Abstract
Whether a tensile failure fracture will penetrate a stratum is difficult to ascertain at present. In view of this, the method of similar simulation and field verification are used to carry out a systematic study. Similar simulations show that tensile failure fractures will penetrate the layered strata if the compressive stress is greater than the compressive strength. Theoretical analysis points out that whether the tensile failure fractures will penetrate the layered strata can be expressed by the value of criterion of interconnected vertical fractures and the compression-tension ratio. When the value of criterion of interconnected vertical fractures is greater than the compression-tension ratio, the layered strata will break. This criterion was qualitatively verified with a field test. The results of this paper are of great significance for the prevention of water inrush in coal mines, and it can also promote the understanding of the law of strata movement.
Highlights
China is a large coal resource country and a large coal consumption country
H is the thickness of layered strata, σt is the tensile strength, and σc is the compressive strength
The load q on the layered strata includes the load from the upper strata and self-weight, T is the resultant force of the compressive stress at the extrusion, a is the range of the compressive stress at the extrusion, h is the thickness of the layered strata, L is the length of the breaking blocks, θ is the rotation angle of the blocks, and Δ is the maximum relative subsidence at the end of the blocks caused by rotation, the load T can be calculated in the equivalent model [32]:
Summary
China is a large coal resource country and a large coal consumption country. Most of the energy supply comes from coal. Because the horizontal fractures cannot connect the working face and the aquifer alone, interconnected vertical fractures are the secondary channel of mine water inrush. Given the shortcomings of the standard formula, Xu et al [24, 25] proposed a formula for predicting the height of interconnected vertical fractures based on the position of the primary key strata (PKS), considering the fact of the layered characteristics of overburden and the fracture characteristics of different lithologies. It is still essentially an empirical formula. The discrimination formula of interconnected vertical fractures is qualitatively verified by an engineering test
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