IMPROVEMENTS IN OR RELATING TO IN SITU PILE FORMATION

Abstract: A method of forming a pile in situ comprises driving a hollow casing (10) into the ground using a vibrator (114), and simultaneously supplying to a hopper (18) through which the casing (10) passes pile forming material, the casing (10) having a plurality of apertures (16) therethrough to allow ingress of pile forming material into the casing as it is descending, whereby on removing the casing (10) the material exits from an aperture (14) in the casing and to fill the hole provided by the casing and forms the pile.

Description: IMPROVEMENTS IN OR RELATING TO IN SITU PILE FORMATION The present invention concerns improvements in or relating to in situ pile formation and to pile driving apparatus, especially but not exclusively vibratory pile driving apparatus. There are many known methods of providing piles for supporting building structures. One of the simplest is to drive a preformed metal or concrete pile into the ground by applying a force to the top of the pile. A further method is to top drive a pile casing into the ground thereafter fit reinforcement, if necessary, and pour concrete into the pile casing. In a modification of this latter method the tubular pile is withdrawn after it has been driven to a sufficient depth and the thus formed hole filled with concrete before it collapses, the concrete then filling the hole in the ground, after setting, providing a concrete pile. This latter method is advantageous in that the relatively expensive steel pile casing can be re-utilised but it is disadvantageous as the hole often collapses before it is filled. If concrete is poured before the casing is removed from the hole and the entire length of the casing has not been completely driven, the open end of the pile through which concrete must be poured is located at a considerable height above ground level. This gives rise to difficulties in supplying concrete to the interior of the pile as concrete lifting or pumping apparatus is required. Vibratory pile driving means are becoming increasingly populer but they are of relatively great weight and this presents problems when the piles that they have to drive are relatively long, for example, over 20 metres in length. To provide transportability the vibrators are often mounted on a rig which in turn is carried by a modified excavator and to facilitate manoeverability, economy etc. it is desirable to use the smallest excavator capable of carrying the loads. This means that the excavator is relatively light but it is incapable of stably supporting the vibrator when it is at the top of the mast, for example, 20 metres above ground level. It is an object of the present invention to obviate or mitigate these and other disadvantages. In this specification the term "pile" is utilised to define not only a conventional integrated solid pile but also a stone column formed by a plurality of unbonded stone particles. According to the present invention there is provided a method of forming piles in situ comprising driving a casing into the ground to be piled whilst simultaneously supplying to the interior of the casing material to form the pile transversely through apertures in the casing. Preferably the casing is driven by a vibratory method, preferably the casing is top driven. Preferably the casing is driven through a hopper arranged at ground level into which the pile material is supplied. Preferably the hole formed by the pile casing is circular, rectangular or any other suitable cross-section. It may have radial protrusions extending therefrom. Preferably a circumferential protrusion is provided adjacent the leading end of the casing whereby the hole it provides in the ground has a cross-sectional area greater than the cross-sectional area of the pile casing. According to a further aspect of the present invention there is provided a pile driving assembly comprising a land vehicle having a mast on which there is moveably mounted a pile vibrator, the vibrator being provided with clamp means adapted to hold a pile to be driven and being mounted on a mast on the excavator which has a height less than the length of the pile such that the pile is driven progressively into the ground by allowing it to descend with the vibrator as it descends down the mast towards its base at which stage the clamp means is released, the vibrator is raised towards the top of the mast, the clamp means are re-engaged and a further driving operation is carried out. Preferably the vibrator comprises two vibratoring assemblies mounted together in spaced apart relationship but interconnected such that they vibrate with the same amplitude and frequency. Preferably the mounting for the vibrator assemblies includes said clamp means. Preferably the axis along which the forces from the vibrator acts coincides substantially with the longitudinal axis of the pile. Alternatively the axis along which the forces from the vibrator acts is spaced from the longitudinal axis of the pile. It is preferable that with this alternative arrangement the vibrator comprises a single vibrating assembly. Said assembly is supported on a lateral extension from the tubular mounting through which the pile passes, the tubular mounting including the clamp means. Preferably means are provided between the vehicle and the vibrator to apply a downwardly directed pulling force on the vibrator during pile driving. Preferably the said means includes a winch on the vehicle and a rope wound on the winch and having its free end connected to the vibrator. Alternatively the said means may be a piston and cylinder arrangement. An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:- Fig. 1 shows apparatus for forming a pile in situ; Fig. 2 shows a side elevation of the apparatus at a feed hopper; Fig. 3 shows an excavator with a vibratory driver for the casing shown in Fig. 1 and 2 mounted thereon; Fig. 4 shows a diagrammatic plan view of the vibrator, and Fig. 5 shows a diagrammatic plan view of a modified vibrator. A pile is formed by driving a tubular casing 10 into the ground 11 by any suitable means but preferably by a vibrator or pile hammer connected to the top 12 of the casing. The leading end of the casing is provided with a sacrificial pile cap 14 which, when the pile casing is removed, remains down the hole. The pile casing 10, with the exception of the lower two metres is provided over essentially its full length, with a plurality of apertures 16, the apertures being sufficiently large to allow the material to form the pile to pass therethrough from the exterior to the interior of the casing. The casing surrounding the apertures is of sufficient size to preserve the longitudinal strength of the casing. The casing passes through a hopper 18 arranged at ground level 11, the hopper comprising a rectangular container having a downwardly diverging base portion 20 merging with a tubular portion 22, the internal diameter of which is only slightly greater than the external diameter of the casing, so that the casing is a sliding fit in a guide sleeve 21 fitted at the lower end thereof. A bond breaker 24 is fixed to the external circumference of the casing adjacent its closed end 14. The bond breaker is simply a protrusion fixedly mounted to the casing circumference and ensures that as the pile is being driven the hole formed behind the closed end has a cross-sectional area slightly greater than the cross- sectional area of the casing. The leading end 25 of the pile can take any convenient form but in Fig. 1 it takes the form described in our co-pending Patent Co-operation Treaty Application No. PCT/GB90/00378. As the casing is being driven the material to form the pile is continuously supplied to the hopper 18 and passes through the apertures to fill the descending casing so that when the pile casing is driven to the required depth it can be removed from the hole by any suitable means, leaving the sacrifical cap 14 down the hole at the bottom of a column of pile forming material. The method described above is particularly advantageous as the pile forming material will be vibrated as the casing is being driven, especially if it is driven by a vibratory method, thereby ensuring its consolidation within the hole. Fig. 2 illustrates that the hopper 18, is fixed to the mast 26 of a conventional pile driving machine in a manner which allows vertical movement of the hopper. As a result by fixing the hopper to the casing for example by use of a bar (not shown) passing through the hopper and the apertures 16 near the top of the casing the hopper can be driven into the ground to form an enlarged pile cap at the top of the pile giving rise to a foundation construction arrangement as disclosed in our co-pending European Patent 0246046. Similarly the hopper can be lifted away from the ground when the pile has been formed by raising the casing until the leading end 25 abuts the end of the tubular guide 21 , the hopper and casing thereafter moving upwards as a unit. The angle of inclination of the hopper base is small so that material flowing from the hopper to the apertures does not cause a wedging action with the casing. To assist in the driving of the hopper into the ground to form the pile head the tubular section 22 is surrounded by an upturned conical section 23 of relatively great cone angle. Casing guide strips 27 are located on the internal walls of the tubular section 22 and guide rollers 28, for the casing 10, can be supported on the top of the hopper. Various modifications can be made without departing from the scope of the invention, for example, the cross-section of the pile casing need not be cylindrical but could be rectangular or any suitable cross-section for example pentagonal, octagonal, oval. The pile forming material can range from quality concrete through "no-fines" concrete to stone particles by themselves . The leading length of the casing behind the pile head 25 may have no apertures over varying lengths. Ths length is chosen to suit the pile forming material being utilised, for example, it may be as long as relatively long when quality concrete is being used, or may be omitted when aggregate or stone particles are being used. In a further modification the pile end cap 14 can be omitted. In this modification the interior of the casing, at its leading end, has a restriction to compact earth entering therein, to effectively block the casing leading end. In a further modification the pile need not be vibratory driven from the top but could be driven by vibrators of the type shown in Figs. 3 to 5. Fig. 3 shows an assembly for driving the casing 10 which is mounted, like the hopper 18 on a relatively lightweight tracked excavator 110, for example, of fifteen to twenty tonnes provided at one of its ends with a mast 112 which may have a length of around 6 metres and supports a pile vibrator 114 for vertical movement between the top 116 and bottom 118 of the mast. The assembly is intended to drive pile casings 10, the length of which can be at least twenty metres. The vibrator comprises two vibratoring assemblies 122, 124, arranged in spaced relationship and mounting therebetween claiiping means shown generally at 126, which are capable of rigidly attaching the vibrator to the pile or pile casing 10. Means 128, which do not form part of the present invention, interconrect the vibratoring assemblies 122 aid 124 such that they vibrate together with the same frequency and amplitude. To drive a pile the vibrator assembly 114 is raised to the top of the mast with a casing 10 arranged within the clamping means 126 and the pile tip at ground level within the hopper 18. The clamping means are then engaged to clamp the vibrator to the pile and the vibrator is set in motion, the vibratory motion driving the pile downwards until the assembly 114 reaches the base 118 of the mast. At this stage only part of the casing 10 is driven so that the clamping means 126 are released, the vibrator assembly 114 raised to the top of the mast and the clamping means re-engaged on the pile so that a further driving operation can be carried out. Operations of this nature are continued until the casing 10 is fully driven, material being fed to the hopper entering the casing, as described above . In the modification shown in Fig. 5 only one vibrating assembly 130 is provided, the assembly being mounted with its longitudinal axis V spaced from but parallel to the longitudinal axis P of the casing. The assembly is mount d on a tub lar mounting 132 incorporating pile clamping means 126. In view of the spacing between the axes additional forces will be set up in the mounting 132 and mast 112 which may require additional reinforcement but the surprising increase in pile driving efficiency achieved by the modification justifies this. On completion of the driving operation the vibrator is actuated such that the vibratory foces have an upwards direction thereby removing the casing 10 as described above. Various other modifications can be made without departing from the scope of the invention, for example, the vibrating assembly may be specifically designed and provided with central passage with clamping means through which the casing can pass and, for course, the assembly can be used to drive a standard pile or pile casing. Further modification introduces apparatus for applying a downward force in the vibrator as pile driving is taking place. It is known to apply a dead weight to a vibrator to assist its penetration but such arrangement is disadvantageous in that the overall weight of the pile driving assembly is increased by the dead weight and this means that the vehicle must be larger, heavier and Tiore expensive in purchase and operating costs. Further each time the vibrator is raised up the mast the dead weight must also be raised thereby necessitating larger machinery Fig. 3 illustrates a means for applying a downwardly directed force on the vibrator 114 comprising an hydraulically or mechanically powered winch 140 mounted on the vehicle and driven by the vehicles power arrangement. A wire rope or hawser 142 is wound on the winch drum 114 and extends between the drum and the vibrator to which the free end of the rope it attached. It will be realised that as pile driving takes place the winch can apply a downward pull on the vibrator, typically of between six and nine tonnes thereby considerably increasing the pile driving efficiency. The elasticity of the rope enhances the pull-down or "crowd" effect especially in a vibrating situation. In a modification the rope and winch arrangement may. be replaced by a piston and cylinder assembly connected between the vibrator and vehicle.

Claims: Claims : 1. A method of forming piles in situ comprising driving a casing into the ground to be piled characterised in that simultaneous with the driving of the casing the interior of the casing is supplied with material to form the pile transversely through apertures in the casing. 2. A method as claimed in claim 1, characterised in that the casing is driven by a vibratory method. 3. A method as claimed in claim 2, characterised in that the casing is top driven. 4. A method as claimed in any one of claims 1 to 3, characterised in that the casing is driven through a hopper arranged at ground level into which the pile material is supplied. 5. A method as claimed in any one of the preceding claims, characterised in that the hole formed by the pile casing is circular, rectangular or any other suitable cross-section. 6. A method as claimed in claim 5, characterised in that the pile casing has radial protrusions extending therefrom. 7. A method as claimed in claim 5 or claim 6, characterised in that a circumferential protrusion is provided adjacent the leading end of the casing whereby the hole it provides in the ground has a cross-sectional area greater than the cross-sectional area of the pile casing. 8. A driving assembly comprises a land vehicle having a mast on which there is moveably mounted a pile vibrator, characterised in that the vibrator is provided with clamp means adapted to hold a pile to be driven and is mounted on a mast on the excavator which has a height less than the length of the pile such that the pile is driven progressively into the ground by allowing it to descend with the vibrator as it descends down the mast towards its base at which stage the clamp means is released, the vibrator is raised towards the top of the mast, the clamp means are re-engaged and a further driving operation is carried out. 9. A driving assembly as claimed in claim 8, characterised in that the vibrator comprises two vibratoring assemblies mounted together in spaced apart relationship but interconnected such that they vibrate with the same amplitude and frequency. 10. A driving assembly as claimed in claim 9, characterised in that the mounting for the vibrator assemblies includes said clamp means. 11. A driving assembly as claimed in any one of claims 8 to 10, characterised in that the axis along which the forces from the vibrator acts coincides substantially with the longitudinal axis of the pile. 12. A driving assembly as claimed in any one of claims 8 to 10, characterised in that the axis along which the forced from the vibrator acts is spaced from the longitudinal axis of the pile. 13. A driving assembly as claimed in claim 12, characterised in that the vibrator comprises a single vibrating assembly. 14. A driving assembly as claimed in claim 13, characterised in that said assembly is supported on a lateral extension from a tubular mounting through which the pile passes, the tubular mounting including the clamp means. 15. A driving assembly as claimed in any one of claims 8 to 14, characterised in that means are provided between the vehicle and the vibrator to apply a downwardly directed pulling force on the vibrator during pile driving. 16. A driving assembly as claimed in claim 15, characterised in that the said means includes a winch on the vehicle and a rope wound on the winch and having its free end connected to the vibrator. 17. A driving assembly a claimed in claim 15, characterised in that the said means may be a piston and cylinder arrangement. 18. A method of forming piles as claimed in any one of claims 1 to 7, in which the casing is driven by a driving assembly as claimed in any one of claims 8 to 17.

Inventors: BULLIVANT ROGER ALFRED, BULLIVANT, ROGER, ALFRED
Applicants: BULLIVANT ROGER ALFRED, ROXBURY LTD, BULLIVANT, ROGER, ALFRED, ROXBURY LIMITED
Application year: 1990
Main classification: E02D7
IPC codes: E02D7, E02D15