Abstract
With the gradual increase in mining depth of coal resource exploitation, deep backfilling mining has effectively solved the impact of strong deep mine pressure and strong mining disturbances. However, after deep backfilling mining, the backfilling material is subjected to high stress for a long time, and its viscoelasticity has a significant impact on the roof control effect. This paper uses a large-scale bulk confinement test device to analyze the viscoelastic properties of gangue, establishes a high-precision fractional viscoelastic creep model, and identifies the gangue parameters. The established fractional viscoelastic model was used as the foundation model of the beam, and the roof model based on the fractional viscoelastic foundation was solved. The top deformation characteristics of elastic foundation and fractional foundation were compared and analyzed, and the time effect, viscoelastic effect, and order effect of the fractional order viscoelastic foundation beam were discussed. The results show that the viscosity of gangue increased under the action of deep high stress. As time increased, the roof deformation also increased. In order to more effectively control the long-term deformation of the roof, the viscosity coefficient of the backfilling material should be greater than 20 MPa. This research provides relevant guidance for the requirements of backfilling materials for deep backfilling mining and the prediction of long-term dynamic deformation of the roof in underground excavations.
Highlights
As the mining depth increases for coal resources exploitation, deep backfilling mining technology has achieved considerable development in China and has achieved significant economic, social, and environmental benefits in many mining areas [1]
Pffiffiffiffiffiffiffiffiffiffiffi Taking characteristic coefficients as α0 = 4 k/4EI, when the gangue backfilling material is regarded as an elastic material, the deflection curve equation of the roof beam can be obtained by solving equation (24): wðxÞ = eα0xðd1 sin α0x + d2 cos α0xÞ
Compared with the elastic foundation and fractional viscoelastic foundation (10 years later), the roof deformation increased by 56.6%
Summary
As the mining depth increases for coal resources exploitation, deep backfilling mining technology has achieved considerable development in China and has achieved significant economic, social, and environmental benefits in many mining areas [1]. The mechanical properties, especially the long-term rheological and viscoplastic properties under the above-mentioned high stress-water environmental conditions, are very important for the roof control and backfilling effect. The viscoelastic properties of gangue have an important impact on the deformation of the roof of the backfilled space in backfilling mining [16,17,18,19]. Some classic viscoelastic models, such as the Maxwell model, Kelvin-Voigt model, and general Kelvin-Voigt model, are improved by using the fractional Abel dashpot [26,27,28] Those fractional viscoelastic models have much better advantages for describing the material’s rheological mechanical properties than the integer-order calculus [29]. This research can be used to predict the dynamic subsidence of the deep backfilling mining roof and provides relevant theoretical guidance for rock strata longterm deformation
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