WO2025093912A1

WO2025093912A1 - Distributed optical fibre sensor system for measuring subterranean parameters

Info

Publication number: WO2025093912A1
Application number: PCT/IB2023/061150
Authority: WO
Inventors: Chathura Madhubhashitha HERATH; Rajapaksha Waththevidanelage Kusumi ANJANA; Jayantha Ananda EPAARACHCHI
Original assignee: Uva Wellassa University Of Sri Lanka
Current assignee: Uva Wellassa University Of Sri Lanka
Priority date: 2023-11-03
Filing date: 2023-11-06
Publication date: 2025-05-08
Anticipated expiration: 2026-05-03

Abstract

An optical fibre sensor system (102) for measuring subterranean parameters by distributed strain sensing method is provided. The system (102) includes an elongated hollow member (202) vertically disposed in a ground (104), an optical fibre (108) extending along a length of the elongated hollow member (202). A membrane (306) is disposed in a chamber (402) defined by the elongated hollow member (202) and embedded with at least a portion of the optical fibre (108). The system (102) further includes an elongated flat member (210) disposed perpendicular to the elongated hollow member (202) and the optical fibre (108) extends along a length of the elongated flat member (210). The optical fibre (108) is connected in series with the elongated hollow member (202), the membrane (306), and the elongated flat member (210) to detect a horizontal displacement of the ground (104), a pressure of water received within the chamber (402), and a vertical displacement of the ground (104), respectively, simultaneously.

Description

DISTRIBUTED OPTICAL FIBRE SENSOR SYSTEM FOR MEASURING SUBTERRANEAN PARAMETERS

TECHNICAL FIELD

[0001] The present disclosure relates to geotechnical monitoring, and more particularly, to an optical fibre-based sensor system for measuring and monitoring subterranean parameters such as pore water pressure, horizontal and vertical ground movements.

BACKGROUND

[0002] Due to the ever-rising population of the earth, the infrastructure requirements are at an all-time high. To cater to the need of billions of inhabitants of our planet and to connect nations, roads and other structures are an integral part of the infrastructure landscape. However, due to rapid deforestation to build roads and constructions of buildings, the quality of the ground and the geotechnical parameters governing it, are deteriorating day by day. This creates a challenge in building and laying durable and reliable roads and other constructions, as they may sink if the ground below the roads sink due to cavitation, rainfall, soil erosion, and other concerning factors effecting the ground stability.

[0003] In order to monitor and maintain the roads, as well as to survey the ground area before laying a new construction, a plurality of subterranean parameters are defined, which are paramount to the longevity of the construction project. Parameters such as, pore water pressure, horizontal displacement of the ground, vertical displacement of the ground, and the like are needed to be constantly monitored to achieve the solution for the above stated problems. Efforts have been made in the field of monitoring the geotechnical and subterranean parameters. However, there is no technology defined to date, wherein the monitoring process is cost effective to construct and even more economical to operate in the long-run.

[0004] The standard method for measuring pore water pressure below the water table employs a piezometer, which measures the height to which a column of the liquid rises against gravity, i.e., the static pressure (or piezometric head) of groundwater at a specific depth. Piezometers often employ electronic pressure transducers to provide data. In addition, traditionally, inclinometers are used to measure displacement in geotechnical engineering. They are installed vertically within boreholes drilled into the ground and measure the inclination of the borehole wall concerning vertical. Inclinometers can be used to monitor both horizontal and vertical displacement and can be installed in both soft and hard soils. However, they’re not suitable for use in areas with a high-water table or where there is a risk of flooding, especially, coastal areas. Also, extensometers are commonly used to measure displacement in geotechnical engineering. They are installed horizontally within boreholes drilled into the ground and measure the change in length of the borehole wall with respect to time. Extensometers can be used to monitor both horizontal and vertical displacements but are only suitable for use in soft soils. Further, in a more modem approach, a remote sensing technique that can be used to measure very small displacements, even down to millimetres, is defined to be (Interferometric Synthetic Aperture Radar) InSAR. It uses satellite-based radar images to create detailed maps of ground surface deformation. InSAR can be cost-prohibitive for many applications in measuring displacement, hindering its adoption in areas with limited financial resources. However, the above stated technologies have one or more factors hindering their adoption at a large scale. Therefore, a need arises for an economical, reliable and flexible system to monitor the geotechnical aspects of a particular area. Hence, it is one aspect of the present disclosure, to provide an optical fibrebased sensing system to monitor a plurality of subterranean parameters simultaneously. SUMMARY

[0005] In accordance with one aspect of the present disclosure, an optical fibre sensor system for measuring subterranean parameters is described. The optical fibre sensor system includes an elongated hollow member configured to vertically dispose in a ground. Further, an optical fibre extends along a length of the elongated hollow member and configured to detect a horizontal displacement of the ground in response to a strain induced on the elongated hollow member. The optical fibre sensor system further includes a membrane disposed in a chamber defined by the elongated hollow member, and the membrane is embedded with at least a portion of the optical fibre. The optical fibre is configured to detect a pressure of water received within the chamber in response to a strain induced on the membrane. Furthermore, the optical fibre sensor system includes an elongated flat member disposed perpendicular to the elongated hollow member. The optical fibre extends along a length of the elongated flat member and configured to detect a vertical displacement of the ground in response to a strain induced on the elongated flat member. Moreover, the optical fibre is connected in series with the elongated hollow member, the membrane, and the elongated flat member to simultaneously detect the horizontal displacement, the pressure of the water, and the vertical displacement, respectively.

[0006] In an embodiment of the present disclosure, the optical fibre sensor system includes an elongated bar having a length equal to or more than the length of the elongated hollow member and configured to support the membrane within the chamber. The optical fibre sensor system further includes a mounting unit configured to detachably engage with the elongated bar and support the membrane in the chamber. The mounting unit includes a hollow body having a flat surface defining an opening and the membrane is disposed on the flat surface to allow deformation thereof through the opening in response to the pressure of the water received within the chamber. The mounting unit further includes a first sealing cap configured to couple with a first end of the hollow body, and a second sealing cap configured to couple with a second end of the hollow body. Further, the mounting unit includes a flange coupled with the second sealing cap and configured to fluid tightly engage with an inner surface of the elongated hollow member to define the chamber for receiving the water therein. Furthermore, the mounting unit includes a first bracket configured to support the membrane on the flat surface of the hollow body and a second bracket configured to couple the first bracket with the hollow body using one or more fastening members.

[0007] The optical fibre sensor system further includes a plurality of the chambers defined within the elongated hollow member. Each chamber of the plurality of chambers includes the membrane configured to detect the pressure of the water at a predefined distance from a surface of the ground. In an embodiment, the flanges of the two adjacent mounting units are configured to define one chamber within the elongated hollow member. A portion of the elongated hollow member defining the chamber includes a plurality of openings to receive the water therethrough.

[0008] In an embodiment, the optical fibre is disposed on an outer surface of the elongated hollow member along a longitudinal axis thereof. In particular, the optical fibre, at least, extends along a first radial plane and a second radial plane defined by the elongated hollow member, and the first radial plane and the second radial plane are 90 degrees apart. The optical fibre connected in series with the elongated hollow member, the membrane, and the elongated flat member is configured to couple with a reflectometer, which in turn connected to a computer system.

[0009] In some embodiments of the present disclosure, the optical fibre is attached to the outer surface of the elongated hollow member using an adhesive. Further, the optical fibre is atached to the elongated flat member using an adhesive. The membrane is made of materials including silicone, rubber, or a combination thereof. Further, the membrane has a diameter in a range of 25 millimeter (mm) to 35 mm defined based on a first set of design parameters including pore water pressure, and dimensional specifications of the elongated hollow member and the mounting unit. The membrane has a thickness in a range of 2 mm to 4 mm defined based on a second set of design parameters including the pore water pressure.

[0010] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0011] A beter understanding of embodiments of the present disclosure (including alternatives and/or variations thereof) may be obtained with reference to the detailed description of the embodiments along with the following drawings, in which:

[0012] FIG. 1 is a schematic diagram of an optical fibre sensor system disposed in a ground to measure subterranean parameters, according to an embodiment of the present disclosure;

[0013] FIG. 2A is a schematic illustration of an elongated hollow member of the optical fibre sensor system, according to an embodiment of the present disclosure;

[0014] FIG. 2B is a schematic illustration of a portion of an elongated flat member of the optical fibre sensor system positioned with respect to the elongated hollower member, according to an embodiment of the present disclosure; [0015] FIG. 3A is a schematic illustration of a portion of an elongated bar coupled with a plurality of mounting units of the optical fibre sensor system, according to an embodiment of the present disclosure;

[0016] FIG. 3B is a schematic illustration of an exploded view of the mounting unit, according to an embodiment of the present disclosure;

[0017] FIG. 4 is a schematic illustration of a chamber defined by the elongated hollow member and the two adjacent mounting units, according to an embodiment of the present disclosure;

[0018] FIG. 5A is a schematic illustration of the optical fibre sensor system showing winding and routing of the optical fibre on the elongated hollow member and the elongated flat member, according to an embodiment of the present disclosure;

[0019] FIG. 5B is a schematic illustration of a cross-sectional view taken along a line A- A’ of the optical fibre sensor system of FIG. 5 A, according to an embodiment of the present disclosure; and

[0020] FIG. 6 is a schematic illustration depicting an implementation of a plurality of the optical fibre sensor system for measuring the subterranean parameters at different locations of the ground, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0021] Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. Moreover, references to various elements described herein, are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice- versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claim.

[0022] It should be noted that the terms “first”, “second”, and the like, herein, do not denote any order, ranking, quantity, or importance, but rather are used to distinguish one element from another. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0023] Referring to FIG. 1, a schematic block diagram, depicting a geotechnical monitoring environment 100 including an optical fibre sensor system 102 for measuring subterranean parameters, is illustrated, in accordance with an embodiment of the present disclosure. The optical fibre sensor system 102 is alternatively referred to as the system 102, hereinafter, for the sake of brevity in explanation. The subterranean parameters may include, but are not limited to, pore water pressure, vertical ground movements, which is otherwise referred to as vertical displacement of the ground, and horizontal ground movements, which is otherwise referred to as horizontal displacement of the ground. The geotechnical monitoring environment 100 includes a ground 104, which refers to any geological area where the system 102 is employed. According to an implementation of the present disclosure, a bore hole 105 may be defined in the ground 104 vertically. The bore hole 105 may have a depth and a width equal to or greater than a length and a width, respectively, of system 102 to be implemented in the ground 104. Further, the system 102 is in optical communication with an input 106a of a reflectometer 106 by an optical fibre 108. In one embodiment, the optical fibre 108 is a bare optical fibre. In another embodiment, the optical fibre 108 is a buffered cable. The optical fibre 108 primarily acts as the sensing element and performs a secondary function of transmitting sensor data to the reflectometer 106. According to the present disclosure, the optical fibre 108 is a single-mode optical fibre having a diameter of 125 micrometer (pm). A provision may be made in the ground 104 to safely and protectively dispose the optical fibre 108 in the ground 104. In general, the reflectometer 106, otherwise known as an optical backscatter reflectometer, uses swept- wavelength coherent interferometry to measure peaks related to reflections as a function of length in an optical system. This feature is used for optical inspections and diagnostic capabilities. Furthermore, an output 106b of the reflectometer 106 is configured to be in communication with an input 110a of a computer system 110 using a data transmission cable 109. In an example, the data transmission cable 109 may include, but are not limited to, an ethemet cable, a USB cable, and an optical cable. In some embodiments, the reflectometer 106 may be communicated with the computer system 110 using a wireless transmission system. The computer system 110 refers to a computing environment responsible for collecting and interpreting a set of data collected by the reflectometer 106 from the system 102 through the optical fibre 108. The computer system 110 is a user-friendly system designed to be operated by users monitoring the system 102 employed in any geological area. The computer system 110, the reflectometer 106, and the transmission cable 109 connecting the computer system 110 and the reflectometer 106 may be together referred to as a data acquisition system 103. The data acquisition system 103 is configured to be in communication with the system 102 to determine the subterranean parameters such as the pore water pressure, the vertical displacement of the ground 104, and the horizontal displacement of the ground 104, simultaneously.

[0024] The computer system 110, typically, includes a variety of computer-readable media. The computer-readable media can be any available media that can be accessed by the computer system 110 and includes both volatile and nonvolatile media, removable and non-removable media. In an example, the computer-readable media may include computer storage media and communication media. The computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. The computer storage media includes, but are not limited to, random access memory (RAM), read only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory devices, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information, and which can be accessed by the computer system 110. The communication media typically embodies computer- readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. In an example, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer-readable media.

[0025] In an embodiment of the present disclosure, the computer system 110 may include a data acquisition software application installed therein. The data acquisition software application may be developed or provided by the manufacturer of the reflectometer 106. Accordingly, the computer system 110 is configured to be compatible to install the data acquisition software application and thereby to effectively communicate with the reflectometer 106 using the data transmission cable 109. The data acquisition software application may be programmed to collect and interpret the set of data collected by the system 102 and the optical fibre 108. [0026] Referring to FIG. 2A, a schematic perspective view of an elongated hollow member 202 configured to vertically dispose in the ground 104 is illustrated, in accordance with an embodiment of the present disclosure. The elongated hollow member 202 is cylindrical in shape. In some embodiments, the cross-section of the elongated hollow member 202 may have a shape of a polygon. In an embodiment, the elongated hollow member 202 may be manufactured using acrylonitrile butadiene styrene (ABS) material. In another embodiment, the elongated hollow member 202 may be manufactured using unplasticized poly vinyl chloride (PVC-U) material. The aforementioned materials are selected for the elongated hollow member 202 to maintain the longevity of maintenance free operation of the elongated hollow member 202. Further, the elongated hollow member 202 include a wall 201 defining an outer surface 201a and an inner surface 201b. A plurality of perforations 204 is defined in the wall 201 across a thickness of the wall 201 defined between the outer surface 201a and the inner surface 201b. The plurality of perforations 204 is defined at pre-defined intervals along a length of the elongated hollow member 202 for water from the ground 104 to enter the elongated hollow member 202 therethrough while implementing the system 102 in the ground 104. The number, size and shape of the perforations 204 may be determined depending upon a site (or location) in the ground 104 and the pore water content at the site.

[0027] In an embodiment, as shown in FIG. 1, the optical fibre 108 extends along the length of the elongated hollow member 202 defined between a first end 202a and a second end 202b thereof. As such, the optical fibre 108, as described above, is configured to detect the horizontal displacement of the ground 104. The elongated hollow member 202 may be made of the material in such a way that the elongated hollow member 202 may undergo deformation in response to the horizontal displacement of the ground 104. As such, the optical fibre 108 uses the strain induced on the elongated hollow member 202 during the horizontal displacement of the ground 104 to measure the horizontal displacement of the ground 104.

[0028] Referring to FIG. 2B, a schematic perspective of an elongated flat member 210, disposed perpendicular to the elongated hollow member 202, is illustrated, in accordance with an embodiment of the present disclosure. The elongated flat member 210 is configured in such a way that the optical fibre 108 extends along a length of the elongated flat member 210. The optical fibre 108 attached to the elongated flat member 210 is configured to detect and measure the vertical displacement of the ground 104. In an embodiment, the elongated flat member 210 may be a rectangular plate having a top surface 210a and a bottom surface 210b defining a thickness . The length and a width of the elongated flat member 210 may be defined based on the location in the ground 104 where the system 102 may be implemented. In one embodiment, the optical fibre 108 may be disposed on the bottom surface 210b of the elongated flat member 210. In another embodiment, the optical fibre 108 may be embedded between the top surface 210a and the bottom surface 210b of the elongated flat member 210. In some embodiments, the optical fibre 108 may have more than one turn defined in the elongated flat member 210 based on the width thereof. In other words, the optical fibre 108 may run back and forth multiple times along the length of the elongated flat member 210 to spread across the width thereof and thereby to effectively detect the vertical displacement of the ground 104. In some embodiments, the elongated flat member 210 may have a square shape, a polygon shape, or any other shape known in the art. The elongated flat member 210 may be made of a material in such a way that the elongated hollow member 202 may undergo deformation in response to the vertical displacement of the ground 104. As such, the vertical displacement of the ground 104 is detected by the optical fibre 108 extending along the length of the elongated flat member 210 due to the strain induced on the elongated flat member 210. In an embodiment of the present disclosure, the elongated flat member 210 may be manufactured using bitumen tape. In another embodiment, the elongated flat member 210 may be manufactured using geotextile material. In yet another embodiment, the elongated flat member 210 may be manufactured using geogrid material. In general, geogrid is geosynthetic material used to reinforce soils and similar materials. Geogrids are commonly made of polymer materials, such as polyester, polyvinyl alcohol, polyethylene, or polypropylene. They may be woven or knitted from yams, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid. In an implementation of the present disclosure, as shown in FIG. 1, the elongated flat member 210 may be disposed perpendicular to the elongated hollow member 202. In particular, a plane defined by the top surface 210a of the elongated flat member 210 may be perpendicular to a longitudinal axis ‘L’ defined by the elongated hollow member 202. Further, while implementing the system 102 in the ground 104, the elongated flat member 210 may be disposed in the ground 104 at a depth from the first end 202a of the elongated hollow member 202. The depth may be defined to safely and protectively dispose the elongated flat member 210 in the ground 104. The depth of the elongated flat member 210 with respect to the first end 202a of the elongated hollow member 202 may also be defined based on a surface of the ground 104.

[0029] Referring to FIG. 3 A, a schematic diagram of a portion of an elongated bar 302 coupled with a plurality of mounting units 304 is illustrated, in accordance with an embodiment of the present disclosure. The elongated bar 302 has a length equal to or more than the length of the elongated hollow member 202. The elongated bar 302 together with the mounting unit 304 is configured to support a membrane 306 and the optical fibre 108. The elongated bar 302 may be manufactured using materials including, but not limited to, PVC, ABS, and a combination thereof, to enhance the longevity of the system 102. According to the present disclosure, the elongated bar 302 may be a hollow tube with circular cross-section. An outer diameter of the elongated bar 302 is smaller than an inner diameter defined by the inner surface 201b of the elongated hollow member 202. In some embodiment, the elongated bar 302 may have the cross-section in the shape of a polygon or any other shape known in the art. Each of the plurality of mounting units 304 may be coupled to the elongated bar 302 at a predefined distance along the length of the elongated bar 302 corresponding to the plurality of perforations 204 defined in the elongated hollow member 202. Each mounting unit 304 may be detachably attached to the elongated bar 302 in such a way that the mounting unit 304 may be coupled to the elongated bar 302 at a desired location.

[0030] Referring to FIG. 3B, an exploded view of the mounting unit 304 is illustrated, in accordance with an embodiment of the present disclosure. In particular, the exploded view of the mounting unit 304 is shown in association with the elongated bar 302 to illustrate detachable coupling of the mounting unit 304 with the elongated bar 302. Referring to FIG. 3A and FIG. 3B, the mounting unit 304 includes a hollow body 310 having a flat surface 312. The flat surface 312 defines an opening 314, which is designed to securely house the membrane 306 within the mounting unit 304. The membrane 306 is disposed on the flat surface 312 provided by the hollow body 310 to allow the deformation of the membrane 306 as a result of the pressure exerted by the pore water entering the elongated hollow member 202 through the plurality of perforations 204. According to the present disclosure, the hollow body 310 is a hollow square pipe having a first end 310a and a second end 310b. The hollow square pipe includes the flat surface 312 having the opening 314 to support the membrane 306. In some embodiments, a cross-section of the hollow body 310 may have a polygon shape. In some embodiments, the hollow body 310 may have any known geometrical shape including a flat portion to support the membrane 306. In an embodiment, the hollow body 310 may be manufactured using aluminium. [0031] In an embodiment, the membrane 306 may be manufactured with silicone and the optical fibre 108 is embedded into the membrane 306 at the time of the casting process of the membrane 306. In some embodiments, the membrane 306 may be manufactured using rubber or any other suitable material without any hinderance to the working of the system 102. In some embodiments, the membrane 306 may be manufactured using silicone, rubber, or a combination thereof. In an embodiment, the membrane 306 is circular in construction and has a diameter ‘D’ ranging from 25 millimeter (mm) to 35 mm. According to the present disclosure, the diameter ‘D’ of the membrane 306 is defined based on a first set of design parameters including, but not limited to, the pore water pressure and dimensional specifications of the elongated hollow member 202 and the mounting unit 304. In some embodiments, the first set of design parameters may include the location in which the system 102 is implemented, historical data of the pore water pressure in the ground 104, and spatial resolution and sensor spacing of the reflectometer 106. The dimensional specification of the elongated hollow member 202 may include, but are not limited to, the outer diameter of the wall 201, the plurality of perforations 204 defined in the wall 201, size and shape of each perforation 204, and the length of the elongated hollow member 202. Further, the membrane 306 has a first surface 306a and a second surface 306b defining athickness ‘T’ therebetween. The thickness ‘T’ of the membrane 306 is in a range of 2 mm to 4 mm and defined based on a second set of design parameters including the pore water pressure. Further, the thickness ‘T’ may be adjusted as per the location in which the system 102 may be implemented. In some embodiments, the first set of design parameters and the second set of design parameters may be identical. It may be understood that a person of ordinary skill in the art may define the diameter ‘D’ and the thickness ‘T’ of the membrane 306 based on the first and second sets of design parameters. As such, the diameter ‘D’ of the membrane 306 may be larger than 35 mm and smaller than 25 mm, and the thickness ‘T’ of the membrane 306 may be larger than 4 mm and smaller than 2 mm based on the first and second sets of design parameters.

[0032] In an embodiment, the mounting unit 304 is configured to detachably engage with the elongated bar 302. The mounting unit 304 is a structural member configured to support and house the membrane 306 embedded with the optical fibre 108. The membrane 306 is flexible in nature, therefore, the mounting unit 304 is employed to structurally support the membrane 306. In some embodiments, the mounting unit 304 may be manufactured using aluminium. The aluminium may be selected from, but are not limited to, 1000 series aluminium, 2000 series aluminium, 3000 series aluminium, 4000 series aluminium, 5000 series aluminium, 6000 series aluminium, 7000 series aluminium, and 8000 series aluminium. In some embodiments, the mounting unit 304 may be manufactured using plastics, and metals including, but not limited to, stainless steel. In some embodiments, the mounting unit 304 may be manufactured using a noncorrosive rigid material. As can be seen from FIG. 3 A, the plurality of the mounting units 304, with the membrane 306, may be repeatedly coupled to the elongated bar 302 in order to further enhance the efficiency and accuracy of the system 102.

[0033] The mounting unit 304 further includes a first sealing cap 316 configured to couple with the first end 310a of the hollow body 310 and a second sealing cap 318 configured to couple with the second end 310b of the hollow body 310. In an embodiment, the first sealing cap 316 and the second sealing cap 318 may be manufactured using ABS material. In another embodiment, the first sealing cap 316 and the second sealing cap 318 may be manufactured using polyethylene terephthalate glycol (PETG). In yet another embodiment, the first sealing cap 316 and the second sealing cap 318 may be manufactured using an elastomer or any other polymer materials that may be non-biodegradable and may have high corrosion resistance properties, and high temperature and pressure resistance properties. Furthermore, the mounting unit 304 includes a flange 320 coupled with the second sealing cap 318 and configured to fluid tightly engage with the inner surface 20 lb of the elongated hollow member 202 to define a chamber 402 (shown in FIG. 4). In some embodiments, the flange 320 may be detachably coupled with the hollow body 310 of the mounting unit 304. In some embodiments, the flange 320 may be an individual component attached to the second sealing cap 318 using fastening members. In some embodiments, the flange 320 may be integral design of the second sealing cap 318.

[0034] The hollow body 310 is coupled with the first sealing cap 316 and the second sealing cap 318 such that a volume is defined within the hollow body 310 by preventing entry of pore water within the hollow body 310. According to the present disclosure, the membrane 306 is embedded with at least a portion of the optical fibre 108. The optical fibre 108, embedded in the membrane 306, is configured to detect the pressure of the pore water received within the chamber 402 through the plurality of perforations 204. The pore water induces the strain on the membrane 306 due to the pressure and the strain is thereby detected and measured by the optical fibre 108 embedded in the membrane 306.

[0035] The mounting unit 304 further includes a first bracket 322 configured to support the membrane 306 on the flat surface 312 provided by the hollow body 310. Further, the mounting unit 304 includes a second bracket 324 configured to mechanically couple the first bracket 322 with the hollow body 310 using one or more fastening members 326. In some embodiments, the hollow body 310 may be provided with mounting holes in such a way that the first bracket 322 may be attached to the hollow body 310 using the one or more fastening members 326. In an embodiment, the first bracket 322 and the second bracket 324 may be manufactured using ABS material. In another embodiment, the first bracket 322 and the second bracket 324 may be manufactured using PETG material. The one or more fastening members 326 may include, but are not limited to, a nut, a bolt, a screw, and the like. [0036] Referring to FIG. 4, a schematic illustration of the chamber 402 defined in the elongated hollow member 202 is illustrated, in accordance with an embodiment of the present disclosure. The system 102 includes the plurality of mounting units 304, and the flanges 320 of each of the two adjacent mounting units 304 define one chamber 402 within the elongated hollow member 202. The chamber 402 is configured to receive the pore water therein through the plurality of perforations 204 present on the elongated hollow member 202. The chamber 402 is further configured such that the mounting unit 304 enclosing the membrane 306 is positioned at a bottom end of the chamber 402. The position of the mounting unit 304 in the chamber 402 allows for seamless and accurate readings of the subterranean parameter such as the pore water pressure. In an embodiment, the system 102 includes a plurality of the chambers 402 defined within the elongated hollow member 202, and each chamber of the plurality of chambers 402 includes the membrane 306 enclosed in the mounting unit 304. The membrane 306 in each chamber of the plurality of chambers 402 is configured to detect the pore water pressure at different depths from a surface of the ground 104. The number of the plurality of chambers 402 and a distance between two adjacent chambers 402 are determined depending upon the location at which the system 102 is installed and the water content present in the location.

[0037] Referring to FIG. 5 A, a schematic illustration of the system 102 showing winding and routing of the optical fibre 108 on the elongated hollow member 202 and the elongated flat member 210 is illustrated, in accordance with an embodiment of the present disclosure. The optical fibre 108 is disposed on the outer surface 201a of the elongated hollow member 202. In particular, the optical fibre 108 is configured to run back and forth along the longitudinal axis ‘L’ of the elongated hollow member 202 such that multiple turns of the optical fibre 108 are formed on the outer surface 201a thereof. Referring to FIG. 5B, a schematic illustration of a cross-sectional view taken along a line A-A’ of the system 102 of FIG. 5 A is illustrated, in accordance with an embodiment of the present disclosure. Referring to FIG. 5 A and FIG. 5B, the optical fibre 108 extends along at least a first radial plane ‘Rl’ and a second radial plane ‘R2’ defined by the elongated hollow member 202. In an embodiment, the first radial plane ‘Rl’ and the second radial plane ‘R2’ of the elongated hollow member 202 are 90 degrees apart from each other. According to the present disclosure, the optical fibre 108 takes three turns along the longitudinal axis ‘L’ of the elongated hollow member 202 at an orientation of 90 degrees. The optical fibre 108 is buffered and protected against soil conditions. In some embodiments, the optical fibre 108 may run along the longitudinal axis ‘L’ of the elongated hollow member 202 to form more than three turns. As shown in FIG. 5B, the mounting unit 304 including the hollow body 310, the first sealing cap 316, the second sealing cap 318, and the flange 320 is engaged with the elongated bar 302. The flange 320 is configured to fluid tightly engage with the inner surface 201b of the elongated hollow member 202 to store the pore water collected in the chamber 402. As the pore water enters into the chamber 402, the membrane 306 deflects proportionally in response to the pressure exerted by the pore water, the elongated hollow member 202 deflects due to horizontal displacements of the ground 104, and the elongated flat member 210 deflects due to the vertical displacements of the ground 104. The strain detected throughout the different lengths of the optical fibre 108 is measured by the distributed strain sensing method. In an embodiment, the system 102 may be designed in such a way that it allows the components such as the elongated hollow member 202, the membrane 306, and the elongated flat member 210 to work in tandem without hindering any of the sensors from detecting any of the plurality of subterranean parameters.

[0038] In an embodiment, the optical fibre 108 is securely attached to the outer surface 201a of the elongated hollow member 202 using an adhesive. The adhesive is applied along the length of the elongated hollow member 202 longitudinally. Further, the optical fibre 108 is securely atached to the botom surface 210b of the elongated flat member 210, as shown in FIG. 5A. The adhesive is applied along the length of the elongated flat member 210 laterally. In an embodiment, the adhesive may be of desired industrial strength and waterproof in nature, to provide a secure adhesion of the optical fibre 108 to the elongated hollow member 202 and the elongated flat member 210 under any undesirable underground conditions.

[0039] Referring to FIG. 6, a schematic illustration of an implementation of the system 102 for measuring the subterranean parameters at different locations of the ground 104 is illustrated, in accordance with an embodiment of the present disclosure. The elongated hollow member 202 and the elongated flat member 210 are repeated and optically communicated in series using the optical fibre 108. In an embodiment, the optical fibre 108 between the elongated hollow member 202 and the elongated flat member 210 or between two adjacent components may be joined together by a fibre optic splicing method. As described above, the plurality of subterranean parameters such as the horizontal displacement of the ground 104, the vertical displacement of the ground 104, and the pressure of the pore water detected by the optical fibre 108 at the different locations of the ground 104 is communicated with the data acquisition system 103. In particular, the optical fibre 108 is connected to the reflectometer 106 using fiber-optic connector (FC) or angled physical contact (APC) connector, and the reflectometer 106 is communicated with the computer system 110 using the data transmission cable 109. Further, the strain values indicative of the pore water pressure, the horizontal displacement of the ground 104, and the vertical displacement of the ground 104 detected throughout the length of the optical fibre 108 is transferred to the reflectometer 106 and the data indicative of the pore water pressure, the horizontal displacement of the ground 104, and the vertical displacement of the ground 104 is stored and interpreted by the computer system 110. As shown in FIG. 6, the optical fibre 108 is connected in series with the elongated hollow member 202, the membrane 306, and the elongated flat member 210 to simultaneously detect the horizontal displacement of the ground 104, the pressure of the pore water, and the vertical displacement of the ground

104, respectively.

INDUSTRIAL APPLICABILITY

[0040] According to the present disclosure, a continuing distributed optical fibre-based sensor system 102 is used to measure the subterranean parameters such as the pore water pressure, the vertical displacement of the ground 104, and the horizontal displacement of the ground 104 in a single scan. The system 102 includes repetitive components of the elongated hollow members 202 and the elongated flat members 210. The elongated hollow member 202 is placed in the bore hole 105 and inside of the elongated hollow member 202 is partitioned into chambers 402 along the length of the elongated hollow member 202. Each chamber 402 includes the membrane 306 that deflects against the applied water pressure. The membranes 306 deflects proportionally to the pore water pressure at different depths. The optical fibre 108 is embedded into the membranes 306 from top to bottom and the same optical fibre 108 is continuously attached to the outer surface 201a of the elongated hollow member 202 in three turns, 90 degrees away from each other. The elongated hollow member 202 deflects due to bidirectional horizontal ground displacements. The elongated hollow members 202 are placed in different geological locations at a distance. The elongated hollow members 202 are connected in series by the optical fibre 108 embedded with the elongated flat members 210. The elongated flat members 210 are laid underground in parallel to the surface of the ground 104. The elongated flat members 210 deflect due to vertical ground displacements. The stain values throughout the different lengths of the continuing optical fibre 108 are measured by distributed strain sensing method. The measured strain values quantify the pore water pressure, the vertical displacement of the ground 104, and the horizontal displacement of the ground 104 at the respective locations. The system 102 of the present disclosure can be implemented for condition monitoring of highways and roads, dams, coastlines, civil infrastructure, oil and gas infrastructure, airport runways, and mining fields.

[0041] With the system 102 of the present disclosure, three significant parameters such as the pore water pressure, the horizontal displacement of the ground 104, and the vertical displacement of the ground 104 for geohazard monitoring may be measured simultaneously. In particular, measurements of magnitude and respective location of the pore water pressure and ground displacements in both the vertical and horizontal directions may be performed simultaneously. The elongated hollow member 202 is capable of flexing due to the horizontal ground movements without interrupting the pore water pressure sensing. The multiple membranes 306 placed inside the elongated hollow member 202 help to detect the pore water pressure at different water heights. The optical fibre 108 embedded in the elongated flat member 210 is used to measure the vertical ground moments and transfer data to the data acquisition system 103 at a distance location. Further, the system 102 is capable of real time condition monitoring for long distances for early warning and disaster resilience. The system 102 may help to predict ground failures including, but not limited to, landslides, erosion, subsidence, and sinkholes caused by natural processes and human activities. Also, after the installation of the system 102 in the ground 104, gauge length and the sensor spacing can be customized based on the required data population. The continuous optical fibre 108 is used for both the sensing and the data transmitting. Moreover, the system 102 is cost- effective due to minimal operational and maintenance cost during the long run.

[0042] While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed methods and systems without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

1. An optical fibre sensor system (102) for measuring subterranean parameters, the optical fibre sensor system (102) comprising: an elongated hollow member (202) configured to vertically dispose in a ground (104); an optical fibre (108) extending along a length of the elongated hollow member (202), and configured to detect a horizontal displacement of the ground (104) in response to a strain induced on the elongated hollow member (202); a membrane (306) disposed in a chamber (402) defined by the elongated hollow member (202) and embedded with at least a portion of the optical fibre (108), wherein the optical fibre (108) is configured to detect a pressure of water received within the chamber (402) in response to a strain induced on the membrane (306); and an elongated flat member (210) disposed perpendicular to the elongated hollow member (202), wherein the optical fibre (108) extends along a length of the elongated flat member (210) and configured to detect a vertical displacement of the ground (104) in response to a strain induced on the elongated flat member (210), wherein the optical fibre (108) is connected in series with the elongated hollow member (202), the membrane (306), and the elongated flat member (210) to simultaneously detect the horizontal displacement of the ground (104), the pressure of the water, and the vertical displacement of the ground (104), respectively.

2. The optical fibre sensor system (102) according to claim 1, further comprising an elongated bar (302) having a length equal to or more than the length of the elongated hollow member (202), and configured to support the membrane (306) within the chamber (402).

3. The optical fibre sensor system ( 102) according to any one of the preceding claims, further comprising a mounting unit (304) configured to detachably engage with the elongated bar (302) and support the membrane (306) in the chamber (402).

4. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the mounting unit (304) includes a hollow body (310) having a flat surface (312) defining an opening (314), wherein the membrane (306) is disposed on the flat surface (312) to allow deformation thereof through the opening (314) in response to the pressure of the water received within the chamber (402).

5. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the mounting unit (304) includes a first sealing cap (316) configured to couple with a first end (310a) of the hollow body (310), and a second sealing cap (318) configured to couple with a second end (310b) of the hollow body (310).

6. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the mounting unit (304) includes a flange (320) coupled with the second sealing cap (318) and configured to fluid tightly engage with an inner surface (201b) of the elongated hollow member (202) to define the chamber (402) for receiving the water therein.

7. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the mounting unit (304) includes: a first bracket (322) configured to support the membrane (306) on the flat surface (312) of the hollow body (310); and a second bracket (324) configured to couple the first bracket (322) with the hollow body (310) using one or more fastening members (326).

8. The optical fibre sensor system (102) according to any one of the preceding claims, further comprising a plurality of the chambers (402) defined within the elongated hollow member (202), wherein each chamber of the plurality of chambers (402) includes the membrane (306) configured to detect the pressure of the water.

9. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the flanges (320) of the two adjacent mounting units (304) are configured to define one chamber (402) within the elongated hollow member (202).

10. The optical fibre sensor system (102) according to any one of the preceding claims, wherein a portion of the elongated hollow member (202) defining the chamber (402) includes a plurality of perforations (204) to receive the water therethrough.

11. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the optical fibre (108) is disposed on an outer surface (201a) ofthe elongated hollow member (202) along a longitudinal axis (L) thereof.

12. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the optical fibre (108), at least, extends along a first radial plane (Rl) and a second radial plane (R2) defined by the elongated hollow member (202), and wherein the first radial plane (Rl) and the second radial plane (R2) are 90 degrees apart.

13. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the optical fibre (108) connected in series with the elongated hollow member (202), the membrane (306), and the elongated flat member (210) is configured to couple with a reflectometer (106), and wherein the reflectometer (106) is connected to a computer system (HO).

14. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the optical fibre (108) is attached to the outer surface (201a) ofthe elongated hollow member (202) using an adhesive.

15. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the optical fibre (108) is attached to the elongated flat member (210) using an adhesive.

16. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the membrane (306) includes silicone, rubber or a combination thereof.

17. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the membrane (306) has a diameter (D) in a range of 25 millimeter (mm) to 35 mm defined based on a first set of design parameters comprising pore water pressure, and dimensional specifications of the elongated hollow member (202) and the mounting unit (304).

18. The optical fibre sensor system (102) according to any one of the preceding claims, wherein the membrane (306) has a thickness (T) in a range of 2 mm to 4 mm defined based on a second set of design parameters comprising the pore water pressure.