Dust generated from bolt hole drilling in roof bolting operation could have high quartz content. As a dust control measure, vacuum drilling is employed on most of the roof bolters in US underground mines. However, fin...Dust generated from bolt hole drilling in roof bolting operation could have high quartz content. As a dust control measure, vacuum drilling is employed on most of the roof bolters in US underground mines. However, fine rock partic- ulates from drilling could escape from the dust collection system and become airborne under some circumstances causing the roof bolter operators expose to quartz-rich respirable dust. A previous research shows that drilling can be controlled through properly selected penetration and rotational rates to reduce the specific energy of drilling. Less specific energy means less energy is wasted on generating noise, heat and over-breakage of rock. It implies that proper control of drilling has a great potential to generate significantly less fine rock dust during drilling. The drilling experiments have been conducted to study the effect of controlling drilling on reducing respirable dust. The preliminary results show that the size distributions of respirable dust were different when controlling drilling in different bite depths. This paper presents the findings from laboratory experimental studies.展开更多
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
文摘Dust generated from bolt hole drilling in roof bolting operation could have high quartz content. As a dust control measure, vacuum drilling is employed on most of the roof bolters in US underground mines. However, fine rock partic- ulates from drilling could escape from the dust collection system and become airborne under some circumstances causing the roof bolter operators expose to quartz-rich respirable dust. A previous research shows that drilling can be controlled through properly selected penetration and rotational rates to reduce the specific energy of drilling. Less specific energy means less energy is wasted on generating noise, heat and over-breakage of rock. It implies that proper control of drilling has a great potential to generate significantly less fine rock dust during drilling. The drilling experiments have been conducted to study the effect of controlling drilling on reducing respirable dust. The preliminary results show that the size distributions of respirable dust were different when controlling drilling in different bite depths. This paper presents the findings from laboratory experimental studies.
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.
