Królewskie kopalnie soli w Wieliczce i Bochni (1978, 2013)
Royal Salt Mines in Wieliczka and Bochnia (1978, 2013)
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The Salt Mines in Wieliczka and Bochnia, together with the Saltworks Castle in Wieliczka, are a serial property located in southern Poland, in the vicinity of Kraków. Both salt mines, combined as one company with royal status, known as Kraków Salt Works, worked continuously from the 13th until the late 20th century, constituting one of the most modern and most important European industrial operations. The mines illustrate the historic stages of the development of mining techniques, comprising an ensemble of hundreds of kilometres of galleries and residual excavations, made into workshops, warehouses, as well as chapels, with remarkable statues and decorative elements sculpted into the rock salt. Underground tourist routes have existed in the mines since the early 19th century. Criterion: (iv) An underground museum, but still a mine The ride down to the underground passages of the Wieliczka and Bochnia mines takes just two minutes. It not only takes the visitors hundreds of metres beneath the surface, but also several hundred centuries back in time. From the start of the mining operation, miners interfered with the original state of equilibrium of the deposit by digging shafts, galleries and huge chambers in search of the precious salt. They were continuously exposed to various dangers. In order to ensure safety for the miners in their search for salt, impressive wooden supporting structures, box cribs, and roof supports of the galleries and chambers were constructed. What is the most impressive, however, is the heritage of enormous chambers sculpted in pure salt. Leaving a salt layer of a specific thickness in the roof and sidewalls has allowed these huge salt caverns to remain both safe and stable. Well-preserved historic machinery, treadmills, lifts, water wheels, and dozens of mining tools add to the extraordinary atmosphere of the underground world of the Royal Salt Mines. The Wieliczka and Bochnia mines have already discontinued their intensive salt mining operation, but the destructive forces of nature have not ceased their work. The task facing the managers of the mines seems obvious: to preserve and maintain the priceless underground in its original form. This can be ensured with the help of science and the modern mining technologies that active mines excavating salt and other minerals still use in practice. The salt rock surrounding the underground chambers acts as their natural support, a support which is constantly exposed to the destructive pressure of the rock above the salt deposits. In order to secure the roof and sidewalls against cracking and potential collapse, the rock spanning the chambers is stitched together with a system of thousands of suitably spaced 10-metre-long epoxy anchors, which are inserted in special boreholes. Thanks to them, the rock has increased its resistance to deformations several times over. In addition, any hollows and non-historic, mined-out spaces, which are adjacent to the most valuable historic chambers are filled with dense backfilling. These activities, which have been carried out for years, reinforce and stabilise the underground structure of the mine and protect against the destruction both of the precious chambers and the magnificent sculptures, reliefs and altars of the underground chapels carved in salt by the artists – the miners themselves. The geological and surveying staff of the mines monitor the mine continuously for even the slightest shifts of the salt and rock structures, both underneath and above ground, to evaluate the effectiveness and appropriateness of the safeguarding measures taken. Paradoxically, an equally serious danger for the historic underground structure of the salt mines is the air necessary for their ventilation, or rather the water it contains. Temperatures inside the mine are relatively stable, ranging between 15-17° C. In the summer months, when the surface air temperature often exceeds 30° C, the air flowing into the mine cools rapidly, as a result of which the moisture it contains condenses on the walls and ceilings of the galleries, dissolving their outer layer of salt. This is particularly dangerous for the underground salt carvings as it irreversibly destroys them. In order to contain this threat, the air delivered underground is treated in special dehumidifying stations. The historic mines, which function as underground museums, are still organised as active mining companies. Their organisational structures and procedures are designed to ensure safety both for the underground visitors and for the miners who perform the works to secure the mine. Besides the communication systems and fire protection measures required in active mines, the mine museums operate systems for continuous monitoring of the underground atmosphere and emergency lighting systems for the underground tourist routes. In this way, experienced engineers and maintenance staff ensure both that people are safe and that the priceless heritage created by numerous generations of Wieliczka and Bochnia miners is preserved intact.
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