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Stability analyses of underground structures cut into porous limestone
Contrôle de la stabilité des cavités souterraines réalisées dans le calcaire grossier
Görög P., Hangodi Á., Török Á.
Department of Construction Materials and Engineering Geology, BUTE, Hungary
ABSTRACT: Porous limestones are easy to cut and work with, therefore these stones were widely quarried and used as construction
materials worldwide. One typical occurrence is in Central Europe, Austria, Hungary, Slovakia and Czech Republic, where surface and
subsurface quarrying were very intense from the Roman period to the end of 19th century. In the present paper the porous limestone
occurrences in Hungary and especially in Budapest and its region were studied. The limestones there were exploited from
underground quarries. These subsurface tunnels and galleries are now found beneath the city. The underground openings cause
several problems, due to the collapse or deformation of the walls and pillars. The present paper gives an overview of the various cellar
types and the most important parameters that are used for stability modelling of these structures. As input parameters dry and water
saturated physical properties, rock mass parameters such as joint system and the geometries of the structures were used. The
underground spaces were modelled by using different FEM softwares. The limestone is very porous with open pore spaces of 24 to
36%. It is very sensitive to water, since water saturation decreases its strength by nearly 30-40%. It is considered as a soft rock/hard
soil. In the models different soil covers and building loads were compared, as well as dry and water saturated conditions were
assessed. These obtained results can be generalized and used in the design of buildings and other engineering structures that are cut
into or built over various types of porous limestones occurring in other countries, too.
RÉSUMÉ : Grâce à l’exploitation simple et la mise en œuvre facile du calcaire grossier, cette roche est largement utilisée et préférée
comme matériau de construction. En partant des temps de l’empire romain jusqu’au XIX
e
siècle, le calcaire a gagné du terrain en
Europe centrale. Il a été exploite surtout en Autriche, Hongrie, Slovaquie et en Rép. Tschéque sous forme d’exploitation en surface et
en souterrain. L’objet de l’étude est de donner un aperçu général sur la présence et l’étendue du calcaire grossier en Hongrie et, tout
spécialement, aux environs de Budapest. Dans ces régions on a favorisé l’exploitation souterraine, les tunnels et cavités qui en
témoignent, se trouvent déjà, dans nos jours, sous la capitale. Les éboulements des cavités et des tunnels sont à l’origine des
nombreux problèmes et difficultés. L’article a essayé de récapituler les divers types de cave et les plus importants paramètres
nécessaires aux calculs de stabilité des parois, piliers, et des voûtes. Une attention particulière a été portée sur les problèmes liés aux
caractéristiques physiques en état sec et saturé de la roche, on a également étudié les paramètres de la structure et de la fracturation
générale du massif, tout en tenant compte de la géométrie des caves. En ce qui concerna la modélisation des cavités souterraines, on
s’est servi des softwars d’éléments finis. Le calcaire grossier est un matériau poreux. Sa porosité apparente varie de 24 %à 36 %, sa
résistance à la rupture en état saturation peut diminuer de 30 % à 40 %. Vu ces pertes de résistance, le calcaire peut être caractérisé
soit comme roche faible, soit comme sol dur. Les échantillons soumis aux essais étaient prélevés des profondeurs différentes, faisant
varier l’état sec et saturé. Les résultats obtenus permettent de les généraliser et peuvent être utilisés à l’étude des immeubles fondés
sur ce calcaire et à celle des autres structures souterraines.
KEYWORDS: limestone, porosity, cellars, FEM analysis
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Stability analyses of underground structures cut into porous limestone
Contrôle de la stabilité des cavités souterraines réalisées dans le calcaire grossier
P. Görög & Á. Hangodi & Á. Török
Department of Construction Materials and Engineering Geology, BUTE, Hungary
ABSTRACT: Porous limestones are easy to cut and work with, therefore these stones were widely quarried and used as construction
materials worldwide. One typical occurrence is in Central Europe, Austria, Hungary, Slovakia and Czech Republic, where surface and
subsurface quarrying were very intense from the Roman period to the end of 19th century. In the present paper the porous limestone
occurrences in Hungary and especially in Budapest and its region were studied. The limestones there were exploited from
underground quarries. These subsurface tunnels and galleries are now found beneath the city. The underground openings cause
several problems, due to the collapse or deformation of the walls and pillars. The present paper gives an overview of the various cellar
types and the most important parameters that are used for stability modelling of these structures. As input parameters dry and water
saturated physical properties, rock mass parameters such as joint system and the geometries of the structures were used. The
underground spaces were modelled by using different FEM softwares. The limestone is very porous with open pore spaces of 24 to
36%. It is very sensitive to water, since water saturation decreases its strength by nearly 30-40%. It is considered as a soft rock/hard
soil. In the models different soil covers and building loads were compared, as well as dry and water saturated conditions were
assessed. These obtained results can be generalized and used in the design of buildings and other engineering structures that are cut
into or built over various types of porous limestones occurring in other countries, too.
RÉSUMÉ : Grâce à l’exploitation simple et la mise en oeuvre facile du calcaire grossier, cette roche est largement utilisée et préférée
comme matériau de construction. En partant des temps de l’empire romain jusqu’au XIX. è siècle, le calcaire a gagné du terrain en
Europe-centrale. Il a été exploite surtout en Autriche, Hongrie, Slovaquie et en Rép. Tschéque sous forme d’exploitation en surface et
en souterrainine. L’objet de l’éltude est de donner un apercu général sur la présence et l’étendure du calcaire grossier en Hongrie et,
tout spécialement, aux environs de Budapest. Dans ces régions on a favorisé l’exploitation souterraine, les tunnels et cavités qui en
témoignent, se trouvent déjà, dans nos jours, sous la capitale. Les éboulements des cavités et des tunnels sont à l’origine des
nombreux problèmes et difficultés. L’article a essapé de récapitular les divers types de cave et les plus impoztants paramètres
nécéssaires aux calculs de stabilité des parois, piliers, et des voûtes. Une attention particulière a été portée sur les problèmes liés aux
caractéristiques physiques en état see et saturé de la roche, on a également étudié les paramètres de la structure et de la fracturation
générale du massif, tout en tenant compte de la géométrie des caves. En ce qui concerna la modellisation des cavitès souterraines, on
s’est servi des softwars d’éléments finis. Le calcaire grossier est un matériau poreux. Sa porosité apparente varie de 24%à 36%, sa
résistancte à la rupture en état saturation peut diminuer de 30% à 40%. Vue ces pertes de résistance, le calcaire peut etra caractérisè
soit comme roche faible, soti comme sol dur. Les échantillons soumis aux essais étaient prélevés des profondeurs différentes, faisant
varier l’état sec et saturé. Les résultats obtenus permettent de les généraliser et pauvent être utilisés à l’étude des immeubles fondés
sur ce calcaire et à celle des autres struc ures souterraines.
KEYWORDS: limestone, porosity, cellars, FEM analysis
1 INTRODUCTION
Stability of subsurface openings such as galleries or tunnels cut
into limestones are often endangered by the collapse of roofs
and side walls similarly to natural sinkholes (Waltham and
Fookes 2003, Xeidakis et al. 2004, Török et al. 2006, Farrant
and Cooper 2008).
Parise and Lollino (2011) demonstrated that for studying the
stability of man-made caverns cut into porous limestone both
field observations and numerical simulations can be used. In the
present paper rock mechanical data obtained from field
sampling and laboratory testing is used as input parameter for
the modeling of underground structures. Geometry of cellars
were also documented during the field survey and used for the
modeling. For the numerical simulations 4 different FEM
software ere used to evaluate the advantages and limitations of
the usage of computer codes in stability analyses of limestone
openings.
2 GEOLOGY
Cellars were cut into porous limestone of Miocene age. The
origin of the subsurface cellar system is related to quarrying,
since the stone has been used as a dimension and ornamental
stone for centuries in Budapest region. The porous limestone is
yellowish-white colour when it is freshly quarried. The quarries
still exist but most of them were operated during the second half
of the 19th century when construction activity was intense and
rapid development of the city was marked by construction of
public buildings.
Three main limestone types have been identified (Török
2002) and widely used in the buildings and monuments of
Budapest. The three lithologies are i) fine-grained limestone; ii)
medium-grained oolitic limestone and iii) bioclastic macro-
porous limestone. No significant difference of mineralogical
composition was found in the quarry samples, since the main
mineral is calcite (92-97%) in all lithotypes (Török 2003).
Minor amount of quartz and sand-sized lithic clasts are also
present according to XRD analyses. The biggest amount of non-
