| In view of the high ground pressure in the metal mine stopes,the high loss rate of natural pillars,the difficulty in roof-contacted of traditional artificial pillars and passive load bearing property,the concept of "expandable support" is proposed in this paper.In addition,a new artificial expandable pillar,which has the performance of positive support and strain-hardening bearing loads,is developed independently.Based on theoretical analysis,laboratory test,numerical simulation and field test method,the mechanical property and stability of the barrel expandable device and the artificial expandable pillars are tested.Meanwhile,the active support mechanism of the expandable pillars,interaction relationship between bearing loads mechanism and roof are revealed.Based on the support of artificial expandable pillars,a new technology of roof stability and ground pressure control is developed and evaluated in hard rock mining stope.The main research contents and conclusions can be summarized as follows:(1)Based on the characteristics of increasing volume after chemical reaction of expandable materials,a barrel expandable device which can provide axial support was developed.Based on laboratory test method,the mechanical properties of barrel expandable device were measured.The active support,bearing loads behavior and stability were analyzed,and the support mechanism and load bearing property of the barrel expandable device were revealed.The barrel expandable device has a free expanding rate of 58.3%,which can generate pre-stress on the restraining body(such as the press of the testing machine)quickly and actively.As the reserved gaps between the barrel expandable device and the restraining body decreases or the filling amount of the expandable materials increases,the active support stress increases and the increasing range increases.The active support stress without reserved gaps is up to 500 kN.At the same time,the barrel expandable device has strain-hardening load bearing property during the loading process.The stiffness of expandable device increases and its own strength is high,which can reach more than 90 MPa.The test shows that the barrel expandable device developed can generate axial support stress effectively in the process of chemical expandable reaction,which can provide effective source for the active roof connection of stope roof support,and has strain-hardening bearing capacity.(2)Based on the barrel expandable device,an artificial expandable pillar suitable for field application was designed.The.loading test system was established to measure its bearing capacity and stability,and the bearing mechanism of the artificial expandable pillar with support structure was revealed.Firstly,the artificial expandable pillar has the characteristics of bearing loads quickly,large active supporting capacity and strain-hardening in the bearing process.Secondly,the influence of high-to-diameter ratio of artificial expandable pillar on its load bearing property and stability was analyzed.With the increase of the high-to-diameter ratio,the strain-hardening bearing area of the artificial expandable pillars shorted or disappeared,and it was more prone to instability.The failure area was located in the center of the support pipe of the support structure,and the unstable mode was considered as bending failure.From the technical point of view,the active support stress(approx.1600kN)and maximum load bearing capacity(approx.2700kN)of the artificial expandable pillars are greater than other types of artificial pillars.In the point view of economic,the cost of artificial expandable pillars is low,and its effective application can realize the efficient recovery of ore body.Comprehensive analysis shows that the new type of artificial expandable pillar has active support and strain-hardening bearing property,which is a technically feasible and economically rational new underground support technology.(3)The interaction mechanism between artificial expandable pillars and stope roof was revealed.Based on the laboratory test results and theoretical analysis with numerical simulation,the influence of timeliness and stiffness of support on stope roof stability was analyzed.On the one hand,the timing of artificial expandable pillar installation and the generation period of pre-stressed are short.On the other hand,the change of the gap between the artificial expandable pillar and the roof and the amount of the expandable material can improve the pre-stress and the strain-hardening bearing property of the expandable pillar,and then adjust its supporting stiffness.Secondly,the artificial expandable pillar can make the roof pressure release properly and ensure the stope roof is in a plastic deformation but stable state.Relatively speaking,the time of the natural pillar support is too early,so the roof loads cannot be fully released,which easily leads to the splitting instability of the pillar.However,the timing of traditional artificial pillar installation is too long and the roof cannot be effectively connected,which leads to too late supporting time and cannot effectively control the roof deformation.On the whole,the support time and support stiffness of artificial expandable pillar can be adjusted,which can achieve the "yielding support"of stope roof substantially,enriching the connotation of the interaction mechanism between stope support body and surrounding rock.(4)Based on the engineering background of the natural pillars recovery in the room-and-pillar mining method in the Chaihulanzi gold mine and the stope span expansion in the upper horizontal cut and fill mining method in the Tiancheng gold mine,a new method of roof stability and ground pressure control in the hard rock stope was developed based on the pressure-arch theory and the artificial expandable pillars support technology.The roof pressure can be effectively transferred from the natural pillars to the artificial expandable pillars in the process of the natural pillar recovery or in the process of the slope expansion,and raising the stope span from 3 m to 9m.The support technology based on artificial expandable pillars can support actively and strain-hardening bearing roof loads.After the roof loads is fully released,the self-stabilizing ability of surrounding rock can be maximized to ensure the stability of stope roof.From the technical and economic point of view,the stope roof loads control technology based on artificial expandable pillars support can improve the productivity and efficiency of mines,with remarkable economic benefits.In a word,the new type of artificial expandable pillars has the characteristics of active support quickly and strain-hardening bearing property,which can realize the"yielding support" of the roof in hard rock mining stope,and finally achieve the goal of safe,efficient and economic recovery of ore. |
PDF Full Text Request