Ug mechanical excavation

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rock excavation, underground, different excavation machines, applicability, limitations, theories of rock interaction, cutting tools, pick lacing pattern, various picks, types of excavation machines,

rock excavation, underground, different excavation machines, applicability, limitations, theories of rock interaction, cutting tools, pick lacing pattern, various picks, types of excavation machines,

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  • 1. ROCK EXCAVATION MACHINES – UNDER GROUND U.Siva Sankar Sr. Under Manager Project Planning Singareni Collieries Company Ltd E-Mail :ulimella@gmail.com or uss_7@yahoo.com Visit at: www.slideshare.net/sankarsulimella Mechanical Rock Excavation 1
  • 2. Mechanical Excavation Systems Different mechanical excavation systems, like machines with; Teeth (Dozer, Shovel, Scraper, Bucket wheel excavator, Bucket chain excavator) Ripping tool (Coal Plough, ripper, rock breaker), Pick mounted rotary cutting head/drum (Roadheader, Shearer, Continuous miner, Surface miner) Disc cutters and button bits (rock drill, Mobile tunnel miner, Tunnel boring machine) Auger tool (Continuous Auger Miner, Surface Auger Miner) Application of Mechanical Systems Under Ground: Continuous Miners, Bolter miners, Auger Miners and shearers for coal or soft nonmetalics Boom type miners (road headers in soft to medium hard rocks) Rapid excavation equipment (Mobile tunnel miners,Tunner borers, raise borers, and shaft sinking rigs) for soft to medium hard and hard rocks) Surface: Rippers for very compact soil, coal, and weathered or soft rock Bucket wheel and cutting head excavators for soil or coal Augers and highwall miners for coal Mechanical dredges for placers and soilClassification of Underground mechanical excavator by rock type Hard rock Soft rock 1.Roadheader 1.Roadheader 2.TBM 2.Continuous Miner 3.Mobile Miner 3.Shearer 4.Raise BorerComparison of mechanical excavation with drill and blast systems Advantages Disadvantages• Generally gives more rapid advance than • Cannot excavate very hard rock blasting in soft to medium-hard rock. • High capital cost• Fewer unit operations • Require specialist maintenance• Smoother excavation profiles • Not as flexible• No blasting damage to surrounding rock• Inherently safer 2
  • 3. Parameters influencing applicability of mechanical miners The decision to introduce a mechanical miner is generally based on the predicted performance of the selected machine in the given geological and operational conditions. Since it is usually not possible to change the geological conditions, a thorough study of the geological and geotechnical parameters (rock mass and intact rock properties) at the feasibility and planning stages should be carried out to match the machine and operational parameters to the geological conditions. Machine considerations The general technical requirements of excavation machines, in addition to safety and economy, are selective mining ability, flexibility, mobility and hard and abrasive rock-cutting ability. Selective mining ability is the ability to cut selectively in mixed face conditions so that the mineral can be excavated separately, reducing dilution. Mobility means easy relocation of machines from one face to another, when necessary. Flexibility means easy adaptability to changing operational conditions, such as face cross-section shape (horseshoe, rectangular, circular, etc.), gradient, turning radius and unevenness of the floor.Machine considerations Hard and abrasive rock-cutting ability is the most important limiting factor on the performance of mechanical miners; applications show that strength, texture, etc., of the geological environment are the basic input parameters for the selection of mechanical miners and performance prediction. the most efficient type of tool in hard and abrasive rock.Geological and geotechnical considerations Rock mass features (such as joint sets, bedding planes, foliation, hydro geological conditions, deposit geometry, etc.) and intact rock properties (such as cuttability, abrasiveness etc).Operational considerations Mine layouts and development drivages are planned in accordance with the mining method, which is selected on the basis of orebody shape and dimensions and other deposit characteristics. For reliable, economic operation the characteristics and layout features of a mechanical miner should reflect whether it is to be used for the excavation of drifts or for ore/mineral. The layout might be modified for a particular mechanical miner if necessary. The back-up equipment (such as muck transportation, support, etc.) selected for a new mine must be chosen to be compatible with the mechanical miner. In an existing mining operation, however, the machine might be selected on the basis of the equipment already in use. 3
  • 4. Main influencing parameters for excavation Rock Rock composition Abrasivity (equivalent quartz content) Matrix Density (porosity/dry gross density) Strength: compressive-tensile-shear Destruction energy Post-failure behaviourMain influencing parameters for excavation Rock mass Joint structure: spacing, roughness, orientation Anisotropy: orientation, formation Primary stress conditions Weathering: type and degree Hydrothermal decomposition 4
  • 5. Compressive strengthDensity AbrasivityDiscontinuitiesMoisture contentInsitu stress conditionOther Material properties 5
  • 6. CM- Continuous Miner, MTM- Mobile Tunnel Miner, TBM- Tunnel Boring Machine Abrasivity of rock ■ Definition: Abrasivity describes the behaviour of rock with regard to its „grinding“ effect on metal surfaces, predominantly picks. Abrasivity is influenced by Rock type and composition Content of hard minerals (quartz, phyrite, hard silicates) Grain size of hard minerals Intergranular bond 6
  • 7. Abrasivity of Rocks 7
  • 8. 8
  • 9. Excavatability Index: N= Excavatability index Ms= Mass Strength number RQD= Rock Quality Designation Jn= Joint set number Js= relative ground structure number Jr= Joint roughness number Ja= joint alteration number 9
  • 10. Table: Mass Strength Number (MS) of rocks Fig: Joint Set Number (JN) for Rocks Fig: Relative ground structure (JS) of rocksFig: Joint RoughnessNumber (Jr) for Rocks 10
  • 11. Fig: Joint Alteration Number (Ja) for Rocks Assessment of Cuttability and excavation Index (Kirsten,1982)Road Header: Roadheaders are the most widely used underground partial-face excavation machines for low to medium strength rocks. They are used for both development and production in soft rock mining industry (i.e. main haulage drifts, roadways, cross-cuts, etc.) particularly in coal, sedimentary rocks, industrial minerals and evaporitic rocks. In civil construction, they find extensive use for excavation of tunnels (railway, roadway, sewer, diversion tunnels, etc.) in soft ground conditions, as well as for enlargement and rehabilitation of various underground structures. Their ability to excavate almost any profile opening also makes them very attractive to those mining and civil construction projects where various opening sizes and profiles need to be constructed. "Roadheading" machines with a cutter head designed to excavate stone rather than coal instead of drilling and blasting. This gives a more continuous process and should give a good drift profile. The use is limited by the grades involved (maximum 1in 4 (140) and the hardness of the material to be cut (maximum 60-150 MPa UCS). 11
  • 12. In addition to their high mobility and versatility, roadheaders are generally low capital cost systems compared to the most other mechanical excavators. Because of higher cutting power density due to a small cutting drum, they offer the capability to excavate rocks harder and more abrasive than their counterparts, such as the continuous miners and borers. Roadheaders were first developed for mechanical excavation of coal in the early 50s. The major improvements achieved in the last 50 years consist of steadily increased machine weight, size and cutterhead power, improved design of boom, muck pick up and loading system, more efficient cutterhead design, metallurgical developments in cutting bits, advances in hydraulic and electrical systems and more widespread use of automation and remote control features. All these have led to drastic enhancements in machine cutting capabilities, system availability and the service life. Machine weights have reached from 17 tons up to 120 tons providing more stable and stiffer (less vibration, less maintenance) platforms from which higher thrust forces can be generated for attacking harder rock formations. The cutterhead power has increased significantly from 37 kW approaching to 500 kW to allow for higher torque capacities. Modern machines have the ability to cut cross-sections over 100 m2 from a stationary point.In comparison to drill and blast methods, the main advantages of roadheaders are: One machine is capable of cutting, loading and assisting in the erection of supports. Compared with conventional driving, a greater advance per manshift is obtained. Roof control is improved since the roof and sides of the roadway are not shattered by shotfiring. The machine is very stable, easily controlled and capable of cutting a large variety of roadway sections and sizes. It is safer since the men are near to the unsupported strata only during the erection of supports. 12
  • 13. Classification of Boom Type road Header:Generation: Weight (Tonnes) Compressive Strength of Generation Rock to be cut (MPa) 1st (1960) 9 40 2nd (1970) 22 to 37 85 3rd (1976) 45 to 70 100 4th (2000) 120 100 to 160 Weight: Tucker (1985) classified roadheaders according to weight as: Class Weight - Light Duty; weight up to 30 t, cutting capabilities up to 70 0 <20 t MPa I 20-30 t - Medium Duty; weight between 34 to 45 t, cutting capabilities II 30-50 t up to 100 MPa III 50-75 t - Heavy Duty; weight over 45 t, cutting capabilities up to 150 IV >75 t MPa Atlas Copco – Eickhoff established the following classification according to weight (Schneider, 1988);Classification of Boom Type road Header: Neil et. al (1994) refer roadheaders as small size up to 30 t, midsize between 30 to 70 t and large size between 70 to120 t. Cutting Action of heads: Milling type or Borer Type (axial head), and Ripping Type (Transverse head) Fig: Cutting action of roadheaders a. Ripping type, b. milling type 13
  • 14. Borer type RoadheaderBorer type Roadheader 14
  • 15. Borer type Roadheader (Side view) Borer type Roadheader 15
  • 16. Ripper type Roadheader Ripper type Roadheader 16
  • 17. Fig: Double head or twin Boom RoadheaderCutting tools on Roadheader Radial picks are generally suitable for cutting soft to medium hard rocks and coal. Forward attack picks are also termed tangential picks, together with point attack picks due to the orientation of their tool axis. Such picks can also be used for cutting soft to medium hard rocks. Point attack picks, also known as pencil point tools, have been increasingly employed in medium to hard rock cutting and become an inevitable tool on medium and heavy duty roadheaders. 17
  • 18. Table; Factors influencing Cutting performance Fig. Comparison of cutting performance (Gehring, 1989) Cutting Mechanism in transverse head Roadheaders: Pick spacings around the cutting head are defined as line spacing (SL) and circumferential spacing (Cs) as shown in Fig. Line spacing is the distance between the cutting lines along the length of the cutting head and depends mainly on the depth of cut and cuttability of material being cut. Circumferential pick spacing is the angular distance between the picks measured perpendicular to the axis of rotation, which is mainly related to the angle of wrap, head diameter, line spacing, total number of picks, tool-holder size and additional space required for water sprays.Fig. Line and circumferential spacings on a cutting head. Fig: RH Cutting Action 18
  • 19. Fig. Lacing patterns of the first (unequal) and the second (equal) cutting heads. Fig. Breakout patterns of the experimental cutting heads. Manufacturing of equal spacing circumferential picks is not possible due to overlap of cutter picks. The performance of equal spaced picks is good in terms of breakout, vibration studies, but overall performance is not as good as unequal patterns. Pick consumption rate (pick/solid bank m3) varies from 0.049 to 0.044. If the rock is very abrasive or the pick consumption rate is more than 1 pick/m3, then roadheader excavation usually becomes uneconomical due to frequent bit changes coupled with increased vibration and maintenance costs. 19
  • 20. Continuous miner is a mining machine that produces a constant flow of ore fromthe working face of the mine. The machine continuously extracts as it is loadingcoal with a cutting steel drum and conveyor system.The continuous miner has been available in some form since the late 1800s. Thefirst machine to resemble a continuous miner was known as the English ChannelMachine.Continuous MinersThough there are many variations in design, continuous miners mostly consist offive main elements:A central body to carry all other components mounted on some type of drivemechanism to provide mobility (most commonly caterpillar tracks).A "cutting head" usually rotating drum(s) and/or chains with cutting picksattachedA loading mechanism to pick up cut coal and deliver it into the central part ofthe machineA conveying system, usually a chain conveyor running in a steel trough fromfront to rear of the minerA rear jib section capable of a degree of vertical and horizontal movement toenable the coal to be delivered into a transport or loaded at a desired point. Continuous Miners 20
  • 21. Continuous Miners For extraction of hard rocks, continuous miner is designed to have both Ripperveyor cutter head and chainless cutter head. The diameter of chainless cutter head is less than that of Ripperveyor Continuous Miner Rate of drivage –50 meters/day Production –1500 Tonnes/day For seams of 1 in 5 gradient and flatter Thickness of 3.0 m to 4.0 m 21
  • 22. Continuous MinerSome continuous miners (at one time almost all) could not cut the fullroadway width in one pass but had to be moved backwards and forwardsand from side to side in order to cut the full profile.This often results in a very rough rib line (bad for stability and ventilationflow) and delays the ability to install support into/under freshly exposedroof for a period. The advantages of the ability to cut the full profile in onepass was recognized early, but was not easy to achieve.Cutting forward in a straight line could be readily accommodated, but it isnecessary to be able to turn corners, mostly at right angles, and to be ableto retreat the cutting machine from one roadway to relocate at frequentintervals.These factors have proved major stumbling blocks to many developments.In machines which covered the full face, steering in the vertical planecould also be a major difficulty. 22
  • 23. The "ideal" continuous miner would: Be able to cut the full face in one pass Be easily moveable between locations without dismantling parts Be able to excavate right angle turns with a minimum radius Have roof and rib bolters fixed to the machine in a location where each row of the designed support pattern can be installed without moving the miner and be installed close to the cut face if necessary Have adequate space alongside to allow good ventilation of the face area for efficient removal of gas and dust. Fig: Mining of Steep seams with roadheader and miller head (drum-type) miners Overview of Continuous Miner machine Manufacturers 23
  • 24. Overview of Continuous Miner machine types vs. Operation heightsLacing pattern on CM Drums Fig: Continuous drum with pick boxes The arrangement of picks on the vanes is called a lacing pattern. CM drum(10) comprises a cylindrical body(11) having an outer cylindrical surface(12). Extending from the surface are start vanes with each vane extending angularly and longitudinally w.r.t. longitudinal axis of the drum. at the drum end there is clearance ring vane up on the picks are positioned On each vane number of picks are placed, each pick having leading, trailing and side faces Upon rotation each pick follows cutting path with adjacent picks at a spacing of 30 to 100mm. 24
  • 25. Fig: Pick Lacing Pattern on Continuous Miner drum for Coal25,26- End Rings, 27 Left Web Section, 29 Right web section 28 central web section Fig: Pick Lacing Pattern on Continuous Miner drum for Stone or Hard rocks 25
  • 26. Fig: Pick Lacing Pattern on Continuous Miner drumThe picks are placed on each vane at an attack angle of between 400 to500.The vanes extend angularly about at an angle 100 to 300The spacing between picks is 50mm to 90mm on drums used for coaland 40 to 50mm on drums used for hard rock cutting. 26
  • 27. CM SUMPING SEQUENCE 1CM SUMPING SEQUENCE 1 27
  • 28. CM SUMPING SEQUENCE 1CM SUMPING SEQUENCE 2 28
  • 29. CM SUMPING SEQUENCE 3CM SUMPING SEQUENCE 4 29
  • 30. CM SUMPING SEQUENCE 5CM SUMPING SEQUENCE 6 30
  • 31. CM SUMPING SEQUENCE 7CM SUMPING SEQUENCE 8 31
  • 32. CM SUMPING SEQUENCE 9CM SUMPING SEQUENCE 10 32
  • 33. CM SUMPING SEQUENCE 11CM SUMPING SEQUENCE 12 33
  • 34. CM SUMPING AND SHEAR SEQUENCE SDSH 1 CM SUMPING AND SHEAR SEQUENCE SDSH 1 2 34
  • 35. CM SUMPING AND SHEAR SEQUENCE SDSH 1 2 3 CM SUMPING AND SHEAR SEQUENCE SDSH 1 2 3 4 35
  • 36. CM SUMPING AND SHEAR SEQUENCE SDSH 1 2 3 4 5 CM SUMPING AND SHEAR SEQUENCE SDSH 1 2 3 4 5 6 36
  • 37. CM SUMPING AND SHEAR SEQUENCE SDSH 1 2 3 4 5 6 7 CM SUMPING AND SHEAR SEQUENCE 8 9 SDSH 1 2 3 4 5 6 7 37
  • 38. Auger Mining: The potential for underground coal production from drilling or augering machines has been recognized since at least the 1940s. These machines could bore into the virgin coal from stabilized entries and provide access to otherwise sterilized coal reserves. Auger drills mounted with cutterheads cut and fracture through both overburden and coal, operating very similar to a drill machine. The cutting action of an auger differs from other coal cutting machines, such as continuous miners, in that it exploits the lower tensile strength of coal rather than overcoming the comparatively high compressive strength of coal. Therefore, auger drills are able to generate a greater amount of power in cutting coal than a continuous miner. This makes augers more efficient in terms of the power needed to cut the coal. There are Thin seam auger miner for extraction in thin UG seams and Surface auger Miner for extraction of seams from highwall of open pit mines Fig: Auger Miner for Thin seam extraction 38
  • 39. Auger performance is principally governed by two main factors; machinepower and cutter head diameter.The greater the power available the deeper the penetration and the higher themining rate, for the same machine configuration.The larger the diameter of the cutter head the greater the rate of productionper metre of hole advance and hence the higher the mining rate.Thin seam miner (TSM) is actually a type of continuous miner that can cutseams from 0.6m to1.2m height and up to 1.5 m high into a coal seamsituated under a highwall in surface minesAugers drills used in surface mining can range from 18 to 61 m in length to twoto seven feet (0.6 to 2.1 m) in diameter. The cutter head on the auger bores anumber of openings into the seam, similar to how a wood drill produces woodshavings. The coal is then extracted and transported up to the surface via thespiral action of flights. Additional auger lengths or flights can then be added asthe cutter head penetrates and drives deeper down into the bored holeAuger mining is a low-cost method of recovering coal from horizontal orslightly pitched seams exposed through geological erosion. The practice ofauger mining is reserved primarily for extracting coal at depths of up to 1,000feet (305 m).One of the drawbacks is that once the cutter head enters the coal seam, theoperator is unable to view the cutting action directly and must rely more on asense of feel for the machine to determine potential problems. Auger AdvantagesProven ability to mine a cleaner coal productProven selective mining capabilitiesExtremely low ground pressureHeavy duty construction for hard cuttingRemote control capabilitiesProven low cost solutions for Ultra Thin Seam Mining 39
  • 40. FiG: Surface Auger Mining High wall Mining Technology – Auger Type• Consisting of single or dual cutting heads with coal being cleared by spiraled flights, creating circular entries 40
  • 41. High wall Mining Technology – Auger TypeDUAL HEAD AUGER Fig: Auger Cutter head and Auger Flights 41
  • 42. Coal Ploughes Essentially a plough is a large mass of steel, usually of a more or less triangular shape when viewed from the coal face or goaf sides, fitted with large "picks" (more like small agricultural plough blade tips) angled from the steel body towards the coal face. The plough height is the working height in the seam being mined (possibly a bit lower if the coal tops can be guaranteed to fall once the coal below is cut. These "picks" act in a fashion similar to chisels and break a narrow web of coal off the face (of the order of 300-400mm thick). In most cases there are no moving parts on a coal plough. The plough itself is mounted on the front of the AFC and is pushed into the face by push cylinders mounted in the supports. The plough has an endless chain haulage attached to the rear, and is driven through sprockets on electric drive(s) at the face end(s).Coal PloughesThe main advantages of ploughs compared to shearers are: Cheap Simple (no moving parts on the cutting machine itself) Relatively low dust make Able to keep exposed roof area very small (but a large number of chock movements would be required to maintain this)Though only a small web is taken, in the right conditions production rates can be comparable to a shearer as the plough is operated at a relatively fast speed along the face.Some disadvantages are: Cutting height is fixed Ability to cut stone is limited With increasing cutting height, machine stability becomes more problematic Grading can only be done using the AFC angle There are safety implications with an exposed chain haulage. 42
  • 43. Plow SystemsPlow systems are intended for coal miningin flat and inclined seams with theinclination up to 40° with coal hardness upto 40 MPa in seams with the height rangefrom 0.6m to 1.8m In dependence on seam thickness and mining conditions plow systems can be operated either with powered roof support or with individual hydraulic support (pit props) Mining Machines Division Plow SystemsBASE PLATE PLOWThe plow system using atypical pan line with plow guide andplow chain on the goaf side.Advantages• It is very suitable forextremely low seams from0.6m.• Easy access to a tow chainof the plow.• High safety while handlingwith a tow chain also ininclinations. Disadvantages • Losses due to friction of the plow body bottom plate on the floor. 43
  • 44. Plow Systems SLIDING PLOW The plow system using atypical pan line with plow guide and plow chain on the face side. Advantages • It is intended for seams from 0.9m to 1.8m. • Well controllable even when the floor is rolling. • Low losses due to friction by a plow body. Disadvantages • It is unsuitable for seams less than 0.9m. • Not easy access to a tow chain of the plow. • Difficult and dangerous while handling with a tow chain. Plow SystemsAdvantages Disadvantages• It is very suitable for extremely low seamsfrom 0.6m. • Losses due to friction of the plow body• Easy access to a tow chain of the plow. bottom plate on the floor.• High safety while handling with a tow chainalso in inclinations.BASE PLATE PLOWThe plow system using atypical pan line with plow guide and plow chain on the goafside. 44
  • 45. Plow Systems Advantages Disadvantages • It is intended for seams from 0.9m to 1.8m. • It is unsuitable for seams less than• Well controllable even when the floor is 0.9m.rolling. • Not easy access to a tow chain of the• Low losses due to friction by a plow body. plow. • Difficult and dangerous while handling with a tow chain. SLIDING PLOW The plow system using atypical pan line with plow guide and plow chain on the face side. Shearers A shearer consists of a machine body containing electric motors, hydraulic equipment and controls which is mounted over the AFC. Horizontal cutting drums are mounted on the face side of the machine, laced with cutting picks and rotating in a plane parallel to the face. If the AFC is pushed towards the face as the cutting drums are rotated and the shearer travels along the face, it is able to cut into the face for the full web width, moving along a snake in the AFC. This is known as "sumping in". Once fully into the web, the shearer can advance the full length of the face cutting out the web. The snake can also be reversed to cut the wedge shaped portion of coal left while sumping in. 45
  • 46. ShearerLarge diameter drums could have a pre-cutter to aid inrib face control on the longwall face. Pre_Cutting Fig: Shearer Drums with Radial and Point attack picks Fig: Side view of Shearer drum 46
  • 47. Fig; Positioning picks on shearer drumsPositioning picks on shearer drums Shearer drums consist of several spiral vanes and a backplate welded on a hollow drum shell. The spiral vanes serve for cutting and loading, while the backplate is mainly used for corner cutting at the face side to relieve the cutting action of the vane picks. The linear advance of a shearer drum per entire revolution is produced by the combined cutting actions of the vanes. Spiral vanes and the backplate provide space for the picks to be mounted on drums. Spiral vanes or cutting sequences on shearer drums are also known as ‘starts’, and the number of starts equal that of the spiral vanes. The total number of starts on a shearer drum varies(3,4,6) depending on the shearer drum design Picks can be classified according to their tilt angles and positions on the cutting head. The tilt angle is the angle between the pick axis and a plane perpendicular to the axis of cutting head rotation (Figure a). Picks, with their axes perpendicular to the axis of cutting head rotation, are named traversing or arcing picks, while those mounted on the region closer to the nose section of the cutting head, with individual tilt angles, are termed gauge picks. Sumping picks are placed on the nose section of the cutting head with their axes parallel to the axis of rotation of the cutting head. The last gauge pick on the face side of the cutting head is known as the corner cutting pick. 47
  • 48. Fig. Pick positioning on a shearer drum: (a) profile view of the drum (b) lacing of spiral and clearance ring picksPositioning picks on shearer drums A modern shearer drum also has three groups of picks cutting the coal seam while it rotates and transfers coal particles from the face onto the armoured face conveyor. The first group of picks that cuts most of the coal-seam, which are mounted on spiral vanes and correspond to the traversing picks on the roadheader cutting heads, are named vane picks. The second group of picks mounted on the backplate section of the shearer drum, and corresponding to the gauge picks on the roadheader cutting heads, are termed clearance ring picks. Today’s shearer drums also have some sumping picks mounted on the outer face of the clearance ring to provide extra protection for the drum The arrangement of clearance ring picks on the shearer drum was reported to be more complicated than that of vane picks The forces required to cut the coal at a certain depth by a clearance ring pick were reported to be two to ten times higher than the forces needed to cut the coal at the same depth by a vane pick More the wear of the clearance ring picks than others 48
  • 49. Mobile Tunnel Miner (MTM)Characteristics and advantages Especially developed for hard rock tunneling and mining This method allows for any shape of tunnel (rectangular, horse-shoe or circular) The technology requires less cutting force than a normal TBM Combines the flexibility of a roadheader and the power of a TBM Mobile Tunnel Miner (MTM) MTM is able to excavate any shape of tunnel (rectangular, horse-shoe or circular) MTM works with the “Under cutting Technique” requiring less cutting forces than with a normal hard rock TBM. The cutting principle with under cutting disc cutters is highly efficient as it overcomes the lower tensile strength of the rock instead of higher compressive strength. The machine is equipped with a crawler unit and a gripper system. The unit allows the MTM to move without using the crawler. The MTM is equipped with 3,4 or 8 arms depending on the size of the tunnel. The muck is transported to the rear of the machine, similar to roadheader Fig: Schematic drawing of the cutting technique 49
  • 50. Tunnel Boring Machine (TBM)TBM is a full face excavator which cuts rock by means of disc cutters mounted on a circular revolving cutting head (figure 7.5). The following design features enable it to cut stronger rock than any other type of mechanical excavator. Large mass Hydraulic stabilising jacks High cutting force provided by hydraulic thrust rams Cutting discs for rock breakage by indentationBecause of the size and weight of the typical TBM, they are suitable only for the excavation of long straight drivages such as civil engineering tunnels. Tunnel Boring Machine (TBM) TBM provides a good, circular profile which is good for stability and ventilation but usually requires a false floor to be laid to create a flat floor for travel. Limited by grades involved and grade control can be problematic is some strata conditions. Not suitable for other than very gradual changes of direction (typically minimum 500m turning radius although tighter radius machines can be designed and utilized). Unlike drill and blast or roadheading methods, tunnel boring machines do not have the capability to readily vary the dimension of the excavation nor are they suitable in varying ground conditions. Disadvantages of TBMs High capital cost (several million dollars) Can only cut circular section Large turning radius (100 m) Time-consuming to install Minimum tunnel length of 2 km required to justify installation 50
  • 51. Wide choice of TBMs for rock tunneling with diameter > 14m for different ground conditions Open or Gripper type for hard ground Single shield – hard ground Double shield – hard ground EPB (Earth Pressure Balance Machines) – Soft ground, pressure< 7 bar Slurry and mix-shield – Soft ground with very high water pressure and large amounts of ground water Fig: Gripper TBM The largest diameter TBM, at 15.43 m, was built by Herrenknecht AG for a recent project in Shanghai, China. The machine was built to bore through soft ground including sand and clay. The largest diameter hard rock TBM, at 14.4 m, was manufactured by The Robbins Company for Canadas Niagara Tunnel Project. 1 Cutterhead 4 Anchor Drilling Devices 2 Cutterhead Support 5 Wire Mesh Erector 3 Ring Erector 5 2 1 4 3 Fig: Gripper TBM 51
  • 52. A TBM breaks rock with disc cutters mounted on the rotating cutter-head in such a pattern that they roll against the rock of the tunnel face in a series of concentric circular grooves or kerfs. The cutting force is produced by powerful hydraulic thrust rams. Each disc cutter is free to rotate within its mounting. The high cutting forces required to break strong rock types produce equally high reaction forces on the machine. To maintain contact with the rock and to maintain the optimum spacing between cutting grooves, the machine is held stable by a combination of its great mass and by hydraulic jacks (grippers) acting against the side of the tunnel. Broken rock is gathered from the floor by scoops mounted around the perimeter of the cutting head and discharged at the crown of the cutter head onto a belt conveyor that runs through the center of the machine Cutter head Grippers Conveyor 1. Start boring stroke 2. EndMain boringbody stroke 3. Start reset stroke Invert Front Thrust Rear Main scraper lift leg cylinder lift leg motors 4. End Fig: Cutting cycle of Atlas Copco TBM reset stroke Fig: Hydraulic jacks holding a TBM in place. 1. Cutter head 2. Front shield 3. Main beam 4. Gripper trolley 5. thrust cylinders 6. Belt conveyor 7. Ring beam erector structure 8. Shortcret Fig: Gripper Shield 52
  • 53. All types of hard rock TBMs excavate rock using disc cutters mounted in the cutter head. The disc cutters create compressive stress fractures in the rock, causing it to chip away from the rock in front of the machine, called the tunnel face. The excavated rock, known as muck, is transferred through openings in the cutter head to a belt conveyor, where it runs through the machine to a system of conveyors or muck cars for removal from the tunnel. Cutter head of soft rock TBM does not use disc cutters only, but instead a combination of tungsten carbide cutting bits, carbide disc cutters, and/or hard rock disc cutters.Fig. Disc type cutter. Fig. (a) Kerf cutter (b) Pineapple cutter. Different Cutter Heads - TBMs 53
  • 54. 54
  • 55. Single Shield TBM 1.Cutter head 2.Shield 3.Belt conveyor 4.Excavated material removal trolley 55
  • 56. Double Shield TBM 1. Cutter head 2. Shields 2a - Front shield 2b - Double shield 2c - Rear shield and gripper Belt conveyor Excavated material removal trolley 56
  • 57. EPBMsFig: Schematicrepresentation of EPBM 57
  • 58. Fig: Schematic representation of EPBM Fig: Types of Cutting face of EPBMs Schematic representation of a slurry type shield machineCutting head sketch of slurry type shield 58
  • 59. Types of cutting face of slurry type shield 59