New method of assessment of damages threat to building objects in the mining terrain

GOSPODARKA SUROWCAMI MINERALNYMI Tom 24 2008 Zeszyt 3/1 JANUSZ OSTROWSKI* New method of assessment of damages threat to building objects in the mining terrain Introduction The important issue touching in mining terrains is the protection of building structures from the mining-induced surface deformations Methods for assessing the threat to buildings caused by continuous deformation demand a knowledge of the predicted values of the horizontal strain of the surface of the terrain, as well as the limiting values of the horizontal strain, which determine the resistance of the building The degree of the threat to a building structure will be clarified by a comparison of both characteristics The validity this of assessment, and further action based on it, depend on the reliability of data on both characteristics Underestimation of the threat brings us too close to the safety limit for the building, or will lead to increased repair costs An overestimation of the threat can unnecessarily increase the mining costs and (or) preventive building measures, albeit guaranteeing a high level of safety In practice, a faultless assessment of the threat to a building caused by continuous deformation of its foundations, is not possible because of the huge degree of complexity of the impact as well as the contribution of random factors to the deformation process Mathematical models describing these impacts are always a mere approximation to reality and describe average states The influence of random factors is usually defined by standard deviation from the modelled characteristics of the phenomenon Assessing the threat of damage to buildings resulting from deformation their foundations, which is related to mining can be done in the following ways: * AGH University of Science and Technology, Kraków, Poland

152 1) a comparison of the categories of building resistance to continuous deformation with the categories of mining area in which the buildings are situated, 2) it can be based on the expert opinions of mining and construction specialists The application of each of these methods demands a determination of the predicted surface deformation indexes around the buildings as well as the nature of their resistance to continuous deformation Currently, a prognosis of surface deformation is in line with Knothe s theory [2] The assessment of the resistance of a building to continuous deformations of its foundations, ie the category of building resistance, is made based on a score method [3] Ad 1 Basic criterion of categories of mining terrain as well as categories of the buildings resistance to continuous deformations of theirs foundations is horizontal strain The values of horizontal strains, marking limits of separate categories are equal in both classifications (Table 1) Table of categories of mining terrain and categories of building resistance Tabela kategorii terenów górniczych i kategorii odpornoœci budowli TABLE 1 TABELA 1 Category of mining terrain (KTG) Maximum horizontal strain ( KTG) max () 0 0 max [mm/m] Category of building resistance (KO) Limiting horizontal strain ( KTG) lim [mm/m] () 0 =03 0 l =03 I II III IV ( I ) max ( II ) max () 1 =15 1 l =15 () 2 =30 2 l =30 ( III ) () 3 max =60 3 l =60 ( IV ) () 4 max =90 4 l =90 V ( V ) >90 Applying of method of comparison of categories of mining terrain with categories of buildings resistance can lead to considerable mistakes in assessment of threat of buildings, from analyzed reasons in publication [4] Ad 2 The basis of expert opinions are results of prognoses of terrain deformations (in range of horizontal strains) as well as values of limiting horizontal strains from category of buildings resistance The assessment of the threat to buildings of mining-induced surface deformation is based on the results of a comparison the predicted (according to Knothe s theory) value of

153 horizontal strain (as the maximum value this index at the terrain local to the building location Kn max [2]): Kn 2 05 ( ) 025 ( ) (1) max x y x y x, y where: x, y are horizontal strains along the axis of Cartesian coordinates system and x,y is non-dilatational strain), with the value of the limiting horizontal strain ( expressed by the category of building resistance ) lim (Table 1) The result of the prognosis of horizontal strains according to the basic version of Knothe s theory is influenced by systematic () and random ( ) factors with definite values This is what causes the discrepancy between the results of prognoses and the results of observations In the basic version of Knothe s theory the value of coefficient B binding vertical and horizontal deformations: where: r is the radius of the dispersion of impacts B 04 r (2) Later research [5, 1] showed that the value of coefficient B in the exploitation of hard coal deposits and also deposits of copper ores is smaller and its average value is: B 032 r (3) The difference results from changes in the conditions of deposit exploitation over the years, mainly due to carrying out the exploitation at deeper and deeper levels From the above a very important conclusion can be drawn: the results of prognoses of horizontal strains Kn max, which were made according to the basic version of Knothe s theory were overestimated by about 25% compared to values resulting from geodetic observations: 025 avr (4) max where: avr max is maximum, average value of horizontal strain It can be deduced from geodetic measurements, that the standard deviation of horizontal strains is [7, 8]:

154 ( 015 025 ) max avr (5) Taking into consideration relations (3) and (4) it was possible to estimate that in this case the probability of the occurrence of a horizontal strain larger than the predicted max P =021[6] Kn is 1 The rules of usage of new method of assessment of damages threat to buildings To remove this error, which results from systematic and random factors, from the result of the prognosis, an not exceedable horizontal strain nexc max was defined at work [4] The value nexc this index, satisfying the condition P( max ) 005,, is calculated from the formula: nexc max Kn max 12 (6) where: Kn max is the extreme (in point and in time) of the horizontal strain calculated according to the basic version of Knothe s theory The resistance of a building to deformation of foundation, or strictly to horizontal strain, it is identified with limiting horizontal strain lim equal to the bottom limit of the resistance category (Table 1), suitable for a given building The category of resistance is established with the score method [3] From the accomplished analysis in the paper [4] it can be concluded that it is possible to estimate the resistance of building as so-called critical horizontal strains cr res, which is counted from formula: cr res 065 lim (7) where cr res critical horizontal strain (critical resistance) marking the limit, exceeding this limit means damage to the building, beyond imperceptible degree [3] difficulty its use, lim limiting horizontal strain marked with the interpolation method from the relation between the number of points (using the score method) and horizontal ( limiting strain ) lim

Comparison of values of indexes nexc cr max and res it enables to determine unambiguously the group of non menaced buildings and menaced buildings from the mining-induced surface deformations In [4] a so-called index of predictable damage to the building I nk was defined Its value is calculated from the formula: 155 I nk nexc max cr res (8) Index I nk determine the predicted degree of damage to the building which can be understood as the extent of necessary repairs or preventive measures (Table 2) TABLE 2 Relation of foreseen degree of damage of building s u from index of predictable damage to the building I nk TABELA 2 Relacja przewidywanego stopnia uszkodzenia budowli s u i wskaÿnika przewidywalnego uszkodzenia budowli I nk Index I nk 10 20 30 40 50 60 Degree of damage s u 01 025 05 075 08 09 One should degree of damage of building s u to interpret in accordance with classification (Table 3) passed by Wodyñski and Kocot [9] Classification of degrees of damage of building s u [9] Klasyfikacja stopni uszkodzeñ budowli s u [9] TABLE 3 TABLE 3 Degree of damage s u = 00 s u 005 005 s u 010 010 s u 025 025 s u 050 050 s u 075 s u >075 Character of damages No scratches and cracks on the wall of building Lengths of microscratches are smaller than 15 m The microscrathes appear locally in small quantities Lengths of microscratches are larger than 15 m The microscrathes appear in large quantities 1 2 scratches aperture smaller than 1 mm appear 1 2 scratches aperture smaller than 2 mm appear It appears some smaller scratches about accumulated aperture to 5 mm The cracks aperture 2 5 mm appear on all height of building (accumulated aperture of cracks are smaller than 20 mm) Horizontal dislocations of edge of cracks are possible The aperture of single crack is larger than 5 mm (accumulated aperture of cracks are larger than 20 mm) Construction of building is indeed menace Emergency state of construction

156 Foreseen degree of damage of building (according to Tables 2 and 3) one should to treat as essential information, helpful in taking of decision about protection of menace buildings Conclusion The presented in this article method allows the assessment of the predicted degree of damage to buildings in mining areas, based on the indexes characterizing the predicted deformations of the surface terrain and estimated resistances of buildings to the impact from the mining-induced ground deformations These indexes (ie not exceedable horizontal strain nexc max and critical horizontal strain cr res ) take into account systematic and random components of inadequacy of theoretical models compared to the reality described by the results of measurements and observations The use of these indexes leads to more unambiguous and more reliable than obtained so far, results of the assessment of threat to buildings, caused by the impact of the planned mining exploitation REFERENCES [1] H e j m a n o w s k i R, K w i n t a A, P a t y k o w s k i G, 2005 Metoda wyznaczania wspó³czynnika proporcjonalnoœci przemieszczeñ poziomych B dla rejonu O/ZG Lubin [W:] Materia³y Konferencji Naukowo-Technicznej: VIII Dni Miernictwa Górniczego i Ochrony Terenów Górniczych GIG Katowice, Ustroñ, 15 17 czerwca, 324 333 [2] K n o t h e S, 1984 Prognozowanie wp³ywów eksploatacji górniczej Œl¹sk, Katowice [3] K w i a t e k J, 2002 Obiekty budowlane na terenach górniczych Wydawnictwo G³ównego Instytutu Górnictwa, Katowice [4] O s t r o w s k i J, 2006 Deformacje powierzchni a zagro enie uszkodzeniami budynków na terenach górniczych w ujêciu probabilistycznym AGH Uczelniane Wydawnictwa Naukowo-Techniczne Rozprawy i monografie 160, Kraków [5] P o p i o ³ e k E, O s t r o w s k i J, 1978 Zale noœæ miêdzy nachyleniami a przemieszczeniami poziomymi terenu w ostatecznie wykszta³conych nieckach obni eniowych Ochrona Terenów Górniczych nr 46 [6] P o p i o ³ e k E, 1989 Ochrona terenów górniczych Skrypt uczelniany nr 1172, AGH, Kraków [7] P o p i o ³ e k E, O s t r o w s k i J, 1981 Próba ustalenia g³ównych przyczyn rozbie noœci prognozowanych i obserwowanych poeksploatacyjnych wskaÿników deformacji Ochrona Terenów Górniczych nr 58 [8] P o p i o ³ e k E, O s t r o w s k i J, N i e d o j a d ³ o Z i in, 1999 Wstêpne wyniki analizy dotychczasowych geodezyjnych badañ wp³ywów eksploatacji górniczej na deformacje powierzchni terenu w LGOM [W:] Materia³y Konferencji Naukowo-Technicznej: V Dni Miernictwa Górniczego i Ochrony Terenów Górniczych Szczyrk 2909 110 Wydawnictwo G³ównego Instytutu Górnictwa, Seria: Konferencje nr 30, 96 107 [9] W o d y ñ s k i A, K o c o t W, 1996 Metodyka oceny stanu technicznego budynków o tradycyjnej konstrukcji zlokalizowanych na terenach górniczych Przegl¹d górniczy Nr 7 8, Katowice

157 NOWA METODA OCENY ZAGRO ENIA USZKODZENIAMI OBIEKTÓW BUDOWLANYCH NA TERENACH GÓRNICZYCH S³owa kluczowe Górnictwo, odkszta³cenia powierzchni, naprê enia poziome, zagro enie budowli Streszczenie Odkszta³cenia powierzchni wywo³ane dzia³alnoœci¹ górnicz¹ s¹ powodem uszkodzeñ budowli Opracowanie przedstawia now¹ metodê oceny zagro enia dla budowli, któr¹ mo na realizowaæ poprzez porównanie tak zwanej przewidywanej wartoœci nieprzenoszalnych naprê eñ poziomych do tak zwanej wartoœci oznaczenia krytycznego naprê enia poziomego odpornoœci budowli NEW METHOD OF ASSESSMENT OF DAMAGES THREAT TO BUILDING OBJECTS IN THE MINING TERRAIN Key words Mining, surface deformations, horizontal strain, threat to building Abstract The mining-induced surface deformations are the reason of damages to buildings The paper presents new method the assessment of threat to building, which can be accomplished by the comparison of so-called the predicted value of impassable horizontal strain to so-called the value of horizontal strain marking critical resistance of the building