5 to 20 per cent. The paper presents some complex building problems against the selected elements of the geographical environment. The location documents are not sufficient to work out a detailed Bochnia site-planning, whilst a poor knowlege of geological and engineering conditions leads to unproper location of the new objects which are thus often liable to a partial or complete destroyment. The drilling cross-sections and profiles favour the statement that Miocene deposits are shaped as loams. They appear on a level 1 to 22 m. They are degraded in the floor and are of quick-ground nature. They are covered by dusts, by dusty clays which are locally sanded up and by loess clays. Ground waters appear in these formations on various depth, from 1 to 22 m. In general, there is no water in loess clays, whilst it is accumulated in loams and in the beds of poor permeability. In valley depressions, the Miocene loams are deposited nearer to the surface and are covered by sands, by dusty clays and by loamy dusts with organic additives while in the bottoms of larger valleys clays, silts, sands and gravels are prevailing. The ground water appears in this formation from 0.3—0.5—1.5—2.0—3.0 m and locally on a depth from 4.0—6.0 m. In the geological and engineering documentation for each building object allowable ground loadings as well as foundation conditions are indicated. However, there is no mention about the quick-ground appearing in the subgrade; only the deeper drillings started due to the wall cracks of the erected objects prooved that the quick grounds were on various levels and having various spacial ranges. After the school at Oracka street had been erected, the quick-ground has been displaced from the slope into the valley bottom which caused uneven setting of the building. A part of the building has been placed on a slope where the ground stress was 1.8 kg/cm2, whilst the other part in the valley bottom where a stress to 0.5 kg/cm2 only is allowed. When working out an engineering physiography or geology, attention to the building condition, to the quick-ground appearing in the subgrade, to the slope stability, to the landslides and to gypsum and salt inclusions is to be paid. The building foundations within Bochnia sites are to be supported by a ground course of a bearing rock below the quick-ground, and the longer buildings on the slopes should be dilatated. The revetments on the slopes must be anchored deeper in order to resist the pressure of the higher situated grounds. The building sites and the excavations on the slopes must be protected against flooding, since a negligence in this domain may give rise to landslides or stimulate them. Concentrated drillings of the subgrade will be utilized when designing the intense- traffic arteries. Additional investment costs increase within the mining areas while the townplanning and realization projects should be agreed with District Mining Office in Cracow.