Assessment of the Tilt Phenomenon and the Tilt Distance of the Land as an Effect of Coal Mining, Jiu Valley Basin, Romania

The aim of the study was to evaluate the phenomenon of land tilting and the tilting distance as a secondary effect of surface coal mining in the Jiu Valley area, Romania. To evaluate the tilting phenomenon, through the two considered elements (inclination – Lt, tilting distance – Td) 16 control points (CP1 to CP16) were used whose coordinates were measured in the Stereographic 1970 projection system, the 1975 Black Sea elevation system at an initial moment (t₀) and at the current moment (t₁). The static method was used by GPS technology to measure the elevations of the control points. Through descriptive statistical analysis, a general characterization of the set of recorded values was obtained, and the ANOVA test confirmed the safety of the data and the presence of variance in the data set. From the analysis of the recorded values, a Spline type model was obtained that described the variation of Lt in relation to Td, under conditions of statistical safety ( ɛ¯ = 0.137302). Regression analysis facilitated the obtaining of equation-type models, which described the variation of Lt and Td in relation to the X, Y and Z coordinates of the control points (t₀, t₁), under conditions of statistical certainty (R² = 0.697, p=0.014 for Td variation according to Z₀ and Z₁; R² = 0.722, p=0.0094 for Td in relation to X₀ and Z₀). According to PCA, PC1 explained 61.303% of variance, and PC2 explained 38.697% of variance. The cluster analysis facilitated the obtaining of a dendrogram based on Euclidean distances, regarding the grouping based on the similarity of the control points in relation to the studied phenomenon, under conditions of statistical safety (Coph. corr.=0.957).