mass falls in the Wachau-Danube Valley (Bohemian Massif
mass falls in the Wachau-Danube Valley (Bohemian Massif mass falls in the Wachau-Danube Valley (Bohemian Massif
Fig. 5 Geomorphological situation in the former quarry at Spitz. The square shows the ruin of a service block. Be that as it may, the railroad track alignment as well as the provincial road were again completely buried, with the debris cone even reaching the Danube River (Fig. 6b). Despite the blast, another rockfall happened close to the northern portal of the Dürnstein tunnel following a period of heavy rainfall in September 1909. Two people were killed and six severely injured by this event, which also buried workers’ barracks (regional newspaper article, Niederösterreichische Presse Nr. 28, 18-Sept-1909). Fig. 6 (a) Rock face at the former quarry near Dürnstein before and (b) after the blast of 1909. The height of the rock wall is about 130 m (view towards E, photo: Mayreder, May 1909). 6
There is not much information on further rock-mass fall events over the following decades. However, a comparison of photographs taken in 1909 and 100 years later, just before the rock-mass fall in 2009, clearly indicates that further rockfalls must have occurred in the time between. There is only one report of a rockfall, which took place in the winter of 2002/2003, after an unusually rainy autumn. The latest rock-mass fall occurred in July 2009, yet again preceded by a period of heavy rainfall. The rail infrastructure was destroyed by this event, and some smaller boulders even reached the main road B3 “Donauuferstraße” (Fig. 7). Fig. 7 Damage to rail infrastructure in 2009 (view towards NNW, photo: Laimer, July 2009). Methods Failure model analysis To determine the mode of failure, which caused the rock-mass falls/rock slides, a kinematic failure analysis was performed, based upon the principals of “block theory” (Goodman and Shi 1985). The application of this method is practicable for both sites (Spitz and Dürnstein), since the exceeding of rock mass strength can be excluded as a cause of failure, because of the fact, that in both cases, the uniaxial compressive strength of the rock mass is by far higher than the overburden stress (subchapter Lithology). Therefore, the rock mass can be seen as a system of rigid blocks separated by discontinuities. Large scale displacements within the rock mass can only occur if blocks are moved relative to each other along distinct shear planes, an effect known as “block failure” in geotechnical engineering (Hoek and Bray 1974). For the analysis, discontinuity orientation data acquired by detailed geotechnical mapping of the rock face were used and put in relation to the spatial orientation of the rock face, using stereographic projection. The main failure modes block sliding (sliding of a block on a single plane), wedge sliding (sliding of a block on two planes in a direction along the line of intersection) and toppling (rotational failure of thin columns caused by discontinuities striking +/- parallel and dipping steeply contrary to the rock face) were examined, using the computer program dips ® (ROCSCIENCE). Kinematically, a block can slide on a single plane, if the following preconditions are met: firstly, the strike of the potential sliding plane must be approximately parallel to the rock face (maximum deviation of about 30°). Secondly, the dip angle of the potential sliding plane must be lower than the dip of the rock face and, thirdly, 7
- Page 1 and 2: Geomorphological and geotechnical c
- Page 3 and 4: Fig. 3 Rock-mass fall near the town
- Page 5: Tectonically, the whole Bohemian Ma
- Page 9 and 10: Fig. 8 Monitoring devices in the fo
- Page 11 and 12: Fig. 9 (a) Orientation of bedding p
- Page 13 and 14: Fig. 11 (a) Orientation of joints a
- Page 15 and 16: strength of eight MPa, and a fricti
- Page 17 and 18: Discussion Interpretation of failur
- Page 19 and 20: Conclusions There are two causes of
Fig. 5 Geomorphological situation <strong>in</strong> <strong>the</strong> former quarry at Spitz. The square shows <strong>the</strong> ru<strong>in</strong> of a service block.<br />
Be that as it may, <strong>the</strong> railroad track alignment as well as <strong>the</strong> prov<strong>in</strong>cial road were aga<strong>in</strong> completely buried, with<br />
<strong>the</strong> debris cone even reach<strong>in</strong>g <strong>the</strong> <strong>Danube</strong> River (Fig. 6b). Despite <strong>the</strong> blast, ano<strong>the</strong>r rockfall happened close to<br />
<strong>the</strong> nor<strong>the</strong>rn portal of <strong>the</strong> Dürnste<strong>in</strong> tunnel follow<strong>in</strong>g a period of heavy ra<strong>in</strong>fall <strong>in</strong> September 1909. Two people<br />
were killed and six severely <strong>in</strong>jured by this event, which also buried workers’ barracks (regional newspaper<br />
article, Niederösterreichische Presse Nr. 28, 18-Sept-1909).<br />
Fig. 6 (a) Rock face at <strong>the</strong> former quarry near Dürnste<strong>in</strong> before and (b) after <strong>the</strong> blast of 1909. The height of <strong>the</strong><br />
rock wall is about 130 m (view towards E, photo: Mayreder, May 1909).<br />
6
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