Subsidence process in the rock mass disturbed by mining can be complicated and can be faster or slower depending on the geological structure and physical and mechanical properties of the rock mass, changes in exploitation geometry, and changes in the rate of exploitation. The most frequently, the subsidence process develops over years in a way that is difficult to observe over a short period (days). It has been proven in practice of coal mines in Poland that Knothe’s model describes subsidence process with high accuracy. It is based on treating the rock mass as a stochastic medium and describing subsidence with stochastic equations.
It can be assumed that, the complicated stress field as a result of mining activities induce a series of displacements of different sizes in rock mass. The inelastic deformation in rock mass is accompanied by a microseismicity that can be recorded and processed. We assumed that seismic noise with weak seismic events is a low-energy part of the microseismicity. We proposed an analytical solution to examine the distribution of the energy of the seismic noise during subsidence process development based on Knothe’s model. In general a qualitative method of subsidence process assessment by the registration of the seismic noise was described.
This paper presents the impact of salinisation on the aquatic mollusc fauna in flooded mine subsidences in the Karvina region (Czech Republic). The results of the previous research on salinity in flooded mine subsidences show that some of them contain a high content of dissolved inorganic substances (above 1000 mg·l-1). These substances can affect the vegetation and animals occurring in the water and the surrounding area. The phylum of Mollusca was selected as a model group for the fieldwork as it includes species with the proven bioindication potential.
The occurrence of aquatic mollusc species was studied at 10 sites. The sites were selected based on the content of dissolved substances (the salinity gradient from <500 to >1000 mg·l-1. A total of 12 aquatic mollusc species were found, including one species identified as a potential bioindicator of the negative effect of salinisation on aquatic biota.
The analysis showed statistically significant positive correlations between the content of dissolved inorganic substances and the presence of alien species Potamopyrgus antipodarum (J.E. Gray, 1843). The gradient of salinity significantly affects the species composition of the mollusc fauna in flooded mine subsidences and may affect the biodiversity of this group.
The main problem of tunnelling with use of TBM in highly dense urban areas is to assign the range of subsiding trough and the impact of tunnelling works on existing buildings and underground or road infrastructure. The paper presents the results of settlements calculations over twin tube metro tunnel using analytical, empirical methods. The tunnel external diameter is 6,5 m ; the overburden vary from 5 m to 8 m ; the distance between tunnel axis is 14 m. Because of quaternary soils and high water table level the TBM type EBP was chosen as the method of tunnel construction. At the length of 502 m of tunnel the monitoring system was carried out in 22 cross sections. The results of settlements monitoring were compared with the values of analytical calculations.
Geodesic measurements of mining area deformations indicate that their description fails to be regular,
as opposed to what the predictions based on the relationships of the geometric-integral theory suggest.
The Knothe theory, most commonly applied in that case, considers such parameters as the exploitation
coefficient a and the angle of the main influences range tgβ, describing the geomechanical properties of the
medium, as well as the mining conditions. The study shows that the values of the parameters a = 0.8 and
tgβ = 2.0, most commonly adopted for the prediction of surface deformation, are not entirely adequate in
describing each and every mining situation in the analysed rock mass. Therefore, the paper aims to propose
methodology for determining the value of exploitation coefficient a, which allows to predict the values
of surface subsidence caused by underground coal mining with roof caving, depending on geological and
mining conditions. The characteristics of the analysed areas show that the following factors affect surface
subsidence: thickness of overburden, type of overburden strata, type of Carboniferous strata, rock mass
disturbance and depth of exploitation. These factors may allow to determine the exploitation coefficient a,
used in the Knothe theory for surface deformation prediction.
Underground mining extraction causes the displacement and changes of stress fields in the surrounding rock mass. The determination of the changes is extremely important when the mining activity takes place in the proximity of post-flotation tailing ponds, which may affect the stability of the tailing dams. The deterministic modeling based on principles of continuum mechanics with the use of numerical methods, e.g. finite element method (FEM) should be used in all problems of predicting rock mass displacements and changes of stress field, particularly in cases of complex geology and complex mining methods. The accuracy of FEM solutions depends mainly on the quality of geomechanical parameters of the geological strata. The parameters, e.g. young modulus of elasticity, may require verification through a comparison with measured surface deformations using geodetic methods. This paper presents application of FEM in predicting effects of underground mining on the surface displacements in the area of the KGHM safety pillar of the tailing pond of the OUOW Żelazny Most. The area has been affected by room and pillar mining with roof bending in the years 2008-2016 and will be further exposed to room-and-pillar extraction with hydraulic filling in the years 2017–2019.
This article presents a comparison of the real amount of structural bending of a traditional residential building on curved mining ground with the bending results from an elastic model of the system: building + ground. Thanks to surveying measurements conducted during the exploitation front, the relationship between the curvature of the building and the curvature of the area in its direct vicinity was determined. The measurement work lasted one and a half years. Observation results collected in nature verify the deformation results of the modelled structure in the approach proposed by the guidelines for designing buildings in mining areas in Poland. Building Research Institute Instructions, Guidelines, Guidance 416 (2006) allows the adoption of an elastic model for the structure, and for the ground, it allows the adoption of linear elastic features characteristic of Winkler elastic ground. The main purpose of the work was to determine the overestimation of stress in the modelled building resulting from the use of a simplified, computational engineering approach.
Coal is the main energy source in China, but its underground mining causes surface subsidence, which seriously damages the ecological and living environments. How to calculate subsidence accurately is a core issue in evaluating mining damage. At present, the most commonly used method of calculation is the Probability Integral Method (PIM), based on a normal distribution. However, this method has limitations in thick topsoil (thickness > 100 m), in that the extent of the calculated boundary of the subsidence basin is smaller than its real extent, and this has an undoubted impact on the accurate assessment of the extent of mining damage. Therefore, this paper introduces a calculation model for surface subsidence based on a Cauchy distribution for thick topsoil conditions. This not only improves the accuracy of calculation at the subsidence basin boundary, but also provides a universal method for the calculation of surface subsidence.