SYNOPSIS:

The regularity with which mining excavation affects neighbouring orebodies is very important in metal mines, particularly those of considerable depth. Based on observations in dangerous locations the regularity is described with which rock pressure occurs. Moreover there is a report on deformation measurements carried out at a depth of 1000 m over a period exceeding 2 years, On the basis of these field observations, the modelling work and analytical investigations it will be shown that the regularity of the displacements and failure mechanisms which occur typically near orebody openings, can be explained by using the stability theory of plates.

RESUME:

Le processus d'exploitation a une influence importante sur les galeries situees près de gisements, surtout dans le cas de mines profondes. Cette communication precise la regularite du mouvement de pression des terrains observe lors d'etudes dans des zones dangereuses. D'autre part on donne les resultats de deux annees de mesures du deplacement de la roche alentour de galeries creusees à une profondeur de mille mètres. La recherche sur modèle et l'etude theorique realisee à partir des donnees obtenues demontrent que la theorie d'instabilite des plaques peut expliquer la regularite du deplacement et le mecanisme de rupture qui se produisent dans les galeries près de gisements.

ZUSAMMENFASSUNG:

Die Regelmaßigkeit, mit der der Abbau benachbarte Erzkörper beeinflußt, ist fuer Erzgruben von großer Bedeutung, insbesondere bei Gruben großer Teufe. Ausgehend von Beobachtungen in gefahrlichen Grubenbereichen wird die Regelmaßigkeit beschrieben, mit der der Gebirgsdruck auftritt. Ferner wird ueber Deformationsmessungen von ueber zwei Jahren Dauer in 1000m teufen Gruben berichtet. Aufbauend auf diesen Gelandebeobachtungen, Modellversuchen und analytischen Untersuchungen wird gezeigt, daß die Regelmaßigkeit der Verschiebungen und Bruchmechanismen, die typischerweise in Strecken in der Nahe von Erzkörpern auftreten, mit Hilfe der Stabilitatsanalyse von Platten erklart werden kann.

DISPLACEMENT OF SURROUNDING ROCK IN OPENINGS NEAR OREBODY

As shown in Fig.l, the angle of dip of ore body is between 80 and 85. Its hanging wall is composed of firm white marble and footwall of interstratified band of thin marble, slaty phyllite, etc. The measured openings lie in the footwall, 980 meters below the ground surface. The measuring points of displacement in both sides are arranged at four different regions A,B, C and D. In each group of measuring points, three measuring rods, 0.5m, 1.5m and 2m long, are contained. The layout of points is shown in Fig.1. The main results of measuring are as follows: a) An increase of displacement is closely correlated with excavating process and regularly varied with its productive operation. Fig. 2 is the representative of hundreds displacement-time curves, which-clearly expresses the variation of displacement velocity at different stages. b)When the sublevel is not worked, a chamber can only obviously influence on the opening within that chamber range. In Fig.3, it is shown that group B which is 10 m from chamber is slightly influenced by stoping, whereas group A situated beyond 60 m is almost not influenced. Practical data of group A indicate that under certain conditions the variation of displacement of surround rocks in openings against time is negligible. Indeed, u-t curve reflects the relationship between displacement and productive factors under the present conditions.

REGULARITY OF GROUND PRESSURE APPEARED IN OPENINGS NEAR ORE BODY DURING SUBLEVEL

  • In sublevel stoping the critical time of ground pressure activation against openings near ore body is at the time of pillar falling down. Before this time openings near ore body may be maintained by different supporting means. After it they will partially or entirely be destroyed, namely no methods can be used to maintain them. This phenomenon can be used as a precise signal which predicts the approaching of staged pillar failure.

  • It is very interesting that the form of final failured opening is similar to that of unfailured opening.

Depending on different factors such as thickness of orebody, structural features of rock mass and distance from orebody, it varies regularly. For example:

  1. Near thin ore vein (2–3m) When the surrounding rock in opening is of laminar structure, degree of failure of both sides is similar; when the surrounding rock is of massive structure, a interesting phenomenon appears, that is the wall near by the stope is entirely destroyed, whereas the opposite wall (away from the stope) is still intact (Fig. 7).

  2. Near thick ore vein No matter what the surrounding rock structure is, the failure reaches up to the roof and makes opening entirely choking up.

  3. Near the intersection of level excavated along the, vein and cross level: A special kind of large scale fall in the form of "pull out" often occurs in the foof (Fig. 8). This made of falling occurs only within the width of roof. Although the visible fracture occurs inside the roof, there is still lack of any relevant fracture on the floor.

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