Composite pile

CA 02270586 2008-02-19

Patent Application

Composite Pile

Composite pile

This invention relates to piling.

Present commercial pile driving practice utilizes piles having a variety of materials and geometric shapes to produce capacities in excess of 30 tons (about 270 kN). These piles are often concrete-filled steel tubes having closed-ends that are driven into a variety of soil types, including those with granular (sand and/or gravel) and cohesive (silt and/or clay) characteristics.

Generally, the piles have a constant cylindrical cross-section. However, it is well known that a gradually increasing tapered configuration often enhances the load bearing capacity of piles, particularly in granular soils. Thus, piles having such geometries, such as fiilllcngth fluted piles with tapered fluted bottom sections below a length of fluted cylindrical tubing having a diameter equal to that at the top of the tapered section, have been shown to be effective by producing higher capacities than cylindrical piles at similar penetrations into those soils. These piles have been used successfully for decades. They are described at pages 158 and 159 of the book “Foundation Construction” by A. Brinton Corson published 1965 by McGraw-Hill Book Company.

The piles for this invention have tapered bottom sections made of steel tubing shaped into a polygon cross-section having substantially equal sides (preferably about 8-16, e.g. 12 sides), or of said polygonal cross-section having a short transitional length to a circular cross-section at the top, which is joined by a fabricated splicer, or by butt welding, to conventional circular steel cylindrical pipe having a diameter that may be equal to, or less than, the top diameter of the taper. Wall thicknesses for both the tapered section and pipe section can be up to 0.5 in. (about 13 mm) compared to 0.24 in (about 6mm) for the conventional fluted piles, top diameters of the tapered section may be from 12 in. (300 mm) to 24 in. (600 mm), bottom diameters may be from 8 in. (200 mm) to 20 in. (500 mm); tapered lengths may be fabricated in lengths of 5 to 40 feet (1.5 m to 12 m), and circular pipe lengths fabricated to lengths of 80 feet (24 m) and longer. For conventional fluted piles, the splice between the tapered section and cylindrical fluted section is a lap weld from the top of the tapered section to the side of the cylindrical section which has been inserted for several inches into the tapered section, maximum metal thickness if 0.24 in. (about 6 mm), tapered sections have a maximum upper diameter of 18 in. (about 450 mm) and bottom diameters are all 8 in. (about 200 mm), and cylindrical fluted sections are made to a maximum length of 40 ft. (about 12 m).

CA 02270586 2008-02-19

These piles will produce comparable and greater capacities than the previously described fluted piles.

Among the advantages of these piles are:

1. A wide range of geometries and lengths for the tapered bottoms can be fabricated by means of existing equipment and technology, such as brake-forming. The pile length, top and bottom diameter, and wall thickness can be made to satisfy sitespecific pile capacities and soil conditions.

2. Significant cost savings are possible by the use of conventional cylindrical pipe for the tops of these piles. Pipe costs considerably less than fluted cylindrical tubing. Added savings will result if the pipe diameter used is less than the top diameter of the tapered section, and by the re-use of pipe remaining from previously driven piles that can easily be spliced.

Furthermore, the use in the practice of this invention of thin-walled pipe (or alternatively corrugated steel shell) that is driven with an internal mandrel will also produce significant cost-savings.

3. Specific design considerations not possible with existing configurations may be designed by using the proposed piles. These include tapered and pipe wall thicknesses of up to 0.5 in. (about 13mm) to provide stiffness and suitable stress levels for both driving conditions and service conditions. Heavier wall thicknesses may be used for proposed piles to avoid damage often caused to fluted tapered piles with available maximum wall thickness. Added pile stiffness and strength also improves the driving efficiency thereby yielding improved pile load capacity.

4. The splices for these piles may be drive-fit, weld-fit or butt-welded. In all cases, the load transfer from the top of the pile to the bottom is made by continuous bearing of each of the components, and not through a shear transfer in a lap-welded splice as is customary for fluted piles. The convenience, effectiveness and economy of these splices will make it possible to perform more splicing at the job site, thereby allowing preferable and less costly shipment of shorter lengths.

5. The circular cylindrical pipe sections of these piles may be manufactured in lengths to 80 feet (about 25 m).Thus, the splicing of the pipe to a typical tapered section of 25 feet (about 8 m) will produce an overall length of about 105 feet (about 33 m). Additional sections of pipe may be conveniently added, if needed, by the use of butt-welded splices or mechanical sleeves. Fluted piles generally have a fabrication length limitation for the cylindrical sections of 40 feet ( about 12 m) which, with tapered lengths of 25 feet (about 8 m),

CA 02270586 2008-02-19 will produce overall lengths of up to only 65 feet (about 20 m). Additional piling length requires costly splicing of the fluted cross-section. Thus, the use of piles of this invention will often eliminate costly added splices when the pile lengths are longer than 65 feet, and allow for effective and efficient splices if needed at any length.

These piles may be produced in a great variety of configurations anf capacity requirements. Examples are:

A pile having a 10 foot (about 3 m) long tapered section of 0.188 in. (about 5mm) thick steel with a bottom diameter of 8 in. (about 200 mm) and a top diameter of 12 in. (about 300 mm), and connected to an 8-5/8 inch (about 220 mm) O.D. x . 188 in. (about 5 mm) thick pipe having a length of 30 feet (about 10 meters) may be used to produce a capacity of 40 tons (about 360 kN) when driven to penetrate through 5 feet (about 1.5 m) of miscellaneous fill, 20 to 25 feet (about 6 to 8 m) of organic silt, and 10 feet (about 3 m) or so into a lower loose sand or medium soft clay stratum having an “N” value of about 15.

Or, a pile having a 25 foot (about 8 m) long tapered section of .312” (about 6 mm) thick steel formed into a tapered structure having 12 substantially equal faces, the upper outside diameter of the tapered section being about 18 inches (about 460 mm) across and its lower outside diameter being about 8 inches (about 200 mm) across, the very top of the tapered section being deformed into a circular crosssection of 18 inch (about 460 mm) outside diameter and butt-welded to an 18 inch O.D. x 0.375 inch (about 10 mm) thick pipe having a length of 40 feet (about 12 m) may be used to produce a capacity of 150 tons (about 1,330 kN) when driven to penetrate through 10 feet (about 3 m) of dredged sand, 5 feet (about 2 m) of organic soil, and 45 to 50 feet (14 to 16 m) into a loose to medium dense sand stratum having a standard penetration value that varies between 10 and 30.

In general, the length of the tapered section should be such as to fully develop the capacity of the pile in the bearing stratum, which is usually a granular soil such as sand, gravel, or a combination thereof. The pipe will have the length necessary for the pile to extend up to the bottom of the foundation (i.e., pile cap or grade beam) for the structure above.

These piles must have a suitable thickness and yield strength to accommodate any dynamic stresses generated during the driving. Pile driving criteria to establish the requisite pile capacity at acceptable driving stresses may be predetermined by wave equation analysis, and load testing may be done to confirm capacity. After driving, the piles are filled with concrete. Generally, it is not necessary to use reinforcement in the concrete, e.g., the internal reinforcing steel cage conventionally employed in fluted steel piles may be omitted, as may the reinforcement often necessary (to prevent buckling during driving) at the tops of

CA 02270586 2008-02-19 the fluted sections of the conventional piles. Where piles are to be driven into corrosive soils additional steel thickness may be used to offset the projected loss to corrosion instead of applying an expensive coating as is done for the conventional fluted piles. The preferred thickness of steel for these piles is between .188 inches (about 5 mm) to .500 inches (about 13 mm). The steel may be mild steel (suitable for welding) with a yield strength of 50 KSI (3.54 kPa). The combined strength of steel and concrete must satisfy the design capacity requirements.

The figures (FIG. 1 through FIG. 15) that are shown describe certain preferred forms of the invention.

FIGS. 1 and 2 are elevations of composite piles having transition rings.

FIGS, 3 and 4 are cross-sectional details showing the rings of 1 and 2. respectively.

FIG. 5 is a cross-sectional detail of a pile driven with a mandrel.

FIG. 6 is a plan view of the tapered bottom section of the composite pile. FIGS. 7 and 8 are elevations showing piles fully driven into various soil strata.

FIG. 9 is a view showing the folding of the plate from which the bottom section of the pile is formed.

FIG. 10 is an elevation showing the result of the folding.

FIG. 11 is an elevation showing a bottom section composed of several short sections.

FIG. 12 is an elevation of a composite pile which does not employ a transition ring.

FIG. 13 is an elevation showing a cross-section of FIG. 12.

FIG. 14 is a cross-section of a welded portion of the bottom portion of the pile.

FIG 15 is a cross-section of a splice at the top of the bottom section of a pile that does not employ a transition ring.

CA 02270586 2008-02-19

FIG. 1 is an elevation of the composite pile having a tapered lower crosssection 1 with a regular polygonal cross-section of a number of equal sides joined by a transition ring 2 to a circular pipe 3 whose diameter is approximately equal to the diameter of the top of the taper and whose thickness is suitable for direct driving. A steel point 6 has a taper of about 60 degrees, or may be rounded, is welded to the bottom of the tapered lower section for closure. A flat plate may be used in lieu of the tapered or rounded point.

FIG. 2 is an elevation of a composite pile having a tapered lower section 1 with a regular polygonal cross-section of a number of equal sides joined by a transition ring 4 to a circular pipe 5 whose diameter is less than the diameter of the top of the taper and whose thickness is suitable for direct driving. A point 6 is welded to the bottom of lower tapered section for closure.

FIG. 3 is a cross-sectional detail showing the transition ring 2 joining the tapered lower section 1 to the circular pipe 3 described for FIG. 1. These are joined by continuous welds 7 and 8. The transition ring 2 has a lower portion 16, of polygonal cross-section to fit snugly into the top 17 of lower section 1 which bears on an integral shoulder 18. The integral socket 9 into which the pipe 3 fits may be configured to produce a “drive-fit” connection with no weld. The pipe bears on an integral shoulder 19. The pile is driven by the blows of a conventional pile driving hammer applied to the top of pipe 3.

FIG. 4 is a cross-sectional detail showing the transition ring 4 joining the tapered lower section 1 to the pipe 5 having a diameter smaller than that for the top of 1 as described for FIG. 2. These are joined by welds 7 and 8. The transition ring 4 has a lower portion 16, of polygonal cross-section to fit snugly into the top of 17 of lower section 1, an integral shoulder 18. The integral socket 9 into which the pipe 5 fits may be configured to produce a “drive-fit” connection with no weld. That pipe bears on the upper part of shoulder 19. The pile is driven by the blows of a conventional pile driving hammer on the top of pipe 3.

FIG. 5 is a cross-sectional detail of a pile whose upper section is a thinwalled steel pipe 13. The pile is driven by pile driving hammer blows to the top of a conventional pipe mandrel 12 which fits inside the thin-walled steel pipe and rests on an extended inner drive shoulder 11 of the transition ring 10. These are joined by continuous welds 7 and 8.

FIG. 6 is a plan of the tapered bottom section 1 viewed from the top. This cross-sectional shape is a polygon having 12 sides 15 of equal length. The number of sides can vary from 4 to 16 or more.

FIG. 7 is an elevation showing a fully driven pile 30 driven through upper soils of miscellaneous fill 31 and organic silt 32 into a stratum of loose to medium

CA 02270586 2008-02-19 sand and gravel 33. The tapered lower section 1 of the pile is usually fully embedded in stratum 33, and the upper section, 5, is made of cylindrical pipe having a diameter smaller than the top of the tapered lower section 1 which extends through the fill and organic silt, and usually some distance into the lower sand and gravel.

FIG. 8 is an elevation showing a fully driven pile 35 driven through the upper soils of soft clay 36 and peat 37 into a stratum of medium to dense sand 38. The tapered lower section of the pile 1 is usually fully embedded in stratum 38, and the upper section, 3, is made of cylindrical pipe having a diameter approximately equal to the top of the tapered lower section 1 which extends through the clay and peat, and usually for some distance into the lower sand and gravel.

FIG. 9 is a view of a partially formed polygon 40 during fabrication. A section of steel plate is cut to the requisite dimensions, and shaped by a brakeforming machine into an equal sided polygonal tube having a uniform taper.

FIG. 10 shows a full length of tube 41 after being formed. A continuous longitudinal weld 42 is made and the ends 43 and 44 are trimmed square to complete the tubular form. The tube may be made of a single sheet of steel for lengths of 25 feet (about 8 m) or more.

FIG. 11 shows a tube made of several shorter sections of matching tubes 45,46, and 47 which are joined together by transverse butt welds 48 to yield lengths of 30 feet (10 m) or more (e.g., 80 feet - about 25 m).

FIG. 12 shows a full pile having a tapered tube 50 of polygonal crosssection for all of its length except at the very top where there is an integral transitional length of tube 51 of circularized cross-section to match the inner (or outer) diameter of the circular pipe, 3. A butt-weld 52 splices the two sections together. The circularization may be effected by inserting an expandable die into the large end of the polygonal structure to cold work and expand that end into the circular form. The whole transition from polygon to circular cross-section may extend over a very short length of the structure, e.g., about 1 inch (25 mm).

FIG. 13 shows the butt weld 52 joining the circular top 51 of the tapered tube 50 to the circular pipe 3.

FIG. 14 shows a transverse cross-section through the longitudinal butt weld 42 joining the outside edges of the folded plate of the tapered tube 50.

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FIG. 15 shows a longitudinal cross-section showing the butt weld splice 52 joining the tapered tube 50 to the pipe 3. Internal backing ring 55 is used to contain the weld metal.

It is understood that the foregoing detailed description is given merely by way of illustration and that variations may be made without departing from the spirit of the invention. The “Abstract” which follows is given merely for the convenience of technical researchers and is not to be given any weight with respect to the scope of the invention.