Apparatus to form columns of granular material

[0002] This invention relates to an improvement in methods and equipment for installing small diameter columns of granular material in soil, such as used to install granular drains, which allows repetition of the column forming procedure without requiring interruption to fill the tank supplying material to the hollow shaft cavity forming tool, and configuring the equipment to induces less stress in the column forming tool to minimize potential breakdowns due to the effects of stress repetition as compared to other apparatus applicable to the economic installation of small diameter granular columns.

[0003] Equipment used for economic installation of small diameter columns of granular material in soil, as disclosed in U.S. Pat. No. 5,647,690, has an oversized hopper to contain a larger volume of backfill material in conjunction with a cavity forming tool with a small cross-section to enable formation of more than one column in soil before interrupting the cavity forming operation to refill the tank containing excess backfill material, and includes means to interrupt the flow of material after each column is formed to avoid waste of excess backfill material which is retained in the tank for use in backfilling subsequent cavities to complete added columns.

[0004] The weight of multiple columns of material in the hopper positioned on the small sized cavity forming tool may require the tool to act as a column to support the weight of the backfill tank and its contents, which causes the tool to deflect in a manner which induces stresses that may cause the tool to fracture or otherwise render it not usable for forming and backfilling cavities in an uninterrupted manner, particularly where columns need to be relatively linear and have a reasonably predictable orientation. The equipment and controls related to limiting flow of backfill from the hopper may result in maintenance problems which can also result in costs related to interruptions in equipment use.

[0005] It is the object of this invention to reduce the cost of granular column installation and increase the durability of the cavity forming tool by reconfiguring equipment disclosed in U.S. Pat. No. 5,647,690, to enable installation of multiple columns using a procedure and apparatus configuration that enables supplying backfill material for one column at a time to an intermediate hopper during the time that the cavity is being formed, which avoids interruption to production, and minimizes the weight on the hollow shaft cavity forming tool by reducing the size of backfill tank used and minimizing detrimental stress on the tool and related costs of repair and loss of equipment use, and eliminates interrupting production to periodically replenish the tank with backfill material.

[0006] The present invention will be more fully understood by reference to the following detailed description in conjunction with the attached drawings, wherein:

[0007] FIG. 1 shows one embodiment of the present invention which utilizes a hollow shaft or mandrel and a form of bucket conveyor and related elements to install columns of granular material, such as sand drains.

[0008] FIG. 2 shows a configuration of the backfill hopper outlet where the backfill tank portal is weighted or spring loaded to be normally closed, and is forcibly opened by the outlet of the backfill hopper when the tank is at its highest position, which occurs after each column is formed, and flow from the backfill hopper to the tank may be assisted by vibration, air flow, or other force means;

[0009] FIG. 3 is a second embodiment of the present invention which utilizes rotation to advance hollow shaft auger and a helical form of conveyor that may utilize air under pressure to flow backfill to the hopper used to feed granular material into elements related to installation of columns of material in soil; and

[0010] FIG. 4 supplements FIG. 2, with a variation wherein the feed tank is not required to rotate during auger advance into the soil.

[0011] It is noted that the invention may also be applied as apparatus to strengthen soil with the application of cement or a granular cement mix that is not rendered fluid by the addition of water, and will arch or not flow freely due to insufficient water or other fluid in its granular matrix.

[0012] The embodiment of the invention in FIG. 1 incorporates unit 1 to provide mobile support and operational capability to the equipment which includes a backfill material storage hopper 2, track support 13, and other appurtenances. Carriage 5, which slides on track support 13, may be used to align and support tank 12 which contains material 11 used to backfill the cavity formed by a pipe or hollow mandrel 15 to form column 14. Hose 19 supplies air under pressure to tank 12 to aid in moving backfill 11 from tank 12 through mandrel 15 and into cavity 10 to form column 14. Guide 16 fixed at the lower end of unit 1 may be used to maintain the alignment of mandrel 15 during its advance and removal from soil 6. Jib 7 can be used to guide flexible cable 8 fixed to tank 12 to control travel of conjoined mandrel 15 toward and through soil 6 and its withdrawal outward from soil 6 in the column forming process. Drive 30 is positioned to operate conveyor 4 to move backfill material 11 from storage hopper 2 to hopper 9 positioned on track support 13. Hopper 9 containing backfill material 11 is aligned with its outlet 17 toward entry 18 to permit passage of backfill material 11 to depressurized tank 12 each time mandrel 15 is withdrawn from soil 6. Delivery of material by conveyor 4 to hopper 9 is monitored to deliver approximately the required amount of backfill 11 for transfer to tank 12 to form column 14. Under static conditions, backfill 11 arches at the outlet 32 at the base of tank 12 and little or no flow of granular material 11 will occur into mandrel 15. The weight of mandrel 15, tank 12, backfill material 11 and other elements moving with carriage 5 and other forces may be applied directly or indirectly to mandrel 15 when necessary to advance mandrel 15 into soil 6. Cap 3, which is initially open causing tank 12 to depressurize, is closed when mandrel 15 is positioned at the point of column formation and cap 3 contacts the soil which holds it closed during advance through the soil to the required depth 8. With cap 3 in its open position when the soil cavity 10 formed as mandrel 15 is withdrawn, air pressure or other applied means, such as vibration, causes flow of backfill material 11 from tank 12 through mandrel 15 to form the required column. In this manner, the cross-section of column 14 is expected to reflect the shape of mandrel 15. Backfill material 11 is moved upward from storage hopper 2 to hopper 9 by means of conveyor 4 operated by drive 30, during the time of column formation and until unit 1 is at its next location. Full withdrawal of the mandrel exposes the open ended mandrel and tank 12 becomes depressurized. With mandrel 15 fully extracted from soil 6 at the completion of a column and hopper 9 and its outlet 17 aligned with inlet 18 open in tank 12, backfill material 11 is again caused to flow from hopper 9 to feed depressurized tank 12 and the column forming process is repeated. The time available to move backfill material from storage hopper 2 on unit 1 by conveyor 4 to hopper 9 and backfill tank 12 positioned at the highest level of track support 13 is closely equal to the time between the start of soil cavity formation and the time unit 1 is positioned at its next location, thus avoiding interruption to the column forming cycle. Storage hopper 2 may be refilled at any time, however it is best that it holds sufficient material to have refilling done at scheduled breaks in production.

[0013] Hopper 9 may be eliminated by altering the embodiment in FIG. 1 to permit tank 12 to be temporarily separated from mandrel 15 when tank 12 reaches the point on track support 13 for conveyor 4 to supply columnar material 11 to tank 12 while mandrel 15 is advanced by its own weight or added force. Tank 12 with material 11 is repositioned on mandrel 15 on or before mandrel 15 reaches depth 26 in soil 6.

[0014] FIG. 2 shows a configuration of outlet 17 of hopper 9, where normally closed pivoted portal 27 is shaped in a manner that contact with the edge of inlet frame 23 of tank 12 opens portal 27, and outlet 17 of hopper 9 is shaped to open pivoted inlet portal 18 of tank 12 at the same time, so as to permit material 11 to pass from hopper 9 to tank 12. Special means, such as vibrator 28, may be used to expedite flow of material 11.

[0015] The embodiment of the invention in FIG. 3 incorporates unit 1 to operate the equipment and provide mobile support for elements such as backfill material storage hopper 2, track support 13, and other elements such as carriage 5 to support rotary drive 20 used to rotate tank 12 and hollow stem auger 21. Hose 19 supplies air with swivel 25 to tank 12 and hose 24 may be used to provides air under pressure to storage hopper 2, if needed, is enclosed to convey granular material to backfill hopper 9. Mandrel 15 is configured with one or more helical flights to form auger 21, and guide 16 at the low end of unit 1 may be used to guide auger 21. Pulley 29 on jib 7 is used to guide flexible cable 8 fixed to tank 12 to control travel of conjoined auger 21 in the production process. Drive 30 runs conveyor 22, which may be an enclosed helical system, to move material 11 from hopper 2 hopper 9 on track support 13. The amount of material 11 moved to hopper 9 by conveyor 22 may be controlled to the amount needed to form column 14. Hopper 9 containing backfill material 11 is aligned with its outlet 17 toward entry 18 which is open when passage of backfill material 11 to depressurized tank 12 each time auger 21 is fully withdrawn from soil 6. Under static conditions granular backfill 11 arches at the base of tank 12 and little or no flow of granular material 11 will occur through the hollow shaft auger 21 without air flow or other force. To form a column, auger 21 is positioned at the point of column formation in a manner for cap 3 to be held in its closed position by the ground surface and soil 6 during its advance to depth 8. The rotation and weight of auger 21 and tank 12 with backfill material 11 apply to advance auger 21 into soil 6. Cap 3 opens when soil support is eliminated as cavity 10 forms on withdrawing auger 21. With cap 3 open, flow of air pressure or other means, such as vibration, applied at tank 12 causes and/or assists the flow of backfill material 11 from tank 12 through auger 21 and into cavity 10 to form column 14. Full withdrawal of the auger 21 from the soil is normally done without reverse rotation, and the cross-section of column 14 reflects the cylinder defined by the outside diameter of auger 21. Tank 12 becomes depressurized with the cavity forming tool out of the ground and cap 3 open to the atmosphere, and the column forming process is repeated.

[0016] FIG. 4 shows a variation of the embodiment of FIG. 1 and FIG. 3, where support 5 and drive system 20 are positioned below tank 12 where tank 12 is conjoined with swivel 25, and thrust bearing 31 if needed, in a manner to permit the passage of backfill 11 from tank 12 though swivel 25 and through the hollow mandrel 15 or auger 21. Another variation enables tank 12 to separate from mandrel 15 or auger 21, to permit feed tank 12 to be filled while the cavity forming tool is advanced to depth 26 in soil 6, either under its own weight or by application of other force. Tank 12 is repositioned on mandrel 15 or auger 21 before depth 26 is reached in soil 6.

[0017] In the embodiment of FIG. 1, cap 3 must be smaller than the outer dimension of mandrel 15 for it to open freely in formed cavity 10, and is best designed to seat at the inside of mandrel 15. Although the rate of flow of material 11 through mandrel 15 may be affected, it may be desirable to taper the outlet of mandrel 23 to reduce the size of cap 3.

[0018] Variations in methods, embodiments and equipment described and illustrated will be evident to those familiar in the art without deviating from the teachings presented in this disclosure.

[0019] One variation of this invention relates to equipment and methods commonly used in soil sampling, where successive short sections of pipe or flight augers are added to extend the depth of such shafts beyond the maximum length handled by the equipment at one time. This use of shaft segments can be applied to the hollow shaft equipment of the present invention with modifications for the needed cavity formation and fill placement teachings of the present invention which may be further varied by applying selected teachings of U.S. Pat. No. 5,647,690.