This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations.Subsidence related high stre...This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations.Subsidence related high stress concentrations are believed to have caused damage to river beds in the Illawarra region, Australia. In the field study, extensometers, stressmeters and piezometers were installed in the overburden strata of a longwall panel at West Cliff Colliery. During longwall mining, a total of1000 mm tensile deformation was recorded in the overburden strata and as a result bed separation and gaps were formed. Bed separation was observed to start in the roof of the mining seam and gradually propagate toward the surface as the longwall face advanced. A substantial increase in the near-surface horizontal stresses was recorded before the longwall face reached the monitored locations. The stresses continued to increase as mining advanced and they reached a peak at about 200 m behind the longwall face. A numerical modelling study identified that the angle of breakage(i.e., the angle of the boundary of caved zone) behind the longwall face and over the goaf was 22–25° from vertical direction. This is consistent with the monitoring results showing the high gradient of stresses and strains on the surface150–320 m behind the mining face.展开更多
paper describes a recent study on using fly ash for backfilling abandoned room and pillar mines.Detailed investigations on fly ash properties such as the strength and stiffness of settled fly ash, flowability of fly a...paper describes a recent study on using fly ash for backfilling abandoned room and pillar mines.Detailed investigations on fly ash properties such as the strength and stiffness of settled fly ash, flowability of fly ash grout, as well as chemistry and environmental aspects of fly ash backfill have been undertaken in the laboratory. Numerical modelling was also conducted to quantify the effects of fly ash backfill on the stability of underground pillars. The laboratory tests showed that with a solid concentration of approximate 50%, fly ash grout has an excellent flowability and very low viscosity. It is capable of penetrating and filling almost any voids underground if designed properly and settling as a reasonably stiff solid to provide support to the pillars. Several different types of strength tests proved that a consolidated fly ash should exhibit a friction angle above 42°. 3D numerical modelling on interaction between fly ash backfill and underground pillars has shown that fly ash backfill to 90% roadway height can raise the factor of safety(Fo S) of a marginally stable area to above 1.6, which is the number often used in rock engineering design for long term stability. Chemistry and leachate analysis of representative fly ash samples from a local power station showed that the elemental concentrations in the fly ash solid sample are lower than the allowed contaminant threshold and specific contaminant concentration levels. Geotechnical monitoring in the high risk areas of an abandoned mine has been carried out as part of the risk management and control for potential subsidence. The monitoring has been very helpful in understanding the ground behaviour around the abandoned mine which can provide timely information to the parties concerned in order to make correct decisions to control the subsidence risk.展开更多
In order to fracture shale gas reservoir with carbon dioxide as the working fluid,laboratory experiments were firstly conducted to measure the influence of carbon dioxide immersion on shale rock's properties,and t...In order to fracture shale gas reservoir with carbon dioxide as the working fluid,laboratory experiments were firstly conducted to measure the influence of carbon dioxide immersion on shale rock's properties,and then the coupling mechanism between stress and seepage during hydraulic fracturing was simulated based on cohesive zone model.The fracturing ability of carbon dioxide and water was also compared under the same working conditions,and finally sensitivity analysis(including elastic modulus of shale,filtration coefficient,pump rate and viscosity of carbon dioxide)were conducted based on field application.The results show that,the elastic modulus of shale increased by 32.2%,the Poisson's ratio decreased by 40.3%and the compressive strength decreases by 22.9%after geothermal reaction with carbon dioxide under 30 MPa and 335.15 K for 2 hours.Compared with water fracturing,carbon dioxide fracturing induces longer fracture(increased by 25.3%)and narrower fracture(decreased to 40.8%).The fracture tends to get longer and narrower with increasing elastic modulus of shale.As filtration coefficient increases,the maximum width of fracture decreases significantly,whereas the length changes little.Both the length and maximum width of fracture increase with increasing pump rate,however the changing rate of length tends to decrease.The influence of viscosity of carbon dioxide on both fracture width and length is negligible,which validates the stable feasibility of carbon dioxide fracturing in different formation conditions.展开更多
基金sponsored by ACARP, BHP Billiton Illawarra Coal and CSIRO
文摘This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations.Subsidence related high stress concentrations are believed to have caused damage to river beds in the Illawarra region, Australia. In the field study, extensometers, stressmeters and piezometers were installed in the overburden strata of a longwall panel at West Cliff Colliery. During longwall mining, a total of1000 mm tensile deformation was recorded in the overburden strata and as a result bed separation and gaps were formed. Bed separation was observed to start in the roof of the mining seam and gradually propagate toward the surface as the longwall face advanced. A substantial increase in the near-surface horizontal stresses was recorded before the longwall face reached the monitored locations. The stresses continued to increase as mining advanced and they reached a peak at about 200 m behind the longwall face. A numerical modelling study identified that the angle of breakage(i.e., the angle of the boundary of caved zone) behind the longwall face and over the goaf was 22–25° from vertical direction. This is consistent with the monitoring results showing the high gradient of stresses and strains on the surface150–320 m behind the mining face.
基金sponsored by QLD State Government Department of Natural Resources and Mines(DNRM)
文摘paper describes a recent study on using fly ash for backfilling abandoned room and pillar mines.Detailed investigations on fly ash properties such as the strength and stiffness of settled fly ash, flowability of fly ash grout, as well as chemistry and environmental aspects of fly ash backfill have been undertaken in the laboratory. Numerical modelling was also conducted to quantify the effects of fly ash backfill on the stability of underground pillars. The laboratory tests showed that with a solid concentration of approximate 50%, fly ash grout has an excellent flowability and very low viscosity. It is capable of penetrating and filling almost any voids underground if designed properly and settling as a reasonably stiff solid to provide support to the pillars. Several different types of strength tests proved that a consolidated fly ash should exhibit a friction angle above 42°. 3D numerical modelling on interaction between fly ash backfill and underground pillars has shown that fly ash backfill to 90% roadway height can raise the factor of safety(Fo S) of a marginally stable area to above 1.6, which is the number often used in rock engineering design for long term stability. Chemistry and leachate analysis of representative fly ash samples from a local power station showed that the elemental concentrations in the fly ash solid sample are lower than the allowed contaminant threshold and specific contaminant concentration levels. Geotechnical monitoring in the high risk areas of an abandoned mine has been carried out as part of the risk management and control for potential subsidence. The monitoring has been very helpful in understanding the ground behaviour around the abandoned mine which can provide timely information to the parties concerned in order to make correct decisions to control the subsidence risk.
基金financial supports from Natural Science Foundation of China(51974173)the Opening Fund of Key Laboratory of Mining Disaster Prevention and Control(MDPC201908)+1 种基金Key Laboratory of Unconventional Oil&Gas Development(China University of Petroleum(East China))Ministry of Education。
文摘In order to fracture shale gas reservoir with carbon dioxide as the working fluid,laboratory experiments were firstly conducted to measure the influence of carbon dioxide immersion on shale rock's properties,and then the coupling mechanism between stress and seepage during hydraulic fracturing was simulated based on cohesive zone model.The fracturing ability of carbon dioxide and water was also compared under the same working conditions,and finally sensitivity analysis(including elastic modulus of shale,filtration coefficient,pump rate and viscosity of carbon dioxide)were conducted based on field application.The results show that,the elastic modulus of shale increased by 32.2%,the Poisson's ratio decreased by 40.3%and the compressive strength decreases by 22.9%after geothermal reaction with carbon dioxide under 30 MPa and 335.15 K for 2 hours.Compared with water fracturing,carbon dioxide fracturing induces longer fracture(increased by 25.3%)and narrower fracture(decreased to 40.8%).The fracture tends to get longer and narrower with increasing elastic modulus of shale.As filtration coefficient increases,the maximum width of fracture decreases significantly,whereas the length changes little.Both the length and maximum width of fracture increase with increasing pump rate,however the changing rate of length tends to decrease.The influence of viscosity of carbon dioxide on both fracture width and length is negligible,which validates the stable feasibility of carbon dioxide fracturing in different formation conditions.
