Abstract:
An apparatus for repairing an underground pipe includes a mandrel having a first expander capable of extending and retracting in a radial direction, a system for causing radial expansion and retraction of the expander when in position at a pipe location in need of repair, a resilient stiffening frame disposable in a tubular configuration outside of the expander, such that the expander can be used to expand the frame into contact with the inside of the pipe, and a suitable arrangement for confining a flowable cement between the expander and the inside of the pipe to form a repair band upon setting of the cement. In a preferred form of the invention, the expander comprises a central inflatable bladder, and the system controlling radial extension and retraction of the expander includes a line supplying pressurized air to the bladder.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to the repair of underground pipes and in particular to the repair of culverts and similar pipes with a repair band installed in the pipe. 
       BACKGROUND OF THE INVENTION 
       [0002]    Concrete pipe is used in a wide variety of applications including sanitary and storm sewers. Concrete pipe is widely used for culverts that drain, and providing drainage though, roadbeds and similar structures. Typically, concrete pipe is installed in pre-cast sections with bell-shaped end connections in which an end of a first section fits into the bell-shaped end of the next section. A gasket or packing is used to seal the connection. 
         [0003]    Concrete pipes are susceptible to failure and leakage due to a variety of factors. The need to repair concrete pipes used in various applications has grown steadily with the aging of existing infrastructures. For example, it has been estimated that when roadbed culverts are cleaned, about 60% of the culverts have separated and/or displaced joints. Poor or under design, improper installation, heaving due to frost, settling, earthquakes and other earth movement can cause cracking, erosion and joint separation. Chemical attack on concrete pipes used as sanitary sewers is also well known. 
         [0004]    A crack or separated joint in a concrete pipe can cause leakage into and out of the pipe. When fluid leaks into the pipe, often spoil is carried into the pipe, decreasing the flow through the pipe and creating a void in the soil or ballast supporting the pipe. When fluid leaks out of a concrete pipe, it tends to loosen or erode the soil or ballast around the pipe, potentially allowing the pipe to settle or, at the least, increasing the stress on the pipe. In either case, if enough of the soil or ballast supporting the pipe is washed away, the pipe and overlying structures may collapse. When the concrete pipe is a culvert through a road bed under a highway or railroad, such a collapse can have serious or catastrophic consequences. 
         [0005]    Techniques for in place repair and rehabilitation underground pipes and in particular underground concrete pipes have become well known and widely used due to the inherent disadvantages of excavating such pipes. See, e.g., U.S. Pat. Nos. 7,018,691, 6,796,334 and 5,388,929. The cost of labor and machinery required for excavation has risen steadily over the years. Excavating a culvert that goes through a roadbed requires closing the road or railroad and diverting traffic, an often costly and time consuming process. Once the pipe has been excavated and replaced, the trench roadbed must be backfilled and the road repaired. Often, settlement occurs after the repair, requiring more repairs to the road and roadbed. In urban areas, excavating pipes running under streets to effect repairs can cause severe traffic disruptions. 
         [0006]    In the case of culverts and similar concrete pipes that are large enough for personnel to physically enter, typically more than 36 inches in diameter, joint separations and similar damage may be repaired with steel repair bands. Repairing small diameter culverts without excavation is more difficult. As used herein, the term “small diameter” refers to pipes 36 inches or less in inner diameter. Generally, it is not possible for personnel to physically enter small diameter pipes to install repair bands. Other methods of repair, such as spraying a concrete mixture over the damaged area may not be satisfactory since the cured concrete has relatively little tensile strength and is vulnerable to the same type of forces that caused the original damage. This is particularly the case where the pipe or culvert must withstand significant static and live loading as in the case of a culvert under a railroad or highway roadbed. 
         [0007]    Lining or re-lining pipes can be carried out by a number of methods for the purpose of pipeline rehabilitation. According to the commercially available “Easy-Liner” process, resin-impregnated sleeves are cured in place after being expanded into position by an inflatable bladder; see e.g. http://www.easy-liner.com/ under “Remote Liner”. According to another method described at www.relineamerica.com, a deflated liner is pulled into the pipeline to be relined, inflated with air, and then cured with UV light to form a hardened lining. See EP1262708 (A1) describing a method for repairing and regenerating a duct by installing a liner having a thick wall in the duct. The method for repairing and regenerating the duct comprises the steps of filling a fiber hose having a wall thickness of 10 mm or more and impregnated with a resin in a damaged part of the duct, mounting the hose on an inner surface of the duct, and then curing the resin. The resin contains an UV initiator and an organic peroxide. The resin is cured by a light source having at least two UV lamps each having at least 400 W output and disposed before and after the resin. A luminosity of the UV light irradiated to the inner wall of the hole needs at least 800 W/m. These and other methods of in-situ relining wherein a fabric liner is everted into the pipe and impregnated with a resin have been used commercially but may not provide sufficient tensile strength to the repaired area to withstand significant stress. 
       SUMMARY OF THE INVENTION 
       [0008]    An apparatus for repairing an underground pipe according to the invention includes a mandrel having a first expander capable of extending and retracting in a radial direction, suitable means for causing radial expansion and retraction of the expander when in position at a pipe location in need of repair, a resilient stiffening frame disposable in a tubular configuration outside of the expander, such that the expander can be used to expand the frame towards the inside of the pipe, and suitable means for confining a flowable cement between the expander and the inside of the pipe to form a repair band upon setting of the cement. The stiffening frame is preferably pervious to the cement and has a spacing element that defines a minimum thickness of the repair band. In a preferred form of the invention, the expander comprises a central inflatable bladder, and the means for controlling radial extension and retraction of the expander includes a line supplying pressurized air to the bladder. 
         [0009]    The means for confining flowable cement between the expander and the inside of the pipe can vary considerably as described below. The site needing repair often is a break in the pipeline, and as such injection of flowable cement without anything to confine it (acting as a mold) would cause it to ooze out of the pipeline into the surrounding soil. Approaches to confining the cement generally include either providing a full or partial covering for the cement that it cannot flow through, or using seals such as air filled bladders to temporarily creating a confined space that fills up with cement as it is cast at the site to be repaired, or a combination of these. These and other examples are discussed in detail below. 
         [0010]    A method for repairing an underground pipe according to the invention, such as by using an apparatus as described above, includes the steps of positioning a flexible stiffening frame inside the pipe at a location to be repaired, positioning an extendable expander inside of the frame, extending the expander to push the frame radially outwardly towards the inside of the pipe, injecting a flowable cement into a space between the expander and the inside of the pipe, and confining the cement so that it forms a repair band having the frame embedded therein upon curing. If the cement takes a significant amount of time to cure, the method can further include steps of maintaining the expander extended until the cement cures sufficiently to be self-supporting, then retracting the expander. Such a method can be carried out without sending a worker into the pipe or conduit, and is especially well adapted for smaller pipes or conduits less than 3 feet in inner diameter. 
         [0011]    The expander may be mounted on a mandrel such that the positioning steps comprise wrapping the stiffening frame around the mandrel and expander, and inserting the mandrel and expander into the pipe and moving it to the location to be repaired. The stiffening frame is preferably coiled or folded around the expander and mandrel into a tubular configuration. As will become clear from the detailed description that follows, these steps are not always performed in the order listed. For example, the stiffening frame could be pre-positioned in the conduit and the apparatus then inserted into it, or could be mounted on the spacer and the apparatus and band inserted into the conduit together. 
         [0012]    A conduit joint according to the invention, which may be formed by the foregoing method, includes a first pipe section, a second pipe section adjacent the first section, and a repair band disposed inside and spanning the first and second pipeline sections. The repair band comprises a resilient frame embedded in a hardened cement. The band is not a liner, i.e., it has a length less than that of the pipeline sections, whereby one end of the repair band opens onto the interior of the first conduit section, and the other end of the repair band opens onto the interior of the second pipeline section. Often, due to shifting of the ground, the pipe sections will have pulled apart from one another and will no longer be coaxial. In such a case, the repair band contacts and conforms to the inner surfaces of the first and second pipeline sections, effectively sealing the break. 
         [0013]    In another aspect, the invention provides a flexible repair band for effecting repairs to an underground pipe. Such a band comprises a resilient frame as described above bendable into a coiled configuration and disposed inside of a sleeve of a fabric impervious to the cement. One or more openings are made in the sleeve prior to use so that the cement may be pumped inside to fill the sleeve. These and other aspects of the invention are further described in the detailed description that follows. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and wherein: 
           [0015]      FIG. 1  is a lengthwise sectional view of an inflatable pipe repair apparatus according to the invention in a conduit prior to full inflation of the bladders; 
           [0016]      FIG. 2  is the same view as  FIG. 1 , with bladders fully inflated; 
           [0017]      FIG. 3  is the same view as  FIG. 2 , with bladders partially deflated following installation of a repair band according to the invention; 
           [0018]      FIG. 4  an end view of the apparatus of  FIG. 1 ; 
           [0019]      FIG. 5  is a schematic end view of a folded repair band according to the invention; 
           [0020]      FIG. 6  is a partial bottom view of a reinforcing frame according to the invention; 
           [0021]      FIG. 7  is a side view of the frame of  FIG. 6 ; 
           [0022]      FIG. 8  is a end view of the frame of  FIG. 6 ; and 
           [0023]      FIG. 9  is a lengthwise section of a completed repair band according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    According to a first example of the invention, an underground pipeline or conduit is repaired by means of a repair band that is formed from a curable cement material reinforced with a resilient metal frame. The apparatus for positioning the repair band is mounted on the end of a drill string and extended into the pipe using a horizontal directional drill (HDD) machine such as a D24x40 Navigator produced by Vermeer Manufacturing of Pella Iowa. When the apparatus is positioned at the location to be repaired, the expander is extended to expand the frame into conformity with the inside of the conduit. Grout is pumped to the area to be repaired and is retained about the frame until cured. The frame becomes embedded in the cured grout, reinforcing the repaired area. 
         [0025]    In a preferred form of the method, the step of positioning the resilient frame precedes the introduction of the grout into contact with the frame, giving the method of the invention a cast-in-place character. For purposes of the present invention, “grout” or “cement” refer to a fluid, flowable substance that is capable of assuming a solid state following curing, setting or cooling. Conventional Portland cements can be used, but commercially available rapid-curing cements or “jet cements” are particularly preferred, since the apparatus cannot be removed until the cast repair band is sufficiently self-supporting. Plastic thermosets, epoxys and thermoplastics can also be used. 
         [0026]    Referring to  FIGS. 1-5 , an apparatus  10  for repairing underground pipes includes an elongated rigid cylindrical support member or mandrel  12  preferably fabricated from a tube  13  made of plastic pipe such as polyethylene (PE), polyvinyl chloride (PVC), high density polyethylene (HDPE) or similar material. A centering cone or end cap  16  on the forward end of apparatus  10  forms a tapered nose and has a rearwardly extending cylindrical extension  19  that extends into mandrel  12  and is held there by screws inserted through the adjoining wall of tube  13 . A rearwardly tapering, plastic rear end cap  14  is secured over the rear end of tube  13  in a manner similar to cap  16 . End cap  14  has a threaded rear opening  20  for connecting mandrel  12  to matching external threads of a steel adapter  22 , which in turn has a threaded socket  23  for connecting mandrel  12  to a drill string driven by an HDD or similar machine. 
         [0027]    Apparatus  10  includes at least one generally cylindrical expander mounted on or fitted over mandrel  12 . In the illustrated embodiment, the expanders include a inner tube-shaped front inflatable bladder  32 , middle inflatable bladder  33  and inflatable rear bladder  34  positioned end to end and secured to mandrel  12  by a cover  35  that is fastened to mandrel  12  at opposite ends of the bladders  32 - 34  by a pair of hose clamps  40 . Bladders  32 - 34  serve to expand the repair band against the inside of a pipe to be repaired and, to the extent needed, hold it in position during the repair to allow the grout to cure. Bladders  32 - 34  are generally cylindrical in shape when inflated, coaxial with mandrel  12 , and are formed from a tough, durable material such as a urethane, nylon or other suitable synthetic material. In a completely deflated state, bladders  32 - 34  collapse from the positions shown in the drawings. In the alternative, if it is desired that bladders  32 - 34  maintain the shape shown in  FIG. 1  without partial inflation, an open-celled plastic foam core can be provided inside of each bladder. 
         [0028]    A pair of air hoses  36 ,  38  extend through a side opening  37  in cap  14  into mandrel  12 . Hose  36  is secured at an outlet port  39  in tube  13  to supply compressed air or similar fluid into middle bladder  33 . Hose  38  is split into two branches through further outlet ports  39  to supply compressed air for simultaneous inflation of front and rear bladders  32 ,  34 . Hoses  36 ,  38  are individually controlled by valves back at the air compressor. 
         [0029]    A repair band  50  for repairing a separated joint, crack or hole in a pipe or culvert is wrapped or folded around apparatus  10 . As illustrated in  FIGS. 1-4 , repair band  50  comprises a resilient reinforcing frame  52  disposed inside a cylindrical cover  54 . As shown in  FIG. 6-8 , frame  52  in a preferred form of the invention comprises a chain link sheet  56  having a series of corrugated steel strips  57  disposed in alternate rows of mesh openings  58  and covered on the opposite side by flat bands  59 . Bands  59  are intermittently spot-welded to the tops of corrugations  61  at welds  62 . A frame with the foregoing design has proven durable and strong for use in environments subject to vibrations, such as railroad beds. In less active sites, a single sheet of mesh or corrugated material may prove sufficient. Frame  52  is preferably permeable to the injected grout and permits the grout to spread out evenly through and on both sides of it. 
         [0030]    Cover  54  comprises a pair of sheets  66  of nylon or similar fabric, such as commonly used as tarp or ground cover, that is impermeable to the grout. Sheets  66  are bonded around their edges with frame  52  between them, sealing frame  52  inside. The resulting band  50  is rectangular in its flat condition, and is bent into a cylinder with its ends  51  touching or overlapping prior to use. Suitable means such as a band  67  of shrink wrap, rope or the like is used to hold band  50  in its cylindrical shape, which is smaller than the internal diameter of the pipeline into which the band will be inserted. The extent to which the ends overlap is not great but will vary depending on the amount that the band  50  will expand when installed. It is possible, for example, to apply band  50  inside a culvert of square or rectangular rather than circular cross-section, but the extent of overlap will be greater. As an alternative to overlapping the ends, band  50  can be compressed into a partly folded shape  70  ( FIG. 5 ), and then held in that shape by one or more bands of shrink wrap  71 . 
         [0031]    A grout inlet manifold  72  is inserted into one end of the band  50  by making a slit in the fabric at the desired entry location, about half way between the two ends. Inlet manifold  72  is a tube having a length slightly less than the width of band  50  and a series of sets of perforations  73  therein, preferably in spaced pairs that are alternately offset by ninety degrees so that grout flows out in four directions. A grout inlet tube  74  is attached to one end of manifold  72  and extends rearwardly therefrom far enough to extend beyond the edge of bladder  34 . An air outlet tube  76  is mounted in a slit in the fabric of cover  54  near one end  51 . 
         [0032]    Prior to use, band  50  is placed over mandrel  12  and preferably at least middle bladder  33  is inflated to the extent necessary such that band  50  is securely mounted thereon with its ends overlapped. Band  50  is preferably positioned so that manifold  72  is at or near the top of band  50  and air outlet  76  is at the bottom. The HDD machine is then operated so that band  50  and mandrel  12  are positioned as shown in  FIG. 1  near a break  81  in a conduit or culvert  82 . Positioning may be by direct visual observation or with the use of a camera inserted into the pipe. If an HDD machine is not available, the assembly can be positioned by manual pushing with a rod from the near side, pulling with a winch-driven cable attached to mandrel  12  from the far side of the pipeline, or the like. 
         [0033]    After apparatus  10  is positioned at the repair location, bladders  32 - 34  are inflated with compressed air fed through hoses  36 ,  28  so that band  50  expands (uncoils or unfolds), stretching or breaking wrap  67 , into contact with the inner periphery of conduit  82 . If the inner surface of the conduit is irregular or no longer completely coaxial, frame  52  is flexible enough to allow band  50  to conform to the actual contour at break  81 . Front and rear bladders  32 ,  34  expand to a greater extent than middle bladder  33  and engage the inside of conduit  82  to anchor the assembly into position. However, an embodiment with only a single bladder  33  could be used in lieu of the three bladder arrangement shown. In such a case, the entire interior of tube  13  could act as the air conduit and it would be unnecessary to run air hoses inside of tube  13 . Band  50  in expanded form preferably has its ends  51  either touching or only slightly overlapping. A space between ends  51  would normally be detrimental because it would create a gap through which water or the like could leak from the pipeline. 
         [0034]    A flowable grout or cement such as fast-setting concrete  80  is pumped through a grout hose that is connected to grout inlet tube  74  which conducts the cement into manifold  72 . The cement exits through holes  73  and flows evenly down both sides of frame  52 , permeating frame  52 . Displaced air from the inside of cover  54  exits through air outlet tube  76 . Filling of band  50  with cement is complete when cement can be observed oozing or sputtering from outlet tube  76 . At this time, pumping of the cement ceases and pressure from bladder  34  collapses the exposed end of manifold  72 , forcing uncured cement out of it. Manifold  72  and tubes  74 ,  76  are preferably then removed and cleaned for re-use. 
         [0035]    The thickness of band  50  when cover  54  is filled with grout is usually in the range of from about 1 to 3 inches, or as needed to fully embed frame  52  and create a casting of sufficient strength that does not excessively restrict the inner diameter of conduit  82 . When a cement of heavy consistency is used as the grout, the thickness of frame  52  generally determines the thickness of band  50 . For this purpose, frame  52  is pervious to the cement but has a laterial spacing element that gives frame  52  its thickness. In this example, corrugated strips or bent wires  57  perform this function. Frame  52  could also comprise a corrugated metal sheet with perforations through it, e.g. in staggered, spaced rows. A thin, essentially two-dimensional frame  52  is not preferred for use with cover  54  and a heavy cement as the grout because it is difficult to fill cover  54  with cement to a unform thickness without frame  52  providing the space for the cement to flow into. 
         [0036]    The injected grout is allowed to cure until band  50  is self supporting and sufficiently strong so that curing can run to completion without the support of bladders  32 - 34 . The time needed may vary from almost none to as much as about 2 or 3 hours, typically 30-60 minutes, especially depending on the cement used and the stress the band will be subjected to (as from trains passing on tracks above a culvert while the band in curing). Fast-curing cements tend to generate considerable heat and this must be taken into account in the design of the apparatus. After preliminary curing, bladders  32 - 34  are deflated and apparatus  10  is removed from pipe  81  by withdrawing the drill string, pulling on the cable, or the like. The described method does not require complete draining of the conduit or pipeline and can even be can even be carried out with a bottom portion of the repair band under water. 
         [0037]    In an alternative embodiment of the foregoing method, cover  54  is omitted entirely or replaced with a sheet or membrane on the outside of frame  52 . The grout is then injected through a tube like tube  74 , or one which passes through the center of mandrel  12  and then radially out past or through bladder  33 . Bladders  32 - 34  thereby form a space or mold in which the grout is confined. Use of a sheet or membrane outside of frame  52  is preferably to avoid leakage of grout through break  81  and into the surrounding soil. In this embodiment, it is more important to keep apparatus  10  in position with bladders  32 - 34  inflated until the grout has hardened enough to maintain its shape. Bladders  32 - 34  must also be made of a material that can release from the grout without sticking. For these reasons, this version of the method of the invention is less preferred than the one described previously. 
         [0038]    According to another variation of the procedure, cover  54  is prefilled with grout prior to insertion into the pipeline, and then formed into its final shape rapidly before the grout hardens to too great an extent. This eliminates some of the difficulty of feeding the grout through long lines which must then be cleaned, but the pre-filled band  50  is much heavier and hence more difficult to put into position. 
         [0039]    In some environments it may be feasible to omit frame  52  altogether and simply create the repair band from the cast grout alone. For this purpose cover  54  might be provided with stiffening ribs on the inside or outside. However, frame  52  reinforces and stabilizes the cured grout. As is well known, many cements including concrete based grouts have high compressive strength, but limited tensile strength. Frame  52  reinforces the cured cement by absorbing tensile stresses and loads that would otherwise crack or break the cement in the repaired area. Thus, the use of frame  52  ensures that the repair will survive subsequent loading and stresses due to movement of the earth around the pipe. Since band  50  in any of the preceding embodiments is flexible enough to be wrapped and/or folded onto apparatus  10  and expanded to conform to the inside surface of a pipe or culvert, the need for personnel to access the repair site is eliminated. This is particularly advantageous in the case of smaller diameter pipes that repair personnel cannot physically enter to manually position a repair band. 
         [0040]    As the means for controlling radial expansion and contraction of the expander, a bladder provided with a line permitting inflation is the simplest method and is most preferred. However, a mechanical system provided with radial legs that push the stiffening frame could be used, such as one similar to the frame structure described in commonly-assigned Wentworth et al. U.S. patent application Ser. No. 11/324,018, filed Dec. 30, 2005, the contents of which are incorporated by reference herein. It is also possible to coil the repair band more tightly prior to inserting it into the pipeline, secure it with a cord, clip or the like, and then sever the cord once the band is in the proper position, whereby it uncoils in a forceful manner and becomes lodged against the inside of the existing pipeline. The “means” in such a case would be the cord or fastener in combination with the resilience of the stiffening frame. 
         [0041]    While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art, such changes being embodied within the scope and spirit of the present invention as defined in the appended claims.