1、中文 3890 字 英文原文 STUDY ON GATEWAY BOLTING EXCAVATED IN INCLINED COAL SEAM (Northeastern University ,Shenyang 110006) (Chengdu University of Technology.Chengdu 610059) Abstract： A typical gateway is analyzed using fully-deformable discrete element method. The fractured zone around the gateway is measur
2、ed in field. Based on the measurement results and theoretical analysis, a comprehensive support scheme adopting bolt and steel belt is proposed. Discrete element method is used to asses the bolting scheme, and displacement monitoring in field is also carried out. Having been put into practice, it is
3、 proved that the scheme is both successful and rational. According to theoretical analysis and monitoring in filed , some important keynotes that should be noticed in gateway bolting practice are presented as well. Keywords: inclined seam； gateway； strata behavior； bolting； discrete element method I
4、ntroduction Inclined coal seam is generally regarded as seam with a dip single 25 45 ,which occupies a considerable proportion in both production and reserves in China. Problems related to strata control are, however, seldom studied, and researches on in-seam gateway are even 1less . The maintenance
5、 expense of gateway in inclined seam is generally 30% higher than that in nearly flat and gently inclined seam. The reason why there exists a such phenomenon is complicated itself, another possible reason is the lack of the inherent strata behavior law. At present, problems related to in-seam gatewa
6、y maintenance are highly emphasized and many studies on strata behavior and support of gateway are carried 24out . Such researches play a positive role in gateway maintenance. However most of the researches are carried out in flat or gently inclined seams. Due to their locating in remarkably anisotr
7、opic media and environment, gateways in inclined seams are often subjected to unfavorable loads and deform unevenly, strata move more intensively than that in gently inclined seam, and the broken region is also large, which makes gateway support even more difficult. In view of the above-mentioned fa
8、cts, we use fully deformable discrete element method in simulating strata behavior of gateway in inclined seam, and the loosed zone around the gateway is also monitored in field. Based on the results, a bolting scheme is proposed. After putting into practice, the scheme is proved to be effective and
9、 rational. 1. Deform and fail features of gateway without any support 1.1 Geologic conditions The study object is the No.36 seam in Baoshan Coal Mine , the dip angle of the seam is 35and thickness is 1.0m, the geologic conditions are rather simple. The average buried depth is 440m. The immediate roo
10、f is 2 meters thick of fine sandstone and shale, the overall strength is low. Above the immediate roof is comparatively hard main roof. The floor is fine sandstone. The gateway width is 2.2m and the gateway is excavated in irregular shape in order to keep the roof intact. The sidewall coal is howeve
11、r rather soft and loose, and easily fails. The surrounding rocks of the gateway are not stable , roof and sidewall are apt to fall or break, which is dangerous to both production and human safety. The working face often stopped due to difficult maintenance of the gateways. 1.2 Simulation of gateway
12、deformation and failure with discrete element method The joint statistical results show that the surrounding rocks of the gateway are cut by two orthogonal joints, one group is the bedding plane of the coal measures, another group is normal to the bedding plane, mainly developed in the immediate roo
13、f. Because of the low strength of immediate roof, there often exist long joints that cross through the immediate roof. Such long joints play a dominant part in roof falling. According to the spatial distribution of joints, a discrete element model is built as shown in Fig.1.Thecomputing parameters r
14、equired are mainly based on measurement in field and some back analysis. The load applied to the model are gravitational stress field. The discrete elements are fully deformable so that he deformation of block can be involved. After the gateway is excavated, under the action of initial stresses, the
15、 upper sidewall coal firstly breaks, then the surface of the lower sidewall coal begins to yield. The abutments of the roof at the two sidewall transfer to deep solid coal in consequence .The immediate roof at the surface of the gateway begins to bend, bedding separate, fail and fall(see fig 2),as a
16、 result, large area of the roof falls until up to the main roof Some broken blocks may collapse when a small disturbance occurs, In the practical face, it is very difficult to deal with the fallen rocks, sometimes a chain collapse of upper immediate roof may occur if special attention is not paid, w
17、hich makes the fallen rock disposal a difficult and dangerous task. The results indicate that two sidewall coals fail differently the upper coal breaks more intensively than the lower sidewall coal. According to the above-mentioned analysis, it can be seen that in middle to lowly hard thin inclined
18、seam, the stability of the two sidewall coals is very important to the overall stability of the gateway. If the sidewall fails, then the abutments of the roof will transfer to deep solid coal, as a result the free span of the roof increases, which aggravates the unstable condition of the whole gatew
19、ay .Such failure of surrounding rocks is even serious when it is subjected to mining influence .It is, thus the key to keep the sidewall solid and intact in order to keep the overall stability of gateway in inclined seams. 2. Measurement of loosed zone around gateway Based on loosed zone theory of e
20、xcavation, a loosed zone is generally formed around the excavation if which the stress is lower than the initial stress. Owing to irregular shape of gateway in inclined seam and anisotropic media, the loosed zone around gateway is certainly in irregular shape. We use an ultrasonic joint detector(Typ
21、e SC-II by Fushun institute of Coal Science and Technology) to measure the loosed zone of the gateway. The test results are shown in Fig.3. The gateway was supported by two roof bolts 1.6m long with very slightly prestressed. The measured loosed zone is upper sidewall coal more than 1.8m, lower sidewall coal 1.4-1.5m, and the roof is 0.95-1.1m.
