Variations of the gravity field due to excavations of the Budapest Metro4 subway line

The effect of the construction of the 4th subway line of Budapest (Metro4) on the potential surfaces of the gravity field has been investigated from the aspects of monitoring vertical deformation. In the study mass loss due to the excavation of the two tunnels and of the stations has been considered. Practically, the effect of the mass loss on leveling measurements was determined at a level 1 m above the ground, roughly simulating common instrument heights. The indirect effect of the actual deformations of the physical surface on the leveling was not considered, so in the investigation a rigid Earth has been assumed. In the study, different arrangements of the leveling lines and of the excavations were examined, furthermore, the steepness of the leveling line and the density of the leveling points were analyzed. According to the results, under certain arrangements of the leveling line, the effect can reach the 0.05 mm order of magnitude, which is equivalent to the accuracy of the precise leveling.