Despite their limiting assumptions, analytical methods for estimating values of K, such as the method of Marston [7, 8] and overburden solutions [5], are useful to mining engineers as they can be used to obtain a preliminary K value.
Open image in new window Fig. 9 Overburden movement characteristics of pillarless mining.
Open image in new window Fig. 4 Overburden movement and fracture evolution in pillarless mining.
They found that the fraction of water soluble selenium in 14 overburden samples was 5 73%, with an average of 22%, of the total.
Only 19 (4.6%) patients dropped out of the study, because of worsening of physical condition (n=4), overburden (n=4), psychiatric condition (n=3), lost contact (n=1) or other reasons (n=7).
Since the well is located at one of the subsidence troughs of the panel, it would suffer from high horizontal stress along with the related horizontal displacement (Figs. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) in the overburden strata.
Furthermore, detailed parametric studies including the Geological Strength Index (GSI from 20 to 80), the overburden depth (H from 40 m to 420 m), in-situ stress ratio (k0 from 0.8 to 3) and excavation roof rise-to-span ratio (h/B ratio from 0.1 to 0.5) were conducted to discuss their influences on the arching area.
I II Average particle size M, mm 0.219 0.262 Sorting coefficient So 1.556 1.575 Primary porosity Φ 0, % 42.96 42.92 Porosity loss with 65 MPa overburden pressure, % 6.29 4.43 Porosity loss during rapid compaction stage, %/2.3 MPa 0.339 0.334 Porosity loss during slow compaction stage, %/2.3 MPa 0.197 0.156.
Many investigators have expressed dissatisfaction with the IRB system, characterizing it as being dysfunctional [ 3], overburdened [ 2, 4], and over-reaching [ 5].
Both the experimental analysis of the stress state of the reconstructed columns in regular working conditions and the failure-free exploitation have confirmed the validity of the reconstruction design, while the BCE excavated approximately 8.5 × 106 t of coal and 1.8 × 106 m3 of overburden after the reconstruction.
