Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using ...Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack's length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam.展开更多
Peatlands have obvious carbon storage capacity and are crucial in mitigating global climate change.As the end-product of peatlands,coals have preserved a large amount of palaeoenvironmental information.The carbon accu...Peatlands have obvious carbon storage capacity and are crucial in mitigating global climate change.As the end-product of peatlands,coals have preserved a large amount of palaeoenvironmental information.The carbon accumulation rate and the net primary productivity(NPP)of coal-forming peatlands can be used as proxies for recovering palaeoenvironments.A super-thick coal seam(42°35'N,91°25'E)was developed in the Middle Jurassic Xishanyao Formation in the Shaerhu coalfield in the southern margin of the Tuha(Turpan-Hami)Basin,northwestern China.In this study,we use the time series analysis to identify the periods of Milankovitch orbital cycles in the Gamma-ray curve of this super-thick(124.85 m)coal and then use the obtained cycle periods of 405 ka,173 ka,44 ka,37.6 ka,22.5 ka to calculate the timeframe of the coalforming peatlands which ranges from 2703.44 to 2975.11 ka.Considering that the carbon content of the coal seam is 78.32%and the carbon loss during the coalification is about 25.80%,the carbon accumulation rate of the targeted coal seam is estimated to be 58.47-64.34 g C/m^(2)·a,and the NPP is estimated to be252.28-277.63 g C/m^(2)·a.The main palaeoenvironmental factors controlling the NPP of peatlands are CO_2content,palaeolatitude and palaeotemperature.The reduced NPP values of the palaeo-peatlands in the Shaerhu coalfield can be attributed to the mid-palaeolatitude and/or too low atmospheric CO_2contents.To a certain extent,the NPP of palaeo-peatlands reflects the changes in atmospheric CO_2,which can further reveal the dynamic response of the global carbon cycle to climate change.Therefore,predicting the level of NPP in the Middle Jurassic and studying the final destination of carbon in the ecosystem are beneficial to understanding the coal-forming process and palaeoenvironment.展开更多
文摘Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack's length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam.
基金supported by Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant No.42321002)the National Natural Science Foundation of China (41572090)。
文摘Peatlands have obvious carbon storage capacity and are crucial in mitigating global climate change.As the end-product of peatlands,coals have preserved a large amount of palaeoenvironmental information.The carbon accumulation rate and the net primary productivity(NPP)of coal-forming peatlands can be used as proxies for recovering palaeoenvironments.A super-thick coal seam(42°35'N,91°25'E)was developed in the Middle Jurassic Xishanyao Formation in the Shaerhu coalfield in the southern margin of the Tuha(Turpan-Hami)Basin,northwestern China.In this study,we use the time series analysis to identify the periods of Milankovitch orbital cycles in the Gamma-ray curve of this super-thick(124.85 m)coal and then use the obtained cycle periods of 405 ka,173 ka,44 ka,37.6 ka,22.5 ka to calculate the timeframe of the coalforming peatlands which ranges from 2703.44 to 2975.11 ka.Considering that the carbon content of the coal seam is 78.32%and the carbon loss during the coalification is about 25.80%,the carbon accumulation rate of the targeted coal seam is estimated to be 58.47-64.34 g C/m^(2)·a,and the NPP is estimated to be252.28-277.63 g C/m^(2)·a.The main palaeoenvironmental factors controlling the NPP of peatlands are CO_2content,palaeolatitude and palaeotemperature.The reduced NPP values of the palaeo-peatlands in the Shaerhu coalfield can be attributed to the mid-palaeolatitude and/or too low atmospheric CO_2contents.To a certain extent,the NPP of palaeo-peatlands reflects the changes in atmospheric CO_2,which can further reveal the dynamic response of the global carbon cycle to climate change.Therefore,predicting the level of NPP in the Middle Jurassic and studying the final destination of carbon in the ecosystem are beneficial to understanding the coal-forming process and palaeoenvironment.