Abstract
High-pressure abrasive water jet flushing (HPAWJF) is an effective method used to improve coal seam permeability. In this study, based on the theories of gas flow and coal deformation, a coupled gas-rock model is established to investigate realistic failure processes by introducing equations for the evolution of mesoscopic element damage along with coal mass deformation. Numerical simulation of the failure and pressure relief processes is carried out under different coal seam permeability and flushing length conditions. Distributions of the seepage and gas pressure fields of the realistic failure process are analyzed. The effects of flushing permeability enhancement in a soft coal seam on the gas drainage from boreholes are revealed by conducting a field experiment. Conclusions can be extracted that the gas pressure of the slotted soft coal seam is reduced and that the gas drainage volume is three times higher than that of a conventional borehole. Field tests demonstrate that the gas drainage effect of the soft coal seam is significantly improved and that tunneling speed is nearly doubled. The results obtained from this study can provide guidance to gas drainage in soft coal seams regarding the theory and practice application of the HPAWJF method.
Highlights
Coal and gas outbursts have been widely studied because of their serious threat to safety in coal mine production (Frid, 1997; Li and Hua, 2006; Cao and Bian, 2019)
With the increase in excavation depth of coal mining, the features of high gas content, high geostress, high geotemperature, and low permeability of soft coal seams have been significantly increasing (Jin et al, 2015), and the increasing number of coal and gas outbursts causes the risk of accidents to increase rapidly
Gas pressure and gas volume distribution will be discussed under different permeability coefficient (λ)
Summary
Coal and gas outbursts have been widely studied because of their serious threat to safety in coal mine production (Frid, 1997; Li and Hua, 2006; Cao and Bian, 2019). High-pressure abrasive water jet flushing (HPAWJF) is a rapidly developing technology used to prevent coal and gas outbursts (Jiang et al, 2009, 2011). The pressure relief space is formed during water jet flushing of a borehole, which can effectively change original stress distribution and improve coal seam permeability (Shen et al, 2012). The high-pressure abrasive water jet can cut a slot to a certain width and depth in a coal seam, which will reduce the three directions of force into two and lead to changes in the energy storage states of small coal mass elements surrounding the slot. To investigate the distributions of seepage and gas pressure fields in the realistic failure process of HPAWJF, numerical simulation is carried out under different coal seam permeability and flushing length conditions. The numerical simulation implemented a transient process, and time step is 0.02 day
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