A method for predicting the water-flowing fractured zone height based on an improved key stratum theory

In the process of using the original key stratum theory to predict the height of a water-flowing fractured zone(WFZ),the influence of rock strata outside the calculation range on the rock strata within the calculation range as well as the fact that the shape of the overburden deformation area will change with the excavation length are ignored.In this paper,an improved key stratum theory(IKS theory)was proposed by fixing these two shortcomings.Then,a WFZ height prediction method based on IKS theory was established and applied.First,the range of overburden involved in the analysis was determined according to the tensile stress distribution range above the goaf.Second,the key stratum in the overburden involved in the analysis was identified through IKS theory.Finally,the tendency of the WFZ to develop upward was determined by judging whether or not the identified key stratum will break.The proposed method was applied and verified in a mining case study,and the reasons for the differences in the development patterns between the WFZs in coalfields in Northwest and East China were also fully explained by this method.

Formation mechanism and height calculation of the caved zone and water-conducting fracture zone in solid backfill mining

To study the heights of the caved zone and water-conducting fracture zone in backfill mining,the failure mechanism of strata during backfill mining was analyzed,and a method for determining the heights of the two zones was proposed based on key strata theory.The movement and failure regularity of the strata above the backfilling panel were revealed through numerical simulation.Considering the geologic conditions of the CT101 backfilling panel,the height of the fracture zone was determined using the proposed method along with empirical calculation,numerical simulation,and borehole detection.The results of the new calculation method were similar to in situ measurements.The traditional empirical formula,which is based on the equivalent mining height model,resulted in large errors during calculation.The findings indicate the reliability of the new method and demonstrate its significance for creating reference data for related studies.

THREE-DIMENSIONAL SIMULATION FOR EFFECTS OF BED DISCORDANCE ON FLOW DYNAMICS AT Y-SHAPED OPEN CHANNEL CONFLUENCES

Channel confluences are universally present in nature. They can be divided into two types： asymmetrical river confluences and symmetric river confluences. The latter is also called as the Y-shaped confluences. Most of previous work has paid more attention to the asymmetrical river confluences, but few studies have been conducted on the Y-shaped confluences. In this article, the effects of bed discordance on the flow patterns at ＂Y＂ shaped open-channel confluences were studied by using a 3-D numerical simulation. It is proved that the model can undertake quantitative assessment of the flow at confluences. The results indicate that there are a lot of differences between the Y-shaped confluence and asymmetrical confluence. The discordant bed height plays an important role at the Y-shaped junction.

Two and three dimensional modeling of fluidized bed with multiple jets in a DEM-CFD framework

Fluidized beds with multiple jets have widespread industrial applications. The objective of this paper is to investigate the jet interactions and hydrodynamics of a fluidized bed with multiple jets. Discrete element modeling coupled with in-house CFD code GenlDLEST has been used to simulate a bed with nine jets. The results are compared with published experiments. Mono dispersed particles of size 550 ~m are used with 1.4 times the minimum fluidization velocity of the particles. Both two and three dimensional computations have been performed. To the best of our knowledge, the results presented in this paper are the first full 3D simulations of a fluidized bed performed with multiple jets. Discrepancies between the experiment and simulations are discussed in the context of the dimensionality of the simulations. The 2D solid fraction profile compares well with the experiment close to the distributor plate. At higher heights, the 2D simulation over-predicts the solid fraction profiles near the walls. The 3D simulation on the other hand is better able to capture the solid fraction profile higher up in the bed compared to that near the distributor plate. Similarly, the normalized particle velocities and the particle fluxes compare well with the experiment closer to the distributor plate for the 2D simulation and the freeboard for the 3D simulation, respectively. A lower expanded bed height is predicted in the 2D simulation compared to the 3D simulation and the experiment. The results obtained from DEM computations show that a 2D simulation can be used to capture essential jetting trends near the distributor plate regions, whereas a full scale 3D simulation is needed to capture the bubbles near the freeboard regions. These serve as validations for the experiment and help us understand the complex jet interaction and solid circulation patterns in a multiple jet fluidized bed system.