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This is a continuation of U.S. patent application Ser. No. 10/919,271, filed Aug. 17, 2004, now abandoned, which claims the benefit of U.S. Provisional Patent Application No. 60/496,379, filed Aug. 20, 2003, now abandoned. The entire disclosures of U.S. patent application Ser. No. 10/919,271 and U.S. Provisional Patent Application No. 60/496,379 are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The invention relates to helical drag bits and rock bolt systems, which can be used for geotech, mining, and excavation purposes. The invention also relates to methods of using such helical drag bits, and systems incorporating such helical drag bits and rock bolts. 
     2. Related Art 
     Known drilling systems may employ roller cone bits, which operate by successively crushing rock at the base of a bore. Roller cone bits are disadvantageous because rock is typically resistant to crushing. Other known rock drilling systems employ drag bits. Conventional drag bits operate by shearing rock off at the base of the bore. Drag bits can be more efficient than roller cone bits because rock is typically less resistant to shearing than to crushing. 
     Most state of the art rock cutting processes are accomplished by the shearing action or grinding motion of some cutting tool. These cutting actions result in a noisy work environment coupled with the undesirable excitation vibrations that are transmitted to the drill unit home structure. A parameter of paramount importance in any drilling process is the “weight-on-bit” which is the axial force acting on the bit during the cutting process. Normally this force is relatively large and may be generated via proper anchoring of the drill machine to the drilled surface or as an alternative, weight-on-bit may be provided by the self-weight of the drill unit structure. 
     U.S. Pat. No. 5,641,027 to Foster (“the &#39;027 patent”; assigned to UTD Incorporated) discloses a drilling system incorporating a bit with thread cutting members arranged in a helical pattern. Each subsequent cutting member is wedge shaped such that the threads cut by the bit are fragmented, i.e., snapped off. The bit disclosed by the &#39;027 patent is suitable for enlarging a bore formed by a pilot drill bit. The entirety of the &#39;027 patent is hereby incorporated by reference herein. 
     A Low Reaction Force Drill (LRFD), such as that disclosed in the &#39;027 patent, is a low-energy, low mass, self-advancing drilling system. Energy expenditures have been demonstrated by studies to be at least five times less than other prior art systems suitable for similar drilling purposes. The distinct advantages of the LRFD are its low energy drilling capability as a function of its unique rock cutting mechanism, its essentially unlimited depth capability due to its tethered downhole motor and bailing bucket configuration, its self-advancing capability by self-contained torque and weight-on-bit by counteracting multiple concentric rock cutters and bracing against rock or regolith. Additional LRFD advantages may be found in its large non-thermally degraded intact sample production (&gt;1 cm 3 ) with position known to within 15 mm, and finally, the large diameter hole it produces that allows for down hole instrumentation during and post drilling. The system has application for shallow drilling (1 to 200 meters) through kilometer class drilling in a broad range of materials. It would be advantageous to utilize the advantages of this system in a new drag bit geometry, while also mitigating disadvantageous characteristics of this system with a new bit. 
     It would be advantageous to have a helical drag bit that utilizes fewer power resources and that can operate with or without fluid lubrication. It would also be advantageous if such a drag bit could operate under extreme cold and near vacuum conditions, such as those found at extra-terrestrial sites. 
     A problem encountered by geologists or other rock mechanics investigators is the difficulty of obtaining accurate compressive strength measurements of rock in the field, particularly in situ during drilling. In conventional drilling, several drilling variables must be simultaneously monitored in order to interpret lithologic changes, including thrust, rotational velocity, torque, and penetration rate. This is true because with each conventional bit rotation the amount of material removed is a function of all of those variables. It would be advantageous for a geo-technical system to enable geologists and others to obtain accurate substrate characteristic measurements in situ. 
     In the mining industry, roof falls in coal mines continue to be the greatest safety hazard faced by underground coal mine personnel. The primary support technique used to stabilize rock against such events in coal and hard rock mines are rock bolts or cable bolts. Both of these primary support techniques involve drilling holes in rock and establishing anchoring in those holes. Current fatality and injury records underscore the need to improve these operations. 
     As the primary means of rock reinforcement against roof collapse, rock bolts play an important role. As collected from rock bolt manufacturers by NIOSH (i.e., the National Institute for Occupational Safety and Health), approximately 100 million rock bolts were used in the U.S. mining industry in 1999 and of those, approximately 80% used grout as a means of anchoring the bolt to the rock (up from approximately 48% in 1991) with the vast majority of the remaining percentage of rock bolts using mechanical anchors. Cuts through mountainous terrains by highways and railways also extensively use rock bolts or cable bolts for rock mass stabilization. 
     While a broad range of anchoring techniques have been developed, grouting and mechanical expansion anchor bolts are the more common, together comprising over 99% of rock bolts used in coal mines in the U.S. The decline in the use of mechanical bolts is attributed to the fact that grouted rock bolts distribute their anchoring load on the rock over a greater area and generally produce better holding characteristics. 
     As a major contributor to a roof control plan, rock bolts have been studied to determine optimum installation spacing, length, and matching of anchoring with geologic conditions. The main ways rock bolts support mine roofs are typically described as follows: beam building (the tying together of multiple rock beams so they perform as a larger single beam), suspension of weak fractured ground to more competent layers, pressure arch, and support of discrete blocks. Cable bolting (where cables are used in place of steel rods as bolts) performs similar functions. While rock bolts play a critical role in mitigating rock mass failure, many other mine design factors come into play to create a stable mine environment including (but not limited to) opening dimensions, sequence of excavation, matching of bolt anchor and length with opening and geologic conditions, and installation timing. Notwithstanding the importance of these other factors, if the rock bolts used in rock stabilization do not perform well, miners are at risk. 
     Bolt installation characteristics near roof falls have been identified as contributing to failure. One documented and regularly occurring rock bolt failure mechanism is loss of grout shear bond to the rock wall of the bolt hole. Key contributors to the integrity of the grout interlocking with the rock mass are the diameter of the hole relative to the diameter of the bolt, resin vs. cement type grouts, rock type and condition of the hole. 
     Smooth bolt holes consistently produce a reduction in rock bolt load bearing capacity over rough walled holes. To address this, bolt hole bit manufacturers intentionally use reduced tolerances in their manufacturing on the center of bit peaks, and setting of bit cutter inserts in such a way as to induce a wobble during drilling, as well as loose bit mounting to drill rod, with the ultimate result of ridges being left on hole walls. The approach generally produces increased anchoring capacity. However, even with these variations in bolt hole smoothness, anchorage capacity increases, but failure of the rock-grout interface is still common. 
     While considerable research into rock bolting has been conducted to date, gaps still exist in areas that could lead to vast improvements in rock bolt performance. For example, significant pull-test studies have been performed and optimal hole diameter to bolt diameter ratios have been identified for maximum anchorage capacity, and hole condition has been identified as an important contributor to ultimate holding capacity. A relatively unexplored feature in rock bolt holding capacity is hole geometry. It would be advantageous to optimize bolt hole geometry for improved holding capacity. 
     Other problems are also encountered in the field of rock bolt hole drilling: dust and noise. During most rock bolt drilling operations, the operator stands directly at the controls, a couple of feet away from the machinery and the actual drilling process. Research by NIOSH has identified potential for high silica dust levels around roof bolters in coal mines and attributes much of the cause to the vacuum collection and filtering of air used in the drilling process. While significant research into dust hazards and health effects has been conducted by NIOSH (and previously by the U.S. Department of Interior, Bureau of Mines), the measures to improve the environment for rock bolt drillers has been limited almost entirely to worker protection actions. 
     Noise near mining machinery has also been studied. Engineering solutions to the mitigation of high noise levels are always preferred over administrative solutions or personal protective equipment. The key is to make those engineering solutions cost-effective. 
     Similarly, dust protective equipment is useful, but low-dust-by-design solutions offer greater opportunity for seamless incorporation and effectiveness in improving the safety and health environment for miners. 
     SUMMARY 
     The invention relates to novel helical drag bits as well as to systems incorporating such helical drag bits and to methods of using them. The invention overcomes to a substantial extent the disadvantages of the prior art. Thus, according to one aspect of the invention, the helical drag bits incorporate one or more spirally/helically positioned cutting arms of increasing radial length as they are positioned in a direction moving away from the tip-end of the drag bit. The cutting arms can create a spiral trench geometry in the sidewall of a predrilled pilot hole. 
     In an alternative embodiment, the cutting arms terminate in scoring cutting blades. These blades serve to cut a relatively smooth pilot hole bore extension into the sidewalls of the hole, thereby enlarging the hole diameter. The cutting arms of this embodiment can be used with those of the previous embodiment without the scoring blades or may be used by themselves. 
     The embodiments of the helical drag bit can be incorporated into a system and method for measuring geo-tech characteristics of drilled substrates. The measurements can be made in situ during drilling. 
     The helical drag bit can be used in a system and method for improving the holding capacity of rock bolts and similar devices for use in the mining industry or in any circumstances where a particulate substrate may benefit from support. The helical drag bit can produce an improved rock bolt hole geometry, which can interact with mechanical or chemical holding means to improve pull-out capacity in the support structure. Conventional as well as novel rock bolts (having new structures) can be used with this improved hole geometry. Such novel rock bolts can incorporate the helical drag bit design or can excavate a rock bolt hole in a similar way. 
     The above-discussed as well as other advantages can be better understood from the detailed discussion below in view of the accompanying figures referred to therein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  and  1   b  are views of a helical drag bit flight portion in accordance with an embodiment of the invention; 
         FIGS. 2   a  and  2   b  are views of a helical drag bit flight portion in accordance with an embodiment of the invention; 
         FIGS. 3   a  and  3   b  are views of a helical drag bit flight portions during fabrication in accordance with an embodiment of the invention; 
         FIGS. 4   a  and  4   b  are views of cutting arm inserts in accordance with an embodiment of the invention; 
         FIGS. 5   a  and  5   b  are views of a helical drag bit flight portion in accordance with an embodiment of the invention, with  FIG. 5   b  being a detail of a portion of the view shown in  FIG. 5   a;    
         FIG. 6  is a perspective view of a helical drag bit flight portion in accordance with an embodiment of the invention; 
         FIG. 7  is a view of two helical drag bit flight portions in accordance with an embodiment of the invention; 
         FIG. 8  is a view of a stack of helical drag bit flight portions in accordance with an embodiment of the invention; 
         FIG. 9  is a view of a drilling system incorporating a helical drag bit in accordance with an embodiment of the invention; 
         FIGS. 10(   a ) through  10 ( e ) show the drilling system of  FIG. 9 , shown in sequential drilling steps  0 - 4  in accordance with an embodiment of the invention; 
         FIG. 11  shows a detailed view of a hole formed by a device in accordance with an embodiment of the invention; 
         FIG. 12  is a view of two helical drag bit flight portions having scoring cutting arms in accordance with an embodiment of the invention; 
         FIGS. 13(   a ) though  13 ( e ) show helical drag bit flight portions having scoring cutting arms in accordance with an embodiment of the invention; 
         FIGS. 14-16  are cross-section views of a substrate and a rock bolt in accordance with exemplary embodiments of the invention; 
         FIG. 17  is a graph comparing the pullout strength of a conventional rock bolt used in a prior art rock bolt hole with that of a conventional rock bolt used in combination with a rock bolt hole formed in accordance with an embodiment of the invention; 
         FIG. 18  shows a cross-section view of a substrate and a rock bolt in accordance with an exemplary embodiment of the invention; 
         FIGS. 19   a - 19   d  show a cross-section view of a substrate and a rock bolt in accordance with an exemplary embodiment of the invention; 
         FIGS. 19   e  and  19   f  show a cross-section view of a substrate and a rock bolt in accordance with an exemplary embodiment of the invention; and 
         FIGS. 20   a - 20   f  show exemplary embodiments of rock bolts in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention relates to helical drag bits, systems incorporating the bits, and to methods of using the bits and systems. Throughout this detailed description, the terms “helical drag bit” and “helicutter” are used interchangeably. The term “flight” indicates a portion of a segmented bit shaft, which comprises cutting arms. The term “cutting arm” is interchangeable with “cutter.” The terms “resin” and “grout” are also used interchangeably. 
     The helical drag bits of the invention provide an advancement mechanism that move cutters along the circumference of a pilot hole, such as a pilot rock bolt hole. Simultaneously, the bit advances the cutter along the length of the pilot hole, thereby introducing machined grooves into the walls of the pilot hole. The rates of cutter movement along the circumference and length of the pilot hole may be varied independently to produce a variety of geometries, including evenly and unevenly spaced grooves. 
     Two exemplary embodiments of helical drag bits in accordance with the invention have spirally/helically positioned cutting arms  10  that are spaced apart over the outer surface of a bit shaft  12 , as shown in  FIGS. 1   a ,  1   b ,  2   a , and  2   b .  FIG. 1   b  shows the bit flight  20  of  FIG. 1   a  from a top view and  FIG. 2   b  shows the bit flight  20  of  FIG. 2   a  from a top view. These figures show bit flights  20  having cutting arms  10  that extend away from the bit shaft  12  with a radial length  14  (measured from the center of rotation) for each arm  10 . The radial length  14  generally corresponds to the cutting depth of the individual arms  10 . The radial length  14  of the arms  10  can increase, as shown in  FIG. 2   b  (and  FIG. 8 ), with each individual arm  10  from a bottom arm  10   a  to a top arm  10   b  so that each successive arm  10  has a deeper cutting depth in a direction moving away from the tip-end  16  of the bit shaft  12  (see  FIG. 8 ). 
     As shown in  FIGS. 3   a  and  3   b , which depict top and side views of an exemplary bit flight  20  during fabrication of the cutting arms  10 , the arms  10  are designed to track in a spiral manner, having a uniform axial pitch  18  following a consistent spiral track, similar to a self-starting thread tap. Bit flights  20  are fabricated with a hub  38 , which is used during operation of the bit system to stack bit flights  20  and turn the stacked flights  20 . The hub  38  may be any suitable shape, but is preferably round with hexagonally formed borehole. Bit flights  20  may initially be fabricated with a continuous spiraling thread  10   a , which is later machined to shape individual cutting arms  10  of a selected radial length  14  and geometry. Various cutting arm  10  geometries are within the scope of the invention, as shown in  FIGS. 1   a - 2   b  and  6 - 8 . As shown in  FIG. 8 , the basic flight members  20  of the bit can be stacked with additional flights  20  also having cutting arms  10  of an ever-increasing radial length  14  in a direction away from the tip-end  16 . In this way, a maximum desired cutting depth can be achieved in a low energy bit. 
       FIGS. 4   a  and  4   b  show edge inserts  11 , which can be part of the cutting arms  10  in embodiments of the invention (see  FIG. 9 ). Such edge inserts  11  are typically attached to the arms  10  by brazing. These inserts  11  can provide a superior cutting material than that of unadorned arms  10 . The inserts  11  can be, for instance, polycrystalline diamond or carbide. On smaller cutting arms  10 , as shown in  FIGS. 5   a  and  5   b , pockets  13  are provided in the bit shaft  12  for brazing the inserts  11  onto the arms  10 . In an alternative embodiment, the cutting edge of the cutting arms  10  can be incorporated into the cutting arm  10  without need for an insert. Such is the case when the cutting arms  10  are made of a heat-treated alloy or when they are made for a one-time use, as in the case of self-drilling bolts, for example. 
     The helical drag bit is used to further cut the sidewalls of a pilot hole to achieve a modified sidewall geometry. The bit excavates the sidewalls of the pilot bore, leaving a relatively well-defined spiral or interlocking cut along the depth of the bored hole. The ultimate depth of the cut into the sidewalls depends on maximum axial cutting arm length  14 . During cutting, debris can be removed from the cutting area and “swept” towards the center of the hole by the shape of the arms  10 . Cuttings can then be removed from the bore hole in a hydraulic, pneumatic, or hollow-stem auger process. Other embodiments, methods, and systems using the bit are envisioned. 
       FIG. 6  shows a bit flight  20  to be used in latter stages of a bit stack. As shown, the cutting arms  10  of the flight  20  are considerably longer than those shown in  FIGS. 1   a  and  2   a , for example. Also,  FIG. 6  shows an embodiment where a distinct cutting arm  10  geometry is used. The cutting arms  10  shown in  FIG. 6  also terminate in edge inserts  11 , which provide increased cutting capability.  FIG. 7  shows a pair of bit flights  20   a  and  20   b  and provides some contrast between an initial flight  20   a , which has shorter cutting arms  10 , and a latter flight  20   b , which has longer cutting arms  10 .  FIG. 8  provides additional perspective as to how flights  20  are stacked for a cutting system and shows the difference in lengths between an initial cutting arm  10   a  and a terminating cutting arm  10   b.    
       FIG. 9  shows an LRFD system  22  incorporating a helical drag bit in accordance with an embodiment of the invention. The system  22  is comprised mainly of down-hole components including a bit system  24 , bailing bucket  26 , down-hole electric motor/gearbox  28 , debris accumulation cup  30 , sheath  32 , pilot bit  34 , and auger  36 . Lifting and lowering of the LRFD in the borehole are accomplished by a tripod frame and winch system on the surface. 
     As shown in  FIGS. 10(   a ) through  10 ( e ), comminution of the rock or soil is performed by several helicutter components (e.g., flights  20 ) that work in series. The individual action of each helicutter relies on the reaction force capability of the remaining stationary helicutters with frictional contact with the rock or soil mass, allowing the system  22  to self-advance, step-by-step, through a broad range of substrate materials. The individual component action also reduces instantaneous power requirements. In  FIGS. 10(   a ) through  10 ( e ), Step  0  depicts the drill system  22  prior to the beginning of a drilling cycle. Step  1  involves the advancing of the pilot bit  34  into the rock or regolith under the influence of the weight of the drilling system  22  and minimal rotational reaction force. 
     Still referring to  FIGS. 10(   a ) though  10 ( e ), a sheath  32  covers the helical auger  36  pilot shaft and permits the conveyance of pilot cuttings to a bailing bucket  26  located above the helicutters system  24 . Once extended to maximum reach, shown in Step  1 , (can be about 0.3 m in one embodiment of the invention, or less if working in highly fractured rock, rubble or sand) the pilot bit  34  rotates in place to allow the helical auger  36  (inside a sheath  32 ) along its shaft to transfer cuttings away from the pilot hole area. The sheath  32  then retracts to engage the first helical flight  20 . The first helical flight  20  is then rotated and thrust forward in a prescribed ratio by the sheath  32  as shown in Step  2 . The flight  20  creates a thread like spiral groove in the pilot hole wall created by the pilot bit  34 . In Step  3 , the sheath  32  drive tube is retracted from the first flight  20  to engage the second helical flight  20 . Step  4  depicts the stage where the second flight  20  reaches its end of stroke. In a consecutive manner, the remaining helical flights  20  are individually advanced to the bottom, deepening the thread groove in the rock. 
     The purpose of the auger shaft is to drive the pilot bit  34  and convey the rock cutting debris to a bailing bucket container. Table I summarizes cutting properties, in various substrates, of an exemplary embodiment of the invention, as depicted in  FIGS. 10(   a ) through  10 ( e ). 
     
       
         
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Media 
                 State 
                 Density (g/cm{circumflex over ( )}3) 
                 Comments 
               
               
                   
               
             
             
               
                 Limestone 
                 Pulverized 
                 1.700 
                 Flowed with some clumping 
               
               
                 Sandstone 
                 Pulverized 
                 1.630 
                 Flowed well 
               
               
                 Sand 
                 Granular 
                 1.500 
                 Flowed with some grinding 
               
               
                   
               
             
          
         
       
     
       FIG. 11  shows a hole created using a device in accordance with an embodiment of the invention, which comprises helical spiral threads  19  at a specified pitch in rock  11 . The helicutters incorporate a basic drag bit approach to shearing a helical groove  19  in the rock  15 . Based on the pitch  18  of the helical spiral, a traceable thread groove  19  is created in the rock  15  that allows for development of downhole reaction forces and the extraction of rock samples that have not seen excessive thermal loading. By modifying the pitch  18  of the cutter arms  10 , individual cutter arm  10  thickness, rake, and back angle, cutter arm  10  section geometry, and number of cutter arms  10  per flight  20 , several drilling parameters can be modified across a broad range. The parameters affected by this include axial force, torque and efficiency for a given RPM. 
     As shown in  FIGS. 1   b ,  2   b ,  3   a , and  6 - 8 , special attention is given to the internal design of the cutter hub  38 . Engagement between a flight  20  and a sheath-driver is made possible through key grooves in the internal surface of the hub  38  and key posts of the sheath-driver. In order to engage a flight  20  to the driving shaft, the driver is threaded into the cutter hub  38 . Once the driver reaches the set position inside the hub  38 , a cam system is activated by the reverse rotation of the pilot bit  34 , lifting the driver to engage its posts into the hub  38  grooves. Engagement between the cutter arm flights  20  and the sheath-driver is designed to smoothly lock and unlock the hub in the cutting mode, while transmitting the cutting torque with a high strength margin. 
     The average power consumption in drilling a 63 mm diameter hole with 1.89 m of advance through sandstone is about 225 Watt-hrs/m. Power consumption on the order of about 100 Watt-hrs/m is achievable, according to one embodiment of the invention, using the system  22  of the invention. Power consumption in sandstone averages about 385 MJ/M 3 , while power consumption in limestone averages about 300 MJ/m 3 . 
     In one embodiment of the invention, system  22  mass has been shown to be about 45 kg for one prototype that was used in the laboratory. Many of the articles of the system  22  are preferably removable. Taking this into account it has been shown that total system  22  mass can be reduced to about 16 kg, in accordance with an embodiment of the invention. 
     In accordance with an embodiment of the invention rock chips of greater than 1 cm 3  can be recovered from holes with the ability to know the location from which samples were derived to within 15 mm. 
     Instead of plunging an entire shaft deep into a substrate, an alternative strategy may be considered for an alternative embodiment of the invention using a detached, self-driven underground autonomous tethered drill system  22  like that shown in  FIG. 9 . In contrast to prior drilling systems and methods, such a system  22  may be lightweight so that it needs only enough power to accomplish the drilling task while propelling itself downward, trailing a thin cable for power and communication. An auxiliary thin wire rope connected to a surface winch may be linked to the system  22  for lifting and clearing of scientific samples and the rest of the drill process cuttings. The elimination of drill-string from the drilling process can dramatically reduce the weight of main system  22  components, along with reduction of power consumption for drilling task. While drill-string systems are limited by the ultimate depth they may achieve, autonomous tethered system  22  may reach almost any desirable destination. 
     In an alternative embodiment shown in  FIGS. 12 and 13(   a ) through  13 ( e ), each cutting arm  10  terminates in a scoring cutting blade  40 , positioned orthogonally relative to the axial arm length  14 , at a tangent to the drag bit body&#39;s  12  outer circumference. The scoring cutting blade  40  serves to cut a relatively smooth bore extension to enlarge the hole  17 , as opposed to the spiral or interlocking trench  19  formed by the above-described first embodiment. Upon removal, the debris from this second embodiment of the helical drag bit can resemble a coil, spring, or “slinky,” or the debris may break-off in pieces for removal. 
     This embodiment provides a new approach to thread stripping (and thus sample removal). As shown in  FIG. 12 , cutter flights  20  were fitted with tungsten carbide scoring cutting blades  40  that can cut a kerf in the top and bottom of each rock thread  19  at the deepest point of the helical groove. Successive scoring cutting blades  40 , shown in  FIGS. 13(   a ) through  13 ( e ), cut the kerf deeper and deeper until the whole rock thread  19  is excavated and captured into the bottom of the bailing bucket as a sample 
     The embodiment illustrated in  FIGS. 12 and 13(   a ) through  13 ( e ) achieves a low-energy drilling bit and provides a superior device for enlarging a pilot hole  17 . The bore extension cut with the invention does not require the “snapping-off” of the spiral cut as does the device of the &#39;027 patent. This embodiment can be utilized with the system  22  of  FIG. 9 , where thread scorers  40  are advanced breaking off the rock ridges as scientific samples. For a final hole diameter of about 80 mm (practical range of finished hole diameter can be 50 mm to 250 mm) the chips formed by thread breaking can be about 2 to 3 cm in length. Chips can be captured in a bailing bucket  26  along with pilot cuttings from the pilot auger shaft that can be captured in a separate bailing bucket compartment. Following a complete drilling cycle the bucket can then be lifted to the surface by a winch wire-line system. 
     The helical drag bit may be used as a geo-tech device for measuring the properties of drilled substrates  15  (e.g., rock), like that shown in  FIG. 11 , by measuring the torque required to advance the helicutter. Such an embodiment of the invention has the advantages of enabling in situ, direct rock compression strength measurements to be made in the field during drilling and also of eliminating the bounce anomaly associated with prior art compressive strength testing techniques, thereby providing on-the-spot, reliable geo-tech measurements. 
     The compressive strength of rock substrate  15  through which the helical drag bit is traveling is measured, in part, based on (i) the cutting arm  10  design of the helical bit and (ii) torque required to turn the helical bit through the rock  15 . Although each successive arm  10  can have an increasingly larger axial length  14 , the cutting depth generally is the same for each, and the average cutting depth of all arms  10  can be used for measurement calculations. The torque on the helical drag bit and each arm  10  is a known variable, which can be controlled or measured. 
     As shown in  FIG. 9 , the drill system  22  incorporating the helical bit can be in communication with a computer  42  or other device having software for calculating the compressive strength of the rock  15  based, in part, on the helical drag bit design and the torque on the drill. The bounce anomaly is corrected because the helical drag bit is designed to have opposing arms  10 . Because the arms  10  of the helical drag bit are always in opposition during use and have increasing lengths, there is no opportunity for bounce and the arms  10  are always cutting, making for balanced forces on the helical bit. 
     The geometry of a helical flight  20  provides symmetry of forces such that the normal force on each cutter is balanced by the cutter arm  10  on the opposite side of the flight  20 . Every rotation of the helical flight  20  results in a prescribed advance into the rock  15  and the cutting depth is defined by the initial hole  17  diameter, the pitch  18  of the cutter arms  10  surrounding the central hub  38  and the geometry of the individual cutter arms  10 . Ultimately the system  22  can interpret lithologic changes based on measuring torque. Drilling in three different lithologies and across small bed separations has shown a direct correlation between measured torque and the compressive strength of the rock  15  via the following equation: 
     
       
         
           
             
               q 
               u 
             
             = 
             
               Tc 
               
                 
                   K 
                   SE 
                 
                 · 
                 w 
                 · 
                 d 
                 · 
                 r 
               
             
           
         
       
     
     In the above equation: q u  is the unconfined compressive strength of the substrate; Tc is the torque per cutter; K SE  is a coefficient of proportionality between specific energy (SE; SE=K SE ·q u ) and the unconfined compressive strength (q u ) of the substrate; w is the cutter width; d is the depth of the cut; and r is the radial distance of the cutting edge (measured from the center of rotation). 
     In accordance with an embodiment of the invention, the helical drag bit is used as a geo-tech device in a similar manner as discussed above in relation to the system  22  shown in  FIG. 9 . A pilot hole  17  is bored in a substrate  15  to fit the body  12  of the helical drag bit. Then the helical drag bit can be used for geo-tech measurements by spirally cutting the sidewalls of the pilot hole  17  while the forces acting on the helical bit are measured to calculate substrate properties. 
     Another embodiment of the invention uses the helical drag bit in the mining and excavating industries, as well as in any scenario where a particulate substrate  50  (e.g., rock or concrete) requires support and stability control. In mines, for example, it is required that an underground opening be reinforced with a supporting/stabilizing rock bolt  52 . The invention can be used to achieve at least a 40% increase in holding capacity and pull-out strength for rock bolts  52  within rock  50 . Additionally, use of the helical drag bit system in forming rock bolt holes reduces the dust and noise compared to prior methods. The helical drag bit system produces relatively large rock chips instead of small particles, which reduces dust formation. Also the helical drag bit system operates at a relatively low rpm, which reduces drilling vibrations and thereby noise. 
     As shown in  FIG. 14 , after boring a relatively smooth pilot hole  54 , the helical drag bit can be used to spirally (or helically) cut the interior sidewall of the hole in an “optimal hole geometry”  56 , thereby texturizing the hole  54  in a manner like that shown in  FIG. 11 . The texturized hole  54  allows resin to spread over a greater surface area inside the hole  54  with a complex (spiral or interlocking) geometry, and thereby achieve a better grip between the rock  50  and bolt  52 . 
     The optimized hole geometry can be configured to the physical and chemical properties of the resin/grout and surrounding rock and rock strata. The optimal hole geometry can modify the mechanism of the pullout force transfer between the grout and rock. In accordance with this embodiment of the invention, it is possible to form right or left handed grooves in the optimal hole geometry. For example, left handed grooves used with a right handed rock bolt rotation can improve resin/grout redistribution. 
     This technique is not limited to providing supporting and stabilizing means for the roof walls of mine openings. The technique can be used in a variety of particulate substrates in a variety of orientations where a bolt-like device would be advantageous. For instance, the helical drag bit can be used to form bolt holes  54  in retaining walls or in concrete surfaces, and in both vertical and horizontal orientations. 
     An embodiment of the invention incorporates use of a rock bolt  52  to complement the superior hole geometry characteristics achieved with the helical drag bit of the invention. Such a bolt  52 , however, is not limited to use in a rock  50  substrate and is not limited to a particular size. The bolt  52  can be used in any particulate substrate and can range in length from mere centimeters to meters. 
     In one embodiment, shown in  FIG. 15 , the rock bolt  60  can have a mechanical anchor  62  at the end of the bolt  60 . The anchor  62  will engage the helical threads  64  located at the end of the associated pilot hole. The mechanical anchor  62  adds another level of holding capacity and pull-out strength to the bolt  60 , thereby providing additional safety. The bolt  60  with the mechanical anchor  62  can be used with or without resin. This is not a self-drilling bolt embodiment. 
     In another embodiment, the bolt (e.g., bolt  52  of  FIG. 14 ) is self-drilling. The helical cutter will be incorporated into the bolt itself. The bolt can screw itself into rock  50  with or without the need of a well-defined pilot hole. The self-drilling bolt can be used with or without (if no pilot hole is used) resin, depending on the depth of the grooves  19  of the optimal hole geometry. 
     In another embodiment, shown in  FIG. 16 , the rock bolt  70  is itself a helical anchor, being either fully threaded or partially threaded. The helical anchor bolt  70  has threads  72  that can loosely or tightly match the spiral cuts  74  made by the helical drag bit. In this embodiment, a threaded portion of the rock bolt  70  fits into the spiral cut portions  74  of the hole  54  in the rock  50 . This bolt embodiment gains added holding strength and pull-out capacity by allowing the rock  50  itself to directly support the bolt  70 . Again, such a bolt  70  could be used with or without resin. Additionally, this embodiment is particularly useful for concrete support and stabilization. The rock bolt  70  can also be configured relative to the optimized hole geometry  56  so as to be removable and reinsertable upon demand. A fully threaded bolt  70  will have maximum anchorage capacity. A partially threaded bolt  70  can serve to reduce roof layer separation by anchoring to the most competent portion of substrate. 
       FIG. 18  shows an embodiment similar to that shown in  FIG. 16 . The rock bolt  70  of  FIG. 18  has partial threads  72 , which in this embodiment refers to the non-continuous design of the threads  72 . The helical groove  74  cut into the rock bolt hole  54  using the helical drag bit system can be slightly smaller than the threads  72  of the rock bolt  70 . Such a design promotes the further cutting of the rock  50  by the threads  72  of the rock bolt  70 , which is facilitated by the prior cutting of the groove  74  by the helical drag bit system. The threads  74  provide additional holding capacity for the rock bolt  70 . Grout, or another adhesive, may be used with this embodiment and the additional cutting of the rock  50  by the rock bolt threads  72  effectively spreads the grout throughout the hole  54 . 
     As discussed above in reference to  FIG. 14 , the pitch of the helical drag bit and the cross-section of the individual cutters can be optimized in view of the properties of the surrounding rock  50  and of the resin grout is used. The ultimate displacement of the rock bolt  52  before pullout occurs can be controlled by the pitch of the grooves  56 . The force transfer mechanism between the grout and the rock  50 , as well as the bolt  52  and the rock  50 , can be controlled by the changes in the cross-section of the grooves  56  of the optimal hole geometry. The pitch may be adjusted in real time to suit the rock properties as measured in situ during the advancement of the helicutters. 
     Another embodiment of the invention is shown in  FIGS. 19   a - 19   d .  FIG. 19   a  shows a cross-section of rock  102  having a rock bolt hole  104  formed therein. In this embodiment, the helical drag bit system is not necessarily used since the rock bolt  100  itself has the capability of forming a groove for holding itself in the hole  104 .  FIG. 19   b  shows a rock bolt  100  having protuberances  106  along at least a portion of its length, preferably at the tip end which will ultimately be positioned nearest the end of the rock bolt hole  104 . These protuberances  106  are not mere irregularities or deformities in the rock bolt  100  such as may be found in typical rebar, for example, but are designed to excavate the rock  102  around the rock bolt hole  104 . The rock bolt  100  is moved into the rock bolt hole  104  in a direction  108 . As shown in  FIG. 19   c , as the rock bolt  100  is forced into the hole  104 , the protuberances  106  will gouge or cut the wall of the rock bolt hole  104 , producing a rough groove  110  along the hole  104 .  FIGS. 19   c  and  19   d  show the groove  110  in a direction along the plane of the drawing; however, the groove  110  will preferably enlarge the hole  104  only with respect to the size of the protuberances  106 , which are preferably isolated and discrete along the shaft of the rock bolt  100  ( FIGS. 20   a - 20   c ). Upon complete insertion of the rock bolt  100  into the rock bolt hole  104 , the rock bolt is partially rotated  112  so that groove  110   a  is formed semi-annularly with respect to the rotation, the rock bolt  100 , and the rock bolt hole  104 . This groove  110   a  provides support for the protuberances  106 , which locks the bolt  100  into the hole  104 . 
       FIG. 19   e  shows an alternative embodiment, where a rock bolt  100  of the same basic configuration as shown in  FIGS. 19   c  and  19   d  is inserted into a rock bolt hole  104 , but instead of being forced straight into the hole  104 , the bolt is rotated  112  while being forced into the hole  104  in the direction  108 . This rotation  112  and forward motion  108  of the bolt  100  and protuberances  106  creates a spiral-type groove  111  along the wall of the rock bolt hole  104 . The rotation  112  may be continued throughout insertion of the rock bolt  100  to create a groove  111  as shown in  FIG. 19   f . This spiral groove  111  will support the protuberances  106  and will hold the rock bolt  100  in the rock bolt hole  104 , particularly if grout is used. 
     The protuberances  106  of the rock bolt  100  shown in  FIGS. 19   a - 19   f  can be of several designs, including but not limited to those shown in  FIGS. 20   a - 20   f .  FIGS. 20   a  and  20   b  shows a rock bolt  100  having rounded protuberances, similar to those as shown in  FIGS. 19   a - 19   f .  FIGS. 20   c  and  20   d  shows a rock bolt  100  having rounded protuberances  106  that increase in radial length from a first protuberance  106  toward the tip end  114  the rock bolt onward. This configuration allows for easier gouging/cutting of the grooves  110  or  111  shown in  FIGS. 19   c - 19   f .  FIGS. 20   e  and  20   f  shows a rock bolt  100  having angular protuberances  106 , which may be in the form of blades or may be pyramid-shaped. This angular shape of the protuberances  106  allows for easier insertion into and gouging/cutting of the rock bolt hole. As stated above, other protuberance  106  shapes and configurations are possible. 
     Protuberances  106  may be formed in a number of ways, including, but not limited to, formation during stamping of a rock bolt as a part thereof. Protuberances  106  may also be formed by attaching them to a rock bolt by brazing or welding. Additionally, recesses or holes may be formed in a rock bolt for insertion of protuberance  106  there into. As stated above, other ways of forming the protuberances  106  are possible. 
       FIG. 17  shows a graph, which compares rock bolt pullout strength using prior art hole geometries (i.e., standard tests  1  and  2 ) to rock bolt pullout strength using an optimized hole geometry (i.e., single and double passes) in accordance with an embodiment of the invention. Tests were performed in the same rock material. The graph plots the load in pounds force required to pull a rock bolt along its axis to a given displacement. As shown in the graph, rock bolts used in combination with the optimal hole geometry show improved bolt pullout performance. 
     Embodiments of the invention can also be used to reduce dust and noise when drilling rock bolt holes  54 . Cutter arm  10  depth can be carefully designed to reduce torque requirements per cutter arm  10  or by increasing depth, to increase the size of chips. In one study, all drilling cuttings were collected from two different helical cutter flights  20 . The cuttings were sieved to separate fines from larger chips using a 0.015 mesh. With a change of only 0.05 inch cutter arm  10  depth, significant differences in drill cuttings characteristics were identified with no detrimental effect on drilling. Table II illustrates the differences in the cuttings characteristics. 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                   
                 Flight 1 
                 Flight 2 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Avg. Torque 
                 55 
                 N-m 
                 41 
                 N-m 
               
               
                 Thread cuttings mass for 2.85 m of 
                 204 
                 gm 
                 146.4 
                 gm 
               
               
                 drilling 
               
               
                 Mass of particles &lt;0.015 mesh 
                 153 
                 gm 
                 127.6 
                 gm 
               
               
                 Mass of particles &gt;0.015 mesh 
                 51 
                 gm 
                 18.8 
                 gm 
               
               
                   
               
             
          
         
       
     
     The processes and devices described above illustrate preferred methods and typical devices of the invention; however, other embodiments within the scope of the invention are possible. The above description and drawings illustrate embodiments, which achieve the objects, features, and advantages of the present invention. However, it is not intended that the present invention be strictly limited to the above-described and illustrated embodiments. Any modifications, though presently unforeseeable, of the present invention that comes within the spirit and scope of the following claims should be considered part of the present invention.

Summary:
A method of supporting a substrate includes inserting a rock bolt into a hole and using the rock bolt to form a groove in a wall of the hole when the rock bolt is inserted therein. The rock bolt is caused to interact with the groove in such a way that the rock bolt is secured in the hole at least in part by the interaction.