Jeolojik süreksizliklerin keskilerin kesme performansı üzerine etkisinin araştırılması

Abstract

Bu çalışmada jeolojik süreksizliklerin keskilerin kesme performansı üzerine olan etkisinin araştırılması amacıyla, İ.T.Ü. Maden Fakültesi Maden Kazı ve Mekanizasyonu laboratuvarlarında mevcut planya, piezoelektrik etki ile çalışan dinamometre, yük amplifikatörü ve verinin alındığı IBM PC-XT tipi bilgisayarda bulunan PC-26 analog dijital karttan meydana gelen küçük boyutlu lineer kazı seti NATO-TU Excavation projesi çerçevesinde kullanılmıştır. TSE 370 standartlarında alınan alçı, %60 su + %40 alçı oranında karıştırılarak 30*15*15 cm boyutlarında numuneler hazırlanmıştır. Jeolojik süreksizlikleri temsil edecek şekilde bu numuneler taş kesme atölyesinde, kesme yönüne dik, 45 derece açılı ve paralel olacak şekilde üç, beş ve yedi süreksizlik içerecek şekilde kesilmiştir. Kesme deneyleri sırasında, keski genişliği 12.5mm, kesme derinliği 5mm olarak sabit alınmış ve keskiler arası mesafe değiştirilerek kesme, normal, yanal kuvvetler ve birim hacimdeki kayacı kesmek için gerekli olan spesifik enerji ölçülmüştür. Aynı şartlarda yapılan deneyler üç defa tekrarlanarak deneysel hatalar minimize edilmeye çalışılmıştır. Bunun sonucunda 158 adet kesme deneyi yapılmıştır. Yapılan deney sonuçlarının incelenebilmesi amacıyla 486 DX-66 tipi bilgisayarda bulunan EXCEL 4.0 paket programı kullanılmıştır. Deney verileri burada grafiksel olarak analiz edilmiş ve bütün deneylerde süreksizlik aralığının kesme, normal, yanal kuvvetlere ve spesifik enerjiye olan etkisi ile optimum keskiler arası uzaklığın birim hacimdeki kayacı kesmek için gerekli olan spesifik enerjiye olan etkisi analiz edilmiştir. Masif olan numunelerden jeolojik süreksizlik içeren numunelere geçildikçe süreksizlik aralığının kesme kuvvetleri ve birim hacimdeki kayacı kesmek için gerekli olan spesifik enerji üzerinde etkili olduğu görülmüştür. Jeolojik süreksizlikler, kesme ve normal kuvvet üzerinde %25'lik bir azalma sağlamaktadır. Optimum keskiler arası mesafe masif olan numunelerde 1 iken jeolojik süreksizlik içeren numunelerde bu s/d oram 2 'ye çıkmıştır. Jeolojik süreksizliklerin bulunduğu formasyonlarda kazı işlemi yapılacaksa daha az kuvvet ve daha az keski sayısı ile kazı işlemi yapılabilir. Ancak bu deneyler gerçek kayaçlar üzerinde de yapılmalıdır.

Turkey has a large potential for tunneling in both civil works and mining. Nearly a total of 140 km/year of tunnels are being constructed for mine developments, drifts, raises and shafts, hydroelectric projects, underground storage, highway, metro, sewer and irrigation tunnels. Although rapid excavation systems, i.e. roadheaders and tunnel boring machine ( TBM ) have been used in few cases, tunnels are mainly driven by the conventional drill and blast methods which are slow and expensive. In some cases misselection of the tunneling machine has a catastrophic effect on tunneling costs. This is caused by the lack of research studies involving optimum cutting head design most suitable for the rock formations and the ground conditions encountered in the tunnel [7]. The majority of rock masses, particular those within a few hundred meters from the surface, behave as discontinua, with the discontinuities largely determining the mechanical behavior. It is therefore essential that both the structure of a rock mass and the nature of its discontinuities are carefully described in addition to the lithological description of the rock type. In time, as descriptions of rock masses and discontinuities become more complete and unified, it may be possible to design engineering structures in rock with a minimum of expenses in situ testing. A selections of terms commonly used in these methods are defined here. Joint A break of geological origin in the continuity of a body of rock along which there has been no visible displacement. A group of parallel joints is called a set and joint sets intersect to form a joint system. Joints can be open, filled or healed. Joints frequently form parallel to bedding planes, foliation and cleavage and may be termed bedding joints, foliation joints and cleavage joints accordingly. - X Fault A fracture or fracture zone along which there has been recognisable displacement, from a few centimeters to a few kilometers in scale. The walls are often striated and polished resulting from the shear displacement. Frequently rock on both sides of a fault is shattered and altered or weathered, resulting in fillings such as greccia and gouge. Discontinuity The general term for any mechanical discontinuity in a rock mass having zero or low tensile strength. It is the collective term for most types of joints, weak bedding planes, weak schistocity planes, weakness zones and faults. The ten parameters selected to describe discontinuities and rock masses are defined below: 1. Orientation: Attitude of discontinuity in space. Described by the dip direction and dip of the line of steepest declination in the plane of the discontinuity. The orientation of a discontinuity in space is described by the dip of the line of steepest declination measured from horizontal, and by the dip direction measured clock wise from true north. Example: dip direction/dip (025°/45°) 2. Spacing: Perpendicular distance between adjacent discontinuities.Normally refers to the mean or modal spacing of a set of joints. The spacing of adjacent discontinuities largely controls the size of individual blocks of intact rock. Several closely spaced sets tend to give conditions of low mass cohesion whereas those that are widely spaced are much more likely to yield interlocking conditions. These effect depend upon the persistance of the individual discontinuities. In exceptional cases a close spacing may change the mode of failure of a rock mass from translational to circular or even to flow. With exceptionally close spacing the orientation is of little consequence as failure may occur through rotation or rolling of the small rock pieces. 3. Persistence : Discontinuity trace length as observed in an exposure. May give a crude measure of the areal extend or penetration length of a discontinuity. Termination in solid rock or against other discontinuities reduces the persistence. Persistence implies the areal extent or size of a discontinuity within a plane. It can be crudely quantified by observing the discontinuity trace lenghths on the surface of exposures. It is one of the most difficult to quantify in anything but crude terms. 4. Roughness : Inherent surface roughness and waviness relative to the mean plane of a discontinuity. Both roughness and waviness contribute to the shear strength. Large scale waviness may also alter the dip locally. XI The wall roughness of a discontinuity is a potentially important component of its shear strength, especially in the case of undisplaced and interlocked features. The importance of wall roughness declines as aperture, or filling thickness, or the degree of any previous displacement increases. 5. Wall Strength: Equivalent compression strength of the adjadent rock walls of a discontinuity. May be lower than rock block strength due to weathering or alteration of the walls, an important component of shear strength if rock walls are in contact. The compressive strength of the rock comprising the walls of a discontinuity is a very important component of shear strength and deformability, especially if the walls are in direct rock to rock contact as in the case of unfilled joints. 6. Aperture : Perpendicular distance between adjacent rock walls of a discontinuity, in which the intervening space is air or water filled. Aperture is the perpendicular distance separating the adjacent rock walls of an open discontinuity, in which the intervening space is air or water filled. Aperture is thereby distinguished from the width of a filled discontinuity. 7. Filling : Material that separates the adjacent rock walls of a discontinuity and that is usually weaker than the parent rock. Typical filling materials are sand, clay, breccia, gouge, mylonite. Also include thin mineral coating and healed discontinuities, e.g. quartz and calcite veins. Filling is the term for material separating the adjacent rock walls of discontinuities. The perpendicular distance between the adjacent rock walls is termed the width of the filled discontinuity. 8. Seepage : Water flow and free moisture visible in individual discontinuities or in the rock mass as a whole. In the case of certain sedimantary rocks the primary permeability of the rock material may be significant such that a proportion of the total seepage occurs through the pores. 9. Number of Sets : The number of joint sets comprising the intersecting joint systems. The rock mass may be further divided by individual discontinuities. Both the mechanical behaviour and the appearance of a rock mass will be dominated by the number of sets of discontinuities that intersect one another. 10. Block Size : Rock block dimensions resulting from the mutual orientation of intersecting joint sets, and resulting from the spacing of the individual sets. Individual discontinuities may further influence the block size and shape [8]. The effect of geological discontinuities on cutting performance of drag tools was investigated in this thesis. A shaping machine and a piezoelectric transducer already XII existed in the Istanbul Technical University Mining Faculty and Mechanization Technology Department were used for the experiments. The following experimental set up was used during this investigation. A shaping machine equipped with a chisel pick having a rake angle of -5°, and width of 12.5 mm was used. This shaping machine works with 18 kW SIEMENS electrical motor. The dimensions of the work table are 30*40*50 cm. The Charge Amplifier Type 5001 is a mains-operated DC amplifier of very high input impedance with capacivite negative feedback, intended to convert the electric charge from a piezoelectric transducer into a proportional voltage on the low impedance amplifier output. The three- component measuring platform 925 7 A is a piezoelectric transducer for measuring forces in three components perpendicular to each other. For each of the three force components a proportional electrical charge is set up in the measuring platform. These charges are led into charge amplifiers where they are converted into proportional voltages which can be displayed or recorded as required. The measuring platform is designed on the basis of quartz three-component force measuring elements. This gives a very rigid measuring rig with correspondingly high resonant frequency, so that very rapid force changes can be measured. Samples with the dimensions of 30x15x15 cm were prepared by mixing 40% of plaster with 60% percent water. These samples were prepared in the rock cutting laboratory with 45 degrees angle parallel to the cutting direction in a way that it forms three, five and seven fractures representing geological fractures. During the cutting experiments normal forces, side forces cutting forces and specific energy were measured by taking constant cutting width of 12.5 mm and cutting depth of 5 mm. Experimental errors were tried to minimize by repeating the experiments three times under the same conditions. As a result of this 158 experiments were carried out. 486 DX 66 computer was used for analyzing the experimental results. Experimental data was analyzed graphically and effects of the fracture spacing on cutting, normal, side forces and specific energy and effects of optimum cutting spacing on specific energy were investigated during experiments. Effects of fracture spacing and S/d were searched by taking the tool spacing 0, 5, 10, 15, 20 mm and unrelieved conditions.. The experiments carried out with fractures perpendicular to the cutting direction shown that cutting and normal forces increased 25%, specific energy decreased in relation to the number of fractures per meter. Due to this fact optimum s/d ratio increases twice with increasing the number of fracture spacing. During the experiments carried out with the fractures taken 45 degrees to the cutting directions, the samples including 3, 5, 7 per sample were used. The effects of the geological fractures on the tool forces and specific energy were examined by taking XIII cutting depth of 5 mm and cutter width of 12.5 mm as constant and the tool spacing as variable. It is concluded that as the fracture distance increases, forces increases about 25%. The tests carried out on samples with fractures parallel to the cutting direction, showed that the geological discontinuities have not very significant effects on cutting parameters such as FC, FN and FS. This investigation in the laboratory showed clearly that geological discontinuities have a tremendous effect of tool cutting performance and such parameters should be taken in consideration when selecting a mechanical excavator and designing a cutting head.