Deformation and damage to buildings caused by ground movements in mining areas (case study)

Human activity causes transformations in the near-surface layers of the rock mass, which result in long-term impacts on buildings and engineering infrastructure. Mining activities are particularly disadvantageous in this context, as they trigger severe deformation processes that reach the soil surface as a result of the excavation of deposits. The prevention of accidents and disasters caused by these impacts is based on knowledge derived from observation. Therefore, the aim of this study was to acquire and update knowledge on the impact of mining-related ground deformation and tremors on buildings. The paper presents the results of measurements carried out on a group of buildings located in an underground mining area. The buildings have been affected by mining impacts since their construction in the 1980s. Despite the implementation of appropriate structural protection, the structures have been suffering deformation and damage. For the purposes of the study, two two-axis inclinometers were installed on the 15.2 m high bell tower, taking measurements at 6-hour intervals. Over a period of 10 months, changes in the leaning of the tower were measured and the condition of the other buildings observed.The study resulted in obtaining: values for the change in tilt of the two perpendicular walls of the tower (over a period of 10 months), correlation of the results with tremors measurements and periodic surveying measurements of the inclination of the vertical edge of the tower, image of damage to buildings caused by mining deformation of the ground. On the basis of an analysis of the location and timing of minefields excavation, the occurrence of real ground movement in the mining areas, continuing even after the end of mining works, was confirmed and irregular deformation of the originally perpendicular walls of the masonry tower building was demonstrated. The tower did not behave as a rigid body; its horizontal profile was deformed.

Seismic Upgrading of a Historical Masonry Bell Tower through an Internal Dissipative Steel Structure

Masonry towers are part of a valuable architectural heritage characterizing the landscape of many historical areas. These towers are vulnerable structures that are prone to earthquake damage. Hence, the design of effective seismic upgrading interventions is an important task for preserving such architectural forms for future generations. In view of that, the objective of this study is to contribute a possible addition to the portfolio of available approaches for seismic upgrading of masonry towers. This goal was pursued by exploring an innovative structural solution that does not alter the external appearance of the tower and its static scheme under gravity loads, yet is able to increase its capacity to withstand seismic actions through added damping. Specifically, the proposed solution consists of a steel structure internal to the masonry tower that incorporates fluid viscous dampers. In order to evaluate its potentialities, a real case study was taken as a testbed structure, historic analysis as well as geometric and architectural surveys were undertaken, an initial design for the upgrading was made, and numerical simulations were performed. The obtained results, although preliminary, highlight the potentialities of the proposed structural solution for the seismic upgrading of masonry towers and might open the way to future developments and applications.

Seismic Capacity Estimation of a Masonry Bell-Tower with Verticality Imperfection Detected by a Drone-Assisted Survey

Masonry towers are considered an important part of cultural heritage due to their architectural and historical value. From a structural perspective these kind of buildings are considered slender elements, the same as a cantilever beam. In real cases it is not easy to model with high accuracy these heritage constructions, since the geometry and mechanical properties of the constituent materials are not adequately known. On the other hand, a deep knowledge of the structural and seismic vulnerability of the masonry towers is needed in order to preserve and retrofit, when necessary, their architectural and cultural value. In the present research an exhaustive study is presented, as it regards the assessment of the seismic vulnerability of a heritage masonry bell-tower, built in the 14th century. An innovative protocol of structural survey followed, and it is proposed herein. The geometry of the tower was easily obtained by digital photogrammetry assisted by a drone. The geometrical model was easily converted into a digitalized input, that was introduced into a finite element method (FEM)-based code. The 3D model was used for linear static, linear dynamic and nonlinear static (pushover) structural analyses. The vulnerability of the masonry tower was assessed and at least one kinematic was found to be not verified.