US3921410A

US3921410A - System and method of permafrost pile forming

Info

Publication number: US3921410A
Application number: US486050A
Authority: US
Inventors: Kenneth W Philo
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-07-05
Filing date: 1974-07-05
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

A system and method for placing a preformed pile in permafrost or other hard ground is disclosed. The initial procedure in the system is to excavate an annulus in the ground having an outer diameter somewhat larger than the outer diameter of the pile, leaving a substantially undisturbed core. The core is then removed to provide a hole for insertion of the pile therein. The system also provides for filling the area surrounded by the inserted pile with wet sand, and allowing the sand to be frozen in place to encapsulate the pile.

Description

United States Patent Philo 1 Nov. 25, 1975 [54] SYSTEM AND METHOD OF PERMAFROST 3,839,874 10/1974 Wyant (ii/53.52

PILE FORMING FOREIGN PATENTS OR APPLICATIONS [76] Inventor: Kenneth W. Philo, 7 Palm Ave., San 706,239 3/1954 United Kingdom v. (Ii/53.52

Rafael, Calif. 92708 Primary Examiner-Jacob Shapiro [22] Flled' July 1974 Attorney, Agent, or FirmTownsend and Townsend [21] Appl. No.: 486,050

. [57] ABSTRACT 52 us. (:1. 61/5352; 61/36 A' 61 /53.64- A System and method Placing Prefmmed Pile 6151,66; 175/84 permafrost or other hard ground is disclosed. The ini- 51 1111. 0. 1, E02D 5/22; E02D 5/60 Procedure in the System is excavate annulus 58 Field Of Search 6l/53.5, 53.52, 53.64, the ground having diameter somewha 61/5366 36 A 175/84. 214/310 larger than the outer diameter of the pile, leaving a 9 substantially undisturbed core. The core is then re- [56] References Cited moved to provide a hole for insertion of the pile therein. The system also provides for filling the area UNITED STATES PATENTS surrounded by the inserted pile with wet sand. and al- 2 l d g @(ZZSSQ lowing the sand to be frozen in place to encapsulate am 2,664,269 12/1953 Knight 61 al. 214/310 x the 3,543,525 12/1970 Phares 61/53.66 19 Claims, 7 Drawing Figures US. Patent Nov. 25, 1975 Sheet10f2 3,921,410

FIG...2 F|G 3 FIG 4 FIGJ US. Patent Nov.25, 1975 Sheet2of2 3,921,410

FlG 7 SYSTEM AND METHOD OF PERMAFROST PILE FORMING BACKGROUND OF THE INVENTION The present invention relates to a system and method for emplacing a pile in the ground, and in particular to a system and method for placing pre-formed piles in permafrost or other hard ground.

The current shortage of fossil fuel and other natural resources, particularly in locations which are accessible to drilling and mining, has resulted in an increased emphasis in tapping reserves-of such resources in the Arctic and other remote areas. One of the limitations in exploiting such reserves is the difficulties in constructing large buildings and other structures in such locations, such structures being necessary to exploit the reserves in an economically feasible manner. One problem of current interest is the construction of long-distance oil pipelines over the Alaskan tundra, elevating at least portions thereof to allow for passage of wildlife and preventing damage to the environment. One of the principle construction problems, especially in the Arctie, is to achieve a solid foundation for such structures in the permafrost. Permafrost is extremely hard when frozen, but thaws at various levels during different seasons of the year.

Since the permafrost is extremely hard, most customary methods of placing piles in the ground cannot be used, at least in an economically feasible manner. The hardness of the ground makes it difficult and economically unfeasible to drive pre-formed piles directly into the ground. Also, it is difficult to drive a casing directly into the ground so that a pile can be formed in place. Conventional methods of impact drilling as illustrated in the patent to Becker, U.S. Pat. No. 3,280,925, or augering, as illustrated in my prior patent, U.S. Pat. No. 3,808,821 are also often unfeasible in permafrost because the required destruction of a large volume of permafrost material is time consuming and subjects tools to substantial wear, thereby greatly increasing the cost ofthe operation.

Another problem with conventional augering techniques is that a casing or other support must be kept in the hole at all times to avoid collapse. During the summer, the surface of the ground thaws causing collapse of the upper region of the hole. During the spring. active layers are often formed between frozen layers in the permafrost and also cause caving. During all seasons of the year, the lower portion of the hole may reach thawed soil and/or the water table to cause caving at the lower end of the hole. Certain apparatus disclosed in the prior art, such as my patent referred to above, provides a temporary casing as the hole is being augered, but does not make provisions for the ready insertion of the pile.

A further problem encountered when placing piles in an augered hole is the filling of the circular gap between the pile and the casing if one is provided or between the pile and the outer walls of the hole if no casing is provided. This space is difficult to fill with sand or other material because the pouring of such material from the top of the hole will result in the material bridging and leaving gaps or voids around the pile.

SUMMARY OF THE INVENTION The present invention relates to a system and method for placing and encapsulating a pile in permafrost or other hard ground. The apparatus of the present invention includes an enlongate hollow casing. and an annular drilling head located at the lower end of the casing. The drilling head excavates an annulus in the ground, leaving a substantially undisturbed core. The core is enclosed by a hollow core tube normally disposed within the casing and concentric therewith. The core tube is removable from the casing when the annulus has been drilled to the desired depth to lift the core from the annulus and thereby provide a hole for placement of the pile.

The hole excavated by the apparatus of the present invention is maintained by the casing during removal of the core tube and placement ofthe pile so that the hole will not collapse. The casing is then removed from the hole, and includes tubes for dispensing sand at the bottom of the casing as it is removed from the hole so that the sand does not bridge and form voids. The sand is wetted to freeze it in place in the permafrost to completely encapsulate the pile.

The present invention allows for the use of preformed piles, eliminating the requirement for pouring concrete in place. The pile is not driven directly into the ground but rather a hole is excavated for placement of the pile therein. At first. an annulus having a relatively small cross sectional area but an outer diameter larger than that of the pile is drilled in the hole, preferably by percussive drilling. Since the annulus has a relatively small cross sectional area, it can be drilled far more easily and rapidly in the hard ground since far more force will be transmitted per unit area for a given percussive drilling rig. The undisturbed core can then be easily removed from the hole by breaking off the core at the bottom thereof and removing it intact, leaving a relatively large hole for placement of the pile without the effort required to auger the entire hole as a unit.

In the preferred embodiment of the apparatus of the present invention, the casing is self-extracting as illus trated in my prior patent, U.S. Pat. No. 3,808,82l. As the casing of the present invention extracts itself from the hole, it is adapted to dispense sand in the area around the pile vacated by the casing. In this manner, the pile will be fully encapsulated with sand, without sand bridging which may cause voids in sand surrounding the pile. The sand is preferably wetted so that it freezes in place to provide a unitary capsule for the pile.

The novel features which are believed to be characteristic of the invention, both as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which a preferred enbodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose ofillustration and description only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of the apparatus of the present invention illustrating the casing and core tube partially broken away;

FIG. 2 is an elevation view similar to that of FIG. 1 with portions of the outer shell of the casing broken away to expose the tubes in the casing;

FIG. 3 is an elevation view of the apparatus of the present invention during removal of the core tube with part of the casing and core tube broken away;

FIG. 4 is an elevation view of the apparatus of the present invention as the casing is being removed from the hole after placement of the pile and showing the hopper partially broken away;

FIG. 5 is a fragmentary view of a drilling tooth of the present invention partially broken away;

FIG. 6 is a cross-sectional view taken along lines 66 of FIG. 1',

FIG. 7 is a cross-sectional view of the hopper portion of the apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drilling apparatus of the present invention is illustrated generally at 10 in FIG. 1. Apparatus 10 includes an outer casing 12 defined by inner and

outer shells

14 and 16 respectively. A percussive drilling head 18 is located at the bottom of casing 12 and includes a plurality of downwardly directed annularly disposed percussive drilling teeth 20. The central core tube 22 is disposed within and is concentric with casing 12.

Drilling teeth 20 in drilling head 18 are relatively narrow so that only a small annulus sufficient to accomodate casing 12 and core tube 22 is excavated by driving the drilling teeth with hammer 26. A substantially undisturbed core 34 of material remains inside the annulus excavated and is circumscribed by core tube 22. The diameter of the annulus excavated by drilling head 18 is slightly greater than that of the pile which is to be placed therein. However, since only an annular volume is excavated rather than the entire hole the force necessary in the excavation is far less than would be required to directly excavate the entire hole to that diameter as done in the prior art.

As the annulus is excavated by apparatus 10 by driving drilling head 18 with hammer 26, earth 40, rocks and the like is dislodged and disintegrated by teeth 20 of the drilling head as illustrated in FIG. 2. Pressurized air is supplied by way of conduit 42 to a plurality of circular tubes 44 extending down the side of casing 12 between

shells

14 and 16. Tubes 22 terminate at several small ports 46 formed in each tooth 20 as illustrated in FIG. 5. Pressurized air from ports 46 forces the disintegrated ground 40 upwardly through square tubes 48 and out of the hole as illustrated by chunks 50. In this manner, loosened earth is constantly forced out of the annulus as it is being drilled so that it will not impede the progress of the drilling.

When apparatus 10 has drilled the annulus to the desired depth, undisturbed core 34 remains trapped inside core tube 22. As core tube 22 is drawn upwardly from within casing 12 as illustrated in FIG. 3, the vacuum created by the closed upper end 24 of core tube 22 and friction along the side walls of the core tube will cause the core 34 to be drawn upwardly as well. In this manner, core 34 can be drawn out of the excavated annulus to form a finished hole for placement of a preformed pile. After core tube 22 is completely separated from casing 12, the upper end 24 thereofis pressurized through tube 51 to force core 34 out of the core tube at the side of the hole. The hole is maintained by casing 12 while core tube 22 is being removed so that the sides of the hole will not cave in.

After core tube 22 has been removed from the interior of casing 12, a pre-formed pile 52 is placed in the resulting hole as illustrated in FIG. 4. If desired. core tube 22 can then be replaced over pre-formed pile 52 prior to removing apparatus 10 from the hole if desired so that the apparatus is intact after removal from the hole. Apparatus 10 is self-extracting by successively moving

plates

54, 56 forming part of outer shell 16 of the casing.

Plates

54, 56 are moved in steps by means of

hydraulic actuators

58, 60 to extract apparatus 10 from the hole. as illustrated in my prior patent, US. Pat. No. 3.808.821.

Prior to withdrawing apparatus 10 from the hole with the pre-formed pile in place, hopper 62 at the upper end thereof is filled with sand 64. The sand flows downwardly through square tubes such as 48 which previously had been used to expel dislodged earth from the annulus. As casing 12 extracts itself from the hole leaving pre-formed pile 52 therein, sand 64 flows out through the lower end of square tubes 48 to fill the annular volume left by the casing. Since sand 64 is dispensed as casing 12 withdraws itself from the hole, the sand will not bridge and cause voids as it would if it were dispensed from the top of the hole. Sand 64 can be wetted either before it is dispensed or after it is dispensed to form a mixture of sand and water. The in place sand should have a water content of 8 to 15 percent in dry weight. The sand should be free of organic or other deleterious materials and should meet the gradation of the following chart:

In order to insure that the sand completely fills the annulus surrounding the pre-formed pile, the pile may be vibrated as the sand is being placed with a standard vibrator. Since the pile is placed in permafrost, the wet sand will be frozen in place to completely encapsulate the pile and prevent caving of the side walls of the hole after casing 12 is removed.

The internal configuration of the casing 12 is more fully illustrated by way of reference to the cross-sectional view of FIG. 6, taken along lines 66 of FIG. 1. As can be seen, casing 12 includes an external shell 16 and an internal shell 14. External shell 16 includes a plurality of

plates

54, 55, 56 and 57 for self-extraction of the casing as illustrated hereinabove. Both round tubes 44 and square tubes 48 pass through the space between inner and

outer shells

14, 16. Smaller round tubes 44 allow for the passage of pressurized air to the bottom of the annulus as it is being excavated. Square tubes 48 serve two purposes. They both allow for the escape of loosened earth particles as the annulus is being excavated, and they also allow the passage of sand to the bottom of the hole as casing 12 is being removed.

Hopper 62 of the present invention is further illustrated in FIG. 7. As the annulus is being drille'd, hopper 62 at the upper end of the casing is empty to allow loosened layers of earth to fly out of the upper end of square tubes such as 48 and out of hopper 62. A plate 70 is provided at the lower end of hopper 62 to provide a manifold section 72 at the lower end of the hopper which is separate from the rest of the hopper. Pressurized air is supplied to manifold 72 by means of conduit 42, which communicates with the upper end of round tubes such as 44. Thus, the pressurized air is forced down through round tubes 44 to force the dirt clods out of square tube 48 as discussed hereinabove. When hopper 62 is filled with sand after the annulus has been excavated, plate 70 will prevent the sand from entering manifold 72, and it will flow down through square tubes In operation, apparatus 10 is mounted in a vertical position at the place where a pile is to be placed, usually by means of a crane, A hammer such as 26 is activated and repeatedly strikes the closed upper end 24 of core tube 22, driving teeth 20 of drilling head 18 down into the ground. Teeth 20 excavate an annular ring of material, which is blown'out of the annulus by pressurized air supplied through tubes 44 from manifold 72. The loosened earth is discharged from the annulus through square tubes 48 so that they do not impede the progress of the drilling. As the annulus is being drilled, the central core of the annulus remains essentially undisturbed, and is enclosed within core tube 22. As drilling head 18 forms the annulus, casing 12 resting on top of the drilling head follows thedrilling head into the annulus and prevents collapse of the outer walls thereof.

After the annulus has been drilled to the desired depth, core tube 22 is drawn upwardly out of the annulus, which is maintained by casing 12 which remains in place. Undisturbed core 34 is drawn out of the annulus along with the core tube so that a finished hole is formed. Core 34 is then dumped to the side of the hole by pressurizing the upper end of the core tube. A preformed pile 52 is then placed in the excavated hole inside casing 12. The core tube 22 can then be placed over pile 52 if desired.

Sand 64 is then placed in hopper 62. Apparatus l slowly extracted from the hole using moving plates 5457. As the apparatus is withdrawn, sand 64 passes downwardly through square tubes 48 to fill the void left around pile 52 as the apparatus is removed. Sand 64 is either previously wetted or wetted in place, and due to its placement in permafrost, freezes to form a solid capsule for the pile, preventing collapse of the side walls of the hole and insuring the structural integrity of the pile. I

While a preferred embodiment of the present invention has been illustrated in detail, itis-apparent that modifications and adaptations of that embodiment will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.

What I claim is:

l. A method for placing a pile in permafrost or other hard ground which is normally frozen, said method comprising the steps of excavating an annulus in the ground having an outer diameter slightly greater than the outer diameter of the pile and leaving a substantially undisturbed core, said excavating step including the step of placing a casing and means for dispensing sand at the lower end of the casing in said annulus; inserting the pile into the hole inside the casing; removing the casing from the hole and simultaneously dispensing sand with said dispensing means at the lower end of the 6 casing to fill the space vacated around the pile as the casing is removed from the hole; and wetting the sand so that the sand is frozen in place to encapsulate the pile.

2. A method as recited in claim 1 wherein said excavating comprises the step of percussive drilling the annulus in the ground.

3. A method as recited in claim 1 wherein said excavating includes the step of placinga core tube in the annulus, said core tube being interior of and concentric with said casing and adapted to enclose the undisturbed core, and wherein said removing step comprises removing the core tube having the core therein leaving the casing in the annulus to prevent collapse of the side walls thereof.

4. Apparatus for placing a pile in permafrost or other hard ground which is normally frozen, said apparatus comprising:

an elongate hollow casing;

means for excavating an annulus and leaving a substantially undisturbed core within said annulus, said excavating means located at the lower end of the casing;

a hollow core tube normally disposed within the easing and concentric therewith, said core tube being removable from the casing and adapted to circumscribe the core so that removal of the core tube from within the casing will lift the core from the annulus to provide a hole for placement of the pile, said hole being maintained by the casing during removal of the core tube and placement of the pile;

means for removing the casing from the hole after placement of the pile; and

means for dispensing sand as the casing is being removed from the hole into the space left by removal of the casing, said sand being wetted to freeze the sand in place to encapsulate the pile.

5. Apparatus as recited in claim 4 wherein the core tube includes means for expelling the core from the core tube after lifting the core from the annulus.

6. Apparatus as recited in claim 5 wherein the upper end of the hollow core tube is sealed, and wherein said expelling means includes means for pressurizing the upper end of the core tube to expel the core out the other end thereof.

7. Apparatus as recited in claim 4 wherein said excavating means includes a percussive drilling head.

8. A method for placing and encapsulating a pile in permafrost or other hard ground which is normally frozen, said method comprising the steps of excavating a hole in the ground having an outer diameter slightly greater than the outer diameter of the pile; placing a hollow casing into the hole; inserting the pile into the hole within the hollow interior of the casing; removing the casing from the hole after insertion of the pile and simultaneously dispensing sand at the bottom of the casing into the annular void surrounding the pile left as the casing is removed from the hole; and wetting the sand so that the sand is frozen in place to encapsulate the pile.

9. A method as recited in claim 8 wherein said wetting is performed prior to dispensing the sand into the annular void.

10. A method as recited in claim 8 wherein said wetting is performed subsequent to dispensing the sand into the annular void.

11. A method as recited in claim 8 wherein said excavating comprises the steps of excavating an annulus in the ground having an outer diameter slightly greater than the outer diameter of the pile and leaving a substantially undisturbed core. and removing the core to provide the hole.

12. A system for placing and encapsulating a pile in an excavated hole in permafrost or other hard ground which is normally frozen. said system comprising:

an elongate hollow casing adapted to occupy the excavated hole;

means for placing the pile into the hole interior ofthe elongate hollow casing;

means for withdrawing the casing from the hole after placement of the pile: and

means for dispensing sand at the lower end of the casing into the annular volume vacated by the casing as said casing is withdrawn from the hole. said dispensing means operating simultaneously with said withdrawing means so that the sand is dispensed as the casing is withdrawn from the hole to prevent the formation of gaps in the sand by bridging. said sand being wetted so that the sand is frozen in place to encapsulate the pile.

13. Apparatus for placing a pile in permafrost or other hard ground. said apparatus comprising:

a percussive drilling head having an annular array of downwardly directed percussive drilling teeth. said drilling head having an inwardly directed flange portion:

an elongate core tube having an open lower end adapted to rest on the flange portion of the drilling head and a closed upper end adapted to provide a striking surface for a hammer so that the drilling head is powered by the hammer to percussively drill an annulus in the ground leaving a substantially undisturbed core; and

an elongate hollow casing adapted to circumscribe the core tube. the outer diameter of the casing being substantially equal to the outer diameter of the percussive drilling head so that the casing prevents collapse of the outer walls of the annulus during the drilling thereof, the side walls of the casing having two sets of tubes extending vertically therethrough. the upper ends of the first set of tubes being connected to a source of pressurized air which passes therethrough to force soil loosened by the teeth of the drilling head upwardly through the second set of tubes and out of the annulus, the core tube being removable from the casing after drilling of the annulus to the desired depth, the undisturbed core being removed with said core tube to provide a hole for placement of the pile.

14. Apparatus as recited in claim 13 and additionally comprising a hopper located at the upper end of the casing. the upper end of the second set of tubes communieating with said hopper to feed sand to the annular void vacated by the casing as the casing is removed from the hole after placement of the pile. said sand being wetted so that the sand freezes in place to encapsulate the pile.

15. A method for placing a pile in permafrost or other hard ground. said method comprising the steps of:

providing a percussive drilling head having an annular array of downwardly directed percussive drilling teeth; locating the open lower end of an elongate core tube overlying at least a portion of the drilling head;

fixing the lower end of an elongate hollow casing to the percussive drilling head so that said hollow casing circumscribes the core tube;

driving the drilling head downwardly into the ground to percussively drill an annulus in said ground while leaving a substantially undisturbed core;

forcing pressurized air downwardly through a first conduit intermediate the casing and the core tube to thereby force soil loosened by the drilling teeth upwardly through a second conduit and out of the annulus;

removing the core tube from the casing after drilling of the annulus to remove the undisturbed core contained within the core tube and provide a hole for placement of the pile; and

preventing the collapse of the outer walls of the annulus with the casing during the drilling of said annulus and removal of said core tube.

16. A method as recited in claim 15 and additionally comprising the steps of removing the casing from the hole after placement of the pile and simultaneously dispensing sand at the lower end of said pile to fill the space vacated around the pile as the casing is removed from the hole, and wetting the sand so that the sand is frozen in place to encapsulate the pile.

17. A method as recited in claim 15 wherein said driving step includes the step of striking the closed upper end of the elongate core tube to drive the drilling head downwardly into the ground.

18. A method as recited in claim 1 wherein said wetting step is performed prior to said dispensing step.

19. A method as recited in claim 1 wherein said wetting step is performed subsequently to said dispensing step.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO. ,921 4 DATED November 25, 1975 INVENTOMS) 1 Kenneth W. Philo it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, line 65, after annulusf' insert removing the core to provide a hole;

Bigncd and Scaled this A ties t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer ('nmmr'ssr'uner uflarents and Trademarks

Claims

1. A method for placing a pile in permafrost or other hard ground which is normally frozen, said method comprising the steps of excavating an annulus in the ground having an outer diameter slightly greater than the outer diameter of the pile and leaving a substantially undisturbed core, said excavating step including the step of placing a casing and means for dispensing sand at the lower end of the casing in said annulus; inserting the pile into the hole inside the casing; removing the casing from the hole and simultaneously dispensing sand with said dispensing means at the lower end of the casing to fill the space vacated around the pile as the casing is removed from the hole; and wetting the sand so that the sand is frozen in place to encapsulate the pile.

3. A method as recited in claim 1 wherein said excavating includes the step of placing a core tube in the annulus, said core tube being interior of and concentric with said casing and adapted to enclose the undisturbed core, and wherein said removing step comprises removing the core tube having the core therein leaving the casing in the annulus to prevent collapse of the side walls thereof.

4. Apparatus for placing a pile in permafrost or other hard ground which is normally frozen, said apparatus comprising: an elongate hollow casing; means for excavating an annulus and leaving a substantially undisturbed core within said annulus, said excavating means located at the lower end of the casing; a hollow core tube normally disposed within the casing and concentric therewith, said core tube being removable from the casing and adapted to circumscribe the core so that removal of the core tube from within the casing will lift the core from the annulus to provide a hole for placement of the pile, said hole being maintained by the casing during removal of the core tube and placement of the pile; means for removing the casing from the hole after placement of the pile; and means for dispensing sand as the casing is being removed from the hole into the space left by removal of the casing, said sand being wetted to freeze the sand in place to encapsulate the pile.

11. A method as recited in claim 8 wherein said excavating comprises the steps of excavating an annulus in the ground having an outer diameter slightly greater than the outer diameter of the pile and leaving a substantially undisturbed core, and removing the core to provide the hole.

12. A system for placing and encapsulating a pile in an excavated hole in permafrost or other hard ground which is normally frozen, said system comprising: an elongate hollow casing adapted to occupy the excavated hole; means for placing the pile into the hole interior of the elongate hollow casing; means for withdrawing the casing from the hole after placement of the pile; and means for dispensing sand at the lower end of the casing into the annular volume vacated by the casing as said casing is withdrawn from the hole, said dispensing means operating simultaneously with said withdrawing means so that the sand is dispensed as the casing is withdrawn from the hole to prevent the formation of gaps in the sand by bridging, said sand being wetted so that the sand is frozen in place to encapsulate the pile.

13. Apparatus for placing a pile in permafrost or other hard ground, said apparatus comprising: a percussive drilling head having an annular array of downwardly directed percussive drilling teeth, said drilling head having an inwardly directed flange portion; an elongate core tube having an open lower end adapted to rest on the flange portion of the drilling head and a closed upper end adapted to provide a striking surface for a hammer so that the drilling head is powered by the hammer to percussively drill an annulus in the ground leaving a substantially undisturbed core; and an elongate hollow casing adapted to circumscribe the core tube, the outer diameter of the casing being substantially equal to the outer diameter of the percussive drilling head so that the casing prevents collapse of the outer walls of the annulus during the drilling thereof, the side walls of the casing having two sets of tubes extending vertically therethrough, the upper ends of the first set of tubes being connected to a source of pressurized air which passes therethrough to force soil loosened by the teeth of the drilling head upwardly through the second set of tubes and out of the annulus, the core tube being removable from the casing after drilling of the annulus to the desired depth, the undisturbed core being removed with said core tube to provide a hole for placement of the pile.

14. Apparatus as recited in claim 13 and additionally comprising a hopper located at the upper end of the casing, the upper end of the second set of tubes communicating with said hoPper to feed sand to the annular void vacated by the casing as the casing is removed from the hole after placement of the pile, said sand being wetted so that the sand freezes in place to encapsulate the pile.

15. A method for placing a pile in permafrost or other hard ground, said method comprising the steps of: providing a percussive drilling head having an annular array of downwardly directed percussive drilling teeth; locating the open lower end of an elongate core tube overlying at least a portion of the drilling head; fixing the lower end of an elongate hollow casing to the percussive drilling head so that said hollow casing circumscribes the core tube; driving the drilling head downwardly into the ground to percussively drill an annulus in said ground while leaving a substantially undisturbed core; forcing pressurized air downwardly through a first conduit intermediate the casing and the core tube to thereby force soil loosened by the drilling teeth upwardly through a second conduit and out of the annulus; removing the core tube from the casing after drilling of the annulus to remove the undisturbed core contained within the core tube and provide a hole for placement of the pile; and preventing the collapse of the outer walls of the annulus with the casing during the drilling of said annulus and removal of said core tube.