Pile Installation

Abstract

Piles are installed by driving a tubular lower pile shell section into the ground to a first location beyond which the shell section refuses to penetrate, thereafter, filling the shell with concrete, allowing the concrete to harden and stiffen the shell, and thereafter continuing to drive the concreted shell down to a final bearing depth substantially beyond the first location.

Description

This invention relates to the formation and driving of piles and more particularly, it concerns novel pile constructions which facilitate installation and provide improved bearing with reduced material costs.

The invention is particularly suited to the formation of cased concrete piles; and the following detailed description of the preferred embodiment of the invention will be made with reference to the piles of this type.

In general, a cased concrete pile is formed by driving one or more lengths of steel tube or shell to a desired bearing depth, thereafter excavating, if necessary, from the interior of the tube and then filling the tube or shell with concrete.

One difficulty which has been encountered in connection with the formation of cased concrete piles of considerable length is that of driving the tube or shell which forms the pile casing. Because of the high soil resistances encountered in driving to great depths, the tube or shell must have a substantial wall thickness, otherwise it will refuse to penetrate beyond a given depth. This refusal to penetrate may manifest itself in various ways. Firstly, the force transmission characteristics of their shell do not, after a certain depth, provide a proper impedance match between the driver, whether a hammer or a vibrator, and the ground. The shell behaves as a spring and the driving forces instead of passing through the shell and into the ground to displace it, merely compress the shell and it springs back and reflects these forces back to the driver. Secondly, the shell may fail in compression because of insufficient column strength to withstand the driving forces required to reach an ultimate bearing depth. Thirdly, the shell may collapse, that is, it may fail by becoming squeezed in by the effects of ground pressure or by the effects of rocks, boulders or other hard objects within the earth as the shell moves by them.

While these various types of penetration refusal can be alleviated by the use of thicker walled shells, this approach becomes very expensive. Removable mandrels have been used with some success in the driving of thin walled shells; however, because of limitations on driving rigs, they often cannot readily be built with leads sufficiently high to handle the length of mandrel needed.

The present invention avoids these problems of the prior art and provides easily and simply executed procedures for constructing a novel cased concrete pile with improved strength and reduced material requirements. Thus, with the present invention, thick driving tubes are not required, nor are excessively long driving mandrels.

According to the present invention, a thin tubular shell, closed at the bottom, is driven down into the earth to a depth less than the depth at which penetration refusal occurs. The shell is then filled with a castable material, such as concrete, which is allowed to harden and stiffen the shell. The thus-stiffened shell is then driven down beyond the aforesaid location to a final bearing depth. Because of the stiffening effect of the concrete, the force transmission characteristics of the shell are changed and it becomes capable of directing the hammer or vibrator driving forces into the ground instead of merely reflecting them back to the driving mechanism. Also, the concrete provides column strength so that the shell is enabled to withstand the driving forces. The shell, moreover, is not subject to collapse as a result of squeezing or other latent forces encountered during driving.

The present invention is to be distinguished from those prior art operations which involved the driving of empty shells to a final bearing depth and thereafter filling the shells with concrete. In some cases, it was found that the concrete filled shells did not possess the expected load bearing capacity; and they were, therefore, hammered until their loading capacity was reached. In those prior art operations, the shells were either sufficiently stiff or were temporarily stiffened, as by mandrels, to enable them to be driven to final bearing depth. The concrete was placed in the shells only after they had been driven to what was intended as the final bearing depth. Any subsequent driving was undertaken only to reset the shells which may have heaved during or before pouring of the concrete.

The present invention, on the other hand, involves the driving of a thin shell only to a first location beyond which the shell refuses to penetrate, then concreting the shell to stiffen it, and finally driving the thus-stiffened shell to final bearing depth, which is substantially beyond the first location.

According to one embodiment of the present invention, a cased concrete pile is formed by first driving a first length of tube or shell into the ground until its upper end is near ground level. The tube or shell is then filled with a castable material such as concrete and the material is allowed to harden sufficiently to gain some initial strength (e.g., 4 to 5 days in the case of concrete). Thereafter, a second length of tube or shell is connected on top of the first, concrete filled, length; and the two lengths, along with the hardened concrete contained in the lower one, are driven together. Concrete is then poured into the second length and allowed to harden. If the second length is at grade level with the tip at bearing level, the pile may be capped; otherwise, a third length of tube or shell may be connected and driven down with the first and second concrete filled tubes ahead of it.

Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example a preferred form of the invention.

In the drawings:

FIG. 1 is an elevational view showing a multiple section pile installation, partially cut away, according to the present invention;

FIGS. 2-6 are elevational section views, partially cut away, illustrating a series of steps in forming the pile installation of FIG. 1;

FIG. 7 is an enlarged fragmentary elevational section view illustrating a pile section connector construction used in the pile installation of FIG. 1;

FIG. 8 is a view similar to FIG. 7, but showing an alternate connector construction;

FIG. 9 is an elevational section view illustrating one form of pile section preassembly in forming the pile installation of FIG. 1;

FIG. 10 is a view similar to FIG. 9, but showing an alternate preassembly construction; and

FIG. 11 is a view similar to FIG. 5, but illustrating the use of a mandrel in driving pile sections.

The pile installation of FIG. 1 comprises a plurality of pile sections 20 extending down into the earth (indicated at 21). These pile sections are arranged in tandem and are coupled together at their ends by means of connector constructions 22. The overall length and cross-sectional size of the pile construction will depend upon the particular soil conditions and on the load to be carried. For example, the overall length of the pile construction may be about 135 feet and its cross-section may be circular with a diameter of about 13 inches.

As can be seen in the lower cutaway portion in FIG. 1, the pile sections 20 each comprise a tubular steel shell 24 which encases a concrete core 26.

Turning now to FIG. 2, it will be seen that the first step in the installation of the pile construction involves driving a first hollow tubular shell section 28 down into the earth 21. The lower end of the shell section 28 is covered with a boot plate 30 to prevent soil from entering up into its lower end. A removable cap block 32 may be provided at the upper end of the shell section 28; and the driving forces may be applied, as indicated at 34, by any known means, such as a hammer. Alternatively, a clamping arrangement may be used in place of the cap block 32 and vibratory forces may be applied to drive the shell section 28 down into the earth.

After the first shell section 24 has been driven to where penetration refusal is experienced, a wet concrete mix 36 is poured into the shell section, as shown in FIG. 3. The concrete mix, which may be a conventional concrete mixture, or a mixture containing an expansion component, is poured through a chute 38 until the shell section 28 is essentially filled. The concrete is then allowed to cure and harden until it attains a substantial portion of its strength. A period of 4 to 5 days will usually suffice.

During the initial stages of curing a portion of the water content of the concrete may rise to the top of the shell section 28. This water may be removed, as by mopping. The resulting void is then filled with a high-early strength grout, as indicated at 40 in FIG. 4. A steel plate 42 is set into the shell section 28 so that it rests upon the grout 40 flush with the upper end of the shell section. The steel plate 42 is preferably welded, as at 44, to the upper end of the shell section 28 so that a rigid compact concrete-grout-steel structure results.

After the concrete and grout have hardened and the steel plate 42 has been fixed in place, a second shell section 46 is positioned on top of the first shell section and is secured thereto, as by a connector sleeve 48, as shonw in FIG. 5. Driving forces, indicated at 50, are then applied to the second section 46 to drive the two sections together down into the earth.

Eventually, the two shell sections 28 and 46 are driven to a desired depth whereupon the driving forces are removed, as shown in FIG. 6. Thereafter, the second shell section may be capped off with or without first filling it with concrete; or, in the event that further pile sections are to be added for additional depth, the second shell section 46 may be filled with concrete and grout and after the concrete and grout have hardened the further pile section may be added as above-described and driving resumed.

The connector sleeve 48 is best shown in the enlarged view of FIG. 7. As can be seen, the sleeve 48 is of generally tubular configuration and its inner surface is tapered outwardly toward the ends to accept the mating ends of the shell sections 28 and 46. An internal flange 52 extends inwardly a short distance from the center of the sleeve 48. This flange rests upon the upper end of the lower shell section 28 while the lower end of the upper shell section 46, in turn, rests upon the flange 52. It will be seen that this provides solid metal-to-metal contact between the shell sections for positive driving.

For some purposes the connector sleeve 48 may be dispensed with and two shell sections 28 and 46 may be welded directly to each other, as indicated at 54 in FIG. 8. When a direct welded connection is employed, the resulting pile construction is enabled to sustain uplift loads. Also, the welded connection permits the use of vibrator-type driving apparatus for all shell sections. Unless the shell sections are positively connected, as by welding, the use of vibrators is limited, for most practical purposes to the lowermost shell section.

FIGS. 9 and 10 show different connector arrangements which may be employed to expedite shell section assembly during pile installation. As can be seen in FIG. 9, the connector sleeve is secured to the upper shell section 46 prior to assembly with the lower shell section 28. This permits partial preassembly in the plant or other remote location so that at the pile installation site, the upper shell section may be assembled onto the lower section simply by setting it with the connector sleeve attached onto the lower shell section. In this case, the upper end of the connector sleeve 48 is dimensioned to have a press fit with the upper shell section 46, while the lower end of the connector sleeve is dimensioned to have a slip fit with the lower shell section 28.

The arrangement of FIG. 10 is reverse to that of FIG. 9 in that the connector sleeve in this case is preassembled onto the lower shell section 28 and is dimensioned to provide a press fit thereon. The upper shell section is then lifted onto the lower shell section and connector sleeve preassembly and is fitted into the upper end of the connector sleeve. The upper end of the connector sleeve, in this case, is dimensioned to provide a slip fit with the upper shell section.

Turning now to FIG. 11, it will be seen that a mandrel 60 may be used in driving the upper and lower sections 46 and 28. As can be seen, the mandrel 60 is inserted into the interior of the upper shell section 46, and its lower end rests upon the steel plate 42 of the lower shell section 28. Hammer blows applied to the mandrel 60 are thus transmitted directly to the lower shell section so that the upper shell section 46 need not transmit these driving forces. The length of the mandrel 60 is made slightly greater than that of the upper shell section 46 so that the greater portion of the driving force is applied through the mandrel. However, as the upper shell section 46 stretches under the force of the hammer blows, the upper end of the mandrel contacts the upper end of the shell section 46 and a portion of the hammer energy becomes directed into the upper shell section. In this manner, driving stresses are distributed throughout the pile system and thus the likelihood of shell section rupture during driving is minimized.

The pile installation arrangements described above are characterized by the driving of a shell section containing concrete which has at least partially hardened. It has been found that there is little tendency for the concrete in the shell section to break up since the driving forces are directed primarily in compression of the concrete. Any fracture of the concrete, which may take place during driving, will not affect the load-carrying capabilities of the pile installation since the concrete is contained laterally by the tensile strength of the tubular steel shell section. This lateral support has been found to provide very greatly improved load-bearing capabilities. This can be further improved by use of a concrete mix containing an expansion component. As the concrete hardens, it expands against the walls of the tubular shell and the reaction of these walls produces a lateral squeezing on the concrete; and this, in turn, greatly increases the longitudinal compressive strength of the pile structure.

By providing a concrete shell section, as above-described, continued driving may take place without danger of buckling or collapsing of the shell sections, either by soil restraint or upon impingement against boulders and the like within the earth.

The strength provided to the shell by the concrete enables the use of a thinner wall shell than would normally be required. Actually, in most pile installations using steel encased concrete pile construction, the required shell wall thickness calculated for load bearing is less than that calculated for driving. Thus, by enabling a thinner wall shell section to be driven, the present invention makes possible a more efficient relationship between shell section wall thickness and load specifications.

For certain applications, it may be desired to increase the tensile strength of the concrete within the shell sections. This can be done by installing conventional reinforcing steel within the shell section before pouring the concrete; or if desired, small lengths of fiber or short steel wire may be distributed randomly throughout the concrete mix.

Having thus described the invention with particular reference to the preferred form thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding the invention, that various changes and modifications may be made therein without departing from the spirit and scope of the invention, as defined by the claims appended thereto.

Claims

What is claimed is:

1. A method of forming a pile in the earth comprising the steps of driving a hollow tube, closed at the bottom, down into the earth to a first location less than the depth at which penetration refusal is experienced, then filling the tube with a flowable castable material to stiffen the tube, allowing the castable material to harden and thereafter further driving the tube with the castable material hardened therein further down substantially beyond said first location to a final bearing depth.

2. A method of forming a pile according to claim 1, wherein the castable material is concrete and said concrete is allowed to harden about four days before said further driving.

3. A method of forming a pile in the earth comprising the steps of driving a first tube down into the earth, filling the tube with a castable material to stiffen same, allowing the castable material to harden, connecting a further tube to the top of the first tube and thereafter driving the tubes together further down into the earth.

4. A method of forming a pile according to claim 3, wherein the castable material is concrete and wherein water which rises to the top of said first tube is removed and replaced with a grout.

5. A method of forming a pile according to claim 3, wherein a steel plate is positioned on top of the castable material prior to connecting said further tube.

6. A method of forming a pile according to claim 3, wherein said further tube is connected by welding its end to the top of said first tube.

7. A method of forming a pile according to claim 6, wherein said tubes are driven together further down into the earth by application of vibratory driving forces.

8. A method of forming a pile according to claim 3, wherein said further tube is connected by means of a connector sleeve.

9. A method of forming a pile according to claim 8, wherein said connector sleeve is preassembled with one of said tubes by a press fit.

10. A method of forming a pile according to claim 9, wherein said connector sleeve is fitted to the other tube with a sliding fit.

11. A method of forming a pile according to claim 3, wherein said further tube, after being driven further down into the earth, is itself filled with a castable material.

12. A method of forming a pile according to claim 11, wherein the castable material in said further tube is allowed to harden and a third tube is connected to the top of said further tube and all said tubes are together driven still further into the earth.

13. A method of forming a pile according to claim 3, wherein said driving of the tubes together into the earth is undertaken by means of a mandrel extending down the interior of said further tube to engage the castable material in the first tube to distribute the force of driving blows between said tubes.