Patent Publication Number: US-2009236146-A1

Title: Machine and method for trenchless conduit installation

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to earth boring machines and conduit installation, and more specifically, to machines for horizontal directional drilling and simultaneous positioning of continuous lengths of conduit. 
     BACKGROUND 
     Underground conduits are employed for a number of conventional applications. For example, they may be used for transmission of water, natural gas, sewage and other fluids, or they may be used to group and/or protect power transmission and communications cables, such as coaxial and fiber optic cables from water and physical damage. 
     The usual method of installing underground conduits and cables is to dig a trench, which is back-filled after the conduit is positioned therein. However, there are numerous situations in which this method is undesired, impractical or prohibitively expensive. In certain applications, there may be buildings, bodies of water, roadways and other obstacles that prohibit digging a trench. Even where obstacles can be avoided, ripping up a roadway, existing landscaping, or environmentally sensitive areas may still be undesirable, often increasing project costs and closing the construction area for an extended period of time. 
     To address these and other concerns, it is known in the art to employ Horizontal Directional Drilling (HDD) methods, which refers to trenchless techniques that allow for the construction of relatively long underground tunnels through which a conduit may then be pushed or pulled. Modern HDD equipment allows the user to construct a tunnel that, within certain limits, may twist and turn to avoid various obstacles, placing the conduit along a desired path. HDD allows a tunnel to be placed with great precision since the location, direction and depth of the drilling head may be controlled and monitored during drilling. A drilling machine is positioned on the drilling surface and a hole drilled at an angle until a desired depth is achieved, after which the cutting or drilling tool is directed along a horizontal path to create the horizontal borehole. The cutting tool/drill head is provided with thrust and/or rotation through motors, electric or hydraulic, which are operatively connected through the drill string, a series of drill rods or pipes that are connected in sequence, end to end, as the bore is formed. Once the desired length of the borehole has been reached, the cutting tool is then directed upwards, back to the surface. A reamer may then be attached to the drill string, which is pulled back through the borehole to remove debris and/or enlarge the bore. A conduit may be connected to the end of the drill string or reamer as it is pulled back through the bore, or the conduit may be positioned in a separate push or pull-back operation. For example, a separate line may be connected to drag the conduit through the well bore for placement thereof. Since ground penetration only occurs at the entrance and termination points, relatively small amounts of surface area are required for implementation, which may result in cost efficiencies, lessening of environmental impact, and other benefits. 
     An additional problem associated with this operation is that the borehole may be compromised during drilling, pull-back or conduit installation. In some applications, drilling mud may be employed during drilling, which is passed through the drill string and/or drill head back through the bore to remove debris as the cutting tool advances. The drilling mud may form a cake on the walls of the bore to prevent collapse of the bore. However, the use of drilling muds may not be desirable in all applications and may not be fully effective. This may increase difficulties in connection with the pull-back or conduit installation process once the bore is formed, and result in increased cost. 
     The present disclosure is directed to overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present disclosure provides a method of conduit installation that includes drilling a generally horizontal bore and simultaneously installing a continuous length of conduit. 
     In another aspect, provided is a drilling machine for horizontal boring and simultaneous conduit installation that includes a conduit forming assembly configured to produce a continuous length of conduit surrounding a drill string. 
     In yet another aspect, provided is a drilling machine for horizontal boring and simultaneous conduit installation that includes a conduit forming assembly configured to produce a continuous length of conduit surrounding a drill string. The machine further includes a clamping assembly operatively connected to a thrust motor, the clamping assembly configured to engage a portion of the conduit. 
     These and other aspects and advantages of the present disclosure will become apparent to those skilled in the art upon reading the following detailed description in connection with the drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a horizontal drilling machine in accordance with one embodiment of the present disclosure; 
         FIG. 2  is a side elevational view of another embodiment of a horizontal drilling machine in accordance with one embodiment of the present disclosure; 
         FIG. 3  is a side elevational view of another embodiment of a horizontal drilling machine in accordance with one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is illustrated one embodiment of a horizontal directional drilling machine (HDD) machine  10  for providing simultaneous drilling and placement of a continuous length of conduit.  FIG. 1  illustrates a cross-section through a portion of ground  12  where a horizontal drilling operation takes place. The HDD machine  10  may be positioned on surface  14 , however, it may also be positioned below surface  14  in an excavated area (not shown). The HDD machine  10  generally includes a frame  16  on which is positioned an inclined longitudinal support member  18 . The machine  10  may be temporarily secured to surface  14  by, for example, ground engaging stakes, pins, or other restraining members (not shown), to prevent the machine  10  from moving during drilling operations. 
     Machine  10  may include a power source  20  and cooling system (not shown) supported by frame  16 . The power source  20 , such as a diesel or gasoline engine, may be operatively coupled through a transmission (not shown) to drive one or more traction devices  22  as known in the art. As shown in  FIG. 1 , traction devices  22  may include tracks disposed on opposing sides of the machine  10 . Alternatively, traction devices  22  may include wheels, belts, or other traction devices  22  known in the art. In an alternative embodiment, machine  10  may not include a power source  20  for propulsion, and may need to be positioned by another machine (not shown), such as a tractor, truck, dozer or the like. Machine  10  may also include an operator station or cab  24  for primary control of the machine  10  during ordinary operations. 
     In one embodiment, a pair of parallel guide tracks  26  are supported in spaced apart configuration on the support member  18 . A carriage  28  is mounted for movement along the guide tracks  26  on rollers, wheels or bushings (not shown). Thus, carriage  28  is configured for movement backward and forward along guide tracks  26 . 
     A threaded drive shaft  30  having a first end  32   a  and second end  32   b  is connected to front  34  and rear  33  ends of support member  18 . A thrust motor  36  is also mounted to the support member  18  and is operatively connected to shaft  30  through a gearbox (not shown) to control the rotational speed and direction of the shaft  30 . The thrust motor  36  may be hydraulically or electrically driven as is known in the art. Shaft  30  is connected to carriage  28  via a nut (not shown) or the like such that rotation of the shaft  30  moves the carriage  28  forward or backward linearly along tracks  26 . 
     Drill assembly  38  is mounted to the carriage  28  for movement therewith, and includes a drill motor  40  having a drill rod coupling  42  for releaseably connecting a drill rod  44  to the drill motor  40 . The drill rod  44  may include a threaded end (not shown) for rotatably engaging a threaded bore (not shown) of coupling  42 , and thus drill motor  40 . Again, the drill motor  40  may be hydraulically or electrically powered as known in the art. 
     A clamping assembly  46  may be mounted to front end  34  of the support member  18 . The clamping assembly  46  may include, for example, a central bore (not shown) for receiving rod  44  and clamping members (not shown) for selectively engaging the rod  44  as is known in the art. 
     As in conventional drilling operations, the rotational/drill motor  40  is initially positioned at upper, first end  32   a,  and is employed to rotate the rod  44 , attached drill string  50  and cutting tool  52 . At the same time, the drill assembly  38  is pushed in a forward direction by the thrust motor  36  toward front end  34 . Once the drill assembly  38  reaches the front end  34 , clamping assembly  46  is engaged to grip the drill string  50  to stop rotation thereof, and to secure the rod  44  for connecting additional rods to the drill string  50 . The drill assembly  38  is then uncoupled from the clamped rod  44 , and pulled back to an upper position at first end  32   a.  A new rod  44  is then added to the drill string  50 , either manually or automatically. The clamping assembly  46  then releases the drill string  50  and the thrust motor  36  is again employed to drive the new rod  44  into the borehole. 
     Positioned ahead of the clamping assembly  46  is a conduit forming assembly  48  that is configured to manufacture a continuous length of conduit as the drill string  50  is advanced. This eliminates the need for a separate process, in which, after the bore is drilled, the desired conduit is either pushed or pulled back through the bore. 
     In one embodiment, the conduit forming assembly  48  may be an extruder for producing either polymeric or metal conduits well known in the art. Such extruders typically consist of a hopper (not shown) for addition and storage of feedstock (chips, pellets, beads, or the like of the base material) which are heated via a heating element (not shown) to a molten form which is forced through a die (not shown) under pressure. At the center of the die may be positioned a pin or mandrel (not shown), configured with a hollow core (not shown) through which the drill string  50  may be fed. Due to the heat that may be involved in the extrusion process, it may be desirable to include a cooling sheath (not shown) surrounding the drill string as it passes through a portion of the forming assembly  48 . In one embodiment (not shown), this may include, for example, a cylindrical sleeve that includes passages through which a coolant, such as water or an ethylene glycol solution, is circulated from a pump (not shown) driven by power source  20 . In an alternative embodiment, the mandrel may be provided with a cylindrical bore for receiving the drill string  50 , the drill string being cooled by drilling fluid that is passed through the bore that then enters the newly formed conduit  11 . 
     In conventional continuous extrusion processes, the extruded material is subsequently cooled by, for example, employing a fluid bath. Moreover, the extrusion process may require that the conduit  11  be cured relatively quickly such that deformation does not occur as the drill string  50  advances. Accordingly, in another embodiment, following the conduit forming assembly  46 , provided is a cooling assembly  62  that may include a fluid bath, sprayers, cooling jacket, or combination thereof (not shown). Cooling fluid may be circulated through the bath or cooling jacket by a pump (not shown) operatively connected to power source  20  in a closed fluid circuit that may also include one or more heat exchangers (not shown). 
     In operation, the extruder may be configured to produce conduit  11  around the pipe string  50  at substantially the same rate as the drill string  50  is moved forward. In one embodiment, the string  50  may be advanced a desired distance, for example, the length of one rod  44 , allowing the extruder to produce a corresponding length of conduit  11  that remains in the cooling assembly  62  until sufficiently cured. After the curing time is achieved, the drill string  50  is advanced and the process is repeated. 
     Operatively connected to the leading end of the drill string  50  is a drilling head or cutting tool  52 . The cutting tool  52  is coupled to the drill string  50  for rotation, driven by drill motor  40 , and is forced forward via thrust motor  36 . The cutting tool  52  may be supplied with a connector  54  for attachment of the leading end  56  of the conduit  11  so that the conduit advances in concert with the cutting tool  52 . As shown in  FIG. 1 , the connector  54  may include a first portion  58  attached to the conduit  11  that can freely rotate with respect to a second portion  60  connected to the cutting tool  52 , thereby eliminating torsional stresses that would otherwise be applied to the conduit. In an alternative embodiment, the conduit  11  may be rotated through the extrusion process at substantially the same rate of rotation as the drill string  50 , in which case, a rigid connection may be provided. 
     The disclosed machine  10 , is thus adapted to perform a horizontal drilling operation while simultaneously installing a continuous length of conduit. The term “continuous” distinguishes this from conventional processes in which lengths of pipe or tubing are joined end to end, either mechanically, or through a welded connection. This eliminates the separate step of having to join the ends and ensure that the connections are properly fitted or sealed. The term “continuous” also should be understood to refer to operations wherein a relatively short, single length of pipe can be employed, for example, in distances greater than  50  feet. While the above embodiment includes an extrusion process, other techniques well known to those of skill in the art may be employed to produce continuous conduits in accordance with the present disclosure. These may include, for example, centrifugal casting and forming a conduit from a sheet of material that is joined longitudinally. 
     Thus, in another embodiment, conduit forming assembly  48  may include a continuous centrifugal casting device that generally includes a rotating tubular mold (not shown) into which a molten casting material is introduced. Specific components and methods of cooling the mold, withdrawing the cast tube, bearings, rotational devices, and the like, are well known in the art. Again, the casting process may take place around the drill string  50 . That is the drill string  50  may pass through the center of the tubular mold during the casting process. In one embodiment, a protective sheath (not shown) may be provided over the portion of the drill string  50  passing through the mold, which may include a cooling jacket incorporated therein that is fluidly connected to a pump for circulating a cooling fluid to protect the drill string  50  from the heat associated with the casting process. In association with this process a cooling assembly  62  may be provided as discussed previously in connection with the extrusion embodiment, as known in the art. 
     In yet another embodiment, the conduit forming assembly  48  may instead include a continuous roll of a polymeric or metallic sheet material that is folded and joined along a longitudinal axis about the drill string  50  as it advances through the borehole. For example, the conduit forming assembly  48  may include a roll of sheet HDPE material (not shown) that is passed through a guide member (not shown) that folds the sheet into a tubular form, optionally with the application of heat to the sheet to improve flexibility thereof. The two longitudinal edges of the sheet may then be joined via well known heat-fusion methods. In summary, a heating plate may be applied to the opposing edges under force, the opposing edges then pass the heating plate and force is continually applied to bring the heated edges together, for example, by passing them through a tubular guide. The exterior bead may generally be left intact, while the interior bead may be removed by a blade as the newly formed length of conduit moves forward. This process may result in a fused longitudinal joint that has a strength substantially equivalent to that of the original sheet material. Again, where needed, a subsequent cooling assembly  62  can be employed. 
     It is well known in the art to employ a drilling fluid or mud, which is typically forced through a hollow interior of a drill string to power the drill head, remove debris from the bore as it is drilled, to provide a smooth bore surface and/or to protect the integrity of the bore prior to placement of a conduit in a subsequent push or pull-back operation. In the embodiment described in  FIG. 1 , the machine  10  may include a tube (not shown) in fluid connection with a source of drilling fluid/mud (not shown), the tube being fluidly connected to a pump (not shown). The pump may, in turn, be fluidly connected directly or through an output conduit (not shown) to direct a flow of drilling fluid/mud through either the drill string  50  and/or conduit  11 . The fluid may exit the drill string  50  or conduit  11  near the leading end  56  thereof (or through the cutting tool  52  or coupling  54 ) to circulate back through the bore  66 , to where it is ultimately dumped into a mud pit (not shown). 
     In yet another alternative embodiment, cutting tool  52  may be of the type known in the art wherein the drilling mud forced through the drill string  50  or conduit  11  is used to power the drill. It may include a cutting tip, for example of the type known in the art that has multiple rotors each having a plurality of cutting teeth. The drill string  50  may be included for purposes of providing thrust through, for example, thrust motor  36 , while the cutting tool  52  is hydraulically driven for rotation. 
     In some applications, the strength of the conduit  11  may be sufficient to eliminate the need for a drill string  50 . This is shown, for example, in connection with  FIGS. 2-3 . In  FIG. 2 , machine  10  includes a conduit forming assembly  48  and, optionally, a cooling assembly  62  as previously described in connection with  FIG. 1  for producing a continuous length of conduit  11 . 
     The machine  10  includes a thrust assembly  70 , generally composed of a clamping assembly  46  associated with a carriage  28  that is configured for movement along longitudinal guide rail(s)  68 , supported on rollers, wheels or bushings (not shown). A thrust motor  36  mounted to support member  18  is operatively connected to a threaded shaft  30  that drives a threaded receiving member (nut) (not shown) connected to the carriage  28  for movement thereof. In operation, the conduit  11  exits the conduit forming assembly  48  and cooling assembly  62 , where it is grasped by clamping assembly  46 . Thrust motor  36  is then engaged to drive carriage  28  from first position  72  toward second, downward position  74  at substantially the same rate as the newly formed conduit  11  exits the extruder. 
     In an alternative embodiment, where the length of time required for curing the conduit  11  exceeds the minimum required time before the conduit  11  can be advanced without distorting or otherwise compromising the integrity thereof, there may be a curing interval provided. For example, a first length of conduit, for example, the length of the guide rail  68 , may be produced, and allowed to cool. A second length of conduit  11  may then be produced, and the first length advanced to position  74 , wherein the cutting tool  52  may be coupled thereto via a connector  54 . At the same time, the clamping assembly  46  may be moved to the upper position  72 , and engaged to grasp the first length of conduit  11 . When the second length of conduit has sufficiently cooled (the curing interval), the thrust motor may then be actuated to drive conduit  11  forward. 
     In the embodiment shown in  FIG. 2 , the cutting tool  52  is hydraulically driven for rotation via a drilling fluid/mud that is provided via a pump  78  through supply conduit  76  and into open rear end of conduit  11 . The supply conduit  76  may extend a distance into conduit  11  to where the conduit  11  is sufficiently cured to be able to withstand the fluid pressure, a seal (not shown) being provided between the interior surface of the conduit  11  and the supply conduit  11 . Drilling fluid passes through conduit  11 , exiting through cutting tool  52 , and returns via the bore  66 . Thus, the drilling fluid/mud is employed in a conventional manner to drive the cutting tool  52 , carry debris to the surface and/or coat the interior of the bore  66 . The drilling fluid may also be employed as part of the cooling strategy for the newly formed conduit  11 . 
     In an alternative embodiment, shown in  FIG. 3 , the conduit  11  is employed to impart both rotation and thrust for the cutting tool  52 . The machine  10  is generally the same as that described in connection with  FIG. 2 , except that a drill motor  40  is provided for rotation of the clamping assembly  46  as the carriage  28  is moved from first position  72  to second position  74 . The speed of rotation imparted by the drilling motor  40  may be substantially the same as the speed of rotation of the newly formed conduit  11  as it exits conduit forming assembly  48 . 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present invention as determined based upon the claims below and any equivalents thereof. 
     INDUSTRIAL APPLICABILITY 
     In conventional horizontal directional drilling and conduit installations, the drilling operation is conducted first, the conduit being installed in a subsequent push or pull-back operation. The drilling operation typically employs connecting and advancing a series of rods or pipes, connected either through threaded connections or fasteners, that form the drill string, at the leading end of which is the cutting tool. Once the drilling operation is complete, a conduit may be attached to the leading end of the drill string and pulled back through the bore for positioning. Alternatively, the conduit may be attached to a reamer or cable in a subsequent push or pull-back operation. 
     The present disclosure provides machines for horizontal drilling operations that simultaneously drill the bore and position the conduit. The machines include a conduit forming assembly, such as an extruder, centrifugal casting, or other device, that produces a continuous length of conduit that is connected at a leading end to the cutting tool, thereby eliminating the need for a separate conduit positioning operation, which may decrease costs and project time, as well as provide other benefits. Moreover, because the conduit is formed in a continuous length, it alleviates problems associated with the integrity of joints in conduits formed of adjoining segments. 
     Other aspects, objects, and advantages of the present disclosure can be obtained from a study of the drawings, disclosure and the appended claims.