US3022634A - Methods for driving pile shells at submerged locations - Google Patents

Description

Feb. 27, 1962 w. P. KINNEMAN ET'AL 3,022,634

METHODS FOR DRIVING FILE SHELLS AT SUBMERGED LOCATIONS Filed June 22, 1960 INVENTORS.

BY Aer/ up TIPPEN.

United States Patent Ofice 3,@ZZ,34 Patented Feb. 2?, 1%62 Jersey Filed June 22, 1966, Ser. No. 38,059 5 Claims. (Cl. 61-54) This invention relates to methods and means for driving p'le shells at submerged locations, for example pile shells such as reinforced prestressed tubular concrete plies such as disclosed in the US. patent to Maxwell M. Upson No. 2,706,498.

While concrete pile shells of the type above referred to have proven highly satisfactory, it has sometimes been noted that in driving same at submerged locations and with the lower end of the shell in open cond tion, there has been a tendency at the time when the shell is receivving impacts from the driving hammer, for small vertical or irregular cracks to occur in the concrete walls of the shell at locations below the water level and where 'water has entered to substantial heights within the shell.

This difiiculty has occurred in instances Where the prestressed concrete walls of the pile shell were assuredly so constructed as normally to have a strength far more than ordinarily needed to resist cracking under the heaviest impacts of the pile driving hammers generally used.

It is well known that when such pile shells are subjected to a driving impact, at the moment of impact the head end of the shell will move downwardly and the toe end also downwardly, but with somewhat less movement than at the head end, and then, immediately following such impact, the head end will rebound upwardly somewhat,

as does also the toe end generally to a lesser degree. Such differences in the movements of the head and toe ends of the concrete shell necessarily during the downward impact cause heavy compression forces in the concrete and during the rebound, causing considerable tension in the concrete. Nevertheless, even though the prestressed pile shell is so designed and constructed that it will ordinarily resist these forces without any danger of cracking, still under the conditions above mentioned, noticeable cracking sometimes has occurred without any apparent explanation.

Upon study of this problem, it was found that in driving such open-ended concrete piles at submerged locations, a relatively firm, dense or hard plug of earth would in some circumstances tend to be formed within the lower end of the shell, and above such plug, arelatively softer and semi-fluid mass of soil or mud would occur and a column of water of substantial height would also occur above such mass. Yet, computations indicated that in cases where the above-noted difliculties occurred, the prestressed concrete shells were of a construction having adequate strength not only sufiicient to be well able to resist the impacts of the driving hammer, but also in addition any static pressures within the shell which could arise by reason of the masses of mud and column of water contained therein.

Further investigation revealed that the above-mentioned plug formed within the lower end of the pile during driving evidently becomes bonded or more or less wedged within the shell so that its behavior is such as to be somewhat comparable to the formation of a quite rigid concrete plug, firmly closing ofl the lower end of the pile, at least during the later stages of the driving of the shell at the submerged location. Also it was found that upon placing a pressure-indicting means within the column of water within the pile shell under these driving conditions,

there was created within such water column, at the times of the hammer impacts, pressures substantially greater than had previously been supposed to exist. For example, when a pressure indicator was hung within the water column at water depth of some 50 feet, during impacts it indicated an increase in pressure greater than pounds per square inch, and greater than pounds per square inch at a depth of some 90 feet. The occurrence of these pressures was surprising in view of the fact that the upper ends of the pile shells were open or contained volumes of air free to escape from the upper ends. However, upon further study of the matter, and the making of related computations, we have discovered that such excessive momentary pressures which are set up in the water Within the pile and which cause the cracking difliculty, were due to hydrodynamic impact effects explainable as follows.

Under the blow of the hammer, the above-mentioned wedged-in-place earth plug within the bottom of the portion of the pile shell moves down with the pile shell and also rebounds back upwardly with the pile shell with movements substantially the same as those of the pile shell itself. And as such plug moves down with the pile, the column of semi-fluid soil or mud thereabove, as Well as the Water above the latter, have considerable inertia and thus evidently do not follow the pile movement immediately. As a result, a considerable degree of cavitation evidently occurs at the top of the column of mud or somewhere in the mud below the lower end of the water column. And on the elastic rebound movement of the pile shell with the plug within the lower end thereof, the plug within the lower end of the shell causes a sudden impact against the liquid or semiliquid masses above the cavitated regions, thereby producing a serious hydrodynamic impact within the water column sufficient to apply outward radial forces to the tubular concrete such as to crack the same under the resulting circumferential tension effects.

These difliculties may be avoided by providing some form of closure means at the lower end of the pile shell, which wll suffice to prevent the mud and water from entering to any troublesome degree, but this expedient in turn may, under some conditions, be uneconomical and give rise to delays in the pile driving operations. Also, some conditions do not readily permit the use of such closure means for the lower end of the shell, for example when eitorts are being made to penetrate sand layers.

In accordance with the present invention, we have, however, discovered that the above-noted diificulties may readily and economically be overcome without providing a closure for the lower ends of the pile shells, but by providing means so inserted or suspended within the water column within the pile as to form or maintain a substantial body or bodies of gas therein, such as air, adequate to cushion and greatly minimize the hydrodynamic impacts in the water and to a point where the cracking of the concrete is safely avoided.

Various further and more specific objects, features and advantages of the invention will appear from the descrip tion givenbelow, taken in connection with the accompanying drawings, illustrating by way of example preferred forms of the invention.

In the drawings:

FIG. 1 is a vertical sectional view of a prestressed concrete pile shell being driven down through a body of water into the earth below and illustrating one example of means which may be used to carry out the method of the present invention; and

FIGS. 2 and 3 are similar views, but showing alternative embodiments of such means.

Referring to the drawings in further detail, a prestressed concrete pile shell is indicated at 19 and which may be for example constructed in accordance with the disclo- V 3 e V sures of the above-mentioned Upson patent. Such a concrete pile shell is here shown as being driven into the earth 11 at a region submerged in a body of water as at 12. Suitable driving cap means is more or less schematically indicated at 13, to which, through a suitable known form of resilient cap block means or otherwise, the driving impacts of a pile driving hammer may be applied downwardly, as indicated by the arrow '14.

As here shown, the concrete pile shell has been driven down into the earth 111 to a distance such that a'firm plug of earth, as above described, has become formed and lodged as at 15 within the lower end of the pile shell. In the regions above this plug, a mass of mud of semi-fluid nature has accumulated as indicated at 16, while higher or upper portions are filled with a column of wateras indicated at 17.

During each driving impact, the toe end of the con- ,crete shell will first be driven downwardly and the plug of earth 15, if firmly lodged in place, will follow along with the movement of the concrete shell, as will possibly also some of the mass of mud 16. But either at the upper regions of the latter mass, as indicated at 18, or possibly at some lower point, cavitation will occur because the water column and fluid masses will have sufficient inertia so that same will not move downwardly concurrently with the other material in the pile therebelow. Then by reason of elastic rebound eifects, the lower end of the pile shell will move upwardly for a short distance, as indicated at 20, carrying along with it the firmly impacted plug 15 and any other mud which is below the region of the cavitation. Then at the same time the column of water will be tending to fall and at the region of the cavitation it will therefore meet the ascending masses therebelow with a heavy impact, causing the above-mentioned hydrodynami: impact effects. Such effects then in turn, tend momentarily to impartto the water 17 sufilcient pressure radially to apply forces to the concrete shell great enough to cause the latter to tend to expand, placingthe concrete circumferentially under tension sufiicient to cause cracking unless steps are taken to minimize or cushion such pressure effects in the water. 7

As shown in FIG. 1, this may be accomplished by suspending a preferably flexible and elastic container 21, as by a rope, wire or the like 22, at a location down within the water column. One or more of such containers may be used and inflated with a volume or volumes of gas such as air and sufiicient in size so that as the pressure in the water tends to increase due to the hydrodynamic impact etfect, the container walls will yield and thereby minimize or cushion the effect of such pressure on the concrete to a sufficient degree whereby the concrete does not become tensioned suificiently to cause cracking thereof.

With the form of means shown in FIG. 2 for carrying out the invention, an inverted bell-like chamber of metal or other material is provided as at 25 and suspended at an adjustable height as by a cord 26 running from a reel as at 27. Here some of the water will rise up into the chamber as indicated at 28, but nevertheless within the upper p ortions of the chamber, there will remain a body of air 29 under pressure, so that when the pressure in the water 28 7 tends to rise excessively by reason ofv the hydrodynamic impact effect, the effect ofsuch pressure will be greatly minimized and cushioned by the volume of gas 29.

With the form of means for carrying out the invention Y 4 thereby protect the concrete against the hydrodynamic impacts.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in-determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is: p p

1. In the driving of tubular pile shells at submerged locations under conditions whereby a plug-like mass of earth becomes firmly lodged in the lower end of the shell and which mass is superposed by mud-like material and a column of water inthe shell so that said plug like mass will move downwardly with the pile shell when subjected to impacts and move upwardly with the shell upon the elastic rebound of the shell following the impact, thereby causing momentary cavitation to occur above the plug-like mass and beneath a substantial portion of the Water, and tending to cause cracking pressure against the shell due to hydrodynamic impacts of the water against the interior of the shell, the method of preventing the occurrence of such cracking pressures upon collapse of such cavitation comprising: maintaining a substantial volume or volumes of gas within such water column to cushion the force of the hydrodynamic impacts occurring therein and then applying driving impacts to the shell.

2. In the driving of tubular concrete pile shells at submerged locations under conditions whereby a plug-like mass of earth becomes firmly lodged in the lower end of the shell and a substantial column of water occurs as shown in FIG. 3, a hose 'as at 30 connected to a source of compressed air is provided to extend down in thecol- V umn of Water as shown, its lower end being weighted, if desired, as by a weight 31, and the hose being perforated, or at least provided with an outlet or outlets at the lower end, so that many bubbles will constantly be formed and rise up through the column of water 17, which bubbles will absorb or cushion the excess pressure effects and within the higher portions of the shell so that said pluglike mass will move downwardly with the pile shell when subjected to impactsv and'move upwardly with the shell upon the elastic rebound of the shell following the impact, while the water column due to inertia fails immediately to fcllow such movements, thereby causing momentary caviation to occur beneath at least a substantial portion of the water, the method of preventing the occurrence of cracking pressures against the interiorsurfaces of the shell due to hydrodynamic impacts by the water therein upon collapse of such cavitation, comprising: maintaining a substantial volume or volumes of gas within such water column to cushion the force of such hydrodynamic impacts and then applying driving impacts to the shell.

3. In the driving of tubular concrete pile shells at submerged locations under conditions whereby a pluglike mass of earth becomes firmly lodged in the lower end. of the shell and a substantial column of water occurs within the higher portions of the shell so that said .plug-like mass will move downwardly with the pile shell when subjected to impacts and move upwardly with such Water column, to cushion the force of such hydrodynamic impacts and then applying driving impacts to the shell.

4. In the driving of tubular pile shells at submerged locations under conditions whereby a plug-like mass of ,earth becomes .firrnly lodged in the lower end of the shell and which massis superposed by mud-like material and a column of water in the shell so that said plug-like mass will movedownwardly with'the pile shell when subjected to impacts and move upwardly with the shell upon the elastic rebound ot' the shell following the impact, thereby causing momentary cavitation to occur above the plug-like mass and beneath a substantial portion of the water, and tending to cause cracking pressure against the shell due to hydrodynamic impacts ofthe water against the interior of the shell, the method of preventing the occurrence of such cracking pressures upon collapse of such cavitation comprising: creating numerous bubbles of gas of substantial total volume within such water column and then applying driving impacts to the shell.

5. In the driving of tubular concrete pile shells at submerged locations under conditions whereby a plug-like mass of earth becomes firmly lodged in the lower end of the shell and a substantial column of water occurs within the higher portions of the shell so that said pluglike mass will move downwardly with the pile shell when subjected to impacts and move upwardly with the shell upon the elastic rebound of the shell following the impact, While the water column due to inertia fails immediately to follow such movements, thereby causing momentary cavitation to occur beneath at least a substantial portion of the water, the method of preventing the occurrence of cracking pressures against the interior surfaces of the shell due to hydrodynamic impacts by the water therein upon collapse of such cavitation, comprising: placing a bell-like container within such Water column and containing a substantial volume of gas under pressure of the water rising in the bell and then applying driving impacts to the shell.

No references cited.

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