Centrifuges, especially for geotechnical testing methods

Abstract: A scale modelling centrifuge has a relatively massive rotary circular base wall 80, which may form part of a drum 10, possibly with a detachable peripheral wall 81 either carrying an annular sample-receiving trough 83 or constituted by such trough, or which may have mounted therearound a plurality of sample-receiving containers 84.

Description: This invention relates to centrifuges and centrifuging methods for scale modelling, especially in the geotechnical field. Beam centrifuges and drum centrifuges are well known for various purposes. One disadvantage of a beam centrifuge compared with a drum centrifuge is that air pressure build-up occurs at the leading faces of the beam, so that it rotates more slowly for a given power input than does a corresponding drum centrifuge. This can be particularly disadvantageous in scale modelling where very high g forces on the model may be desired. Abstract 82, K-6742E of Soviet Patent Abstracts, Section EI, week 8232, 1982, Derwent Publications, discloses a beam centrifuge in which a tiltable container at the end of an arm of the beam contains a platform reciprocable tangentially of the centrifuge by electromagnets on respective opposite walls of the container. It also discloses that a building model may be fixed to the platform, the beam rotated to tilt the container to bring the platform to an almost vertical position and a dynamic load on the building, for example to represent an earthquake, produced by periodic energization of the electromagnets. Another beam centrifuge is disclosed in Abstract 91-063380 of Database WPIL, Section EI, week 9109, 1991, Derwent Publications, in which a container for a soil sample is reciprocable circularly peripherally of the centrifuge. A further beam centrifuge seems to be disclosed in Abstract 89-328578, Database WPIL, Section EI, week 8945, 1989, and seems to include a pair of horizontal arms fixed to a vertical drive shaft and with a pair of buckets tiltably coupled to the outer ends of the arms for containing soil sample boxes, and an actuator to exert a test load on the sample box. Use of a beam centrifuge for dynamic and earthquake geotechnical centrifuge modelling is disclosed in a correspondingly titled article by Professor A.N.Schofield of Cambridge University in the Proceedings of the International Conference on Recent Advances in Geotechnical Earthquake Engineering & Soil Mechanics, Volume III, 1982, pages 1081-1100. Differing shaking means for shaking the model, which could be a soil sample, are disclosed. One consists of a reaction mass attached by stiff leaf springs to a shaking box containing the sample. Before a test, the mass is jacked away from the box and one or more spacers inserted therebetween. The spacers are driven away during flight, to cause the mass and the box to shake. An alternative shaking means consisted of a "bumpy road" track extending in an arc of about one third of a revolution around the beam. During flight, a wheel passes along the track and is held clear of it until shaking of the model is required, when the wheel is moved radially outward to land on the track. The wheel is mounted on a bell crank lever connected to the shaking box. A slider and a shaft can be adjusted in flight by a screw jack to vary the ratio between the respective amplitudes of motion of the wheel and the model. The shaking of the model is tangentially and is monitored by linear variable differential transformers mounted in the model container roof and the signals therefrom are sent through slip rings to a control room. Page 50 of a book entitled "Centrifuges in Soil Mechanics" by Professors James and Schofield and published by A.A. Balkema of Rotterdam, Holland, in 1988, shows a section through a geotechnical drum centrifuge with upper and lower bearings, with the drum being driven from below by an hydraulic motor via a vertical drive shaft, the upper bearing having a central manhole through which a person can obtain access to the interior of the drum. The Proceedings of the International Conference on Geotechnical Centrifuge Modelling held in Paris in April 1988 and called "Centrifuge 88" and published by A.A. Balkema of Rotterdam in 1988 containes the following articles:- (a) "Design and Operation of a Drum Centrifuge" by Professor Kusakabe and others, which discloses a geotechnical centrifuge used for scale modelling and comprised of a drum rotatable solely about a horizontal axis. A scale model extending around substantially the whole periphery of the interior of the drum is disclosed. (b) "Automatic Data Acquisition and Processing of Centrifugal Model Tests" by L. Liu and others discloses the arrangement of a model in the swing bucket of what appears to have been a beam centrifuge with detection by one or more transducers at the model and the electrical signals therefrom being delivered to a recording apparatus fixed relative to the ground. A master-slave computer working mode was adopted; the signals from the transducer(s), after being amplified, were collected and converted from analogue to digital by the slave computer, then delivered to the master computer through signal slip rings and wires, with the master computer undertaking operational control of the system, data storage and processing. (c) "Levee Failures Modelled in a Drum Centrifuge" by Professor Kusakabe and others discloses the development in a drum centrifuge of a modelling technique of levee failure during flood, the drum centrifuge used having been that described in the article "Design and Operation of a Drum Centrifuge" mentioned above. Abstract 85-255321 in Soviet Inventions Illustrated, Section EI, week 8541, 22 November 1985, Derwent Publications, discloses a centrifuge with power supply, speed control, timer control and regulated water input from a header tank. The centrifuge is provided with opposed cups filled with saline soil samples and inserted in a moving body on a rotary shaft. The water is fed from the tank through a central bore in the shaft. Abstract 91-093475 of Soviet Patent Abstracts, Section EI, week 9113, 15 May 1991, Derwent Publications, discloses a material samples test device which has a drive to rotate a circular platform about its own axis and another drive to set it selectively in a horizontal plane or a vertical plane. A guide extends diametrally of the top surface of the platform to guide diametral reciprocation of clamps releasably fixed to respective opposite ends of a test piece. With the platform in a vertical plane, at low speed weights on the clamps produce impact loading during interaction with limiters in the guide, while at high speed cyclic loading of the test piece occurs. With the platform in a horizontal plane, the speed is altered to change axial loading. Abstract 91-280007 of Soviet Patents Abstracts, Section EI, week 9138, 6 November 1991, Derwent Publications, discloses a flat stressed sample centrifugal tester which has releasable fixers to release torque links connecting weights to clamps attached to respective opposite sides of a sample. A rotary platform has fixed thereto at its outer face a pair of radially oppositely extending guide channels serving to guide inward and outward movement of the weights. It is explained that the fixers are released according to a pre-set programme, whereupon the hinged torque links ensure high speed movement of the weights to a larger radius of rotation, to provide impact overloading of the test piece. Abstract 88-299191 of Soviet Inventions Illustrated, Section EI, week 884, 30 November 1988, Derwent Publications, discloses a centrifugal test device for groups of test pieces which has an hydraulic cylinder to turn platforms each carrying a group of test pieces. The test pieces are fixed in active and passive clamps on the platforms and are loaded in bending, compression and tension when the platforms are turned. The platforms are rotatably mounted upon an annularly flanged plate driven by way of an annular gear fixed to the flange. US-A-4,807,483 discloses a centrifugal test drum having inserted therein an annular slat belt for supporting and containing integrated circuits bring stress tested. According to a first aspect of the present invention, there is provided a scale modelling centrifuge comprising a member rotatable about an axis, rotary receiving means carried by said member at a spacing from said axis and serving to receive scale model means so that said scale model means also is spaced from said axis, characterised in that tilting means is arranged to tilt said member and said receiving means so as to tilt said axis between a substantially vertical first condition and a second condition at a substantial angle to the vertical. According to a second aspect of the present invention, there is provided a centrifuging method comprising rotating a centrifuge member while its axis of rotation is substantially vertical and thereby rotating receiving means carried by said member at a spacing from said axis and receiving scale model means so that the latter also is spaced from said axis, characterised in that said rotating of said centrifuge member while said axis is substantially vertical is preceded by rotating said centrifuge member and thus said receiving means and said scale model means while said axis is at a substantial angle to the vertical, and then tilting said member and thus said receiving means and said scale model means to tilt said axis to its substantially vertical condition. The member, which may be an arm or a drum, is advantageously so disposed that the substantial angle is a right-angle, i.e. the longitudinal axis is substantially horizontal. This arrangement has the advantage that static balancing of one or more scale model(s) (and one or more counterweights) on the member is simplified because the member tends to turn under gravity unless in static balance. The rotation of the member to subject the scale model(s) to high centrifugal force can be performed either with the axis still at that substantial angle to the vertical or after tilting of the axis into a vertical condition. The centrifuge member may comprise a rotary wall having an annular outer periphery and rotatable about its own axis, and the receiving means may be releasably attached to a face of that wall in the region of that periphery for containing the scale model means. An advantage of having the receiving means detachable from the rotary wall is that the scale model means can be prepared in its receiving means in a convenient manner at a suitable remote location, for example in a consolidometer, and then the sample and its receiving means attached to the rotary wall. In this way, the centrifuge can be used much more efficiently than if the sample were prepared in the centrifuge itself. The receiving means may be an annular trough facing inwards, in which case the rotary wall and the trough form a drum, or the receiving means may be a plurality of containers distributed around the outer peripheral region of the wall, in which case the containers may be radially outwardly encircled by an annular shroud, again giving the appearance of a drum, to reduce wind drag. The rotary wall may be massive relative to the receiving means. The relatively massive diametral wall has the advantage of stiffly resisting outward deflection of the receiving means under centrifugal force. It also has the advantage of reducing the effect upon the bearings(s) of any shaking of the sample. Such shaking may be produced by first shaking means effective to produce shaking of the receiving means to-and-fro in a first sense, and second shaking means operable independently of the first shaking means and effective to produce shaking of the receiving means to-and-fro in a second sense transverse to the first sense. It is thus possible to model the actual wave pattern of a complex earthquake, since such earthquakes comprise waves transverse to each other and the phase relationship between the waves in one sense and the waves in the transverse sense may vary greatly from one earthquake to another. The centrifuge may be in the form of an arm or a drum. In practice, the first sense could be tangential and the second sense radial. There may be a plurality of rotary masses distributed around the axis and carried by the centrifuge member, at least one of the masses comprising the receiving means for receiving the scale model means, a plurality of shaking means distributed around the axis and acting between the respective masses, on the one hand, and the centrifuge member, on the other hand, to produce shaking of the respective masses radially of the axis in such manner that the vector sum of the radial forces generated at the zone of the member at the axis by the radial shaking is substantially zero. This has the advantage of minimizing impact load on a rotary bearing for the member at the axis. The plurality of shaking means may additionally produce shaking of the masses tangentially with respect to the axis in such manner that the vector sum of the tangential forces is reacted by the inertia of the rotary wall or drum. The rotary wall may be provided with an annular recess substantially co-axial with the wall and opening towards the axis, the receiving means being disposed radially outwardly of the recess, a stationary conduit for supplying liquid to the recess, and duct means extending from the recess towards the scale model means for conducting the liquid under centrifugal force from the recess towards the scale model means. This system provides a simple way of supplying liquid to scale model means, without requiring the high standard of sealing necessary if using hydraulic slip rings, for example. The centrifuge may comprise duct means for communicating with a region of the interior of the receiving means at which the hydraulic pressure is exerted, and drive means which serves to displace an outlet end of the duct means selectively in a direction of increasing hydraulic pressure in the receiving means or in the opposite direction. Each of these systems is particularly useful for selectively preventing and allowing liquid flow in circumstances in which conventional on-off valves become unreliable, for example where the valves would have to operate under high pseudo-gravitational forces or where the liquid or particles therein may cause the valves to malfunction. Alternatively, the device for controlling liquid flow may comprise duct means for conducting the liquid, and thermoelectric means in thermal communication with the interior of the duct means for producing cold in the interior to solidify the liquid therein. The centrifuge may comprise a work support located centrally of the wall, with the receiving means being accessible from the work support. The support can be used to support experimental testpieces, tools, or an operator. It may be fixed, or be rotatable with the rotary wall, or be rotatable relative to the rotary wall. The support may take the form of a vertical shaft (i.e. a column) or a platform, for example a turntable. The work support may be so mounted centrally of the wall as to be retractable axially of the wall, even while the wall rotates, and as to be able to remain stationary while the wall rotates. This arrangement has the advantage of allowing the work support to be retracted into a relatively accessible position even during centrifuging. Where the scale model means is soil, the subjection of the scale model means to centrifugal force has the effect of consolidating the soil. In such circumstances, in order to reproduce the effect of earthquakes, the soil may be subjected to shaking to provide shocks or vibrations, especially to provide a sinusoidal wave vibration. Where the scale model means is liquid, it may be desirable to freeze the liquid; for example where the liquid is seawater, to freeze the seawater for so-called sea-ice work. The scale model means advantageously extends completely or almost completely round the axis, so as to provide a large inwardly exposed area for simultaneous performance of a plurality of experiments. The scale modelling centrifuge may comprise a drum and upper and lower bearings at respective ends of the drum and mounting the drum for rotation about its longitudinal axis, which is substantially vertical. Having bearings at both ends of the drum enables the speed of rotation of the drum to be higher than with only one bearing. With such a centrifuge, access for an operator or materials to the interior of the drum may be obtained through the centre of one or both of the bearings. Alternatively, in order to give very good access, the drum may include a detachable lid itself centrally mounted in the upper bearing. The present scale modelling centrifuge including a substantially circular rotary wall or drum has the advantage over known scale modelling arm centrifuges that higher forces can be obtained. One reason for this is that the wall or drum has better aerodynamic properties than the arm, so permitting a greater speed of rotation of the wall or drum than of the arm. Another reason is that the wall or drum has better balancing properties than does the arm. We believe it to be possible with a drum to obtain values of at least 500G with a tonne specimen, compared with the present commercially available arm centrifuges which attain values of up to about 200G with a tonne specimen. The centrifuge may additionally comprise instrumentation carried by the rotary wall, data processing means also carried by the rotary wall, slip ring means between the rotary wall and the stationary means, data utilizing means carried by the stationary means, and electrically conductive means connecting the instrumentation to the data utilizing means by way of the data processing means and the slip ring means, the data processing means serving to convert analogue electrical signals from the instrumentation into digital signals. The conversion of the analogue signals into digital signals on the rotary wall has the advantage of mitigating the effect of signal distortions produced by electrical interference, which may be generated at such slip ring means. It also enables the number of slip rings and their associated electrical conductors to be minimized. It is possible to provide consolidating apparatus, comprising a consolidation chamber for receiving a scale modelling sample to be consolidated, a movable wall of the consolidation chamber, a pressure chamber serving to receive a pressing fluid which presses the movable wall inwardly of the consolidation chamber, and mechanical means serving to apply a force to the fluid in the pressure chamber to pressurize the fluid. This arrangement has the advantage of avoiding any need for the pressing fluid to be continually connected to a supply of pressing fluid. It is also possible to provide consolidating apparatus, comprising an annulus bounding peripheral channel means open towards the axis of the annulus for receiving a sample to be consolidated, and movable wall means arranged around the annulus axis inwardly of the peripheral channel means and serving to press radially outwardly on the sample to consolidate the same. This apparatus is particularly suitable for providing consolidated samples for circular centrifuges. In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which Figures 1 to 18 illustrate embodiments outside the scope of the present claim 1 and Figures 19 and 20 illustrate embodiments inside the scope of claim 1, and in which:- Figure 1 is a vertical axial section through a geotechnical drum centrifuge, Figure 2 shows a sectional plan view along the line II-II in Figure 1, Figure 3 is a view similar to Figure 1 of a modified version of the drum centrifuge, Figure 4 is a view similar to Figure 2 taken on the line IV-IV in Figure 3, Figure 5 is a view similar to Figure 1 showing another modified version of the centrifuge, Figure 6 is a view similar to Figure 1 of a third modified version of the centrifuge, Figure 7 is a view similar to Figure 2 taken on the line VII-VII of Figure 6, Figure 8 is a view similar to Figure 1 of fourth and fifth modified versions of the centrifuge, Figure 9 is a view similar to Figure 2 taken mainly on the line IX-IX in Figure 8, Figure 10 is a view similar to Figure 8 of sixth and seventh modified versions of the centrifuge, Figure 11 is a view similar to Figure 9 taken mainly on the line XI-XI in Figure 10, Figure 12 is a view similar to Figure 8 of eighth and ninth modified versions of the centrifuge, Figure 13 is a view similar to Figure 9 taken mainly on the line XIII-XIII in Figure 12, Figure 14 shows a vertical axial section through a consolidometer for producing geotechnical samples for, e.g., the seventh modified version shown in Figures 10 and 11, Figure 15 is a view similar to Figure 14 of a modified version of the consolidometer, Figure 16 is a fragmentary section taken on the line XVI-XVI of Figure 15, Figure 17 shows a vertical axial section through a consolidometer for producing geotechnical samples for, e.g., the modified versions shown in Figures 12 and 13, Figure 18 shows a vertical axial section through a tenth modified version of the centrifuge, Figure 19 is a view similar to Figure 18 of an eleventh modified version of the centrifuge, Figure 20 shows a side elevation of a twelfth modified version of the centrifuge, Figure 21 shows an axial section through a modification of any one of the centrifuge versions of Figures 1 to 13 and 18 to 20, Figure 22 shows a top plan view of the modification of Figure 21, Figure 23 shows a fragmentary axial section through another modification of any one of the centrifuge versions of Figures 1 to 13 and 18 to 20, Figure 24 shows a fragmentary top plan view of the modification of Figure 23, and Figure 25 shows a fragmentary half-section through a further modification of any one of the centrifuge versions of Figures 1 to 13 and 18 to 20. Referring to Figures 1 and 2, the centrifuge comprises a keyhole-shaped pit 1 heavily lined with steel-reinforced concrete 2, with a steel-reinforced concrete arch 3 having a planar vertical face 4 and an arcuate vertical face 5 co-cylindrical with the cylindrical face 6 of the pit 1. The cylinder bounded by the faces 5 and 6 is substantially closed at its top by a rigid, annular, steel cap 7 solidly mounted at its outer, lower rim in the concrete 2. At its upper, inner rim, the cap 7 mounts a roller bearing 8 having a vertical axis A. Mounted co-axially in the bearing 8 is a stub tube 9 forming part of a drum 10 which also includes a coaxial stub tube 11 at its lower end. The stub tube 11 is mounted in a self-aligning barrel bearing 12 mounted securely in a heavy steel mounting 13 coaxial with the drum 10 and firmly fixed in the concrete 2 at the bottom of the pit 1. Fixed to an internal peripheral surface of the drum 10 coaxially with the drum 10 are upper and lower annular flanges 14 and 15 bounding between them an annular channel 16. Shown in the channel 16 is a scale modelling sample 17, in this instance soil, containing various detecting devices (for pressure, displacement, et cetera) electrically connected by leads to some of slip rings 18 fixed to the mounting 13. Mounted centrally of the mounting 13 is an electric motor 19 which drives a vertical shaft 20 co-axial with the drum 10 and fixed at its upper end to a turntable 21. Various detecting devices carried by the turntable 21 are connected, if desired by way of a control box 22, to slip rings 23 themselves electrically connected via leads to some of the slip rings 18. Shown mounted on the turntable 21 is a testpiece 24 simulating the legs of an off-shore platform. Formed in the bottom wall 10a of the drum 10 is a manhole 25 with a cover through which manhole an operator may gain access to the interior of the drum 10 from below the drum. Such operator is diagrammatically indicated at 26. The bottom wall 10a of the drum 10 is spaced from the floor of the pit 1 sufficiently that the operator 26 may enter the manhole 25 from below and, as shown, have the upper part of his body at a level suitable for him to work upon the sample 17 present in the channel 16, while standing on the bottom of the pit 1. The bottom wall of the drum 10 is at approximately the height of the hips of the operator 26. If desired, the operator may enter the drum 10 by way of the interior of the stub tube 9. The operator 26 is shown at 26' seated upon the turntable 21. There may be more than one manhole provided in the bottom wall of the drum 10, for example as at 25'. A drive belt 27 is used to drive the stub tube 9 and thus the drum 10 about the axis A. In order to drain liquid from the drum 10, at least one drain pipe 28 extends to an annular drain conduit 29 fixed to the surfaces 5 and 6. In use, while the drum 10 is spinning, soil to be tested may be introduced through the stub tube 9 and laid in the channel 16, for example via a flexible hose (not shown). Rotation of the drum 10 about its axis A is used to produce consolidation of the soil. The continuous internal annular face provided by the cap 7 and the continuous annular face provided by the surfaces 5 and 6 discourage turbulence in the air adjacent to the drum 10 and thus facilitate the achievement of relatively high speeds of rotation of the drum. Referring to Figures 3 and 4, the version shown therein differs from the version shown in Figures 1 and 2 in that the annular channel 16 receives a plurality of arcuate troughs 30 which are connected via respective links 31, passing through respective circumferential slots 32 in the peripheral wall of the drum 10, to respective rollers 33 connected to that wall of the drum 10 by way of respective links 34. The links 31 are articulated to the troughs 30 and to the rollers 33, whilst the links 34 are articulated to the rollers 33 and the drum 10. Another difference is that the annular face provided by the surfaces 5 and 6 has fixed thereto a cam track 35 of a sinusoidal form. The purpose of the cam track 35 and the rollers 33 is to cause the troughs 30 to perform a sinusoidal wave motion to simulate the effect of an earthquake in the soil 17 in the troughs 30. The rollers 33 follow the sinusoidal surface of the track 35 under centrifugal force as the drum 10 is rotated, oscillating radially under the control of the links 34. By way of the links 31 they push the troughs 30 tangentially relative to the drum 10, so imparting a circumferential oscillation to the system of troughs 30 to simulate the effect of an earthquake. The items 30 to 35 are all demountable and removable from the centrifuge in order that it can be used for the type of testing illustrated in Figures 1 and 2. The version shown in Figure 5 differs from that shown in Figure 1 in that the scale modelling sample 17 is in the form of seawater carried in an annular channel 40 of thermal insulation itself fitting in the annular channel 16. Again, in order to introduce the liquid 17 into the channel 40, the drum 10 is spun about its axis A and the seawater 17 supplied to the channel 40 by way of a flexible hose (not shown) introduced through the stub tube 9. If it is desired to freeze the exposed surface 17' of the liquid 17, a cryogenic duct system 41 may be arranged in the drum 10 to feed a freezing gas or liquid to immediately adjacent to the seawater 17 to freeze the same. The version shown in Figures 6 and 7 differs from that shown in Figures 3 and 4 mainly in that the earthquake-simulating system 30-35 is replaced by an earthquake-simulating system comprised of the annular channel 16 for containing the soil 17, horizontal, annular brake flanges 50 of the drum 10, and pairs of hydraulically-operated brake shoes 51 regularly spaced around the periphery of the drum 10 and mounted on the steel-reinforced concrete 2, 3. Pulsed application of the brake shoes 51 to the flanges 50 produces an earthquake effect circumferentially in the soil 17. There are two versions shown in Figures 8 and 9, one shown to the left-hand side of the Figures and the other shown to the right-hand side thereof. Two main differences between the versions shown in Figures 8 and 9 and the versions shown in Figures 3, 4, 5 and 6 are that, firstly, the bottom wall 10a of the drum 10 is of a relatively massive construction (and without an access such as the manhole 25) and, secondly, the earthquake-simulating system is contained within the drum 10. At the left-hand side is shown a system in which the soil 17 is contained in an annular channel 60 mounted between pairs of upper and lower hydraulic rams 61 operating circumferentially of the drum 10. An elastomeric annulus 62 may be interposed between the channel 60 and the internal peripheral surface of the drum 10 to support the channel 60 radially relative to the drum 10. The relatively massive bottom wall of the drum 10 gives the drum 10 a relatively high reaction mass to minimize transmission through the drum of the circumferential oscillation motions produced by the rams 61. The drum 10 includes a lid 63 bolted at flanges 64 to the remainder of the drum 10 and centrally including the stub tube 9 mounted in the bearing 8. Following removal of the steel cap 7, the lid 63 is readily removable to give very good access to the interior of the drum 10. The relatively massive bottom wall also provides strength to react local forces that may be applied to the wall. At the right-hand side is shown a system in which the soil 17 is contained in a trough 70 mounted within a trough 71 by way of a pair of hydraulic rams (of which one is seen and referenced 72) arranged to oscillate the trough 70 radially relative to the trough 71. The trough 71 is itself mounted upon the internal peripheral surface of the drum 10 by way of pairs of upper and lower hydraulic rams 73 acting circumferentially of the drum. The rams 72 and 73 can be programmed to operate independently of each other simultaneously to impart to the soil 17 oscillations in two senses (namely radially and circumferentially, respectively, of the drum) substantially perpendicular to each other. The programme can be such that the rams operate in phase relationship the same as that of the earthquake wave pattern which it is desired to simulate. The assembly 17,71-73 is one of at least two equal masses mounted upon and regularly distributed around the internal peripheral surface of the drum to ensure dynamic and static balance of the drum about its axis, whereby the vector sum of forces at the centre of the drum will be zero. The sub-assembly 17,70 is one of a corresponding number of equal sub-masses included in the equal masses. These sub-masses are so oscillated radially of the drum 10 by pairs of rams (72) that the vector sum of the radial forces at the centre of the drum 10 will be zero. In Figure 10 the centrifuge is relatively small and the bottom bearing 12 in Figure 1 has been replaced by a pair of bearings 87 and 88 which can resist moments. This small drum is capable of operation at a useful speed without the assistance of an upper bearing. The relatively massive base wall in the form of a diametral plate 80 now carries a detachable peripheral wall 81 of the drum 10, together with a lid 82 closing the interior space 86 within which the scale modelling sample(s) 17 is/are placed. On the left-hand side of Figures 10 and 11 is shown a section of a ring channel 83, within which the sample 17 can be mounted, located above the plate 80. In Figure 11, on the right-hand side, is shown an individual sample container 84 in a gimbal mounting 89, which is an alternative way of mounting a geotechnical sample. The strength and stiffness of the plate 80 is adequate to support the bracket system 85 secured to the plate 80. The mounting 89 allows the container 84 to swing to an angle determined by the mass and the speed of rotation. Alternatively, the container 84 can be fitted without the use of a pivot mounting. One or more appropriate counterweights can be mounted on one or more bracket systems at the opposite side of the plate 80 if required. As in Figures 8 and 9, it is also possible to apply earthquake forces and react these forces by applying loads to the plate 80. In Figure 10 it is also possible to incorporate a central platform 21 as shown in Figure 1. In Figure 12 the centrifuge is again relatively small but the sample 17 has been made relatively high. In such circumstances, it is appropriate to reintroduce the top bearing 91. There is an extension section 92 to the peripheral wall of the drum and a stiff holder 93 with a stiff lid 94 and a stiff stub axle 95, the holder 93 serving to receive the sample 17. This stub axle 95 is supported by a self-aligning bearing 96 mounted in the cap 90. In Figures 12 and 13 on the left-hand side is shown a central work steady or mandrel 97. This mandrel 97 is mounted between the upper bearing 91 and the lower bearing 87 and provides a stiff mounting for a work support 98. A range of tools and/or experimental equipment can be mounted on the support 98, permitting the movement of equipment relative to the sample 17. In order that a number of scale modelling samples may conveniently be prepared away from the drum and then tested in sequence (for example where a small drum centrifuge is used for teaching a laboratory class) a variety of consolidometers may be used, such as are shown in Figures 14 to 17. Where geotechnical material such as clay is tested, the samples may require many days of preparation in consolidometers. The use of consolidometers considerably improves the utilisation of centrifuges in that samples are consolidated without the need to operate a centrifuge for prolonged periods. Figure 14 shows a consolidometer for the compaction of a circular-cylindrical sample 17. Gas, for example air, is contained in the cylinder 100; this air may be at a pressure of greater than 1 BAR. The pressure exerted by the air reacts against a piston 103 to exert a force on the movable cylinder 100 and thus on the sample 17 which is contained by sample cylinders 102 and a base 108. The piston 103 is driven down, to compress the air, by a screw 104 which is actuated by a worm-and-wheel 105. The worm may be turned by powered means or manually. Turning of the worm will cause changes in pressure in the cylinder 100 and thus on the sample 17. If the worm is powered, an automatic system of sensing the air pressure can be introduced, permitting the air pressure to be "topped-up" when necessary, or permitting the pressure to be programmed to a set sequence. During consolidation, water in the sample can drain through ducts 106 in the base 108. Figures 15 and 16 show a consolidometer in which the sample 17 is held in a container 110 which is of rectangular cross-section. The system for consolidating the sample is similar to that of Figure 14, except that a piston plate 111 is rectangular. One side of the container 110 includes a transparent viewing panel 12. This panel permits the viewing of the specimen during consolidation and during test on a centrifuge. In-flight viewing (with the centrifuge rotating) may be achieved by a variety of means including stroboscopic illumination, closed circuit television with rugged cameras, and short duration flash illumination synchronised with a stationary camera located adjacent the centrifuge. Where a sample 17 is to be consolidated into a ring channel 83, as shown in Figures 10 and 11, for example, it is appropriate to have a circular consolidation press as shown in Figure 17. In this press, there is a central cylinder 120 and an inflatable elastomeric tubular member 121 encircling the central cylinder 120. The ring channel 83 is placed on a support table 127 which also locates the central cylinder 120. The sample 17, for example a clay slurry, is poured into the channel and sealed with a cover plate 124. A fluid under pressure is fed into the inner chamber 128 and creates a pressure within the annular interior 129 of the elastomeric member 121. This pressure acts upon the sample 17 and over a period of time the sample will be consolidated. Holes 125 in the periphery of the channel 83 allow for the drainage of water from the sample. By feeding water under pressure through one or more ducts 126 into the sample, a downward hydraulic gradient can be achieved during consolidation. With the consolidometers shown in Figures 14, 15 and 16, this downward hydraulic gradient is also obtainable using the ducts 126. The application of downward hydraulic gradient produces a softness of the sample at its upper or inner face at which the hydraulic pressure is applied directly to the pores of the sample. The sample will automatically be stiffer at its outer or lower face at which hydraulic flow drains to a lower pressure. Figure 18 shows a drum centrifuge in which the drum 10 consists of the plate 80 and the detachable ring channel 83 and rotates about a horizontal axis A which is also its longitudinal axis. The drum 10 is mounted by way of a hollow axle 131 in horizontal bearings 130 and 132 carried by respective pillars 133 and 134 mounted upon a massive plinth 135. The hollow axle 131 and thus the drum 10 are rotated by an electric motor 136 via a belt-and-pulley system 137. Mounted horizontally and coaxially within the axle 131 by way of bearings 138 is a horizontal shaft 139 carrying a work support 140. The shaft 139 and thus the work support 140 are rotatable about the horizontal axis A by an electric motor 141 through a belt-and-pulley drive 142. Fixed to the axle 131 and the shaft 139 are respective sets of slip rings 143 and 144 whereby control et cetera signals may be transmitted to and from the rotating sample(s) 17 and the apparatus on the rotating work support 140. Fixed to the plinth 135 is a bracket 145 carrying a horizontal hydraulic ram 146 provided at its leading end with a latch device 147 for releasably seizing the adjacent end of the shaft 139, whereby the ram 146 may displace the shaft 139 and the work support 140 to-and-fro between a retracted position shown in full lines, in which the apparatus upon the support 140 is readily accessible, and a position shown partially in dot-dash lines, in which the work support 140 is received within the drum 10. The shaft 139 and the work support 140 can be retracted even while the drum 10 is still being rotated by the motor 136, although the motor 141 would be stopped prior to such retraction. The major difference between the version shown in Figure 18 and the version shown in Figure 19 is that the centrifuge is turnable between the horizontal position shown in full lines in Figure 19 and the vertical position shown in dot-dash lines therein, about horizontal trunnions 150 mounted in a massive bracket 151. This enables the user to obtain relatively easy access horizontally to the drum 10 and the work support 140 during construction of models and then to tilt the centrifuge into a vertical position to avoid during centrifuging the fluctuations in g force which would occur during rotation of the drum 10 about a horizontal axis. The trunnions 150 project from respective opposite sides of a sleeve 152 supporting the motors 136 and 141 and the axle 131. The major difference between the version shown in Figure 19 and the version shown in Figure 20 is that the centrifuge is free-standing and smaller. It includes a support stand 160 upon which is turnably mounted via the trunnions 150 a casing 161 including the sleeve 152 and a shroud 162 which serves to encircle the drum and thereby protect the operators. A ram-operated linkage 163 acting between the stand 160 and the casing 161 is used to turn the casing between the horizontal position shown, in which the operator has relatively easy access to the drum and the support 140, and a vertical position (not shown) in which the drum can be rotated at very high speed about its vertical axis, a safety interlock device (not shown) preventing rotation of the drum in its horizontal position except at slow speed. A problem sometimes encountered with transmission of analogue data signals from instrumentation at the rotating sample(s) is that electrical interference, produced by controllers for the drive motors (such as 136 and 141) and/or by the slip rings (such as 143) and/or extraneously distorts the analogue signals, with the result that incorrect or unintelligible readings are obtained. In order to mitigate this problem, the modification shown in Figures 21 and 22 may be made. The diametral plate 80 carries a computer 170 within a recess 171 closed by a main id 172 and an auxiliary lid 173. A recess 174 diametrically opposite to the recess 171 contains a dish 176 supporting electrical terminals 175 connected by electrical leads (not shown) to detection and measurement instrumentation associated with the sample(s). Other electrical leads (not shown) extend from the terminals 175 to the computer 170 through ducts 177 formed in the interior of the plate 80. The computer 170 converts the analogue signals received from the instrumentation into digital signals which are transmitted, via further electrical leads (not shown) extending through ducts 178, to slip rings corresponding to the slip rings 143 but much less in number. In this way, the deleterious effects of electrical nterference upon the readings obtained can be mitigated and the number of slip rings (143) and their associated electrical leads can be very significantly reduced. It is frequently desired to control the flow of liquid, particularly water, from the sample(s) 17, especially a sample 17 such as shown in Figure 25, under the high g forces, but conventional valves are unreliable since the high forces upon their moving parts can cause them to malfunction. This problem can be overcome by employing the modification of Figures 23 and 24. A metal tube 180 extends from adjacent the outer periphery of the sample 17 to a location in the plate 18 radially inwards of that outer periphery, the radial extent of the tube 180 being set to determine the radial water level in the sample 17 during high-speed rotation. The tube 180 extends in thermal insulation 181 in a recess 182 in the plate 80, the recess 182 also containing a good thermally conductive support 183. Bonded to the tube 180 in a good thermally conductive manner is a plate 184 of good thermal conductivity, between which and the support 183 is fitted a Peltier-effect device 185. The passing of electric current through the device 185 produces a steep temperature gradient between the support 183 and the plate 184. If the plate 184 constitutes the "cold" side of the device 185, then any water in the tube 180 can be frozen to obstruct water flow through the tube. By careful control of the current supply to the device 185, thereby carefully to control the temperature of the plate 184, the permitted water flow through the tube 180 can be reduced and increased as desired. In the modification shown in Figure 25, there is again seen the drum 10 consisting of the plate 80 and the ring channel 83, which is releasably attached by bolts (of which one is seen and referenced 190) to the plate 80. The scale model sample 17 here consists of an outer layer 17a of sand, two clay layers 17b sandwiching a sand acquifer layer 17c between them and an inner layer 17d of water. A system of maintaining constant pressure in the water in the aquifer layer 17c and allowing flow of the water into or out of the aquifer layer 17c at that constant pressure is illustrated; it includes a flexible tube 191 connected to the outlet of a bore 192 through the lowest wall of the ring channel 83. By way of branch bores 192a, 192b and 192c communicable with various locations spaced radially of the interior of the channel 83 (the bore 192b being shown open and the bores 192a and 192c shown closed), the bore 192 communicates with a selected region of hydraulic pressure in the interior of the channel 83 during centrifuging. The bore 192 is connected to a pipe 199 which is constantly supplied with a flow of water and the bore is maintained at a selected pressure by continual overflow of water from the adjustable outlet provided by the outlet end of the pipe 191. The system includes a horizontal channel piece 193 mounted upon a vertical pivot 194 and turnable thereon against the action of centrifugal force by a motorized winch 195 connected to the channel piece 193 by a cable 196. The position of the outlet end of the tube 191 radially of the drum during centrifuging determines the hydraulic head in the sample 17 and that position is adjustable by means of the winch 195 during centrifuging. In order simply and yet efficaciously to introduce water into one or more pipes such as the pipe 199, the plate 80 is provided co-axially with one or more, in this case three, annular recesses 197 at its underside. These recesses 197 open towards the axis of the centrifuge and are connected to a corresponding number of sets of connecting tubes 198 of which the tubes in each set are distributed in an arc about the axis of the centrifuge. These tubes 198 are themselves connected to the respective pipes (of which the pipe 199 is shown) themselves connected to the right-angled bores 192a to 192c in the ring channel. Each such bore is fitted with a sealing plug and when this is removed a connection is established between the water in the pipe 199 and the water in the sample 17 near to the end of the open bore. Water is injected into the recesses 197 by one or more stationary supply nozzles 201 extending through a hole or holes 202 in the base wall of the casing 161. As the plate 80 rotates, centrifugal force causes the water to flow from the recesses 197 through the tubes 198, the pipes 199, past the open bores 192b, and on to the outlet end of the tube 191 where it continually overflows. This controls the pressure of water at the end of the open bores 192b, and allows water either to drain into or out of the bores 192b as may be demanded by the sample 17 at any particular stage of an experiment. If desired, there can be a plurality of nozzles 201 supplying liquid at differing rates of flow or differing liquids to a plurality of recesses 197. The invention is applicable to increasing the maximum centrifugal forces obtainable with centrifuges, to increasing the versatility of centrifuges and to improving the design of structures on dry land and on the seabed, inter alia.

Claims: A scale modelling centrifuge comprising a member (80) rotatable about an axis (A), rotary receiving means (83) carried by said member (80) at a spacing from said axis (A) and serving to receive scale model means (17) so that said scale model means (17) also is spaced from said axis (A), characterised in that tilting means (163) is arranged to tilt said member (80) and said receiving means (83) so as to tilt said axis (A) between a substantially vertical first condition and a second condition at a substantial angle to the vertical. A centrifuge according to claim 1, wherein said second condition is substantially horizontal. A centrifuge according to claim 1 or 2, wherein said member (80) comprises a substantially horizontal rotary wall (80) having an annular outer periphery and rotatable about said axis (A), which is also the axis of said rotary wall (80). A centrifuge according to claim 3, wherein said wall (80) and said receiving means (83) are parts of a rotary drum. A centrifuge according to claim 3 or 4, wherein said wall (80) is massive relative to said receiving means (83). A centrifuge according to claim 3, 4, or 5, wherein said wall (80) is formed with an annular recess (197) substantially co-axial with said wall (80) and opening towards said axis (A) and disposed radially inwards of said receiving means (83), said centrifuge further comprising a stationary conduit (201) for supplying liquid (17) to said recess (197) and duct means (198-200) extending from said recess (197) towards said receiving means (83) for conducting said liquid (17) under centrifugal force from said recess (197) towards said receiving means (83). A centrifuge according to any one of claims 3 to 6, wherein said receiving means (83) is releasably attached to said wall (80). A centrifuge according to any preceding claim, and further comprising shaking means arranged to subject said scale model means (17) to shaking. A centrifuge according to claim 8, and comprising a plurality of masses distributed round said axis, at least one of said masses comprising said receiving means, said shaking means comprising a plurality of shaking means distributed round said axis (A) for shaking the respective masses. A centrifuge according to claim 8 or 9, wherein said shaking means comprises first shaking means effective to produce shaking of said scale model means (17) to-and-fro in a first sense and second shaking means operable independently of said first shaking means and effective to produce shaking of said scale model means (17) to-and-fro in a second sense transverse to said first sense. A centrifuge according to claim 10 as appended to claim 3, wherein said first sense is substantially tangential to said outer periphery and said second sense is substantially radial thereto. A centrifuge according to claim 9, or claim 10 or 11 as appended to claim 9, wherein said plurality of shaking means act to produce shaking of the respective masses radially of said axis (A) in such manner that the vector sum of the radial forces generated at the zone of said rotary wall (80) at said axis (A) by the radial shaking is substantially zero. A centrifuge according to claim 9 or 12 as appended to claim 3, or claim 10 or 11 as appended to claim 9 as appended to claim 3, wherein said plurality of shaking means act to produce shaking of the respective masses tangentially with respect to said axis (A) in such manner that the vector sum of the tangential forces is reacted by the inertia of said rotary wall (80). A centrifuge according to any preceding claim, and further comprising duct means (191) for communicating with a region of said receiving means (83) at which hydraulic pressure of liquid (17) is exerted, and drive means (195) which serves to displace an outlet end of said duct means (191) selectively in a direction of increasing hydraulic pressure in said receiving means (83) or in the opposite direction. A centrifuging method comprising rotating a centrifuge member (80) while its axis (A) of rotation is substantially vertical and thereby rotating receiving means (83) carried by said member (80) at a spacing from said axis (A)and receiving scale model means (17) so that the latter (17) also is spaced from said axis (A), characterised in that said rotating of said centrifuge member (80) while said axis (A) is substantially vertical is preceded by rotating said centrifuge member (80) and thus said receiving means (83) and said scale model means (17) while said axis (A) is at a substantial angle to the vertical, and then tilting said member (80) and thus said receiving means (83) and said scale model means (17) to tilt said axis (A) to its substantially vertical condition. A method according to claim 15, and further comprising, while said member (80) is rotating, supplying liquid (17) to an annular recess (197) formed substantially co-axially with a substantially horizontal rotary wall (80) of which said member (80) is comprised, said recess (197) opening towards said axis (A) and being disposed radially inwards of said receiving means (83), and conducting said liquid (17) under centrifugal force from said recess (197) to said receiving means (83). A method according to claim 15 or 16, and further comprising subjecting said scale model means (17) to shaking. A method according to claim 17, wherein said shaking comprises shaking a plurality of masses distributed round said axis, at least one of said masses comprising said receiving means. A method according to claim 17 or 18, wherein said shaking comprises shaking said scale model means (17) to-and-fro in a first sense and, independently of the latter shaking, shaking said scale model means (17) to-and-fro in a second sense transverse to said first sense. A method according to claim 19, wherein said first sense is substantially tangential to an outer periphery of said member (80) and said second sense is substantially radial of said axis (A). A method according to claim 17, 18, or 19, wherein said shaking comprises shaking the respective masses radially of said axis (A) in such manner that the vector sum of the radial forces generated at the zone of said rotary wall (80) at said axis (A) by the radial shaking is substantially zero. A method according to claim 18 or 21, or claim 19 or 20 as appended to claim 18, wherein said shaking comprises shaking the respective masses tangentially with respect to said axis (A) in such manner that the vector sum of the tangential forces is reacted by the inertia of said member (80).

Inventors: SCHOFIELD ANDREW NOEL, SCHOFIELD, ANDREW NOEL
Applicants: UNIV CAMBRIDGE TECH, CAMBRIDGE UNIVERSITY TECHNICAL SERVICES LIMITED
Application year: 1992
Main classification: G01M19
IPC codes: G01N3, G01N33