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RELATED APPLICATIONS 
   This application claims priority of U.S. Provisional Patent Application Ser. No. 60/675,524 filed Apr. 27, 2005. The contents of all related applications listed above are incorporated herein by reference. 

   TECHNICAL FIELD 
   The present invention relates to methods and apparatus for inserting rigid members into or extracting rigid members from the earth and, more particularly, to systems and methods for driving and/or extracting a pile. 
   BACKGROUND OF THE INVENTION 
   For certain construction projects, rigid members, such as piles, anchor members, caissons, sheet pile barriers, and mandrels for inserting wick drain material, must be placed into the earth. The term “piles” will be used herein to refer to the rigid members typically driven into the earth during construction projects. It is well-known that such rigid members may often be driven into or extracted from the earth without excavation by applying a driving or extracting force on an upper end of the pile. 
   To drive or extract a pile, a driving force is typically applied to the pile along a longitudinal axis A of the pile. The driving force may be created in various ways. A drop hammer comprises a ram member that is repeatedly raised and dropped such that the impact of the ram member drives the pile into the earth. A diesel hammer comprises a ram member that compresses and ignites fuel between the ram member and the pile; the impact of the ram member drives the pile, while expansion of the ignited fuel both drives the pile into the earth and raises the drop hammer for the next impact. A hydraulic drive system uses a hydraulic ram to force or crowd the pile into the earth. A crane may be used to apply an extraction force on a pile through a cable. 
   In addition, vibratory forces may be applied to the pile. Vibratory forces are also applied along the longitudinal axis A of the pile, typically in combination with a passive driving force created by the weight of the vibration equipment on top of the pile. The combination of the passive driving force and the vibratory forces is often sufficient to drive a pile in certain soil types. Typically, a suppressor is used to isolate support equipment such as a crane or the like from the vibratory forces. 
   Attempts have been made to combine vibratory forces with active driving forces such as a hydraulic drive system. U.S. Pat. Nos. 6,039,508 and 6,431,795 to White disclose systems and methods for inserting wick drain material comprising a bottom drive system that combines a vibratory device with a gear drive to drive a mandrel supporting the wick drain mater. The gear drive crowds the mandrel into the earth, and the vibratory device is operated to assist the gear drive under some soil conditions. 
   The need exists for improved vibratory pile driving systems and methods. 
   SUMMARY OF THE INVENTION 
   The present invention may be embodied as a drive system for driving and/or extracting an elongate member. The drive system comprises a piston drive assembly, a hydraulic system, and a vibration drive assembly. The piston drive assembly comprises a piston member, and the piston member engages the elongate member. The hydraulic system is operatively connected to the piston drive assembly to apply a drive force to the piston member. The vibration drive assembly generates a vibratory force. The vibration drive assembly is operatively connected to the piston drive assembly. The drive system operates in a first mode in which the drive force and the vibratory force are applied to the piston member along a drive axis. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  are somewhat schematic side, elevation, partial sectional views of a vibratory pile driver of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 2  of the drawing, depicted therein is a pile driving system  20  constructed in accordance with, and embodying, the principles of the present invention. The pile driving system  20  comprises a piston drive assembly  22  and a vibration drive assembly  24  and is adapted to drive a pile  26  into the earth  28 . 
   In the example use of the system  20  depicted in  FIGS. 1 and 2 , the drive assemblies  22  and  24  are connected to a support structure  30  by a first suppressor system  32 . In addition, a guide system  40  is connected to the support structure  30  by a second suppressor system  42 . 
   In use, the piston drive assembly  22  applies a constant downward or upward driving force on the pile  26  along a drive axis B that is substantially aligned with the pile axis A. The vibration drive assembly  24  generates vibration forces that are also aligned with the drive axis B. In some soil conditions, the piston drive assembly  22  can be used alone. In other soil conditions, the driving force of the piston drive assembly  22  is combined with the vibratory forces of the vibration drive assembly  24  to facilitate driving of the pile  26 . 
   The support system  30  may take many different forms but should be of sufficient strength to support the weight of the pile driving system  20 , the pile  26 , and any associated equipment such as the guide system  40  and the suppressor systems  32  and  42 . Preferably, the support system  30  allows the pile driving system  20  and pile  26  to be moved to an appropriate location and angle relative the ground  28 . The first suppressor system  32  also is or may be conventional and inhibits the transmission of the vibration forces generated by the vibration drive assembly  24  to the support system  30 . 
   The example support system  30  is attached to the boom of a spotter or excavator as conventionally used in the construction industry. The spotter or excavator is a vehicle that can be moved along the ground and which also allows rotation of the pile driving system  20  and pile  26  about a horizontal axis of rotation. 
   The guide system  40  is optionally used to guide the pile  26  as the pile  26  is driven into the earth  28 . In particular, the guide system  40  is connected to the support system  30  such that guide system  40  helps maintain the axis A of the pile  26  in substantial alignment with the drive axis B defined by the pile driving system  20 . The second suppressor system  42  also is or may be conventional and inhibits the transmission of the vibration forces generated by the vibration drive assembly  24  to the support system  30  through the guide system  40 . 
   With the foregoing general understanding of the operation of the present invention in mind, the details of construction and operation of the example pile driving system  20  will now be described. 
   The piston drive assembly  22  comprises a piston housing  50  and a piston member  52 . The piston housing  50  defines a piston chamber  60 , first and second shaft openings  62  and  64 , and first and second ports  66  and  68 . The piston member  52  comprises a piston flange  70  and first and second shaft portions  72  and  74 . The first and second shaft portions  72  and  74  define first and second distal ends  76  and  78 . The second distal end  78  is adapted to engage the pile  26 . The example piston member  52  is steel and is depicted as being a hollow tube, but the piston member  52  may be made of different materials and in other forms. 
   The piston member  52  is arranged such that the piston flange  70  is within the piston chamber  60  and the first and second shaft portions  72  and  74  extend through the first and second shaft openings  62  and  64 , respectively. The first and second shaft openings  62  and  64  are sealed substantially to prevent fluid flow through these openings  62  and  64  during normal operation of the system  20 . 
   When the system  20  is assembled, the distal ends  76  and  78  of the piston member  52  are located outside of the piston chamber  60 . In addition, the piston flange  70  divides the piston chamber  60  into first and second chamber portions  60   a  and  60   b . The first port  66  is configured to allow fluid flow into and out of the first chamber portion  60   a , while the second port  68  is configured to allow fluid flow into and out of the second chamber portion  60   b.    
   A hydraulic system  80  is connected by first and second fluid conduits  82  and  84  to the first and second ports  66  and  68 , respectively. The hydraulic system  80  is configured to force hydraulic fluid into either of the chamber portions  60   a  or  60   b  to displace the piston member  52  relative to the piston housing  50 . In particular, fluid forced into the first chamber portion  60   a  acts on the piston flange  70  to cause the piston member  52  to move in a direction indicated by arrow C in  FIGS. 1 and 2 ; fluid forced into the second chamber portion  60   b  acts on the piston flange  70  to cause the piston member  52  to move in a direction opposite to that indicated by arrow C. 
   The volumes of the first and second chamber portions  60   a  and  60   b  change in inverse proportion to each other as the piston member  52  moves. The hydraulic system  80  is thus configured to allow fluid to flow out of the non-pressurized chamber portion  60   a  or  60   b  back to the hydraulic system  80  as the piston member  52  is displaced as described above. 
   The second end  78  of the piston member  52  engages the pile  26  such that the driving and vibratory forces are applied along the pile axis A. Typically, the second end  78  is clamped or otherwise connected to the pile  26  such that the vibratory forces are effectively transmitted from the piston member  52  to the pile  26 . In the example system  20  depicted in  FIGS. 1 and 2 , the second end  78 , defines a flange  90  that is bolted or otherwise secured to a similar flange  92  formed on an exposed end  94  of the pile  26 . However, the second end  78  may be clamped to the exposed pile end  94  or elsewhere to a side surface  96  of the pile  26 . In some situations, it may be possible for the second end  78  not to be connected to the pile  26 . 
   Referring now to the vibration drive assembly  24 , the vibration drive assembly  24  is attached to or otherwise rigidly fixed relative to the piston housing  50  as shown in  FIGS. 1 and 2  or possibly to the piston member  52 . If attached directly to the piston member  52 , the vibratory forces are directly transmitted to the piston member  52 . 
   When attached to the piston housing  50 , the vibratory forces generated by the vibration drive assembly  24  are transmitted to the piston housing  50  and through the hydraulic fluid within the piston chamber  60  to the piston member  52 . For maximum transmission of vibratory forces through the hydraulic fluid, the hydraulic system  80  is configured to prevent fluid flow through either of the ports  66  or  68 . However, the vibration drive system  24  may be operated with one or both of the ports  66  and  68  open as may be required to operate piston drive assembly  22 . 
   The vibration drive assembly  24  is or may be conventional and is depicted in  FIGS. 1 and 2  as comprising a vibro housing  120  and first and second counter-rotating eccentric weights  122  and  124 . The vibro housing  120  may take many forms but should at a minimum have structure that allows it to be rigidly attached to the piston housing  50  or piston member  52 . The vibro housing  120  should also provide structure for rotatably supporting the eccentric weights  122  and  124 . 
   The eccentric weights  122  and  124  can take different forms but typically comprise an axle portion and a weight portion, where the center of gravity of the weight portion is offset from the axis of the axle. Typically, the axle is rotated by a hydraulic motor. More than two weights can be provided, but the weights should be balanced such that, when counter-rotated, lateral forces are canceled and drive forces are summed. 
   The support structure  30  can take many different forms and is only highly schematically represented in  FIGS. 1 and 2 . The support structure will typically take the form of a rigid metal structure having a coupler portion  130 , a first support portion  132 , and a second support portion  134 . The coupler portion  130  is adapted to be connected to a boom  136  of a spotter, excavator, crane, or the like. The first support portion  132  is adapted to be connected to the first suppressor system  32 . 
   The example first suppressor system  32  comprises a plurality of elastic members  140  that are connected between the first support portion  132  and either the piston housing  50  as shown or the piston member  52 . The elastic members  140  resiliently oppose movement of the pile driving system  20  relative to the support structure  30  to inhibit transmission of shocks from the pile driving system  20  to the support structure  30 . 
   The second support portion  134  is adapted to be connected to the second suppressor system  42 . As will be described below, the guide system  40  engages the pile  26  such that vibrations on the pile  26  may be transmitted to the guide system  40 . The example second suppressor system  42  also comprises a plurality of elastic members  142 ; the elastic members  142  are connected between the second support portion  134  and the guide system  40 . The elastic members  140  and  142  resiliently oppose movement of the guide system  20  relative to the support structure  30  to inhibit transmission of shocks from the guide system  40  to the support structure  30 . 
   The guide system  40  comprises a guide housing  150  and guide members  152 . The guide housing  150  supports the guide members  152  to engage the pile  26  such that the axis A of the pile  26  is substantially aligned with the drive axis B as shown in  FIGS. 1 and 2 . The guide members  152  may be formed by rollers, gears, bumpers, or the like that engage opposing portions of the side surface  96  of the pile  26 . Four guide members  152  are depicted in  FIGS. 1 and 2 , but typically an additional four guide members will be arranged to engage the pile  26  in a plane orthogonal to the plane in which the depicted guide members lie. 
   From the foregoing, it should be clear that the present invention may be embodied in forms other than the form described above. The above-described embodiment is therefore to be considered in all respects illustrative and not restrictive.

Summary:
A drive system for driving and/or extracting an elongate member. The drive system comprises a piston drive assembly, a hydraulic system, and a vibration drive assembly. The piston drive assembly comprises a piston member, and the piston member engages the elongate member. The hydraulic system is operatively connected to the piston drive assembly to apply a drive force to the piston member. The vibration drive assembly generates a vibratory force. The vibration drive assembly is operatively connected to the piston drive assembly. The drive system operates in a first mode in which the drive force and the vibratory force are applied to the piston member along a drive axis.