A system and method for determining properties of a rod for pushing a probe into a subsurface region

Abstract

The present disclosure generally relates to a system comprising a probe (108) for determining properties of a subsurface region, a rod (106) for pushing the probe into the subsurface region, and a fiber-optic sensor (204) located within the rod configured to sense strain at at least one location along the rod. The present disclosure further relates to a method of determining properties of a rod for pushing the probe into the subsurface region during a subsurface test using the system. Unlocking insights from Geo-Data, the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world.

Description

A SYSTEM AND METHOD FOR DETERMINING PROPERTIES OF A ROD FOR PUSHING A PROBE INTO A SUBSURFACE REGIONFIELD

[0001] This disclosure relates to a system and method for determining properties of a rod for pushing a probe into a subsurface region. More particularly, this disclosure relates a system and method in which a measurement of strain can be used to determine an accurate maximum safe penetration depth when pushing a probe into a subsurface region using a rod. Unlocking insights from such Geo-Data, the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world.BACKGROUND

[0002] There is a general and ongoing need to improve data acquisition of subsurface surveying. The determination of subsurface characteristics is used to identify objects below the surface of the ground, as well as determining the soil characteristics, such as soil type, density, moisture content, shear modulus, and the like, which may be used in foundation planning and / or management. Subsurface information may be used for e.g., site characterisation for infrastructure projects, foundation calculations, and the like. For such applications, it is important to generate a comprehensive understanding of the subsurface with a high degree of accuracy in an efficient manner.

[0003] One of the methods of performing such tests is generally known as a cone penetration test (CPT). The cone penetration test is a geotechnical investigation method for determining, e.g., soil and groundwater characteristics, where a cone penetrometer is pushed into the soil to perform a measurement or measurements. Typical parameters measured by such a cone penetrometer are cone tip resistance and sleeve friction. Pore-water pressure can additionally be measured where the test is a piezocone penetration test (CPTu). The test method comprises pushing an instrumented cone penetrometer, with the tip facing down, into the ground at a controlled rate. Other types of probes and penetrometers can be pushed into the ground to determine a variety of subsurface properties.

[0004] For CPTs and other tests, the testing equipment generally comprises a penetrometer or other suitable probe mounted to a rod. The rod is, in turn, mounted to a platform or a truck. Also mounted to the platform or truck is an advancing mechanism for advancing the rod and probe into the ground, such as a hydraulic ram.

[0005] The maximum safe penetration depth (i.e., the depth at which the insertion of the rod must be stopped to avoid damage to or failure of the rod, probe or any other part of the testing equipment) attainable during such test is generally determined by an operator based on parameters, such as the push force required to advance the rod exceeding a maximum threshold. If an operator stops a test before a maximum safe penetration depth is attained, this would negatively impact the outcome of thetest in terms of the amount of data collected. If an operator doesn’t stop a test before a maximum safe penetration depth is attained, the testing equipment may become damaged or fail entirely.

[0006] With tests such as CPTs and other tests involving the use of a rod to insert a probe into the ground, there is a need to more accurately determine a maximum safe penetration depth.SUMMARY

[0007] The present disclosure provides systems and methods which address the above described problems and provide for improved accuracy in determining a maximum safe penetration depth for tests to determine properties of a subsurface region, ensuring that an optimal depth is attained when pushing a cone penetrometer, or any probe suitable for determining properties of a subsurface region, into the ground using a rod.

[0008] According to a first aspect of the present disclosure, there is provided a system comprising a probe for determining properties of a subsurface region. In some example implementations, the system comprises a rod for pushing the probe into the subsurface region. In some example implementations, the system comprises a fiber-optic sensor located within the rod configured to sense strain at at least one location along the rod.

[0009] Advantageously, measurement of strain by the fiber-optic sensor located in the rod can be used to assist in determining bending of the rod, for example using a shape sensing algorithm, to provide an accurate maximum safe penetration indication. The data from the fiber-optic sensor can also be used to determine the exact slope and azimuth of the slope over depth. In this way, the location over depth of the cone is known to a high amount of accuracy. Known techniques can be applied to determine bending of the rod using a measurement of strain by the fiber-optic sensor located in the rod and also to determine the exact slope and azimuth of the slope over depth. For example, the techniques described in Khan et al “Pose Measurement of Flexible Medical Instruments Using Fiber Bragg Gratings in Multi-Core Fiber” IEEE SENSORS JOURNAL, VOL. 20, NO. 18, SEPTEMBER 15, 2020, which is incorporated by reference.

[0010] In some example implementations, the fiber-optic sensor comprises at least one fiber-optic strain sensing element located within the rod. In some example implementations, the at least one fiber-optic strain sensing element comprises at least one intrinsic fiber-optic strain sensing element. In some example implementations, the fiber-optic strain sensing element comprises three sensing regions. In some example implementations, the three sensing regions are radially spaced within the rod.

[0011] The fiber-optic strain sensing element provides an indication of strain on the element as deformation of the element changes the optical properties of the element, providing an indication of strain on the sensing element. The fiber-optic strain sensing element may be provided with three sensing regions in order to determine direction of the bending of the rod. The fiber-optic strain sensing element may also be an intrinsic fiber-optic strain sensing element, meaning that the sensing element utilises a change that takes place within the fiber itself in order to sense strain.

[0012] In some example implementations, the fiber-optic strain sensing element comprises a Fiber Bragg Grating, FBG. FBGs comprise mirrors which reflect specific wavelengths of light differently upon deformation of the FBG, providing an indication of strain.

[0013] In some example implementations, the fiber-optic strain sensing element comprises a support configured to secure the fiber-optic strain sensing element to the rod. In some example implementations, the support comprises a centraliser.

[0014] The support secures the fiber-optic strain sensing element within the rod. This is advantageous as it means that strain measurements can be associated with a known location along the rod.Advantageously, the support may also be configured to secure the fiber-optic strain sensing element in fixed position in relation to the circumference of the rod, such as at a centre of the rod. In some example implementations, cross-sections of the circumference of the fiber-optic strain sensing element and the circumference of the rod are positioned concentrically, at the at least one location along the rod, where the measurements are being taken. Advantageously, the support may position the fiber-optic strain sensing element at a fixed position in relation to the circumference of the rod. This means that accurate determinations can be made about bending of the rod and, optionally, direction of the rod.

[0015] In some example implementations, the support comprises a measurement section supporting the fiber-optic strain sensing element. In some example implementations, the measurement section is configured to conform to deformation of the rod whilst maintaining a longitudinal axis of the fiber-optic strain sensing element in a fixed position relative to a longitudinal axis of the rod.

[0016] Advantageously, the measurement section of the support facilitates accurate strain sensing as the longitudinal axis of the fiber-optic strain sensing element is maintained in alignment with the longitudinal axis of the rod. In this way, strain measurements provided by the fiber-optic strain sensing element can be used to accurately determine bending of the rod.

[0017] In some example implementations, the support comprises securing sections either side of the measurement section, In some example implementations, the securing sections are secured to the rod to prevent axial movement of the fiber-optic strain sensing element relative to the rod and to fix the orientation of the fiber-optic strain sensing element relative to the rod. In some example implementations, the securing sections are secured to the rod via an adhesive or welding of the support to the rod. In some example implementations, the measurement section is more flexible than the securing sections.

[0018] Advantageously, the securing sections of the support facilitate accurate strain sensing as they ensure that axial movement of the fiber-optic strain sensing element relative to the rod is prevented, as well as rotation of the fiber-optic strain sensing element relative to the rod. In this way, strain measurements provided by the fiber-optic strain sensing element can be used to accurately determine bending of the rod as the relative position and orientation of the fiber-optic strain sensing element is fixed relative to the rod.

[0019] In some example implementations, the fiber-optic sensor comprises a plurality of fiber-optic strain sensing elements located at discrete locations along the rod, In some example implementations, theplurality of fiber-optic strain sensing elements are located at regular intervals along the rod. In some example implementations, the intervals are 0.5 m or less. In some example implementations, the fiberoptic strain sensing elements are optically coupled via a fiber-optic cable or, in some example implementations, the fiber-optic strain sensing elements are formed within a fiber-optic cable.

[0020] Advantageously, strain can be determined at a plurality of locations along the length of the rod, improving accuracy when determining bending of the rod leading to improved accuracy in providing a maximum safe penetration indication. Reducing the interval between fiber-optic strain sensing elements increases measurement resolution, further improving accuracy in providing a maximum safe penetration indication.

[0021] In some example implementations, at least one of the fiber-optic strain sensing elements is configured to provide an optical response in a different wavelength range to the other fiber-optic strain sensing elements.

[0022] Advantageously, this enables each sensor to be provided on the same fiber-optic cable as optical responses can be distinguished by virtue of the different wavelength ranges.

[0023] In some example implementations, the system further comprises an interrogator configured to transmit optical interrogation signals to the fiber-optic sensor and receive respective response optical signals from the fiber-optic sensor. In some example implementations, the response optical signals have been modulated by a fiber-optic strain sensing element of the fiber-optic sensor based on optical characteristics of the fiber-optic strain sensing element. In some example implementations, the response optical signal of each fiber-optic strain sensing element is in a wavelength range unique to the fiber-optic strain sensing element.

[0024] Advantageously, output of the sensor can be used to determine bending of the rod to provide an accurate maximum safe penetration indication. The data from the fiber-optic sensor can also be used to determine the exact slope and azimuth of the slope over depth. In this way, the location over depth of the cone is known to a high amount of accuracy.

[0025] In some example implementations, the fiber-optic sensor comprises a fiber-optic strain sensing element located along a length of the rod. In some example implementations, the length of the rod is 50% of the total length of the rod or greater. In some example implementations, the length of the rod is 75% of the total length of the rod or greater. In some example implementations, the length of the rod is 90% of the total length of the rod or greater. In some example implementations, the length of the rod is 95% of the total length of the rod or greater.

[0026] In some example implementations, the fiber-optic sensor comprises a single fiber-optic strain sensing element located along the length of the rod. In some example implementations, the fiber-optic strain sensing element comprises a fiber-optic cable. In some example implementations, the fiber-optic strain sensing element comprises three fiber-optic strain sensing regions.

[0027] In this example, a single fiber-optic strain sensing element can be used to sense strain along multiple locations along the length of the rod. Three fiber-optic strain sensing elements may be provided in order to determine direction of the bending of the rod.

[0028] In some example implementations, the fiber-optic strain sensing element comprises a support located along the length of the rod and configured to secure the fiber-optic strain sensing element to the rod. The provision of a support is advantageous as it means that strain measurements can be associated with a known location along the rod. In some example implementations, the support comprises a centraliser.

[0029] In some example implementations, the support is configured to secure the fiber-optic strain sensing element to the rod at a first end of the rod. In some example implementations, the support is configured to secure the fiber-optic strain sensing element to the rod only at the first end of the rod. In some example implementations, axial movement of the fiber-optic strain sensing element is permitted at a second end of the rod. In some example implementations, a resilient member is provided at the second end of the rod for permitting the axial movement of the fiber-optic strain sensing element at the second end of the rod.

[0030] In some example implementations, the support is configured to conform to deformation of the rod whilst maintaining a longitudinal axis of the fiber-optic strain sensing element in a fixed position relative to a longitudinal axis of the rod.

[0031] Advantageously, the support facilitates accurate strain sensing as the longitudinal axis of the fiber-optic strain sensing element is maintained in alignment with the longitudinal axis of the rod. In this way, strain measurements provided by the fiber-optic strain sensing element can be used to accurately determine bending of the rod.

[0032] In some example implementations, the support is secured to the rod to prevent axial movement of the fiber-optic strain sensing element relative to the rod and to fix the orientation of the fiber-optic strain sensing element relative to the rod. In some example implementations, the support is secured to the rod via an adhesive or welding of the support to the rod.

[0033] Advantageously, the support facilitates accurate strain sensing as it prevents axial movement of the fiber-optic strain sensing element relative to the rod, as well as preventing rotation of the fiber-optic strain sensing element relative to the rod. In this way, strain measurements provided by the fiber-optic strain sensing element can be used to accurately determine bending of the rod.

[0034] In some example implementations, the system further comprises an interrogator configured to transmit optical interrogation signals into the fiber-optic sensor and receive respective response optical signals that have been modulated by impurities and inherent variations in the fiber-optic strain sensing element.

[0035] Advantageously, output of the sensor can be used to determine bending of the rod to provide an accurate maximum safe penetration indication. The data from the fiber-optic sensor can also be used todetermine the exact slope and azimuth of the slope over depth. In this way, the location over depth of the cone is known to a high amount of accuracy.

[0036] In some example implementations, the system further comprises an interrogator configured to transmit optical interrogation signals into the fiber-optic sensor and receive respective response optical signals that have been modulated by the fiber-optic sensor based on optical characteristics of the fiberoptic sensor.

[0037] According to a second aspect of the present disclosure, there is provided a method of determining properties of a rod for pushing the probe into the subsurface region during a subsurface test. In some example implementations, the system of the above first aspect can be used in this method or any system described herein. In some example implementations, the method comprises pushing the probe into a subsurface region using the rod. In some example implementations, the method comprises obtaining strain measurements from the fiber-optic sensor. In some example implementations, the method comprises determining a degree of bending of the rod based on the strain measurements. In some example implementations, this process can be repeated over time.

[0038] In some example implementations, the method further comprises determining whether a maximum bending threshold has been exceeded by comparing the determined degree of bending to a threshold value. In some example implementations, the method further comprises outputting an alert if the maximum bending threshold has been exceeded.

[0039] Advantageously, an alert is generated when a maximum bending threshold is exceeded indicating a maximum safe penetration depth. In some example implementations, this process can be repeated over time.

[0040] In some example implementations, the method further comprises repeatedly obtaining strain measurements from the fiber-optic sensor as the probe is being pushed into the subsurface region. In some example implementations, the method further comprises determining a degree of bending of the rod and a direction of bending of the rod based on the strain measurements. In some example implementations, the method further comprises determining a slope and azimuth of the slope of the probe based on the determined degree and direction of the bending of the rod.

[0041] In this way, the location over depth of the cone is known to a high amount of accuracy.

[0042] According to a third aspect of the present disclosure, there is provided a method of calibrating the fiber-optic sensor of the system of the above first aspect or any system described herein. In some example implementations, the method comprises obtaining strain measurements from the fiber-optic sensor when the rod is in a known configuration In some example implementations, the method comprises comparing the strain measurements with expected strain measurements for the known configuration. In some example implementations, the method comprises calibrating the fiber-optic sensor based on the comparison.

[0043] According to a fourth aspect of the present disclosure, there is provided a rod for pushing a probe into a subsurface region, the rod comprising a fiber-optic sensor located within the rod configured tosense strain at at least one location along the rod. In some example implementations, the fiber-optic sensor is in accordance with the fiber-optic sensor of the above first aspect or any fiber-optic sensor described herein.

[0044] According to a fifth aspect of the present disclosure, there is provided a fiber-optic sensor for use in a rod for pushing a probe into a subsurface region. In some example implementations, the fiber-optic sensor is in accordance with the fiber-optic sensor of the above first aspect or any fiber-optic sensor described herein.According to a sixth aspect of the present disclosure, there is provided a support for a fiber-optic sensor. In some example implementations, the support is in accordance with the support of the above first aspect or any support described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to describe the manner in which the above-recited and other advantages and features of the disclosure can be obtained, a more particular description of the principles briefly described above will be provided by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary implementations of the disclosure and are therefore not to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail by way of example to illustrate aspects of the disclosure and with reference to the accompanying drawings, in which:Figure 1 shows an example geotechnical apparatus according to the present disclosure;Figure 2 shows an example of a rod shown in Figure 1 ;Figure 3 shows an example of a fiber-optic sensor shown in Figure 2;Figure 4 shows a cross section of the fiber-optic sensor shown in Figures 2 and 3;Figure 5 shows a cross section of the fiber-optic sensor shown in Figures 2 and 3;Figure 6 shows an example implementation of a rod 106 shown in Figure 1 ;Figure 7 shows a cross section of the rod shown in Figure 6;Figure 8 shows a method of determining properties of a rod; andFigure 9 shows a computer system for carrying out the various methods of the present disclosure.

[0046] Throughout the description and the drawings, like reference numerals refer to like features.DETAILED DESCRIPTION

[0047] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the drawings.

[0048] Various implementations and examples of the disclosure are discussed in detail below. While specific implementations and examples are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognise that other components and configurations may be used without parting from the spirit and scope of the disclosure. Thus, the followingdescription and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well- known or conventional details are not described in order to avoid obscuring the description. A reference to an implementation or example in the present disclosure can be a reference to the same implementation or example, or any other implementation or example. Such references thus relate to at least one of the implementations or examples herein.

[0049] The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Alternative language and synonyms may be used for any one or more of the terms discussed herein, and no special significance should be placed upon whether or not a term is elaborated or discussed herein. In some cases, synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only and is not intended to further limit the scope and meaning of the disclosure or of any example term. Likewise, the disclosure is not limited to various implementations given in this specification. References to ranges of values or values “between” two values should be interpreted as encompassing the end points of those ranges unless otherwise specified.

[0050] Figure 1 shows an example geotechnical apparatus 100 comprising a rod dispensing unit 102, comprising a rod 106 in a coiled configuration, and a drive unit 104 for driving the uncoiled rod 106 into a subsurface target region beneath a surface of the earth. The depicted dispensing unit 102 is merely an example of a dispensing unit and other types of dispensing unit may be used. The depicted drive unit 104 is also merely an example of an advancing mechanism and other types of advancing mechanism may be used, depending on the environment within which the geotechnical apparatus 100 is to be used. It will be understood that other means for inserting the probe 108 may be used in place of the rod 106. For example, a segmented rod could be used in which segments of the rod are screwed together or otherwise coupled as it is inserted into the ground.

[0051] At its free end, the rod 106 supports a probe 108 for determining properties, such as geotechnical properties, of the subsurface target region if the subsurface into which the probe is inserted. The geotechnical apparatus 100 could be located on land or on the bed of a body of water, such as a seabed.

[0052] The probe 108 is coupled to the rod 106. The probe 108 shown in Figure 1 is merely presented an example of a probe. It will be understood that wherever reference is made to a probe 108, a number of different types of probe could be used, such as a cone penetrometer, a T-bar penetrometer or a ball probe penetrometer.

[0053] The probe 108 may comprise a cone penetrometer suitable for conducting a cone penetration test, CPT. In another example, the cone penetrometer is suitable for conducting a piezocone penetration test, CPTu. The cone penetrometer may be a standard cone penetrometer commonly used in industry. The probe 108 is coupled to the rod 106, which is arranged to translate a pushing force to probe 108 as it is being driven into a target soil.

[0054] The probe 108 may comprises one or more sensors for determining properties, such as geotechnical properties, of the subsurface target region of the subsurface region into which the probe is inserted. In an example, one or more seismic sensors for use in a seismic cone penetration test, SCPT, or other seismic velocity test are provided. Other example sensor modules include sensors suitable for performing a thermal conductivity test, a temperature test, a magnetometer test and electrical conductivity test and a pore water dissipation test.

[0055] In an example, the probe 108 may additionally include one or more openings (not depicted) for allowing a friction reducing fluid to be distributed to the surrounding area from the probe 108. In this example, the rod 106 may also include a conduit (not depicted) along which friction reducing fluid can be passed from the surface to the one or more openings in the probe 108.

[0056] The rod 106 translates a push force to the probe 108 in order to drive the probe 108 into a target soil. The maximum safe penetration depth can be defined as the depth at which the insertion of the rod must be stopped to avoid damage to or failure of the rode, probe or any other part of the testing equipment. The maximum safe penetration depth attainable during a test is generally determined by an operator based on parameters, such as the push force required to advance the rod exceeding a maximum threshold. However, this does not take into account the force distribution over the rod and, therefore, does not provide an accurate input for a determination of maximum safe penetration depth.

[0057] A tilt sensor provided in the probe 108 can also be used to back calculate the shape and / or curvature of the rod 106 and estimate related stresses. However, this is an inaccurate process as the tilt sensor itself is too inaccurate to enable an accurate back calculation of the shape and / or curvature of the rod 106, and direction is also difficult if not impossible to distinguish.

[0058] This inaccuracy can lead to an operator stopping penetration too soon before the actual maximum safe penetration depth or not stopping penetration in time.

[0059] If an operator stops a test before a maximum safe penetration depth is attained, this could negatively impact the outcome of the test as the amount of data collected would fall short of what would actually have been possible without risking damage or failure. If an operator doesn’t stop a test before a maximum safe penetration depth is attained, the testing equipment may become damaged or even fail entirely.

[0060] There is a need to more accurately determine a maximum safe penetration depth to ensure an optimum outcome for tests, such as CPTs and the other aforementioned tests.

[0061] The systems shown in Figures 2 to 7 addresses these and other issues by facilitating accurate determination of a maximum safe penetration depth, as shall now be described.

[0062] Figure 2 shows an example implementation of the rod 106 shown in Figure 1 for use in the geotechnical apparatus 100. The rod 106 comprises a fiber-optic cable 202, fiber-optic sensors 204 and a strengthening member 206. The fiber-optic cable 202, fiber-optic sensors 204 and strengthening member 206 are all located within the rod 106. An additional conduit (not shown) may also be provided within therod 106 containing cabling required for communication with any sensors and other equipment present in the probe 108.

[0063] The fiber-optic cable 202 is configured to optically couple each of the fiber-optic sensors 204 to a source (not shown) that emits an input optical signal to the fiber-optic sensors 204 and to a detector (not shown) that receives a response optical signal from the fiber-optic sensors 204. In an example implementation, the source and / or the detector may be located above ground. For example, the geotechnical apparatus 100 may comprise the source and the detector.

[0064] In an example implementation, the source and the detector may be provided in the form of an interrogator (not shown) configured to transmit optical interrogation signals to the fiber-optic sensors 204 and receive respective response optical signals from the fiber-optic sensors 204. In an example implementation, the optical interrogation signals are modulated by a fiber-optic strain sensing element 302 (shown in Figure 3) of each of the fiber-optic sensors 204 based on optical characteristics of the fiber-optic strain sensing element 302. The response optical signal of the fiber-optic strain sensing element 302 of each fiber-optic sensors 204 may be unique to each fiber-optic sensor 204 such that they can be distinguished from one another. For example, the response optical signal may be in a wavelength range unique to each sensor fiber-optic sensors 204.

[0065] In an example implementation, the processing system 900 shown in Figure 9 may be provided to control operation of the source, the detector and / or the interrogator.

[0066] At least one fiber-optic sensor 204 of the fiber-optic sensors 204 is configured to sense strain at a location along the rod 106 at which the fiber-optic sensors 204 is located. The measurement of strain by each fiber-optic sensor 204 can be used to determine bending of the rod 106 as it is being pushed into the ground using a shape sensing algorithm, for example by applying the known techniques referenced above. Once the bending of the rod 106 has been determined, this can be used to determine an accurate maximum safe penetration depth. For example, if bending of the rod 106 is determined to exceed a maximum threshold, an alert or other indication can be generated to indicate that the maximum safe penetration depth has been reached. In an example implementation, the processing system 900 shown in Figure 9 may be configured to analyse output signals from the fiber-optic sensors 204 to determine strain and determine bending of the rod 106 based on the analysis of the output signals. The processing system 900 may also be configured to determine the maximum safe penetration depth and generate an alert of indication when the maximum safe penetration depth has been reached.

[0067] In an example implementation, only one fiber-optic sensor 204 is provided in the rod 106 to sense strain at a single location along the rod 106. In other example implementations, only two, three, four or more fiber-optic sensors 204 are provided in the rod 106.

[0068] Where more than one fiber-optic sensor 204 is provided in the rod 106, they may be separated at regular intervals along the rod 106 by distance ‘d’ shown in Figure 2. In an example implementation, distance ‘d’ is 0.5 m or less.

[0069] Strengthening member 206 may optionally be provided to support the fiber-optic cable 202 along the length of the rod 106. The primary function of the strengthening member 206 is to help ensure the fiber-optic sensors 204 are located at the same place inside the rod 116 over the entire length of the rod 116. This helps improve accuracy of the output of any shape sensing algorithm used.

[0070] Figure 3 shows an example implementation of the fiber-optic sensors 204 shown in Figure 2. The fiber-optic sensor 204 comprises a support 300, the support 300 having a measurement section 304 and securing sections 306 either side of the measurement section 304. The fiber-optic sensor 204 further comprises a fiber-optic strain sensing element 302 coupled to the fiber-optic cable 202. The fiber-optic cable 202 and strengthening member 206 are also shown. In some example implementations, the support 300 is a centraliser.

[0071] The support 300 is configured to secure the fiber-optic strain sensing element 302 to the rod 106. The support 300 comprises a measurement section 304 for supporting the fiber-optic strain sensing element 302. The measurement section 304 is configured to conform to deformation of the rod 106 whilst maintaining a longitudinal axis of the fiber-optic strain sensing element 302 in a fixed position relative to a longitudinal axis of the rod 106. As shown in Figure 3, the measurement section 304 includes regions with a larger diameter spaced by regions with a smaller diameter in order to facilitate conforming of the measurement section 304 to deformation of the rod 106 whilst maintaining a longitudinal axis of the fiberoptic strain sensing element 302 in a fixed position relative to a longitudinal axis of the rod 106. The measurement section 304 may additionally or alternatively be made of a more flexible material than the securing sections 304.

[0072] The support 300 further comprises securing sections 306 either side of the measurement section 304. The securing sections 306 are secured to the rod 106 to prevent axial movement of the fiber-optic strain sensing element 302 relative to the rod 106 and to fix the orientation of the fiber-optic strain sensing element 302 relative to the rod 106. The securing sections 306 may be secured to the rod 106 via an adhesive or welding 308. In some example implementations, only a single securing section 306 is provided on one side of the measurement section 304.

[0073] Figure 4 shows an cross section a securing section 306. The securing section 306 is secured to the rod 106 via weld 308. The fiber-optic cable 202 and strengthening member 206 are also visible. It will be appreciated that welding or otherwise securing the securing section 306 to the rod 106 in this way via either or both securing sections 306 of each support 300 prevents axial movement of the fiber-optic strain sensing element 302 relative to the rod 106 and fixes the orientation of the fiber-optic strain sensing element 302 relative to the rod 106.

[0074] In some example implementations, the fiber-optic strain sensing element 302 is an intrinsic fiberoptic strain sensing element, that is the fiber-optic strain sensing element 302 utilises a change that takes place in the fiber-optic strain sensing element 302 itself to sense strain.

[0075] In some example implementations, the fiber-optic strain sensing element 302 comprises a Fiber Bragg Grating, FBG, for sensing strain. A Fiber Bragg Gratings is constructed in a short segment ofoptical fiber, in this instance the fiber-optic strain sensing element 302, that reflects particular wavelengths of light and transmits all others. The reflected wavelength, also known as the Bragg wavelength, is altered by effects such as a change in strain on the optical fiber. In some example implementations, the fiber-optic strain sensing element 302 is configured to utilise Brillouin scattering or Rayleigh scattering effects to detect strain.

[0076] In some example implementations, the fiber-optic strain sensing elements 302 of one or more of the fiber-optic sensor 204 in the rod 106 comprise one or more of: point sensors based on Fiber Bragg Gratings, quasi-distributed sensors, interferometric Fiber Bragg Grating sensors, sensors Based on Micro-Fabry-Perots, distributed strain sensors based on Rayleigh Scattering, distributed strain sensors based on Brillouin Scattering.

[0077] In some example implementations, the fiber-optic strain sensing element 302 has three sensing regions that a radially spaced within the rod 106. Each sensing region may be configured to individually sense strain. The output of these sensing regions can be used to determine a direction of the bending of the rod 106.

[0078] Figure 5 shows an cross section of an example implementation of the sensing element 302 of the fiber-optic sensor 204 shown in Figure 3. Three sensing regions 502 that are radially spaced within the rod 106 are visible. The sensors are radially spaced from a geometrical centre 504 of the rod 116. Using the known geometry of the sensing element 302 and sensing regions 502, including their precise axial location and orientation within the rod 106, it is possible to determine a direction of bending of the rod 106 at the location of the sensing element 302 from the strain measurements taken by each sensing region 502. Taking measurements over time enables a 3D path of the rod 106 to be reconstructed. Strain measurements from the sensing elements 302 of multiple fiber-optic sensors 204 within the rod 106 can be used to provide a more accurate determination of direction of bending of the rod 106 and to reconstruct a 3D path of the rod 106. In this way, the location over depth of the rod 106 is known to a high amount of accuracy. Known techniques can be applied to determine a direction of bending of the rod 106 and reconstruct a 3D path of the rod 106. For example, the techniques described in Khan et al “Pose Measurement of Flexible Medical Instruments Using Fiber Bragg Gratings in Multi-Core Fiber” IEEE SENSORS JOURNAL, VOL. 20, NO. 18, SEPTEMBER 15, 2020, which is incorporated by reference, can be used..

[0079] Going from strain measurements to the a determination of bending of the rod 106 can be done via a shape-sensing algorithm. There are many different known shape-sensing algorithms and any suitable shape sensing algorithm can be used to determine bending of the rod 106 from strain measurements and, optionally, a direction of bending of the rod 106. For example, a shape sensing algorithm could be used to determine the exact slope of the rod 106 and azimuth of the slope over depth.

[0080] In some example implementations, the fiber-optic strain sensing element 302 is part of the fiberoptic cable 202. In this example, the fiber-optic strain sensing element 302 of each fiber-optic sensors 204 located in the rod 106 may form part of the same fiber-optic cable 202.

[0081] Figure 6 shows an example implementation of the rod 106 shown in Figure 1 for use in the geotechnical apparatus 100. The rod 106 comprises a fiber-optic cable 602 supported by a support 604 along the length of the rod 106. The fiber-optic cable 602 and support 604 are all located within the rod 106. However, rather than the discrete fiber-optic sensors 204 shown in Figure 2, the entire fiber optic cable 602 can act as a strain sensing element. The fiber optic cable 602 is supported within the rod 106 by the support 604. An additional conduit (not shown) may also be provided within the rod 106 containing cabling required for communication with any sensors and other equipment present in the probe 108.

[0082] As mentioned above, in the example rod 106 shown in Figure 6, the entire fiber optic cable 602 can act as a strain sensing element. Here, impurities and inherent variations in the fiber optic cable 602 acting as fiber-optic strain sensing element can be utilised to determine strain on any particular location along the fiber optic cable 602. An interrogator (not shown) can transmit optical interrogation signals into the fiber-optic cable 602 and receive respective response optical signals that have been modulated by impurities and inherent variations in the fiber-optic cable 602. Other optical characteristics of the fiberoptic cable 602 may also be used in place of impurities and inherent variations.

[0083] In this example, only a single fiber-optic strain sensing element may be provided in the rod 106 in the form of the fiber-optic cable 602. In some example implementations, the support 604 is a centraliser

[0084] In some example implementations, fiber-optic cable 602 may comprise three fiber-optic strain sensing regions along its length, similar to those shown in Figure 5 and providing the same function in terms of enabling a direction of bending of the rod 106 to be determined and a 3D path of the rod 106 to be reconstructed over time when taking measurements over time in the same manner as is described above in relation to the three sensing regions 502 shown in Figure 5.

[0085] Figure 7 shows a cross section of the example implementation of the rod 106 shown in Figure 6. As can be seen in Figure 7, the fiber-optic cable 602 is supported at a fixed location relative to a geometrical centre 704 of the rod 116 by the support 604.

[0086] The support 604 is configured to conform to deformation of the rod whilst maintaining a longitudinal axis of the fiber-optic strain sensing element in a fixed position relative to a longitudinal axis of the rod 106 and a fixed orientation relative to the rod 106. To achieve this, the support 604 is secured to the rod 106 via weld 708. It will be appreciated that welding or otherwise securing the support 604 to the rod 106 in this way prevents axial movement of the fiber-optic cable 602 relative to the rod 106 and fixes the orientation of the fiber-optic cable 602 relative to the rod 106. The weld 708 may comprise a member which sticks out internally from the rod 106 and the support 604 may have a corresponding groove that engages the weld 708 to prevent relative rotation of the support 604 (and therefore the fiberoptic cable 602) and the rod 106. Further adhering the weld 708 to the support 604 may prevent axial movement off the support 604 (and therefore the fiber-optic cable 602) relative to the rod 106. A similar arrangement may be provided for weld 308 shown in Figures 3 and 4.

[0087] In the example shown in Figure 7, the support 604 also has a hollow central portion 706 around the geometrical centre 704 of the rod 116 and recessed portions 710 either side of the of the hollowcentral portion 706. These portions aid the support 604 in conforming to deformation of the rod 106 whilst maintaining a longitudinal axis of the fiber-optic cable 602 in a fixed position relative to a longitudinal axis of the rod 106. In some example implementations (not shown), the support 604 may additionally or alternatively included regions with a larger diameter spaced by regions with a smaller diameter, similar to the measurement section 304 shown in Figure 3, along the length of the fiber-optic cable 602.

[0088] In some example implementations (not shown), the support 604 is configured to secure the fiberoptic cable 602 to the rod 106 at a first end of the rod 106. The support 604 may also secure the fiberoptic cable 602 to the rod 106 only at the first end of the rod 106 and axial movement of the fiber-optic cable 602 may be permitted at a second end of the rod 106. For example, a resilient member can be provided at the second end of the rod 106 for permitting the axial movement of the fiber-optic cable 602 at the second end of the rod 106.

[0089] The fiber-optic cable 602 is optically coupled to a source (not shown) that emits an input optical signal to the fiber-optic cable 602 and to a detector (not shown) that receives a response optical signal from the fiber-optic cable 602. In an example implementation, the source and / or the detector may be located above ground. For example, the geotechnical apparatus 100 may comprise the source and the detector.

[0090] In an example implementation, the source and the detector may be provided in the form of an interrogator (not shown) configured to transmit optical interrogation signals to the fiber-optic cable 602 and receive response optical signals from the fiber-optic cable 602. In an example implementation, the optical interrogation signal interacts with microscopic impurities and inherent variations in the fiber material of the fiber-optic cable 602, causing Rayleigh scattering. This scattering is sensitive to the fiber's local environment, such as changed in strain. Changes in strain on the fiber-optic cable 602 alter the intensity and phase of the scattered Rayleigh light. These changes are encoded in the light that is scattered back toward the source that forms a response optical signal. The response optical signal is collected by the interrogator. This response optical signal carries detailed spatial information about the points along the fiber where changes in strain have occurred.

[0091] Optical Time-Domain Reflectometry (OTDR) techniques can be used to measure the time it takes for the scattered light to return to the interrogator, to pinpoint the location of the scattering events along the fiber-optic cable 602. Phase Shift Analysis can be used to analyse changes in the phase of the backscattered light to determine the magnitude of strain changes at locations along the fiber-optic cable 602. This phase-sensitive detection allows for high-resolution mapping of strain at locations along the fiber-optic cable 602. The time and phase data output can be processed by the interrogator to produce detailed maps of strain variations along the fiber-optic cable 602. This processing may include calibration steps to correct for any system-induced errors or baseline shifts. The processed strain data from multiple points along the fiber-optic cable 602 can be integrated to reconstruct the 2D or 3D shape of the rod 106. An output that indicates the changes in shape and strain of the rod 106 may be provided, facilitating immediate interpretation and ongoing monitoring of the rod 106 as it is inserted into the ground.

[0092] The output can be used to determine an accurate maximum safe penetration depth. For example, if bending of the rod 106 is determined to exceed a maximum threshold, an alert or other indication can be generated to indicate that the maximum safe penetration depth has been reached. In an example implementation, the processing system 900 shown in Figure 9 may be configured to process optical signals collected by the interrogator to determine strain and determine bending of the rod 106 based on the analysis of the output signals. The processing system 900 may also be configured to determine the maximum safe penetration depth and generate an alert of indication when the maximum safe penetration depth has been reached.

[0093] In an example implementation, the processing system 900 shown in Figure 9 may be provided to control operation of the source, the detector and / or the interrogator.

[0094] Figure 8 shows a method 800 of determining properties of a rod, such as rod 106 described above, for pushing a probe, such as probe 108 described above, into the subsurface region during a subsurface test. Although the method is described in the context of the geotechnical apparatus 100 shown in Figure 1 , it will be understood that the method 800 could be performed using any suitable geotechnical apparatus.

[0095] At step 802, the method 800 comprises pushing the probe 108 into a subsurface region using the rod 108.

[0096] At step 804, method 800 comprises obtaining strain measurements from a fiber-optic sensor located within the rod 106 configured to sense strain at at least one location along the rod 106. The fiberoptic sensor may be any of the above described fiber-optic sensors. For example, the fiber-optic sensor may be one or more of the fiber-optic sensors 204 shown in Figures 2 to 5 and / or the fiber-optic cable 602, which acts as a fiber-optic sensor, shown in Figures 6 and 7.

[0097] At step 806, method 800 comprises determining a degree of bending of the rod based on the strain measurements, for example, using any of the herein described or referenced techniques.

[0098] Steps 802 to 806 can be repeated over time to provide a real-time determination of the degree of bending of the rod.

[0099] In some examples, the method 800 further comprises determining whether a maximum bending threshold has been exceeded by comparing the determined degree of bending to a threshold value and outputting an alert if the maximum bending threshold has been exceeded. This can be repeated over time to provide a real-time monitoring of the degree of bending of the rod and an indication that a maximum safe penetration distance has been reached as soon as the degree of bending exceeds a threshold.

[0100] In some examples, the method 800 further comprises repeatedly obtaining strain measurements from the fiber-optic sensor as the probe 108 is being pushed into the subsurface region, determining a degree of bending of the rod 106 and a direction of bending of the rod 106 based on the strain measurements. A slope and azimuth of the slope of the probe may then be determined based on the determined degree and direction of the bending of the rod. Here, the fiber-optic sensor may comprisethree sensing regions, such as the three sensing regions 502 shown in Figure 5 or where the fiber-optic cable 602, shown in Figures 6 and 7, comprises three sensing regions.

[0101] A method of calibrating the fiber-optic sensor of the systems described above is also disclosed, for example a rod 106 comprising one or more of the fiber-optic sensors 204 shown in Figures 2 to 5 and / or the fiber-optic cable 602, which acts as a fiber-optic sensor, shown in Figures 6 and 7. The method comprises obtaining strain measurements from the fiber-optic sensor when the rod 106 is in a known configuration, comparing the strain measurements with expected strain measurements for the known configuration, and calibrating the fiber-optic sensor based on the comparison.

[0102] In an example implementation, the rod 106 is in an known coiling radius over the full length of the rod 106 and this configuration is used as a the known configuration. The known configuration could also involve laying the rod 106 out flat on a surface and in a straight line.

[0103] In an example implementation, the known configuration is the configuration of the rod 106 when it is in a stored position, prior to being pushed into the ground ahead of a test. This could be the 'coil' shape of the rod 106 shown in Figure 1 . As the geometry of the rod 106 (e.g. coil radius) is the same when the rod 106 is in a stored position before each test is carried out, a pre-check against the strain measurements from the fiber-optic sensor when the rod 106 is in a stored position can be carried out before it is pushed into the ground to perform a test. Deviations can then be filtered out on a per-test basis.

[0104] In an example implementation, the method comprises applying predefined deviations to the rod 106 from the known configuration, measuring the predefined deviations applied to the rod and checking these against strain measurements from the fiber-optic sensor when the predefined deviations have been applied to the rod 106.

[0105] With reference to Figure 9, a computing device or system suitable for carrying out the methods described herein will now be described. Figure 9 shows a block diagram of one implementation of a processing system 900 in the form of a computing device within which a set of instructions for causing the computing device to perform any one or more of the methodologies discussed herein, may be executed. In alternative implementations, the computing device may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The computing device may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The computing device may be a personal computer (PC), a tablet computer, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single computing device is illustrated, the term “computing device” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein.

[0106] The example processing system 900 includes a processor 902, a main memory 904 (e.g., readonly memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 906 (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory (e.g., a data storage device 918), which communicate with each other via a bus 930.

[0107] Processor 902 represents one or more general-purpose processors such as a microprocessor, central processing unit, or the like. More particularly, the processor 902 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processor 902 may also be one or more special-purpose processors such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processor 902 is configured to execute the processing logic (instructions 922) for performing the operations and steps of the methods discussed herein.

[0108] The processing system 900 may further include a network interface device 908. The processing system 900 also may include a video display unit 910 (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device 912 (e.g., a keyboard or touchscreen), a cursor control device 914 (e.g., a mouse or touchscreen), and an audio device 916 (e.g., a speaker).

[0109] It will be apparent that some features of the processing system 900 shown in Figure 9 may be absent. For example, the processing system 900 may have no need for display device 910 (or any associated adapters). This may be the case, for example, for particular server-side computer apparatuses which are used only for their processing capabilities and do not need to display information to users. Similarly, user input device 912 may not be required. In its simplest form, processing system 900 comprises processor 902 and main memory 904.

[0110] The data storage device 918 may include one or more machine-readable storage media (or more specifically one or more non-transitory computer-readable storage media) 928 on which is stored one or more sets of instructions 922 embodying any one or more of the methodologies or functions described herein. The instructions 922 may also reside, completely or at least partially, within the main memory 904 and / or within the processor 902 during execution thereof by the processing system 900, the main memory 904 and the processor 902 also constituting computer-readable storage media 928.

[0111] The various methods described above may be implemented by a computer program. The computer program may include computer code arranged to instruct a computer to perform the functions of one or more of the various methods described above. The computer program and / or the code for performing such methods may be provided to an apparatus, such as a computer, on one or more computer readable media or, more generally, a computer program product. The computer readable media may be transitory or non-transitory. The one or more computer readable media could be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, or a propagationmedium for data transmission, for example for downloading the code over the Internet. Alternatively, the one or more computer readable media could take the form of one or more physical computer readable media such as semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disc, and an optical disk, such as a CD-ROM, CD-R / W or DVD.

[0112] The computer program is executable by the processor 902 to perform functions of the systems and methods described herein.

[0113] In an implementation, the modules, components, and other features described herein can be implemented as discrete components or integrated in the functionality of hardware components such as ASICS, FPGAs, DSPs, or similar devices.

[0114] A “hardware component” is a tangible (e.g., non-transitory) physical component (e.g., a set of one or more processors) capable of performing certain operations and may be configured or arranged in a certain physical manner. A hardware component may include dedicated circuitry or logic that is permanently configured to perform certain operations. A hardware component may be or include a special-purpose processor, such as a field programmable gate array (FPGA) or an ASIC. A hardware component may also include programmable logic or circuitry that is temporarily configured by software to perform certain operations.

[0115] Accordingly, the phrase “hardware component” should be understood to encompass a tangible entity that may be physically constructed, permanently configured (e.g., hardwired), or temporarily configured (e.g., programmed) to operate in a certain manner or to perform certain operations described herein.

[0116] In addition, the modules and components can be implemented as firmware or functional circuitry within hardware devices. Further, the modules and components can be implemented in any combination of hardware devices and software components, or only in software (e.g., code stored or otherwise embodied in a machine-readable medium or in a transmission medium).

[0117] Unless specifically stated otherwise, as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “transmitting”, "receiving”, “determining”, “comparing”, “calibrating”, “obtaining”, “maintaining”, “identifying”, “providing”, “outputting” or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

[0118] The preceding detailed description is merely exemplary in nature and is not intended to limit the disclosure and its uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, overview, or the detailed description.

[0119] Examples of the present disclosure may be described herein in terms of functional and / or logical block components and various processing steps. It should be appreciated that such block components may be realised by any number of hardware, software, and / or firmware components configured to perform the specified functions. For example, an example of the present disclosure may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that examples of the present disclosure may be practised in conjunction with any number of systems, and that the systems described herein are merely exemplary embodiments of the present disclosure.

[0120] For the sake of brevity, conventional techniques compared to signal processing, data transmission, signalling, control and other functional aspects of the systems (and the individual operating components of the systems) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and / or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connection may be present in an example of the present disclosure.

[0121] The term “apparatus” as used herein may refer to either a single apparatus or plural apparatus and should not be understood as being particularly limited to either a single discrete apparatus or a plurality of discrete apparatus unless a particular apparatus is further described as such.

[0122] Those skilled in the art will recognise that a wide variety of modifications, alterations, and combinations can be made with respect to the above described examples without departing from the scope of the disclosed concepts, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the disclosed concepts.

[0123] Those skilled in the art will also recognise that the scope of the invention is not limited by the examples described herein but is instead defined by the appended claims.

Claims

CLAIMS1 . A system comprising: a probe for determining properties of a subsurface region; a rod for pushing the probe into the subsurface region; and a fiber-optic sensor located within the rod configured to sense strain at at least one location along the rod.

2. The system of claim 1 , wherein the fiber-optic sensor comprises at least one fiber-optic strain sensing element located within the rod.

3. The system of claim 2, wherein the fiber-optic strain sensing element comprises a Fiber Bragg Grating, FBG.

4. The system of either of claim 2 or claim 3, wherein the fiber-optic strain sensing element comprises a support configured to secure the fiber-optic strain sensing element to the rod.

5. The system of claim 4, wherein the support comprises: a measurement section supporting the fiber-optic strain sensing element, wherein the measurement section is configured to conform to deformation of the rod whilst maintaining a longitudinal axis of the fiber-optic strain sensing element in a fixed position relative to a longitudinal axis of the rod.

6. The system of claim 5, wherein the support comprises: securing sections either side of the measurement section, wherein the securing sections are secured to the rod to prevent axial movement of the fiber-optic strain sensing element relative to the rod and to fix the orientation of the fiber-optic strain sensing element relative to the rod.

7. The system of any preceding claim, wherein the fiber-optic sensor comprises a plurality of fiberoptic strain sensing elements located at discrete locations along the rod.

8. The system of claim 7, wherein at least one of the fiber-optic strain sensing elements is configured to provide an optical response in a different wavelength range to the other fiber-optic strain sensing elements.

9. The system of claims 1 to 8, wherein the system further comprises an interrogator configured to transmit optical interrogation signals to the fiber-optic sensor and receive respective response optical signals from the fiber-optic sensor.

10. The system of claim 1 , wherein the fiber-optic sensor comprises a fiber-optic strain sensing element located along a length of the rod.11 . The system of claim 10, wherein the fiber-optic strain sensing element comprises a support located along the length of the rod and configured to secure the fiber-optic strain sensing element to the rod.

12. The system of claim 11 , wherein the support is configured to conform to deformation of the rod whilst maintaining a longitudinal axis of the fiber-optic strain sensing element in a fixed position relative to a longitudinal axis of the rod.

13. The system of claim 11 or claim 12, wherein the support is secured to the rod to prevent axial movement of the fiber-optic strain sensing element relative to the rod and to fix the orientation of the fiberoptic strain sensing element relative to the rod.

14. The system of any preceding claim, wherein the system further comprises an interrogator configured to transmit optical interrogation signals into the fiber-optic sensor and receive respective response optical signals that have been modulated by impurities and inherent variations in the fiber-optic strain sensing element and / or modulated based on optical characteristics of the fiber-optic sensor.

15. A method of determining properties of a rod for pushing the probe into the subsurface region during a subsurface test using the system of any preceding claim, the method comprising: pushing the probe into a subsurface region using the rod; obtaining strain measurements from the fiber-optic sensor; and determining a degree of bending of the rod based on the strain measurements.

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