t Research and development of safe and effective control technology of hard roof is an inevitable trend at present. Directional hydraulic fracturing technology is expected to become a safe and effective way to control...t Research and development of safe and effective control technology of hard roof is an inevitable trend at present. Directional hydraulic fracturing technology is expected to become a safe and effective way to control and manage hard roof. In order to make hard roof fracture in a directional way, a hydraulic fracture field test has been conducted in the third panel district of Tashan Coal Mine in Datong. First, two hydraulic fracturing drilling holes and four observing drilling holes were arranged in the roof, followed by a wedge-shaped ring slot in each hydraulic fracturing drilling hole. The hydraulic fracturing holes were then sealed and, hydraulic fracturing was conducted. The results show that the hard roof is fractured directionally by the hydraulic fracturing function of the two fracturing drilling holes; the sudden drop, or the overall downward trend of hydraulic pressure from hydraulic monitoring is the proof that the rock in the hard roof has been fractured. The required hydraulic pressure to fracture the hard roof in Tashan coal mine, consisting of carboniferous sandstone layer, is 50.09 MPa, and the fracturing radius of a single drilling hole is not less than 10.5 m. The wedge-shaped ring slot made in the bottom of the hydraulic fracturing drilling hole plays a guiding role for crack propagation. After the hydraulic fracturing drill hole is cracked, the propagation of the resulting hydraulic crack, affected mainly by the regional stress field, will turn to other directions.展开更多
Since the pioneering use of radioactive ion beams(RIB)in the1980s at Lawrence Berkeley National Laboratory in USA,production and investigation of exotic nuclei far from stability have become possible for a wide range ...Since the pioneering use of radioactive ion beams(RIB)in the1980s at Lawrence Berkeley National Laboratory in USA,production and investigation of exotic nuclei far from stability have become possible for a wide range of nuclear chart.Over the past few decades,the RIB has triggered tremendous advancements in the study of exotic nuclei.For instance,over 3300 nuclides have been discovered[1],with a substantial number of them produced by employing RIBs.Experimentally,there are several methods to generate radioactive nuclei.Among them,the in-flight production methods,specifically projectile fragmentation and in-flight fission,are proven to be two of the most crucial approaches.In-flight methods have been widely used to create the radioactive nuclei lying away from the valley of stability,such as those situated on or close to the r-process path(e.g.,see Refs.[2-4]),thereby allowing scientists to explore the previously inaccessible nuclear territory.In the past few decades,a number of fragment separators have been constructed worldwide in order to produce exotic nuclei utilizing the in-flight techniques[5].展开更多
基金Supported by the National Natural Science Foundation of China （51274194, 51004104） the Program for New Century Excellent Talents in University （NCET- 12-0958）
文摘t Research and development of safe and effective control technology of hard roof is an inevitable trend at present. Directional hydraulic fracturing technology is expected to become a safe and effective way to control and manage hard roof. In order to make hard roof fracture in a directional way, a hydraulic fracture field test has been conducted in the third panel district of Tashan Coal Mine in Datong. First, two hydraulic fracturing drilling holes and four observing drilling holes were arranged in the roof, followed by a wedge-shaped ring slot in each hydraulic fracturing drilling hole. The hydraulic fracturing holes were then sealed and, hydraulic fracturing was conducted. The results show that the hard roof is fractured directionally by the hydraulic fracturing function of the two fracturing drilling holes; the sudden drop, or the overall downward trend of hydraulic pressure from hydraulic monitoring is the proof that the rock in the hard roof has been fractured. The required hydraulic pressure to fracture the hard roof in Tashan coal mine, consisting of carboniferous sandstone layer, is 50.09 MPa, and the fracturing radius of a single drilling hole is not less than 10.5 m. The wedge-shaped ring slot made in the bottom of the hydraulic fracturing drilling hole plays a guiding role for crack propagation. After the hydraulic fracturing drill hole is cracked, the propagation of the resulting hydraulic crack, affected mainly by the regional stress field, will turn to other directions.
基金supported partially by the National Natural Science Foundation of China(12325506,11922501,U1832211,11961141004,and 11905260)the Western Light Project of the Chinese Academy of Sciencesthe open research project of CAS large research infrastructures。
文摘Since the pioneering use of radioactive ion beams(RIB)in the1980s at Lawrence Berkeley National Laboratory in USA,production and investigation of exotic nuclei far from stability have become possible for a wide range of nuclear chart.Over the past few decades,the RIB has triggered tremendous advancements in the study of exotic nuclei.For instance,over 3300 nuclides have been discovered[1],with a substantial number of them produced by employing RIBs.Experimentally,there are several methods to generate radioactive nuclei.Among them,the in-flight production methods,specifically projectile fragmentation and in-flight fission,are proven to be two of the most crucial approaches.In-flight methods have been widely used to create the radioactive nuclei lying away from the valley of stability,such as those situated on or close to the r-process path(e.g.,see Refs.[2-4]),thereby allowing scientists to explore the previously inaccessible nuclear territory.In the past few decades,a number of fragment separators have been constructed worldwide in order to produce exotic nuclei utilizing the in-flight techniques[5].
