The present invention relates to a linear driver and particularly, but not exclusively, to a linear driver for use in the field of civil engineering or construction, for example in the formation of piles or piers as foundations.

It is conventional to provide a foundation as the lowest supporting layer of a structure to be built or else to shore up the ground. In general, foundations can be split into two different categories, so-called shallow foundations and deep foundations, with the only real difference between the two categories of foundation being the depth to which they are embedded in the ground.

A well-known form of deep foundation is a so-called pile, or pier, which is typically an elongate structure that is located in the ground. Piles can either be

prefabricated, in which case they are generally driven into the ground by a pile driver, or they can be cast-in-situ. There are many existing techniques for forming cast-in-situ piles, very often involving the formation of a hole in the ground, and filling such a hole with cementitious material. Upon setting, the cementitious material solidifies to provide the desired pile.

One of the challenges faced during the provision of cast-in-situ piles is the formation of the hole in which the pile necessarily sits. Traditional methods include using a rotation auger, or hammering or vibrating an upper end of a tube or mandrel into the ground, and then either removing the tube or mandrel before or during the operation of filling the hole with concrete, or leaving the tube or mandrel in position to form part of the pile. There are, however, several disadvantages associated with such methods.

In order to reach the depth required in the ground, a large amount of energy needs to be employed. Furthermore, the length of a pile former used to reach the required depth in the ground often necessitates the use of large support structures and associated equipment, which can be expensive, time consuming to mobilise, and which may pose a significant risk to the safety of workers involved in the formation of the required pile. These disadvantages in general make the provision of cast-in-situ piles unsuitable for a number of applications, and thus cast-in-situ piles are generally used only in large scale, or large load-bearing, construction projects.

A further disadvantage arising from the need to impart a large amount of energy to the pile formers is the large amount of noise and disruption that pile driving generally creates. A typical percussive pile driver comprises a mechanical or hydraulic actuation system for repeatedly raising a weighted impact member, or hammer, which is then allowed to fall under the influence of gravity onto the top of a pile former or pile to drive it into the ground. Each impact generates a large amount of noise, which is particularly undesirable if construction is taking place in already built-up areas, eg close to existing residences or office buildings.

An alternative driving method which avoids such impacts is a so called 'diesel hammer', where the driving is achieved by a weight which acts as a piston in what is effectively a large single cylinder two-stroke diesel engine. The weight is initially raised by mechanical means, drawing air into a cylinder formed between the piston and the head of a pile former. Diesel fuel is then injected into the cylinder and the weight is released, compressing the fuel-air mixture to the point where combustion takes place. The combustion drives the pile former downwards, and simultaneously drives the weight upwards drawing more air into the cylinder. The cycle then repeats, driving the pile further into the ground. Diesel hammers thus avoid the physical impacts between the weight and the pile former, but the combustion events mean that they are typically even louder in operation than percussive hammers, so do not overcome this shortcoming. One approach to mitigating noise is to use a vibratory pile driver containing a system of counter-rotating eccentric weights designed in such a way that horizontal vibrations cancel out, while vertical vibrations are transmitted into the pile. One major drawback with vibratory pile driving is that soil conditions and the installation procedure can greatly affect the bearing capacity of vibrated piles, so the method is only suitable for use with certain soil types, and even then the bearing capacity of vibratory driven piles is difficult to predict with any degree of certainty. In addition, the intensity of ground vibrations generated can be problematic, and it is extremely important to avoid resonance in the ground or at adjacent structures or structural elements. The method is also relatively costly as it requires special equipment.

It is an aim of the invention to provide an improved driving method, suitable for use in a pile formation system, which overcomes or substantially mitigates the aforementioned and/or other disadvantages associated with the prior art.

According to a first aspect of the invention there is provided a hydraulically or pneumatically operated linear driver as defined in the appended claim 1 . Further advantageous features of the invention are recited in the associated dependent claims.

The linear driver comprises a driving member, a weighted sleeve slidable relative to the driving member, and a valve arrangement connected to the driving member, wherein the valve arrangement controls fluid pressure in a region between the driving member and the weighted sleeve to linearly move the weighted sleeve in first and second directions relative to the driving member. Closing the valve arrangement during use stops movement of the weighted sleeve in said second direction such that the momentum of the weighted sleeve is transferred to the driving member without physical impact between the weighted sleeve and the driving member.

When used as a pile driver, the invention is oriented vertically and the driving member is engaged with a pile former. The weighted sleeve is then raised, lowered and stopped relative to the driving member using controlled pneumatic or hydraulic pressure. Using the valve arrangement and fluid pressure to stop the sleeve transfers the momentum of the weighted sleeve to the driving member without any physical impact. The valve, seals and hydraulic fluid take the 'impact', such that the loud noise (and vibration) of a typical hydraulic hammer is avoided.

The weighted sleeve may be internal or external to the driving member.

Preferably, the valve arrangement is located in the region between the driving member and the weighted sleeve. The valve arrangement can thereby divide this region into two separate regions or chambers, and selectively allow flow between the chambers via a relatively short flow path.

For ease of assembly, the driving member may comprise first and second parts which are connected, for example by screw threads, to opposite sides of the valve arrangement. The first and second parts of the driving member may have substantially the same external dimensions, or may have different external dimensions to provide a simple means of providing two different external dimensions/diameters on the driving member.

The driver may further comprise attachment means, such as a clamp or latch, for attaching the driver to a pile former or similar elongate article. The driving member may be a tube, and may surround the pile former or elongate article in use.

Alternatively, driving member may be a solid rod or similar, possibly with a driving flange, for use as an end drive hammer/driver. The attachment means may provide selective engagement with the pile former. The driver may further comprise a housing, surrounding and slidably connected to the driving member, which comprises means for attaching the driver to a support structure. Due to the reduced noise generated by the driver of the present invention, the housing need not be acoustically sealed, and may be an open sided housing such as a cage to minimise weight of the driver.

The driver may further comprise an actuator to provide a signal to close the valve arrangement before the weighted sleeve impacts the driving member. The actuator may comprise an actuator rod which is depressed by the weighted sleeve as it moves in the second direction. Engagement of the sleeve with the actuator rod shortly before impact with the elements of the driving member would provide a simple means for ensuring correct timing of the valve closure. The driver may also comprise an adjustable valve for controlling the fluid pressure applied during operation and/or one or more sensors to monitor fluid pressures during operation.

The invention also provides a driving system for a piling operation as defined in appended claim 19. The system incorporates a linear driver as previously described.

In the driving system, a mast or similar support is provided for supporting the driver in a substantially vertical orientation. A lower end of the mast may be held in contact with the ground during use of the driving system.

An adjustable carrier may be provided, mounted between the mast and the driver, to permit vertical movement of the driver relative to the mast, and movement of the driver relative to the mast may be controlled by the adjustable carrier. The adjustable carrier may comprise, for example, a belt or chain and pulley system or a hydraulic actuator/cylinder.

The mast may be mounted to a purpose built rig or, due to the weight savings of the present invention, to a number of alternative carriers such as the arm of a tracked excavator.

Finally, the invention provides a method for testing soil properties prior to a piling operation as defined by the appended claim 27. The method uses a particular embodiment of the linear driver previously described.

The testing method comprises mounting a driver with at least one sensor to a support, repeatedly driving an elongate member into the ground to be tested using the driver, and monitoring and recording the pressure readings during the driving operation.

Any of the optional features described in relation to any single aspect of the invention may be applied to any other aspect of the invention.

Practicable embodiments of the invention are described in further detail below with reference to the accompanying drawings, of which: Figure 1 is a schematic view of a pile driver according to a first aspect of the present invention;

Figure 2 is a schematic view of a valve arrangement from the pile driver of Figure 1 ;

Figure 3 is a cross-section of the valve arrangement shown in Figure 2;

Figures 4 to 1 1 are schematic views of the pile driver and valve

arrangement at various stages in its operation;

Figure 12 is a side view of a system according to an example of the invention when supported in use;

Figures 13 and 14 are side views of the system driving a pile former into the ground;

Figures 15A and 15B show an alternative driver according to the present invention;

Figures 16A and 16B show an actuator for use in the present invention;

Figures 17 to 21 are schematic views showing an alternative driver and valve arrangement according to the invention in operation; Figure 22 is a graph indicative of the force transferred to a pile by a conventional hammer/driver during use; and

Figure 23 to 24 are similar graphs indicative of the force transferred to a pile by a driver according to the present invention.

A first embodiment of a pile driver according to the present invention, in the form of a pile driver 1 , is shown in Figure 1 . The pile driver 1 comprises a driving tube 2 which is shown located around a pile former 4 and attached thereto by a clamp 6 at its lower end. A cage 8 is slidably mounted to the driving tube and provides a means for attaching the pile driver to a mast 10 or other supporting fixture. Typically, piling hammers have to incorporate a housing that is fully sealed to attenuate airborne noise. Such housings are heavy, which increases the overall weight of the hammer. The quieter operation of the driver according to the invention avoids the need for such housings, so that a simpler, lighter housing, for example a cage type housing, can be used.

A weighted sleeve 12 is located around the driving tube 2 and within the cage 8. Both end portions 14,16 of the weighted sleeve 12 are in sealing contact with an outer surface of the driving tube 2, while a length of the sleeve 12 between these portions is spaced from the driving tube 2 to define an annular space 18 for receiving hydraulic fluid. The weighted sleeve 12 comprises a hydraulic cylinder body with a separate heavy collar which is fastened to a flange on the cylinder body. This allows the weight of the sleeve 12 to be adjusted as required by substitution of the collar.

A valve arrangement 20 is located at approximately the mid-point of the driving tube. The pile driver 1 is assembled such that the valve arrangement 20 is received in the annular space 18 provided between the weighted sleeve 12 and the driving tube 2. In this regard, the lower end portion 16 of the weighted sleeve 12 is shown as a separate component to allow assembly of the weighted sleeve 12 around the valve arrangement 20. As shown in Figure 1 , the weighted sleeve 12 is at its lowermost position such that the valve arrangement 20 is at the upper end of the annular space 18. However, it will be appreciated that as the weighted sleeve 12 moves relative to the driving tube 2 the valve arrangement will effectively divide annular space 18 into upper and lower chambers.

The pile former 4 is shown as an elongate T section beam with a number of apertures 40 therein. In certain embodiments, the apertures may form a

convenient means of attaching the driving tube 2 to the pile former 4 such that substantially all physical impact between components, and thus all associated noise, can be avoided. There will, inevitably, be some physical contact due to mechanical clearances etc, but all avoidable contact is minimised by the present invention.

The cage 8 of the pile driver 1 is attached to the mast 10 by two brackets 50. The brackets 50 are connected to the mast 10 in such a way that upwards movement of the cage 8 relative to the mast 10 is at least selectively prevented, while downwards movement of the cage 8 relative to the mast 10 is permitted. For example, the brackets 50 may incorporate a ratchet or similar, or may be mounted to a carrier, such as a chain or belt, which is selectively movable relative to the mast 10. The cage 8 would be rigidly connected to such a drive mechanism, permitting the pile driver 1 to be driven up and down the mast. When not in active use the assembly can be locked in position to prevent any unexpected movement. In a mechanical system this could be achieved by a mechanical brake, and if a hydraulic actuator is fitted, then hydraulic lock valves should be fitted.

The valve arrangement 20 is shown in greater detail in Figures 2 and 3. The valve arrangement 20 comprises two galleries in the body of the valve arrangement 20. The two galleries effectively take the form of pipes, which for ease of reference will be referred to as a return pipe 22 and a feed pipe 24, each connected to a fluid line 26,28 from a three position control valve 30. The position of the control valve 30 is set by pilot operation valve feeds 31 ,33. The control valve 30 is shown in Figure 2 in a central 'float' position, with no pressure applied to either the feed or return pipes 22,24. The return pipe 22 leads to an upper return port 32 and a lower return port 36, and a first valve spool 42 is provided to selectively open or close the ports 32,36. Similarly, the feed pipe 24 leads to upper and lower feed ports 34,38, and a second valve spool 44 is provided to open or close these ports 34,38. Both valve spools 42,44 are shown in their neutral, central, position in Figure 2 with all four ports 32,34,36,38 open. Further pilot feeds 43,45 are employed within the valve arrangement 20 to move the valve spools 42,44 as required.

For ease of manufacture, the valve arrangement 20 is formed as a standalone component and is assembled into the driving tube 2 as follows. The driving tube 2 is provided in two sections 2A,2B as indicated in Figure 2. The valve arrangement 20 is joined to the upper section 2A of the driving tube 2 in the region indicated at 46 in Figure 2 via an external thread on the valve arrangement 20 and a

corresponding internal thread on the upper section 2A of the driving tube 2. The lower section 2B of the driving tube 2 is similarly joined to the valve arrangement 20 in the region indicated at 48. Figure 2 shows the weighted sleeve 12 in a raised position compared to that shown in Figure 1 , so that the annular space 18 is divided into an upper chamber 18A and a lower chamber 18B by the valve arrangement 20. The ends 14,16 of the weighted sleeve 12 are not shown in Figure 2, and the actual weight is also omitted for clarity.

Although not clearly shown in Figure 2, the outside diameter of the upper section 2A of the driving tube 2 is larger than the outside diameter of the lower section 2B. The internal diameter of the weighted sleeve 12 is constant, with the result that the cross-sectional area of the upper annular chamber 18A is smaller than that of the lower chamber 18B. The reasons for this will be explained later, but the use of separate upper and lower sections 2A,2B simplifies the inclusion of two different outer diameters on the driving tube 2 to achieve this result. In the illustrated example, the outside diameter of the upper section 2A is 212mm and the outer diameter of the lower section 2B is 21 1 mm, while the inside diameter of the weighted sleeve 12 is 225mm, so the difference in area between the upper and lower chambers 18A,18B is relatively small. It will be readily appreciated, however, that alternative dimensions could be used and/or that a larger difference could easily be achieved through the provision of an upper section 2A with a larger outer diameter and/or a lower section 2B with a smaller diameter.

Figure 3 shows a cross-section taken through the valve arrangement 20, the lower section 2B of driving tube 2 and the weighted sleeve 12 of Figure 2. Again, the weight is omitted for clarity. Figure 3 also shows the T section pile former 4 around which the valve assembly is positioned in use. The feed and return pipes 22,24 of the valve arrangement 20 are accommodated in the spaces between the web and the flanges of the T section pile former 4 (it should be noted that the views of Figures 2 and 3 are taken at 90° to that of Figure 1 ). This helps to minimise the outside diameter of the apparatus, although different arrangements would be possible for differently shaped pile formers.

Operation of the pile driver 1 will now be described with reference to Figures 4 to 1 1 .

Figure 4 shows the pile driver 1 , attached by its clamp 6 to a pile former 4, with the weighted sleeve 12 still resting in its lowermost position as in Figure 1 , and the valve arrangement 2 at an upper end of the annular space 18. The pile former 4 is first pushed into the ground by forcing the pile driver 1 vertically downwards. It will be understood that any upwards movement of the cage 8 relative to the mast 10 will be resisted by the brackets 50 and/or the carrier such that the entire pile driver 1 will move downwards as a unit. The pile former 4 is forced into the ground in this way until the ground resistance equals the downward force applied to effectively 'set' the pile former 4 prior to operation of the pile driver 1 . Once the pile former 4 is set, the weighted sleeve 12 is raised from its rest position. As shown in Figure 5, the control valve 30 is actuated to apply a low pressure to the feed pipe 24, and the second valve spool 44 has been moved to close the lower feed port 38 while leaving the upper feed port 34 open.

Simultaneously, the first valve spool 42 has been moved to close the upper return port 32 while leaving the lower return port 36 open. An upper port 34 of the valve arrangement 20 is therefore pressurised while a lower port 36 is connected to tank, which will force the weighted sleeve 12 to rise relative to the driving tube 2.

This lifting operation generates a reaction that could force the driving tube 2 and pile former 4 downwards. Setting the pile former 4 as outlined above provides a reaction force which prevents this uncontrolled movement and ensures a known position prior to the driving operation. This is important for calibration and monitoring of the driving operation.

The weighted sleeve 12 is raised to a position approximately 25mm below its fully raised position within the cage 8, and end damping is then applied to the lower port 36 to retard movement of the weighted sleeve 12 and prevent hard impact with the lower face of the valve arrangement 20. This prevents any impact damage and reduces noise emitted from the driver.

After damping the weighted sleeve 12 is taken to its fully raised position and sensors check when the sleeve 12 has come to rest. This monitoring of the fully raised position before the weight is fired downwards is important to ensure that a desired stroke length of the weighted sleeve is reliably and repeatably applied. It should be appreciated that both the start of the damping and the fully raised position of the weighted sleeve 12 can be adjusted and controlled hydraulically if desired to alter the stroke length and/or the size of the damping region. Figure 6 shows the weighted sleeve 12 at its fully raised position. The annular space 18, full of hydraulic fluid, can now be seen above the valve arrangement 20. The relatively small cross-sectional area of the annular space 18 in the illustrated example means that relatively little hydraulic fluid must be moved in order to raise the weighted sleeve from the position shown in Figure 4 to the position shown in figure 6. For a 100mm section pile former 4, typically less than one litre of hydraulic fluid is required. Furthermore, the small size and central location of the valve arrangement 20 provides a short path for the transfer of fluid from the lower chamber 18B to the upper chamber 18A. The cross-sectional area is dictated by the hydraulic forces necessary to raise and lower the weighted sleeve 12 with maximum efficiency and reduce flow rates through the valves and pipework to minimize back pressure and efficiency losses. From the position shown in Figure 6, pressure is applied to both sides of the valve arrangement 20, as illustrated in Figure 7. The control valve 30 is shown moved to a third position applying pressure to both the feed pipe 24 and the return pipe 22. The pressure applied is higher than that applied to raise the weighted sleeve 12 as described in relation to Figures 4 and 5. Both the first and second valve spools 42,44 are centrally located so that all ports 32,34,36,38 of the valve arrangement are open. Equal pressure is therefore applied above and below the valve arrangement 20, and free flow through the valve arrangement 20 is permitted. Figure 8 shows the weighted sleeve 12 moving downwards from its fully raised position. An upper annular chamber 18A is shown separated from a lower annular chamber 18B by the valve arrangement 20. As described previously, the cross- sectional area of the upper chamber 18A is smaller than that of the lower annular chamber 18B. Accordingly, the equal pressure applied to both chambers 18A,18B creates a force imbalance that acts along with gravity to drive the weighted sleeve 12 downwards. During this driving step the valve arrangement 20 remains open as shown in Figure 9.

The force applied to the sleeve 12 is dependent both on the relative areas of the upper and lower chambers 18A,18B and on the pressure applied during the driving step. Therefore, for a given apparatus the force can still be varied by increasing or reducing the pressure applied using an adjustable 'force control' valve 52. In the illustrated example the additional force is sufficient to cause the sleeve 12 to accelerate at around 15ms ^"2 , to a velocity of around 4.5ms ^"1 .

The weighted sleeve 12 is driven downwards until it reaches a position about 25mm from impact with the upper face of the valve arrangement 20, as shown in Figure 10. Depending on the particular operational requirements, the set distance may be greater or less than 25 mm. At this point, a predetermined induced back pressure is applied between the weighted sleeve 12 and the valve arrangement 20 in the upper chamber 18A.

Figure 1 1 shows the valve spools 42,44 in position to apply the back pressure. The first valve spool 42 is moved to close the upper return port 32, thereby cutting off the return path for fluid from the upper chamber 18A. Fluid trying to exit the upper chamber via the open upper feed port 34 is blocked from flowing back to source by the non-return valve 53, and is forced instead towards the force control valve 52.

The blocking of return flows effectively closes off the upper chamber 18A, and the pressure of the fluid remaining in this region resists further downward movement of the weighted sleeve 12.

The applied back pressure stops the movement of the weighted sleeve 12 before it contacts the valve arrangement 20. As movement of the weighted sleeve 12 is stopped, its momentum is transferred to the driving tube 2 and thereby to the pile former 4 to drive the pile former into the ground. The transfer of momentum occurs without any physical contact between components of the pile driver 1 , with the 'impact' instead being taken by the hydraulic fluid and seals within the valve arrangement 20. Assuming the ground resistance is less than the induced force applied to the driving tube 2, then all the force will be transferred to the pile former 4, moving it downwards until the ground resistance equals the applied force. A 'push' will be applied throughout the driving cycle rather than relying on a sudden impact blow. By virtue of the brackets 50 allowing downward movement of the cage 8 relative to the mast, the cage is free to move downwards as the driving tube 2 is driven downwards. If the ground resistance is greater than the applied force, or at the point where the forces are balanced during normal operation, hydraulic fluid will be forced through the force control valve 52 which acts as a relief valve. The relief part of the force control valve 52 will be set to a particular pressure rating, such that fluid will pass through the valve 52 only if the back pressure exceeds a certain predetermined value, chosen based on numerous criteria relating to the particular driving process, and limited by the rating of the seals and other hydraulic components. Once the back pressure drops below this value, the system will again be effectively 'locked' such that force is again transferred to the driving tube 2. In the case of extremely hard ground, the hydraulic fluid will be forced through the force control valve 52 until exhausted. Movement of the weighted sleeve 12 into contact with the valve assembly is thereby damped, avoiding the noise and potential damage associated with a sudden impact.

In some circumstances, such as in very soft ground, where a void exists below a hard crust, or in circumstances where the pile former has not been correctly 'set', the driving tube 2 may move downwards more quickly than the cage 8. In these circumstances, an upper stop 54 connected to the driving tube 2 will engage with an upper surface 56 of the cage 8 to pull down the cage until the free movement of the cage 8 overtakes the driving tube 2 and returns it to the rest position. In the illustrated example contact between the stop 54 and the upper surface 46 of the cage 8 occurs after 160mm of relative movement between the driving tube 2 and the cage 8.

This failsafe is important in ensuring that the invention continues to function in the event of 'runaway' of the driving tube 2 as set out above. However, relying on this is undesirable since the impacts between the stop 54 and the cage 8 generate precisely the type of noise which the invention seeks to avoid, and can also cause damage to the cage 8 and the pile driver 1 as a whole. The need to rely on the failsafe can be largely avoided by ensuring the pile former 4 is correctly set before operation. However, in some circumstances the ground conditions are such that very little resistance is provided to the pile former 4, and in such circumstances 'runaway' can still occur even if the pile former 4 is set correctly. In these circumstances it is possible to adjust the back pressure applied and increase the size of the damped impact zone using the adjustable valve 52. This results in a longer and softer hit or push being applied to the driving tube 2, reducing the risk of runaway. The same adjustment may also be used to for the first few blows of any operation to give an indication of the ground strength and resistance.

As described above, the valve arrangement 20 of the invention is designed to transfer the force/momentum of the sleeve to the driving tube 2 to avoid physical contact between metal components and reduce, or eliminate, the associated noise. The hydraulic system also allows all variables, eg speed, stroke length, damping etc. to be readily controlled/adjusted as required, even during operation of the pile driver 1 , and by incorporating appropriate sensors the pressures throughout operation can be monitored and recorded to provide a record of the energy imposed. This allows properties of the ground to be demined and recorded during the pile driving operation.

Indeed, the simple control, measuring and recording of forces applied using the invention permit use of the device as a standalone investigation or analysis tool, for example for use in cone penetration testing. This beneficially allows a single apparatus to be used to first test the properties of the ground at a worksite and then subsequently to undertake the piling operation.

The relatively small size and weight of the pile driver 1 , and the relatively small volume of hydraulic fluid required for its operation, allows the mast to be fitted onto a quick hitch of a 9 to 13 tonne tracked excavator rather than requiring a large dedicated piling rig. Figure 12 shows this arrangement, with the pile driver 1 mounted on a mast 10 which is attached to the arm 56 of such a vehicle 60.

Investigations have revealed that a JCB JS130 will safely lift 1 .4 tonnes with its arm 56 fully extended. The use, in the present invention, of hydraulic pressure to actively drive the pile former 4 downwards means that the weight of the pile driver 1 can be kept within allowable limits while still being able to generate as much force as a much larger piling rig.

The pile driver 1 is shown in Figure 12 attached to a pulley system 58 which is in turn attached to a mast 10 supported by the arm 56. With the mast 10 held in contact with the ground 62, the pulley system 58 allows easy adjustment of the height of the pile driver 1 relative to the pile former 4. It should be noted that the height of the mast 10 and pulley system 58, and therefore the maximum height 66 of the pile driver is 5.5m, which is significantly lower than the length, and thus overall height 64, of the 8m long pile former 4. The combination of the lower weight and operating height of the pile driver 1 of the present invention are both clearly beneficial for the safety of site workers.

Figure 13 shows the pile former 4 partly driven into the ground. The pile driver 1 has been allowed to move downwards during operation by the pulley system 58. At this point, the clamp 6 is detached from the pile former 4 and the pile driver 1 is raised to a higher point on the pile former 4 using the pulley system 58 and reattached using the clamp 6. The driving operation is then repeated to continue driving the pile former 4 into the ground 62 as illustrated in Figure 14, at which point the pile former 4 has been driven to a depth 68 of 5 metres. At this point the pile former 4 can be removed, using the pulley system 58, to leave a hole 70 for filling with cementitious material, or the pile driver 1 can be raised again relative to the pile former 4 to allow for further driving.

Throughout the operation shown in Figures 12 to 14, it can be seen that there need be no movement of the arm 56 of the tracked excavator 60, or of the excavator itself. The mast 10 at the end of the arm 56 can held in contact with the ground to provide a stable platform during the piling operation.

The operation of the invention, along with its resulting small size and weight, allow the piling operation to be completed using a tracked excavator 60 rather than a dedicated piling rig. Tracked excavators 60 are almost inevitably required for other building operations, so this minimises the number of machines required on site. In addition, the size and weight of typical piling rigs means that there is a requirement to provide a piling mat, generally constructed from stone and waste spoil, to support and stabilise the weight of the rig. By avoiding this requirement a developer would benefit from significant time and cost savings.

Even if not optimised for use with a standard tracked excavator, minimising size and weight is further beneficial in avoiding the costs and administration associated with moving large heavy loads/machinery by road.

The above description relates to a preferred embodiment of the invention and is not intended to limit the scope of the appended claims. Various modifications would be possible. For example, alternatives to the pulley system 58, such as a slider arrangement, could be used to allow adjustment of the height of the pile driver.

Although the illustrated embodiment shows the pile driver 1 clamped to a pile former 4, the principles of the invention would apply equally to a similar device configured to rest on top of a pile former in a more conventional manner. For example, a flat plate could be included in the place of the clamp 6, and the arrangement could be pushed down against the pile former in the initial step to set the pile former as outlined above. The lack of a firm connection between the pile driver 1 and the pile former 4 has a number of drawbacks, including the likelihood of additional noise generation between these components. However, by allowing the driver to start from a position of contact with the pile former, the overall noise level is still expected to be lower than that of a conventional system.

Figures 15A and 15B provide an example of an alternative driver 101 in a configuration as a top drive hammer. The top drive hammer 101 is similar in certain respects to the pie driver 1 shown in Figure 1 , and shares many of the same benefits including quiet operation and light weight for versatile mounting and ease of transportation etc. However, the top drive hammer 101 comprises a solid cylinder rod 102 and driving flange 106 rather than a hollow driving tube and clamp for securing around a pile former.

A cylinder body 1 1 1 is provided with a removable/exchangeable weighted collar 1 13, these components together forming a weighted sleeve similar to that previously described. A housing 108 is provided around the weighted sleeve 1 1 1 ,1 13, and is provided with upper and lower slider bearings 107,109.

Figure 15A shows the top drive hammer in its raised position, while Figure 15B shows the lowered or dropped position, with damping provided by the fluid in an upper chamber 1 18A as in Figure 10.

Figures 16A and 16B show a pilot actuator 72 for use with a driver 1 ,101 according to the present invention. The actuator briefly comprises an actuator rod 74 and return spring 76 housed within an actuator body 78. The actuator body 78 is housed within a swivel housing 80 which is provided with a height adjustment thread 82. A pilot pressure port 84 is provided in the lower end of the actuator 72, and an air bleed valve and filter 86 is located at the upper end. The actuator 72 is shown in its free, unactuated, state in Figure 16A, while Figure 16B shows the actuator compressed in its energised state. The difference between the free height 88 and the compressed height 90 of the actuator rod 74 can be clearly seen. The actuator 72 is located, in use, at the lower end of the cage 8 or housing 108 surrounding the driver. For example, with reference to Figure 15A, on the lower part of the hammer support housing 108, just outboard of the lower slider bearing 109. The precise radial location will vary depending on the location of components such as hydraulic pipes and the associated available clearances. The role played by the actuator 72 will be explained during the following explanation of the driving operation as illustrated in Figures 17 to 21 . Figure 17 shows a driver/hammer at rest. A piston head/regeneration valve body 120 is shown which shares certain features and characteristics with the valve arrangement 20 described with reference to Figure 2, along with hydraulic schematics for operation of driver. The valve body 120 is secured between an upper cylinder rod 102A and a lower driving rod 102B. The cylinder body 1 1 1 surrounds this arrangement and abuts the external surface of the valve body 120 so that an upper chamber 1 18A is defined by the cylinder body 1 1 1 the valve body 120 and the upper cylinder rod 102A, and a lower chamber 1 18B is defined by the cylinder body 1 1 1 the valve body 120 and the driving rod 102B.

The upper and lower chambers 1 18A,1 18B are connected by 'C shaped

regeneration paths 123. This relatively short length of the regeneration paths, along with the central location of the valve body 120 within the system, minimises back pressure in the system during operation and permits high efficiency regeneration during the active part of the driving cycle.

To comply with the safety requirements of this type of installation, two independent controls have to be activated for the hammer to function. Accordingly, a hammer select valve 129 is provided upstream of a hammer operation valve 130. These two valves 129,130 control the flow of fluid to and from accumulators 125 upstream of the hammer select valve 129.

A pilot signal control valve 192 is included to provide a pilot signal to a pair of valve spools 142,144 within the valve body 120, to close off the regeneration path 123 as required.

A damping actuation signal 194 is provided by the pilot actuator 72 when the cylinder body 1 1 1 approaches a damping zone during operation. The damping pressure is controlled by a 400 bar pressure relief and unloading valve 196 which also permits unloading of this pressure, when the weight comes to rest. The system also includes a pilot relief valve 198. Figure 18 shows priming of the system ready for use. The hammer select valve

129 is actuated by solenoid or pilot signal, or possibly a combination, if high flows are involved. This directs pressure and flow to the hammer operation valve 130, which defaults to both signal ports being connected to the input. Oil is directed from here through the fluid lines 127 to both high pressure inlet ports on the piston head/valve body 120. With no pressure applied to either valve spool 142,144 pilot port, the valve then permits free flow to either side of the piston head 120.

As previously described in relation to Figure 2, the cross sectional area of the lower chamber 1 18B is greater than that of the upper chamber 1 18A, and therefore the lower piston head area exceeds the upper piston head area. As a result, the hammer weight remains in position at the bottom of its stroke, held in position by the force generated by the piston head differential area. This information is signalled to the electrical/electronic control system, which indicates that the system is ready to commence the hammer cycle.

The hammer weight raise is illustrated in Figure 19. The hammer operation valve

130 is selected automatically by the electric/electronic control system, whilst simultaneously the control system selects the pilot signal control valve 192. Pilot oil is delivered to both spools 142,144 of the piston head valve assembly 120, moving the two spools 142,144 in opposite directions. Specifically, as shown, the right hand valve spool 142 is moved upwards, and the left hand valve spool 144 is moved downwards. This results in the regeneration path 123 between the two chambers 1 18A,1 18B being cut off to allow pressurization of one chamber.

Main system pressure is now diverted through the fluid line 127 to the right hand inlet port of the piston head valve 120, while the left inlet port is connected to the tank return line. On the right inlet port to the piston head valve 120, the path to the lower cylinder chamber 1 18B is blocked, and pressurized oil is diverted to the upper chamber 1 18A. On the left port the path to the upper chamber 1 18A is blocked, therefore oil being ejected from the lower chamber 1 18B is allowed to return back to tank. Due to the pressure difference between the upper and lower chambers

1 18A,1 18B, the cylinder body 1 1 1 accelerates upwards at a rate dictated by the pressure difference. Electronic sensors then signal the control system to arrest the movement at a pre-set height.

Figure 20 shows the driving phase, or the hammer 'fall'. The electrical/electronic control system deselects the pilot signal control valve 192 and the hammer operation valve 130, connecting both piston head 120 valve spool pilot ports to tank. This returns the two spools 142,144 to their original balanced position, allowing free flow between the two chambers 1 18A,1 18B of the cylinder.

The hammer operation valve 130 is returned to its original position to divert pressurized oil via fluid lines 127 to both inlet ports of the piston head 120. Since the lower piston head area exceeds the upper piston head area, the cylinder body 1 1 1 and weight 1 13 accelerate downwards as the pressure is applied to both sides, due to the forces generated by the differential area and the acceleration due to gravity. This acceleration can be adjusted by varying the pressure applied to the cylinder. The adjustment can be executed manually or automatically, using inputs from pressure and speed sensors suitably positioned in the hammer.

Finally, the damping operation is illustrated in Figure 21 . At a predetermined position the actuator rod 74 of the pilot actuator 72 shown in Figure 2 is depressed by the hammer weight/cylinder body 1 1 1 ,1 13, shown in Figure 1 . This movement of the pilot actuator rod 74 generates a damping actuation signal 194 causing pressure and flow from the pilot pressure port towards the piston head 120 valve spool pilot ports, via a shuttle valve 199. This results in the left hand valve spool 144 moving sharply downwards, while the right hand valve spool 142 moves sharply upwards, synchronous with the movement of the weight 1 13. Balanced spools 142,144 are shown to permit this operation to be carried smoothly.

The right inlet to the lower chamber 1 18B is quickly blocked, stopping any oil regeneration from the upper chamber 1 18A via the regeneration path 123.

Similarly, the left inlet to the upper cylinder chamber 1 18A is quickly blocked, preventing any oil regeneration through that route. Ejected oil from the upper cylinder chamber 1 18A is now forced through the 400 bar relief valve 196 (this pressure limit can be adjusted to vary the applied force by the hammer). Make up oil is still supplied to the lower cylinder chamber 1 18B by the pressure feed through the left inlet, supplemented if necessary by the accumulator.

The pressure setting of the relief valve 196 should be mirrored by the pressure in the upper chamber 1 18A, thus imparting an equal and opposite force to the driving rod 102B and pile, which will be maintained until the energy has been dissipated. Accordingly, movement of the cylinder body 1 1 1 to a position where damping is required automatically generates the pressure signal 194 to initiate back pressure to stop the relative movement and provide damping to the system. This ensures, in a simple way, that movement is stopped and damping is applied at the correct time, regardless of differences in the movement of the cylinder due to varying conditions of, eg, ground during a piling operation, and is only provided when required.

When the cylinder body/weight 1 1 1 ,1 13 has come to rest, high pressure will be locked into the upper cylinder chamber 1 18A which could cause malfunction of the hammer operation valve 130 and possibly the pilot signal control valve 198 and prevent the piston head 120 reaching the end of its stroke. The pressure relief valve 196 is therefore fitted with an unloading feature to permit controlled venting of this trapped pressure, permitting the piston head 120 to return to its original position in a controlled manner. Once this has been executed, the hammer cycle can be commenced again.

It should be understood that, wherever practicable, the features defined in relation to any one aspect of the invention may be applied to any further aspect.

Accordingly the invention may comprise various alternative configurations of the features defined above.

Certain benefits of the drive provided by the present invention will now be described. A more traditional 'drop' hammer or driver, consisting of a weight accelerated either under gravity or hydraulic pressure, produces a certain amount of kinetic energy which is suddenly transferred to a pile or column at the point of impact. This kinetic energy is converted to work done on the pile or column, defined as the average force applied to the pile or column multiplied by the distance over which it is applied. In a graph plotting force against distance, the area under the curve is the total work done. Figure 22 shows an example trace 200 as would be expected for a typical drop hammer striking a pile at the set condition or striking very hard ground. Figure 23 shows a trace 202 indicative of the present invention operating with the same weight. In both Figures, the force F is plotted on the vertical axis and the distance s on the horizontal axis.

The first point to note is that the area under each graph is similar, but the force distribution is quite different. The present invention will deliver a more constant force over a longer distance, with a much lower peak than the conventional hammer. This provides a smoother 'push' than the sudden impact provided by a typical hammer/driver.

Another problem with the conventional systems is that the maximum force generated is not generally known. As a result, it is common to have to produce an SPT (standard penetration test) analysis of the ground, to establish the ground resistance and the depth to be driven.

The present invention advantageously allows a known particular driving force 204 to be selected for a driving operation. In the piling industry, the force may be selected to be appropriate for a particular size of pile. If the hammer force and pile specification are matched, there is much less possibility of damaging the pile.

Also, at set, if the driving force is known (as permitted by the invention), the pile resistance, and hence the pile load capacity, can be calculated from this information. In other words, the hammer/driver 1 ,101 can self-certificate each pile capacity.

To adjust the force applied, a known constant force could be pre-set and different relief cartridges provided to provide a different generated force from the same driver 1 ,101 . For example, three different force cartridges could be supplied with a hammer/driver 1 ,101 , each correlated/tuned to a different pile cross-section within a range. Additional cartridges could be supplied for special pile cross-sections to ensure the perfect driver is provided for each pile size and type.

Taking Figure 23 as indicative of a the set force for a typical driver/hammer 1 ,101 according to the invention, a lower set force 204A would likely provide a trace 206 as shown in Figure 24, and a larger set force 204B would likely provide a trace 208 as shown in Figure 25. The trace 206 of Figure 24 might be more suitable for smaller diameter piles and the trace 208 in Figure 25 might be better for larger piles. However, in each case, the area under each curve, and thus the total work done, would be similar.

A summary of some of the benefits provided by the present invention is provided below:

• The hydrostatic drive system with instrumentation can deliver a

predetermined level of kinetic energy and force to the driven member.

These values can be adjustable to suit a user's specific requirements.

· The unique piston head/valve body 20,120 with close coupled valve

arrangement which automatically closes off the regeneration oil path to divert the oil through a pressure control valve at the predetermined location, thereby creating a predetermined driving force to the driving member.

• The unique actuating system 72 which uses the hammer weight momentum to generate the pressure signal 194 to initiate the back pressure to permit the transmission of energy to the driving member. • The unique piston head/valve body 20,120 with close coupled valve arrangement which permits a direct oil path from inlet to outlet through the valve, offering minimal resistance and back pressure to regenerated oil during the working stroke, giving enhanced operating efficiencies.

· The hydrostatic drive system which transmits an energy and force to a

driven member without any metal to metal contact, greatly reducing sound generation from the impact.

• The cylinder body forms part of the overall hammer weight, this dual

function component saves on the weight of the driver assembly. Savings created by their being no need for soundproof cladding further reduces the overall weight.

• The drive system which can generate energy by accelerating a weight with hydraulic pressure or gravity or both, so can thereby operate at any attitude.

• The through rod configuration lends itself to equally end drive 101 or

through drive 1 configurations.

Finally, although developed as a pile driver for use in construction work, the general principles underlying the invention are also applicable to other smaller or larger scale devices for use wherever force transfer, in particular controllable measurable force transfer, is required. For example, smaller scale drivers for alternative uses, or percussive hammers for braking or compacting materials could make use of the driver according to the invention. Other specific uses of the invention include, but are not limited to, a top drive piling hammer for concrete or steel piles, a sheet pile driving hammer, a through drive piling hammer for a mandrel or poker and a soil displacement driver or boring tool such as a

Grundomat (RTM).

The active driving of the weighted sleeve makes use of the invention possible in orientations other than vertical, since gravity is not required for the driving process.