Analysis of Mining Damage Noti fi cations in Single-Family Buildings after the Occurrence of Intensive Mining Tremors * * 1

Mining damage is caused by changes in ground surface topography due to the movement of the rock mass elements towards the working, by mining tremors, possibly by a change in hydrological conditions in the substrate (e.g. [5]). The damage may occur in building structures in the form of failures, accelerated technical wear and additional nuisance of use (e.g. [4, 13]). In accordance with the applicable provisions of the Polish law [11, 12], the entrepreneur running the mining plant is held responsible for the damage caused by the activities of the mine, as well as has an obligation to remove the damage caused. In practice, however, to assess the extent of the damage and to estimate the value of the loss turns out to be problematic. Valuation of mining damage in a building should be preceded by an analysis of the potential causes of damage and failures. Damage or accelerated wear may in fact be caused by other factors, unrelated to mining [13]. The purpose of such an analysis should therefore be isolating these failures which, in whole or in part, are the result of mining activities and for the removal of which the Mining Plant is held responsible. The main elements of mining impacts on space development in the Legnica-Głogów Copper District are mining tremors. They occur due to a sudden movement, bursts or cracking of the rock mass layers. The associated release of energy is a threat both to workings in the underground part of the mine, as well as to objects located on the surface, e.g. [2, 7–10]. Occurrence of mining tremors in the area of the Legnica-Głogów Copper District is stimulated by both natural factors as well as technical and operational ones. Deposits of limestone, sandstone and anhydrite, lying over copper ore deposits, have the ability to accumulate elastic energy, releasing it during the burst of the rock mass. A circumstance which is favourable for energy accumulation is also considerable operating at a depth, of 600 to over 1000 meters [10].


Introduction
Mining damage is caused by changes in ground surface topography due to the movement of the rock mass elements towards the working, by mining tremors, possibly by a change in hydrological conditions in the substrate (e.g.[5]).The damage may occur in building structures in the form of failures, accelerated technical wear and additional nuisance of use (e.g.[4,13]).In accordance with the applicable provisions of the Polish law [11,12], the entrepreneur running the mining plant is held responsible for the damage caused by the activities of the mine, as well as has an obligation to remove the damage caused.In practice, however, to assess the extent of the damage and to estimate the value of the loss turns out to be problematic.Valuation of mining damage in a building should be preceded by an analysis of the potential causes of damage and failures.Damage or accelerated wear may in fact be caused by other factors, unrelated to mining [13].The purpose of such an analysis should therefore be isolating these failures which, in whole or in part, are the result of mining activities and for the removal of which the Mining Plant is held responsible.
The main elements of mining impacts on space development in the Legnica--Głogów Copper District are mining tremors.They occur due to a sudden movement, bursts or cracking of the rock mass layers.The associated release of energy is a threat both to workings in the underground part of the mine, as well as to objects located on the surface, e.g.[2,[7][8][9][10].Occurrence of mining tremors in the area of the Legnica-Głogów Copper District is stimulated by both natural factors as well as technical and operational ones.Deposits of limestone, sandstone and anhydrite, lying over copper ore deposits, have the ability to accumulate elastic energy, releasing it during the burst of the rock mass.A circumstance which is favourable for energy accumulation is also considerable operating at a depth, of 600 to over 1000 meters [10].
High-energy tremors, with energies E ≥ 10 8 J, are considered to be of signifi cant importance in the issues of protection of building structures in mining areas [6].
The article presents an analysis of notifi cations to recognize mining damage in single-family housing estates in Polkowice after the occurrence of three strongest tremors in that area.This applies to: -the tremor of 20 February 2002 with the energy of 1.5 • 10 9 J, -the tremor of 16 May 2004 with the energy of 8 4 • 10 8 J, -the tremor of 21 May 2006 with the energy of 1.9 • 10 9 J.
A group of 256 single-family residential buildings were studied, representing the three housing estates in Polkowice, located in the mining area.The construction data of individual buildings were collected during a detailed architectural and constructional inventory, complemented by the analysis of the available design documentation as well as interviews with the owners and users of the real properties.A violent stress relief in the rock layers in the epicenter of the tremor at the hypocentral depth H generates elastic seismic waves that propagate to the surface layer, generating longitudinal and transverse surface waves, propagating over long distances and aff ecting the housing development in the area (Fig. 1).
They are an additional dynamic load for building structures.The horizontal component of the vibration has a particularly signifi cant impact on the threat to a housing development [3,6,10].
The informations about the damage in the buildings reported by the residents, which occurred after each of the analyzed tremors, were obtained at the Mining Plant.The analysis took into account the structural and material characteristics of the buildings, as well as subdivision into damage to structural elements and to secondary elements.
The location of the epicenters of the analyzed tremors in relation to the development of the studied housing estates has been presented in Figure 2.

Specifi cations of the Studied Buildings
The subject of the analysis were single-family residential buildings located on three housing estates in Polkowice, erected after 1980 (Tab. 1).
Considering the scope of the research, the study was limited to the buildings erected before the fi rst of tremors that is before 2002.These buildings are either detached (30.1%), semi-detached (29.7%) or terraced (40.2%).The shapes of the plans and of the buildings took a variety of forms (Tab.2), but the majority of the buildings had a simple or slightly fragmented plan (70.3%) and a compact form (55.5%).All the analyzed buildings were situated at a constant level on concrete foundations.Basement and foundation walls were monolithic concrete (51.6%) or made with concrete blocks (48.4%).
Most commonly, envelopes were diaphragm walls with thermal insulation inside, and a masonry layer of the façade made of ceramic bricks from the outside.The load-bearing walls of higher fl oors were built of cellular concrete (57.0%) or slag concrete blocks (43.0%).Stairs and lintels were generally made of monolithic reinforced concrete.
All the analyzed building structures had basements, under the whole or part of the structure, but always a constant level of foundation was retained.
The studied sample exhibited considerable variation in both basement ceilings and upper fl oors (Tab.3).In the case of the buildings erected in the 80s of the twentieth century, the dominant group consists of prefabricated reinforced concrete fl oors, mainly of hollow core slabs, and ribbed slabs, mostly of DZ-type, prefabricated in whole (75.1% and 74.6%, respectively).Later, more popular were monolithic reinforced concrete fl oor slabs and ribbed, partially prefabricated slabs, most commonly of Teriva or Fert types (78.7% and 82.7%, respectively).A characteristic feature of the analyzed objects was diversifi ed levels of ceiling supports within each fl oor (tie beams shifted by about 1 m -62.9% of the considered buildings).The building systems of the 1980s most frequently used bipartite ventilated fl at roofs with roofi ng of prefabricated hollow core roof plates based on openwork walls and covered with roofi ng paper.The buildings erected in the 90s of the twentieth century, and later, mostly had steep roofs with wooden rafter framing and were covered with steel sheet or ceramic tiles.
In the study group, the vast majority, i.e. 202 buildings (78.9%), had no protection against mining tremors.The other 54 objects were issued with a decision or planning permission by the District Mining Offi ce, taking into account mining impacts on the planned investment.They specifi ed, inter alia, the predicted maximum horizontal acceleration or velocity of the vibration on the surface, but only one building had a documented protection against tremors in the form of concrete studs.

Structure of Mining Damage Notifi cations
Damage reported by the residents was divided into two groups: regarding the structural and non-structural elements (in individual cases, the notifi cations also concerned furnishings that were omitt ed in the analysis).The set of structural components included foundations, load-bearing walls (foundation, basement, overground), lintels, walls (under the windows, fi rewalls), ceilings, roofs, roof structures, balconies and loggias.The secondary, non-structural elements included partition walls, internal plasters, façade layers, wall cladding, fl oors, damp proof insulation, roofi ng, fl ashings, gutt ers and downspouts, entrances to the buildings, windows, doors and installations.
The structure of the mining damage notifi cations after the above-mentioned tremors have been presented in Table 4, and their classifi cation by the Mining Plant has been depicted in Table 5.The presented data depicts that most notifi cations (73 cases) were submitt ed after the fi rst high-energy tremor on 20 February 2002.As a result of the on-site inspections carried out by the staff of the Department of Mining Damage of the Mining Plant "Rudna" in the reported buildings, the majority of notifi cations (64 cases, or 87.7%) were recognized as valid.Therefor, the mine paid the owners one-off damages for the resulting losses or ordered reparation of the recognized damage by restoring the buildings to their original condition.The subject of the notifi cations submitt ed by the owners were mostly cracks and scratches occurring both on structural elements (load-bearing walls, ceilings) as well as on secondary elements (partition walls, wall and fl oor cladding, entrance to buildings).
As a result of the tremor on 16 May 2004, the Mining Plant had a much smaller number of reported damage to these buildings (13 notifi cations).This was probably due to the eff ectiveness of the repair and safety works carried out after the previously analyzed tremor.This thesis can be substantiated by the fact that the owners of 57 buildings (which is more than 89.0%), who in February 2002 reported the mining damage, which was then confi rmed, did not submit the notifi cation again in 2004.As a result of the on-site inspections conducted in the reported buildings, about half of the notifi cations (53.8%) were accepted.
The strongest tremor in Polkowice in the analyzed period occurred on 21 May 2006, with the energy of 1.9 • 10 9 J.As a result, the number of applications for compensation for mining damage increased again (55 cases).As in previous years, the majority of them (70.9%) were found to be justifi ed, which resulted in a one-off payment of damages or repair of the resulting damage.
Due to the limited number of notifi cations after the tremor of 16 May 2004, further research examined the eff ects of the two high-energy tremors, of 20 February 2002 and of 21 May 2006.

Structure of Mining Damage Notifi cations and Technical Features of the Buildings
The studied buildings are either detached, semi-detached, or terraced.Shapes of the plans and building forms vary (c.f.Tab. 2), but predominantly these are objects characterized by a simple or slightly fragmented plan and compact form.Therefore, the structure of the damage notifi cations after the tremors was examined, depending on the type of a development, the shape of the plan and the shape of the building form.Pearson's chi-square test of independence was used, based on a comparison of the observed values with the hypothetical ones for categorical (qualitative) variables.The level of signifi cance was adopted at p = 0.05.The obtained results have been presented in Table 6.The above data proves that there are signifi cant, in statistical terms, relationships between the structure of the damage reported by the owners, and both of the studied development features.
Table 7 illustrates the reported damage in percentage, and their qualifi cation by the Mining Plant, depending on the category of the studied feature in a given group of buildings.These data show that the percentage of submitt ed applications for payment of damages was nearly twice as high for terraced houses than for detached and semi-detached ones.This trend is common both for the reported damage to structural elements and to secondary elements.
While analyzing the development of the housing estates with respect to the shape of the plan and building form, it can be noticed that the overwhelming number of submitt ed notifi cations regarded greatly fragmented buildings with elongated shapes.The percentage of reported notifi cations (both regarding the damage to structural and secondary elements) was more than three times higher than for the buildings with a simple or slightly fragmented plan and compact shape.
Among all the analyzed cases, about 75-80% of notifi cations were considered justifi ed by the Mining Plant, confi rming the occurrence of damage caused by mining activities.

Structure of Mining Damage Notifi cations and Design Features of the Buildings
The structure of the damage reported after the tremors was also examined, depending on the structural and material solutions used in the buildings.Damage to both secondary and structural elements was identifi ed.
Again, Pearson's chi-square test of independence was used, with the level of signifi cance adopted at p = 0.05.The obtained results have been presented in Table 8.A statistically signifi cant relationship was observed between the adopted structural and material solutions of the load-bearing walls of higher fl oors and the occurrence of varied levels of ceilings, and notifi cations of damage to both load-bearing elements and non-structural elements.In other cases, there was no signifi cant correlation between the variables observed.
Table 9 illustrates the reported damage in percentage, and its qualifi cation by the Mining Plant, depending on the cases, signifi cant in the statistical sense.
These data show that the percentage of damage to the structural and secondary elements in the buildings with walls made of cellular concrete is about 50% higher compared to the buildings with the walls made of slag concrete blocks.While analyzing the eff ect of varying height of ceiling supports, it is apparent that about 50% greater number of notifi cations (both referring to structural and non-structural elements) were submitt ed in the case of varied levels of the ceilings.As it was in the case of the development features analyzed in Chapter 4, about 75-80% of the notifi cations were considered justifi ed by the Mining Plant.

Summary
The article analyzes the notifi cations of mining damage to buildings in single-family housing estates in Polkowice.The damage occurred after three high-energy mining tremors on 20 February 2002, 16 May 2004, and 21 May 2006.The study group was comprised of 256 houses built in the traditional brick technology between 1980 and 2002.The paper att empted to fi nd a relationship between the structure of mining damage reported after the tremors and the development and design features of the buildings.
The obtained results proved the existence of statistically signifi cant relationships between damage to both structural and secondary elements, as well as the type of development and geometry of the buildings (Chapter 4).

Fig. 2 .
Fig. 2. Location of the epicenters of the analyzed high-energy mining tremors and of the development of the studied housing estates

Table 1 .
Location of the test stand (256 buildings)

Table 2 .
Development type and shape of the plan and building form of the studied building structures

Table 3 .
Structure of the ceilings of basements and higher fl oors in the analyzed buildings

Table 4 .
Structure of mining damage notifi cations in the analyzed buildings after high-intensity tremors

Table 5 .
Structure of qualifying mining damage notifi cations by the Mining Plant

Table 6 .
Levels of statistical signifi cance of Pearson's chi-square test obtained during the study of a relationship between development features and the structure of notifi cations after the tremors in 2002 and 2006

Table 7 .
Percentage of damage in a given group of reported buildings and its qualifi cation by the Mining Plant, depending on the development features

Table 8 .
Levels of statistical signifi cance of Pearson's chi-square test obtained during the study of a relationship between design features of the buildings and the structure of the notifi cations after the tremors in 2002 and 2006

Table 9 .
Percentage of damage in a given group of reported buildings and its qualifi cation by the Mining Plant, depending on the structure of the building elements