WO1999028560A1

WO1999028560A1 - Ground thawing apparatus and method

Info

Publication number: WO1999028560A1
Application number: PCT/US1998/025477
Authority: WO
Inventors: Stewart E. Erickson; Stephen Graning; Daniel J. Halvorson
Original assignee: Seec, Inc.
Priority date: 1997-12-01
Filing date: 1998-12-01
Publication date: 1999-06-10

Abstract

A mat for use in a system for and a method of thawing ground. In one embodiment, the invention provides a thaw mat (124) having a flexible heating fluid conduit (132) held in a prearranged configuration and having a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use. A flexible insulative batting (143) is carried by the heating fluid conduit and overlays the upper surface thereof, the batting and the heating fluid conduit being capable of being repeatedly flexibly deformed as a unit into a compact configuration and deployed as a unit over ground to be thawed. An inlet fitting is attached to an end of the heating fluid conduit and connects the heating fluid conduit to a heated fluid supply. A fluid return fitting is in fluid communication with the heating fluid conduit and with the heated fluid supply in use.

Description

GROUND THAWING APPARATUS AND METHOD

FIELD OF THE INVENTION

The present invention provides a system and method for thawing ground. The invention is particularly useful for thawing ground at varying locations to permit ground to be excavated for construction, natural gas or electrical line installation, etc., but can also be used in other applications, such as maintaining poured concrete or cement above a threshold temperature for curing, melting unwanted "ice dams", or preventing a pile of loose dirt or the like adjacent a work site from freezing.

BACKGROUND OF THE INVENTION

Winter excavation in some jurisdictions is problematic because the ground hardens (freezes). The depth of the frozen ground is referred to as the frost line, and it varies as to latitude, dependent upon the ambient temperature above. For example, in regions above 45° latitude north of the equator, the frost line typically extends three to five feet below the ground, and is even deeper in the Northern-most regions of the United States and in Canada. Excavation by hand is thus quite difficult. Any significant excavation, such as for utility work or for laying foundations, requires power machinery to pierce and dislodge the frozen earth. This presents some difficulty to utility companies who must access buried utility lines such as electrical, water, cable, natural gas, etc. In the case of natural gas lines, the main lines are typically buried 24 inches (minimum) below the ground, while residential service lines are typically buried 18 inches (minimum) below the ground. One means of access to an existing line is to simply dig a hole, or if access is needed along the line, to dig a trench. This approach significantly disrupts the surface of the ground. For laying new utility lines, trenching is required or a ground piercing tool is used. Such tools can lay a cable or utility conduit generally below the ground by self-tunneling or forcing means. This has proved useful in laying utility lines under existing structures, such as sidewalks and roadways, without the necessity for tearing up the existing structure and thereby impeding traffic thereon. However, such piercing tools have difficulty piercing the ground above the frost line, since the ground is frozen and quite solid. Various proposals have been made for mechanisms to thaw the ground prior to excavation. However, none of these provides a suitable means for doing so without some disruption for traffic on a sidewalk or roadway. In addition, prior schemes have been rather complicated, sometimes involving open flames, and are typically rather labor intensive.

SUMMARY OF THE INVENTION

The present invention encompasses both an apparatus for thawing frozen ground and a method for thawing frozen ground which may use the same or a different apparatus. In accordance with a first embodiment of the invention, a flexible, portable thaw mat comprises a flexible heating fluid conduit held in a prearranged configuration and having a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use. A flexible insulative batting is carried by the heating fluid conduit and overlays the upper surface thereof, the batting and the heating fluid conduit being capable of being repeatedly flexibly deformed as a unit into a compact configuration and deployed as a unit over ground to be thawed. An inlet fitting is attached to an end of the heating fluid conduit in use and adapted to releasably connect the heating fluid conduit to a heated fluid supply. A releasable fluid return fitting is in fluid communication with the heating fluid conduit and with the heated fluid supply in use. In one particular adaptation of this embodiment, the thaw mat also includes at least one (and optimally more) retaining array member, the retaining array member(s) defining the prearranged configuration of the heating fluid conduit.

An alternative apparatus of the invention includes a thaw mat comprising a first flexible heating fluid conduit and a first flexible, insulative batting. This first heating fluid conduit is held in a prearranged configuration by at least one retaining array member and it also has a lower surface oriented toward the ground and an upper surface oriented away from the ground. The first batting overlays the upper surface of the heating fluid conduit, positioning the heating fluid conduit between the batting and the ground. A heated fluid supply is provided and a first inlet fitting attached to an end of the first heating fluid conduit releasably connects the first heating fluid conduit to the heated fluid supply. A first fluid return fitting is in fluid communication with the first heating fluid conduit and with the heated fluid supply. Optimally, the first heating fluid conduit includes a first heating line and a first return line, The first input fitting is attached to an inlet end of the first heating line and an outlet end of the first heating line is attached to a first outlet fitting; the first fluid return line fitting is in fluid communication with an outlet end of the first return line and an inlet end of the first return line is connected to a first return line inlet fitting. If so desired, this embodiment may further include a second thaw mat comprising a second flexible heating fluid conduit and a second flexible, insulative batting. Much like the first thaw mat, the second heating fluid conduit may include a second heating line and a second return line, with the heating line being held in a prearranged configuration by at least one retaining array member and having a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use. Similarly, the second batting overlays the upper surface of the heating fluid conduit. A second input fitting is attached to an inlet end of the second heating line and an outlet end of the second heating line is attached to a second outlet fitting. A second fluid return line fitting is in fluid communication with an outlet end of the second return line and an inlet end of the second return line being connected to a second return line inlet fitting. This second thaw mat may be connected with the first thaw mat so fluid may flow through both mats, such as by having the first outlet fitting in fluid communication with second inlet fitting and the second return line fitting in fluid communication with the first return line inlet fitting. Another alternative apparatus of the invention provides a portable thawing system, which could be mounted on a vehicle if so desired. This portable thawing system includes a flexible thaw mat comprising a flexible heating fluid conduit and a flexible insulative batting. This heating fluid conduit is held in a prearranged configuration and has a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use. The insulative batting is sized to overlay the upper surface of the heating fluid conduit in use. A supply of heated heating fluid is provided and a pump is operatively connected to the heating fluid conduit and to the heating fluid supply. This system also includes a reel rotatable about an axis and operatively connectable to the flexible thaw mat to permit at least the flexible heating fluid conduit to be rolled into a compact configuration. An input fitting is attached to an end of the heating fluid conduit in use and it is adapted to connect the heating fluid conduit to the heating fluid supply. In use, an outlet fitting is in fluid communication with the heating fluid conduit and with the heated fluid supply.

The invention also contemplates a method of thawing frozen ground. In one such method, a portable thawing system is provided, the system comprising a flexible thaw mat including a flexible heating fluid conduit and a flexible insulative batting, with the heating fluid conduit being held in a prearranged configuration by at least one retaining array member. The system also includes a heating fluid supply and a reel carrying at least the heating fluid conduit of the thaw mat in a rolled configuration, though both the heating fluid conduit and the insulative batting may be carried by the reel in a combined rolled configuration. This portable thawing system is positioned adjacent an area of frozen ground to be thawed. The heating fluid conduit is unrolled from the reel to deploy the heating fluid conduit over the ground to be thawed, the at least one retaining array member serving to maintain the heating fluid conduit in said prearranged configuration for deployment as a unit. Heating fluid is pumped from the heating fluid supply through the heating fluid conduit to thaw the area of frozen ground. After the heating fluid is so pumped, this method may further include ceasing pumping the heating fluid through the heating fluid conduit and rolling at least the heating fluid conduit on the reel in said rolled configuration. (As noted above, if so desired, both the heating fluid conduit and the insulative batting may be rolled on the reel together in a combined rolled configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic layout illustrating one thawing system arrangement for use in accordance with the present invention;

Figure 2 is a schematic layout illustrating an alternative thawing system arrangement for use in accordance with the present invention;

Figure 3 is a top view schematically illustrating a thaw mat in keeping with one embodiment of the invention;

Figure 4 is a schematic side view of the thaw mat of Figure 3;

Figure 5 is a schematic cross sectional view taken along line 5-5 of Figure 3;

Figure 6 is a broken-away side isolation view schematically illustrating a portion of the thaw mat of Figure 3;

Figure 7 is a broken-away top isolation view schematically illustrating a portion of the thaw mat of Figure 3;

Figure 8 is a side view schematically illustrating the thaw mat of Figure 3 in a rolled configuration suitable for transport and storage;

Figure 9 is a schematic cross-sectional illustration depicting one possible relationship between a retaining array member and a heating fluid conduit in a thaw mat of the invention;

Figure 10 is a top view similar to Figure 3, but schematically illustrating a thaw mat having an alternative arrangement of the heating fluid conduit;

Figure 1 1 is a schematic cross sectional view of another alternative thaw mat of the invention laid on an area of ground for thawing; Figure 12 is a bottom view schematically illustrating the arrangement of the heating fluid conduit of the thaw mat of Figure 11 ;

Figure 13 is an exploded isolational view of a retaining array member suitable for use in the thaw mat of Figures 11 and 12; Figure 14 is a top view schematically illustrating the fluid and insulation connections of the thaw mat of Figures 11-13; and

Figure 15 is a schematic illustration of a vehicle-mounted portable thawing system in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, the present invention provides both an apparatus and a method for thawing frozen ground or the like. A variety of embodiments of the apparatus and the method are discussed in more detail below in connection with the drawings of Figures 1-15.

In one embodiment, an apparatus of the invention employs specially- designed pads (also referred to herein as "thaw mats") having heated fluid in tubes flowing therethrough for use in thawing the ground therebelow. These pads are design to be reusable, and in some cases driven over by vehicles for use on roadways, and are relatively easy to manage for placement, transportation and reuse. A series of pads can be connected for particular job site needs, and the fluid therein is heated by an adjacent heater. This particularly preferred arrangement avoids the open flame adjacent the ground used in some prior art ground thawing equipment, does not tie up utility installation and repair crews on tasks with low productivity (such as setting up thawing equipment), and is an extremely flexible solution. It allows quicker new building construction by allowing other foundation construction to take place faster, as well as speedier service line work for the utilities. It is also be more efficient than previous ground thawing arrangements in manpower, time and economic terms. In addition, the inventive solution will be more ecologically friendly in those jurisdictions (e.g., Canada) which still may use coal fires to thaw the ground.

As discussed more fully below in connection with Figure 15, the inventive thawing equipment may be transported to the work site by truck or trailer. If necessary, snow must be cleared from the work site. The heating pads are then unrolled or laid in place in desired locations for hole excavation or trenching therebelow. Coupling tubes are used to couple the pads together and to couple the pads to a fluid heating unit. The heating unit is activated to heat the fluid in the pads and begin thawing of the frost in the ground therebelow. If desired, the pads can be pressurized by air pressure to a low pressure to aid the thermal insulative properties of the insulation above the heating tubes therein. For the street pad, traffic is optimally slowed and diverted to a center section of the pad which is covered with heavier material so that the street pad is not damaged by traffic passing thereover. For utility purposes, holes are often excavated to the main utility line, to allow access thereto and provide for new or repaired service lines. Such holes are referred to as "bell holes." A bell hole is typically dug approximately four feet deep.

Figures 1 and 2 schematically illustrate typical applications of the inventive heating pad system. In Figure 1 , a bell hole heating pad 20 is connected by fluid line hoses to a fluid heating unit 22. One hose delivers heated fluid from the heating unit 22 to the bell hole pad 20, while the other hose is a return circulation line for the fluid. A service line pad 24 is connected in series to the bell hole pad 20. Fittings on the bell hole pad 20 and service line pad 24 allow coupling via fluid line hoses for delivering heated fluid from the bell hole pad 20 to the service line pad 24 and return circulation thereof The service line pad 24 is laid out from the bell hole pad 20 to a residence building 25 or other desired location. The heated fluid thus follows a closed loop from the heating unit 22, to the bell hole pad 20 and then to the service line pad 24, and then back in return. As the fluid in the series of tubes in the bell hole pad 20 and service line pad 24 becomes hotter, the underlying ground is likewise heated.

After heating for a sufficient time (sometimes several days), the ground is thawed below and immediately adjacent to the bell hole pad 20 and service line pad 24 sufficiently to allow excavation and trenching thereunder. Typically, the bell hole pad 20 would be placed over a section of a utility main line buried underground to allow access thereto, while a service line pad 24 is useful for allowing trenching from that access point to the residence or building which is being serviced by the utility. Once the necessary thawing has occurred in the ground, the heating unit is turned off, the hoses between the heating unit and pads are disconnected, the pads are moved or rolled up and the excavation process begun. If desired, the bell hole pad 20 can also be used to cover soil which has been excavated, thereby keeping it warm and more readily moveable for refilling the bell hole once the work is completed. In Figure 1 , the pads 20 and 22 are shown to the right of a street 26. In

Figure 2, a street pad 28 and an additional bell hole pad 30 are shown. In this case, the street pad 28 lays over the street and is connected for heating fluid transfer from bell hole pad 20 to bell hole pad 30 by fluid line hoses. This arrangement is used when the utility line is on the opposite side of the street from the residence or building to which service is desired. Accordingly, the ground must be thawed under the street for complete access. The street pad 28 and second bell hole pad 30 are connected to the bell hole pad 20 to allow heated fluid therefrom (originally from the heating unit 22) to flow through tubes in the pads 28 and 30 and return to the bell hole pad 20 and heating unit 22 for reheating. A closed circuit is thus formed for the transfer and circulation of heating fluid, as in the system of Figure 1.

In a situation where there is snow on the ground, the frost line may not be as deep because the snow acts as an insulator. However, streets are typically cleaned of snow by plows and thus the frost line is commonly deeper under a street then under a lawn. This may require additional time for the street pad 28 to operate to obtain the necessary depth of thawing for the ground thereunder.

Where a street pad 28 is used, traffic need not be stopped from flowing along the street 26, but is diverted to a central 10-12 foot wide section of the street pad 28 which is reinforced to support traffic passing thereover. Cones, signs or flashers may be used to slow down and divert traffic to a slow speed, allowing the vehicles to cross the street pad 28 without damage to the pad 28 or to the vehicles.

Figure 3 illustrates a top plan view of a preferred embodiment of the street pad 28. This pad should be sized to permit it to extend across much of the street. While streets may vary in width, in one suitable embodiment the pad 28 is approximately 22 inches wide and 484 inches long. The illustrated pad contains a serpentine heating fluid tubing 32, serviced by inlet and outlet ports 34 and 36. One port is at each end of the street pad 28, and the tubing 32 snakes back and forth through the elongated street pad 28 in a serpentine manner from port 34 to port 36 (see Figures 3 and 4). As best illustrated in Figures 3 and 5, the tubing 32 in this embodiment makes five passes along the length of the street pad 28. A fluid return tube 38 extends along one side of the street pad 28, between inlet and outlet ports 40 and 42. The street pad 28 can thus be hooked for series flow of heating fluid entering the pad by a port 34, exiting the pad by a port 36 and going to another pad, or simply to a sub-loop of fluid line hose connecting port 36 to port 42 which then would return the heating fluid by the tube 38 to port 40 for return to the heating source. The heating fluid tubing or line 32 and the fluid return tube or line 38 may be thought of as components of a heating fluid conduit adapted to control the flow of heating fluid through the pad or thaw mat 28.

As illustrated in Figure 5, insulation 43 may be provided in the pad 28 above and around the tubing 32 and 38. Preferably, the pad 28 has a depth of approximately 4 inches and includes insulation such as fiberglass batting material. At one end of the pad 28, an air fitting 44 in the fabric enclosure may be provided to allow inflation of the pad 28 (which is otherwise airtight). The pad 28 is preferably inflated to approximately one psi to provide support for the insulation 43, and also to aid in allowing the pad 28 to be resilient to vehicle traffic thereover.

As illustrated in Figure 3, the top portion of the pad 28 may have markings thereon (such as yellow stenciled lines 46) to indicate that traffic should only pass between such lines across the pad 28. The portion of the pad 28 between and adjacent lines 46 is preferably formed from a reinforced or heavier weight fabric material on its top section.

Figures 5, 6 and 7 show enlarged sectional or schematic views of portions of the street pad 28 of Figures 3 and 4. Figure 8 shows a pad 28 which has been disconnected and depressurized for transport, illustrating how it may be rolled up like a flattened hose.

Figure 9 illustrates a schematic sectional view of the attachment of the tubing 32 to the base fabric 48 of the pad 28. This is accomplished by a lateral loop 50 which is passed over the longitudinal runs of the tubing 32 and adhered between adjacent tubing runs (at 49) to the underlining fabric 48 of the pad 28, by suitable adhesive or mechanical fasteners. These loops may be spaced approximately 24 inches apart along the length of the street pad 28, as illustrated in Figure 3. Each of these loops may be thought of as a member of an array for retaining the tubing in a prearranged configuration. (While this configuration is deformed somewhat when the pad is rolled up, as in Figure 8, these retaining array members help retain a relative orientation of adjacent runs of the tubing even when the pad is rolled up.) The connecting fluid line hoses between adjacent pads are preferably no more than 2 feet long. Optimally, quick release couplings are provided on such hoses and the pads, so that fluid stays in the tubing of the pad and in connecting hoses when disconnected. The fluid is preferably heated to approximately 180° F, which is usually sufficient to melt frost three feet deep after several days exposure. The heating unit heats the fluid and may also include a pump to move the heated fluid through the closed circulation loop formed by the pads. If so desired, though, the heating unit and the fluid pump may comprise separate devices, as illustrated below in connection with Figure 15.

As illustrated in Figure 8, the illustrated pad 28 is configured for ready transport. For example, a 100 foot long service line pad would have a weight of approximately 400 pounds. This may be rolled up on a reel on a trailer for transport and relocation from job site to job site. It is also contemplated that pads of other sizes and shapes can be configured than those disclosed herein. For example, a large service pad (for utility main line operations') of 3 feet by up to 500 feet may be used for joint trenching of utility mains.

Figure 10 illustrates an alternative tubing pattern 52 for a service line or street pad 54 of the present invention. The bell hole pads likewise have serpentine tubing patterns therein, are low profile (approximately 4 inches high) and include fittings and insulation like those disclosed with respect to the street pad 28 in Figures 3-9.

The center reinforced or stronger fabric section of the street pad 28 also has a plurality of grommets 56 thereon, (see Figure 3) which are used to pin the street pad to the street using suitable fasteners or anchors.

Figures 11-14 schematically illustrate an alternative heating pad 124 of the invention. In Figures 11-14, elements having function analogous to elements illustrated in connection with the pad 28 shown in Figure 3 bear like reference numbers, but incremented by 100. (For example, the insulation 43 of Figure 5 is illustrated in Figure 11 as insulation 143.)

While the operational principles of the thaw mat 124 shown in Figures 11- 14 are similar in many respects to those of the thaw mat 28 shown in Figures 3- 7, there are some notable differences between these designs. In the embodiment of Figures 3-7, the heating fluid conduit (in this embodiment, including both the heating fluid line 32 and the fluid return line 38) is retained within the flexible fabric enclosure with the insulation 43. In the embodiment shown in Figure 11 , though, the heating fluid conduit (which may be thought of as comprising the heating fluid line 132 and may also include the fluid return line 138) is positioned outside the fabric enclosure enclosing the insulation 143 and are instead in direct contact with the ground G. This is believed to yield a more efficient thermal transfer from the heating fluid within the heating conduit to the ground G. The insulation 143 will still help limit heat loss to the ambient atmosphere.

In order to improve the heat retention qualities of the insulative batting 143, the lower surface of the base fabric 148 may be provided with an infrared reflective coating. This infrared reflective coating may take any form, but may be typified as a reflective foil lining carried by the lower surface of the fabric 148. Any suitable foil may be used, such as the insulative foil commercially available under the trade name Super R Diamond from Innovative Insulation Inc. of Arlington, Texas, USA.

With the heating conduit positioned on the ground and the flexible insulative batting 143 overlaying the upper surface of the heating conduit, it may be possible for heat to escape laterally around the periphery of the insulative batting. This may be minimized by extending the periphery of the insulation well beyond the periphery of the heating conduit, but this may be unnecessarily wasteful. In a particularly preferred embodiment, the outer periphery of the insulative batting 143 is provided with a peripheral seal which lies in direct contact with the ground, thereby enclosing a relatively small airspace between the ground and the batting.

This peripheral seal may take any of a wide variety of forms. In the illustrated embodiment, this peripheral seal 160 generally includes a flexible fabric enclosure 162 which retains a relatively dense, conformable material 168 therein. The bottom surface 164 of the peripheral seal is adapted to contact the ground G. The material 168 retained within the enclosure 162 will help keep the bottom surface 164 in close contact with the ground, thereby effectively limiting the passage of air into and out of the vicinity of the heating fluid conduit. The dense, conformable filling material should remain ultimately flexible even at low temperatures and may comprise a flowable particulate, such as dry sand or a product available under the trade name Sylgard 527 from DuPont.

The peripheral seal 160 may not initially seat very well against uneven ground under its own weight. This is particularly true when it is very cold outside and the fabric enclosure 162 of the seal may not be as flexible as it is at warmer temperatures. In order to ensure a good seal, a worker may simply walk along the peripheral seal to push it down into contact with the ground. To further limit the flow of cold air under the insulative batting 143, snow can be piled up on the peripheral seal to form a further windbreak. In the illustrated embodiment, the peripheral seal further includes a snow flap 170 extending outwardly from the enclosure 162 of the seal. This flap 170 can be used to further seal the periphery of the mat against the ground. It should be noted that the snow flap 170 is merely optional; to illustrate this fact, this snow flap 170 has been omitted from Figures 12 and 14. The snow flap 170 is desirably fairly flexible and may be formed of the same type of fabric used to form the enclosure 162. During storage or transport, the snow flap 170 can be rolled into a fairly compact configuration which lies adjacent the enclosure 162. (This rolled-up condition is shown on the left side of Figure 11.) In use, the snow flap 170 can be unrolled to lie on the ground and, optimally, conforms to the surface of the ground. (This deployed configuration is shown on the right side of Figure 11.) To further enhance the seal with the ground, some weight may be place on top of the flap 170. While any weight would suffice, if there is snow adjacent the site to be thawed, some of that snow can be piled on top of the snow flap to hold it in place. When the ground has been thawed, the user can remove the snow or other weight on top of the snow flap 170 and roll the flap up into its compact configuration for storage or transport to another site.

Figure 12 is a schematic view of the bottom of the thaw mat 124 of Figure 11. Most of the length of the mat has been broken away to focus on the structure adjacent the ends of the mat. Figures 3 and 10, discussed above, illustrate two possible arrangements of a single, continuous length of tubing within the flexible fabric enclosure. Figure 12 illustrates another arrangement that will provide a heating fluid conduit held in a prearranged serpentine figuration extending along the majority of the length of the thaw mat 124. In this embodiment though, the heating line 132 is comprised of a series of independent lengths 132 ^' of flexible hose which are connected to at least one other hose at each end. Since it is anticipated that the thaw mat 124 may be rolled up lengthwise (as illustrated in Figure 8), the lengths of the tubing 132^' are desirably relatively flexible. The fittings connecting one length of tubing to the next are positioned adjacent an end of the mat and need not be flexible to permit the mat to be rolled up. Instead, they may comprise a relatively rigid PVC fitting mounted on the bottom fabric 148.

In each of the illustrated embodiments, the fluid will follow at a rather long, serpentine path along the entire length of the tubing. If so desired, though, not all of the fluid need travel through the entire length of the hose. Instead, a distribution manifold (not shown) may be carried by the base fabric 148 of the batting 143 adjacent the ends of the batting in much the same manner that the fittings 133 are deployed in the embodiment of Figure 12. A series of parallel lengths of tubing 132 ' can then extend from one manifold to the other, with each length of tubing 132 ^' carrying a proportionate fraction of the total heating fluid flowing through the heating fluid conduit.

As noted above, the embodiment of Figures 3 and 9 maintain multiple runs of the tubing 32 in a prearranged configurafion by means of a lateral loop 50 which serves as a retaining array member. In the embodiment of Figure 11 , a series of retaining array members 150 may also be spaced along the length of the pad in much the same fashion illustrated in Figure 3. However, Figures 12 and 13 illustrate a particularly preferred retaining array member for use in connection with the invention. This retaining array member 150 includes a relatively rigid base 152 and a strap 154 which defines a series of spaced-apart loops 156. The base 152 may be formed of a relatively rigid metal, e.g., a 1-2 inch-wide piece of sheet metal. The strap 154 is advantageously formed of a relatively durable fabric, such as the material employed in making the fabric enclosure of the insulative batting 143.

The base 152 of the retaining array member 150 may be held onto the bottom surface of the base fabric 148 in any suitable fashion. In the illustrated embodiment, each retaining array member 150 is held in place by inserting the base 152 in a pair of laterally opposed pockets 156 provided on the bottom surface of the base fabric 148. This permits the retaining array members 150 to be relatively quickly fastened to the fabric enclosure of the insulative batting 143, but may also be disconnected therefrom to allow the thaw mat to be deployed in two separate stages, with the heating conduit being applied to the ground in a prearranged configuration dictated by the members 150 and the insulative batting 143 being laid over the upper surface of the heating conduit in a separate step.

These relatively rigid retaining array members 150 will also help provide some lateral dimensional stability to the fabric enclosure surrounding the insulation 143. As noted above, the insulative batting 143 may be inflated to help provide additional insulating loft to the material within the fabric enclosure. These relatively rigid members 150 will help keep the bottom fabric 148 of the inflated fabric enclosure relatively flat. This can be even more useful if the insulating material used within the fabric enclosure is blown in (as discussed below) rather than being a static mat of fiberglass or the like.

Figure 14 is a simplified, schematic top view of the same thaw mat 124. (As in Figure 12, most of the length of the thaw mat has been broken away to permit enlargement of the structure at the ends of the mat.) Much like the thaw mat 28 shown in Figures 3-7, the embodiment of Figure 14 includes an inlet fitting 134 connected to one end of the heating line 132 and an outlet fitting 136 attached to the other end of the heating line. Similarly, a return line inlet fitting 142 is attached to one end of the return line 138 and a fluid return line fitting 140 is attached to the other end of the return line 138. As with the prior embodiment, in use the outlet fitting 136 is in fluid communication with the return line inlet fitting 142 either by appropriate connection to another thaw mat in series with the illustrated thaw mat or simply by connecting a relatively short linking hose (not sown) connected at one end to the outlet fitting 136 and at its other end to the return line inlet fitting 142. The thaw mat 124 is also desirably provided with at least one inflation fitting 144 which allows the pad 124 to be inflated. This can be done simply by inflating the fabric enclosure containing the insulation 143 in the same manner discussed above in connection with Figure 3.

In a preferred embodiment, though, the filling of the insulative batting 143 need not be a static fiberglass mat or the like which will remain in place within the enclosure at all times. Instead, the insulative batting may comprise a flowable filler retained within the fabric enclosure. Optimally, this flowable filler can be added into and may also be removed from the fabric enclosure. The filler may, for example, take the form of insulative foam beads or cellulose fibers. In use, the fabric enclosure of the insulative batting would be deployed and at least one inflation fitting 144 would be connected to a supply of the flowable filler. A blower or the like can be used to blow this filler into the fabric enclosure and fill it up. This blower can take any form, but may simply comprise a blower of the type commercially available for blowing insulation into the attic of a house or other structure.

While this filling operation may be accomplished with a single inflation port 144, it will be much easier to accomplish suitable filling of the enclosure utilizing a pair of such fittings, as shown in Figure 14. The supply of flowable filler will be attached to one of the fittings while a screen will be attached to the other fitting. As the filler is blown in one end, air can exit out the other fitting, with the screen helping retain the filler within the fabric enclosure. Once the fabric enclosure is suitably filled with the filler, both of the inflation ports 144 can be capped to prevent moisture from entering the insulation cavity.

Figure 15 illustrates a trailer 200 which may be used in connection with the present invention. This trailer makes it easier for the end user to transport the ground thaw system of the invention from site to site and also aids in deployment and retrieval of the thaw mats 28 at the site.

The trailer 200 includes a trailer bed 210 which serves to support the other elements of the system during transport and storage. This trailer bed 210 is designed to be connected to the hitch of a truck or other vehicle to be hauled from site to site. As the entire trailer 200 will typically have to remain in place during thawing, this arrangement allows a single truck to haul a number of trailers to the desired positions without having to have any additional equipment dedicated to each ground thawing site. It should be understood, though, that the trailer bed 210 may be replaced with any other suitable vehicle. For example, the trailer bed 210 may be replaced by a dedicated service truck. If a complete truck is used instead of the trailer bed 210, some of the elements illustrated on the trailer bed 210 in Figure 15 may be shared with or replaced by other elements of the truck. (For example, the dedicated fuel tank 230 can be replaced by the standard fuel tank for the truck.)

Figures 1 and 2 illustrate a heating unit 22 positioned adjacent the area of ground to be thawed. This heating unit 22 can take any desired form. In the embodiment schematically illustrated in Figure 15, the heating unit 22 includes a supply or reservoir 220 of the heating fluid, a pump 224, a heater 228 and a fuel tank 230. The heating fluid supply 220 can comprise a simple reservoir filled with a suitable heating fluid, e.g., a mixture of water and glycol to minimize the changes of having the fluid freeze in the thaw mat 28. The heater 228 may be a standard boiler which heats the fluid with burners fueled by liquid propane, fuel oil, or the like. The fuel tank 230 may be connected to the heater 228 to deliver fuel to the burners.

As noted above, the thaw mat 124 of Figures 11-14 is adapted to be filled with a flowable, insulative filler such as foam beads or cellulose fibers. If such a thaw mat is used, the trailer 200 may also include a supply of the filler material and a mechanism for filling the flexible enclosure of the thaw mat with that material. This is schematically illustrated in Figure 15 as a hopper 240 for retaining the filler material and a blower 242 in communication with that hopper to blow the filler into the thaw mat. Of course, the blower may be releasably connected to the thaw mat by means of suitable hosing or tubing, which has been omitted from the schematic view of Figure 15 for purposes of clarity. The trailer 200 includes a reel 250 which can be used to assist in deploying and retrieving the thaw mat 28 in a manner described more fully below. The reel 250 generally includes a central core 252 which defines the axis of the reel and about which the thaw mat 28 is rolled. This core may be supported above the floor of the trailer bed 210 by means of laterally spaced- apart support struts 254. Some mechanism should be provided to facilitate rolling of the thaw mat 28 on the core 252. This is schematically illustrated in Figure 15 as a handle 256 which can be manually rotated. Given the likely weight of the thaw mats, though, it is more likely that a motor-driven mechanism would be advisable rather than requiring an operator to manually crank the thaw mat up onto the reel 250.

As mentioned above, the present invention also contemplates a method which is useful for thawing frozen ground. While this method will be discussed in the context of the apparatus designs shown in Figures 1-15, it should be understood that these methods are not limited to the specific devices shown in those drawings. To the contrary, any apparatus which will allow an operator to accomplish the various steps of the method could be used instead of or in conjunction with the devices shown in these drawings.

In accordance with one embodiment of the invention, a user is provided with a portable thawing system which includes a flexible thaw mat. The thaw mat 28 of Figures 3-7 or the thaw mat 124 of Figures 11-14 could be used, but the following discussion will refer to the embodiment illustrated in Figures 11-14. The portable thawing system may further include a trailer 200 having a trailer bed 210, a heating unit 22, a reel 250 and a hopper 240 as illustrated in Figure 15. The portable thawing system is positioned adjacent an area of frozen ground to be thawed. If a trailer is used, this may be accomplished simply by pulling the trailer to the work site. The trailer need not be positioned immediately next to the work site, but it should be close enough to allow the thaw mat to be deployed without undue difficulty. The thaw mat may then be deployed over the ground to be thawed. This can be accomplished in any suitable fashion. If the thaw mat is carried on a reel 250 as discussed above, the thaw mat should be unrolled from the reel to deploy it. If it is convenient to do so, the trailer may be positioned over the ground to be thawed and one end of the thaw mat 124 can be laid on the ground. Simply by holding that end of the thaw mat stationary and driving the trailer 200 away, the thaw maw can be unrolled from the reel to deploy it over the ground. If that is impractical, though, one can simply remove the mat 124 from the trailer 200 and then drag it to cover the ground to be thawed using any suitable means, such as by trailing it behind a snow blower used to clear snow overlying the ground to be thawed. If the thaw mat is too heavy to be pulled along by a snow blower or the like, a piece of heavy construction equipment, such as a bulldozer, can be used.

In the embodiments illustrated in the drawings and detailed above, the flexible insulative batting 143 is carried by the heating fluid conduit 132 and overlays the upper surface thereof. In one simplified embodiment of the invention, though, the insulation need not be attached to the heating conduit 132. Instead, the heating conduit 132 and the thaw mat could be deployed in two separate stages. In such an embodiment, it is preferred that the heating fluid conduit 132 be held in a prearranged configurafion by at least one retaining array member 150. This will allow the operator to lay the heating conduit on the ground to be thawed in a prearranged configuration without necessitating any undue work. The separate insulation could then be laid on top of the heating fluid conduit in a separate step. One certainly could operate the heating fluid conduit without any overlying insulation. This would allow a lot of heat to escape to the ambient atmosphere, though, and may not provide very effective thawing in particularly cold weather. As noted above, the thaw mat 124 may include a peripheral seal 160 to better retain the heat from the heating fluid conduit 132 adjacent the ground to be thawed. If the thaw mat includes such as peripheral seal 160, the operator may walk on this seal to better seat it against the ground, as noted above. If the seal 160 also includes a snow flap 170, the snow flap may be deployed to lie over the ground and, if so desired, snow or other material may be placed on top of the snow flap to provide a more effective seal.

Once the thaw mat is deployed, heating fluid may be pumped from the heating fluid supply 22 through the heating fluid conduit 132 to thaw the area of frozen ground. As noted above, this may take a number of days, depending on the ambient temperatures, the ground temperature and the depth to which the ground needs to be thawed. If the thaw mat 124 is connected to the heating fluid supply 22 by means of connectable fittings, once the mat is deployed, the connecting hoses may be attached to the thaw mat and to the heafing fluid supply and the pump 224 may be activated to circulate the heating fluid. It should be understood, though, that the connection between the thaw mat 124 and the heating supply 22 need not be detachable, but could instead be permanently attached. This is particularly true if the thaw mat is not intended to be used in a modular fashion in connection with a variety of other mats, but is instead intended to be a single, stand-alone element. (If the thaw mat is intended to be used as a sole, stand-alone element, there would be no need for a separate return line 138; instead, the heating line 132 may comprise the entire heating fluid conduit, with one end of the heating line 132 being connected to the inlet fitting 134 and the other end of the heating line 132 being attached to the fluid return fitting 140.)

Once the ground has been thawed, the flow of the heating fluid through the conduit 132 can be terminated, e.g., by turning off the pump 234. If so desired, the thaw mat can then be promptly rolled on to the reel 250 on the trailer 200 to store it in its rolled configuration for transport to another site. As noted above, the heating fluid conduit 132 and the insulation 143 may be deployed in two separate steps as separate parts. If such separate elements are used, the insulation may be removed from the top of the heating fluid conduit and the heating fluid conduit may be rolled on to the reel. The conduit will be retained in much the same configuration as it is rolled due to the presence of the retaining array members 150. In some circumstances, it may be possible to simply lift one end of the thaw mat up to the reel 250 to allow it to be rolled upon the core of the reel. This may be possible, for example, if the thaw mat is relatively light. If the thaw mat is heavier, though, it may be difficult to manually lift the thaw mat up to the reel to begin rolling it up. In such a circumstance, a leader line (e.g., a length of a sturdy rope or cable, not shown) may be connected to the reel and to the thaw mat. By rolling the leader line on to the reel, the thaw mat will be brought up to the reel and may be simply rolled onto the reel on top of the leader line. The leader line is optimally detachable from the thaw mat to make it easier to suitably position the thaw mat with respect to the trailer 200. If so desired, the insulative batting may be inflated with air to improve insulation properties. As noted above, the insulative batting 143 shown in Figures 11-14 can comprise a flexible fabric enclosure with a flowable filler therein. In deploying such a thaw mat, the thaw mat 124 may be positioned over the ground such that the flexible fabric enclosure lies on top of the upper surface of the heating fluid conduit 132. The hopper 240 of the flowable insulation may then be pumped into the flexible enclosure using the blower 242, as described above.

Once the ground has been thawed, the flowable filler may be removed from the flexible enclosure, such as by reversing the blower to suck out the flowable filler and deploy it into the hopper 240. This will make the thaw mat lighter and more compact so that it can be handled more easily in rolling it up for storage and deploying it again at a new site. It is contemplated that in many circumstances, the thaw mat will be rolled onto a reel 250 on a trailer 200 and moved to a remote site. If the next area of ground to be thawed is not terribly far removed from the area of ground which has just been thawed using the thaw mat 124, the thaw mat may be simply dragged from its first location to a new location. This may even be done without connecting any of the fluid supply lines by simply dragging the thaw mat across the ground to the new area of frozen ground to be thawed.

In accordance with a further embodiment of the invention, the mat is deployed on the ground to be thawed. Once it is deployed and the ground is thawed, the user may move the thaw mat away from the thawed ground. While this can be done by rolling it up onto the reel 250 into its transport configuration, it may instead simply be pulled off to the side sufficiently to allow workers to gain access to the ground for excavation. The soil or other overburden removed during the excavation process will typically be piled to one side of the excavation site in what is sometimes referred to as a "spoil pile". The thaw mat 124 may be used to cover this spoil pile and keep it from freezing while workers work in the excavation site. This may be done by simply dragging the previously deployed thaw mat on top of the spoil pile or by again unrolling the previously rolled thaw mat from the reel 250 in much the same manner as the thaw mat is deployed to cover ground to be thawed.

Once the work is completed at the excavation site, the thaw mat 124 can be retracted from the spoil pile. For example, the mat may be rolled onto the reel 250 either as a single unit or by first removing the insulative batting 143 as a separate part and then rolling the heating fluid conduit 132 onto the reel. The warmed overburden may then be backfilled into the excavation site. If the thaw mat 124 is not used to cover this spoil pile, the exposed spoil pile may become frozen, making it much more difficult to backfill the dirt into the excavation site.

While the drawing figures and the above discussion set forth certain preferred embodiments, other embodiments of the invention are also contemplated, as noted in the discussion. This disclosure presents illustrative embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. The drawing figures have not been drawn to scale, as it has been necessary to enlarge certain portions for clarity.

Claims

WHAT IS CLAIMED IS:

1. A flexible, portable thaw mat, comprising: a) a flexible heating fluid conduit held in a prearranged configuration and having a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use; b) a flexible insulative batting carried by the heating fluid conduit and overlaying the upper surface thereof, the batting and the heating fluid conduit being capable of being repeatedly flexibly deformed as a unit into a compact configuration and deployed as a unit over ground to be thawed; c) an inlet fitting attached to an end of the heating fluid conduit in use and adapted to releasably connect the heafing fluid conduit to a heated fluid supply; d) a releasable fluid return fitting in fluid communication with the heating fluid conduit and with the heated fluid supply in use.

2. The flexible, portable thaw mat of claim 1 further comprising at least one retaining array member, the retaining array member defining the prearranged configuration of the heating fluid conduit.

3. The flexible, portable thaw mat of claim 2 wherein the at least one retaining array member is operatively connected to both the heating fluid conduit and the batting.

4. The flexible, portable thaw mat of claim 1 wherein the insulative batting and at least a length of the flexible conduit and are both retained by a flexible enclosure.

5. The flexible, portable thaw mat of claim 4 wherein the flexible enclosure is substantially fluid-tight, further comprising an inflation fitting for pressurizing the enclosure.

6. The flexible, portable thaw mat of claim 5 wherein the flexible enclosure comprises a fabric designed to withstand inflation pressures within the enclosure of at least one psi.

7. The flexible, portable thaw mat of claim 1 wherein the insulative batting comprises a flexible enclosure filled with a flowable, retrievable filler.

8. The flexible, portable thaw mat of claim 1 wherein the insulative batting is retained within a flexible enclosure, a lower surface of that flexible enclosure being positioned immediately adjacent the upper surface of the heating fluid conduit.

9. The flexible, portable thaw mat of claim 7 wherein the lower surface of the flexible enclosure comprises an infrared reflective layer positioned in use to reflect heat from the heating fluid conduit downwardly toward the ground.

10. The flexible, portable thaw mat of claim 1 further comprising a reel and a leader, the leader extending from the reel to a connection at an end of at least one of the heating fluid conduit and the insulative batting, the reel being rotatable about an axis to roll the leader, the batting and the heating fluid conduit as a unit about the reel into said compact configuration.

1 1. A modular thawing system, comprising: a) a first thaw mat comprising a first flexible heating fluid conduit and a first flexible, insulative batting; the first heating fluid conduit being held in a prearranged configuration by at least one retaining array member and having a lower surface oriented toward the ground and an upper surface oriented away from the ground; the first batting overlaying the upper surface of the heating fluid conduit; b) a heated fluid supply; c) a first inlet fitting attached to an end of the first heating fluid conduit and releasably connecting the first heating fluid conduit to the heated fluid supply; and d) a first fluid return fitting in fluid communication with the first heating fluid conduit and with the heated fluid supply.

12. The modular thawing system of claim 1 1 wherein the first heating fluid conduit comprises a first heating line and a first return line, the first input fitting being attached to an inlet end of the first heating line and an outlet end of the first heating line being attached to a first outlet fitting, the first fluid return line fitting being in fluid communication with an outlet end of the first return line and an inlet end of the first return line being connected to a first return line inlet fitting.

13. The modular thawing system of claim 12 further comprising a linking hose connected at one end to the first outlet fitting and at its other end to the first return line inlet fitting.

14. The modular thawing system of claim 12 further comprising: a) a second thaw mat comprising a second flexible heating fluid conduit and a second flexible, insulative batting; the second heating fluid conduit comprising a second heating line and a second return line, the heating line being held in a prearranged configuration by at least one retaining array member and having a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use; the second batting overlaying the upper surface of the heating fluid conduit; b) a second input fitting attached to an inlet end of the second heating line and an outlet end of the second heating line being attached to a second outlet fitting; c) a second fluid return line fitting in fluid communication with an outlet end of the second return line and an inlet end of the second return line being connected to a second return line inlet fitting; d) the first outlet fitting being in fluid communication with second inlet fitting and the second return line fitting being in fluid communication with the first return line inlet fitting.

15. The modular thawing system of claim 14 further comprising a linking hose connected at one end to the second outlet fitting and at its other end to the second return line inlet fitting.

16. A portable thawing system comprising: a) a flexible thaw mat comprising a flexible heating fluid conduit and a flexible insulative batting; the heating fluid conduit being held in a prearranged configuration and having a lower surface oriented toward the ground in use and an upper surface oriented away from the ground in use; the insulative batting being sized to overlay the upper surface of the heating fluid conduit in use; b) a supply of heated heafing fluid; c) a pump operatively connected to the heating fluid conduit and to the heating fluid supply; d) a reel rotatable about an axis and operatively connectable to the flexible thaw mat to permit at least the flexible heating fluid conduit to be rolled into a compact configuration; e) an input fitting attached to an end of the heating fluid conduit in use and adapted to connect the heating fluid conduit to the heating fluid supply and an outlet fitting in fluid communication with the heating fluid conduit and with the heated fluid supply in use.

17. The portable thawing system of claim 16 further comprising a vehicle, the heating fluid supply, the pump and the reel being mounted on the vehicle and the thaw mat being releasably rolled upon the reel during storage and transport with the vehicle.

18. A method of thawing frozen ground comprising: a) providing a portable thawing system comprising a flexible thaw mat including a flexible heating fluid conduit and a flexible insulative batting; the heating fluid conduit being held in a prearranged configuration by at least one retaining array member; a heating fluid supply; and a reel carrying at least the heating fluid conduit of the thaw mat in a rolled configuration; b) positioning the portable thawing system adjacent an area of frozen ground to be thawed; c) unrolling the heating fluid conduit from the reel to deploy the heating fluid conduit over the ground to be thawed, the at least one retaining array member serving to maintain the heating fluid conduit in said prearranged configuration for deployment as a unit; d) pumping heating fluid from the heating fluid supply through the heating fluid conduit to thaw the area of frozen ground.

19. The method of claim 18 further comprising, after unrolling the heafing fluid conduit from the reel, covering the deployed heating fluid conduit with the insulative batting, thereby deploying the thaw mat over the area of frozen ground.

20. The method of claim 18 further comprising, after pumping the heating fluid, ceasing pumping the heating fluid through the heafing fluid conduit and rolling at least the heating fluid conduit on the reel in said rolled configuration.

21. The method of claim 20 wherein at least the heating fluid conduit is rolled on the reel by attaching a leader line from the reel to the thaw mat and rolling first the leader line then the heating fluid conduit onto the reel.

22. The method of claim 18 wherein the heating fluid conduit and the insulative batting are connected to one another, the insulative batting being unrolled from the reel together with the heating fluid conduit to deploy the thaw mat as a unit over the ground to be thawed.

23. The method of claim 18 wherein the insulative batting comprises a fabric enclosure and a flowable filler, further comprising filling the fabric enclosure with the flowable filler.