CA2829206A1 - Device for measuring deformations of the ground - Google Patents
Device for measuring deformations of the ground Download PDFInfo
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- CA2829206A1 CA2829206A1 CA2829206A CA2829206A CA2829206A1 CA 2829206 A1 CA2829206 A1 CA 2829206A1 CA 2829206 A CA2829206 A CA 2829206A CA 2829206 A CA2829206 A CA 2829206A CA 2829206 A1 CA2829206 A1 CA 2829206A1
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- cable
- ground
- anchor
- thrust plate
- fastening member
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- 238000001514 detection method Methods 0.000 claims abstract description 45
- 230000003287 optical effect Effects 0.000 claims abstract description 9
- 230000000295 complement effect Effects 0.000 claims description 3
- 239000013307 optical fiber Substances 0.000 abstract description 17
- 238000009826 distribution Methods 0.000 abstract description 7
- 230000008859 change Effects 0.000 abstract description 5
- 230000006378 damage Effects 0.000 abstract description 2
- 230000001419 dependent effect Effects 0.000 abstract 1
- 238000012544 monitoring process Methods 0.000 description 9
- 238000000034 method Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- 230000005855 radiation Effects 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 230000003014 reinforcing effect Effects 0.000 description 3
- 238000010008 shearing Methods 0.000 description 3
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000005284 excitation Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 230000005483 Hooke's law Effects 0.000 description 1
- 230000001154 acute effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 239000004746 geotextile Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000000116 mitigating effect Effects 0.000 description 1
- 238000012806 monitoring device Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000010257 thawing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/08—Testing mechanical properties
- G01M11/083—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT]
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Force Measurement Appropriate To Specific Purposes (AREA)
- Length Measuring Devices With Unspecified Measuring Means (AREA)
- Length Measuring Devices By Optical Means (AREA)
- Optical Transform (AREA)
Abstract
The invention relates to devices for measuring a deformation using an optical fiber as sensing element, with the option of measuring the distribution of a deformation of the optical fiber in the longitudinal direction. The invention makes it possible to limit the force transmitted by an anchor to a detection cable in the event of the anchors shifting relative to one another as a result of movements of the ground which are not dependent on the properties of the ground, which properties may be known imprecisely or may change over time, and, on the basis of this, to extend the service life of the detection cable. The device for measuring deformations of the ground comprises an optical detection cable which is sensitive to deformation, a measuring unit which is connected to the cable, and anchors which are connected to the cable and to the ground, and is equipped with a system for protecting the cable from destruction, said system comprising a safety device built into each anchor.
Description
DEVICE FOR MEASURING DEFORMATIONS OF THE GROUND
The invention relates to devices for measuring strain distribution that use optical fiber as the sensing element.
The integrity and operability of distributed objects are mainly determined by properties and condition of a ground where they are laid. As a rule, damages to distributed objects, such as underground pipelines, roads, tunnels, etc., are caused by ground movements or by unauthorized digging. Problems relating to the integrity of underground distributed objects are most acute when such objects are laid under water, in mountain regions (on slopes) and in the conditions of thawing and freezing of a ground surrounding them. In order to prevent emergencies in distributed objects, continuous or periodic monitoring of ground movements (dislocations) and its temperature in a close proximity to an object is used. A optical detection cable is laid in the ground region subject to the risk of dislocations in such a way that ground movements can cause elastic tensile and compression strains in segments of optical fibers constituting the cable.
Longitudinal strain of an optical fiber is measured and used for analyzing ground movements. An optical fiber designed for measuring strain distributions is arranged in a special detection cable that, on one side, enables the fiber to deform (expand and compress) under the influence of external forces and, on the other side, protects it against adverse external effects in the processes of assembly and operation.
Optical fibers, as used in a detection cable, have a limited range of allowable strains and a corresponding range of cable tensile loads. If a maximum allowable tensile load of a detection cable that usually corresponds to extension of an optical fiber by 1% - 2% is exceeded, the optical fiber breaks, which results in the impossibility of using the whole detection cable or a part thereof as a sensing element. Therefore, in order to restore operability, it is required to restore the integrity of the detection cable, which is associated with labor-intensive earth works for replacing its damaged section.
A device for measuring strain is known (see: RU Patent No. 2346235, published on 27.07.2008), wherein a method is used that is based on the phenomenon of stimulated Brillouin scattering appearing in an optical fiber. According to this method, an optical fiber is used as a sensing element for detecting strain and/or temperature in a medium wherein the optical fiber is arranged. This device comprises an excitation light radiation ' ' source 1, a sensitive optical fiber 2, an optical coupler 3, a sounding light radiation source 4 and a detector 5 (Figure 1). One end of the sensitive optical fiber 2 is connected to the excitation light radiation source 1, and the second end is connected to the sounding light radiation source 4 and the detector 5 through the optical coupler 3.
At present, instruments are manufactured and commercially available wherein a method of measuring axial strain (tension or compression) distribution is used that are based on the phenomenon of stimulated Brillouin scattering. Examples of such devices are the Brillouin analyzer Ditest STA-R
manufactured by Omnisens SA [URL:
http://www.omnisens.ch/ditest/3521-ditest-sta-r.pbp, logging in date 11/02/111, Switzerland, and the Brillouin reflectometer AQ8603 OPTICAL FIBER STRAIN
ANALYZER manufactured by Yokogawa Electric Corporation [URL:
http ://tmi.yokogawa.com/products/optical-measuring-instruments/optical-sensing-products/aq8603-optical-fiber-strain-analyzer/, logging in date 11/02/11].
A method and a device for monitoring a pipeline are also known [Long-distance fiber optic sensing solutions for pipeline leakage, intrusion and ground movement detection.
Marc Nikles Omnisens S.A. "SPIE Defense, Security and Sensing Conference", April 15-17, 2009, Orlando, Florida, USA, Proceedings of SPIE Vol. 7316, 7316-01 (2009)].
The method includes continuous monitoring of ground movements and temperatures in a close proximity to a pipeline 6 with the use of the device comprising a monitoring unit 7 that includes a Brillouin analyzer, an optical switch and an optical cross-connect and may be located, e.g., in pipeline compressor stations, and detection cables 8 for measuring temperatures 8 and detection cables 9 for measuring ground movements that are connected thereto (Figure 2). The monitoring unit 7 may be coupled via a network interface 10 to a distant control point 11. The pipeline monitoring device 5 fulfills the requirements to pipeline integrity monitoring systems, measuring temperature and strain distributions along respective detection cables at distances typical for pipelines, e.g., corresponding to a distance between pipeline compressor stations.
A device is known [DITEST SMARTEX SENSOR. - URL: http://www.smartec.ch /PDF/SDS%2011.1050%20DiTeSt%20SMART Geo Tex% 20Fabric.pdf, logging in date 13.07.2010] that is intended for improving ground dislocation monitoring accuracy and that has an increased cable adhesion to ground surrounding it. The device is a geotextile =
material having a detection cable integrated therein for measuring strain. The device consists of non-woven material bands that are arranged on a cable and envelope it with a gap. This enables to achieve an increased area of contact between bands and ground and, hence, improved adhesion. But this device has the following disadvantages. It does not enable to accurately fix initial lateral dislocations of ground due to the gap between the cable and the bands as well as due to compliance of the band material.
Initially, when lateral movements of ground are small, the bands move together with the ground relative to the cable within the limits of the gap, then, after the gap is closed, the bands deform and transfer a part of the load to the cable, and then, when ground movements become greater, the bands and the cable move jointly. All this leads to lower results during determination of initial lateral movements of the ground. Furthermore, since the bands are not attached to the cable longitudinally, axial slipping of the cable occurs in regions located on both sides from the area of a ground movement. Such cable slipping introduces errors into accuracy of determining a location of a ground movement. A
length of every region of cable longitudinal slipping is determined according to a friction force increasing along the cable length and required in order to keep it in a stable part of the ground.
The closest technical solution (prototype) is a device (Defining and monitoring of landslide boundaries using fiber optic systems. M. Iten, A. Schmid, D.
Hauswirth &
A.M. Puzrin. Prediction and Simulation Methods for Geohazard Mitigation - Oka, Murakami & Kimoto (eds), 2009 Taylor & Francis Group, London, ISBN 978-0-415-80482-0) comprising a Brillouin analyzer manufactured by Omnisens and a sensing system embedded into the ground. A Brillouin analyzer enables to measure strain distribution on a detection cable. The sensing system comprises anchors 12 rigidly fixed on the detection cable for measuring strain 13 in pre-determined points (Figure 3). The dimensions of the anchors 12 are determined experimentally, according to a measured force of securing an anchor 12 in the ground. The design of each anchor 12 ensures movement of the cable together with the surrounding ground, preventing the ground from flowing around the cable 13. This device has been used for defining boundaries of ground movements (landslides).
But this device has the following disadvantages. Since the anchor is rigidly fixed on the detection cable, a maximum load transferred by the anchor to the detection cable is determined by strength of anchor fixation in the ground. Strength of anchor fixation in the ground depends on the anchor shape and ground properties that may change during operation, for example, when a ground density is changed over time, as a result of compaction, lowering of temperature or change of a ground moisture. If dislocation of the ground and the anchors together with the ground is significant (occurring quickly or slowly developing over time), a load transferred to the detection cable by the anchor may exceed an allowable tensile load of the cable, which will put it out of operation irreversibly. Secure engagement with the ground becomes a disadvantage in such extreme operation conditions.
The technical effect of the invention is limitation of a load transferred to the detection cable by the anchor, when the anchors dislocate together with the ground irrespective of the ground conditions that may be known imprecisely or may change over time, and, due to this, an increase in the service life of the detection cable. An accompanying particular technical effect of the invention is maintenance of operability of the deformable mechanical safety device after its operation.
The said technical effect is achieved due to the fact that the known device for measuring ground strain, which comprises a strain-sensitive optical cable, a measuring unit coupled with the cable, anchors connected to the cable and to the ground, is provided, according to the claimed invention, with a system protecting the cable against breaking, the system including a safety device for each anchor.
Each anchor may be connected to the cable by a releasable clamp and to the ground by a thrust plate.
The safety device may include a fastening member provided with the possibility of fastening the thrust plate to the releasable clamp, the said fastening member breaking when a pre-determined load is applied to the fastening member, thus ensuring free movement of the cable relative to the thrust plate.
The fastening member may be made as latches located on the anchor thrust plate and being in engagement with the releasable clamp.
The safety device may include a fastening member provided with the possibility of securing the cable to the releasable clamp, the said fastening member deforming when a pre-determined load is applied to the fastening member, thus ensuring free movement of the cable relative to the thrust plate.
The fastening member may be made as an longitudinal slot through which the cable is placed into the longitudinal channel, and the thrust plate is rigidly connected to the releasable clamp. The invention is illustrated on the drawings, wherein:
Figure 1 shows the device for measuring strain;
Figure 2 shows a diagram of a device for monitoring a pipeline;
Figure 3 shows a diagram of a sensing system embedded into the ground, which comprises anchors arranged on a detection cable;
Figure 4 shows a sensing system comprising anchors arranged on a detection cable;
Figure 5 shows a top view of a device embodiment with an anchor having a breakable mechanical safety device;
Figure 6 shows a front view of a device embodiment with an anchor having a breakable mechanical safety device;
Figure 7 shows a front view of one of the two identical parts 24 composing a thrust plate for the device embodiment with an anchor having a breakable mechanical safety device;
Figure 8 shows a top view and a longitudinal section of the anchor in the device embodiment with the anchor having a deformable mechanical safety device;
Figure 9 shows a front view of the device embodiment with the anchor having the deformable mechanical safety device.
The claimed device comprises a measuring unit, which is a Brillouin analyzer or another similar device for measuring strain distribution of an optical fiber, and a sensing system embedded into the ground. The sensing system comprises a optical detection cable 14 and anchors 15, 16, 17 rigidly arranged thereon in pre-determined points (Figure 4). The sensing system is arranged under the surface of the ground 18 at a certain depth.
According to the claimed invention, the detection cable 14 senses a tensile load along its axis, and each anchor 15, 16, 17 has a thrust plate 19 perpendicular to the cable axis and secured to the detection cable 14 (Figures 5-8). The anchor thrust plate 19 cooperates with the immovable ground and transfers a dislocation load of the detection cable 14 and =
the anchors 15, 16 being in a movable and transitional ground regions. The anchor thrust plate 19 has a surface area sufficient for preventing the anchor from moving in the ground under influence of a load acting upon it from the side of the cable along its axis.
If a ground movement (dislocation) 30 occurs, the anchors 15, 16 move together with the ground in the direction shown by the arrows in the area of the ground movement (Figure 4). The anchor 17 located in the region of immovable ground is fixed therein.
Thus, the cable rigidly secured to the anchors will deform (become longer) on the movement area boundary where a distance between the anchors changes (increases). A relative elongation of the cable and, correspondingly, the optical fiber is measured with a Brillouin analyzer and is used for analyzing a position and parameters of ground movements. The relative elongation 0 (a dimensionless quantity) of a uniformly elongated cable segment with a length L may be calculated according to the following formula:
El = D/L, where: L ¨ a length of a segment in the non-deformed condition, in mm; and 0 - change in the segment length in the result of deformation, in mm.
Further, a tensile load of any cable segment secured on its both ends to anchors is associated with a cable specific elongation caused by shift of the anchors relative to each other in the result of a ground movement. In accordance with the Hooke's law, they are proportional to each other within the range of small strains (El 1).
F = kEID, where: F ¨ tensile load, in newtons; and k ¨ proportionality coefficient (rigidity), in newtons.
However, the cable resistance to a tensile load is limited by a quantity typical for each cable type, which is usually indicated in the specification (DiTeSt SMARTube Sensor-URL:
http://www.roctest-group.com/sites/default/files/datasheets/products/SDS%2011.1040%20DiTeSt%20SMA
RT ube%20Sensor.pdf, , Logging in date 27.02.2011).
In order to prevent a cable from breaking, the claimed device is provided with a system for protecting a cable against breaking, which system comprises a safety device embedded into each anchor, and the safety device operates in a case where a load acting upon the detection cable from the anchor exceeds a pre-determined value (operation threshold). As the safety device operates, the cable moves in the ground under the action of a tensile load, and, consequently, the tensile load in a dangerous region lessens, thus preventing the cable from breaking. Since a tensile load on the cable is increased by the value of the load under the action of the force acting upon the cable from the side of the anchor, the operation threshold should be significantly (depending on supposed parameters of ground movements) lower than the cable resistance to the tensile load. If it is supposed that a movement is possible only in one point of the sensing system, as embedded into the ground, in a segment between two anchors, then it is sufficient that the operation threshold will be insignificantly lower than the cable resistance to the tensile load (by the value of the sum of errors in determination of such parameters). The setting of the operation threshold in the anchor design enables to avoid uncertainties associated with changeability of ground mechanical properties in different places and over time.
The claimed device embodiments comprise a mechanism for protecting the detection cable against tensile loads exceeding allowable values applied in the two structural embodiments of the mechanical safety devices.
According to the first embodiment of the structure with a breakable mechanical safety device (Figures 5, 6), an anchor comprises a thrust plate 19 and a releasable clamp 21.
The anchor is symmetrical relative to the cable. Two identical halves of the releasable clamp 21 are fixed on the cable 14 with a screwed fastening member 22, and the cable 14 is gripped in a slot 23. The thrust plate 19 consists of two identical parts 24 that are attached to the releasable clamp 21 with latches 25, and the parts 24 are also connected therebetween with reinforcing rods 26 and latches 27. The reinforcing rods 26 and the latches 27 make the structure of the thrust plate 19 more rigid, preventing the parts 24 from bending and ensuring perpendicularity of the thrust plate 19 to the axis of the cable 14. The structure of the thrust plate 19 is provided with receptacles 29 for installing the reinforcing rods 26.
The function of a safety device in this structure is performed by the latches 25 (Figure 7).
Since the surface area of projection of the releasable clamp 21 on a plane perpendicular to the axis of the detection cable 14 is significantly less than the similar surface area of the thrust plate 19, a load acting upon the releasable clamp 21 from the side of the thrust plate 19 is approximately equal to a load acting upon the detection cable from the side of the anchor. In a case where a load acting upon the detection cable from the side of the anchor exceeds a pre-determined value, the mechanical safety device operates by breaking the latches 25. The latches 25 are broken by shearing along planes 28. In the result of shearing the latches 25 along the planes 28 the thrust plate 19 is mechanically disconnected from the releasable clamp 21, whereupon the cable 14 moves, under the action of a tensile load, relative to the ground (and the thrust plate fixed therein), which causes a decrease in the cable relative elongation and, consequently, the tensile load on the dangerous segment, preventing the cable from breaking. An operation threshold of the mechanical safety device is selected by changing the strength of the thrust plate material or by changing the geometrical parameters of the latches 25 so as their shearing strength is equal to half a load acting upon the releasable clamp from the side of the thrust plate 19 at which the mechanical safety device should operate.
According to the second embodiment of the structure with a deformable mechanical safety device (Figures 8, 9), the structure has the elements similar to those of the structure with a breakable mechanical safety device, except for the following differences in the thrust plate 30 and the releasable clamp 31. The structure of the thrust plate 30 is different in that it is secured to the releasable clamp 31 reliably in the whole range of loads for which the anchor is intended. Dimensions and a material of the parts of the thrust plate 30 are selected so as to ensure their integrity when a load acting upon the detection cable from the anchor side reaches a pre-determined value at which the mechanical safety device operates.
The structure of the releasable clamp 31 is different in that the slot 32 of the releasable clamp 31 is made with internal recesses on each of the clamping plates 33 and 34. Each recess has a broadened portion in the beginning and in the end of the slot 32.
An elastic insert 35 with a pre-determined elastic coefficient is immovably installed in the slot 32, the said insert having the surface complementary to that of the recesses and being provided with an inner longitudinal channel with a semi-oval cross-section which greater axis is oriented parallel to the release plane of the clamping plates 33 and 34. A rigid calibration plate 36 consisting of two identical parts is arranged in the splitting of the clamping plates 33 and 34. The elastic insert 35 has at least one longitudinal cut for the detection cable 14.
The function of a mechanical safety device in this structure is performed by the releasable clamp 31. The anchor is held on the cable 14 due to a friction force between it and the elastic insert 35. In a case where a load acting upon the detection cable from the anchor side exceeds a pre-determined value, deformation of the elastic insert 35 occurs that causes operation of the mechanical safety device because the cable 14 slips relative to the anchor fixed in the ground, and such slipping is accompanied by a decrease in the said load. This process continues until the said load is equal to the operation threshold of the safety device. The said slipping of the cable relative to the ground causes a reduction in the cable relative elongation and, consequently, in the tensile load in the dangerous region, thus preventing the cable from breaking.
The operation threshold of the safety device is determined by the shape and depth of the detection cable outer surface, by the force of pressing the cable to the anchor, and by the coefficient of friction (static and sliding) of the anchor relative to the detection cable.
The operation threshold Fc (in newtons) of the mechanical safety device is determined experimentally or calculated according to the formula: Fc = k1 .P, in newtons, where k1 ¨
friction coefficient of the elastic insert relative to the detection cable, P, in newtons ¨
force of pressing the elastic insert to the detection cable. The operation threshold is adjusted by replacing one elastic insert with another one having a different coefficient of elasticity and/or by selecting the thickness of the calibration plate 17.
The tensile load of the detection cable is limited at a level lower than a maximum allowable one by introducing the said safety devices to the device structure.
The load to the detection cable is limited either by limiting the force of securing the anchor thrust plate at the releasable clamp (breakable mechanical safety device), or by limiting the force of securing the releasable clamp on the detection cable (deformable mechanical safety device). In the case of a deformable mechanical safety device the force of securing the anchor on the detection cable is limited by selecting elastic inserts with a given elasticity coefficient and by adjusting a distance between clamping plates 9, 10 by means of the calibration plate 17. In the case of breakable mechanical safety device the force of securing the anchor thrust plate on the releasable clamp is limited by selecting materials used for making anchors and by changing geometrical parameters of the anchor parts.
The invention relates to devices for measuring strain distribution that use optical fiber as the sensing element.
The integrity and operability of distributed objects are mainly determined by properties and condition of a ground where they are laid. As a rule, damages to distributed objects, such as underground pipelines, roads, tunnels, etc., are caused by ground movements or by unauthorized digging. Problems relating to the integrity of underground distributed objects are most acute when such objects are laid under water, in mountain regions (on slopes) and in the conditions of thawing and freezing of a ground surrounding them. In order to prevent emergencies in distributed objects, continuous or periodic monitoring of ground movements (dislocations) and its temperature in a close proximity to an object is used. A optical detection cable is laid in the ground region subject to the risk of dislocations in such a way that ground movements can cause elastic tensile and compression strains in segments of optical fibers constituting the cable.
Longitudinal strain of an optical fiber is measured and used for analyzing ground movements. An optical fiber designed for measuring strain distributions is arranged in a special detection cable that, on one side, enables the fiber to deform (expand and compress) under the influence of external forces and, on the other side, protects it against adverse external effects in the processes of assembly and operation.
Optical fibers, as used in a detection cable, have a limited range of allowable strains and a corresponding range of cable tensile loads. If a maximum allowable tensile load of a detection cable that usually corresponds to extension of an optical fiber by 1% - 2% is exceeded, the optical fiber breaks, which results in the impossibility of using the whole detection cable or a part thereof as a sensing element. Therefore, in order to restore operability, it is required to restore the integrity of the detection cable, which is associated with labor-intensive earth works for replacing its damaged section.
A device for measuring strain is known (see: RU Patent No. 2346235, published on 27.07.2008), wherein a method is used that is based on the phenomenon of stimulated Brillouin scattering appearing in an optical fiber. According to this method, an optical fiber is used as a sensing element for detecting strain and/or temperature in a medium wherein the optical fiber is arranged. This device comprises an excitation light radiation ' ' source 1, a sensitive optical fiber 2, an optical coupler 3, a sounding light radiation source 4 and a detector 5 (Figure 1). One end of the sensitive optical fiber 2 is connected to the excitation light radiation source 1, and the second end is connected to the sounding light radiation source 4 and the detector 5 through the optical coupler 3.
At present, instruments are manufactured and commercially available wherein a method of measuring axial strain (tension or compression) distribution is used that are based on the phenomenon of stimulated Brillouin scattering. Examples of such devices are the Brillouin analyzer Ditest STA-R
manufactured by Omnisens SA [URL:
http://www.omnisens.ch/ditest/3521-ditest-sta-r.pbp, logging in date 11/02/111, Switzerland, and the Brillouin reflectometer AQ8603 OPTICAL FIBER STRAIN
ANALYZER manufactured by Yokogawa Electric Corporation [URL:
http ://tmi.yokogawa.com/products/optical-measuring-instruments/optical-sensing-products/aq8603-optical-fiber-strain-analyzer/, logging in date 11/02/11].
A method and a device for monitoring a pipeline are also known [Long-distance fiber optic sensing solutions for pipeline leakage, intrusion and ground movement detection.
Marc Nikles Omnisens S.A. "SPIE Defense, Security and Sensing Conference", April 15-17, 2009, Orlando, Florida, USA, Proceedings of SPIE Vol. 7316, 7316-01 (2009)].
The method includes continuous monitoring of ground movements and temperatures in a close proximity to a pipeline 6 with the use of the device comprising a monitoring unit 7 that includes a Brillouin analyzer, an optical switch and an optical cross-connect and may be located, e.g., in pipeline compressor stations, and detection cables 8 for measuring temperatures 8 and detection cables 9 for measuring ground movements that are connected thereto (Figure 2). The monitoring unit 7 may be coupled via a network interface 10 to a distant control point 11. The pipeline monitoring device 5 fulfills the requirements to pipeline integrity monitoring systems, measuring temperature and strain distributions along respective detection cables at distances typical for pipelines, e.g., corresponding to a distance between pipeline compressor stations.
A device is known [DITEST SMARTEX SENSOR. - URL: http://www.smartec.ch /PDF/SDS%2011.1050%20DiTeSt%20SMART Geo Tex% 20Fabric.pdf, logging in date 13.07.2010] that is intended for improving ground dislocation monitoring accuracy and that has an increased cable adhesion to ground surrounding it. The device is a geotextile =
material having a detection cable integrated therein for measuring strain. The device consists of non-woven material bands that are arranged on a cable and envelope it with a gap. This enables to achieve an increased area of contact between bands and ground and, hence, improved adhesion. But this device has the following disadvantages. It does not enable to accurately fix initial lateral dislocations of ground due to the gap between the cable and the bands as well as due to compliance of the band material.
Initially, when lateral movements of ground are small, the bands move together with the ground relative to the cable within the limits of the gap, then, after the gap is closed, the bands deform and transfer a part of the load to the cable, and then, when ground movements become greater, the bands and the cable move jointly. All this leads to lower results during determination of initial lateral movements of the ground. Furthermore, since the bands are not attached to the cable longitudinally, axial slipping of the cable occurs in regions located on both sides from the area of a ground movement. Such cable slipping introduces errors into accuracy of determining a location of a ground movement. A
length of every region of cable longitudinal slipping is determined according to a friction force increasing along the cable length and required in order to keep it in a stable part of the ground.
The closest technical solution (prototype) is a device (Defining and monitoring of landslide boundaries using fiber optic systems. M. Iten, A. Schmid, D.
Hauswirth &
A.M. Puzrin. Prediction and Simulation Methods for Geohazard Mitigation - Oka, Murakami & Kimoto (eds), 2009 Taylor & Francis Group, London, ISBN 978-0-415-80482-0) comprising a Brillouin analyzer manufactured by Omnisens and a sensing system embedded into the ground. A Brillouin analyzer enables to measure strain distribution on a detection cable. The sensing system comprises anchors 12 rigidly fixed on the detection cable for measuring strain 13 in pre-determined points (Figure 3). The dimensions of the anchors 12 are determined experimentally, according to a measured force of securing an anchor 12 in the ground. The design of each anchor 12 ensures movement of the cable together with the surrounding ground, preventing the ground from flowing around the cable 13. This device has been used for defining boundaries of ground movements (landslides).
But this device has the following disadvantages. Since the anchor is rigidly fixed on the detection cable, a maximum load transferred by the anchor to the detection cable is determined by strength of anchor fixation in the ground. Strength of anchor fixation in the ground depends on the anchor shape and ground properties that may change during operation, for example, when a ground density is changed over time, as a result of compaction, lowering of temperature or change of a ground moisture. If dislocation of the ground and the anchors together with the ground is significant (occurring quickly or slowly developing over time), a load transferred to the detection cable by the anchor may exceed an allowable tensile load of the cable, which will put it out of operation irreversibly. Secure engagement with the ground becomes a disadvantage in such extreme operation conditions.
The technical effect of the invention is limitation of a load transferred to the detection cable by the anchor, when the anchors dislocate together with the ground irrespective of the ground conditions that may be known imprecisely or may change over time, and, due to this, an increase in the service life of the detection cable. An accompanying particular technical effect of the invention is maintenance of operability of the deformable mechanical safety device after its operation.
The said technical effect is achieved due to the fact that the known device for measuring ground strain, which comprises a strain-sensitive optical cable, a measuring unit coupled with the cable, anchors connected to the cable and to the ground, is provided, according to the claimed invention, with a system protecting the cable against breaking, the system including a safety device for each anchor.
Each anchor may be connected to the cable by a releasable clamp and to the ground by a thrust plate.
The safety device may include a fastening member provided with the possibility of fastening the thrust plate to the releasable clamp, the said fastening member breaking when a pre-determined load is applied to the fastening member, thus ensuring free movement of the cable relative to the thrust plate.
The fastening member may be made as latches located on the anchor thrust plate and being in engagement with the releasable clamp.
The safety device may include a fastening member provided with the possibility of securing the cable to the releasable clamp, the said fastening member deforming when a pre-determined load is applied to the fastening member, thus ensuring free movement of the cable relative to the thrust plate.
The fastening member may be made as an longitudinal slot through which the cable is placed into the longitudinal channel, and the thrust plate is rigidly connected to the releasable clamp. The invention is illustrated on the drawings, wherein:
Figure 1 shows the device for measuring strain;
Figure 2 shows a diagram of a device for monitoring a pipeline;
Figure 3 shows a diagram of a sensing system embedded into the ground, which comprises anchors arranged on a detection cable;
Figure 4 shows a sensing system comprising anchors arranged on a detection cable;
Figure 5 shows a top view of a device embodiment with an anchor having a breakable mechanical safety device;
Figure 6 shows a front view of a device embodiment with an anchor having a breakable mechanical safety device;
Figure 7 shows a front view of one of the two identical parts 24 composing a thrust plate for the device embodiment with an anchor having a breakable mechanical safety device;
Figure 8 shows a top view and a longitudinal section of the anchor in the device embodiment with the anchor having a deformable mechanical safety device;
Figure 9 shows a front view of the device embodiment with the anchor having the deformable mechanical safety device.
The claimed device comprises a measuring unit, which is a Brillouin analyzer or another similar device for measuring strain distribution of an optical fiber, and a sensing system embedded into the ground. The sensing system comprises a optical detection cable 14 and anchors 15, 16, 17 rigidly arranged thereon in pre-determined points (Figure 4). The sensing system is arranged under the surface of the ground 18 at a certain depth.
According to the claimed invention, the detection cable 14 senses a tensile load along its axis, and each anchor 15, 16, 17 has a thrust plate 19 perpendicular to the cable axis and secured to the detection cable 14 (Figures 5-8). The anchor thrust plate 19 cooperates with the immovable ground and transfers a dislocation load of the detection cable 14 and =
the anchors 15, 16 being in a movable and transitional ground regions. The anchor thrust plate 19 has a surface area sufficient for preventing the anchor from moving in the ground under influence of a load acting upon it from the side of the cable along its axis.
If a ground movement (dislocation) 30 occurs, the anchors 15, 16 move together with the ground in the direction shown by the arrows in the area of the ground movement (Figure 4). The anchor 17 located in the region of immovable ground is fixed therein.
Thus, the cable rigidly secured to the anchors will deform (become longer) on the movement area boundary where a distance between the anchors changes (increases). A relative elongation of the cable and, correspondingly, the optical fiber is measured with a Brillouin analyzer and is used for analyzing a position and parameters of ground movements. The relative elongation 0 (a dimensionless quantity) of a uniformly elongated cable segment with a length L may be calculated according to the following formula:
El = D/L, where: L ¨ a length of a segment in the non-deformed condition, in mm; and 0 - change in the segment length in the result of deformation, in mm.
Further, a tensile load of any cable segment secured on its both ends to anchors is associated with a cable specific elongation caused by shift of the anchors relative to each other in the result of a ground movement. In accordance with the Hooke's law, they are proportional to each other within the range of small strains (El 1).
F = kEID, where: F ¨ tensile load, in newtons; and k ¨ proportionality coefficient (rigidity), in newtons.
However, the cable resistance to a tensile load is limited by a quantity typical for each cable type, which is usually indicated in the specification (DiTeSt SMARTube Sensor-URL:
http://www.roctest-group.com/sites/default/files/datasheets/products/SDS%2011.1040%20DiTeSt%20SMA
RT ube%20Sensor.pdf, , Logging in date 27.02.2011).
In order to prevent a cable from breaking, the claimed device is provided with a system for protecting a cable against breaking, which system comprises a safety device embedded into each anchor, and the safety device operates in a case where a load acting upon the detection cable from the anchor exceeds a pre-determined value (operation threshold). As the safety device operates, the cable moves in the ground under the action of a tensile load, and, consequently, the tensile load in a dangerous region lessens, thus preventing the cable from breaking. Since a tensile load on the cable is increased by the value of the load under the action of the force acting upon the cable from the side of the anchor, the operation threshold should be significantly (depending on supposed parameters of ground movements) lower than the cable resistance to the tensile load. If it is supposed that a movement is possible only in one point of the sensing system, as embedded into the ground, in a segment between two anchors, then it is sufficient that the operation threshold will be insignificantly lower than the cable resistance to the tensile load (by the value of the sum of errors in determination of such parameters). The setting of the operation threshold in the anchor design enables to avoid uncertainties associated with changeability of ground mechanical properties in different places and over time.
The claimed device embodiments comprise a mechanism for protecting the detection cable against tensile loads exceeding allowable values applied in the two structural embodiments of the mechanical safety devices.
According to the first embodiment of the structure with a breakable mechanical safety device (Figures 5, 6), an anchor comprises a thrust plate 19 and a releasable clamp 21.
The anchor is symmetrical relative to the cable. Two identical halves of the releasable clamp 21 are fixed on the cable 14 with a screwed fastening member 22, and the cable 14 is gripped in a slot 23. The thrust plate 19 consists of two identical parts 24 that are attached to the releasable clamp 21 with latches 25, and the parts 24 are also connected therebetween with reinforcing rods 26 and latches 27. The reinforcing rods 26 and the latches 27 make the structure of the thrust plate 19 more rigid, preventing the parts 24 from bending and ensuring perpendicularity of the thrust plate 19 to the axis of the cable 14. The structure of the thrust plate 19 is provided with receptacles 29 for installing the reinforcing rods 26.
The function of a safety device in this structure is performed by the latches 25 (Figure 7).
Since the surface area of projection of the releasable clamp 21 on a plane perpendicular to the axis of the detection cable 14 is significantly less than the similar surface area of the thrust plate 19, a load acting upon the releasable clamp 21 from the side of the thrust plate 19 is approximately equal to a load acting upon the detection cable from the side of the anchor. In a case where a load acting upon the detection cable from the side of the anchor exceeds a pre-determined value, the mechanical safety device operates by breaking the latches 25. The latches 25 are broken by shearing along planes 28. In the result of shearing the latches 25 along the planes 28 the thrust plate 19 is mechanically disconnected from the releasable clamp 21, whereupon the cable 14 moves, under the action of a tensile load, relative to the ground (and the thrust plate fixed therein), which causes a decrease in the cable relative elongation and, consequently, the tensile load on the dangerous segment, preventing the cable from breaking. An operation threshold of the mechanical safety device is selected by changing the strength of the thrust plate material or by changing the geometrical parameters of the latches 25 so as their shearing strength is equal to half a load acting upon the releasable clamp from the side of the thrust plate 19 at which the mechanical safety device should operate.
According to the second embodiment of the structure with a deformable mechanical safety device (Figures 8, 9), the structure has the elements similar to those of the structure with a breakable mechanical safety device, except for the following differences in the thrust plate 30 and the releasable clamp 31. The structure of the thrust plate 30 is different in that it is secured to the releasable clamp 31 reliably in the whole range of loads for which the anchor is intended. Dimensions and a material of the parts of the thrust plate 30 are selected so as to ensure their integrity when a load acting upon the detection cable from the anchor side reaches a pre-determined value at which the mechanical safety device operates.
The structure of the releasable clamp 31 is different in that the slot 32 of the releasable clamp 31 is made with internal recesses on each of the clamping plates 33 and 34. Each recess has a broadened portion in the beginning and in the end of the slot 32.
An elastic insert 35 with a pre-determined elastic coefficient is immovably installed in the slot 32, the said insert having the surface complementary to that of the recesses and being provided with an inner longitudinal channel with a semi-oval cross-section which greater axis is oriented parallel to the release plane of the clamping plates 33 and 34. A rigid calibration plate 36 consisting of two identical parts is arranged in the splitting of the clamping plates 33 and 34. The elastic insert 35 has at least one longitudinal cut for the detection cable 14.
The function of a mechanical safety device in this structure is performed by the releasable clamp 31. The anchor is held on the cable 14 due to a friction force between it and the elastic insert 35. In a case where a load acting upon the detection cable from the anchor side exceeds a pre-determined value, deformation of the elastic insert 35 occurs that causes operation of the mechanical safety device because the cable 14 slips relative to the anchor fixed in the ground, and such slipping is accompanied by a decrease in the said load. This process continues until the said load is equal to the operation threshold of the safety device. The said slipping of the cable relative to the ground causes a reduction in the cable relative elongation and, consequently, in the tensile load in the dangerous region, thus preventing the cable from breaking.
The operation threshold of the safety device is determined by the shape and depth of the detection cable outer surface, by the force of pressing the cable to the anchor, and by the coefficient of friction (static and sliding) of the anchor relative to the detection cable.
The operation threshold Fc (in newtons) of the mechanical safety device is determined experimentally or calculated according to the formula: Fc = k1 .P, in newtons, where k1 ¨
friction coefficient of the elastic insert relative to the detection cable, P, in newtons ¨
force of pressing the elastic insert to the detection cable. The operation threshold is adjusted by replacing one elastic insert with another one having a different coefficient of elasticity and/or by selecting the thickness of the calibration plate 17.
The tensile load of the detection cable is limited at a level lower than a maximum allowable one by introducing the said safety devices to the device structure.
The load to the detection cable is limited either by limiting the force of securing the anchor thrust plate at the releasable clamp (breakable mechanical safety device), or by limiting the force of securing the releasable clamp on the detection cable (deformable mechanical safety device). In the case of a deformable mechanical safety device the force of securing the anchor on the detection cable is limited by selecting elastic inserts with a given elasticity coefficient and by adjusting a distance between clamping plates 9, 10 by means of the calibration plate 17. In the case of breakable mechanical safety device the force of securing the anchor thrust plate on the releasable clamp is limited by selecting materials used for making anchors and by changing geometrical parameters of the anchor parts.
Claims (6)
1. A device for measuring deformations of the ground, comprising a strain-sensitive optical detection cable, a measuring unit coupled to the cable, anchors connected to the cable and to the ground, characterized in that the device is provided with a system for protecting the cable against breaking, which system includes a safety device embedded in each anchor.
2. The device for measuring deformations of the ground according to Claim 1, characterized in that each anchor is connected to the cable by means of a releasable clamp and to the ground by means of a thrust plate.
3. The device according to Claim 2, characterized in that the safety device includes a fastening member provided with the possibility of securing the thrust plate to the releasable clamp, the latter breaking when a pre-determined load is applied to the fastening member, thus ensuring free movement of the cable relative to the thrust plate.
4. The device according to Claim 3, characterized in that the fastening member is made as latches arranged on the anchor thrust plate and being in engagement with the releasable clamp.
5. The device according to Claim 2, characterized in that the safety device includes a fastening member provided with the possibility of securing the cable to the releasable clamp, the latter deforming when a pre-determined load is applied to the fastening member, thus ensuring free movement of the cable relative to the thrust plate.
6. The device according to Claim 5, characterized in that the fastening member is made as an elastic insert with an inner longitudinal channel for placing the cable, which insert is arranged in a slot, and a rigid calibration plate arranged in the splitting of the clamp, the elastic insert having the outer surface complementary to the slot surface and the longitudinal channel surface complementary to the detection cable surface and at least one longitudinal cut through which the cable is placed into the longitudinal channel, and the thrust plate is rigidly connected to the releasable clamp.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| RU2011109936 | 2011-03-17 | ||
| RU2011109936/28A RU2485448C2 (en) | 2011-03-17 | 2011-03-17 | Device for soil deformation measurement |
| PCT/RU2012/000154 WO2012125078A1 (en) | 2011-03-17 | 2012-03-02 | Device for measuring deformations of the ground |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2829206A1 true CA2829206A1 (en) | 2012-09-20 |
| CA2829206C CA2829206C (en) | 2016-05-10 |
Family
ID=46830959
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2829206A Expired - Fee Related CA2829206C (en) | 2011-03-17 | 2012-03-02 | Device for measuring deformations of the ground |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA2829206C (en) |
| EA (1) | EA023997B1 (en) |
| RU (1) | RU2485448C2 (en) |
| WO (1) | WO2012125078A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU2540252C1 (en) * | 2013-08-13 | 2015-02-10 | ЗАО "Лазер Солюшенс" | Device for soil control |
| CN107014542A (en) * | 2017-04-21 | 2017-08-04 | 中国水利水电科学研究院 | A kind of intelligent safety monitoring slope system |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002317451A (en) * | 2001-04-23 | 2002-10-31 | Dai Ichi High Frequency Co Ltd | Optical fiber stretching system for observation of ground deformation |
| EP2128571B1 (en) * | 2008-05-28 | 2014-07-23 | Smartec SA | Fiberoptic strain sensor with distributed strain coupling |
| RU84547U1 (en) * | 2009-01-15 | 2009-07-10 | Общество с ограниченной ответственностью "Мониторинг-Урал" | MEANS FOR MEASURING DEFORMATION AND VIBRATION |
| JP4858884B2 (en) * | 2009-03-09 | 2012-01-18 | 独立行政法人日本原子力研究開発機構 | Optical fiber type displacement meter system in bedrock |
| WO2011012406A1 (en) * | 2009-07-30 | 2011-02-03 | Hottinger Baldwin Messtechnik Gmbh | Device and method for the spatially-resolved recording of ground motion |
-
2011
- 2011-03-17 RU RU2011109936/28A patent/RU2485448C2/en not_active IP Right Cessation
-
2012
- 2012-03-02 CA CA2829206A patent/CA2829206C/en not_active Expired - Fee Related
- 2012-03-02 WO PCT/RU2012/000154 patent/WO2012125078A1/en active Application Filing
- 2012-03-02 EA EA201391197A patent/EA023997B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| CA2829206C (en) | 2016-05-10 |
| EA201391197A1 (en) | 2014-02-28 |
| WO2012125078A1 (en) | 2012-09-20 |
| EA023997B1 (en) | 2016-08-31 |
| RU2485448C2 (en) | 2013-06-20 |
| RU2011109936A (en) | 2012-09-27 |
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