Rock cutting techniques after Roxborough and Rispin, In the following discussion, predic- with successively smaller disk diameters giving a tapered or tion methods are placed into two broad categories depending on conical arrangement.
Frequently these multi-row disks employ whether the interaction model is theoretical or empirical. Care must always be taken the translatory motion of the cutting head, the disk rolls forward to determine whether quoted "cutting rates" refer to what may cutting a groove in the rock.
Cutting rates determined under highly con- important influence on cutting efficiency. Under typical operational Roller or mill-tooth cutting is similar to disk cutting except conditions, cutting time is generally taken as synonymous with that instead of a tapered disc edge, the tool is equipped with utilization.
Minor delays resulting, for example, from adjusting circumferential teeth Fig. As the cutter moves in re- the boom position at the end of each cutting traverse, or reduced sponse to rolling forces, each tooth in turn is pushed into the rates of production during final profiling, are neglected.
Cutting rock, acting like a wedge, and causing local failure. Clearly, performance predictions based Back analyses suggest Button cutters consist of cylindrical or conical tool bodies that operational cutting rates commonly have values in the range inset with tungsten carbide buttons Fig.
The tool is of 0. For final mounted in a bearing in the same way as disk cutters or roller profiling, this figure may drop to 0. Thrust forces cause high stress con- Specific energy is a commonly used measure of cuttability centrations beneath each button as they roll across the rock that is defined as the work done to excavate a unit volume of surface, resulting in local failure and pulverization of the rock.
In the context of rock cutting, specific energy should not The area of influence of each button is small and results in a be thought of as a fundamental property of the rock. Rather, it fine-grained product. Button cutting function of specimen size, shape, and test conditions. Measured is used in applications in which high rock strength and abrasivity specific energies are many times greater than theoretically deter- preclude the use of other methods.
These cutters also find appli- mined values, the difference being accounted for in energy lost cation as reaming cutters used for final profiling on RBMs and to frictional heating, vibration, and so on. Utilization is the time remaining for excavation when planned and unplanned machine stoppages have been accounted Stoppages are required for a variety of reasons including When considering the feasibility or cost effectiveness of em- support installation, survey work, pick replacement, routine and ploying a mechanical excavation system, the central questions non-routine maintenance,.
Clearly Advance rate is the rate of tunnel or drift advance, usually there is a need for a reliable method of performance prediction. First, machine performance in terms of cutting rates or penetration rates must be assessed.
In the following discussion, methods of predicting or estimating cutting rates or penetration rates will be described, The link between these three groups of data is provided angles.
All these models have certain weaknesses that limit their by what may be termed rock-tool or rock-machine interaction usefulness for solving practical problems in machine design and models, and the result of applying such a model is an estimate performance. In addition, materials are generally considered to tion is not required. Theoretical approaches gen- erally assume a simplified two-dimensional stress distribution, where o-c is unconfined compressive strength UCS , 8 is disk such as a point or line load, and neglect the properties of the edge angle, D is disk diameter, and p is depth of penetration.
Further, in practical they concluded that the failure process is controlled by shear cutting applications, multiple tools are arranged in a manner stresses acting on the plane connecting the apices of adjacent that promotes interaction between adjacent cuts, which has been grooves.
This Comparison of experimentally determined forces for Bunter introduces a further level of complexity to the three-dimensional sandstone with calculated values presented by these workers stress distribution that tends to be neglected in theoretical indicated good correlation.
Farmer and Glossop have models. Failure criteria based on both tensile and shear stresses has been Again, good correlation distribution changes during crack propagation. Thus a rigorous was demonstrated between calculated and observed Sip ratio for theoretical description of rock cutting must incorporate a sophis- Bunter sandstone. Using Eq. However, there can be little justification for spacing for a given penetration p can be calculated. Using this developing or applying such a failure model until equally sophis- value of p, it should then be possible to calculate Fr and Ft for ticated three-dimensional stress distribution models are individual tools, using Eqs.
The total number available. In the case of roadheaders, the limitations of can be determined. However, these will be overestimated because theoretical models are compounded by the relatively large num- Eqs. Fowell tical design approaches use empirical methods, as described in and McFeat-Smith, ], and a generally less-controlled cut- Cutting theories applicable to roadheaders are not considered sufficiently developed at this time to be useful as prediction tools and are not discussed further here.
In the case of full-face Boom-type Tunneling Machines excavation systems, theoretical modeling problems are less acute. Here, variations in cutter geometries are limited to variations in Because of the theoretical difficulties of modeling road- disk diameter and blade width.
In addition, the cutting process header cutting performance, approaches to this problem are es- is more controlled, involving relatively constant penetration rate sentially empirical. It can be claimed that theoretical considera- and depth of cut, and only a single cutting mode.
Because of this, tions have shed some light on which material and machine some progress has been achieved in the application of theoretical parameters have an important influence on performance, but cutting models, albeit oversimplified, to prediction of the per- while these parameters appear in many empirical performance formance of full-face TBMs.
The better theoretical models of equations, they are always associated with dimensionless con- TBM performance are widely used as prediction tools, however, stants derived from actual cutting trials or performance data. Whether the problem The simplest empirical prediction methods are based on the is in the model or in the ability of the sample or geotechnical extrapolation of performance records of specific roadheader data to represent the rock mass is not clear.
It is very difficult penetration in relieved cutting. Conversely, the models may pre- to collect high-quality roadheader performance data under other dict achievable penetration given machine constraints governing than the highly controlled conditions of a research project.
Per- available thrust and rolling forces. Correlation of laboratory specific energy and in situ spe- , Furthermore, a good match between geotechnical conditions at the proposed site and a past site may not exist.
Comparison of observed operational cutting rates and of British Coal Measure rocks. Application ofmultivariate statis- operational cutting rate predicted using data from McFeat-Smith tical methods to the results of laboratory tests enabled these and Fowell. Field specific energy was shown to be related to teraction model given by Eq. When rock Fig.
Included on this plot is a present. Many of the points model: included in Fig. It would appear, therefore, that these predictive equations instantaneous cutting rate.
This curve provides a very good up- may be applicable to a range of machines, provided that appro- per bound fit to the measured data, and in most cases shows that priate cutting time factor corrections are made.
Also, direct actual specific energy was less than predicted to achieve a given determinations of specific energy using core grooving tests could cutting rate. This may reflect the tendency of rock mass struc- be used in conjunction with Eq. Roadheader performance vs. Comparison of observed and predicted roadheader per- formance using Aleman's method after Aleman, The predictive a 12 equations are used in conjunction with a more sophisticated co Cl: machine model than that of Fowell and McFeat-Smith.
It is worth noting at this point that many of the indices or 4 parameters that appear in predictive equations, or are referred to in the literature as being significant predictors of roadheader performance, are often strongly correlated. Several parameters show strong correlation with unconfined compressive strength. Relationship between machine advance rate and rock compressive strength.
The results of this type of study provide a useful means of predicting performance of a specific machine type under a variety of geological conditions. But since the results are not presented low-strength, heavily fractured rocks corresponding to low in terms of specific energy McFeat-Smith and Fowell, RMR values. Two good examples of this type of rock material properties. Statistical analyses showed significant study have been reported by Sandbak and Bilgin et al.
Sandbak demonstrated correlations between performance Although the Pk 2r at other sites and found a reasonable correlation. These scatter in the results is rather large Fig. Cutting rates are lowest in strong rock with few machines provided that an adequate allowance can be made fractures, corresponding to high RMR values, and highest in for variations in head power. Needs correction lightweight- for other machine pow- mediumweight ers and non-shielded or road headers.
SL Hurt et al. Herrenknecht machine was shield mounted, a condition which deterministic in nature; however, actual case history data indi- generally results in a more rigid system and hence higher cutting cate considerable scatter even within a single rock type, which rates than for a non-shielded machine.
A better approach to both on fundamental material properties, have been proposed. Farmer the analysis of case history data and the prediction of machine and Garritty make use of a strain energy approach to performance is the use of probabilistic methods.
Using this ap- predict roadheader performance. Input data for this model in- proach, geotechnical and operational variables are input to the cludes DCS and deformation modulus of the rock mass. The analysis in the form of probability distributions, the output also machine model consists of head power coupled with an energy being in the form of a probability distribution.
Howarth , methods discussed above, including limitations on applicability. All of the approaches outlined above are etration rates from 20 case histories.
A brief review of these two methods is provided 1. Kd Farmer and Glossop derived a relationship between the average 1. Basic penetration as a function of drilling rate index DRI , average thrust per disk, and cutter diameter after Lislerud, with P measured in in. Conversion factors: 1 in. A similar equation has been suggested by Graham based on use of the Robbins TBM in hard rock with unconfined compressive strengths ranging from 20, to 29, psi to MPa.
As simple ratios are typically used to relate tensile and uniax- 3 Ill-IV ial compressive strength e. Lislerud III 10cm has developed a TBM performance prediction method based II - III on rock mass factors rock mass jointing, intact rock strength, I1 20cm brittleness, and abrasivity and machine factors thrust per cut- ter, cutter edge bluntness, cutter spacing, cutter diameter, torque As noted by Howarth , this method requires a consid- Empirical methods currently provide the best means of esti- erable amount of geotechnical and laboratory test data and is mating machine performance.
Such estimates can be made di- probably only suited to foliated, high-grade metamorphic rocks rectly based on previous experience in similar ground conditions such as those found in Scandinavia. In less anisotopic rocks, use or can utilize one of the predictive equations. In considering the of the simpler relationships suggested by Farmer and Glossop results, the user should be aware of the limitations of each and Graham is warranted.
Runge Cased Study and J. Zeni H. Hunter H. Hunter Crookston et al. Reference Source Mobilization days 5 12 7 4 Drilled depth ft Drilled diameter in. II system and to assist with method selection.
Ground l. System components and opera- tional considerations are described below. A generalized blind Fig. Schematic blind shaft drilling equipment setup. A shaft collar is typi- cally excavated using either an auger rig or conventional drill- and-blast mining during mobilization of the blind shaft drilling drill pipe and down-hole drill tools are supported by the mast equipment.
Collar depth depends on the overall length of the through a conventional crown and traveling blocklhook assem- bottom-hole drilling assembly and is designed so that the assem- bly. Static hook load capacities, for large-diameter blind-shaft bly can be positioned below the drilling rig's rotary table. The drilling, may range from several hundred thousand pounds kilo- collar may be lined with steel, shotcrete, or concrete, depending grams to more than a million pounds half million kilogram on ground conditions.
A cast-in-place, reinforced concrete foun- requiring more substantial masts than typically used for conven- dation will be designed to support the drill rig. Major components of the drilling rig include from the rotary table to the drill pipe using a square section kelly a mast and substructure, drawworks and tugger hoists, rotary bar.
Mud is pumped to the down-hole system via a swivel located table, crown and traveling blocks, hook, swivel and kelly.
The above the kelly. Mud circulation systems for Direct Circulation Reverse Circulation blind shaft drilling. Compressor Air compressor Air, mud Air, mud and cuttings These include the drill pipe plenum chamber in the drillbit and dual string drill pipe. Mud and bottom-hole drilling assembly. Drill pipe is selected based and compressed air are pumped down the outer annulus of the on maximum tensile and torsional loading conditions and consid- drill pipe to the plenum chamber where the air separates from eration ofmud circulation requirements; data sheets are available the mud.
Mud flows through the plenum chamber and is forced from the pipe manufacturers. A common US drill pipe, used for through fluid jets located in the bit in order to clean the hole large-diameter blind shaft drilling, has an outside diameter of 13 bottom. Cutters are mounted in Overflow from the first mud pit goes to the second and third cutter mounts or saddles and bolted to the underside of the flat- where the remaining cuttings settle out.
A cake of mud is deposited on the shaft that serves as a base for locating donut weights. Donut weights walls during drilling. The thickness and strength of this cake are added to provide the required normal force at each cutter may be optimized based on cuttings removal and ground support typically from 10, to 20, Ib Control of which is a function of the relative hardness of the formation to mud density and head i.
Donut weights are secured to the drill pipe by a hold- this impermeable surface permits shaft excavation in poor down clamp which forms the top of the bottom-hole assernbly.
The final lining for a blind drilled shaft the top of the bottom-hole assembly to assist directional control. An important element of blind shaft drilling with external guides to facilitate grout line deployment and is is to maintain a straight, vertical alignment. The key to effective outfitted internally. This maximizes the up to 60 ft 18 m in length. The liner is lowered into the mud- pendulum effect experienced by the bottom-hole assembly and, filled hole using either casing jacks or the drill rig.
Each liner in conjunction with stabilizers, provides a straighter shaft. Loads on the casing jacks circulation. Drilling mud is added to the hole at ground level may be limited, in the case of deeper shafts, by capping the and circulated through the cutters and up the inside of the drill bottom liner section so that the liner can be "floated" into place. Air is added inside the drill pipe causing a density imbal- Water is pumped into the casing to control buoyancy as the ance that induces flow rates sufficient to remove the drill capped liner is lowered into the shaft.
When liner installation is cuttings. Air-assisted reverse circulation and alternative mud complete, the annulus between the steel liner and the shaft wall circulation systems have been described by Lackey for is filled with grout. The BSB used a full-face rotary cutterhead equipped with 56, Management 2 in.
Drillhole surveys 1 Hendricks presents a detailed prediction of the per- Other inc. These include slip forming both bottom-up and top-down , jump forming, precast concrete cylinders, and remotely placed shotcrete. Finally, if ground conditions permit, First intro- may be used. Summary data for these case studies are presented in Table utilization.
Penetration rate is, in turn, a function of the geology The equipment, shown in Fig. Moss et al. Variations in average penetration controlled by the operator to provide the required penetration rates were smaller than expected and correlation with the index rate.
Muck is removed into a pilot hole by scrapers located on was poor. Several important observations were made as a result the cutterhead. The shaft lining is placed from work platforms of this case study: located above the gripper assembly providing a continuous exca- 1. Lower than predicted rates of penetration in clay were vationllining cycle. Services and support equipment are de- thought to be due to plugging of the bit.
Associated problems ployed using techniques traditionally associated with conven- included reduced mud circulation rates and poor control of shaft tional shaft sinking. In addition to the obvious differences in down-hole tools, 2. An increase in the rolling resistance when drilling in rock the V-mole requires a pilot hole for muck removal. The results of this study serve to illustrate the potential shortcomings in generic performance prediction systems.
The operational penetration rate for a blind-shaft drilling project can System components and opera- hole components corrected for buoyancy from the drilling mud tional considerations are described below. A generalized raise and imperfect hole cleaning Maurer, Table ConventIonal shaft to total project costs. It can readily be seen that the project costs collar excavation and lining techniques typically are used to are dominated by the acquisition and installation cost of the steel construct the raise collar.
The raise drill is positioned on a steel casing used for final lining. Blind-shalt-borer down-hole equipment courtesy: Robbins Co. It can be removed from the shaft, after the raise drill great care is taken to ensure that the pilot hole is drilled within and steel foundation are demobilized, using a small crane.
Directional surveys are routinely A comprehensive paper by Worden provides a de- performed every 25 or SO ft 7. A skid-mounted raise drill typically consists of a crosshead, Ground Support-Raises are commonly unlined since raise positioned between two cylindrical guideposts, and hydraulic boring is typically used in relatively competent formations. How- rams that lift the head and apply thrust, via the drill rods, to the ever, if ground conditions or use dictate the installation of a final reaming head.
Rotary motion is provided through a ring gear lining, there are a few rapid lining systems to choose from. A small proportion of The raise borer reaming head is transported underground raise-bored shafts have been excavated using an upward-drilled during drilling of the pilot hole. Underground set-up involves pilot hole with downward reaming to full shaft diameter.
The assembly and attachment of the reaming head to the raise drill advantage of reduced pulling capacity, associated with down- rods and preparation of the underground mucking system. Shaft size limitations in con- tor to provide optimum penetration for each stratum encoun- ventional raise boring are primarily associated with 'exponen- tered. As noted earlier in this chapter, practice involves maintaining the cutting pile flush with the mine the required torque is a function of the sum of the individual roof to reduce airborne dust levels.
Upper deck with Fig. Shaft boring machine, 20 to hydraulic and electrical panels 24 ft 6 to 7. Excavation of shaft diameters beyond the single- up to 32oo-ft m deep Schmidt and Fletcher, Many pass capability machine and drill-pipe capacity of onsite equip- of the early problems, typically associated with a protypical ment can be accomplished by reaming a smaller shaft with sec- method, have been resolved according to Schmidt and Fletcher ond-pass reaming to full size.
Reaming heads should be selected Outstanding issues, traditionally associated with large- to optimize the torque distribution and drilling load.
Stabilizers diameter shaft construction, include excavation in poor quality are essential when second-pass reaming in longholes to prevent and blocky ground, presence of large groundwater influx, and drill string whip. Alternatively, the raise may be sequentially the impact of pilot hole accuracy on final shaft verticality. This reamed in short sections. The two-stage sequential reaming head was first introduced in Blind Raise-boring-Blind raise boring, or boxhole drilling South Africa in as an alternative method of reaming larger- has been used in the South African goldfields to construct small- diameter, deeper shafts in hardrock.
In operation, the smaller diameter 5 to 6 ft [1. Raise boring can be conducted with a predrilled pilot This head is then retracted, and the remaining shaft area is hole or blind without pilot hole at advance rates between 4 and reamed by the larger head; this cycle is repeated until the raise 6 ft 1. The first sequential-head raise borer, using an 8-ft Raise-boring System Performance Estimation-System per- 2.
For Areas Goldmine. Assume From Eq. Predicted performance of shaft boring machine after detailed breakdown of a raise-bore contractor's bid is presented Hendricks, Wirth V-mole-vertical mole after Raine, As previously noted, the and geohydrological conditions, design criteria e.
This analysis equipment, plus a determination of their relative impact on proj- may be supported initially by conceptual designs as described ect cost and schedule. Cost is nominally the overriding consider- in this section. However, a final decision should be made in ation; however, timing may be critical, and higher shaft construc- consultation with personnel experienced in the field application tion costs may be off-set by rapid access to the ore body.
The geotechnical Factors influencing the selection of each shaft construction data set required for shaft design and construction bid package method have been assembled and are presented in Table The site investigation program should incorporate a At a broad conceptual level, the blind-shaft drilling method is fully logged core hole located within one shaft diameter of the preferred for conditions where proposed shaft centerline.
Note: a borehole on shaft centerline 1. Freezing would be required for groundwater control dur- is preferred; however, the verticality of this borehole may impact ing conventional shaft excavation. This borehole 2. Shaft lining requirements dictate the use of a fully hydro- should be geotechnically logged e. Rapid access outweighs added cost. Disturbance of the surrounding rock is a prime criterion. Samples may also 5. Access is not available for subsurface muck removal. Hydrogeologic data should be obtained by profiling the where borehole using a down-hole in line with drilling or straddle 1.
Adverse impacts of groundwater inflow can be economi- packer test tool. Data analysis will provide the location and cally mitigated prior to construction e. Redpath, 81 Norite, Gabbro 40, 2, 84 9. Redpath, 65 26, 1, 84 Redpath, 90 Fine-grained Calcite 14, 1, 1, 84 Redpath, 90 Quartz Diorite, Porphyry 34, 2, 96 Redpath, 90 40, 2, 96 Redpath, 90 20, 1, 1, 96 Redpath, 67 Silicified Limestone 44, 3, Redpath, Redpath, 70 Silicified Limestone 14, 1, Redpath, 65 Quartz Diorite 47, 3, Redpath, 90 Fine-grained Calcite 14, 1, Rock quality permits stand-up times compatible with the Under these conditions, raise drilling may offer a less costly V-mole's mining cycle.
Minimum disturbance of the surrounding rock is a prime criterion. Three rapid excavation systems are described in this seg- 7. Immediate access to drilled strata for geologic logging, ment, namely, full-face tunnel boring, mobile miners, and road- instrument installation, and testing is required. Data are included to 8. There are no existing mine openings BSB only. Site conditions e. Access is available for setup and underground muck re- Full-face boring systems or TBMs have been in common use 3.
Geologic structure permits pilot-hole drilling to the toler- in civil tunneling for many years but are used less' frequently in ances required by the shaft designer. Nevertheless, TBMs in European coal mines 4. Design requirements e. Alternative raise boring methods after Friant et al. Equipment available for most required raise inclinations. These experiences may the periphery of the cutter head, and muck is removed via a spur more widespread acceptance and utilization of this method central conveyor system.
Preparations for TBM excavation typically ment and improved tooling have resulted in machines that are involve portal construction, placement of a concrete pad on capable of advancing large-diameter openings in strong igneous which the TBM will be assembled, and installation of support and metamorphic formations at rates that compete favorably, services and equipment.
Careful excavation, including the use of and in many cases exceed, conventional drill and blast methods. TBM excavation profile and minimize ground support requirements. A disadvan- is a continuous process, with cutting, mucking, and support tage of TBMs is their wide turning circle, although a range of installation proceeding concurrently.
As the cutting head rotates, mini-fullface machines are available that have smaller turning it moves forward, reacting against the grippers. The grippers are radii. The high initial cost of these machines is balanced by low repositioned periodically when they reach the limit of their running costs compared to drill and blast excavation systems.
Robbins and Domag TBMs steer while boring of a hard-rock double-shield machine designed for use in using a floating main beam. Mucking in the immediate vicinity of the face is done by The bridge conveyor allows access for track System components and operational considerations are described laying and service installation without" disrupting the mucking below.
A generalized TBM equipment setup is shown in Fig. A variety of mucking systems can be used to haul Full-face boring machines consist used. Adequate muck removal rates are critical to optimum face of a rotating cutting head. Advanced ma- The orientation of the TBM is controlled by the grippers, in chines are available on which the tool type can be changed and conjunction with a laser beam and microprocessor-controlled tool spacing varied.
These developments have arisen from the guidance system. These allow precise positioning of the machine, need for machines that can cope with a variety of poor ground but problems may still be encountered in weak or soft ground in conditions. The cutting head may be an open structure with which the effectiveness of the grippers is greatly reduced. In spoke-like cutting arms, or it may completely conceal the face these situations, 3-dimensional orientation control is facilitated except for muck-removal openings and access ways for tool by TBMs, that steer while boring.
The trailing gear fol- and tools, and can be used with a forepoling arrangement. Components, and their configura- the tunnel face. Reaction to this thrust is provided by grippers tion, are primarily a function of tunnel size and may include: mounted on the TBM body, which in turn react against the 1. Bridge conveyor required to transport muck from the tunnel sidewalls. Mucking is performed by buckets mounted on TBM to the muck cars.
Dual-track rail system with remote muck car loading and handling for larger diameter tunnels. Hydraulic power unit, transformer s , and trailing cable. Supply hoist for unloading and moving supplies. Rock drill for bolt installation , rock drill power unit, and rock bolt supplies storage. Mechanical shop and cutter and supply storage area.
System components are briefly described below; more de- tailed descriptions and specifications are contained in the refer- ences cited at the end of this chapter. Various types of muck cars and trailing gear are available that facilitate continuous loading. Additional details, regarding conventional muck haulage sys- tems, are presented in Chapter 9.
Alternate muck removal systems, incorporating pneumatic or hydraulic transport of crushed muck, have been used in a small nUITlber of civil tunnel- ing projects. Ventilation System-The ventilation system typically con- sists of to in. The system is designed and deployed to max- imize the cross-sectional area available for mucking equipment and is normally configured to exhaust air to the portal Chapter Electrical System-The electrical system typically consists of a high-voltage feeder cable with stepdown transformers mounted on the trailing gear and at strategic locations along the tunnel to service ventilation fans, lighting, pumps, etc.
Chapter Total installed power requirements can be roughly approx- imated at twice the predicted TBM consumption. Rock support requirements Chapter Hard-rock TBMs are commonly equipped with a partial or slotted shield, and when support is required, conventional rock support methods are used. Both soft-rock and hard-rock TBMs can be equipped with a full shield and segmental linings installed. As noted in These simplified formulas are consistent with the conceptual level planning approach incorpo- rated herein.
However, the owner is well advised to maximize geotechnical data collection and interaction with the TBM man- ufacturer so that uncertainties in performance prediction. System Utilization-TBM utilization is defined as the ratio of the productive TBM operating time to the total time available for tunnel drivage.
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