GB2278691A - Measuring the volume of void(s) in structures - Google Patents

Abstract

In a method of measuring the volume of void(s) within an artificial or natural structure, compressed gas is applied to the void(s) until a preset pressure is attained; the natural leakage rate from the void(s) is determined; a further leakage path with a known leakage rate may then be opened; the supply of gas to the void(s) is terminated and the time taken for the pressure in the void(s) to drop to a preset value, at a known leakage rate, is recorded; and that time is compared with prerecorded data to indicate the volume of the void(s). A method is also disclosed in which an elevated pressure is to be maintained in the void(s), and the elevated pressure constitutes the preset value.

Description

FLUID FLOW APPARATUS.

This invention relates to apparatus and a method for indicating the volume of a fluid, for example measuring the volume of a compressible fluid within a void.

Compressible fluids, by way of example air, may be contained within inacoessible or irregular void(s) or container(s). The volume of such a fluid may require detection or measurement for the purpose of anufacture, construction; maintenance1 injection, filling or investigation. This measurement may be required, for example1 in order to estimate the required extent of subsequent filling of a void or container by an incompressible or less oompressible material. The void or container may have intentional or unintentiopal route(s) to the atmosphere or adjacent void(s) through which fluids, e.g. liquids, gases or vapour may pass. Such passage of fluids will hereafter be called natural leaks.

The invention provides a method of indicating the volume of voids within an artificial or natural structure, cavern, mlneworklng, porous ground. structural element, bridge, slab, foundation, hydraullc structure, machinery, castling0 moulding, tank, boiler, duct, pipework or plant any of which may contalai solids, chambers or fissures by applying 8 gaseous pressure to n voled, measuring leakage rates with a mass flow controller, releasing the pressure through sn aperture, and indicating the volume by measuring the time taken for pressure to fall through e measured range, and comparing the time with that under calibration tests under similar conditions.The method may be varied wherein the natural leakage from the void under pressure is measured, and an additional leakage is added to form a part or all of the total leakage under which the pressure drop is timed.

Applications requiring significantly increased gas flowrates may be measured with a turbine flowmeter, or an orifice meter and pressure transducers, or series of flowmeters in series or parallel.

The pressure range may be maintained at an elevated level to suit the process within the structure, br means oi a valve, and selection of test pressure ranges to suit.

The timing of leakage may be controlled by simultaneous operation of a clock and removal of applied pressure to a void by use of pressure transducers. A fixed or variable deliberate leak may be added for the purpose of volume measurement.

The basis of volume measurement may be comparison of leakage times with those obtained musing the same equipment under calibration conditions.

A trap and snmple collector may form part of the calibruted connection equipment. The value of a measured pressure within a void may be used to select the pressure range over which a subsequent test to indicate void volume.

is underlaken. The pressure within the void is maintained above a minimum value during the test.

Fluid pressurE mar be used to time the ending of gas leakage in order to indicate void volumes. Signals generated from gas flows and measured leakage times may be combined with calibration information in a dataprocessor to indicate void volume.

Sealing of a duot following testing may be achieved br melting of plastic by means of the passing of electric current through an embedded wire.

The apparatus may indicate volume of gas within caverns, mineworkings and groundwork etc, for instance beneath foundations and slabs. The invention may provide useful information during the surveying of any such structures before, during- and/or after operation(s) to fill the voids. Data obtained by means of the invention assist the planning of such operations and the evaluation of effectiveness. The invention may provide information on voids around and between locations from and between which ground is inJected and/or consolidated.

Amongst examples the invention may be used for are the measurement of the volume of castings, mouldings and manufactured machinery. The invention estimates volumes of materials required and/or used, voids e.g chombers and/or ducts, and assists quality control.

The invention moy be used for the indication of void(s) within structures during maintenance and assessment, e.g. estimating the build up of deposits within ducts, boiler casings and water systems.

One important application of the present invention is inspection of post-tensioned concrete structures, e.6 bridge structures. It has been discovered that the ducts and/or void(s) within such structures may not be properly filled with cementitious or other grout during nonstruction. This results in the prestressing wires or strand within voids being vulnerable to corrosion. e.g. if water and/or de-icing salts used on a highway gain ingress.

Measurement of the volume of such void(s) and natural leakage to it indicates vulnerability of such structures to potential collapse. Existing test ethos, comprising for example radiography or radar, are difficult to interpret, take excessive time to perform1 and may be safety hazards.

This invention relates to voids, e.g. ducts1 located by, within or below natural and/or artificial structures, caverns, mineworkings, porous ground, groundwork, dams, bridges, beams, slabs, foundations, hydraulic structures, machinery, castings, mouldings, tanks, boilers, ducts, pipework or plant, any of which may contain voids. Some examples of voids are chambers or fissures.

in the accompanying drawings, which are by way of exumple: Figure 1. shows sections within the apparatus and connections between them.

Figure 2. shows section A, the compressed gas supply.

Figure 3. shows section B, the electrical supply.

Figure 4. shows/section C, the flow control section.

figure 5. shows section D, the leak assembly.

Figure 6. shows section E, the pressure timing section.

Figure 7. shows section Fl, connection type 1.

Figure 8. shows section F2, connection type 2.

Figure 9. shows an example of simplified apparatus to measure voids In a duct.

In the figures, components and pneumatic connections are numbered, and electrical connections are lettered. The identification of components and connections remains unchanged throughout the figures.

In the following descriptions of the sections the term conduit will be used to embody any tube, pipe, duct etc used to transmit pneumatic pressure or flow. The term cable will be used to embody any cable or wire etc. used to transmit electric current.

Section A, the Compressed gas Supply, is shown in figure 2, and may be described os follows: Compressed gas supply 10. from either a compressor, pump or bottle, passes by conduit 11 to filter 12, then by conduit 13 to valve 14.

Inlet pressure is read by gauge 16 and conduit 15 delivers cleansed gas at a known inlet pressure to supply conduits 1, 2 and 3.

Section B, the Electrical Supply. is shown in figure 2, and may be described as follows: Electrical supply 17, from either mains, battery or generator, passes by cable r to transformer 19 (ifvoLtage change required), and then by cables a,b,c. and d to sections D,C,E, and G respectively.

Section C, the Flow Control, is shown in figure 4, and may be described as 'follows The gas supply is fed br conduit 2 to regulator valve 21, by conduit 22 to pressure anugo 23, and by conduit 24 to mass flow controller 25.

This mass flow controller samples gas flow supplied by conduit 24 so as to produce at least one electrical signal in cables y which vary according to the volume passings through the mass flow controller 25. The signal in cables y is read by gauge 27. The gas then passes by conduit 26 through pilot valve 29, which, (if open), allows the gas to pass through conduit 30. Gas then either passes by conduit 4 to the leak assembly section D, and/or by conduit 7 to the connection section F it pilot valve 31 is open. Conduit 32 supplies gas at inlet pressure from conduit 2 to switch 33. if stitch 33 is open the gas inlet pressure passing to conduit 34 will close pilot valve 31.Alternatively, switch 33 may operate pilot valve 31 by electrical power delivered by cable w. Pilot valve 31 may also be closed by signals in cable k from the pressure timing section E. Cable a also supplies electrical power to switch 33 and mass flow controller 25. Pilot valsre 29 is closed by signals in either conduit 6 or cable i from the prossure timing section E. The apparatus in section C may be varied from this description according to the application. For example, for increased flow rates the mass flow controller may be replaced by a turbine flowmeter. For even greater flowrates the flow may be measured by use of an orifice meter and pressure transducers.

Section D, the Leak Assembly Section, is shown in figure 5, and mag be described as follows: Conduit 3 supplies gas at inlet pressure to switches 40. 43 and 46.

which are thus able to open or close pilot valves 42, 45 and 48 respectively when gas at inlet pressure is allowed through to conduits 41. 44 and 47. Alternativelg, electric supply b to switches 40, 43 and 46 enables them to operate the pilot valves by current in cables t, v and m respectively. Conduit 4 conveys gas from the flow control section, and hence through conduits 49, 51 and 53 to pilot valves 42, 45 and 48 respectively. then pilot valve 42 is open, gas from conduit 4 leaks to the atmosphere through a variable aperture 50. When pilot valve 45 is open, gas from conduit 4 leaks to the atmosphere through fixed aperture 52. then pilot valve 48 is open, gas from conduit 4 leaks to the atmosphere through fixed aperture 54.The position of the pilot valves is transmitted to the data processing section by cables e.

Section E, the Pressure Timing Section. is shown in figure 6, and may be described as follows: Conduit 1 supplies gas at inlet pressure to switch 60. When switch 60 is open, this gas st inlet pressure will pass to conduits 62 and 6. Pressure in conduit 62 will then activate transducer 63 , and pressure in conduit 6 (to the flow control section) will simuàneously close pilot valve 29 in the flow control section. Activation of transducer 63 will send a signal in cable p to start clock 64.

Alternatively. switch 60 may connect electric current supplied in cable o to cables 1 and n. Switch 60 will thereby close pilot valve 29 by current in cable i, and simultaneously start clock 64 by current in cable n. The clock is powered by cable o from electric supply cable c.

Pressure in conduit 9 from the connection F1 type 1. or F2 type 2, Is sensed by variable pressure transducer 65, which can be adjusted to activate at a variable pressure.

then aclIvaled, transducer 65 will send B signal in cable q to stop clock 64. Alternatively, clock 64 may be stopped by an electrical signal in cable J from the connection section valve 82 in connection type 2. When signals in cables J or q stop clock 64, a signal may also be sent In certain applications to the flow control via cable k to close pilot valve 31. The times of starting and stopping of clock 64 may be transmitted to the data processing section by signals in cables 6.

Section F1 and F2, the Connection Sections Types 1 and 2, are shown in Figures 7 and 8 respectively. The type of connection varies according to the application. Section F1, Figure 7 Illustrates an example for use when measuring the volume of void in a post-tensioned beam. The void 70 in the beam is intersected by a hole (conduit) 71. A pressure tight connection 72 is made between conduit 71 and conduit 75, to which a trap 74 is connected. Trap 74 collects liquids and solids passing from the void, which may be removed for sampling. Conduit 75 carries gas to and from trap 74, and the pressure of the gas is measured by gauge 76. Gas pressure is applied to conduit 77 by conduit 7 from the flow control section. Gas pressure in conduit 77 passes by conduit 9 to the pressure timing section. thus activating transducer 65 at its preset pressure, and thereby stopping clock 64.

Section F2, the Connection type 2, is shown in figure 8, and may be described as follow: This connection type Is shown by way of example for measuring volume of a void whilst maintaining the void at an elevated pressure, such as may be required during a grouting operation. The void within the structure is shown labelled 80. Filter 81 prevents liquids and solids within the void from contaminating valve 82. The filter 81 and v.ilve 82 may be embedded within the structure and connected to the outer surface by conduit 83 as shown. or may in some applications be at surface level or omitted. Gas pressure is applied to valve 82 by conduit 7 from the flow control section.

Opening of valve 82 transmits a signal to the timing section either pneumatically by conduit 9 or electrically by cable J. Opening of valve 82 may also be sensed by sechanicnl connection 86, which may, if required. also manually operate opening and closing of valve 82. Conduit 83 has n pressure tight seal 84 at surface level to isolale voids within n structure from atmospheric pressure and cables and conduits to other modules. Closure and/or sealing of conduits 83, 7. and/or 9 may be made at completion of tests by filling by injection from the void or exit point, sealing of the injection pipe at the surface, and/or closure of a plastic conduit by electrical heat sealing by means of embedded wiring.

Figure 9 shaws, by way of example, simplified apparatus sufficient for measurement of volume of voids within a post-tensioned duct. The numbering of components is os uscd in descriptions of the individual modules.

According to the invention. gaseous pressure may be applied to the void through conduits made during or subsequent to manufacture. Gas may escape from the void to adjacenL voids or to the atmosphere. Such leaks are natural leaks. Stable conditions will be reached at which the inlet gas flowrate, as measured by a mass flow controller for example, equals the natural leaks at a measured pressure.

Gas flowrate ut this stable pressure is the natural leak fiowrate. A sealed void will have zero natural leak flowra te.

A further deliberate leak may then be added by section D, the leak assembly, until the total leak is equal to one of a predetermined set of values. Switch 60 in the pressure timing section E is then used to out gas supply to the void by means of piligt valve 29- in the flow control section, and simultaneously start clock 64. Gas will then leak from the void through conduits 7 and 4 and the measured leaks in section D, as well as any natural leaks from the void. The clock 64 stops when pressure in the void as, indicated br conduit 9, activates transducer 65 at its preset value.

Thus the time for the pressure to drop between known values at a known total leakage rate is recorded. The volume ot void is indicated br comparison of this tire with times recorded under calibration conditions with similar equipment, leakage flow rates and pressure ranges.

According to the invention, when testing is required to be currled out whilst maintaining an elevated pressure within the void, connection section type 2 as in figure 8 is used. The ae method is then as follows. A potentially suitable deliberate leak rate is selected in section D, and quantified by use of the tlow controller 25 by closure of pilot valve 31 by switch 33. Switch 33 is then altered to supply gas at inlet pressure to the void iia the connection section type 2. The inlet pressure is increased br regulator 21. Valve 82 will open when applied inlet pressure first exceeds the pressure within the void.

Opening of valve 82 is sensed mechanically by control 85, electrically by cable J, and/or pneumatically by conduit 9.

Thus transducer 65 may be set to this pressure, called the test finish pressure. The inlet pressure is then increased by regulator 21 to the selected test start pressure, at which the timing is commenced br switch 33 as described above. It a compressible fluid exists within the void, flow of gas will have been indicated by gauge 27 as the pressure was increased to the test start pressure, and it will be the time taken for the return of this gas that will be recorded by clock 64. The volume of voids will be indicated by comparison of times with those recorded under calibration conditions. The void will be maintained at a pressure based upon that existing in the void before testing commenced. This is achieved either by closure of valve 82 by either liquid back pressure only. by mechanical connection 85, or by activation of pilot valve 31 by signal in cable k when transducer 65 reaches test finish pressure.

Injection or filling of the void may then be continued It measured conditions are not considered satisfactory.

The gas flow, as indicated by gauge 27, may 8180 computed with time to evaluate conditions within the void.

The present invention as described and/or shown in the drawings may be modified if desired, in the light of all of the above disclosures of the invention.

Claims (21)

1. A method of indicating volume of void(s) within a subject containing void(s), comprising: applying gaseous pressure to said subject; measuring leakage and/or leaking rate(s) from said subject of said applied pressure; releasing said applied pressure through at least one aperture; measuring time taken for said released pressure to fall through a measured pressure range; and comparing said time with that under calibration test(s under similar conditions, so as to indicate said volume oL void(s).

2. A method as claimed in claim 1, or a modification thereof, comprising measuring natural leakage and/or leakage rate(s) of gas from said void(s); and that measured leakage and/or leakage rate is used as part or all of the total released gas and/or leakage rate during measuring of said released pressure.

3. A method as claimed in claim 1 or 2, wherein said measuring of leakage rate(s) is measured by utilising a mass flow controller.

4. A method as claimed in claim 1 or 2, wherein said measuring of leakage rate(s) is measured by utilising a turbine flowmeter.

5. A method as claimed in claim 1 or 2, wherein said measuring of leakage rate(s) is measured by utilising an orifice meter and pressure transducers.

6. A method as claimed in claim 1 or 2, wherein said measuring of leakage rate(s) is measured by utilising flowmeters in series and/or in parallel.

7. A method as claimed in any one of claim 1 to 6, wherein said pressure range is maintained at an elevated level relative to said subject by utilising valve means and selection of suitable test pressure range(s).

8. A method as claimed in any one of claims 1 to 7, wherein timing of said leakage is controlled by simultaneous operation of clock means and removal of said applied pressure, by utilising pressure transducer(s).

9. A method as claimed in any one of claims 1 to 8, comprising a fixed or variable deliberate leak, for the purpose of volume measurement.

10. A method as claimed in any one of claims 1 to 9, comprising a trap and sample collector.

11. A method as claimed in any one of claims 1 to 10, wherein the value of a measured pressure within void(s) is used to select the pressure range over which a subsequent test to indicate void volume is undertaken, the gas within the void(s) being optionally maintained above a minimum value during testing.

12. A method as claimed in any one of claims 1 to 11, wherein gas pressures are used to time ending of gas leakage, in order to indicate void volume(s).

13. A method as claimed in any one of claims 1 to 12, wherein signal(s) generated from gas flows and measured leakage time(s) are combined with calibration information in data processor means so as to indicate void volume(s).

14. A method as claimed in any one of claims 1 to 13, comprising sealing of a duct following testing, by utilising melting of plastic.

15. A method as claimed in claim 1 or 2, when applied to post-tensioned concrete stucture(s).

16. A method as claimed in any one of claims 1, 2, and 15, when applied to bridge structures.

17. A method of indicating volume of void(s) within a subject containing void(s), substantially as hereinbefore described.

18. A method of indicating volume of void(s) within a subject containing void(s) as claimed in claim 1 or 2, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

19. Apparatus for indicating volume of void(s) within a subject, adapted for carrying out a method as claimed in any one of claims 1 to 18.

20. Apparatus as claimed in claim 19, substantially as hereinbefore described.

21. Apparatus as claimed in claim 19, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.