Abstract:
A wick assembly for installation under a roadway according to the invention includes a perforated drain pipe, an inner sheet of a wicking fabric disposed on the perforated drain pipe in a manner effective to cover the perforations therein, an outer sheet of a wicking fabric, and a layer of filter aggregates confined between the inner and outer wicking fabric sheets to form a wick drain in combination with the perforated drain pipe. Water passes through the sheets and filter aggregates in order to enter the perforated drain pipe through the perforations therein. The wick drain may be disposed inside an outer pipe with the outer fabric sheet in slidable contact with the inner periphery of the pipe casing. The outer pipe casing serves to protect the wick drain during installation and is later removed once the wick drain is in position.

Description:
[0001]    This application is a divisional of Ser. No. 11/640,782, filed Dec. 18, 2006, which is a continuation-in-part of Ser. No. 11/087,305, filed Mar. 23, 2005, now abandoned, which claims the benefit of U.S. provisional patent application No. 60/556,536 filed Mar. 26, 2004. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to methods and systems for the installation of underdrains beneath roads and other structures. 
       BACKGROUND OF THE INVENTION 
       [0003]    Highways and other paved or concrete roadways can be damaged by water or other accumulated liquids under the roadway. The formation of bumps or frost heaves begins as water seeps under the roadway. As the water freezes and expands in cold weather, the resultant ice pushes up the roadway and forms bumps in the road. These road bumps require considerable cost and time to cut out the damaged areas and repave or reapply concrete. Further, such roadway repairs require additional costs in closing down traffic and providing traffic control. 
         [0004]    Haas U.S. Pat. No. 4,808,024, Feb. 28, 1989, provides a method for installing a pavement underdrain wherein underdrains in the form of perforate pipes, preferably covered with a geotextile sock as a filter, are disposed transversely to the lengthwise direction of the roadway in close proximity to faults, cracks, joints and other fissures in the roadway. The underdrains conduct water away from such fissures thereby preventing roadbed particulate material from being pumped upwardly through the fissures together with water which collects below the concrete roadway. However, these underdrains have a relatively limited life in the field, such as 5 years or so, due to the, tendency for the filter fabric to become clogged. The present invention provides a wick drain having a much greater useful life, as well as a method for installing such a wick drain in situations where open cutting or trenching is impractical. 
       SUMMARY OF THE INVENTION 
       [0005]    A wick assembly for installation under a roadway according to the invention includes a perforated drain pipe, an inner sheet of a wicking fabric disposed on the perforated drain pipe in a manner effective to cover the perforations therein, an outer sheet of a wicking fabric, and a layer of filter aggregates confined between the inner and outer wicking fabric sheets to form a wick drain in combination with the perforated drain pipe, such that water passes through the sheets and filter aggregates in order to enter the perforated drain pipe through the perforations therein. The wick drain may be disposed inside an outer pipe with the outer fabric sheet in slidable contact with the inner periphery of the pipe casing. As described further, the outer pipe casing serves to protect the wick drain during installation and is later removed once the wick drain is in position. 
         [0006]    The invention further provides a method for installation of a wick drain in the ground. First, if necessary, a passageway is formed through the ground having an entry opening and an exit opening. A wick drain such as the one described above disposed inside a pipe casing is drawn into the passageway until the wick drain is positioned inside the passageway. Then the pipe casing is removed from the passageway by sliding it off of the wick drain, leaving the wick drain in the passageway in a position that allows accumulated liquids to be drawn into the wick drain and drain out of the passageway. The method can be used with a preexisting passageway, although most commonly a new passageway will be drilled using a directional drilling machine. To aid in removing the pipe casing while leaving the wick drain in place, it is preferred to secure the wick drain against lengthwise movement inside the passageway prior to removing the pipe casing, such as by tying it at one end to an anchoring object and pulling on the pipe casing from the other end. 
         [0007]    The foregoing method can be practiced with a horizontal directional drilling machine such as the Vermeer Navigator. Using an HDD machine, a pilot hole is drilled from the entry opening to the exit opening, and a back reamer is then connected to the distal end of the drill string, which back reamer is in turn connected to the pipe casing. The HDD machine then pulls the back reamer and pipe casing with the wick drain inside. back through the pilot hole to fully form the passageway. If there is an existing pipe or drain in place, then the step of drilling the pilot hole is omitted, and the back reamer can be provided with pipe bursting capability so that existing pipe is burst as the pipe casing and wick drain are drawn in. One such pipe bursting pipe puller is described in Wentworth et al. U.S. Patent Publication 20040218982, Nov. 4, 2004, the contents of which are incorporated herein by reference. 
         [0008]    The invention further relates to an underdrain for a railroad bed comprising a railroad track and bed on which the track is built. The underdrain includes an elongated perforate pipe for collecting water from the railroad bed, which, pipe is disposed in the railroad bed directly below the track and runs along the lengthwise direction of the track, preferably along the centerline of the bed or close to it. At least one outlet pipe is in communication with the perforate pipe, which outlet pipe extends laterally from the perforate pipe and has an outlet opening on one side of the railroad bed which conducts water from the underdrain out of the railroad bed. The invention further provides a method for installing the foregoing railroad underdrain using a directional drilling machine. This and other aspects of the invention are set forth in the detailed description which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the accompanying drawings: 
           [0010]      FIG. 1  is a cross section of a wick drain according to the invention; 
           [0011]      FIG. 2  is a cross section of a wick drain according to the invention wherein the aggregate layer has been subdivided into lobes; 
           [0012]      FIG. 3  is a cross section of the wick drain of  FIG. 2  inserted inside a pipe casing prior to installation; 
           [0013]      FIGS. 4-8  are a series of schematic diagrams illustrating a method of installing a wick drain according to the invention; 
           [0014]      FIG. 9  is a top view of a railroad bed drain installation according to the invention; 
           [0015]      FIG. 10  is a side view of the installation shown in  FIG. 9 ; and 
           [0016]      FIG. 11  is an end view of the installation shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  illustrates a wick drain  10  according to the invention. Wick  10  is formed by assembling inner and outer sheets  11 ,  12  with a layer of filter aggregate  13  in between. Sheets  11 ,  12  are preferably made of a rot-proof woven or non-woven fabric geotextile permeable to water but substantially impermeable to fines, i.e. soil particles. The filter materials  13  may include tire crumb rubber, a rock aggregate, ⅛″ granular sand, a combination of these materials, and/or other suitable filter materials. The size of the filter material may be 3/8-inch chunks, for example. The multi-layer wick  10  may be loosely held together, sewn together, fabricated and/or fastened in a suitable manner. Wick  10  is then wrapped around a plastic drain pipe  14  having perforations  15  along its length to allow water to drain inside. Opposing side edges of wick  10  are sewn together, stapled, glued, bonded, or the like along its top margin  16 . A suitable cord such as a length or rope or “mule tape” (nylon cord)  17  is also sewn into place along top margin  16  and has free ends  18  extending from each end of wick  10 . 
         [0018]    In a preferred form of a wick  20  according to the invention as shown in  FIGS. 2-3 , a series of seams  21  are sewn, stapled, or the like in a lengthwise direction to form five lobes  22  in cross section as shown. The lobed structure prevents the aggregate  13  from shifting down to the bottom during the fabrication of the wick or during the installation process. The extent to which this is a problem will vary depending on how the wick is handled during installation and the nature of the filter material. Other means for preventing settling of the filter material, such as a series of spaced apart, radially-extending screens or partitions subdividing the filter layer  13 , may be used as well. Edges of extra material at opposite sides of outer sheet  12  are superposed and sewn together to form an outwardly extending flap  25  to which cord  17  is secured on one side. 
         [0019]      FIG. 3  shows the wick  20  inserted inside an outer pipe or pipe casing  24  used during the installation of the hydraulic wick  20  as described below. Pipe  24  may be a 6⅛-inch high density polyethylene (HDPE) plastic pipe, for example. Pipe  24  is preferably not perforated so that, in the event the wick is installed through an area already saturated with water; the water will not start entering the wick drain until the wick drain is fully installed. Such water can greatly add to the weight of the assembly and cause breakage during installation. However, in areas where there is no risk of standing water entering wick drain  20  at the time of installation, it may be feasible to form perforations in outer casing  24  and leave it in place rather than pull it off of the wick drain. Pipe casing  24  also acts as a protective covering for the hydraulic wick which could otherwise become torn if pulled into a hole by itself. Wick  20  is secured along a pair of superposed edges forming a flap  26  to which the cord  17  is secured. 
         [0020]      FIGS. 4-7  illustrate a method for installing a wick drain  10  or  20  according to the invention underneath a roadway  30 . In a horizontal, double-ended drain installation, a horizontal directional drilling (HDD) machine  31  is used to drill a horizontal pilot hole  32  with a duckbill or Trihawk® bit at the desired location. Entry and exit openings  33 ,  34  may already be exposed on the shoulders of the roadway  30 , as where roadway  30  has a pair of drainage ditches  36  on either side, or it may be necessary to dig entry and exit pits. A foaming agent, water or another fluid may be ejected from the bit to aid in drilling and float excess material out of the bore during drilling in a manner known in the art. At the end of the drilling step, a drill string  35  connected to HDD machine  31  emerges from exit opening  34 . 
         [0021]    A series of 20 foot sections of HDPE pipe are fused together end-to-end to the desired length to make the pipe casing  24 , which preferably has a length which is about the same as the length of hole  32 . A rope or nylon cord is blown through pipe  24  (or fed through by tying a weight to the end) and tied to one free end of cord  17 . Wick  20  is then pulled inside casing  24  using the rope so that it assumes the position shown in  FIG. 3 . During this step, the lobes  21  of wick  20  contact the inner periphery of casing  24  and compress to some extent as shown. The foregoing steps are normally carried out to one side of the road near exit opening  34 . 
         [0022]    The drill bit is then removed and a back reamer  41  is mounted on the exposed end of the drill string  35  at exit opening  34 . Casing  24  is attached thereto with any desired conventional pipe pulling accessory, such as a pipe pulling mesh that contracts on the outside of pipe casing  24  when pulled on. HDD machine  31  is then operated in pullback mode, whereby back reamer  41  passes along the length of the pilot hole  32  and widens it as shown in  FIG. 4 . The assembly of pipe casing  24  and wick  20  is pulled along behind reamer  41 . For this purpose, casing  24  has the same or slightly smaller diameter than the greatest outer diameter of reamer  41 . During this step, wick drain  20  stays inside pipe casing  24  due to its weight; it is not otherwise secured. When the casing  24  and wick drain  20  are fully installed as shown in  FIG. 5 , back reamer  41  will have emerged from the original entry opening  33 . At this stage, the rear free end of the sewn-in cord  17  is tied to an anchoring object  42  (tree, stake set in the ground, post, etc.) Pulling on casing  24  then continues, resulting in pulling the pipe casing  24  off of wick drain  20 , leaving drain  20  in place in the bore. If back reamer  41  is not already at the HDD machine  31  at the end of the run, this can be done by continuing to pull back reamer  41  towards machine  31 . Once back reamer  41  is fully retracted, HDD machine  31  itself (which is self-propelled on treads) backs away from entry opening  33  in order to continue pulling casing  24  out (see  FIG. 6 ). This step could also be done manually by detaching casing  24  from reamer  41  and pulling on it with human workers, the feasibility of this depending on the length of pipe casing  24  and tightness of engagement between it and the soil. When casing  24  has been fully removed, wick drain  20  is fully installed as shown in  FIG. 7 . Exposed ends of cord  17  are removed and screens (not shown) may be placed over the exposed end openings of the wick drain  20 . The lobed structure shown in the drawing having two geotextile layers with aggregate in between can last up to 100 years. 
         [0023]      FIG. 8  shows a form of blind drain  50  installed using the same method as described above, except that the wick drain is at an angle so that water drains out of its exposed exit opening  51 . Its entry opening may be left exposed and covered with a screen, or sealed off with a cap and the original entry hole  33  filled in above it, forming the blind drain  50 . 
         [0024]    The wick drain  10 ,  20  according to the invention remains in place under the roadway to draw any accumulated water and other liquids into the perforated drain pipe  14 . The multi-layer materials  11 - 13  act like a wick to absorb, filter and conduct the liquids into drain pipe  14 , which allows the collected liquids to be pulled by gravity and flow out of the exit point(s) of the drain. The filter materials  11 - 13  further prevent debris from clogging the perforated drain pipe  14  and ensures the proper operation of the hydraulic wick  20 . 
         [0025]    The hydraulic wick apparatus and method of the invention avoid the expense of cutting the highway, traffic control, and repaving or reapplying concrete to repair the roadway. The installation of the hydraulic wick may be performed while traffic is traveling on the roadway, therefore minimizing impact to traffic. Only limited traffic control is needed to ensure driver and road crew safety. 
         [0026]      FIGS. 9 to 11  show a double-ended underdrain  60  formed beneath a raised railroad bed  61 . For this type of installation, unlike the transverse underdrains used beneath roadways, it is efficient to collect water along the centerline of the railroad bed in an area where it tends to accumulate. For this purpose, drain  60  is generally z- or s-shaped, with a midsection  62  running along the centerline of the railroad bed  61 , and a pair of end sections  63 ,  64  foaming outlet pipes angling downwardly from opposite ends of mid-section  62  and at obtuse angles relative to midsection  62 . HDD machine  31  is used to steer at the junctures between sections, and pipe casing  24  has sufficient flexibility to follow the path shown, the method of installation otherwise being the same as that practiced for a roadway as described above. The actual dimensions can be varied from those shown to make drilling and reamer pullback easier. The underdrain may be a wick drain as described herein or a simpler form of drain, such as a perforate pipe by itself or covered with a geotextile sock as described in Haas U.S. Pat. No. 4,808,024, Feb. 28, 1989, the contents of which are incorporated by reference herein. 
         [0027]    While the invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. The aggregate could, for example, be filled into geotextile sleeves forming sandbags which are then wrapped around the inner perforate pipe side by side along its length, eliminating the need for long, quilted blanket having the same length as the perforate inner pipe. These sandbags could wrap all the way around the perforate pipe or only part way around, as long as the perforations are adequately covered. There and other modifications and combinations of the illustrative embodiments will be apparent to persons skilled in the art upon reference to the description. Such variations and additions are specifically contemplated to be with the scope of the invention. It is intended that the appended claims encompass any such modifications or embodiments.