Method For Insitu Anchoring Piling

Abstract

Method for securing tubular piling or pile casing in the ground which comprises inserting tubular piling into the ground, preferably heavy piling adapted to be driven into the ground, inserting an expandable mechanism, e.g., an expandable hydraulically actuated mandrel, into the tubular piling at one or more spaced intervals or positions longitudinally along the piling, expanding the mechanism at each such position to expand the piling outwardly to form one or more protrusions spaced longitudinally along the piling, and retracting the expandable mechanism at each such position.

Description

This invention relates to a method for securing tubular piling in the ground, and is particularly concerned with procedure for inserting tubular piling, preferably formed of thick wall heavy pipe, in the ground, as by driving same, and after being inserted to a predetermined depth in the ground, forming protrusions at spaced intervals on the piling to securely anchor the piling in the ground.

The load-bearing capacity of longitudinally flat or straight tubular piling is dependent chiefly upon a combination of load-bearing capacity of the soil or ground at the lower end or tip of the piling, and the coefficient of friction between the ground or soil and the piling skin along the length thereof. Where the piling is made of metal such as steel, such coefficient of friction may be relatively low and hence a major portion of the load-bearing capacity is dependent upon the load-bearing capacity at the lower end of the piling. Under these conditions, the cross-sectional area of the piling must be increased, resulting in increased cost of the piling and also of its insertion into the ground.

Continuously corrugated piling, that is pile casing having corrugations which extend over the full length of the casing, as illustrated in FIG. 1 of U.S. Pat. No. 3,375,670, similarly utilizes friction between the ground and the continuously corrugated skin of the piling, and end bearing loading capacity, to permit loading when inserted into the ground. Additionally, the soil trapped between such continuous corrugations is to some extent mobilized into resistance against itself, but this additional resistance to movement of the pile casing under loading is often insufficient to securely anchor the piling, particularly under heavy loading or when subjected to extreme vibration or shock loading.

In the above-noted Pat. No. 3,375,670, continuously corrugated light metallic tubular casing is inserted into a predrilled hole in soft soil, after which an expanding mechanism is used to expand the casing to substantially remove the corrugations and to render the walls substantially straight longitudinally. Although this operation increases the total volume of the casing and radial pressure is exerted by the casing against the surrounding soil as a result of this operation, to thereby aid in anchoring the piling, the flattening out of the corrugations according to this process to render the pile casing again longitudinally flat or straight, removes the load-bearing resistance of the soil initially trapped between the corrugations, and the resulting pile casing again depends for load-bearing capacity in large measure only upon the coefficient of friction between the soil and the piling skin.

The above patent states that if desired, the tubular pile casing previously rendered flat or straight by the initial expanding operation, can be further expanded by the formation of further corrugations in the wall of the casing after the original corrugations have been substantially removed. The resulting "re-corrugation" produces a continuously corrugated piling as illustrated in FIG. 4 of the patent. Although the resulting re-corrugations are annular in shape rather than helical, the re-corrugated pile casing is again essentially a continuously corrugated piling which in many instances, even with the compaction of the surrounding soil produced by the initial expansion and the resistance of the soil trapped in the small areas between the annular re-corrugations, has a load-bearing capacity which often is insufficient to securely anchor the piling, particularly against heavy or shock loading or vigorous vibration.

Also, as previously noted, the above patent is directed to securing light tubular casing in the ground, and which is usually inserted into a predrilled hole. Such light casing cannot ordinarily be driven into the ground, except by the use of a mandrel to support it as it is driven, as noted in the patent. Moreover, such light tubular piling cannot be employed in many applications for supporting heavy structures and requiring high loading capacity, and is usually filled with concrete to finish the pile.

It is accordingly the object of the present invention to afford a method of inserting and securing tubular piling, particularly thick heavy wall tubular piling, in the ground, and to anchor same in the surrounding soil against vertical movement therein as result of the application of high static loading, shock loading or high vibrational forces.

There is provided according to the present invention a method of securing tubular piling, preferably formed of thick wall heavy pipe, in the ground, which comprises inserting tubular piling having straight longitudinal walls into the ground, e.g. by driving same, inserting an expandable means into the tubular piling at one or a plurality of spaced predetermined positions longitudinally along the piling, expanding such means at each such position to expand the piling outwardly a predetermined extent to form one or a plurality of protrusions or corrugations extending outwardly at spaced intervals longitudinally along the piling, and retracting the expandable means at each such position after expansion thereof, to thereby secure the piling against the soil of the adjacent ground formation.

The resulting piling with appropriately spaced protrusions or corrugations extending outwardly to a significant extent, as pointed out in greater detail hereinafter, effectively mobilizes the resistance of the adjacent soil, particularly the soil trapped between adjacent protrusions, against itself over virtually the entire length of the tubular piling with high effectiveness, so that the soil adjacent the tubular piling effectively is in shear against itself throughout substantially the length of the piling, rather than being in shear against the side of the piling. The distance between the protrusions or corrugations, accordingly, is maintained particularly so that the above-noted condition prevails, that is, so that the angle of shear of the soil adjacent the casing is of a magnitude such that the soil is in shear solely with itself substantially along the entire length of the piling between the uppermost and lowermost protrusions on the piling.

According to another feature of the invention, in order to provide maximum effectiveness of the protrusions formed insitu on the piling according to the invention, it has been found that the ratio of the outside diameter of the piling to the wall thickness of the piling be within certain limits, as noted hereinafter.

Generally, the protrusions or corrugations formed at spaced intervals insitu on the piling wall have substantially the same configuration and extend outwardly substantially the same amount from the piling wall, although these conditions can vary as desired, for example the extent of protrusion of the corrugations can vary, since it is often difficult when expanding the piling wall by the expandable means described more fully below, to have each corrugation or protrusion extend outwardly from the piling wall the same amount. Also, the distance between adjacent corrugations or protrusions formed on the piling wall can be substantially the same or can be varied as desired depending upon the soil conditions encountered.

Also, where formations of different types are encountered along the length of the tubular piling, for example stratas of sand and clay, only a portion of the longitudinal length of the tubular piling can be corrugated insitu according to the invention, e.g., where the adjacent formation is of a sandy nature, the remainder of the tubular piling wall remaining longitudinally straight.

The tubular piling is generally formed of metals or metal alloys such as iron, steel, copper, and the like. Any suitable material of construction can be utilized which is sufficiently ductile to be expanded to form the spaced corrugations or protrusions thereon according to the invention.

In preferred practice, the tubular piling is inserted into ground having a high shear strength value relative to its coefficient of friction against the pile surface. Hence the insitu corrugated piling according to the invention has high effectiveness in soils having a sandy content, such as sand itself, and particularly in shale. The resistance to axial forces of the insitu corrugated piling of the invention is generally in proportion to the difference between the insitu properties of a particular soil in shear versus friction against the piling skin. As an illustration, in sand, the insitu piling produced according to the invention successfully resists pullout forces of about twice the level of longitudinally straight or flat piling, and substantially higher then that of continuously corrugated pile casing of the type illustrated in FIGS. 1 and 4 of above Pat. No. 3,375,670. In shale, the relative difference in pullout forces between the insitu corrugated piling of the invention and the straight or continuously corrugated piling noted above increases dramatically in favor of the piling having the spaced corrugations formed insitu according to the invention, e.g., to the extent of say as much as 10 times the pullout resistance of longitudinally straight piling.

Any suitable expandable means or mechanism can be employed for insertion into the tubular piling after it is placed in the ground, for expanding the tubular piling at one or more predetermined positions along the piling to provide the insitu corrugations or protrusions on the piling wall. Thus for example a tool having a hydraulically inflatable mandrel comprising a short rubber-like packing element can be employed to bulge the piling outwardly to form the corrugations and the packing retracted by relieving the pressure. Alternatively, suitable mechanical, explosive or vibrating type tools can be employed for this purpose.

The invention will be more fully understood from a detailed description of certain embodiments thereof taken in connection with the accompanying drawing wherein:

FIG. 1 is a longitudinal and partial sectional view of tubular piling in position in the ground prior to expansion or deformation of certain portions thereof according to the invention;

FIG. 2 is a longitudinal and partial sectional view of the tubular piling in the ground following expansion of the circumference of the casing to form the protrusions or corrugations thereon;

FIG. 3 is a longitudinal view partly in cross section of a hydraulically actuated tool for insertion into the tubular piling of FIG. 1, to expand the piling and form the protrusions at predetermined spaced intervals as shown in FIG. 2;

FIG. 4 is a longitudinal view of continuously corrugated tubular casing positioned in the ground, not in accordance with the invention, but for comparison purposes;

FIG. 5 illustrates practice of the invention wherein tubular piling is expanded only in certain locations along the length of the piling;

FIG. 6 is a longitudinal view partly in section of insitu corrugated piling in the ground and illustrating a modification of the invention wherein the distance between adjacent protrusions or corrugations varies and also the extent of bulging of the respective protrusions varies; and

FIG. 7 is a longitudinal view partly in section of step taper tubular piling having protrusions or corrugations formed insitu thereon after the piling is inserted in the ground.

Referring to FIG. 1 of the drawing, tubular steel piling 10 having a longitudinally straight wall 12 is driven into the ground 14 by any suitable means. The invention is particularly directed to the use of thick wall heavy tubular piling which can be driven into the ground without predrilling a hole therein, and without use of special means such as a supporting mandrel as is required for driving light tubular casing. Thus, the wall thickness of the tubular piling employed according to the invention can range from about three-sixteenths to about 11/4 inch. However, tubular piling of smaller or larger wall thickness can be employed, and if desired, a hole can be predrilled in the ground and the tubular piling dropped therein, or a combination of these procedures can be employed, that is the tubular piling can be driven into a predrilled hole of somewhat smaller diameter, or alternatively, vibrating or circulating techniques can be employed to insert the piling in the ground.

The outside diameter of tubular piling employed according to the invention can vary, and can range, e.g. from about 6 inches to about 48 inches. The invention principles are particularly applicable for tubular piling wherein the ratio of outside diameter of the piling to the wall thickness ranges from about 25 to about 75.

Generally, and as illustrated in FIG. 1, the tubular piling is closed by an end bearing 16 at the lower end of the piling, but it will be understood that alternatively the tubular piling can be open at both ends and after insertion into the ground, soil or sand trapped within the piling can be removed by any suitable means.

A hydraulically actuated expander mechanism illustrated in FIG. 3 is lowered into the hollow tubular piling 10 of FIG. 1 to a predetermined position therein. The mechanism illustrated in FIG. 3 comprises a hollow casing 18 carrying a short resilient and inflatable, e.g., rubber-like, packing element 20 around its outer surface. The resilient packing element is in contact with a plurality of circumferentially spaced plates 23, each carrying an arcuate segment 22, and such plates carrying the segments 22 are adapted to be movable radially outward on the tubular casing 18. The tubular element 18 is closed at its lower end by a plug 24.

When the expander is lowered into the tubular piling 10 illustrated in FIG. 1, the packing element 20 is in normal retracted position around the tubular element 18, and the plates 23 and segments 22 are in the positions shown in full lines in FIG. 3. Upon passage of a hydraulic fluid under pressure into the tubular element 18 and via a passage 26 in the casing and into the tubular packer 20, the packer is expanded radially and simultaneously expanding the plates 23 and segments 22 to their position shown in phantom in FIG. 3, and into compressive contact with the inner surface of the tubular piling 10, and bulging or expanding the adjacent circumference of the piling wall 12 to form the protrusion or corrugation indicated at 28 in FIG. 2. It will be understood that the hydraulically actuated cylindrical expander illustrated in FIG. 3 is simply illustrative of any suitable expandable means for expanding the tubular piling to form corrugations or protrusions therein according to the invention, and hence such expander mechanism forms no part of the present invention.

Following expansion of the expander mechanism to produce the protrusion or corrugation indicated at 28 in FIG. 2, the hydraulic pressure in the expansion mechanism is relieved, causing the expandable packer 20 and segments 22 carried thereon to retract to the full line position shown in FIG. 3. The expansion mechanism can then be moved to another predetermined position within the tubular piling and the operation repeated to form another corrugation or protrusion indicated at 28a in FIG. 2. This operation can then be repeated to form any desired additional number of spaced protrusions indicated at 28b in FIG. 2.

The spaced apart protrusions or corrugations as illustrated at 28, 28a and 28b in FIG. 2, can have a bulge or outward extension generally of at least 1/4 inch and usually not more than about 3 inches beyond the outer surface of the tubular piling wall 12, the extent of bulge or expansion depending on the outside diameter of the piling. Preferably it is desired to obtain the greatest extent of outward bulging of the corrugations or protrusions as possible, dependent on the ability of the tubular piling to be deformed without rupturing. The greater the outer extent of the protrusion, the more effectively is the soil mobilized against itself between the adjacent corrugations.

The shape of the corrugations indicated at 28, 28a and 28b is of generally rounded contour as result of expansion of the outer skin of the tubular piling by the expandable tool in the manner described above. In the embodiment illustrated in FIG. 2, the amount of outer radial extension of the respective corrugations is approximately equal, and the distance between adjacent corrugations, e.g., between 28 and 28a, between 28a and 28b and between the other successive corrugations, is substantially equal, making for a substantially symmetrical arrangement of the corrugations formed insitu on the tubular piling wall. This arrangement is preferably employed where the soil conditions are substantially the same throughout the length of the corrugated portion of the tubular piling.

As a specific example, but not in limitation of the invention, the straight sided tubular piling 10 has an outside diameter of 14 inches, a wall thickness of 3/8 32 inch, and is corrugated according to the invention as illustrated in FIG. 2, to an outside diameter of 16 inches, that is the corrugations form an outward bulge of 1 inch from the outer wall of the casing, the corrugations being spaced 13 inches apart along the length of the tubular casing, starting 18 inches from the lower end or tip 16 of the piling. In a test carried out on tubular piling of this type in sandy soil, with spaced apart corrugations formed thereon as noted above according to the invention, the straight sided piling indicated in FIG. 1, initially driven into sand, moved upon the imposition of a test pull of 47,000 lb. net, whereas the insitu corrugated piling illustrated in FIG. 2 and produced according to the invention moved upon application of a test pull of 64,000 lb. net.

As previously noted, the spacing between corrugations, say between the adjacent corrugations 28b in FIG. 2, is designed so that the shear angle of the soil, e.g., sand, at the ends of the respective protrusions or corrugations, and illustrated at A in FIG. 2, is such that the soil is in shear against itself throughout the entire length of the space between corrugations 28b and is not in shear against the side of the tubular piling. This condition is satisfied by spacing the corrugations so that the shear line 30 of the shear angle A extends from the outer end 31 of one corrugation, e.g., 28b, to the inner end 33 of the adjacent corrugation 28b. In addition, the other angle of shear of the soil, illustrated at B, adjacent the corrugations 28b is such that stress is applied along the shear line 32 to a substantially large volume of adjacent soil 14. It is thus seen that the soil trapped between the adjacent corrugations or protrusions of the tubular piling in FIG. 2 and the adjacent volume of soil effectively mobilizes the resistance of the soil against itself over virtually the entire length of the piling, to effectively aid in anchoring the piling securely in the formation. It has been found that the distance between adjacent protrusions preferably is about 2 to about 30 times the extent of such protrusion beyond the outer surface of the piling.

On the other hand, in the case of conventional continuous corrugated piling illustrated at 34 in FIG. 4, the small amounts of soil indicated at 36 and trapped between the adjacent corrugations 38, although mobilized into resistance against itself, such resistance is substantially reduced due to the small amount of such compacted soil between such corrugations and the overlapping of the cones of soil-shear angle from one corrugation to the next, as indicated at 40.

It will be understood that the soil shear angles indicated at A and B are illustrative and that such shear angles will vary with varying soils. Also it will be understood that the invention is not intended to be limited as to the above-described theory whereby the invention piling is securely anchored.

Referring to FIG. 5 of the drawing, there are illustrated embodiments in which (1) the tubular piling 10a, of a structure substantially the same as tubular piling 10, has formed insitu thereon according to the invention principles, only a single protrusion or corrugation 28 adjacent the lower end of the tubular piling, (2) a tubular piling 10b again similar to that of tubular piling 10, with four protrusions or corrugations 28 spaced apart and located adjacent the lower end of the piling, and (3) tubular piling 10c, similar to piling 10, having six corrugations or protrusions 28 formed insitu at the lower end of the piling, illustrating insitu corrugation of only a portion of the tubular piling where the soil conditions at 14 adjacent the insitu formed corrugations, e.g., comprising sand, may be different from the soil conditions of the soil 14a adjacent the upper end of the uncorrugated portion of the respective pilings, e.g., the soil 14a for example being clay. In clay, which does not freely flow and reconsolidate, as contrasted to sand, and which does not have high shear strength values relative to its coefficient of friction against the tubular skin of the piling, the insitu formed corrugations according to the invention are not as effective as in the case of said which has a high shear strength value relative to its coefficient of friction against the piling skin.

Referring to FIG. 6, there is illustrated an unsymmetrical arrangement of corrugations or protrusions on the insitu corrugated piling according to the invention, wherein the distance between adjacent corrugations 28c and 28d is different from the distance between the adjacent pair of corrugatios 28d and 28e. This embodiment is applicable where the soil conditions are different along the various longitudinal locations of the piling. Also, in the embodiment of FIG. 6, it is seen that the extent of bulge or outward projection of the corrugations varies, for example, corrugations 28c, is smaller than the extent of bulge or outward projection of other corrugations such as 28d and 28e. To a large extent this can be due to the difficulty in expanding each of the spaced apart corrugations the same amount, by the expandable means employed.

In FIG. 7 there is shown another modification of the invention employing step taper tubular piling 41 and in which one or more protrusions or corrugations 28f are formed insitu on one or more of the respective step portions 42, 44 and 46 of varying diameter, after insertion of the piling in the ground.

It will be understood that instead of employing an expandable mechanism which forms only one corrugation or protrusion at a time, a mechanism can be employed having multiple expansion elements, e.g., multiple packers of the type illustrated at 20 in FIG. 3, and multiple sets of cooperating plates 23 and segments 22 to form a plurality of spaced apart protrusions or corrugations at the same time. However, the use of a tool of the type illustrated in FIG. 3 which forms but a single protrusion at a time is preferable, since it permits greater flexibility in adjusting and varying the distance between adjacent insitu corrugations on the tubular piling.

If desired, following formation of the protrusions or corrugations on the tubular piling, e.g. in the embodiments of FIGS. 2, 5, 6 and 7, the tubular piling can be filled with concrete, but it will be understood that this is not necessary.

The invention procedure can be employed for anchoring tubular pilings for suport particularly of heavy structures such as buildings, offshore oil drilling platforms, dams, and for tying down bridge abutments of suspension type bridges.

From the foregoing, it is seen that the invention provides a novel procedure for inserting and anchoring tubular piling in the ground, particularly where thick heavy wall piling is required. In effect the result of the invention procedure which produces insitu spaced apart corrugations longitudinally along the tubular piling is to substitute the shear strength of the formation itself, e.g. sand, for the shear value as between the formation and the piling skin. This results in substantially increasing the vertical resistance to movement of the insitu corrugated piling of the invention as compared to smooth or uncorrugated piling or as compared to continuously corrugated piling.

Claims

I claim:

1. The method of securing tubular piling in the ground, which comprises inserting tubular piling into the ground having straight longitudinal walls and a wall thickness ranging from about three-sixteenths inch to about 11/4 inches, inserting an expandable means into said piling, expanding said means against the interior of said piling at intervals along the lengths of said piling to form a plurality of external annular protrusions spaced from each other about 2 to about 30 times the lateral extent of each protrusion beyond the outer surface of said piling and without increasing the internal diameter of the piling between said protrusions, to thereby secure said piling against the soil of the adjacent ground formation, and retracting said expandable means after expansion thereof to enable said means to be moved longitudinally within said piling; said means being expanded against the interior of said piling to form said protrusions extending laterally outwardly beyond the outer surface of said piling an amount ranging from about one-fourth inch to about 3 inches, the piling inserted into the ground having an outside diameter to wall thickness ranging from about 25 to about 75, in which protrusions formed by said expanding means are spaced from each other by a distance such that the angle of shear of the soil surrounding said piling and its protrusions is of a magnitude so that said soil is in shear solely with itself substantially along the entire length of said piling between the uppermost and lowermost protrusions on said piling.

2. The method as defined in claim 1; in which said piling is inserted into ground having a high shear strength relative to its coefficient of friction against the external piling surface.

3. The method as defined in claim 1; in which said piling is inserted into ground comprising sand by driving the piling into said ground to a desired depth.