This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for...This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for HHR was established by considering the gangue support coefficient,through which the modified expressions of limit breaking span and breaking energy of HHR were deduced.Combined with the relationship between the dynamic-static loading stress of supporting body(hydraulic support and coal wall)and its comprehensive supporting strength,the criteria of ground pressure behaviour(GPB)induced by HHR were discussed.The types of Ⅰ_(1),Ⅰ_(2),Ⅱ_(1),andⅡ_(2) of GPB were interpreted.Results showed that types Ⅰ_(1) and Ⅰ_(2) were the main forms of SGPB in extra-thick coal seam mining.The main manifestation of SGPB was static stress,which was mainly derived from the instability of HHR rather than fracture.Accordingly,an innovative control technology was proposed,which can weaken static load by vertical-well separated fracturing HHR.The research results have been successfully applied to the 8101 working face in Tashan coal mine,Shanxi Province,China.The results of a digital borehole camera observation and stress monitoring proved the rationality of the GPB criteria.The control technology was successful,paving the way for new possibilities to HHR control for safety mining.展开更多
High-pressure pulsed water jet technology has considerable development potential in the field of rock fragmentation.To overcome the shortcomings of existing pulsed jets,a self-supercharging pulsed water jet(SSPWJ)gene...High-pressure pulsed water jet technology has considerable development potential in the field of rock fragmentation.To overcome the shortcomings of existing pulsed jets,a self-supercharging pulsed water jet(SSPWJ)generation method is proposed,which is based on the theory of the pulsed water jet and the principle of hydraulic boosting.The proposed method changes the flow direction of the fluid medium through the valve core to make the piston reciprocate in the cylinder and relies on the effective area difference between the front and rear chambers in the stroke stage of the piston to realize the organic combination of“pulse”and“supercharging”of the jet,thus forming an SSPWJ.On the basis of the formation principle of the SSPWJ,a SSPWJ testing platform was constructed,and tests were performed on the jet pressure acquisition,morphology capture,and granite erosion.Both the jet pressure and the jet morphology exhibited periodic changes,and a higher pulse pressure was obtained at lower inlet pressure.The error of the pressure ratio calculated according to the experimental results was<3%relative to the theoretical design value,confirming the feasibility of the method.The pulse pressure and pulse frequency are controllable;that is,as the inlet flow rate increases in the stroke stage of the piston,the pulse pressure and pulse frequency increase,and the pulse duration decreases.As the inlet flow rate increases in the backward-stroke stage of the piston,the pulse frequency increases,and the pulse pressure and pulse duration remain unchanged.Under the combined action of the waterhammer pressure,high-speed lateral flow,and high-frequency dynamic load of the SSPWJ,local flaky exfoliation was observed when the granite surface was eroded.The results of this study lay the foundation for enriching the theory of pulsed jet generation and expanding its application range.展开更多
基金This work was jointly supported by the National Natural Science Foundation of China(No.51974042)the Shanxi Province Science and Technology Plan Exposed Bidding Project(No.20191101015)+3 种基金the Open Project Program of Key Laboratory of Mine Disaster Prevention and Control(No.JMDPC202102)the Scientific Research Project of Introducing Talents in Guizhou University(No.202045)the Open Project Program of National Engineering Technology Research Center of Development and Utilization for Phosphorus Resources(NECP202210)the Growth Project of Young Scientific and Technological Talents in Universities of Guizhou Province(KY2022139).
文摘This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for HHR was established by considering the gangue support coefficient,through which the modified expressions of limit breaking span and breaking energy of HHR were deduced.Combined with the relationship between the dynamic-static loading stress of supporting body(hydraulic support and coal wall)and its comprehensive supporting strength,the criteria of ground pressure behaviour(GPB)induced by HHR were discussed.The types of Ⅰ_(1),Ⅰ_(2),Ⅱ_(1),andⅡ_(2) of GPB were interpreted.Results showed that types Ⅰ_(1) and Ⅰ_(2) were the main forms of SGPB in extra-thick coal seam mining.The main manifestation of SGPB was static stress,which was mainly derived from the instability of HHR rather than fracture.Accordingly,an innovative control technology was proposed,which can weaken static load by vertical-well separated fracturing HHR.The research results have been successfully applied to the 8101 working face in Tashan coal mine,Shanxi Province,China.The results of a digital borehole camera observation and stress monitoring proved the rationality of the GPB criteria.The control technology was successful,paving the way for new possibilities to HHR control for safety mining.
基金National Natural Science Foundation of China(Grant Nos.51774055,51625401)National Natural Science Foundation of Chongqing(Grant No.cstc2018jcyjAX0542)Changjiang Scholar Program of Chinese Ministry of Education(Grant No.IRT17R112).
文摘High-pressure pulsed water jet technology has considerable development potential in the field of rock fragmentation.To overcome the shortcomings of existing pulsed jets,a self-supercharging pulsed water jet(SSPWJ)generation method is proposed,which is based on the theory of the pulsed water jet and the principle of hydraulic boosting.The proposed method changes the flow direction of the fluid medium through the valve core to make the piston reciprocate in the cylinder and relies on the effective area difference between the front and rear chambers in the stroke stage of the piston to realize the organic combination of“pulse”and“supercharging”of the jet,thus forming an SSPWJ.On the basis of the formation principle of the SSPWJ,a SSPWJ testing platform was constructed,and tests were performed on the jet pressure acquisition,morphology capture,and granite erosion.Both the jet pressure and the jet morphology exhibited periodic changes,and a higher pulse pressure was obtained at lower inlet pressure.The error of the pressure ratio calculated according to the experimental results was<3%relative to the theoretical design value,confirming the feasibility of the method.The pulse pressure and pulse frequency are controllable;that is,as the inlet flow rate increases in the stroke stage of the piston,the pulse pressure and pulse frequency increase,and the pulse duration decreases.As the inlet flow rate increases in the backward-stroke stage of the piston,the pulse frequency increases,and the pulse pressure and pulse duration remain unchanged.Under the combined action of the waterhammer pressure,high-speed lateral flow,and high-frequency dynamic load of the SSPWJ,local flaky exfoliation was observed when the granite surface was eroded.The results of this study lay the foundation for enriching the theory of pulsed jet generation and expanding its application range.