In this paper, the effects of water-inrush from floor stratum caused by coal mining have been deeply studied, and the mechanism and influential factors of water-inrush have been analysed comprehensively by the finite element method and in-situ measurements. It is shown that the results calculated by F.E.M. agree well with those obtained in situ. The calculation has been done with the CBKD elasto-plastic finite element programme developed by the authors.
Cet article va presenter une recherche approfondie sur l'influence d'une exploitation sur le degagement instantane d'eau dans le mur d'une couche de charbon, par la methode de calcul des elements fini et les mesures pratiquees dans les mines. On va voir aussi 1'analyse du mecanisme de degagement instantane d'eau et les facteurs d' influence sur le degagement. Les resultats de calcul et de mesure sont essentiellement egales. D'ailleurs touts les calculs sont realises par notre programme elas-plastique d'element fini (CBKP).
In diesem Aufsatz werden druch Finite Elemente Berechnung und betriebliche Beobachtung der Einfluβ des Abbaus auf die Wasserzufuehrung erforscht, und auch das Prinzip der Wasserzufuehrung und der Einfluβfaktor analysiert. Die Berechnungsergebnisse sind mit den betrieblichen Meβdaten grundsatzlich uebereinstimmt. Auβerdem werden die ganz Berechnungen durch das eigene aufgestellte CBKP elastisch-plastisch Finit-Elemente Programm durchgefuehrt.
In this paper, the actual information collected from nine coal fields in North China has been used. It includes hundreds of inrushing cases (see ref. l). The observational data of water-inrush are taken into consideration during the processes of numerical analysis and the results obtained agree well with the data. An example selected is face 2701 in coal mine No.2 of Fengfeng Mining Administration where the geological conditions are typical in North China. They geological conditions are as follows: The length along face advancing direction is 350m the length along face varies from 70 to 120m, the inclination ranges from 100 to 200, the mining depth is 132 to 167m and the mining height is 1.5m. The mining area is surrounded by unmined coal seams and is free from large tectonics. The immediate roof consists of limestone 0–1.2m in thickness the main roof consists of mudstone and sandymudstone with thicknesses of 2.5m and 1.7m respectively. The floor strata are composed of fine-grained sandstone and mudstone 1–2m and 4m in thickness respectively. The seam and the karst strata are 52m apart. The water pressure in the karst is 1.23 MPa. The distance between the coal seam and the so called Large Green limestone is about 17m. The thickness of the Large Green limestone is 6m. It has been known as a highly water-bearing stratum. In the mining process, metal props were used to support the roof. The spaces between adjacent props are 0.8m along the strike and 0.6m along the face line respectively. A special observation tunnel was driven within the Large Green coal seam which is located 24m below the Small Green coal seam. It includes a drift 80m in length and an ascending working which is 70m long as shown in figs. l and 2. In each of the upper, middle and lower parts of the ascending working, these is a set of inclined boreholes to be used for strata movement observation, geophysical measurements and water pressure testing. All of these holes were drilled upward. Eight surveying ways were adopted:
The loading test for the props.
The stress distribution measurement of rock mass with oil pressure cells.
The strata movement surveying.
The tunnel movement surveying.
The fault movement surveying.
The water injecting test.
The borehole ultrasonic measurement.
The radio profile measurement.
The results of comprehensive analyses of the data in situ are as follows: 1st zone: it ranges from 0 to 32m ahead of the coal face, called the ground pressure increasing area. The effects of the ground pressure in this area are as follows: with the face advancing, the roof pressure increases gradully. It may amount to several times of the original stress. Finally, it decreases to zero. The roof is compressed and subsides. The seam and the floor strata are also compressed. The deformations are about 1 to 14mm/m, mostly 2 to 8mm/m. The influenced depth is 15m below the seam being mined.
