Analysis of the Consequences of Mining Exploitation in Substantially Disturbed Strata Based on Spatial Measurements of a Building’s Tilt

Mining in a rock mass substantially disturbed by many years of exploitation may lead to serious consequences for the surface and buildings. This paper presents an analysis of the consequences of mining in such conditions. The analysis has been based on the measurements of the tilt of a church tower situated over the intersection point of the edges of two previously mined longwall panels. The exploitation of the next panel, in a seam below, resulted in the reactivation of the goaf. The results presented in this paper have been obtained through the use of a remote building deformation monitoring system. One of the elements of this system is a vibrating-wire (VW) tiltmeter which permits a spatial measurement of the tilt. The tests performed aimed to establish how a given building reacts to the impact of mining operations. The measurement system elaborated at the Strata Mechanics Research Institute of the Polish Academy of Sciences (SMRI PAS) is able to continuously (with a pre-set frequency) monitor the tilt. The results obtained permitted the observation of the building's behaviour during the time when the effects of mining exploitation were gradually revealed. The time of the first reaction of the building and the tilt direction justify a conclusion that the main reason for the results observed was the impact of the previously exploited longwall panels. The consequence of the fact that the panel edges were situated under the building was that it remained for a prolonged time in the area of positive strain of the ground and permanent sloping of the surface. When a lower lying seam was being mined and before the principal impact of these operations reached the church its tower tilted sharply in the direction opposite to the direction that should theoretically be expected to result from the impact of the moving mining face. Then, as the longwall panel advanced a gradual turn of the tilt plane was recorded. The measurement system described in this paper can be used in scientific research done in the context of building protection as well as an engineering tool to help evaluate the safety of buildings in mining areas. Thanks to gaining new knowledge about how buildings react to mining operations conducted in the circumstances of a substantially disturbed rock mass, appropriate methods can be elaborated to optimally design mining operations in order to protect the surface and the existing buildings.