WO2019048728A1

WO2019048728A1 - A method for controlling the driving of the hammer and the movements of the ram in an impact pile driving apparatus, as well as an impact pile driving apparatus and an impact pile driving machine

Info

Publication number: WO2019048728A1
Application number: PCT/FI2017/050634
Authority: WO
Inventors: Jaakko Paavola; Antti Halonen; Jyrki HOLOPAINEN
Original assignee: Junttan Oy
Priority date: 2017-09-07
Filing date: 2017-09-07
Publication date: 2019-03-14

Abstract

The application relates to a method for controlling the pressing of the hammer (5) and the impacts of the ram in an impact pile driving apparatus (20), in which method the hammer (5) of the impact pile driving apparatus (20) is pressed by a pressing device (10) against a pile (30) during driving the pile (30) into the ground, wherein the impact energy (Ej) imposed on the pile by a ram moving back and forth within the hammer (5) of the impact pile driving apparatus (20), and the pressing force (Fp) imposed on the pile (30) by the pressing device (10), are automatically controlled on the basis of the measured embedding depth (s) of the pile, by the control system of the pile driving apparatus (20). The application also relates to a pile driving apparatus (20) and a pile driving machine (1).

Description

A METHOD FOR CONTROLLING THE DRIVING OF THE HAMMER AND THE MOVEMENTS OF THE RAM IN AN IMPACT PILE DRIVING APPARATUS, AS WELL AS AN IMPACT PILE DRIVING APPARATUS AND AN IMPACT PILE DRIVING MACHINE

Field of the invention

The invention relates to a method for controlling the driving of the hammer and the movements of the ram in an impact pile driving apparatus, as well as an impact pile driving apparatus and an impact pile driving machine.

Background of the invention

In an impact pile driving apparatus, the hammer moving along the rig is sub- jected to a gravitational force that pulls it downwards during the driving of the pile into the ground, and forces the ram, placed in the lower part of the hammer, against the head of the pile during impact driving of the pile. However, due to acceleration of the ram hydraulically moved within the hammer (after the upper dead centre of the impact), as well as impulses caused by the impact of the ram, the hammer is also subjected to forces which tend to lift the hammer temporarily upwards. Movement of the hammer upwards during the pile driving process is not desirable, because the part of the impact energy produced by the ram which is consumed on these movements does not contribute to the process of driving the pile into the ground. Conventionally, upward movements of the hammer during the pile driving have been constrained by making the hammer sufficiently heavy so that the forces which are caused by the ram moving in the hammer and are transferred to the hammer would not generate forces exceeding the gravitational force effective on the hammer. Particularly in the case of hard soil, however, strong impacts having a high impact energy are often needed for pile driving. A high ram velocity is required for producing such impacts. In these situations, it is typical in pile driving machines of prior art that the hammer still moves upwards during the impacts, because the ram is accelerated by a very great force during the impact and, on the other hand, the high impact energy subjects the pile to an impulse whose effect may be sufficient to move the hammer upwards as well. For keeping the hammer abutting against the pile, it is known to apply a force generating device that presses the pile against the hammer. Document GB 2316430 discloses a vibrating/rapidly oscillating hammer, wherein the hammer is pressed against the pile during vibrating/rapid hammer pile driving. The hammer pressing device presented in GB 2316430 is based on a hydraulic pull-down winch pressing the hammer against the pile with a force W by means of a rope. In the pile driving apparatus presented in GB 2316430, the aim is to adjust the force W to prevent vibration of the hammer in all situations when it abuts against the hammer during driving of the pile into the ground.

Brief summary of the invention It is an aim of the present invention to provide a method in which the pressing device pressing the hammer of the impact pile driving apparatus against the pile, as well as the impact energy produced by the ram moving back and forth within the hammer, are automatically controlled during pile driving, for optimation of the pile driving process with respect to profitability, costs, and the quality of pile driving. Moreover, it is an aim of the invention to provide an impact pile driving apparatus and an impact pile driving machine for applying the method according to the invention.

The aim of the invention is achieved by a method as well as by an impact pile driving apparatus and an impact pile driving machine, in which the embedding depth of the pile is measured, and the pressing device pressing the pile into the ground and the movement of the ram are adjusted according to the measured embedding depth so that when the impact-specific embedding depth is smaller than a predetermined minimum value, the impact energy generated by the ram moving back and forth within the hammer is increased (unless the maximum impact energy defined for the pile is exceeded), and the pressing force is decreased if the impact-specific embedding depth of the pile is greater than a predetermined maximum value (if the pressing force applied is lower than the highest applicable pressing force); if, on the other hand, the value of the impact-specific embedding depth is between the predetermined minimum and maximum values, the impact energy and the pressing force are kept unchanged. To put it more precisely, the method according to the invention is characterized by what will be presented in the independent claim 1 , the impact pile driving apparatus by what will be presented in the independent claim 9, and the impact pile driving machine by what will be presented in the independent claim 19. Dependent claims 2 to 8 present advantageous embodiments of the method according to the invention, dependent claims 10 to 18 present advantageous embodiments of the impact pile driving apparatus according to the invention, and dependent claims 20 to 21 present advantageous embodiments of the impact pile driving machine.

The method, the impact pile driving apparatus and the impact pile driving machine according to the invention have the advantage that impact pile driving into the ground can be optimized in such a way that the productivity of pile driving is increased and the costs per meter of pile driven into the ground are reduced, and thanks to pile driving information produced by the method, quality control and controlling of pile driving are facilitated. Furthermore, the method according to the invention has e.g. the advantage that noise and vibration involved in impact pile driving are reduced, because the pile may be partly driven into the ground by merely applying a static pressing force on the pile.

Description of the drawings In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows an impact pile driving machine comprising an impact pile driving apparatus equipped with a pressing device, in a side view;

Fig. 2 shows the impact pile driving machine of Fig. 1 seen in a front view; and Fig. 3 shows an operational chart of an embodiment of the a method according to the invention, applicable in an impact pile driving machine according to Figs. 1 and 2. Detailed description of preferred embodiments of the invention

Figures 1 and 2 show an impact pile driving machine 1 comprising an impact pile driving apparatus 20 equipped with a pressing device 10 operating according to the method of the invention. The impact pile driving machine 1 shown in Fig. 1 is intended, for example, for driving various piles, made of concrete or steel and used for the foundation of buildings and constructions, into the ground, for building a foundation with a desired load bearing capacity. In Figs. 1 and 2, such a pile to be driven into the ground is indicated with the reference numeral 30.

In Figs. 1 and 2, the impact pile driving machine 1 comprises a base machine 2 and an impact pile driving apparatus 20 in the front part of its frame 3, comprising a rig 4 and a hammer 5 movably mounted on the front side of the rig 4, to be movable along guides 6 in the longitudinal direction of the rig 4. For supporting the hammer 5 and for putting it down in a controlled manner against the pile 30 to be driven into the ground, the impact pile driving machine 20 comprises a hammer winch (not shown in the figures) mounted on the base machine 2, and a necessary supporting cable extends from the hammer winch via a supporting structure 7 or a so-called crown block at the top of the rig 4 to a fastening point at the top of the hammer 5. Thus, by means of the hammer winch controlled from the cabin 19 of the impact pile driving machine 1 , the hammer 5 can be lowered against the pile 30 held up parallel to the rig and to be driven into the ground. The base machine 2 is, for example, a non-road machine movable on the ground by a crawler or wheels, or on a railway by railway wheels; the rig 4 and the other devices and equipment needed for impact pile driving in the impact pile driving machine 1 can be mounted on the machine.

At the end of the hammer 5 to be abutted against the pile 30, a cushion element 8 is provided, against which the head of the pile 30 is abutted when the hammer is put down onto the pile 30. The function of the cushion element 8 is, among other things, to transmit and to dampen, in a suitable way, the impact loads imposed by the hammer 5 on the pile during driving of the pile 30 into the ground. A ram, movable back and forth by means of a hydraulic actuator, is provided within the frame of the hammer 5. In the bottom dead centre of the impact movement, the ram hits the cushion element 8. From the cushion element, the impact energy generated by the hammer is transferred to the pile 30 abutting it. By these impacts controlled from the cabin 19 of the pile driving machine 1 , and by the static force imposed on the pile 30 by the hammer 5, the pile 30 is driven into the ground in a controlled manner so that, in the end, the desired proportion of the total length of the pile 30 remains below ground level. When driving the pile 30 into the ground, the rig 4 is normally in the vertical position or in a desired oblique position with respect to the vertical direction. Thus, the hammer 5 rests against the top of the pile 30 so that it can move with the pile 30 downwards during the impact phase. The hammer 5 is pulled against the pile 30 by the gravitational force Gj of the hammer and by impulses effective on the cushion element 8 at intervals determined by the impact frequency of the ram. Furthermore, in the impact pile driving machine 1 shown in Figs. 1 and 2, the hammer 5 can be pressed against the head of the pile 30 by a pressing device 10. It comprises a force generating device for generating the necessary pressing force, and a transmitting member for transmitting the force generated by the force generating device to the hammer 5. In the embodiment of Figs. 1 and 2, the force generating device is a pulling winch 1 1 , and the transmitting member is a pulling rope 15.

In the embodiment of Figs. 1 and 2, the pressing device 10 comprises the pulling winch 1 1 , upper pulleys 12, a lower pulley 13, a resilient fixing element 14, and the pulling rope 15 wound from the pulling winch 1 1 via the upper pulleys 12 and the lower pulley 13 to the resilient fixing element 14 fixed to the hammer 5. The pulling winch 1 1 is, for example, a winch driven by a hydraulic motor, whereby the hydraulic motor rotates a drum on which the pulling rope 15 is coiled when the drum is rotated in one direction, and from which the pulling rope 15 is uncoiled when the drum is rotated in the other direction opposite to the preceding direction. The pulling winch 1 1 can be used to provide the pulling rope 15 with a pulling force Ft of a desired value; in other words, providing the hammer 5 with a pressing force F_p pressing the pile into the ground, in the range of F_p = 0 ... F_pmax. In this embodiment, the pressing force F_p to be provided is adjustable in a stepless manner by a controller in the cabin of the impact pile driving machine 1 . The pulling winch 1 1 also comprises a measuring device for determining the magnitude of the pressing force F_p generated by the pulling winch 1 1 (e.g. on the basis of a measurement of the pressure of pressurized medium supplied to the hydraulic motor, or by separate force sensors).

In this case, the pulling winch 1 1 is fixed to the rig 4 at the location shown in Fig. 2, on the left hand side of the rig 4, seen from the direction of Fig. 2. Naturally, the pulling winch 1 1 could be located e.g. at another point on the rig 4 as well, or it could also be placed at a point in the frame of the pile driving machine 1 , but this would require the use of more pulleys than in the embodiment shown in Figs. 1 and 2.

The upper pulleys 12, two in this embodiment, are located at the top of the rig 4 as shown in Figs. 1 and 2. The function of the upper pulleys 12 is to guide the pulling rope 15 extending from the pulling winch 1 1 in the direction opposite to the direction of impact, from the top of the rig 4 back in the direction of impact of the pile 30. The upper pulleys 12 may be freely rotatable rope pulleys made of e.g. steel or another material of sufficiently strength, and mounted on bearings on supporting frames to be installed in the structures of the rig 4. On the outer track of the upper pulleys 12, a rope groove having a suitable depth is provided, in which the pulling rope 15 remains when placed in the rope groove on the upper pulleys 12. The rotation axes 16 of the upper pulleys 12 are placed in such a way in relation to the rig 4 that they extend horizontally forward (in the direction of movement of the impact pile driving machine) as shown in Fig. 2. Thus, the pulling rope 15 running via the upper pulleys 12 winds, in this embodiment, via the upper pulleys 12 from the side of the rig 4 on the side of the pulling winch 1 1 (from the left, seen in the direction of Fig. 2) to the opposite side of the rig 4 (to the right, seen in the direction of Fig. 2).

The lower pulley 1 3 is placed in the lower part of the rig 4, in a location shown in Figs. 1 and 2, close to pile clamps 1 7 used for keeping the pile 30 upright and for guiding it. The lower pulley 1 3 is also a freely rotatable rope pulley which is made of steel or another suitable material and whose outer track is provided with a rope groove having a suitable depth for keeping the pulling rope 1 5 on the lower pulley 1 3. The rotation axis 1 8 of the lower pulley 1 3 is horizontal as well, but its direction deviates 90° from the direction of the rotation axes 1 6 of the upper pulleys 1 2 so that it points to the right, seen from the direction of Fig. 2. The pulling rope 1 5 winds around the lower pulley 1 3 from below, whereby the pulling rope 1 5 is guided to run in a direction parallel to the direction of movement of the hammer 5, opposite to the pile driving direction. Thus, the lower pulley 1 3 makes it possible to use the pulling rope 1 5 for pulling the hammer 5 along the rig 4 in the pile driving direction (that is, for driving the hammer 5 against the pile 30).

In the impact pile driving machine 1 according to Figs. 1 and 2, the resilient fixing element 1 4 comprises a fixing construction which is fixed to the hammer 5 and to which the pulling rope 1 5 is connected in a resilient way so that when the pulling rope 1 5 is pulled by a force Ft, its fixing point is movable, with respect to the fixing construction, in the pulling direction of the pulling rope, that is (when the rig 4 is in the position shown in the figures) downwards, when a determined minimum value Ftmin for the tensile force is exceeded. After this minimum tensile force Ftmin, any further movement of the fixing point will require a linearly increasing tensile force (according to a spring constant k) — rtmin + k^*s ( 1 ), wherein k is the spring constant,

s is the travel distance of the fixing point of the pulling rope 1 5. Consequently, when the hammer 5 is in its place against the pile 30 to be driven into the ground, the location of the fixing point of the pulling rope 1 5 with respect to the fixing construction will depend on the force by which the pulling rope 15 is pulled. After a given maximum tensile force Ftmax, the resilient fixing element 14 does not yield any more. However, if desired, the force Ftmax can be arranged so high that it will not be possible for the pulling winch 1 1 to generate a force exceeding the value Ftmax. Thanks to the resilient fixing element, the parts of the pressing device 10 are not overloaded when the hammer is pressed by the pressing force imposed by the device, i.e., in this embodiment by the pressing force F_p = Ft imposed by the pulling winch 1 1 . Naturally, this is best implemented when Ft does not reach the value Ftmax, because the resilient fixing element 14 will thus have some resilience left for dampening the transmission of the loads caused by the impacts to the different parts of the pressing device 10.

In practice, the resilient fixing element 14 may comprise e.g. a fixing construction with plate or beam structure, fastened to the hammer 5 in a suitable way and having a horizontal supporting element equipped with a hole through which the pulling rope 15 is fitted. A sleeve-like pressure spring (e.g. a coil spring, a cylindrical rubber spring or the like) is fitted above the hole, the diameter of the spring being clearly larger than the hole, and the pulling rope being fitted through the spring so that the end of the pulling rope extends further to the opposite side of the spring member. A pulling member (e.g. a base plate or a corresponding piece) which does not fit through the opening in the centre of the spring member is fastened to the end of the pulling rope that extends to the opposite side of the spring member. Thus, when the pulling rope 15 is pulled in the direction of driving the pile 30, the pulling member is placed on the spring member and tends to compress the spring member if the pulling rope 15 is pulled downwards. Thus, when the hammer 5 is in its place against the pile 30, the fastening point of the pulling rope 15 is movable in the pulling direction only if the pulling rope 15 is subjected to a tensile force Ft < Ftmin; a tensile force with a higher value causes compression of the spring member. In some cases, the spring member may be such that the threshold value Ftmin is very low, i.e. in practice Ftmin = 0, whereby the resilient fixing element 14 will start to yield immediately or almost immediately when the pulling rope 15 is subjected to a force that tightens it. Thus, the spring constant k may, however, be relatively high so that the pulling winch does not produce such a high force Ftmax by which the spring member would achieve its maximum movement. On the other hand, the Ftmin may also be so high that it is not reached by the pulling winch 1 1 but the spring member will still yield when the pile 30 is driven into the ground, because the impulses caused by the impacts will temporarily lead to forces resulting in exceeding the minimum tensile force Ftmin.

In this embodiment, the pulling rope 15 is a steel wire, but in principle it could also be a pulling rope of a different material having a sufficient strength. The pulling rope 15 should have such a tensile strength that it stands not only the tensile stress caused by the maximum pressing force F_pmax produced by the pulling winch 1 1 but also the dynamic load caused by the impact driving of the pile 30. In principle, the pulling rope 15 could also be made resilient, for example in whole or in some part, whereby it or its resilient part could replace the resilient fixing element 14 or act as one in addition to the resilient fixing element 14. In some cases it might be advantageous if the pulling rope 15 comprised a resilient part, or if the pulling rope were made of a slightly resilient material, because the pulling rope 15 would then provide extra resilience after the resilience of the resilient fastening element 14 has been exhausted. The spring constant of the pulling rope 15 in its pulling direction could be higher than the rigidity of the resilient fixing element 14, because the resilience would then always be expediently based primarily on the function of the resilient fixing element 14. On the other hand, this does not necessarily have to be the case, but in principle it is sufficient that in spite of its resilience, the pulling rope 15 withstands the maximum tensile force produced by the extraction winch 1 1 as well as the dynamic loads caused by the impact driving of the pile.

The adjustment of the pressing force F_p generated by the pulling winch 1 1 may be implemented manually or automatically as shown in the operational chart of Fig. 3. For adjusting the pressing force, it is possible to apply various methods of measuring the pressing force F_p. In the case of a hydraulic pulling winch 1 1 , the pressing force F_p can be determined from the pressure of the pressurized medium. In addition to or instead of this, it is possible to apply various measuring devices for direct measurement of the pressing force F_p, for example a power sensor, a load pin, a strain gauge, or another suitable sensor installed in a suitable location between the pulling winch 1 1 and the hammer, for measuring the pressing force F_p effective on the hammer.

If manual control is used, the operator of the machine adjusts the desired pressing force F_p by control devices in the cabin of the pile driving machine. This may also be implemented in a semi-automated way, for example in such a way that the cabin is equipped with a user interface, such as a touch screen or the like, on which the desired value of the pressing force F_p is entered. Thus, the automatic control device based on the measurement of the pressing force F_p adjusts the pressing force F_p according to the entered value. In this embodiment, the greatest pressing force Fvmax to be produced by the pulling winch 1 1 is 48 kN, but this value may vary in different embodiments of the invention, depending on e.g. the impact pile driving machine. Particularly when automatic control of the pressing force and the impact energy is used, the pressing force F_p should have a predetermined minimum value F_pmin. The minimum value F_pmin of the pressing force, that is, the lowest pressing force value used, may in some case be F_pmin = 0, whereby the hammer 5 is not pressed at all. On the other hand, the minimum value F_Pmin of the pressing force should be sufficiently high to prevent vibration of the hammer in a suitable way, and to keep the pulling rope of the pressing device taut. Thus, the pressing force F_pmin > 0 but still low (e.g. below 20% of the maximum value F_pmax of the pressing force) in a normal case. When driving the pile 30 into the ground by both impact driving and pressing, and applying manual control, the impact energy E, of the hammer 5 is adjusted as well (in the impact pile driving machine 1 of Figs. 1 and 2, by adjusting the height level and the accelerating force of the ram). The highest possible impact energy for the impact pile driving machine of the type shown in Figs. 1 and 2 is, for example, Eimax = 80 kNm when a height level of 1200 mm is used. However, these adjustment values may also vary, depending on the pile driving apparatus and the hammer used in it.

Applying automatic control of the pressing force and the impact energy according to the operational chart shown in Fig. 3, the operator of the pile driving machine 1 applies a switch, a control device or a button on a touch screen in the cabin of the device to select automatic control of the pressing force F_p and the impact energy E, for the impacts generated by the hammer. Thus, the control system of the pile driving machine 1 controls the pressing force F_p produced by the pulling winch 1 1 used as the pressing device 10, and the magnitude of the impact energy E, applied, by the principle of Fig. 3. For this, the pulling winch 1 1 is equipped with feedback to the control system of the pile driving machine 1 and thereby to the control of the movements of the ram within the hammer 5 as well. Furthermore, when applying automatic control of the pressing force F_p and the impact energy E,, the impact-specific embedding depth (embedding depth per impact) and the total embedding depth s^tot of the pile and the load carrying capacity Fk of the pile, so that the control system is informed of the progress of the pile driving process and the time when the final embedding depth stot and/or the final load carrying capacity Fk of the pile has been reached. On the basis of this data, the control system can adjust the magnitude of the pressing force F_p and the impact energy E, used, and determine when the pile has sunk to the desired embedding depth stot and/or when the desired load carrying capacity Fk has been reached. For determining the impact energy E, produced by the ram, measuring transducers are placed inside the hammer 5, for measuring the height level and the speed of movement of the ram. These may include e.g. two or more position sensors placed in different locations in the direction of movement of the ram and indicating the position of the ram during its impact movements back and forth. For taking precise measurements, a given reference point may be defined in the ram, whose position is recorded by the position sensors by changing their state when the reference point passes the position sensors during impact movements. By measuring the time between the state changes of the position sensors (i.e. the time taken by the ram for moving the distance between the position sensors), it is possible to determine the speed of movement of the ram before it hits the ram. The height level may be determined by position sensors and alternatively/additionally e.g. by means of the volume of the pressurized medium supplied into the piston-side cylinder chamber of the hydraulic cylinder moving the ram, because it determines the distance moved by the ram from the bottom dead centre upwards. Moreover, e.g. acceleration sensors fastened to the frame of the hammer may be used for determining the impact energy E,.

The embedding depth s of the pile 30 may be measured by measuring the position of the hammer 5 in a suitable location in the pile driving machine 1 , or with respect to a reference point in the ground. Normally, during impact pile driving, the rig 4 (or an integral part thereof) of the impact pile driving apparatus 20 is against the ground, so that a suitable reference point may be e.g. a point in the rig 4 (or an integral part thereof). Thus, the measurement of the embedding depth of the pile 30 may be based on e.g. a pulse sensor place in the pulling winch 1 1 , a pulse pulley between the hammer 5 and the rig 4, or laser distance measurement of the distance between a reference point in the rig 4 and the frame of the hammer 5. As presented in the operational chart in Fig. 3, when applying automated control, the control system controls the pressing force F_p produced by the pulling winch 1 1 and the impact energy E, of the ram moving within the hammer 5 (that is, typically e.g. the height level and the acceleration force of the ram) on the basis of the embedding depth of the pile by the following principles:

- If the embedding depth of the pile remains below a defined minimum value per impact s_min, the control system will reduce the pressing force F_p, unless the pressing force is below the minimum value F_pmin, and the control system will increase the impact energy E, unless the maximum impact energy E.max determined for the pile is exceeded.

- If the pile sinks deeper than the maximum embedding depth per impact s_max corresponding to one impact, the impact energy is reduced and the pressing force F_p is increased if this is possible (i.e. the pressing force is lower than the maximum pressing force F_pmax that can be achieved).

- If the pile sinks at least the minimum value s_min per impact or not more than the maximum value s_max per impact, the impact energy E, of the ram and the pressing force F_p are maintained. Furthermore, the control system controls the impact cylinder moving the ram in such a way that if the hammer 5 moves in the impact direction merely by the pressing force F_p caused by the pulling winch 1 1 and the gravity Gj of the hammer, the movements of the ram are not started at all or are totally stopped (if the embedding of the pile in an earlier pile driving phase has required impact driving of the pile). Thanks to this function, in some situations it is possible to totally avoid impact driving of the pile 30, causing noise and vibration, which is advantageous particularly when noise and vibration should be avoided in the area to be piled.

In the case of the impact pile driving machine 1 shown in Figs. 1 and 2, when piles 30 are driven into the ground, the impact-specific minimum value for the embedding depth s_min = 20 mm, and the impact-specific maximum value for the embedding depth s_max = 100 mm. However, these values may vary, depending on e.g. the pile driving apparatus/machine and the pile to be driven into the ground. In the selection of these values, the operator of the pile driving machine 1 may also exercise his discretion, e.g. according to the type of soil into which piles are being driven. Therefore, the impact-specific minimum value s_min and maximum value for the embedding depth s_max may be set as desired. The control system of the pile driving machine may also function in such a way that it determines the impact-specific limit values s_min and s_max for the embedding depth by means of data on the pile, the expected hardness of the soil, the data on the hammer, and other possibly relevant data.

In the practice of pile driving, the impact pile driving machine 1 according to Figs. 1 and 2 is transferred by moving the base machine 2 to a desired location where the impact driving of the pile 30 into the ground should take place. After this, the rig 4 is used to place the pile 30 onto the ground at the location where the pile 30 is to be driven, and by inclination control of the rig, the rig 4 is placed in a desired position, typically in a precisely upright position. Next, the hammer 5 is lowered by the hammer winch onto the head of the pile 30, whereby its upper end is placed against the cushion element 8. Also, an element 9 placed at the lower end of the rig 4 and telescopically movable in relation to the fixed frame of the rig 4, is moved against the ground so that the rig 4 will remain as stationary as possible during the impact driving of the pile 30 into the ground. After this, a desired pressing force F_p, which may be e.g. equal to the minimum pressing force F_pmin or a value slightly higher than that, is adjusted in the pulling winch 1 1 of the pressing device 10, to be used for starting the pile driving. As a result, the pulling rope 15 is tightened so that the fastening point for the end of the pulling rope 15 in the resilient fixing element 14 is movable in the direction of the impact driving of the pile 30 (downwards in Figs. 1 and 2) if the tensile force Ft effective on the pulling rope exceeds the value Ftmin. It should be noted that the tensile force Ft does not have to exceed the value Ftmin. Typically, however, at the beginning of pile driving with the pulling winch 1 1 , the tensile force Ft of the pulling rope 15 needed for producing the pressing force F_p is higher than the value Ftmin but normally always lower than Ftmax. Thus, the pile 30 is subjected to a total force F_pt₀t pressing it against the ground and having a value equal to the sum of the tensile force Ft and the gravitational force Gj of the hammer 5. Driving the pile 30 into the ground by applying the method of automatic control of the pressing force F_p and the impact energy Ej of the ram, as shown in Fig. 3, is continued as follows:

1 . If the soil is sufficiently soft, it may occur that the pile 30 begins to sink into the ground already at this stage, that is, without impact driving by the ram. If this is the case, the control system will not start the movement of the impact cylinder and the ram, but the pile 30 is allowed to sink into the ground as long as the combined action of the pressing force F_p produced by the pulling winch 1 1 and the gravitational force Gj of the hammer (i.e. the total pressing force F_pt₀t) is sufficient for this. If the combined effect of the pressing force F_p and the gravitational force Gj effective on the hammer corresponds to or is higher than the targeted load bearing capacity of the pile 30, the ram is not used at all. Thus, the hammer 5 is held against the end of the pile 30 until its progressive movement is stopped, the pressing force F_p being adjusted so that the total pressing force F_pt₀t effective on the pile 30 corresponds to the desired carrying capacity. After that, the pressing force F_p produced by the pulling winch 1 1 is removed, the hammer 5 is lifted upwards, and the pile clamps 17 are released. After these measures, the driving of said pile 30 into the ground is completed and the pile driving machine 1 may be moved to the location of driving the next pile. 2. If the soil is so soft that the pile 30 first begins to sink into the ground by merely the combined effect of the pressing force F_v produced by the pulling winch 1 1 and the gravitational force Gj caused by the mass of the hammer 5, but the final load bearing capacity of the pile 30 is still greater than the sum of these forces, the pile 30 may first be allowed to sink into the ground by merely the effect of the pressing force F_p produced by the pulling winch 1 1 and the gravitational force Gj of the hammer 5 (whereby noise pollution caused by impact driving is avoided). However, right at the stage when the pressing force F_p produced by the pulling winch 1 1 and the gravitational force Gj caused by the mass of the hammer 5 are no longer sufficient to drive the pile 30 any further, the control system will start impact driving of the pile by means of the ram. The aim is to determine the height level of the pile to be used in such a way that the pile sinks by about 20 to 100 mm per impact, whereby the pile 30 sinks into the ground as soon as possible but without a risk of sinking too deep as a result of an impact. In this situation, however, the pressing device 10 which is formed of the pulling winch 1 1 , the upper pulleys 12, the lower pulley 13, and the resilient fixing element 14, will further increase the efficiency of embedding the pile 30, because it seeks to keep the hammer 5 tightly against the head of the pile 30 (i.e. prevents it from moving from the top of the pile in the direction opposite to the direction of impact driving when the ram starts to move and/or hits the cushion element 8 placed against the head of the pile 30), as well as increases the pressure effective on the pile 30 in the direction of driving the pile 30, in addition to the impacts and the gravitational force Gj of the hammer 5.

3. If the soil is so hard (firm) that the pile 30 does not sink into the ground at all without impact driving, the impact movements of the ram are started right after the pile 30 has been placed in the desired location against the ground and a suitable pressing force F_p has been generated in the hammer by the pulling winch 1 1 of the pressing device 10. Thus, during the whole driving of the pile 30 into the ground, the pressing device 10 will act in the same way as in the final part of point 2 above, that is, restrain the hammer 5 from rising upwards, which may typically be caused by a sudden strong acceleration of the ram at the beginning of the impact movement, or by an impulse caused by the cushion element 8 on the head of the pile 30 at the moment when the ram hits the cushion element 8 placed against the head of the pile 30. In this situation, the pressing force F_p produced by the pulling winch 1 1 is adjusted to be sufficient for preventing the movement of the hammer 5 in a direction opposite to the direction of the impact driving of the pile 30, and intensifies the driving of the pile 30 into the ground in a suitable way. However, this does not always require the use of the maximum tensile force F_pmax produced by the pulling winch 1 1 , but the desired effect is often achieved by even lower pressing forces F_p.

Further, it should be noted that the above mentioned three different example uses of the impact pile driving machine 1 of Figs. 1 and 2 are not the only ones possible, but the driving of the pile into 30 the ground may also be implemented by e.g. the conventional "impact pile driving method" so that the pressing force effective on the hammer 5 is not produced by the pulling winch 1 1 at all, that is, F_p = 0, whereby the hammer 5 is pressed against the head of the pile 30 by merely the gravitational force Gj caused by its mass.

The method, the pile driving apparatus and the pile driving machine according to the invention may be implemented, in many respects, in ways different from the example embodiment presented above. The pressing force to be generated in addition to the gravitational force caused by the weight of the hammer may be produced in many different ways in different embodiments of the invention. In principle, instead of being pulled by the pulling rope, the hammer might be pressed from above by a suitable transmitting member for pushing the hammer, which member may be resilient as such, or which may be fastened to the hammer by means of a resilient fixing member. Such a solution could be implemented, for example, by means of an actuator with a linear movement (e.g. a hydraulic cylinder generating a long thrust motion), placed in a suitable location above the hammer. Thus, the transmitting member could be a rigid transmission shaft, and the resilient fixing element could be another shaft placed between this shaft and the frame of the hammer and being telescopically movable in relation to the shaft, its movement with respect to the transmission shaft being made resilient by means of a helical spring (cf. a shock absorber). Also, the pressing device that pulls the hammer against the pile could be implemented by placing an actuator corresponding to the pulling winch 1 1 in the lower part of the rig. In this case, too, the pressing device could be a device different from the pulling winch, for example a hydraulic cylinder or another actuator producing a linear movement. In an embodiment, the pressing device could be formed of an actuator that generates a rotary motion and moves a transmitting member pressing the hammer against the pile, e.g. by means of a gear wheel or a chain wheel mounted on the drive shaft of the actuator, and a gear rack connected to the gear wheel or a chain connected to the chain wheel. In pressing devices based on a pulling rope, the location of the pulling winch for moving the pulling rope could also be, for example, in the lower part of the rig (e.g. approximately at the lower pulley 13 in the embodiment according to Figs. 1 and 2). On the other hand, the pulling winch could also be placed outside the rig 4, for example in connection with other parts of the impact pile driving machine 1 . In principle, the pulling winch could, in an embodiment of the present invention, be placed in connection with the hammer winch and be implemented e.g. in such a way that the actuator of the hammer winch would drive the rope drum actuating the pulling rope of the pulling winch by means of e.g. a coupling or the like. Thus, the pulling winch would not necessarily require a separate actuator at all, although a separate actuator makes it easier to make the pulling winch operate independently of the hammer winch.

Also, the arrangement for measuring the pressing force, the method of determining the impact energy, and the measurement of the embedding depth applied in the method according to the invention may be implemented in a way different from those presented above. For example, the embedding depth could be measured by a measuring device (e.g. a camera) installed to be completely separate from the pile driving machine and connected to the control system of the pile driving machine for determining suitable values for the pressing force and the impact energy. Furthermore, in a pile driving machine applying the method according to the invention, comprising a base machine equipped with a diesel drive engine, the control system of the pile driving apparatus is configured to control the rotation speed of the drive engine according to the magnitude of the impact energy of the ram and/or the pressing force of the pressing device. In addition to this, it is also possible to adjust the volume flow of the hydraulic pump per revolution (i.e. for example the angle of the slant plate of a hydraulic pump of a radial piston type). Thanks to such an arrangement, the power and thereby the fuel consumption of the of the drive engine of the pile driving machine is automatically adjusted to an optimal level, whereby the diesel fuel consumption and emissions per meter of pile driven into the ground are as low as possible in pile driving. Thus, the method, the pile driving apparatus and the pile driving machine according to the invention are not limited to the embodiment examples presented above, but in many respects, they may be implemented in different ways within the scope of the appended claims.

Claims

Claims:

1 . A method for controlling the pressing of a hammer (5) and the impacts of a ram in an impact pile driving apparatus (20), in which method the hammer (5) of the impact pile driving apparatus (20) is pressed by a pressing device (10) against a pile (30) during driving the pile (30) into the ground, characterized in automatically controlling the impact energy (Ej) imposed on the pile by a ram moving back and forth within the hammer (5) of the impact pile driving apparatus (20), and the pressing force (F_p) imposed on the pile (30) by the pressing device (10), on the basis of the measured embedding depth (s) of the pile, by the control system of the pile driving apparatus, in the following way:

- if the embedding depth (s) of the pile (30) remains below a predetermined minimum embedding depth per impact (s_min), the pressing force (F_p) is reduced and the impact energy (Ej) is increased), unless a maximum impact energy (Ejmax) determined for the pile (30) is exceeded;

- if the pile (30) sinks deeper than a maximum embedding depth per impact (Smax) corresponding to one impact, the impact energy (Ej) is decreased and the pressing force (F_p) is increased, provided that the pressing force (F_p) is lower than the highest pressing force (F_pmax) achievable by the pressing device (10);

- If the pile (30) sinks at least the minimum value (s_min) per impact or not more than the maximum value (s_max) per impact, the impact energy (E,) and the pressing force (F_p) are maintained.

2. The method according to claim 1 , wherein the pressing force (F_p) is reduced but not to a level lower than a given minimum pressing force (F_pmin).

3. The method according to claim 1 or 2, wherein the impact driving of the pile (30) is automatically stopped, if the pile (30) sinks into the ground without impact driving of the pile (30).

4. The method according to any of the claims 1 to 3, wherein impact driving of the pile (30) is started, if the driving of the pile (30) into the ground by mere pressing is stopped before the desired total embedding depth (stot) and/or the desired carrying capacity (Fk) of the pile is achieved.

5. The method according to any of the claims 1 to 4, wherein the impact- specific embedding depth (s) of the pile is measured by measuring the travel distance of the hammer (5) caused by one impact.

6. The method according to any of the claims 1 to 5, wherein the pressing force (F_p) imposed on the pile (30) by the pressing device (10), and the impact energy (B) produced on the pile by the ram moving within the hammer (4), are measured simultaneously during driving the pile (30) into the ground.

7. The method according to any of the claims 1 to 6, wherein the pressing force (F_p) caused by the pressing device (10) is measured by a power sensor.

8. The method according to any of the claims 1 to 7, wherein the speed of movement of the ram moving within the hammer is measured for determining the impact energy.

9. An impact pile driving apparatus (20), the impact pile driving apparatus (20) comprising a rig (4) and a hammer (5) which is movable along the rig (4) and comprises a ram movable back and forth within the hammer (5) for producing impacts on the head of a pile (30) to be placed against the hammer (5), the impact pile driving apparatus (20) comprising a pressing device (10) for pressing the hammer (5) against a pile (30) during driving the pile (30) into the ground, characterized in that the impact pile driving apparatus (20) comprises a control system configured to control the impact energy (Ej) to be applied on the pile by the ram movable back and forth within the hammer (5), and to control the pressing force (F_p) produced by the pressing device (10) according to the embedding depth (s) of the pile as follows:

- if the embedding depth (s) of the pile (30) remains below a predetermined minimum embedding depth per impact (s_min), the pressing force (F_p) is reduced and the impact energy (E,) is increased), provided that a maximum impact energy (Eimax) determined for the pile (30) is not exceeded; - if the pile (30) sinks deeper than a maximum embedding depth per impact (Smax) corresponding to one impact, the impact energy E,) is decreased and the pressing force (F_p) is increased, provided that the pressing force (F_p) is lower than the highest pressing force (F_pmax) achievable by the pressing device (10);

10. The impact pile driving apparatus (20) according to claim 9, wherein the pressing device (10) comprises a pulling winch (1 1 ) driven by a hydraulic actuator and connected by a transmitting member (15) to the hammer (5).

1 1 . The impact pile driving apparatus (20) according to claim 10, wherein the transmitting member (15) is resilient and/or connected to the hammer (5) by means of a resilient fixing element (14).

12. The impact pile driving apparatus (20) according to any of the claims 9 to

1 1 , wherein a power measurement sensor for measuring the pressing force is provided in the pressing device (10), between the pressing device (10) and the hammer (5), or in the hammer (5).

13. The impact pile driving apparatus (20) according to any of the claims 9 to

12, comprising a measuring device for measuring the speed of movement, or the height level, of the ram movable within the hammer (5).

14. The impact pile driving apparatus (20) according to claim 13, wherein the device for measuring the speed of movement of the ram comprises at least two position sensors configured to change their state when the ram moves past the position sensors, whereby the speed of movement of the ram can be determined by means of the period of time between the state changes of the position sensors.

15. The impact pile driving apparatus (20) according to any of the claims 9 to 14, comprising a device for measuring the embedding depth of the pile (30).

16. The impact pile driving apparatus (20) according to claim 15, wherein the device for measuring the embedding depth of the pile (30) is a pulse sensor placed in a pulling winch (1 1 ).

17. The impact pile driving apparatus (20) according to claim 15, wherein the device for measuring the embedding depth of the pile (30) is a pulse pulley arranged in the hammer (5).

18. The impact pile driving apparatus according to claim 15, wherein the device for measuring the embedding depth of the pile (30) is a distance measuring device for measuring the distance from a reference point in the rig (4) to the hammer (5).

19. An impact pile driving machine (1 ) comprising a base machine (2) and a pile driving apparatus (20) according to any of the claims 9 to 18.

20. The impact pile driving machine (1 ) according to claim 19, wherein the base machine (2) comprises a diesel-fuelled drive machine, and wherein the control system of the pile driving apparatus (20) is configured to control the rotation speed of the drive machine on the basis of the amount of the impact energy (Ej) of the ram and/or the magnitude of the pressing force (F_p) of the pressing device.

21 . The impact pile driving machine (1 ) according to claim 19 or 20, comprising at least one hydraulic pump with adjustable volume flow per rotation, wherein the control system of the pile driving apparatus (20) is configured to to control the volume flow of the hydraulic pump per rotation on the basis of the amount of the impact energy (Ej) of the ram and/or the magnitude of the pressing force (F_p) of the pressing device.