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SUMMARY: This paper deals with drilling results through a weathered sequence of rocks using two different drilling methods: down-the-hole hammer and diamond core drilling. Rate of penetration is log-related with rock physical parameters(density; Vickers microhardness; Ultrasonic longitudinal velocity) and rock mass quality (R.Q.D.). Calculated specific energy also shows the same variations in the uppermost part of the drilling profile as the indicated physical parameters. It is this same portion of the hole the major difficult part for the drilling operation. RESUMÉ: Dans le travail on presente des resultats de forabilite dans des sequences de roche alterees en utilisant deux methodes de forages: marteaux en fond de trou et carottage rotatif avec outil diamantee. La vitesse de forage presente des relations diagraphiques avec des caracteristiques physiques des roches (densite; microdurete Vickers; vitesse lalgitudinal des ultrasons) et la qualite du massif de roche (R.Q.D.). L'energie specifique de forage calculee presente des variations importantes dans la partie superieur du puit comme les paramètres physyques. Cette même partie du puit c'est nonnallement la plus difficile à traversee pour les foreurs. ZUSAMMENFASSUNG: Dieses referat befabt sich mit bohrergebnissen durch eine vezwitterbe gestensfolge, unter benutzung zweier verschiedener bohrmethodem: sinkbohrloch hammer und diamantkernbohrung. Die bohrgeschwindigkeit ist mit den gesteinsphyskalischen parametern(dichte; vickers-rnikroharte;ultraschalllongitudinalgeschwindigkeit) und der gebirgsqualitat(R.Q.D.) log-verbunden. Die berechnete spezifische energie zeigt im obersten teil des bohrprofils auch die gleiche variation wie die angegebenenphvsikalischen parameter. Es ist genau dieser abschnitt des bohrloches, der den schwierigsten teil fur den bohrablaufdarstellt. 1 INTRODUCTION Drilling through weathered rocks is always a concern for the drilling engineer. Not only intact core samples are difficult to obtain from weathered materials but also when drilling through weathered rocks the sudden and sometimes unexpected changes in drillability requires special attention by the operators. Two types of drilling operations (waterwell drilling using down-hole hammers and diamond coring for geotechnical site investigation) supplied a large amount of data which can be considered of interest for drillability characterization of weathered materials. In a previous paper (MELLO MENDES & MOURAZ MIRANDA (1979)was shown how physical parameters varied along drilled cores on different grades of weathered greywacke. 2 FIELD WORK AND RESULTS Down-hole drilling is a common practice by water well industry in granite and metassedimentary schist-greywacke areas in Portugal (MOURAZ MIRANDA,1982) Drilling diameters are commonly 215 mm and 165 mm. The larger diameter is used for the first part of the hole to 10–15m depth. Rotary diamond core drilling is normally conducted with 86 mm for the beginning of the role and 76 mm for the rest of the drilling, for geotechnical site investigation. Using data from drilling recorders mounted on rigs it was possible to use as a field drilling parameter the instantaneous rate-of-penetration (R.O.P.) Collected cuttings from down-the-hole drilling enabled same physical characterization of drilled rock Vickers microhardness (VHN)and density (d). The diamond cored samples enabled the use of one more physical parameter:longitudinal ultrasonic velocity (VL). A typical section through weathered granite is shown in Fig.1 Diamond drilling was conducted close to a down-hole drilled hole. The intermediate top part of the weathered profile shows the most irregular variation of all the parameters (R.O.P.; large dispersion of VHN). Using data gathered from several drilled holes (±50) in different rock types since top-soil to sand rock it was found that R.O.P. decreased from top to bottom of the hole with large variations in intermediate part of the profile. Calculating the specific energy of drilling, using BULLOCK (1976) formulae as in MOURAZ MIRANDA & MELLO MENDES(1983), it is possible to observe some correlation with the measured physical parameters. Fig.2 indicates the calculated specific energy for the weathered profile of Fig.1 with reduction of the specific energy in the beginning of the hole followed by a steady increase with depth. Trying to understand the small variations on the production parameter(R.O.P.) in terms of geological variations the RQD was also noted (Fig.2). The upper part of the profile can be considered almost a soil and the intermediate upper portion a mixture of soil and rock. 3 INDICATIONS FOR DRILLABILITY PREDICTION OF WEATHERED ROCKS As per our knowledge it does not exist the universal optimum drilling method for a weathered sequence. The upper part of the profile where drilling parameters show an irregular variation and to an unknown depth. Per drillers practice the selection of the drilling method is done empirically, with economic consequences, whim could be optimised if the distribution of the various weathering degrees within a profile could be predicted in advance, particularly for the most weathered part. Our aim of investigation was to predict the correction of drilling operation, optimizing it through the control of actual drilling parameters.
- Geology > Geological Subdiscipline > Geomechanics (0.72)
- Geology > Rock Type > Igneous Rock > Granite (0.50)
ABSTRACT: At Panasqueira mine the mining method for the subhorizontal quartz veins has changed from longwall stopes with partial filling to room and pillar stopes. To obtain with the last referred, under safe conditions, the maximum ore recovery, it became necessary to design different stope patterns. based on the knowledge of the geomechanical implications of mining. The paper describes the fundamental part of this knowledge which data collection began more than 25 years ago. The geological and geomechanical characteristics of the rock mass, Where low deformable schists are dominant, are referred. The behaviours showed by both the longwall and the room and pillar stopes, as well as its interpretations, are described. The subsidence and also the whole mine stability are analysed on the basis of the actual knowledge and considering the modifications to be implemented on the stoping method. RESUME: A la mine de Panasqueira, la methode d'exploitation des filons de quartz sub-horizontaux a evolue de la longue taille avec remblayage partiel jusqu'aux chambres et piliers. Pour obtenir, au moyen de ces dernières methodes, en de bonnes conditions de securite, un maximum de recuperation du gisement, il fut necessaire d'envisager des variantes basees sur la connaissance des implications geomecaniques de l'exploitation. Dans ce travail on presente l'essentiel de cette connaissance dont l'acquisition se fait depuis 25 annees. On mentionne les characteristiques geologiques et geomecaniques du massif, ou prevalent des roches schisteuses très raides. On refere les comportements observes dans les chantiers tabulaires de longue taille et de chambres et piliers, tout comme les interpretations correspondantes. La subsidence et la stabilite generale de la mine sont analyses, d'après les connaissances obtenues jusqu'à present, et aussi face aux variantes d'exploitation qu'on envisage d'introduire. ZUSAMMENFASSUNG: In Bergwerk Panasqueira hat sich das Abbauverfahren der subhorizontalen Quarzgaenge von Strebbau mit Teilversatz in Kammerpfeilerbau geaendert. Um mit diesem letzteren Verfahren, und unter guten Sicherheitsbedingungen, ein Maximum an Lagerstaettengewinnungsgrad zu erreichen, wurde as noetig, auf Grund der Kenntnis der geomechanischen Auswirkungen des Abbaus, Varianten zu entwerfen. In der Arbeit wird das Wesentliche jener geomechanischen Kenntnis vorgestellt, mit deren Erwerbung vor mehr als 25 Jahren begonnen wurde. Die geologischenund geomechanischen Merkmale des Gebirges, in dem sehr gering Schiefergesteine, werden angegeben. Danash werden die in den tafeligen Streb-und Kammerpfeilerbauen beobachteten Verhalten erwaehnt, sowie der darueber gemachten Auslegungen. Abschliessend, werden Betrachtungen aufgestellt ueber die im Licht der bis jetzt gewonnenen Erkenntnisse untersuchten Gebirgssenkung und allgelneinen Bergwerksstandfestigkeit, angesichts der gegenwaertig eingefuehrt werdenden Varianten des Abbauverfahrens. INTRODUCTION At Panasqueira mine, the greatest underground wolframite production unit in the world, subhorizontal quartz veins with some tens of cms in thickness are mined, being the distance between them usually of some metres; in a more rigorous description we can say that geological units, which for exploitation purposes are named veins, are in fact formed by series of quartz lens. The referred veins can be regularly mined by subhorizontal tabular stopes. As shown in fig.1, the orebody as a whole has a tendency to dip to SE. The exploitation of a multiple Vein system necessitated the development of a complex access and haulage network, the actual extent of which is illustrated in fig.2. The constant increase in production costs forced to perform an evolution on the stoping method, along the years; the follow up of this evolution, partially assisted by the progress on the mining equipment, only can be carried out within acceptable safety levels if an improvement on the existing geomechanical knowledge of the mine is achieved. We can say that, from the start of the mine exploitation, towards the beginning of this century until the Sixties, the several stoping methods used were not very different from the conventional longwall, sometimes filling partially the voids using blocks of surrounding waste rock to build packwalls or using some other support systems which were expected to (Figure in full paper) perform the same role of the packwalls. After the sixties and for economical reasons related with the unbearable costs of erecting packwalls, longwall methods were replaced by room and pillars in which mechanization, introduced at pre-programmed steps, is now a fact. However, a final satisfactory solution for the main problem of this method which is the attainment of an acceptable level on the orebody recovery, has since then being under investigation. One attempt that during some time seemed ad equated consisted in total removal, with the help of timber-packs, of pillars which were previously left; but due to the cost increases both on timber and labour and the low value of wolfram, that solution soon became impracticable.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral > Silicate > Tectosilicate > Quartz (0.85)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)