AUGER PILING

Abstract: A monitoring device (14) for a continuous flight auger is connected between a continuous flight auger (11) and a drive mechanism (12) and rotates with the auger. A strain measurement arrangement provides strain signals for use in deriving the rotational torque and axial force of the auger. The axial strain and rotational torque information are used to build up a model of the ground. In particular, the shear strength of the soil can be determined which enables the maximum pile capacity to be calculated without a detailed site investigation.

Description: AUGER PILING This invention relates to auger piling, and in particular the monitoring of a continuous flight auger piling process. Continuous flight auger piling has been used in the construction industry in increasing volume since the early 1980's. Piles are constructed by drilling to the required depth with a continuous flight auger mounted on a piling rig. During withdrawal of the auger, concrete grout or slurry is pumped into the excavated hole through the auger. A steel reinforcement cage may subsequently be lowered into the pile, either under its own weight or with the assistance of a vibrator. During the initial boring stage, the auger is rotated into the ground at a rate intended to minimise the disturbance of the ground. The rate of advance of the auger during boring should depend upon the nature of the soil so as to cause this minimum disturbance. One indication of the nature of the ground is provided by measuring the torque on the auger during the boring process. This has conventionally been achieved by means of feedback signals from the drive motor. During extraction, the rate of withdrawal of the auger should be sufficiently low that the appropriate amount of concrete can be delivered through the auger. The rate of extraction and/or the flow rate of supplied concrete also need to be controlled to prevent collapse of soil from the walls of the excavation, which would contaminate the concrete cross section. It is known to monitor the concrete pressure in the concrete feed pipe at a suitable location in order to ensure that concrete is being supplied to the auger tip during the extraction process. A positive concrete pressure is maintained as the auger is withdrawn. However, positive pressure readings can result even when insufficient concrete has been delivered, for example as a result of blockages to the concrete supply pipe. It is desirable therefore to provide pressure measurement at the bottom end of the auger instead of in the supply pipe further upstream. Difficulties then arise in establishing the connections to a pressure transducer located at the lower end of the auger to a control device. These problems are particularly severe when the auger is arranged as a multi-section device, since the coupling between auger sections also requires a coupling to be provided for the pressure transducer signal line. This line would be exposed to adverse conditions during the piling process. According to a first aspect of the present invention, there is provided a monitoring device for a continuous flight auger, comprising a shaft for connection between a continuous flight auger and a drive mechanism or for connection between adjacent auger sections, the shaft comprising a coupling at each end for connection to respective couplings of the drive mechanism and/or of the auger such that the shaft rotates with the auger, the device further comprising a strain measurement arrangement for providing strain signals for use in deriving the rotational torque and axial force of the auger. The invention provides an additional section to be mounted either at the top of the auger or between auger sections for direct measurement of the rotational torque and axial force on the auger during the piling process. The monitoring device may remain above ground level if mounted adjacent the drive mechanism, or may be mounted part way down the auger. The axial strain information can be used in combination with the rotational torque to build up a model of the ground. In particular, the shear strength of the soil determines the maximum pile capacity, and the axial strain can be used to determine the soil shear strength, to enable pile capacity to be determined without a detailed site investigation. The strain measurement arrangement may comprise a plurality of strain gauges disposed around the shaft. The monitoring device preferably also comprises a pressure detection device for mounting at the lower end of the auger and a connection arrangement for coupling signals from the pressure detection device to a receiver of the monitoring device. This enables measurement of the pressure at the lower end of the auger to ensure the correct supply of concrete. The connection arrangement may comprise a hydraulic line. A hydraulic connection can easily be provided between auger sections for a multi-section auger. The pressure measurement is then achieved by a pressure transducer mounted above ground on the monitoring device, for example on the shaft. Alternatively, the pressure detection device comprises an electrical pressure transducer coupled to the receiver by an electrical line. The receiver may comprise a radio transmitter for sending measured data to a control station. The data from the monitoring device provides data which enables a predictive judgement of pile capacity on completion of the pile. However, the data may also be used as an aid for the rig driver in controlling the process. Alternatively, an automatically controlled process may be envisaged. In this respect, the invention also provides a control device for controlling the driving of a continuous flight auger, comprising a monitoring device of the invention and a control means for providing control signals for the control of the drive mechanism in dependence on signals provided by the monitoring device. An automatically controlled continuous flight auger rig of the invention uses this control device. The auger may comprise a core and a flight, in which the core comprises two concentric walls. In this case, a hydraulic line for transmitting pressure signals from the lower end of the auger may be defined using the spacing between the concentric walls of the core. According to a second aspect of the invention, there is provided a monitoring device for a continuous flight auger, comprising a pressure detection device for mounting at the lower end of the auger, a pressure transducer for mounting above ground, and a hydraulic line for coupling signals from the pressure detection device to the pressure transducer. According to this aspect of the invention, hydraulic coupling is provided between a pressure detection device mounted at the lower end of the auger and a pressure transducer mounted above the ground. This simplifies the connections for the pressure signals between adjacent auger sections. An example of the invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 shows a continuous flight auger piling rig, with one section of a multiple section auger assembled on the rig; Figure 2 shows the apparatus of Figure 1 in which a second auger section has been added; Figure 3 is a diagram showing the operation of the continuous flight auger piling process; Figure 4 shows in greater detail the monitoring device of the invention; and Figure 5 shows in greater detail a pressure detection device for mounting at the tip of the auger with hydraulic coupling. Figure 1 shows an auger rig 10 of the invention for performing a continuous flight auger piling operation. The rig 10 shown in Figure 1 includes one section 11a of a multiple section continuous flight, hollow-shafted auger 11 which is rotatably mounted on a drive mechanism 12 which is in turn mounted for vertical movement on an upright pillar 13. The auger section 11a is one of many selectively attachable auger sections. Typically, each auger section 11a will have a length of approximately 6m, whereas the desired depth of the concrete pile will usually be between 10m and 26m. The auger sections are arranged to be attached to each other by appropriate couplings. The auger sections may be connected together before commencing the piling or alternatively, for very deep piling or in limited headroom circumstances, drilling the full length cavity may be performed in short incremental stages. The drive mechanism 12 includes a depth encoder for determining the depth of penetration of the auger into the ground. Furthermore, concrete is supplied to the auger by a supply system including a flow meter. In accordance with the invention, a monitoring device 14 is provided in the form of a shaft which is coupled for rotation with the auger. In the example shown in the drawings, one monitoring device is provided between the auger 11 and the drive mechanism 12. The device 14 may instead be provided between auger sections, and more than one such device may be provided. For example, one monitoring device may be provided adjacent the drive mechanism, and one may be provided near the bottom tip of the auger. The device 14 may comprise an auger section, and thus be provided with a flight, or it may comprise a short section with no flight, as shown in the drawings. The shaft 14 has a coupling 15 at each end for connection to a coupling of the drive mechanism 12 and/or of the auger 11. The monitoring device 14 is connected to rotate with the auger 11 and has a strain measurement arrangement providing strain signals which enable the rotational torque and axial force of the auger to be derived. For this purpose, the strain measurement arrangement measures circumferential and axial strain. This torque and force data can be used to control the rotational speed and/or the advance of the auger 11 into the ground as a function of the ground conditions. Preferably, the auger is controlled so that the flights of the auger are kept loaded with soil originating from the auger tip 19. This can be achieved by evaluating the ground conditions based on the resistance presented to the auger by the ground, which influences the rotational torque and the axial strain in the auger. This information is provided by the monitoring device 14, which gives more accurate information concerning the ground conditions than the measurement of parameters relating to the motor of the drive mechanism 12. Different techniques may be employed for driving the auger into the soil. For example, the soil shear stress may be calculated by pulling back on the auger whilst maintaining rotation. Measurement of the axial strain together with the rotational torque can enable the shear stress of the soil to be calculated. This can be carried out incrementally as the depth is increased to build up a model of the soil characteristics. The invention provides a modular system. The monitoring device is provided with standard connections at each end, so that is may be used with any auger piling system following this standard. The tip 19 of the auger is provided with a pressure detection device, and the signals from the detection device are coupled to a receiver at the top of the auger, in the region of the monitoring device 14. The pressure detection device is used during the extraction of the auger to ensure the presence of concrete at the tip 19. In the case that multiple monitoring devices are provided, only one will need to have an associated pressure detection device. The pressure detection device may comprise a chamber having a deformable membrane which is exposed to the concrete at the tip 19. The pressure exerted on the membrane is transmitted by a hydraulic line to a pressure transducer located above ground level. Alternatively, an electrical pressure transducer may be provided at the tip 19 with coupling using an electrical cable to a monitoring device at the head of the auger. A further possibility is to provide the pressure transducer at the tip of the auger with a radio transmitter, so as to avoid the need to provide electrical cable connections at the junctions between auger sections. The monitoring device at the head of the auger would then be provided with a appropriate receiver. Figure 2 shows a second auger section 1 lb introduced between the first auger section 11a and the monitoring device 14. The two auger sections 11a, l ib may be assembled before piling commences, and a monitoring unit of the invention may be provided between the auger sections instead of or as well as the monitoring device at the head of the auger. When there is a physical conductor of signals from the pressure detection device at the tip 19 and the monitoring device 14 (a hydraulic or electrical line), the connection 20 between the auger sections 11a, l ib must include an appropriate connector for the pressure detection device signals. When radio transmission is provided, this is not required. Figure 3 is used to illustrate the steps of the continuous flight auger piling process. During drilling stage shown at 22, the auger 11 is rotated and allowed to advance into the ground. The data from the monitoring device may also be used as an aid for the rig driver in controlling the piling process. Alternatively, an automatically controlled process may be envisaged. In this case, a control device is provided which provides control signals for the control of the drive mechanism 12. This may be used to alter the rotational speed and/or the rate of advance of the auger 11 into the ground. Once the auger 11 has advanced to the required depth, concrete is pumped through the auger 11 as shown at 24. The concrete flow rate is monitored by the concrete supply system. The pressure detection device in the tip 19 of the auger is used either by the rig driver, or by the automatic control system, to ensure that there is a constant supply of concrete to the auger tip 19. The auger 11 is progressively withdrawn from the bore by a hydraulic lifting mechanism forming part of the drive mechanism 12. The drive mechanism 12 is controlled to vary the rate of auger withdrawal, again either manually or automatically. In either case, the rate of withdrawal can be a function of the concrete flow rate and the pressure signal provided by the pressure detection device. The representation at 26 shows almost complete withdrawal of the auger 11, and with optional reinforcement added a completed pile is shown at 28. The data obtained from the monitoring device 14 can be used to control the piling process, as described above. However, the data alternatively or additionally may be used to enable a predictive judgement of pile capacity on completion of the pile. Figure 4 shows in greater detail the monitoring device 14 of the invention. The device comprises a shaft 30 with a male spigot connector 15a at one end and a female corresponding bore 15b at the other end. In the example shown, the spigot 15a has a hexagonal cross section and torque is transmitted by the spigot-bore connection between the monitoring device 14 and the adjacent auger 11 as well as between the monitoring device 14 and the adjacent drive mechanism 12. In order to measure the rotational torque and axial strain in the auger 11, strain gauges 32 are provided on the surface of the shaft 30. The axial strain through the shaft and the torque vary as the depth of the bore increases and also vary as the nature of the soil at the tip 19 changes. It will be apparent to those skilled in the art how to mount the strain gauges to provide torque and axial strain information. Typically an arrangement of at least two surface-mounted strain gauges may be employed, in a configuration enabling torque and axial strain to be resolved. This may be a diamond configuration of strain gauges. The monitoring device 14 is also provided with a receiver 34 which receives the signal from the pressure detection device located at the tip 19. In one example, the receiver 34 comprises a pressure transducer which communicates with a hydraulic line running the entire length of the auger and communicating with a diaphragm at the auger tip 19. As described above, an electrical system is also possible. The signals from all of the strain gauges and the pressure receiver 34 are preferably provided by a radio link to a central computer in the cab of the piling rig machine. A data collection and transmission device 36 for this purpose is shown schematically in Figure 5. As an alternative, a commutator arrangement may be used, which enables the signals to be tapped off the monitoring device 14 to an appropriate control device (not shown). Figure 5 shows in greater detail the design of the tip 19 of one possible auger construction 11, which comprises a core 40 and a flight 42. The core 40 comprises inner and outer skins 44, 46. The inner skin 44 defines the passage for the supply of concrete 48 and extends to an opening 50 adjacent the tip 19. The opening 50 is shown provided at a lateral position to reduce the likelihood of blockage, The space between the inner and outer skins 44, 46 defines a chamber which runs the entire length of the auger 11. This chamber is used to define the hydraulic line coupling the pressure detection device 52 and the receiver 34 located at the monitoring device 14. In its simplest form, the pressure detection device 52 comprises a membrane, as shown in Figure 5, which is responsive to the pressure at the auger tip 19, The auger construction of Figure 5 is a double skin auger, and a pressure sensor with hydraulic signal coupling is provided. Of course, a single skin auger may also be chosen. The invention provides improved monitoring of the auger conditions during a continuous flight auger piling process, which can improve the quality of the concrete pile formed. The monitoring device can be inserted into existing piling rigs without significant modification to those existing systems, at least in the case of the strain measurement systems associated with the monitoring device 14. Various modifications will be apparent to those skilled in the art. Similarly, the exact construction of the piling rig and of the concrete supply and flow monitoring equipment has not been described in detail, since this is all conventional in the art.

Claims: Claims 1. A monitoring device for a continuous flight auger, comprising a shaft for connection between a continuous flight auger and a drive mechanism or for connection between adjacent auger sections, the shaft comprising a coupling at each end for connection to respective couplings of the drive mechanism and/or of the auger such that the shaft rotates with the auger, the device further comprising a strain measurement arrangement for providing strain signals for use in deriving the rotational torque and axial force of the auger. 2. A device as claimed in claim 1, wherein the strain measurement arrangement comprises a plurality of strain gauges disposed on the shaft. 3. A device as claimed in claim 1 or 2, further comprising a pressure detection device for mounting at the lower end of the auger, and a connection arrangement for coupling signals from the pressure detection device to a receiver of the monitoring device. 4. A device as claimed in claim 3, wherein the connection arrangement comprises a hydraulic line. 5. A device as claimed in claim 4, wherein the receiver comprises a pressure transducer mounted on the shaft. 6. A device as claimed in claim 3, wherein the pressure detection device comprises an electrical pressure transducer coupled to the receiver by an electrical line. 7. A device as claimed in any one of claims 3 to 6, wherein the receiver comprises a radio transmitter for sending measured data to a control station. 8. A continuous flight auger rig comprising a continuous flight auger, a drive mechanism for driving the auger into the ground, and a monitoring device as claimed in any one of claims 1 to 7. 9. A control device for controlling the driving of a continuous flight auger, comprising a monitoring device as claimed in any one of claims 1 to 7, and a control means for providing control signals for the control of the drive mechanism in dependence on signals provided by the monitoring device. 10. A continuous flight auger rig comprising a continuous flight auger, a drive mechanism for driving the auger into the ground, and a control device for controlling the drive mechanism as claimed in claim 9.. 11. A rig as claimed in claim 8 or 10, wherein the auger comprises a core and a flight, the core comprising two concentric walls. 12. A rig as claimed in claim 11, wherein the monitoring device comprises a pressure detection device mounted at the lower end of the auger, and a hydraulic line coupling signals from the pressure detection device to a pressure transducer mounted on the shaft, and wherein the hydraulic line is defined by the spacing between the concentric walls of the core. 13. A rig as claimed in any one of claims 8, 10, 11 or 12, in which the auger comprises multiple sections. 14. A monitoring device for a continuous flight auger, comprising a pressure detection device for mounting at the lower end of the auger, a pressure transducer for mounting above ground, and a hydraulic line for coupling signals from the pressure detection device to the pressure transducer. 15. A device as claimed in claim 14, comprising a shaft for connection between a continuous flight auger and a drive mechanism or for connection between adjacent auger sections, the shaft comprising a coupling at each end for connection to respective couplings of the drive mechanism and/or of the auger such that the shaft rotates with the auger, and wherein the pressure transducer is mounted on the shaft. 16. A device as claimed in claim 15, further comprising a strain measurement arrangement for providing strain signals for use in deriving the rotational torque and axial force of the auger. 17. A continuous flight auger rig comprising a continuous flight auger, a drive mechanism for driving the auger into the ground, and a monitoring device as claimed in any one of claims 13 to 16. 18. A control device for controlling the driving of a continuous flight auger, comprising a monitoring device as claimed in claim 14,15 or 16, and a control means for providing control signals for controlling driving of the auger into the ground in dependence on signals provided by the monitoring device. 19. A continuous flight auger rig comprising a continuous flight auger, a drive mechanism for driving the auger into the ground, and a control device for controlling the drive mechanism as claimed in claim 18, 20. A rig as claimed in claim 19, wherein the auger comprises a core and a flight, the core comprising two concentric walls, and wherein the hydraulic line is defined by the spacing between the concentric walls.

Inventors: MURE NORMAN, SCOTT JASON, MURE, NORMAN, SCOTT, JASON
Applicants: BALFOUR BEATTY PLC, MURE NORMAN, SCOTT JASON, MURE, NORMAN, SCOTT, JASON
Application year: 2001
Main classification: E02D5
IPC codes: E02D5, E02D33, E21B44