IN SITU CASTING OF CONCRETE FOUNDATION PILES WITH A RECOVERABLE TUBE-SHAPED FORM

Abstract: A method for the in situ casting of a foundation pile supplied with a recoverable tube-shaped form (2), said pile having an improved and measurable capacity load at its sill, and the device for carrying out the method, said device being designed for the installation within said tube-shaped form and comprising means (3) for the transmission of a compressive stress direct or indirect onto the bottom of the digging through means for the distribution of the stress, said means resting on supporting means (1) supplied at the basis of the cage, and means (12) for generating a compressive action on said transmission means, said generating means being connected to said tube-shaped form at a point corresponding to its upper edge and being associated to means for measuring the compressive stress exerted on the bottom of the digging, concrete being introduced into the form through said means which transmit said stress or otherwise being introduced into the hollow space (8) between said means and said tube-shaped form.

Description: In-situ casting of concrete foundation piles with a recoverable tube-shaped form The present invention relates to a method for the in-situ cast- ing of foundation piles with a recoverable tube-shaped form, as well as to the device for carrying out said method. More particularly, the invention relates to a method for obtaining an in-situ cast founda¬ tion pile supplied with a provisional tube-shaped form, said pile being of improved and measurable sill capacity load, as well as to the device for carrying out the method itself. It is well known that in-situ cast foundation piles of the type set forth above, while showing the advantage of a good fitting to the stratigraphic features of the underground, on the other side do not always ensure the obtain ent of a capacity load at the pile sill cor- responding to the design capacity. Indeed, because of the possible presence of turned soil below the concrete casting, i.e. below the base or sill of said pile, the design capacity load determined by calculations based on the mechan¬ ical and geotechnical characteristics of the soil is actually de- creased., Moreover, it is to be remarked that a contribution to the re¬ duction of the calculated value of the sill capacity load of a foun¬ dation pile of the kind set forth above is also given by the tendency both of concrete and of the cage to raise up during the extraction of the tube-shaped form as a result of the dragging action due to the friction between the inside walls of said tube-shaped form and the fresh concrete, and also due to the friction between the cage and the . o xde walls of the tube-shaped form, with a consequent st.. . _ . collapsing of the soil about the pile end. The drawback of the re¬ duction of the sill capacity load occurring with foundation piles supplied with a recoverable tube-shaped form which is not provided with a closing bottom member is also observed in the case of struc¬ tures provided with closing means at their bottoms. Indeed, it is well known that there is the possibility of a partial blocking of the closing system within its housing, both as a result of the ex¬ cessive initial forcing of the coupling operation, and as a result of deformations arising along the path from the soil surface down to the final depths. Thus, in that case also the capacity load at the pile sill is decreased because of the lifting of the closed base of the tube- shaped form and of the consequent slipping or collapsing of the soil about the pile tip. A further drawback observed in the technology of in-situ cast¬ ing foundation piles with recoverable tube-shaped forms is the lack of a method for carrying out checking or testing operations after the in-situ casting of a pile in order to know whether the drawbacks mentioned above have occurred and at what extent. The present engineering design opposes said drawback by increas¬ ing the safety coefficients to the detriment of saving of realization costs. According to the present invention, in order to reduce the ef- fects of the drawbacks mentioned above it is suggested to cause a temporary-overpressure on the bottom soil of the hole direct or through the closing system, by exerting on the same a force equal to the force needed to extract the tube-shaped form from the soil and of the sense opposite to that of such force. It is well evident that said force increases with inci—-... 3 the deepening of the tube-shaped form into the soil, but that it is very easy to measure said force by means of a gauge instrument such as a pressure gauge, and it is also evident that such force can be increased by simple means which are well known in the art in case the side strength of the soil shows inadequate for the purpose. Thus, the solution proposed according to the present invention allows the capacity load of the pile tip which is on the way of forming to be increased as a result of the distribution of pressure on the bottom of the hole, so undoing the negative effect of the possible presence of soil debris on the bottom. A further advantage according to the present invention consists in the possibility of blocking simultaneously on the bottom the lower end of the cage which is opportunely shaped, so as to prevent said cage as well as the fresh concrete contained within the tube-shaped form from being dragged up together with said form as a result of friction. Indeed, by succeeding in such way in undoing the friction ef¬ fects, the higher weight of concrete with respect to the hydrostatic pressure ensures that lifting phenomena do not occur at any place of the manufacture while it is realized and particularly at the pile sill. On the basis of the mentioned innovatory observation, according to the present invention a method is defined for the realization of an in-situ cast pile supplied with a recoverable tube-shaped form, said pile being of improved and measurable capacity load at its sill or base, said method comprising the operations of providing a cage in a recoverable tube-shaped form bearing or not a closing bottom member and driven into the soil down till the desired depth, said cage having at its base a number of supporting means for stress distribu- 33 -' - . means, tube means being further provided inside said ^ tube means being designed for contacting said means for the distri- bution of stress on the bottom of the digging; concrete being cast and next compressing said tube means so exerting a stress on the bottom of said digging which is sufficient to give rise, as a reac¬ tion, to the force that is needed for extracting the tube-shaped form. In order to carry such method into effect, a device is suggest¬ ed according to the present invention which is to be installed within a tube-shaped form for an in-situ cast foundation pile in which a cage is provided comprising means for transmitting a compressive stress direct or indirect on the bottom of the digging through means for dis¬ tributing said stress which rest on the supporting means supplied at the cage base, and ' means for generating a compressive action on said transmission means which are connected to the tube-shaped form at a point corresponding to its upper edge and are associated to means for measuring the compressive stress exerted on the bottom of the dig¬ ging, concrete being introduced through said means for transmitting said stress or otherwise being introduced into the hollow base between said means and the tube-shaped form. Advantageously, said means for the transmission of the compressive stress are made up of a hollow column which is provided, by preference at its lower end resting on said means for the distribution of the stress, with outlets for the concrete which is introduced preferably at a point corresponding to its upper edge, engagement means being provided for the engagement with said means for generating the com¬ pressive stress at a point corresponding to its top part. Preferably, according to said latter solution, said means for generating the compressive stress consist of a pair of hydraulic jacks connected at their lower parts with a horizontal framework which is .-gral with the top part of the tube-shaped form, and at «.. per parts with another horizontal framework having means for the engagement with said hollow column and in which said means for meas¬ uring the compressive stress consist of pressure gauge means. The present invention will be disclosed in the following with particular reference to a specific embodiment of said device, said invention being illustrated in the enclosed drawings according to some of its variant forms of application. In the drawings: Figure 1 is a vertical cross sectional view of the device ac¬ cording to the present invention in which the tube-shaped form shows no closing system at its bottom part; Figures 2, 3 and 4 show partial vertical views of different solutions for the supporting part of the means which are designed for distributing the stress and belong to the device shown in Figure 1; Figures 5 and 6 show a partial vertical cross sectional view of the device of Figure 1 in the case of a tube-shaped form that is closed at its lower part; and Figure 7 shows a partial vertical view of the device shown in Figure 1 having a different closing system. With reference now to Figure 1, a tube-shaped form 2 can be observed driven into the soil 20, in the inside of which form a cage 6 is provided wherein the longitudinal bars are bent towards the inside in correspondence.to the bottom so as to form a supporting surface for the expendable plate 1 for the distribution of the com¬ pressive stress when the basis of the tube-shaped form 2 reaches the depth according to the design (see also Figure 2). As an alternative, nown in Figure 3, the support for the plate 1 can be ob . by welding the longitudinal bars with coplanar transversal bars 7 in a number adequate for housing the plate 1. As an alternative, the hollow column 3 rests direct on the supporting means provided at the base of the cage 6 (see Figure 4). The lower end of a hollow column member 3 rests on the plate 1, said member being provided near its lower end with openings or mouths 5 for the outlet of concrete fed at a point corresponding to its upper end 4. A number of projecting parts 15, 16, 17 are provided on the upper part of the outside surface of said hollow column 3, said projecting parts being designed for successive engagement with the hooks 14 integral with a horizontal framework 13 making part of a system which generates the compressive stress and is made up of a pair of hydraulic jacks 12 operating on said horizontal framework 13 and connected at their lower parts to a horizontal framework 10 that is integral with a tightening device 11 at the top of the tube-shaped form 2. The operation of the device according to the present invention occurs in the following way: when the hydraulic jacks 12 are acted upon downwards, the horizontal framework 13 is also acted upon and the same, through the hooks 14 and the projecting part 15 of which said tube 3 is providεd in its upper part, puts under compression said tube 3, and simultaneously stresses the tube-shaped form 2 upwards with a force which is capable of outweighing both the fric- tional forces and the weight of said tube-shaped form 2 so as to extract the same from the soil by a range corresponding to the clos¬ ing stroke of jacks 12. Next, the hydraulic jacks 12 are extended and said hooks 14 go into engagement with the next projecting part 15 of _ _ υϋbe 3 in the upper position and so on till the tube-- 2 has been extracted from the ground at least by a length such that the pile portion already formed is sufficient to ensure the absence of dragging phenomena upwards of concrete and/or of the cage. At that point, the last length of the tube-shaped form 2 and of the hollow column 3 are extracted by standard well known means. Moreover, it is an important fact that if the horizontal frame¬ work 10 for the connection to the tube-shaped form 2 and for support¬ ing the hydraulic jacks 12 is made up of a rotating head unit for realizing piles with the tube-shaped form inserted into the ground with a rotohelicoidal system, a rotating joint can be inserted into the horizontal framework 10 or into the horizontal framework 13 or otherwise into the hollow column 3 in order to allow the lower part of the device according to the present invention to rotate or oscil- late together with the tube-shaped form 2 and possibly together with the closing system 19 (Figures 5 and 6) in any step of the procedure. Moreover, the fact is remarkable that it is possible to know the value of the force applied to the tip of any pile, by reading that value on a pressure gauge (not shown in the Figure) connected to the hydraulic jacks 12. The system for coupling the closing plate 19 to the tube-shaped form 2 can be observed in Figures 5 and 6, said system being realized through a collar integral with said plate 19, which collar engages internally (Figure 5) or externally (Figure 6) with said tube-shaped form 2. It is well evident that the tube 3 can be locked in contact with the closing system 19 of the tube-shaped form 2 with or without the interposition of the cage for contrasting the tendency of the closing system 19 to inflect or bend towards the tube-shaped form 2 inside as a result of the pressure exerted by the soil 20 during the . .υduc ion of said tube-shaped form into the ground. All ,_ the possibility of reducing the thickness of the closing system 19. Finally, the closing member of the tube-shaped form can be ob¬ served in Figure 7, said member being made up of a plug 21 of a con- crete mixture. Moreover, it can be observed that at the moment of the extrac¬ tion of the tube-shaped form 2, the tube 3 acts as an expeller of the closing system 19 or 21, outweighing automatically the forces that contrast the separation which could act in the coupling connection between the tube-shaped form 2 and the closing system 19 or 21, which forces could be present as a result of the lack of clearance at the beginning of the operation as well as because of deformations of the closing system 19 and 21 occurring during the introduction of the tube-shaped form 2 into the ground. The present invention has been disclosed for illustrative and not for limitative purposes, according to some of its preferred em¬ bodiments, but it is to be understood that modifications and changes can be introduced by those who are skilled in the art without de¬ parting from its spirit and scope for which a priority right is claimed.

Claims: 1. A method for the realization of an in-situ cast pile supplied with a recoverable tube-shaped form, said pile being of improved and measurable sill capacity load, the method being characterized in that it comprises the operation of providing a cage in a recoverable tube- shaped form, said form having or not a bottom closing member and being fixed into the ground down to the necessary depth, said cage being provided at its basis with supporting means for means designed for dis¬ tributing the stress; and further characterized in that it provides inside said cage a number of tube means designed for contacting said means for the distribution of stress on the bottom of the digging; and characterized in that the concrete is cast and next said tube means are put under compressive stress so as to exert a stress on the bottom of the digging which is sufficient to give rise, as a reaction, to the force which is needed for extracting said tube-shaped form from the ground. 2. A device for carrying into effect the method according to claim 1, said device being designed for its installation within a tube-shaped form of an in-situ cast foundation pile, in which a cage is provided, said device being characterized in that it comprises means for the transmission of a compressive stress direct or indirect onto the bottom of the digging through means which are to distribute the stress and rest on supporting means provided at the base of the cage, and means for gen¬ erating a compressive action on said means which are to transmit the compressive stress and are connected to the tube-shaped form at its upper edge and are associated to means for measuring the compressive stress exerted on the bottom of the digging, the concrete being intro¬ duced through said means for the transmission of the stress or otherwise being introduced into the hollow space between said means and the tube- 33 . l 0 . shaped form. 3. A device according to claim 2, characterized in that said compressive stress transmitting means are made up of a hollow column which is provided at its lower part with outlet mouths for the con¬ crete which. is fed at its free upper part, engagement means being provided at that part for the engagement with said compressive stress generation means. 4. A device according to claims 2 and 3, in which the com¬ pressive stress generation means consist of a pair of hydraulic jacks connected at their lower parts with a horizontal framework which is integral with the top part of the tube-shaped form and at their upper part with another horizontal framework, which has means for the en¬ gagement with said hollow column and in which said means for measuring said compressive stress consist of pressure gauge means. 5. A device according to claim 4 in which said means for engage¬ ment with said hollow column are made up of hook members which are integral with said horizontal framework and of projecting parts spaced from one another and provided on the top part of said hollow column. 6. A method and a device according to the preeceding claims and substantially as disclosed and illustrated above.

Inventors: FIORUZZI AMBROGIO, FIORUZZI, AMBROGIO
Applicants: ICELS PALI SPA
Application year: 1986
Main classification: E02D5
IPC codes: E02D5, E02D9, E02D15