Stability of Underground Excavation in Porous Limestone

cellar system of Budapest (Hungary). All lithologies have high
porosities ranging from 16 to 30%. The laboratory analyses focused
on the mechanical properties testing to assess the strength changes
due to water saturation. The density, ultrasonic sound wave
propagation, uniaxial compressive strength (UCS) and indirect
tensile strength (determined by Brazilian test) test were measured
on cylindrical specimens according to EN and ASTM standards in
the laboratory. Both dry and water-saturated samples were tested.
The results indicate that four lithotypes have distinct strength
parameters, and both the UCS and the indirect tensile strength
decrease with water saturation. The largest decrease in strength was
observed at fine-grained porous limestone and at fine- to mediumgrained limestone with a decrease in strength of over 50%. On the
contrary, the strength loss of coarse porous limestone is in the order
of 16 to 14% of UCS and indirect tensile strength, respectively.
Comparing the data set of this study with previous works on various
limestones, a good correlation was found between density and
Brazilian tensile strength. The presented data set was used as the
input parameters for calculating the stability of dry and water
inundated cellars. The FEM (Finite Element Methods) calculations
of cellar stability indicate that the displacement of water-saturated
cellars is nearly triple of the dry ones and that the factor of safety
reduced from 1.74 in air-dry condition to 1.07 in water-saturated
conditions.