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ABSTRACT: The National Monument -the SpiS Castle belonged to the largest castles in ... The original dome-shaped form of the traverti-ne body reflects several ...
Separit 12 PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE AND ΠELDヽVORKSHOP ON LANDSLIDESIN CZECH AND SLOVAK REPUBLICS/28 AUGUST-15 SEPTEMBER 1993

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SEVENΠ IINrERNAHONAL CONFERENCE AND曰 田LD WORKSHOP ON LANDSLIDES

The influence of slope movements on SpiS Cast1e stability J.Ⅵ ёko ぉり 3ra耐 CanaP3お 伽 ルι

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National Monument -the SpiS Castle belonged to the largest castles in Central Europe. It was founded in 1120. The historic development of the castle was rather complicated showi-ng traces of many historic epoches up to the Baroque, In 1780 the castle burnt out and since that time the process of destruction caused both by the natural and manmade factors was going on.

ABSTRACT: The

1..

INTRODUCTION

fn 1985 the restoration works including some remedial works started without previous engineering geological investj-gation (removal of vegetation from natural rock faces, cleaning down the rock debris, groutlng, rock bolt-ing, etc.). However, it was quickly enough recognized that the hazards of slope failures of the castl-e rock were so rapi-d that they could endanger the security of the oldest part of the castle the Romanesque Palace/ some parts of the castle wal-l-s/ etc. The remediaf works proved to be insuffic"ient. It was decided to undertake an engineering geological j-nvestigation connected wj-th engineering geological mapping at a scale of 1:500, detailed study of slope deformations and other geodynamic features (karst, weathering), measurement of the joint orientation, detailed description of significant faifures and TV damages found on the castl-e. use was made of drilling, geophysi-caf karst cavities, camera for detecting photogrammetry in measurements as weff as of terrestrial surveying the joint orj-entation patterns in places which had been identified as potenti-al source of great danger The aim of the i-nvestigation was to establish the order in which the additj-onal restoration works shoufd proceed. 2. GEOLOGICAL SETTING The SpiS Castle Located near the village Spidsk6 Podhradie mound in the Hornddska kotlina was buift on a travertine Basin in Eastern Slovakia. From the smooth, gentle morphology formed of Paleogene claystone-sandstone strata of the Central Carpathian flysh several Miocene-Pliocene travertine mounds 305

outcrop (Drevehlk, Ostry vrch, Sobotisko, PaZica a Sivd Brada, the SpiS Castle Rock). The rock face of the SpiS Castl-e Rock j-s the highest on the NW to SE side where it reaches 15 Lo 22 m, sloping at an inclination of 70 to 8Oo in some places up to 90o with a number of overhangings. In the lower part of the slope where slope deposits prevail the j-nclination is about 30 to 32o. Rock slopes on the SW side of the castle reach the incl-inati-on of 160. The travertines are white to yeJ-Iow in colour, micro to macroporous with fluidal structure, s11ght1y weathered along the joints karstj-fied. The karst and weathering phenomena as well as joj-nting significantly affect the properties of the rock materj-al- reducing the uniaxial compressj-ve strength from 70 to 14 MPa. Claystones outcropping near Perun,s rock(near the entrance) are highly weathered to decomposed, brown in col-our with traces of the original beddi-ng and j oint patterns. Accordi-ng to physj-co-mechanicaf properties they belong to the group of soft rocks with a compressive strength of 1r5 , o" > 2,75 Mpa. The original dome-shaped form of the traverti-ne body reflects several features of destruction and is disturbed by a serj-es of faults/ cracks and joints. Tvro prevailing joint sets can be (Fiq. 1 ) found, subvertical joi-nts striking approximately NW to SE with a general dip to SW (dip dj-rection,/dip 220 to 250 /80-90 ) and joints str-iking approximately north - south di-pplng to the west (250 to 270/85). Thq destruction is the resul-t of gravitational slope failures brought about by the creep movement of rigid travertines on relatively pJ-astic claystone bedrock along the former faul-t system. The origin of the Temn6 jaskyia Cave j-s strongly bound to thj-s system as well. The central- part of the castl-e rock is formed by block rifts the thj-ckness of travertine bl-ocks bej-ng approximateJ-ly 52 m. The marginal parts of the castle rock are formed by a block fleld with individual- blocks reachi-ng from 25 to 30 m and or 15 to 18 m (Fj-9.2). The absence of a bl-ock f ield in the SW part of the casLl-e rock is due to the uplift of Paleogene claystones along the f aul-t llne 220 /80 whi-ch inhibited totaf desintegration of the block field, followed by rock fall_s, toppling and tilting of huqe bl-ocks of travertines. 3.

MONITORING OF SLOPE MOVEMENTS

fn order to monitor and quantify creep movements at the Spid castle three dilatometres of the TM-71 type (Fussganger, 1985) were installed in 1980: the first one-in.., open ciack on the western side of the castle rock near perunrs Rock,the second one in the Lower Courtyard in a crack separating the transversal and the outer wal1s and the third equipment was located in a tensj-on crack separating a downslope movJ_ng travertine bl-ock from the northern margj-n of the castle rock just below the Romanesque Palace (Fig.2, Fig.3). The resul-ts of measurements f rom the f i-rst dilatometer _in the period 1980-83 proved the displacement of Perunrs Rock with at a velocj-ty of 0,1 mm/year. The di-splacement indicates 306

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Fj-g.1 Geological map of the SpiS Castle' 1-Romanesque Palace;2-Chape11; 3-Palace ( Iate Gothic) ;4-Keep; 5-Water Reservoir; 6-First Romanesque Courtyardl 7-Second RomanesqueCourtyard;B-LowerCourtyard;9-SouthGate(entrance)1 l0-block rifts; 11-blockfield; 12-cross-section lines; 1 3-debris 307

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of the two different movements: the settlement and tilting block up the slope towards the entrance of the Podhradsk5 jaskyia Cave. The entrance in reality represents a 74 cm wide tension crack. According to historic data concerning the construction of the central parts of the castfe in the years L249-1270,. the width of the crack corresponds to the mean block movement of 1,03 mm/year. we may assume that the movement movement had the character of a "sIip-stick" (di-fferent in speed and time) orientated toward karst cavity. The explosion of the gunpowder storage by the fire on 27.4.1543, intense past earthqukes, as well as the blasting in the open-pit quarry Drevenlk coul-d have influenced the block movements. In 1983 the dilatemeter No.2 detected that the 23 cm wide crack separating lrw margin of the castle rock was widened at the mean veloci-ty of 1,13 mm/ in N-NW direction. By using Lhe back calculation analysis (when dividing the mean velocity of 1,13 mm by the width of the present tensj-on crack 23 cm) we obtain the resulL of 203 years i.e. exactl-y the year 1-780t and the time the castle left the year of the l-ast fire abandoned. The last resuLts from equipment No.2 proved the existence of northward movements with the mean veloci-ty of by 0,97 mm/year. fhe peripheral walI is upllfted approximately 0 t.2B mm/year which can be explained by its ti lti ng According to the results obtained by measuri-ng from equlpment- No.3 that the creep movement Lj-1ted the block towards north. In addition to the results of precise measurements carri-ed out by means of the dilatometer TM-71 in the years 1980-83 within the castle area a whole series of facts gi-ve evj-dence of the movement of travertine blocks and its effect on the castle wa11s. 4. THE

INFLUENCE OF SLOPE MOVEMENTS ON THE CASTLE

The founders of the castle took j-nt.o account the t.opography refl-ecting the geol-ogi-caf and tectonic structure of the castl-e rock as well- as moving blocks and other natural hazards. The slow destruction of the SpiS CastLe was effected by several factors: predominantly by the weathering of the walls and the underlyj-ng rock, earthquake, dynamic effects of bl-asting in a near travertj-ne quarry and mainly rheologic creep movements of travertine blocks. The weathering of the castl-e wal,f s j-s a generally occurring process which can be affected to a great extent by a number of factors. The castle wa11s were buift of travertine rubble joined by mortar. The travertines are relatj-ve1y resi-stant to weathering j-n contrast to mortar which is subjected Lo slow weathering and this further causes the dripping-off of masonry. The most intensive weathering of the castle waLls can be observed directly at the contact between the stonework and the subgrade. At places along this contact the stone-work has dripped off so that overhangings developed. A relatively high degree of weatheri-ng-resistance manifest the Gothic vaults built of flat travertines. 309

fault Karst processes along the gravitational--tectonic lines produced typical- karst phenomena in the form of caves relatively large in sj-ze (the caves Temnd jaskyf,a, Podhradsk6 jasky[a). - Tha effects of seismic shocks on the physical state of the castle stone-work cannot be excluded even though this area esu 73 0036 has been assigned according to the Standards "seismic Loading on BuiJ-dings" up to 6 o MCS' Due to neotectonic faults orj-ented N-S and occurring on the boundary between the Branisko Mts. and the Hornticiska kotli-na Basi-n. seismic effects might have loca1J-y occurred. Direct evidence of earthguake effects on the castle wall-s has not been gained. Tiavertine extract-ion in a nearby quarry.could have Induced in the case of excessive blasting substantial dynamic effects between 1900-1970. At present this influence can be excluded. Bl-ock movements of travertines along the plastic bedrock brought about the development of cracks in the castle stonework whlch often resul-ted in the collapse of parts of the castle constructions. The first evidence of substantial damage goes back to the phases of construction (beginning of the 12th initial century) when the centre of the castl,e complex Ya9 represlnted by the round res-idental tower - the Keep which faifure wai erected on an important gravitational-tectonic During the constructj-on it was even widened NW-SE direction, so that a large j-rregular space was formed and later used as basement. In comparison with the other parts of the castfe the Keep did not exist for a long time. Its quick destruction i-s connected with a faifure in the subgrade, or with the occurrence of constructional fail-ures Ieading to the collapse at of the Keep as well as to collapse of the fortification the NE side, The traces of a gravitational fail-ure can be found on the beams in rooms located befow the relatively well-preserved Romanesque Palace which are as a result of sJ-ope movements parLIy deformed. The most marked damage occurs on the bailey of the central and upper castle. These findings show quite clearly the great i-nfluence of the creep The disruption of the movement on underlying travertines. outer castle walIs, the format-ion of overhangings near the foundation ground and the collapse of. parts of the outer can be directly correlated with the geologicalfortification tectonic structure of the castle rock (Fi-q.1). The most intensive damage of the ouLer walls occurred at the l-i-nes. There intersections of the main gravitational-tectonic exists numerous evidence of medj-evaf restoration works aiming at the reconstruction of damaged parts of the castle using retaining structures. 5.

PLANNING REMEDIAL

WORKS

The slope stabiJ-j-ty analysis proved that attention has to be paid to the subgrade of the castle to the depth of 4 m where Lravertines are strongly weathered and jointed and the rock face shows several features of destruction directly affecting stability of the castle walls. The planned remedial the 310

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works based on the resul-ts of detailed englneering geological as follows (Price et investigatj-on may be classified aI.,19BB)i - preservation works incl. cleaning down the rock face from the vegetation and debris and grouting, - support works comprising rock bolting (Fj-g.3) usinq 4- m long steel bars installed after pregrouting of the bolt ho1e, etc. The application of remedial works to those parts of the castfe which were buil-t on movj-ng travertine blocks seems to be very complicated and presuppose precise monitoring of slope movements and continual maintenance of the castle wa]1s. ●コ

REFERENCES:

Fussgiinger, E. 1985. Knowledge from investigation of creep movements of travertine blocks in SpiSsky hrad castle ( in Slovak). Mneralia Slovaca 17, Nr.1, pp.15-24. Malgot, J.BaIiak, F., Sikora, J.1988. Engineering geoJ-ogical ciuses of failure of the middleage castl-es in Slovaki-a and the methods of their geotechnicat stabilization. Rotterdam, Balkema. Marinos,Koukis (eds. ). Malgot, J. et a1 .),992. Spid CastIe. Engineering geologicaland geotechnical investigation. Research report (in Slovak). Nemdok, A. 1982. Slope movements in Slovak Carpathians. Veda SAV (eds. ) Price D.G., Hollingbery J.W.,MaxweJ-1/ . l9BB.Rock stabilization work to preserve the castles at Edinburgh and Stirling. Rotterdam, Balkema. MarinosrKoukis (eds. ).

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