US3881320A

US3881320A - Pile installation in submerged bearing strata

Info

Publication number: US3881320A
Application number: US373977A
Authority: US
Inventors: George J Gendron
Original assignee: Raymond International Inc
Current assignee: Raymond International Inc
Priority date: 1973-06-27
Filing date: 1973-06-27
Publication date: 1975-05-06
Anticipated expiration: 1992-05-06

Abstract

Piles are installed in locations wherein a bearing stratum is submerged beneath a soft nonsupporting stratum. A tubular displacement element is driven down into the bearing stratum by means of a driving member capable of transmitting dynamic driving forces and load resistance effects from one end to the other. The driving member is than removed and a static load carrying column is installed on the displacement element.

Description

United States Fatent [191 Gendmn May 6,1975

[ PILE llNSTALLATlON IN SUBMERGED BEARING STRATA [75] Inventor:

[73] Assignee:

George J. Gendron, Houston, Tex.

Raymond International Inc., Houston, Tex.

221 Filed: June 27, 1973 211 Appl. No.: 373,977

2,146,645 2/1939 Newman 61/536 X 3,344,611 10/1967 Philo 61/5364 3,356,164 12/1967 Mount 61/53.7 X 3,423,944 1/1969 Goodman 61/5366 3,736,757 6/1973 Hartzell 61/5366 3,751,931 8/1973 Merdan 1 1 61/5352 Primary Examiner.lacob Shapiro Attorney, Agent, or Firm-Fitzpatrick, Celia, Harper & Scinto [57] ABSTRACT Piles are installed in locations wherein a bearing stratum is submerged beneath a soft nonsupporting stratum. A tubular displacement element is driven down into the bearing stratum by means of a driving member capable of transmitting dynamic driving forces and load resistance effects from one end to the other. The driving member is than removed and a static load carrying column is installed on the displacement element.

17 Claims, 8 Drawing Figures 'PATENTEDHAY ems SHEET 10F 2 @ERQQ This invention relates to pile installations and more particularly it concerns novel supporting piles and methods and apparatus for their installation.

The present invention is particularly advantageous in environments where supporting piles must extend down through a softer upper stratum of earth down to a submerged or underlying supporting stratum. In such situations the upper stratum, which may be primarily clay or silt, is not capable of providing appreciable or reliable support, and accordingly the pile must be driven down through this non supporting material and into the firmer material lying below. This firmer material, which may be glacial till or hardpan, is usually of a gravelly nature, and is capable of providing substantial support to a displacement element driven into it. The degree of support provided by this underlying material is generally proportional to the total displacement produced in the material by the driven element.

In general, pile loading capacities are based upon socalled dynamic pile driving formulae. A dynamic pile driving formula is one which takes into account the depth of pile penetration into the earth for each blow of a pile driving hammer, or conversely, the number of hammer blows required for each additional inch of pile penetration. When a pile has been driven to a depth at which the number of hammer blows required to drive the pile an additional inch, reaches a predetermined amount, then the ultimate load carrying capacity of the pile in the earth can be ascertained.

Where the primary support offered by the earth to a driven pile is located at a considerable depth beneath an overlying non-supporting earth layer, special problems arise because the pile must be capable not only of supporting the static load for which it is designed, but it must also be capable of transmitting the dynamic forces applied by the driving hammer at its upper end down to its lower end for forcing the lower end a known amount into the bearing stratum. In the past, heavy walled pipe piles were used to transmit these driving forces. These however, were very expensive because they were not recoverable. Consequently, mandrels which were recoverable, were also used to drive thin walled tubular pile shells which, after removal of the mandrel, were filled with concrete.

The present invention provides an improvement to the prior art and eliminates the need, even for thin walled shells around concrete piles which are driven accurately to a dynamic resistance into an underlying stratum a substantial distance below the surface of the earth.

According to the present invention there is provided a tubular, closed bottom, overboot having a diameter and height sufficient to displace a known bearing stratum by an amount to establish a predetermined load resistance without becoming fully immersed in the stratum. The boot is fitted over the lower end of an elongated driving member such as a heavy Walled tubular mandrel. The mandrel, with the boot attached, is driven down through the earth to the bearing stratum. The mandrel serves to transmit dynamic hammer driving energy down to-the boot without substantial losses due to resiliency and side friction. Thus, the boot may be driven into the bearing stratum by an amount sufficient to produce a desired load carrying capacity and in a manner such that the attainment of that load carrying capacity is accurately related to the driving resistance encountered by the hammer at the upper end of the mandrel.

When the boot has been driven to its desired load carrying capacity in the bearing stratum, a castable static load carrying substance, such as wet concrete, is pumped down through the tubular mandrel and into the overboot. The pressure of the concrete is sufficient to force the overboot off the end of the mandrel. The mandrel is then listed at a rate which enables the concrete or equivalent substance to form an elongated structure extending from inside the overboot up through the overlying non-supporting strata, to the surface of the earth. When the concrete or equivalent substance has hardened, it is capable of transmitting static load forces down to the overboot, so that these loads are supported in the bearing stratum. The heavy walled tubular mandrel may, of course, be reused in subsequent pile forming operations.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures or methods for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions and methods as do not depart from the spirit and scope of the invention.

One embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings forming a part of the specification, wherein:

FIG. 1 is a sectional elevational view showing a preformed opening in the earth into which a pile, formed according to the present invention, may be installed;

FIG. 2 is a side elevational view, partially in section, illustrating a preliminary step in forming a pile according to the present invention;

FIG. 3 is a side elevational view showing a first driving step in the formation of a pile according to the present invention;

FIG. 4 is a view, similar to FIG. 3, showing a second driving step in the formation of a pile according to the present invention;

FIG. 5 is a view, similar to FIG. 4, showing a further step in the formation of a pile according to the present invention;

FIG. 6 is a view, similar to FIG. 5, showing a final step in the formation of a pile according to the present invention;

FIG. 7 is an enlarged elevational section view, partially cut away, showing a mandrel and overboot assembly used in the pile formation operations of FIGS. 2-6; and

FIG. 8 is a further enlarged view showing a modified mandrel and overboot assembly.

As shown in FIG. 1, a section of earth 10, into which piles formed according to the present invention are advantageously driven, is seen to comprise an upper nonsupporting stratum 11 which extends downwardly from an upper surface 12 to a submerged lower bearing straturn 14. The upper, non-supporting stratum 11, as mentioned above, may be primarily of clay or silt; and as such, is not capable of providing appreciable or reliable support to pile elements driven thereinto. The thickness of the upper non-supporting stratum 11 may vary from a few feet to lOO or more feet. The lower bearing stratum 14, which underlies the softer upper stratum 11, is of a higher resistance material such as glacial till or hardpan. This material, which is usually gravelly in nature, is capable of providing positive load support in an amount corresponding to the degree of displacement produced by an element driven into it. In many instances solid rock 16 underlies the lower bearing stratum 14.

As shown in FIG. 1, a pre-excavated hole 18 extends down through the upper non-supporting stratum 11 and into the lower bearing stratum 14. This preexcavated hole 18 may be formed by rotary drilling or other suitable technique; and it may be filled with water or a slurry of drilling mud or other material which will serve to brace the sides of the hole 18 to prevent the surrounding earth from filling it in. Since the upper, non-supporting, stratum 11 provides no appreciable support for the pile to be driven, the formation of a preexcavated hole 18 does not adversely affect the ultimate loading capability of the pile; and further, it permits easier and more accurate driving of the element from which the pile is to be formed.

FIG. 2 shows the assembly of a tubular overboot 20 over the lower end of a heavy walled tubular driving member or mandrel 22. As can be seen in FIG. 2, the overboot 20 is of hollow tubular configuration and is closed at its bottom with a bottom plate 24 which is welded or otherwise secured in place. The overboot 26 is set with its bottom plate 24 resting on'an assembly mat 26; and the mandrel 22 is forced down into the open upper end of the overboot. The mandrel 22 is provided with O-ring seals 28 around its periphery at a location such that these seals are just below the upper edge of the overboot 20 when the lower end of the mandrel 22 contacts the bottom plate 24. The seals 28 serve to prevent intrusion of water or other fluids into the interior of the overboot during the driving of the assembly into the pre-excavated hole 18; and they also serve frictionally to hold the overboot 20 and the mandrel 22 in assembly prior to and during driving.

As shown in FIG. 3 a driving hammer 30 is mounted to apply driving blows to an upper section 32 of the driving member or mandrel 22. These driving blows are transmitted down through the mandrel to its lower end so that the lower end of the mandrel 22, and the tubular overboot 20 mounted thereon, are driven downwardly through the hole 18 past the upper non-supporting stratum l and into the lower bearing stratum 14. The driving hammer 30 continues its driving operation until the resistance offered by the lower bearing stratum 14 to further downward movement of the tubular overboot requires the driving hammer 30 to produce a predetermined number of blows to advance the mandrel 22 by a predetermined amount. This amount is calculated by means of well known dynamic pile driving formulae; and it takes into account the ultimate load carrying capacity desired, the nature of the supporting stratum 14, the weight and frequency of the driving hammer and the force transmission characteristics of the mandrel 22. Since the mandrel 22 is of heavy walled construction, and since the upper non-supporting stratum 11, which has been been predrilled, offers insignificant resistance to the downward movement of the mandrel the actual driving, the resistance imposed upon the tubular overboot 20 by the lower bearing stratum 14 may be directly observed by the reactions of the upper section 32 of the mandrel 22 to the forces applied to it by the driving hammer 30.

As shown in FIG. 3 the upper section 32 of the driving member or mandrel 22 is of somewhat larger diameter than the main portion of the mandrel and thereby forms a shoulder 34 with the main mandrel portion. An upper, thin walled, corrugated tubular pile section 36 surrounds the upper mandrel section 32 and is engaged at its lower end by the shoulder 34 of the mandrel. The length of the mandrel 22 is designed such that when it has driven the tubular overboot 20 to a depth at which the predetermined driving resistance has been reached,

the shoulder 34 has also passed below the upper surface 12 of the earth and has pulled the corrugated pile section 36 a short but finite distance down into the earth. As can be seen in FIG. 4, the corrugated upper pile section 36 is of a length such that when driving is complete a portion 36a of the pile section 36 extends above the upper surface 12 of the earth.

It will also be noted from FIG. 4 that upon completion of driving, the upper end of the tubular overboot 20 extends a short distance 20a into the upper nonsupporting stratum 1 1. This insures that the lower bearing stratum 14 will maintain continuous positive load supporting resistance to the overboot 20, since any additional downward movement of the-overboot will produce an increase in displacement of the lower bearing stratum 14. Also, by designing the tubular overboot 22 to extend part way up into the upper non-supporting stratum 1 l, the entire resistance provided by the lower bearing stratum 14 will be imposed upon the overboot 22.

Upon completion of the driving of the driving member or mandrel 22 and the tubular overboot 20, concrete 39 or other suitable castable static load carrying material is pumped from a source (not shown) through a supply conduit 40 to a fitting 42 in the upper section 32 of the mandrel 22. This concrete or other castable material flows down through the interior of the driving member or mandrel 22 and out through its bottom end into the interior of the tubular overboot 20. At the same time, a lifting mechanism 44, attached to the upper end mandrel 22, raises the mandrel at a predetermined rate coinciding with the rate of inflow of castable material, so that as the lower end of the mandrel 22 is raised, the concrete 39 flows downwardly to fill the interior of the overboot 20 and to form a column 45 which extends up from the overboot. The pressure of the concrete 39 is maintained sufficiently high to hold the tubular overboot 20 down in firm engagement with the earth at the depth to which it had been driven, while the mandrel seals 28 are pulled up by the mandrel 22 out from the interior of the overboot, thereby releasing the overboot from the mandrel. It can also be seen from FIG. 5 that the corrugated pile section 36 remains in place with only its upper section 36a extending above the earth surface 12 during this upward movement of the mandrel 20.

Concrete or equivalent material continues to be supplied down through the mandrel 22 as it is raised, so

that the column 45 is automatically built up within the turn 11 and into the tubular overboot which has been previously driven to a predetermined dynamic resistance. As seen in FIG. 6, after the lower end of the mandrel 22 clears the corrugated pile section 36, the concrete forced out from the lower end of the mandrel fills the interior of the corrugated pile section 36 and thereby forms a well defined upper pile end configuration which is readily adaptable for the formation thereon of a pile cap 47 or other structure for communicating the loads to be carried to the column 45.

Turning now to F IG. 7 it will be seen that the fitting 42 is connected to an internal conduit 46 which extends down inside the mandrel 22 along its length. The internal conduit 46 opens into a lower cavity 48 formed coincidently with the tubular overboot 20. It will also be seen from FIG. 7 that the walls of the mandrel 22 may be made of any desired thickness suitable for transmission of the blows of the driving hammer down to the bottom of the overboot 20.

It will further be seen that the bottom of the mandrel 22 is maintained in intimate contact with the bottom plate 24 of the tubular overboot 20 to insure that proper driving resistance is transmitted from the overboot up through the mandrel 22 to the driving hammer 30.

A modified arrangement of the overboot and mandrel is illustrated in FIG. 8. As there shown, the bottom of the mandrel 22 is formed with a shoulder 50 which engages the upper edge of the tubular overboot 20. With this arrangement the driving forces of the mandrel 22 are distributed between both the upper and lower regions of the overboot 20, thereby preventing undue tensile or compressive stresses along the overboot walls. That is, the lower end of the mandrel 22 drives the overboot 22 via its bottom plate '24 to pull the overboot down into the earth whereas the shoulder 50 of the mandrel 22 drives the overboot 22 via its upper edge to push the overboot down into the earth.

The invention having been thus described with particular reference to the preferred forms 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 hereto.

What is claimed is:

l. A method of installing a pile in a bearing stratum which underlies a softer non-supporting stratum of earth, said method comprising the steps of detachably fitting an elongated, hollow, tubular, closed bottom overboot over the lower end of an elongated drive member capable of transmitting driving forces applied to its upper end down to the lower end of said overboot, driving said overboot down through the earth and into said bearing stratum by application of said driving forces to the upper end of said drive member until said overboot reaches a depth in said bearing stratum sufficient to produce a predetermined maximum driving resistance but less than the length of said overboot so that at least a portion of the upper end of said overboot extends up beyond said bearing stratum and into said 6 non-supporting stratum, thereafter removing said drive member from said overboot and installing a load carrying column "to extend from within said overboot up through said softer stratum. V i

2. A method according to clairn'l wherein said elongated drive member is capable ofaccurate transmission a of dynamic driving and load resistance forces throughout its length and wherein said application of driving forces to the upper end of said'driv'e member is continued until the response of said upper end to further forces corresponds to the attainment by said overboot of said predetermined driving resistance.

3. A method according to claim 1 wherein said load carrying column is formed by withdrawing said drive member from the earth and filling the space voided by such withdrawal with a castable load carrying material.

4. A method according to claim 3 wherein said castable material is pumped down through the interior of said drive member and out through its bottom end during raising thereof.

5. A method according to claim 1 wherein said overboot is frictionally secured to said drive member in a manner such that it can be forced off by application of fluid pressure through the interior of said drive memher.

6. A method according to claim 1 wherein said driving member is caused to extend into the interior of said overboot for driving thereof and wherein, upon completion of driving, a castable substance is forced down through said driving member and into the interior of said overboot.

7. A method according to claim 1 wherein during said driving said overboot is frictionally held to said driving element by frictional sealing means.

8. A method according to claim 1 wherein during said driving said driving element is caused to apply driving forces to said overboot at different locations along its length.

9. Apparatus for forming a displacement pile, said apparatus comprising an elongated, hollow, closed bottom, tubular overboot, an elongated drive member of substantially greater length than said overboot, the lower end of the said drive member extending into said overboot from the upper end thereof down to its closed bottom, friction type sealing means between said overboot and said drive member for sealing the interior of said overboot and for maintaining said overboot frictionally attached to said drive member, the lower end of said drive member being formed with a cavity coincident with the tubular overboot and a conduit extending down through said drive member and opening into said cavity for directing pressurized fluid down through said drive member and into said overboot for separating said overboot from said drive member.

10. Apparatus according to claim 9 wherein said sealing means comprises O-ring seals extending about the periphery of said drive member near its lower end.

1 1. Apparatus according to claim 9 wherein said sealing means contact the interior of said overboot near its upper end.

12. Apparatus according to claim 9 wherein the lower end of said drive member engages the bottom of said overboot for pulling same into the earth during driving.

13. Apparatus according to claim 9 wherein said drive member is formed with a shoulder which overlies and engages the upper edge of said overboot for pushing same into the earth during driving.

14. Apparatus according to claim 9 wherein said driving element is formed with an upper shoulder engaging the lower inner edge of an upper shell section for pulling same part way into the earth during driving of said displacement element.

15. A pile installation comprising a load located near the surface of the earth, an elongated pile structure extending from said load down through a soft nonsupporting layer of earth down into the interior of a hollow, elongated, tubular overboot, said soft nonsupporting layer being incapable of attaining a load crete.

Claims

1. A method of installing a pile in a bearing stratum which underlies a softer non-supporting stratum of earth, said method comprising the steps of detachably fitting an elongated, hollow, tubular, closed bottom overboot over the lower end of an elongated drive member capable of transmitting driving forces applied to its upper end down to the lower end of said overboot, driving said overboot down through the earth and into said bearing stratum by application of said driving forces to the upper end of said drive member until said overboot reaches a depth in said bearing stratum sufficient to produce a predetermined maximum driving resistance but less than the length of said overboot so that at least a portion of the upper end of said overboot extends up beyond said bearing stratum and into said non-supporting stratum, thereafter removing said drive member from said overboot and installing a load carrying column to extend from within said overboot up through said softer stratum.

2. A method according to claim 1 wherein said elongated drive member is capable of accurate transmission of dynamic driving and load resistance forces throughout its length and wherein said application of driving forces to the upper end of said drive member is continued until the response of said upper end to further forces corresponds to the attainment by said overboot of said predetermined driving resistance.

5. A method according to claim 1 wherein said overboot is frictionally secured to said drive member in a manner such that it can be forced off by application of fluid pressure through the interior of said drive member.

11. Apparatus according to claim 9 wherein said sealing means contact the interior of said overboot near its upper end.

15. A pile installation comprising a load located near the surface of the earth, an elongated pile structure extending from said load down through a soft non-supporting layer of earth down into the interior of a hollow, elongated, tubular overboot, said soft non-supporting layer being incapable of attaining a load supporting characteristic in response to displacement thereof, said overboot extending from an upper location in said non-supporting layer down into a harder supporting layer and displacing said harder supporting layer by an amount such that said supporting layer imposes sufficient resistance on said overboot to support said load.

16. A pile installation according to claim 15 wherein said overboot is a tubular member filled with concrete.

17. A pile installation according to claim 15 wherein said load transmission structure is a column of concrete.