【正文】 。lez Nicieza et al.,2001), either in breaking or in development of the coalbed (Hardgraves, 1983). 3. Conclusions Coalbed is still a major hazard affecting safety andproductivity in some underground coal mines. This paper highlights the propensity of the 8th Coalbed to give rise to gas outbursts, due to fulfilling a series of risk factors, that have been quantified for 8th Coalbed for the first time and that are very related to mining hazards: gas pressure and its variation, with high valuesmeasured in the coalbed, obtaining lower registers at Montsacro than at San Nicol225。s (where 480 kPa were reached in the gas pressure measurements at the greatest depth). These parameters, together with the systematic measurement of concentration and desorption rate that were already being carried out by the mine staff, require monitoring and control. A gasmeasurementtube set was designed, for measuring gas pressure and its variations as well as the influence of nearby workings to determine outburstprone areas. The efficacy of injection as a preventative measure was shown by means of these measurement tubes. Injection decreases the gas pressure in the coalbed, although the test must be conducted maximizing all the precautionary measures, because gas outbursts may occur during the process itself. The instrumentation results indicated the convenienceof mining the 7th Coalbed at least one sublevel ahead of the 8th Coalbed. This means having pleted longwall caving of the corresponding sublevel both eastward and westward, and having allowed the necessary time to elapse for distention to take effect. This distention time was estimated between two and three months. The constructed instrumentation likewise allowed the effect of overlapping of workings to be measured: as the longwall caving of the coalbed situated to the roof of the instrumented coalbed approaches the area of advance of the 8th Coalbed, an increase in the pressure of the gas is produced in the 8th Coalbed. This may even triplicate the pressure of the gas and is more pronounced as the longwall caving approaches the position of the measuring equipment. A spatial range of the influence of longwall caving of some 55–60 m was estimated and a time duration of 2–3 months. The main contribution of this article resides in theproposal of measures of control and risk of gas outbursts that plement the systematic measurements in the mine itself, with the aim of improving safety in mining work. This proposal, apart from certain practical improvements in mining work, above all regarding the exploitation sequence, would involve the installation of gas measurement tubes before initiating the advance or at the overlap of workings. It would consist intemporarily detaining the advance in the 8th Coalbed when an overlap of workings may occur or prior to the mencement of an advance in the 8th Coalbed, installing measurement tubes in the face. The values and the trend of the measured gas pressures, together with the values obtained from gas concentration tests, would enable control of the conditions of the coalbed and the establishing of what moment would be appropriate to renew the advance. The gas measurement tubes would hence be a reliable, economic control and evaluation measure of the risk of gas outbursts. Furthermore, this equipment would enable the openingof other lines of research, both for calibrating the time and range of influence of mining work in each advance, as well as for calculating the permeability of the coal. By means of the designed test (gas flow between two gasmeasurementtube sets), permeability could be estimated by numerical models calibrated with site data, both in areas of the mine that have still to be affected by mining work and in those already subject to mining works. These calibrations would also allow the variation in permeability with the depth of the coalbed itself to be analyzed.References[1] Alexeev, ., Revva, ., Alyshev, ., Zhitlyonok, ., 2004.[2] True triaxial loading apparatus and its application to coal outburst prediction. Int. J. Coal Geol. 58, 245–250.[3] Alpern, B., 1970. Tectonics and gas deposit in coalfields: a bibliographical study and examples of application. Int. J. Rock Mech. Min. Sci. 7, 67–76.[4] Beamish, ., Crosdale, ., 1998. Instantaneous outbursts in underground coal mines: an overview and association with coal type. Int. J. Coal Geol. 35, 27–55.[5] Bra252。ner, G., 1994. Rockbursts in Coal Mines and Their Prevention. Balkema, Rotterdam, Netherlands. 137 pp.[6] Cao, Y., He, D., Glick, ., 2001. Coal and gas outbursts in footwalls of reverse faults. Int. J. Coal Geol. 48, 47–63.[7] Creedy, D., Garner, K., 2001. UKChina Coalbed Technology Transfer. Report N176。 Coal R207 DTI/Pub URN 01/584, 24 pp.[8] D237。az Aguado, ., 2004. An225。lisis, Control y Evaluaci243。n de Riesgo de Fen243。menos Gaseodin225。micos en Minas de Carb243。n, PhD Thesis, University of Oviedo (Spain) Publishing Service, .: 8483174340, 301 pp. (in Spanish, with English Abstract).[9] Durucan, S., Edwards, ., 1986. The effects of stress and fracturing on permeability of coal Min. Sci. Technol. 3, 205–216.[10] Flores, ., 1998. Coalbed methane: from hazard to resource. Int. J.Coal Geol. 35, 3–26