US3114245A - Earth pile anchorage - Google Patents

Description

1963 R. c. JENNINGS, JR., ETAL 3,114,245

EARTH PILE ANCHORAGE Filed April 3, 1958 FIG. I 1. Ni /32 3O INVENTORS ROSCOE C. JENNINGS, JR. 8: Y JOHN 0. KING ATTORNEY United States Patent 3,114,245 EARTH PHJE ANQHQRAGE Roscoe C. Jennings, .l'rz, Solon, and John C. King, Euclid,

Ulric, assignors, by mesne assignments, to intrusion- Prepalrt, inc, Cleveland, ()hio, a corporation of @hio Filed Apr. 3, 19555, Ser. No. 725M388 4 Claims. (Q1. 61-5362) This invention pertains to the art of pile anchorages wherein the earth consists of a layer or strata bed-rock with an overburden of soil, and more particularly to such a pile anchorage which must resist both uplift and downward-bearing forces.

The invention is particularly applicable to earth pile anchorages where the anchorage is in the form of a vertically extending concrete column in the over-burden of soil, and will be described with particular reference thereto although it will be appreciated that the invention has broader applications.

Such columns perform the function of transferring the uplift and downward-bearing forces in a uniformly distributed manner to the surrounding soil. As the forces to be resisted increase, it is normally conventional to increase the diameter or the vertical height, or both, of the column so as to maintain the force on unit areas of the surrounding soil below a value which the soil can successfully resist.

Where the over-burden of soil is relatively thin, or of poor consistency, it is conventional to extend the column downwardly to the bed-rock in which case almost any downward-bearing force can be successfully supported. However, with such a thin or poor over-burden of soil, oftentimes the uplift force is greater than the surrounding soil can successfully resist with columns of any conventional diameter. in such cases, it would appear logical to use a metallic tie member extending from a point above the column downwardly into the bed-rock with the thought that some of the uplift forces would be transf rred to the soil and the remainder directly to the bed-rock. In this way it was thought the uplift forces should be proportionately divided and the problems of anchoring to the rock or the size of the rod extending into the rock, or both, would be proportionately reduced.

Experience indicated, however, that this was not the case. The rod, at points just above where it entered the rock, would fail at uplift forces substantially below the design uplift force. Analysis of the problem indicated that the uplift force was not dividing between the column and the bed-rock, but instead almost all was being transmitted to the bed rock.

Analysis of the reasons for this phenomena soon indicated that the soil resists the shearing forces induced therein by the uplift forces by means of friction between the particles of soil, and or or for this friction to develop, it is necessary that there be an appreciable movernent upwardly ofthe concrete column relative to the soil. Thus, before the soil had developed any appreciable resistance against uplift forces, the concrete column had moved upwardly a sufficient amount to place the tie rod under appreciable tension forces. These tension forces all existed between the lowest point of fastening of the tie-rod to the concrete and the bed rock, which of course is able to absorb the uplift forces without any appreciable upward movement.

In some instances the tie rod was stressed beyond its yield point in which case the concrete column could move upwardly a sufficient amount to thereafter transrnit a portion of the uplift force to the soil itself. Fracture of the tie rod at the bed rock did n t thus occur on the first such stress. The tie rod, however, was permanently elongated and actually, because stressed be- HIQ 2 yond its yield point, necked in slightly just above the bed rock. Thereafter the same sequence of events would occur when an uplift force was exerted. The concrete column would move upwa lly relatively freely and the tie rod, at the point where L extended -o the rock, was again stressed beyond its yield point b ore the concrete column would transfer any appreciable portions of the uplift force to the soil. Repeated applications of this uplift force ultimately resulted in the tie-rod breaking.

The characteristic of the soil, that an appreciable movement of the concrete column therethrough before the soil accepts any of the uplift load, is somewhat similar to the elasticity in metals, and while not exactly accurate, will be referred to hereinafter as the elasticity of the soil which it will be appreciated is much greater than that of either the tie rod metal or the bed rock.

The present invention contemplates a new and improved pile anchorage of the general type described which overcomes all of these difilCUiiiGS, and others, and provides a pile anchorage in thin over-burden of soil where the uplift forces can be proportionately distributed to both the soil and to the bed-rock without danger of the tie rod breaking upon repeated applications of the uplift force.

In accordance with the broadest aspect of the invention, there is provided in combination with the earths surface, including arock layer and a soil over-burden, a concrete column in the over-burden, a tie rod rigidly fastened to both the column of concrete and to the bedrock, and resiliently extensible means between the points of fastening to the tie rod and the rock whereby the column may move upwardly under uplift forces and such forces may be proportionately divided between the bedrock and the soil over-burden.

The resiliently extensible means may be as desired but, in the preferred aspect of the invention, are comprised of a length of the tie rod itself effected by longitudinally spacing the points of fastening of the rod to the column and bed-rock.

Further, in accordance with the invention, a method of forming earth pile anchorages in the earth comprised of a rock-strata and an over-burden of soil is provided, comprising the steps of forming a plastic concrete column in situ in the over-burden, inserting a tie-rod through the column into the bed-rock fastening the tie-rod to the concrete column at a point substantially spaced from a point of fastening to the bed-rock, the amount of spacing of the fastening points being proportioned so that the tie-rod will be resili ntly extensible in amounts suflicient to enable the concrete column to move upwardly in amounts sufficient to transfer portions of the uplift forces to the soil over-burden.

The principal object of the invention is the provision of a new and improved pile anchorage which gives a maximum downward bearing and uplift force resistance for a minimum amount of materials.

Another object of the invention is the provision of a new and improved pile anchorage which is readily and easily positioned in the earth.

Another object of the invention is the provision of a new and improved pile anchorage particularly intended where the earth surface is made up of a rock layer and an over-burden of soil which enables selective distribution of the uplift forces between the rock and the soil 1 over-burden.

Another object of the invention is the provision of a new and improved pile anchorage for thin layers of soil over rock layers which can resist repeated high uplift and requires a minimum of men, equipment, and materials.

The invention may take physical form in certain parts, combinations of parts, steps and combinations of steps, preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:

FIGURE 1 shows somewhat schematically a fragmentary cross-sectional view of the earths surface with a pile anchorage illustrating a preferred embodiment of the invention; and

FIGURE 2 is a cross-sectional view thereof.

Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiicut of the invention only and not for the purposes of limitin same, FIGURE 1 shows a layer of bed-rock and an overlying over-burden of soil llli such as is conventionally found generally throughout the world. A concrete structure 12 in the form of an elongated column extends vertically through the soil 11 from a point close to or at the upper surface 13 downwardly to a point close to or at the upper level 14 of the bed-rock 10. A pipe 16 extends vertically and co-axially through the structure 12 from a point above the surface 13 to a point at the surface 14 defining a space 17 through the structure 12. (lo-axially within the space 17, a tie rod extends from a point above the surface 13 downwardly to a point adiacent the plane of the surface 14 and is anchored to the bed-rock 10 by means of an anchor 21 extending into an opening 19 in the bed-rock 10.

The tie rod 18 is also anchored to the pipe 16 at a point spaced from the anchor means 21, the pipe 16 in turn being firmly fastened to the concrete structure 12. The soil 11 may be of any known characteristics including sand, clay, or a mixture of rock therewith, the only requirement being that it have a vertical thickness and consistency such as to be able to resist uplift forces if transferred thereto.

The rock strata 10 may be of any known characteristic or of any known thickness so long as its thickness in conjunction with that of the soil i1 is sufficient to resist the uplift forces to be imposed thereon.

The concrete structure 12 may have any desired vertical height, either equal to or less than the vertical height of the soil lit and may or may not extend downwardly to the rock layer It! as desired, and depending upon the particular load requirements which it will be called upon to meet. The concrete structure may also have any desired horizontal width, thickness, or cross-sectional shape.

Concrete, as used throughout this specification and claims, is made up of a mixture of a liquid vehicle, a cementitious material, and usually, but not necessarily, one or more granular materials. These granular materials may include without limitation, soil, sand, fly ash, or gravel rock, or aggregate of any desired size. The cementitious material may be any of the known cementitious materials such as, without limitation, Portland cement or the like, which when mixed with or suspended in the liquid vehicle and upon being allowed to stand or cool, or both, will harden and bind the granular material, if any, into a solid rigid body. The liquid vehicle may be of a type such that when mixed with the cementitious material employed, will either evaporate or combine with the cementitious material, to leave the cementitious mateial in a hardened state which will then bind the granular material, if any, into a solid rigid body.

The concrete, unless otherwise stated, may be either in the plastic or hardened state, it being understood that plastic concrete when allowed to stand for periods of time, which may be referred to as the hardening time, will change to the hardened state.

The term vertical as used throughout this specification and claims, is used in the broader sense of being in any direction leading below the earths surface as fitting within the sense of the particular requirements of the concrete structure being installed.

By the term in situ is meant the forming of the concrete structure from a plastic concrete placed in the ultimate position of use of the structure, the concrete being allowed to harden prior to the placing of loads thereon.

The concrete structure 12 may, in accordance with the invention, be formed in any known or desired manner. Preferably however, the concrete structure is formed in situ and while the concrete is still in the plastic state, it is placed under hydraulic pressure so that a plurality of tiny fingers or protrusions 29 will extend horizontally and laterally into the soil 11 beyond the actual limits of the structure 12 itself.

In order to obtain such fingers 2%, the structure 12 is preferably formed as is taught in US. Patent No. 2,729,067, issued January 3, 1956; or, US. Patent No. 2,782,606, issued February 26, 1957, and both assigned to the assignee of this application. In the first of these patents, an auger having a hollow shaft, is screwed into the soil to the depth desired by the ultimate structure. The anger is then gradually withdrawn without rotation while simultaneously pumping concrete under pressure through the hollow shaft to the lower end of the anger, the concrete under pressure forcing itself laterally into the soil N to form the fingers 23. In following this method, the concrete is mixed as desired above the surface of too earth and is pumped downwardly through the shaft.

in the second mentioned patent, a hollow shaft having sidewardly projecting mixing arms is rotated vertically into the earth while simultaneously forcing concrete under pressure into the earth in advance of the mixing arms. Normally such concrete contains the same amount of liquid vchicie as conventional concrete and the arms mix the soil with the concrete as the tool is advanced into the earth. In effect, the soil itself becomes part of the granular material in the concrete. The tool is advanced the desired depth of the concrete structure and is then withdrawn while continuing the rotation. The result is a thoroughly mixed sub-surface structure wherein at least part of the granular material of the concrete is the soil 11 broken into pieces by the action of the arms of the rotating tool. The concrete is forced through the hollow shaft under pressure and forces itself laterally into the crevices of the soil ill to form the fingers 20. Obviously other ways of forming the concrete structure 12 may be employed, for example, by forming a cavity and subsequently pouring concrete thereinto, and its upper end may be above, beiow, or flush with the earths surface.

A longitudinal passage through the structure 12 in which the rod member 18 may move relatively to the structure 12 must then be provided. This may be done by coating the rod member 18 with anti-friction means and advancing it through the plastic concrete in such a manner that the lower end of the rod member 18 will become firmly fastened to the bed-rock. In the preferred embodiment, and assuming that the structure 12 is either cast in place or mixed in place, as above described, while the concrete is still plastic, the pipe 16 is advanced longitudinally to the plastic concrete down to the bed-rock it). Upward and outwardly diverging arms 23 on the lower end serve to locate this lower end relative to the sides of the structure 12. Alternatively, the concrete may be allowed to harden, and then a vertical hole drilled therethrough. In such casc, the pipe 16 is obviously not required.

Thereafter, conventional drilling tools are advanced through the opening 1'7 and the hole 19 in the bed-rock is drilled. It will be appreciated that if desired, a stopper in the lower end of the pipe 16 may be employed to prevent the plastic concrete from entering the space 17. Alternatively, while the concrete is still plastic or even after it has hardened, it may be drilled from the pipe 16 to form the opening 17.

The rod member 18 is then ready to be positioned. The anchoring means 21 are first fastened to the lower end. In the embodiment shown, these anchor means comprise a zigzag steel bar of high tensile carbon steel fastened to the lower end of the rod 18 by means of a collar 25 suitably fastened to both. Obviously any fastening means may be employed. Either prior to the insertion of the anchoring means 21 in the opening 19 or afterward, concrete 26 placed in the opening 19 in such volumes that the upper surface 27 will be below the lower end of the pipe I16 or in the alternative, some means are provided for preventing the pipe 16 or any portion of the structure 12 from becoming permanently fastened to the bedrock 1i Thereafter the upper end 18 of the tie rod 18 is suitably fastened to the concrete structure 12, the only requirement of the invention being that the point of fastening is sufficiently spaced from the point of fastening of the anchor means 21 to the bedrock that the portions of the tie rod 13 between such points of fastening are resiliently extensible in amounts sufficient to allow the concrete structure 12 to move upwardly in the soil in amounts sufficient that the soil 11 has the proportionate amount of the uplift forces transmitted thereto.

The portion 18 of the rod 18 may be fastened to the structure 12 in any known or desired manner, but in the referred embodiment, concrete is used. Thus, a packing of fibrous or other material 36 is placed in the space 17 at a distance :1 above the surface 27, that is, the point of fastening of the anchor means 21 to the bed-rock 10. The distance a represents the length of the rod 18 which is free to resiliently elongate under uplift forces and thus permit movement of the structure 12 relative to the bedrock 10. After the packing 3b is placed, concrete 3?. is poured into the space between the portion of the rod 13' in the pipe 16 to rigidly fasten the portion 18' to the pipe 16, and thus to the concrete structure 12. Obviously any other suitable fastening means may be employed.

It will also be appreciated that once the concrete 12 is hardened, the pipe 16 may be removed. Also, it will be appreciated that the space 17 may be suitably filled with a plastic composition such as grease or the like which will exclude moisture and prevent rusting of the rod 18. Obviously such material should be placed before the packing 3% is inserted.

It will also be appreciated that the pipe l6 extends upwardly above the structure 12 and may be connected to above surface structures for the purpose of transmitt ting uplift and downward bearing forces to the anchorage.

It will be appreciated that, if desired, the tie rod 18 may be fastened to the concrete structure over its entire length and actual spring members be employed in place of the collar 25 for fastening the lower end of the rod 18 to the anchor means 21.

It will also be appreciated that, if desired, the concrete structure 12 may be elongated in any one dimension and one or a plurality of rod members similar to those described may extend therethrough into the bed-rock fill.

in operation, downward bearing forces are transmitted directly through the concrete structure 12 to the bed-rock it). No actual movement of the concrete structure occurs in the soil 11.

However, when uplift forces are applied, the first thing that happens is the concrete structure 12 moves upwardly in the soil 11 with relatively little resistance. Substantialiy all of the uplift force is transmitted to the bed-rock 10. However, the long portion of the tie rod 18 is free to elongate under such uplift forces and as the rod 18 does elongate and the structure 12 moves upwardly, the soil ll begins to develop resistance against such upward movement and as the uplift forces increase, a greater and greater portion of such forces is transferred to the soil 11 and this greater and greater proportion of the forces will be transferred to the soil 11 until the soil 11 can no longer resist, in which case any increases in the uplift forces will then continue to be transferred to the bedrock it. But in any event, the soil 1:1 is accepting a share of the uplift force which it would not accept if the tie rod 13 were fastened to the structure 12 over its entire length, that is to say, if no resiliently extensible means were provided between the points of fastening to the concrete structure 12 and to the bed-rock ill.

The invention has been described with reference to preferred embodiments. Obviously modifications and alterations differing radically from the preferred embodiments will occur to others upon a reading and understanding of this specification and it is our intention to include all such modifications and alterations insofar as they come within the scope of the appended claims.

Having thus described our invention, we claim:

1. An earth pile anchorage wherein the earth is comprised of a layer of bed-rock and an overburden of soil, a concrete structure in said overburden and bearing against said bed-rock, said concrete structure having an external surface provided with randomly arranged outwardly extending protrusions which key into said overburden, a load absorbing rod extending from said structure into said bed-rock, means rigidly fastening said load absorbing rod to said bed-rock, means rigidly fastening said load absorbing rod to'said concrete structure at a point substantially spaced above the point of fastening to said bed-rock, said latter rigid fastening means transmitting forces from said load absorbing rod to said con crete structure in both the upward and downward directions, said load absorbing rod being free from restraining movement between said points and in a direction toward each of said points whereby said lead absorbing rod may elongate under uplift forces to enable the concrete structure to move upwardly and transmit a portion of the uplift forces to said overburden.

2. An earth pile anchorage wherein earth is comprised of a layer of bed-rock and an overburden of soil, a concrete structure in said overburden and bearing against said bed-rock, said concrete structure having an external surface provided with randomly arranged outwardly extending protrusions which key into said overburden, a metal load absorbing rod extending vertically through said structure into said bed-rock, means rigidly anchoring said lead absorbing rod to said bed-rock, means rigidly anchoring said load absorbing rod to said concrete structureat a point substantially vertically spaced above the point of anchorage to said bed-rock, said latter rigid anchoring means transmitting forces from said rod to said concrete structure in both the upward and downward directions, and sleeve means surrounding said load absorbing rod and located between said points of anchoring and preventing fastening of said load absorbing rod to said concrete structure between said points, said load absorbing rod being free from restraining movement by said sleeve means in a direction toward each point whereby said load absorbing rod may be elongated between said points under uplift forces to enable the concrete structure to move upwardly and transmit a portion of the uplift forces to said overburden 3. An earth pile anchorage for earth comprised of a layer of bed-rock in an overburden of soil, a concrete structure in said earth having a vertically extending opening therethrough, said structure bearing against said bedrock and having an external surface provided with randomly arranged outwardly extending protrusions which lrey into said overburden, an aligned opening in said bedrock, a load absorbing rod extending vertically through said openings, means in .said bed-rock opening rigidly fastening said load absorbing rod thereto, plastic means surrounding said load absorbing rod in the lower end of said concrete structure opening and preventing adhesion between said load absorbing rod and said concrete structure, said load absorbing rod being free from restraining 7 movement by the plastic means in a direction longitudinally of said rod, and hardened concrete means adjacent the upper end of said concrete structure opening rigidly fastening said load absorbing rod to said concrete structure at a point substantially spaced from the point of fastening said load absorbing rod to said bed-rock.

4. in combination with the earth wherein the earth consists of a layer of bed-rock and an overburden of soil, a hardened concrete column in said soil, said column having an axially extending opening therethrough, said column bearing against said bed-rock to support downward forces, said column having an external generally cylindrical surface provided with randomly arranged outwardly extending protrusions which key into said overburden, an elongated tension and load absorbing member extending through said column opening into said bedrock, means rigidly fastening said tension member to said bed-rock and means rigidly fastening said tension member to said hardened concrete column at only a position substantiaily remote from the lower portion of said opening, said latter rigid fastening means transmitting forces from said load absorbing member to said concrete column in both the upward and the downward directions, said tension and load absorbing member being free from restraining movement betwcen said rigid fastening means in a direction longitudinally of said member whereby said load absorbing member can move relative to said hardened concrete column in the lower portion of said opening between said rigid fastening means.

References Cited in the file of this patent UNITED STATES PATENTS 813,966 Harrah Feb. 27, 1906 1,449,236 Maione Mar. 20, 1923 1,609,260 Malone Nov. 30, 1926 1,647,925 May Nov. 1, 1927 1,798,468 Hartzler et a1 Mar. 31, 1931 2,063,142 Anstermuhle Dec. 8, 1936 2,187,677 Brumley Jan. 16, 1940 2,332,990 Collins Oct. 26, 1943 2,335,433 Minck Nov. 30, 1943 2,428,070 Frenkil Sept. 30, 1947 2,507,259 Levasseur May 9, 1950 2,512,831 Holmes June 27, 1950 2,528,999 Bruns Nov. 7, 1950 2,554,896 Caudill May 29, 1951 2,558,529 Thornley June 26, 1951 2,690,074 Jones Sept. 28, 1954 2,741,910 Thornley Apr. 17, 1956 2,875,584 Turzillo Mar. 3, 1959 FOREIGN PATENTS 267,656 Germany Nov. 25, 1913 669,661 Great Britain Apr. 9, 1952 548,837 taly Oct. 2, 1956

Claims (1)

1. AN EARTH PILE ANCHORAGE WHEREIN THE EARTH IS COMPRISED OF A LAYER OF BED-ROCK AND AN OVERBURDEN OF SOIL, A CONCRETE STRUCTURE IN SAID OVERBURDEN AND BEARING AGAINST SAID BED-ROCK, SAID CONCRETE STRUCTURE HAVING AN EXTERNAL SURFACE PROVIDED WITH RANDOMLY ARRANGED OUTWARDLY EXTENDING PROTRUSIONS WHICH KEY INTO SAID OVERBURDEN, A LOAD ABSORBING ROD EXTENDING FROM SAID STRUCTURE INTO SAID BED-ROCK, MEANS RIGIDLY FASTENING SAID LOAD ABSORBING ROD TO SAID BED-ROCK, MEANS RIGIDLY FASTENING SAID LOAD ABSORBING ROD TO SAID CONCRETE STRUCTURE AT A POINT SUBSTANTIALLY SPACED ABOVE THE POINT OF FASTENING TO SAID BED-ROCK, SAID LATTER RIGID FASTENING MEANS TRANSMITTING FORCES FROM SAID LOAD ABSORBING ROD TO SAID CONCRETE STRUCTURE IN BOTH THE UPWARD AND DOWNWARD DIRECTIONS, SAID LOAD ABSORBING ROD BEING FREE FROM RESTRAINING MOVEMENT BETWEEN SAID POINTS AND IN A DIRECTION TOWARD EACH OF SAID POINTS WHEREBY SAID LOAD ABSORBING ROD MAY ELONGATE UNDER UPLIFT FORCES TO ENABLE THE CONCRETE STRUCTURE TO MOVE UPWARDLY AND TRANSMIT A PORTION OF THE UPLIFT FORCES TO SAID OVERBURDEN.

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