Construction work above previous mining area is always a great challenge from the engineering point of view. In the southern part of Budapest, the previous mining activities resulted more than a hundred thousands of square meters of cavities. These cellars cut into porous limestone with different depth, but mostly close to the surface; nowadays, these cellars are located inside a residential area, and some part of the undermined area is planned to build because this is an empty and valuable area. For the construction of these improvements, it is necessary to perform detailed investigations and stability calculations. This paper is introducing the detailed investigation process of a significant cellar which will be involved by construction activities. Three buildings are planned to build above it. The studied cellar located in the 22nd district of Budapest, Hungary, with a depth between 4.3 – 7.7 m, with a wide range of pillars’ width between 0.73 – 7.7 m according to the studied cross-sections. The investigation starts with geometrical measurements and core drillings to map the rock mechanical properties of the host rock. Several laboratory tests were done for obtaining rock mechanical parameters for modelling. After creating the geotechnical model, it was used for FEM calculations using RS2 software. Four cross-sections were chosen across the cellar system in different locations and various directions modelling the surface load of the planned building. The stability of the cellar was studied from two different viewpoints: firstly, the factor of safety was determined, and secondly, the settlement was calculated as an effect of the surface load. A displacement measurement system was set up in several cross-sections of the cellar to compare the calculated and real displacements in the future.

There are historic subsurface dimension stones in the capital of Hungary (Budapest) that were excavated in porous limestone. The stability of these subsurface openings is important, since most of them are located in urban areas, where existing buildings or new structures are planned to be built. The paper presents a detailed study considering the geometry of the system and the mechanical parameters of the limestone. The geometry of the cellar system was obtained using terrestrial laser scanning (TLS). The cover beds are few meters in thickness, and the width of the pillar is between 2.50 and 3.98 m, according to the measurements. The rock mass parameters which were used in the calculations were obtained from laboratory tests. A finite element (FEM) software Rocscience (RS2) were applied to model the stability of the galleries. Calculations were made for various geometries taking into account the thickness of cover beds and the width of pillars. Altogether 70 models were made. A surface load of 150 kN/m2 was also applied to model the buildings. New relationships between cover bed thickness, pillar width and displacements are outlined to compare these results to previous works. The strength reduction factor was also calculated for all geometries, indicating the changes in the stability of these underground quarries and pointing out the importance of cellar geometries.

The stability of natural and man-made cavities is a very important topic nowadays especially if it is located under new construction areas. There are a lot of residential areas in Budapest and other cities of Europe such as Rome, Paris, and Cracow with stability problems because of cavities. For stability calculations, the geometry of the cavity, strength properties of the rock mass and joints are needed as input parameters, which can be obtained by field and laboratory tests. The FEM software is effective for stability calculations and with them; it is not so difficult to perform parametric analysis. This paper is focusing on the effect of the thickness of the cellar cover on their stability. The investigation site is in Budapest, Hungary, where there are several cellars cut into porous limestone. These cellars are more than 100 years old and nowadays cause difficulties for the building improvements. The geometrical parameters of the cellars and strength properties were measured. The cover of the studied cellar is around 6.0 m, but other cellars in the area have various cover thicknesses from 2.0 to 9.0 m. Therefore, the paper studied the effect of the cover on the stability to find the relation between the depth and the cellar stability. The modelling has been done by Rocscience software (RS2), using a real cross-section that crosses six branches of the cellar system.