Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased co...Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased confining pressure and reduced free surface were its main characteristics.In order to break down a hanging roof,a new method based on shock wave collision and stress superposition was developed.In this method,two blastholes containing multi-primer at different positions are simultaneously initiated at first.By doing this,a new free surface and a swell room can be created.After these holes are fired,a long delay time is given to the next blasthole so that the fragments from the first twohole blasting have enough time to fall down.This new method was applied to three hanging roofs in one production area,and all of them were successfully broken down.Field inspection indicated that almost no damage was caused in the nearby drifts/tunnels due to the new method.In addition,the far field vibrations were found to be smaller than the maximum vibrations induced by some other blasts.展开更多
While roundabouts have already been proven to be an effective intersection treatment, there are many instances where low-clearance vehicles have problems using roundabouts. Low-clearance vehicles, such as lowboy trail...While roundabouts have already been proven to be an effective intersection treatment, there are many instances where low-clearance vehicles have problems using roundabouts. Low-clearance vehicles, such as lowboy trailer trucks, have problems, damaging the curbs and truck aprons at roundabouts when there is not sufficient ground clearance. This area has been generally neglected by designers and U.S. states. The latest roundabout manual has guidelines available to design various features of the roundabouts, but they are not specific for low-clearance vehicles. While some previous studies have identified roundabout locations with ground-clearance problems for lowboy trailers that have truck-apron heights that are greater than three inches, no published information is available about truck-apron heights based on three-dimensional analyses. This study addresses the ground-clearance problems for low-clearance vehicles at roundabouts by proposing a procedure where truck-apron heights, truck-apron slope, circulatory roadway slope, and approach roadway slope are analyzed to determine the optimum design measurements for a roundabout’s vertical profile in order to accommodate low-clearance vehicles without terrain conflict. The study procedure was demonstrated on standard single-lane roundabouts and double-lane roundabouts designed according to latest roundabout guide, and recommendations were provided for truck-apron heights and the grade for various features of the roundabouts. This research can guide transportation planners and decision makers when determining the optimum roundabout vertical-profile design when low-clearance vehicles are expected. The study uses TORUS software to design roundabouts, and the AUTOTURN and AUTOTURN Pro 3D software for generating two-dimensional and three-dimensional vehicle simulations as well as for conducting three-dimensional vehicle-clearance analysis.展开更多
The incipient condition of hang-up for three Geldart-D powders has been experimentally studied in a 21 m long standpipe hopper system. Experimental results show that the pressure gradient for hang-up to occur is indep...The incipient condition of hang-up for three Geldart-D powders has been experimentally studied in a 21 m long standpipe hopper system. Experimental results show that the pressure gradient for hang-up to occur is independent of the materials height in the hopper and the diameter of orifice and equals to (dpw/dl)s, which can be predicted by Eq. (7). While the corresponding gas velocity in the standpipe equals to the incipient fluidized velocity of particles at the high pressure and can be predicted by Kwauk's equation.展开更多
文摘Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased confining pressure and reduced free surface were its main characteristics.In order to break down a hanging roof,a new method based on shock wave collision and stress superposition was developed.In this method,two blastholes containing multi-primer at different positions are simultaneously initiated at first.By doing this,a new free surface and a swell room can be created.After these holes are fired,a long delay time is given to the next blasthole so that the fragments from the first twohole blasting have enough time to fall down.This new method was applied to three hanging roofs in one production area,and all of them were successfully broken down.Field inspection indicated that almost no damage was caused in the nearby drifts/tunnels due to the new method.In addition,the far field vibrations were found to be smaller than the maximum vibrations induced by some other blasts.
文摘While roundabouts have already been proven to be an effective intersection treatment, there are many instances where low-clearance vehicles have problems using roundabouts. Low-clearance vehicles, such as lowboy trailer trucks, have problems, damaging the curbs and truck aprons at roundabouts when there is not sufficient ground clearance. This area has been generally neglected by designers and U.S. states. The latest roundabout manual has guidelines available to design various features of the roundabouts, but they are not specific for low-clearance vehicles. While some previous studies have identified roundabout locations with ground-clearance problems for lowboy trailers that have truck-apron heights that are greater than three inches, no published information is available about truck-apron heights based on three-dimensional analyses. This study addresses the ground-clearance problems for low-clearance vehicles at roundabouts by proposing a procedure where truck-apron heights, truck-apron slope, circulatory roadway slope, and approach roadway slope are analyzed to determine the optimum design measurements for a roundabout’s vertical profile in order to accommodate low-clearance vehicles without terrain conflict. The study procedure was demonstrated on standard single-lane roundabouts and double-lane roundabouts designed according to latest roundabout guide, and recommendations were provided for truck-apron heights and the grade for various features of the roundabouts. This research can guide transportation planners and decision makers when determining the optimum roundabout vertical-profile design when low-clearance vehicles are expected. The study uses TORUS software to design roundabouts, and the AUTOTURN and AUTOTURN Pro 3D software for generating two-dimensional and three-dimensional vehicle simulations as well as for conducting three-dimensional vehicle-clearance analysis.
文摘The incipient condition of hang-up for three Geldart-D powders has been experimentally studied in a 21 m long standpipe hopper system. Experimental results show that the pressure gradient for hang-up to occur is independent of the materials height in the hopper and the diameter of orifice and equals to (dpw/dl)s, which can be predicted by Eq. (7). While the corresponding gas velocity in the standpipe equals to the incipient fluidized velocity of particles at the high pressure and can be predicted by Kwauk's equation.
