GB1584357A - Pile driving apparatus - Google Patents

Description

(54) PILE DRIVING APPARATUS (71) We, HOLLANDSCHE BETON GROEP N.V., a Dutch Company of Generaal Spoorlaan 489, Rijswijk z.h. Holland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is performed, to be particularly described in and by the following statement: This invention relates to apparatus for driving piles by the stroke of a hammer in the form of a ram or dropweight. The present application is divided out of our copending application No. 45592/76 (Serial No. 1,584,356).

The specification of our British Patent No.

1,168,547 described a pile driving apparatus which has resilient impact transmitting buffer means in the path of travel of the hammer for transmitting the impact of the hammer stroke to a pile, conveniently through a pile cap or anvil on the top of the pile. The resilient impact transmitting buffer means comprises precompressed gas in a closed chamber and the stroke energy of the hammer is transmitted via the gas and a strike cap to the pile, the strike cap being supported in, and projecting from the chamber.

The precompressed gas is further compressed on impact enabling the minimum force required to overcome the ground resistance, which opposes penetration of the pile, to be directly available under the impact, and smoothing out force peaks so that the maximum force does not exceed the force which causes damage to the pile.

The present invention consists a pile driving apparatus comprising a hammer for delivering an impact force to a pile, resilient impact transmitting buffer means disposed in the path of travel of the hammer and comprising a precompressed gas in a closed chamber defined by wall means and containing a strike piston which normally projects from said chamber for transmitting the impact force from the hammer through the gas to the pile, and stop means which are separate from, and act independently of, said precompressed gas for cutting out the effect of the resilient buffer means on the impact force by bypassing said resilient buffer means after a predetermined extent of a hammer movement whilst said precompressed gas is partially compressed and delivering a nonresilient steel-to-steel blow to the pile during each impact stroke.

in this manner monmentary peak force is delivered by the hammer during each impact.

By means of the invention the pile can be subjected to a predetermined and desired peak force at a selected period of time when needed and since the resilient impact during which the strike piston hits the pile at a relatively lower impact force, enables the moving parts of the pile driving apparatus and the top of the pile to be gently brought together and reduce any misalignment of the pile before the non-resilient impact, damage to the pile from the higher peak force of the non-resilient impact is minimised or prevented.

The gas pressure or stem length of the strike cap piston may be so chosen that the non-resilient impact is provided by the hammer directly striking the pile, or striking the pile through a wall of the chamber or through the strike piston striking a wall of the chamber.

The resilient impact transmitting buffer means may be incorporated in the hammer itself or in a separate body as described in our aforementioned British Patent Specification.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, in which - Fig. 1 is a section through a part of a simplified form of the pile driving apparatus incorporating resilient impact transmitting buffer means described in our British Patent Specification No. 1,168,547 and positioned above the top of a pile, Fig. 2 is a similar view to that of Fig. 1 but showing a part of the hammer in a different position, Fig. 3 is a time/impact force diagram obtained when using the apparatus of Figure 1, Fig. 4 is a total time/impact force diagram of which the diagram of Fig. 3 forms a part, Fig. 5 is a section through a part of a simplified form of pile driving apparatus according to the invention, having resilient impact transmitting buffer means incorporated in the hammer and being positioned above the top of a pile, Fig. 6 is a time/impact force diagram obtained using the apparatus of Fig. 5, Fig. 7 is a total time/impact force diagram of which the diagram of Fig. 6 forms a part, Figs. 8 and 9 are sections of another embodiment showing the hammer in two positions respectively, and in which the resilient impact transmitting buffer means are incorporated in a separate body, Figs. 10 and 11 are sections of a modification of the embodiement of Figs. 8 and 9, and Fig. 12 is a section of another embodiment.

Fig. 1 shows a hammer in the form of a dropweight 1 of a simplified form of the pile apparatus described in our British Patent Specification No. 1,168,547. In a part 2 of the dropweight is incorporated the impact transmitting buffer resilient means comprising a gas compressed in a chamber 3 which is closed at its lower end by a strike cap piston 3a for delivering an impact to a pile 4 through a pile cap or anvil 7 on the top of the pile. The strike cap piston 3a normally rests against a shoulder 3b on the bottom wall of the chamber 3. Fig. 2 shows the position of the dropweight 1 after it has delivered an impact to the pile 4 through the strike cap piston 3a from which it can be seen that the lower projecting end 5 of the dropweight part 2 does not contact the anvil 7.

The stroke diagram of the pile driving apparatus shown in Figs. 1 and 2 may be represented schematically as shown in Fig.

3. At the moment Tl, the dropweight 1 hits the pile or anvil and immediately force Fl imparted by the precompressed gas through the strike cap piston actively works on the pile. The dropweight part 2 continues its downward movement as illustrated in Fig. 3 until its velocity has reached zero which is at the time T2 on the diagram where the force has only gradually increased to a value F2. The dropweight part 2 then moves upwards again because of the gas pressure in the chamber 3. At the moment Tithe "buffer closes", i.e. the strike cap piston returns to the position shown in Fig. 1, and the force is suddenly taken off the pile.As described in our aforementioned British Patent Specification, the gas is precompressed to such an extent that under the impact the minimum force exceeding the ground resistance is directly available. Thus the pressure of the gas can be brought into the order of the ground resistance.

The diagram of Figure 3, in fact, can be looked upon as a part of a total time/ stroke impact force diagram which is shown in Fig. 4 which resembles the force/ compression graph of a spring where the elasticity curve starts at zero where compression is nil at zero force. The curve, which for simpicity's sake is shown here as a straight line, represents the elasticity curve of the spring. Since the spring is precompressed, this means that the part of the diagram, a-T, in Figure 4 remains inactive.

As will be appreciated from our aforementioned British Patent Specification, the degree or value of the gas pressure in the chamber 3 is chosen such that the total weight of the dropweight 2 does not contact the anvil 7 or pile 4 as is shown in Fig. 2.

In accordance with the invention, before the downward velocity of the dropweight has reached its zero value, the dropweight 2 hits the anvil 7 or pile 4 at its lower end 5 in steel-to-steel fashion so that the dropweight also delivers a rigid or non-resilient blow via the lower end 5 of the dropweight during each impact stroke.

This may be achieved either by choosing a shorter stem length 6 (see Fig. 5) for the strike cap piston 3a or a lower gas pressure in the chamber 3. In this case, the time/ impact force diagram changes from that shown in Fig. 3 and is represented schematically in Figure 6. Referring to Fig. 6, again at the moment Tl, force Fl becomes immediately active on the top of the pile.

From moments T, to T4 the elasticity curve of the spring is followed. During the downward momement of the dropweight part 2, its lower end 5 hits the anvil 7 at the moment T4 causing an uncontrolled steelto-steel impact peak force to occur of magnitude F4. This peak force quickly falls back to a force level indicated at F3 at the moment T and from moments T. to TG the elasticity curve shown in Fig. 3 is followed until the "buffer closes" at the moment T6.

Since the peak force is momentary, damage to the pile is minimized or avoided.

As in the case of Figure 3, the diagram of Fig. 6 is part of a total force stroke impact diagram which is shown in Fig. 7 where zero represents the nil force at zero time (equal to no precompression of the gas in the chamber 3).

Figs. 8 to 11, show embodiments in which the precompressed resilient means is incorporated in a separate body 8 instead of in the dropweight which can be in the form of simple solid body 2'. In Figs. 8 and 9, the separate body 8 is arranged directly on top of the pile 4 and therefore serves as an anvil instead of the anvil 7. The separate body 8 has an upwardly projecting part 5' on the top wall of the chamber 3, similar to the lower end 5 of the dropweight 2 of the embodiment of Fig. 5 and the pressure of the gas in the chamber 3 is of such a value that the dropweight part 2' strikes the part 5' in steel-to-steel fashion thereby delivering a rigid or non-resilient blow to the pile. The stroke diagram of the embodiment of Figs. 8 and 9 is identical to that shown in Fig. 6.

The modification shown in Figs. 10 and 11 differs from Figs. 8 and 9 in that the steel-to-steel impact does not occur at the part 5' but at an upwardly projecting interior part 10 on the bottom wall of the chamber 3. In this case, and as will be apparent from Fig. 11, the stem length 6' of the strike cap piston 3a is increased and is of such a length that the dropweight part 2' can never touch the top wall 11 of the body 8. Again, the stroke diagram is as depicted in Figs. 6 and 7.

The embodiment shown in Fig. 12 also comprises a separate body 8' but, in contrast to the separate body 8 of Figs. 8 to 11, the separate body 8' is incorporated at the upper end of a downwardly extending tubular extension 12 of a housing (not shown) for the dropweight 2' and is inverted so that an anvil 7 is required on top of the pile 4. The extension 12 which has a recess in which the pile cap or anvil 7 is held captive also inclues a tubular guide portion or pile sleeve 12a which servies to guide the pile driving apparatus onto and receives the top of the pile without any other means of support or guidance being required. Thus the hammer 2' delivers the initial impact to the top wall, as illustrated, 13 of the body 8' and thus through the strike cap piston 3a to the anvil 7.The higher peak force impact is provided by having such a gas pressure in the chamber 3 or stem length of the piston 4 that the part 5" of the separate body strikes the anvil 7 in steel-to-steel fashion.

Alternatively, the higher peak force impact may be provided by increasing the stem length of the strike cap piston 3a and providing the interior wall of the chamber 3 with a projecting part 10' in a similar manner to the embodiment of Figs. 10 and 11 such that the strike cap piston hits the projecting parts.

WHAT WE CLAIM IS : 1. A pile driving apparatus comprising a hammer for delivering an impact force to a pile, resilient impact transmitting buffer means disposed in the path of travel of the hammer and comprising a precompressed gas in a closed chamber defined by wall means and containing a strike piston which normally projects from said chamber for transmitting the impact force from the hammer through the gas to the pile, and stop means which are separate from, and act independently of, said precompressed gas for cutting out the effect of the resilient buffer means on the impact force by bypassing said resilient buffer means after a predetermined extent of hammer movement whilst said precompressed gas is partially compressed and delivering a non-resilient steel-to-steel blow to the pile during each impact stroke.

2. Pile driving apparatus as claimed in claim 1, wherein said stop means comprises one of said chamber wall means and the combination of the chamber wall means with the strike piston.

3. Pile driving apparatus as claimed in claim 2, wherein the resilient means is incorporated in a body which is separate from the hammer, and wherein said stop means comprises a projection in said chamber and projecting from said chamber wall means to be struck by the piston during each impact stroke.

4. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 5 to 7 of the accompanying drawings.

5. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 6 to 9 of the accompanying drawings.

6. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 6, 7, 10 and 11 of of the accompanying drawings.

7. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 6, 7 and 12 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. anvil instead of the anvil 7. The separate body 8 has an upwardly projecting part 5' on the top wall of the chamber 3, similar to the lower end 5 of the dropweight 2 of the embodiment of Fig. 5 and the pressure of the gas in the chamber 3 is of such a value that the dropweight part 2' strikes the part 5' in steel-to-steel fashion thereby delivering a rigid or non-resilient blow to the pile. The stroke diagram of the embodiment of Figs. 8 and 9 is identical to that shown in Fig. 6. The modification shown in Figs. 10 and 11 differs from Figs. 8 and 9 in that the steel-to-steel impact does not occur at the part 5' but at an upwardly projecting interior part 10 on the bottom wall of the chamber 3. In this case, and as will be apparent from Fig. 11, the stem length 6' of the strike cap piston 3a is increased and is of such a length that the dropweight part 2' can never touch the top wall 11 of the body 8. Again, the stroke diagram is as depicted in Figs. 6 and 7. The embodiment shown in Fig. 12 also comprises a separate body 8' but, in contrast to the separate body 8 of Figs. 8 to 11, the separate body 8' is incorporated at the upper end of a downwardly extending tubular extension 12 of a housing (not shown) for the dropweight 2' and is inverted so that an anvil 7 is required on top of the pile 4. The extension 12 which has a recess in which the pile cap or anvil 7 is held captive also inclues a tubular guide portion or pile sleeve 12a which servies to guide the pile driving apparatus onto and receives the top of the pile without any other means of support or guidance being required. Thus the hammer 2' delivers the initial impact to the top wall, as illustrated, 13 of the body 8' and thus through the strike cap piston 3a to the anvil 7.The higher peak force impact is provided by having such a gas pressure in the chamber 3 or stem length of the piston 4 that the part 5" of the separate body strikes the anvil 7 in steel-to-steel fashion. Alternatively, the higher peak force impact may be provided by increasing the stem length of the strike cap piston 3a and providing the interior wall of the chamber 3 with a projecting part 10' in a similar manner to the embodiment of Figs. 10 and 11 such that the strike cap piston hits the projecting parts. WHAT WE CLAIM IS :

1. A pile driving apparatus comprising a hammer for delivering an impact force to a pile, resilient impact transmitting buffer means disposed in the path of travel of the hammer and comprising a precompressed gas in a closed chamber defined by wall means and containing a strike piston which normally projects from said chamber for transmitting the impact force from the hammer through the gas to the pile, and stop means which are separate from, and act independently of, said precompressed gas for cutting out the effect of the resilient buffer means on the impact force by bypassing said resilient buffer means after a predetermined extent of hammer movement whilst said precompressed gas is partially compressed and delivering a non-resilient steel-to-steel blow to the pile during each impact stroke.

2. Pile driving apparatus as claimed in claim 1, wherein said stop means comprises one of said chamber wall means and the combination of the chamber wall means with the strike piston.

3. Pile driving apparatus as claimed in claim 2, wherein the resilient means is incorporated in a body which is separate from the hammer, and wherein said stop means comprises a projection in said chamber and projecting from said chamber wall means to be struck by the piston during each impact stroke.

4. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 5 to 7 of the accompanying drawings.

5. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 6 to 9 of the accompanying drawings.

6. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 6, 7, 10 and 11 of of the accompanying drawings.

7. Pile driving apparatus substantially as hereinbefore described with reference to Figs. 6, 7 and 12 of the accompanying drawings.