Effective stress static penetrometer based on fiber bragg grating

Abstract

The invention discloses an effective stress static penetrometer based on a fiber bragg grating, and belongs to the technical field of geotechnical engineering in-situ testing, the effective stress static penetrometer based on the fiber bragg grating comprises a probe, a feeler lever and integrated fiber sensing assemblies distributed in the probe and the feeler lever, and the probe and the feeler lever are connected with each other; the probe comprises a conical head and a conical head deformation column; the probe rod comprises an effective stress ring column, an inclinometer ring column, a side wall friction cylinder, a demodulation ring column, a grating demodulation module arranged in a cavity of the demodulation ring column, a damping cylinder and a built-in optical fiber channel; the integrated optical fiber sensing assembly comprises an optical fiber taper tip resistance sensing module, an optical fiber side wall friction resistance sensing module, an optical fiber inclinometry sensing module and an optical fiber effective stress sensing module, and is connected to the grating demodulation module based on a built-in optical fiber path. According to the invention, the data acquisition and analysis system of the effective stress penetrometer is unified through the integrated optical fiber sensing assembly, and the data precision and the exploration efficiency are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of in-situ testing technology of geotechnical engineering, in particular to an effective stress static cone penetration tester based on fiber Bragg grating. BACKGROUND

[0002] In the field of geotechnical engineering exploration and design, accurately obtaining the physical and mechanical properties of soil is the premise of ensuring the safety and economy of engineering. The traditional drilling sampling method is seriously disturbed by soil, has a long test period and large data fluctuation, and is difficult to truly reflect the in-situ properties of soil. The static cone penetration technology (CPT, Cone Penetration Test) is efficient, fast, has small disturbance, and continuous data, and can record the changes of cone tip resistance and side friction resistance in real time during penetration, and directly show the structure, strength and deformation characteristics of soil layer, and is widely used in geological exploration. The current pore pressure static cone penetration (CPTU, Cone Penetration Test with Pore Pressure Measurement) integrated with a pore water pressure sensor can simultaneously measure the change of pore water pressure of soil, and provide a reference for the analysis of the strength and deformation characteristics of soil.

[0003] Effective stress is a key factor affecting the deformation and strength characteristics of soil, and accurate in-situ measurement of effective stress is crucial for safety evaluation of engineering design. However, although the conventional CPTU system is equipped with multiple types of sensors, it still needs to derive the effective stress by indirect calculation of "total stress minus pore water pressure", and it is difficult to directly obtain the true parameters, and the traditional strain gauge sensor has defects such as significant measurement error and poor anti-electromagnetic interference ability.

[0004] As a new type of sensing technology, fiber Bragg grating (FBG, Fiber Bragg Grating) has high precision, wide range and strong anti-interference characteristics, and has been successfully applied in the fields of slope stability monitoring and tunnel deformation control. Although some studies have tried to combine FBG with CPT, most of them use deformation beam strain indirect measurement mode, therefore, it is urgent to develop a high-precision static cone penetration tester based on FBG to measure the cone tip resistance, side friction resistance and effective stress during static cone penetration, so as to break through the technical bottleneck and improve the safety evaluation level of geotechnical engineering.

[0005] Therefore, the prior art still needs to be improved and improved. SUMMARY

[0006] In view of the above defects of the prior art, the present application provides an effective stress static cone penetration tester based on fiber Bragg grating, which aims to solve the problem that there is no cone penetration tester based on fiber Bragg grating for direct measurement of effective stress of soil in in-situ testing in the prior art, and the measurement error of the current static cone penetration tester is significant and the anti-electromagnetic interference ability is weak.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is as follows: The application provides an effective stress static sounding instrument based on a fiber Bragg grating, which comprises a probe, a probe rod and an integrated fiber sensing assembly distributed in the probe and the probe rod, and the probe and the probe rod are connected to each other. The probe comprises a cone head and a cone head deformation column. The probe rod comprises an effective stress ring column, an inclinometer ring column, a sidewall friction cylinder, a demodulation ring column, a grating demodulation module arranged in a cavity of the demodulation ring column, a damping cylinder and an embedded fiber channel. The integrated fiber sensing assembly comprises a fiber cone tip resistance sensing module, a fiber sidewall friction resistance sensing module, a fiber inclinometer sensing module and a fiber effective stress sensing module, and is connected to the grating demodulation module based on the embedded fiber channel, wherein the fiber cone tip resistance sensing module is arranged in the probe, the fiber inclinometer sensing module is arranged at the center of the inclinometer ring column, the fiber sidewall friction resistance sensing module is arranged above the inner side of the sidewall friction cylinder, and the fiber effective stress sensing module is arranged outside the effective stress ring column.

[0008] In an implementation manner, the fiber cone tip resistance sensing module comprises a first rectangular base, a first fiber strain sensor, a first fiber temperature sensor, a first deformation sheet and a first connecting member. The first deformation sheet is a rectangular steel sheet which is deformed when subjected to the action of the cone head deformation column. The first fiber strain sensor is arranged at the center of the inner wall of the first deformation sheet and is used for measuring the deformation at the center of the sheet. The first fiber temperature sensor is arranged in the cavity of the first rectangular base and is used for measuring the temperature change in the penetration process. The first rectangular base is used for fixing the fiber cable, the first fiber strain sensor and the first fiber temperature sensor in the fiber cone tip resistance sensing module. The first connecting member is used for connecting the first rectangular base and the first deformation sheet.

[0009] In an implementation manner, the first deformation sheet is a rectangular sheet, the first fiber strain sensor is arranged at the center of the inner wall of the rectangular sheet, and when the effective stress static sounding instrument based on the fiber Bragg grating measures the effective stress of the soil body, the resistance borne by the probe is calculated based on a cone tip resistance formula, and the cone tip resistance formula is as follows: ; Wherein, is the cone tip resistance.D bending stiffness of the first deformed sheet, thickness of the first deformed sheet, a and b length and width of the first deformed sheet, respectively, cone tip surface area, effective photoelastic coefficient, initial Bragg wavelength, strain-induced wavelength change, fiber thermal expansion coefficient, fiber thermal expansion coefficient, temperature change amount.

[0010] In an implementation, the fiber sidewall friction force sensing module includes a second rectangular base, a second fiber strain sensor, a second fiber temperature sensor, a second deformed sheet, and a second connecting member; The second deformed sheet is a rectangular steel sheet that deforms when subjected to the friction deformation column; The second fiber strain sensor is arranged at the center of the inner wall of the second deformed sheet for measuring the deformation at the center of the sheet; The second fiber temperature sensor is arranged in the cavity of the second rectangular base for measuring the temperature change during the penetration process; The second rectangular base is used to fix the fiber cable of the fiber sidewall friction force sensing module, the second fiber strain sensor, and the second fiber temperature sensor; The second connecting member is used to connect the second rectangular base and the second deformed sheet.

[0011] In an implementation, the fiber inclination sensing module includes a cylindrical weight, a third connecting member, and an inclination sensor; The cylindrical weight is used to apply a load on the sensor in the fiber inclination sensing module when the probe rod is inclined to determine the inclination direction and inclination angle of the probe rod; The third connecting member is a connecting spring used to connect the cylindrical weight and the inclination sensor and to transfer the load to the inclination sensor; The inclination sensor includes a third fiber strain sensor and a third fiber temperature sensor, and multiple of them are arranged around the cylindrical weight, and work together to measure the inclination direction and inclination angle of the probe rod.

[0012] In an implementation, the fiber effective stress sensing module is hollow cylindrical and includes a sidewall deformed sheet, an annular perforated base, a fourth fiber strain sensor, a fourth fiber temperature sensor, and a fourth connecting member: The outer surface of the side wall deformed sheet is used to bear the effective stress and pore water pressure in the soil, and the inner side wall is used to bear the pore water pressure; The annular perforated base is used to conduct the pore water in the soil into the inside of the optical fiber effective stress sensing module to exert the pore water pressure on the inside of the side wall deformed sheet; The fourth optical fiber strain sensor is arranged at the axial center point of the inner wall of the side wall deformed sheet to measure the strain of the side wall deformed sheet; The fourth optical fiber temperature sensor is arranged in the cavity of the optical fiber effective stress sensing module to measure the temperature change in the penetration process; The fourth connecting member is used to connect the side wall deformed sheet and the annular perforated base into a hollow cylindrical cavity.

[0013] In an implementation, when the optical fiber Bragg grating based effective stress static sounding instrument measures the effective stress of the soil, the effective stress of the soil is calculated based on an effective stress formula and a sheet theory when the optical fiber Bragg grating based effective stress static sounding instrument is used to detect the soil, and the effective stress formula is: wherein, is the effective stress of the soil, r is the radius of the inner wall of the side wall deformed sheet, is the elastic modulus of the side wall deformed sheet, is the thickness of the side wall deformed sheet, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the wavelength change caused by the strain, is the thermal expansion coefficient of the optical fiber, is the thermal expansion coefficient of the optical fiber, is the temperature change amount.

[0014] In an implementation, the water inlet of the optical fiber effective stress sensing module uses water permeable stones to prevent the entry of external particles, and uses a gradient aperture one-way water permeable fiber membrane to form a pore water film, thereby establishing a hydraulic connection between the water in the optical fiber effective stress sensing module and the pore water of the soil. The hydrophilic film and the hydrophobic film are arranged on the two sides of the fiber membrane respectively to increase the amount of pore water entering while reducing the outflow of water in the optical fiber effective stress sensing module.

[0015] In an implementation, before the static sounding operation is performed, the optical fiber effective stress sensing module is placed in distilled water without air, and the internal cavity of the optical fiber effective stress sensing module is saturated to ensure that there is no residual gas in the hydraulic pressure conduction channel of the optical fiber effective stress sensing module, and the saturation state is achieved.​

[0016] In an implementation, the grating demodulation module is located in the demodulation ring column internal cavity, including a broadband light source, a coupler, a fiber F-P tunable filter, a photodetector, a signal amplifier and a data acquisition card; The broadband light source is used for emitting broadband light of fixed wavelength to provide optical signals for the integrated optical fiber sensing assembly; The coupler transmits the light signal emitted by the broadband light source to the integrated optical fiber sensing assembly and transmits the reflected light signal back to the grating demodulation module; The fiber F-P tunable filter is used for wavelength scanning on the reflected light signal transmitted by the coupler to realize separation and screening of different wavelength light signals; The photodetector is used for converting the filtered and separated light signal into an electric signal to complete the photoelectric conversion process; The signal amplifier is used for amplifying the electric signal output by the photodetector to improve the signal noise ratio and measurement accuracy; The data acquisition card is used for collecting the amplified electric signal and converting the amplified electric signal into a digital signal to be transmitted to the upper computer to obtain accurate measurement values of each physical parameter in real time.

[0017] Compared with the prior art, the application provides an effective stress static sounding instrument based on a fiber Bragg grating, which comprises a probe, a probe rod and an integrated fiber sensing assembly distributed in the probe and the probe rod, and the probe and the probe rod are connected with each other; the probe comprises a cone head and a cone head deformation column; the probe rod comprises an effective stress ring column, an inclinometer ring column, a sidewall friction cylinder, a demodulation ring column, a grating demodulation module arranged in a cavity of the demodulation ring column, a damping cylinder and an embedded fiber channel; the integrated fiber sensing assembly comprises a fiber cone tip resistance sensing module, a fiber sidewall friction resistance sensing module, a fiber inclinometer sensing module and a fiber effective stress sensing module, and is connected to the grating demodulation module based on the embedded fiber channel, wherein the fiber cone tip resistance sensing module is arranged in the probe, the fiber sidewall friction resistance sensing module is arranged above the inner side of the sidewall friction cylinder, the fiber inclinometer sensing module is arranged at the center of the inclinometer ring column, and the fiber effective stress sensing module is arranged outside the effective stress ring column. The effective stress static sounding instrument based on the fiber Bragg grating solves the problems that there is no sounding instrument based on the fiber Bragg grating for directly measuring the effective stress of a soil body in an in-situ test in the prior art, and the measurement error of the current static sounding instrument is significant and the anti-electromagnetic interference capability is weak. Based on the effective stress static sounding instrument based on the fiber Bragg grating provided in the application, the effective stress in the static sounding can be directly measured, which is more convenient than the pore pressure static sounding, and in the embodiment, the fiber Bragg grating sensor based on the thin plate theory is adopted to realize the measurement of the cone tip resistance, the sidewall friction resistance, the effective stress and the inclination direction and angle of the probe rod in the static sounding process in different arrangement forms, the data acquisition and analysis system is unified, and the soil body parameter detection efficiency and precision are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0019] Figure 1 The structural diagram of the embodiment of the effective stress static sounding instrument based on the fiber Bragg grating provided in the present application is shown in the figure. Figure 2 The three-dimensional diagram of the fiber cone tip resistance sensing module of the embodiment of the effective stress static sounding instrument based on the fiber Bragg grating provided in the present application is shown in the figure. Figure 3A front view of a fiber cone tip resistance sensing module of an embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 4 A top view of a fiber inclination sensing module of an embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 5 A sectional view of the fiber inclination sensing module of the embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 6 An inclination angle of a penetration process probe rod of an embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 7 A penetration process probe rod inclination direction of an embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 8 A top view of a fiber effective stress sensing module of an embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 9 A front view of the fiber effective stress sensing module of the embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; Figure 10 A pore water filter ring structure of an embodiment of the effective stress static cone penetrometer based on fiber Bragg grating provided by the present application; BRIEF DESCRIPTION OF THE DRAWINGS 10, probe; 20, probe rod; 30, integrated fiber sensing assembly; 11, cone head; 12, cone head deformation column; 21, effective stress ring column; 22, inclinometer ring column; 23, sidewall friction cylinder; 24, demodulation ring column; 25, grating demodulation module; 251, fiber F-P tunable filter; 252, coupler; 253, broadband light source; 254, photodetector; 255, signal amplifier; 256, data acquisition card; 26, damping cylinder; 27, built-in optical fiber passage; 28, friction deformation column; 29, sealing ring; 31, fiber cone tip resistance sensing module; 311, first rectangular base; 312, first fiber strain sensor; 313, first fiber temperature sensor; 314, first deformation sheet; 32, fiber sidewall friction resistance sensing module; 33, fiber inclinometer sensing module; 331, cylindrical counterweight; 332, connecting spring; 333, inclinometer sensor; 34, fiber effective stress sensing module; 341, sidewall deformation sheet; 342, annular holed base; 343, fourth fiber strain sensor; 344, fourth fiber temperature sensor; 345, pore water filter ring; 3451, water-permeable stone; 3452, water-permeable hole; 3453, gradient aperture one-way water-permeable fiber membrane; 3454, hydrophilic membrane; 3455, hydrophobic membrane; 40, probe rod connecting member; m, incompressible fluid.

[0020] The specific embodiments of the present application have been shown and described in the above-described drawings, and will be described in more detail hereinafter. These drawings and written descriptions are not intended to limit the scope of the present application concept in any way, but to illustrate the present application concept to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and effects of the present application more clear and explicit, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. The described embodiments are only possible technical implementations of the present application, and are not all possible implementations. Based on the embodiments in the present application, those skilled in the art can certainly combine the embodiments of the present application to obtain other embodiments without creative labor, and these embodiments are also within the protection scope of the present application.

[0022] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or wireless coupling. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0023] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0024] The technical solutions of this application will be described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0025] like Figure 1 As shown, this embodiment provides an effective stress static cone penetrometer based on a fiber Bragg grating. The effective stress static cone penetrometer based on a fiber Bragg grating includes a probe 10, a probe rod 20, and an integrated fiber optic sensing assembly 30 distributed in the probe 10 and the probe rod 20. The probe 10 and the probe rod 20 are interconnected. The probe 10 includes a cone-shaped head 11 and a cone-shaped deformable post 12. In this embodiment, the probe 10 can be conical, spherical, or T-shaped, etc.

[0026] The probe rod 20 includes an effective stress ring post 21, a tilting ring post 22, a sidewall friction cylinder 23, a demodulation ring post 24, a grating demodulation module 25 disposed in the cavity of the demodulation ring post 24, a damping cylinder 26, and a built-in optical fiber path 27.

[0027] Furthermore, the probe 20 also includes a sealing ring 29, which is used to isolate moisture in the soil so that the grating demodulation module 25 remains dry.

[0028] The integrated optical fiber sensing assembly 30 includes an optical fiber cone tip resistance sensing module 31, an optical fiber sidewall friction resistance sensing module 32, an optical fiber inclinometer sensing module 33, and an optical fiber effective stress sensing module 34, which are connected to the grating demodulation module 25 based on the built-in optical fiber channel 27, wherein the optical fiber cone tip resistance sensing module 31 is arranged in the probe 10, the optical fiber inclinometer sensing module 33 is arranged at the center of the inclinometer ring column 22, the optical fiber sidewall friction resistance sensing module 32 is arranged above the inner side of the sidewall friction cylinder 23, and the optical fiber effective stress sensing module 34 is arranged outside the effective stress ring column 21.

[0029] The grating demodulation module 25 includes an optical fiber F-P tunable filter 251, a coupler 252, a broadband light source 253, a photodetector 254, a signal amplifier 255, and a data acquisition card 256.

[0030] The probe rod 20 is connected to the sounding instrument main body based on a probe rod connecting member.

[0031] Referring to Figure 2 and Figure 3 , Figure 2 is a three-dimensional view of the optical fiber cone tip resistance sensing module 31, Figure 3 is a front view of the optical fiber cone tip resistance sensing module 31.

[0032] Specifically, the optical fiber cone tip resistance sensing module 31 includes a first rectangular base 311, a first optical fiber strain sensor 312, a first optical fiber temperature sensor 313, a first deformed sheet 314, and a first connecting member; The first deformed sheet 314 is a rectangular steel sheet that deforms when subjected to the action of the cone head deformation column 12; The first optical fiber strain sensor 312 is arranged at the center of the inner wall of the first deformed sheet 314, for measuring the deformation at the center of the sheet; The first optical fiber temperature sensor 313 is arranged in the cavity of the first rectangular base 311, for measuring the temperature change during the penetration process; The first rectangular base 311 is used to fix the optical fiber cable of the optical fiber cone tip resistance sensing module 31, the first optical fiber strain sensor 312, and the first optical fiber temperature sensor 313; The first connecting member is used to connect the first rectangular base 311 and the first deformed sheet 314, and it is noted that the first connecting member is not shown in the figure.

[0033] Further, the first deformed sheet 314 further includes a non-compressible fluid m above it, which is used to uniformly transmit external loads to the deformed sheet, so that the sheet deforms.

[0034] Referring to Figure 3 It can be seen that the first fiber strain sensor 312 is placed at the center of the first deformed sheet 314 for measuring the deformation of the first deformed sheet 314 under the action of external load, and the first fiber temperature sensor 313 is arranged in the cavity of the first fiber strain sensor 312, and the cone tip resistance is determined based on the measured strain and temperature.

[0035] The first deformed sheet 314 is a high-strength rectangular sheet, and the first fiber strain sensor 312 is arranged at the center of the inner wall of the rectangular sheet. When the effective stress static cone penetration tester based on fiber Bragg grating measures the effective stress of the soil, the resistance borne by the probe 10 is calculated based on the cone tip resistance formula, and the cone tip resistance formula is: ; Wherein, is the cone tip resistance, D is the bending stiffness of the first deformed sheet, is the thickness of the first deformed sheet, a and b are the length and width of the first deformed sheet, respectively, is the cone tip surface area, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the wavelength change caused by strain, is the fiber thermal expansion coefficient, is the fiber thermal expansion coefficient, is the temperature change.

[0036] Specifically, the fiber cone tip resistance sensing module is used to measure the resistance borne by the cone head in the penetration process of the penetration tester. According to the basic principle of the FBG sensor, the reflection Bragg wavelength offset It can be described by the first formula: ; Wherein, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the wavelength change caused by strain, is the strain along the length direction at the center of the first deformed sheet, is the fiber thermal expansion coefficient, is the fiber thermal expansion coefficient, is the temperature change.

[0037] It is assumed that the external load p is uniformly applied to the first deformed sheet, and according to the plate theory, the strain along the length direction at the center of the plate The second formula can be used to calculate: ; wherein, is the thickness of the first deformed sheet, a and b are the length and width of the first deformed sheet, respectively, D is the bending stiffness of the first deformed sheet, and , is the elastic modulus of the first deformed sheet, is the Poisson's ratio.

[0038] Substituting the second formula into the first formula, a third formula of the relationship between the load and the strain can be derived: p ; Since the tip resistance is transmitted to the sensor deformed sheet through the cone head deformed column during the penetration process, the tip resistance and the sensor deformed sheet have the following relationship, as shown in the fourth formula: ; wherein, is the surface area of the tip, that is, the force area. Substituting the third formula into the fourth formula can obtain the tip resistance formula: ; Referring to Figure 1 , the optical fiber side wall friction resistance sensing module 32 includes a second rectangular base, a second optical fiber strain sensor, a second optical fiber temperature sensor, a second deformed sheet, and a second connecting member; The second deformed sheet is a rectangular steel sheet that will be deformed when subjected to the friction deformed column 28; The second optical fiber strain sensor is arranged at the center of the inner wall of the second deformed sheet, for measuring the deformation at the center of the sheet; The second optical fiber temperature sensor is arranged in the cavity of the second rectangular base, for measuring the temperature change during the penetration process; The second rectangular base is used to fix the optical fiber cable of the optical fiber side wall friction resistance sensing module, the second optical fiber strain sensor, and the second optical fiber temperature sensor; The second connecting member is used to connect the second rectangular base and the second deformed sheet.

[0039] The optical fiber side wall friction resistance sensing module 32 has the same structure as the optical fiber tip resistance sensing module 31, and further, referring to Figure 1 ​It can be seen that the probe rod 20 further comprises a friction deformation column 28, the friction resistance of the side wall is transmitted to the friction deformation column 28 through the side wall friction cylinder 23, and further transmitted to the cone tip resistance sensing module through the incompressible fluid m.

[0040] Referring to Figure 4 and Figure 5 , Figure 4 FIG. 4 is a top view of the fiber inclination sensing module, Figure 5 FIG. 5 is a sectional view of the fiber inclination sensing module: The fiber inclination sensing module 33 comprises a cylindrical counterweight 331, a third connecting member, and a fiber inclination sensor 333; The cylindrical counterweight 331 is used to apply a load to the inclination sensor 333 in the fiber inclination sensing module 33 when the probe rod 20 is inclined, so as to determine the inclination direction and inclination angle of the probe rod 20; The third connecting member is a connecting spring 332, which is used to connect the cylindrical counterweight 331 and the inclination sensor 333, and transmit the load to the inclination sensor 333; The inclination sensor 333 comprises a deformation sheet, a third fiber strain sensor, and a third fiber temperature sensor, and a plurality of them are arranged around the cylindrical counterweight 331, and work together to measure the inclination direction and inclination angle of the probe rod 20. It should be noted that the deformation sheet, the third fiber strain sensor, and the third fiber temperature sensor are not shown in the figure.

[0041] Specifically, the inclination sensor 333 is 4, which is uniformly distributed in four directions of the cylindrical counterweight 331, referring to Figure 4 1, 2, 3, and 4 in FIG. 1, which respectively correspond to a first target inclination sensor, a second target inclination sensor, a third target inclination sensor, and a fourth target inclination sensor.

[0042] Specifically, the fiber inclination sensing module is used to measure the inclination angle and direction of the probe rod during the penetration process. As Figure 6 shown, if the probe rod is inclined to the direction of the third target inclination sensor and the fourth target inclination sensor during the penetration process, at this time, the force generated by the inclination of the cylindrical counterweight acts on the third target inclination sensor and the fourth target inclination sensor, thereby causing the deformation sheet to deform. At this time, the force acting on the inclination sensor can be calculated by the force formula: ; Suppose the third target inclination sensor and the fourth target inclination sensor are subjected to forces of and The probe rod inclination direction can be calculated by the target inclination formula: ; ; wherein, is the inclination angle of the probe rod relative to the horizontal direction, is the inclination angle of the probe rod relative to the vertical direction, and G is the gravity of the cylindrical weight. As shown in Figure 6 and Figure 7 .

[0043] Referring to Figure 8 , Figure 8 is a top view of the optical fiber effective stress sensing module 34. It can be seen that the optical fiber effective stress sensing module 34 is a hollow cylinder, including a side wall deformation sheet 341, an annular perforated base 342, a fourth optical fiber strain sensor 343, a fourth optical fiber temperature sensor 344, and a fourth connecting member: The outer surface of the side wall deformation sheet 341 is used to bear the effective stress and pore water pressure in the soil body, and the inner side wall is used to bear the pore water pressure; The annular perforated base 342 is used to conduct the pore water in the soil body, so that it enters the inside of the optical fiber effective stress sensing module 34 to act on the pore water pressure inside the side wall deformation sheet 341; The fourth optical fiber strain sensor 343 is arranged at the axial center point of the inner wall of the side wall deformation sheet 341 to measure the strain of the side wall deformation sheet 341; The fourth optical fiber temperature sensor 344 is arranged in the cavity of the optical fiber effective stress sensing module 34 to measure the temperature change during the penetration process; The fourth connecting member is used to connect the side wall deformation sheet 341 and the annular perforated base 342 into a hollow cylindrical cavity.

[0044] When the optical fiber Bragg grating-based effective stress static sounding instrument detects the soil body, the effective stress of the soil body is calculated based on the effective stress formula and the thin plate theory. The effective stress formula is: ; wherein, is the effective stress of the soil body, r is the inner wall radius of the side wall deformation sheet, is the elastic modulus of the side wall deformation sheet, is the thickness of the side wall deformation sheet, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the wavelength change caused by the strain, coefficient of thermal expansion of the optical fiber, coefficient of thermal expansion of the optical fiber, temperature change.

[0045] Specifically, the front view of the optical fiber effective stress sensing module 34 is shown in FIG. 4, wherein the fourth optical fiber strain sensor 343 and the fourth optical fiber temperature sensor 344 are respectively used to measure the strain caused by the effective stress and the temperature change during the penetration process. Figure 9 When measuring, the pore water in the soil body enters the optical fiber effective stress sensing module 34 through the pore water filter ring 345 of the water inlet, so that the pore water pressure inside and outside the optical fiber effective stress sensing module 34 is balanced, at this time, the pressure acting on the optical fiber effective stress sensing module 34 is the effective stress of the soil body, therefore, the optical fiber effective stress sensing module 34 can be used to directly measure the effective stress of the soil body during the penetration process.

[0046] According to the effective stress principle, the effective stress in the soil body can be calculated by the fifth formula: ; wherein, and are the total stress and the effective stress of the soil body, respectively, is the pore water pressure in the soil body.

[0047] According to the thin plate theory, the internal stress and the external stress of the side wall deformation thin plate satisfy the thin plate theory formula: ; wherein, r is the inner wall radius of the side wall deformation thin plate, d and are the height and the thickness of the side wall deformation thin plate, respectively, is the circumferential stress of the side wall deformation thin plate. Therefore, the strain at the center of the side wall deformation thin plate can be calculated by the center strain formula: ; According to the fifth formula, the effective stress formula can be obtained as: ; wherein, is the effective stress of the soil body, r is the inner wall radius of the side wall deformation thin plate, is the elastic modulus of the side wall deformation thin plate, is the thickness of the side wall deformation thin plate, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the wavelength change caused by the strain, coefficient of thermal expansion of the optical fiber, The fiber thermal expansion coefficient, The temperature change amount.

[0048] Further, with reference to Figure 10 , Figure 10 The pore water filter ring 345 structure of the water inlet of the optical fiber effective stress sensing module 34, specifically, the water inlet of the optical fiber effective stress sensing module 34 uses the water-permeable stone 3451 to prevent the entry of external particles, and uses the gradient pore size one-way water-permeable fiber membrane 3453 to form a pore water film, establishing hydraulic connection between the water in the optical fiber effective stress sensing module 34 and the soil pore water; The hydrophilic membrane 3454 and the hydrophobic membrane 3455 are arranged on both sides of the fiber membrane respectively to increase the amount of pore water entering while reducing the outflow of water in the optical fiber effective stress sensing module 34.

[0049] Specifically, the pore water filter ring 345 includes the water-permeable stone 3451 and the gradient pore size one-way water-permeable fiber membrane 3453, as shown in Figure 10 The water-permeable stone 3451 is in direct contact with the soil, allowing pore water to flow while preventing soil particles from entering. The water-permeable stone 3451 is arranged with the gradient pore size one-way water-permeable fiber membrane 3453 near the pore water side. The gradient pore size one-way water-permeable fiber membrane 3453 is arranged with the hydrophilic membrane 3454 and the hydrophobic membrane 3455 on both sides, respectively, to increase the amount of pore water entering while reducing the outflow of water in the optical fiber effective stress sensing module 34. In this embodiment, before the static sounding operation, the optical fiber effective stress sensing module 34 is placed in distilled water without gas, and the internal cavity of the optical fiber effective stress sensing module 34 is saturated to ensure that there is no residual gas in the hydraulic transmission channel of the optical fiber effective stress sensing module 34, reaching a saturated state.

[0050] Specifically, the optical fiber effective stress sensing module 34 needs to be placed in distilled water without gas before use, so that it is saturated inside, forming a water film inside the water-permeable membrane, ensuring that the optical fiber effective stress sensing module 34 is water-permeable and air-tight. In the penetration process, the pore water in the soil forms a hydraulic connection with the water in the optical fiber effective stress sensing module 34, thereby conducting the soil pore water pressure.

[0051] Specifically, the effective stress static sounding instrument based on fiber Bragg grating in the process of penetration, when the soil is normally consolidated soil, the pore water pressure of the soil is positive, the pore water in the soil enters the inside of the side wall deformation sheet 341 and exerts pressure on the inside of the side wall deformation sheet 341, and balances with the pore water pressure outside the side wall deformation sheet 341. When the soil is overconsolidated soil, the pore water pressure is negative, at this time the water in the fiber effective stress sensing module 34 flows out through the gradient pore one-way water permeable fiber membrane 3453, so that a negative pressure is formed in the inside of the fiber effective stress sensing module 34, which acts on the inside of the side wall deformation sheet 341. The fiber effective stress sensing module 34 can be used to measure the effective stress in normally consolidated soil and overconsolidated soil.

[0052] That is, before the penetration of the effective stress static sounding instrument based on fiber Bragg grating, saturation is required to be carried out with air-free distilled water to ensure that the inside of the fiber effective stress sensing module 34 is in a saturated state.

[0053] Referring to Figure 1 , the grating demodulation module 25 is located in the inside of the demodulation ring column 24, which includes a broadband light source 253, a coupler 252, a fiber F-P tunable filter 251, a photodetector 254, a signal amplifier 255 and a data acquisition card 256; The broadband light source 253 is used to emit broadband light of a fixed wavelength to provide an optical signal for the integrated fiber sensing assembly 30; The coupler 252 transmits the light signal emitted by the broadband light source 253 to the integrated fiber sensing assembly and transmits the reflected light signal back to the grating demodulation module 25; The fiber F-P tunable filter 251 is used to perform wavelength scanning on the reflected light signal transmitted by the coupler 252 to realize the separation and screening of different wavelength light signals; The photodetector 254 is used to convert the filtered and separated light signal into an electrical signal to complete the photoelectric conversion process; The signal amplifier 255 is used to amplify the electrical signal output by the photodetector to improve the signal-to-noise ratio and measurement accuracy; The data acquisition card 256 is used to collect the amplified electrical signal and convert the amplified electrical signal into a digital signal to be transmitted to the upper computer to obtain accurate measurement values of various physical parameters in real time.

[0054] During the penetration process of the penetrometer, the broadband light source 253 emits broadband light of a fixed wavelength, and meanwhile, the coupler 252 transmits the broadband light to the fiber Bragg grating sensor and receives the reflected light thereof; the fiber F-P tunable filter 251 is used for dynamically scanning the transmission wavelength, and the photoelectric detector 254 is used for converting the optical signal into an electrical signal, then the weak electrical signal is amplified by the signal amplifier 255, the input end of the signal amplifier 255 is connected to the signal acquisition card, and finally connected to the built-in optical fiber channel 27, that is, the optical-electrical signal processing channel, and the data of the cone tip resistance, the sidewall friction resistance, the effective stress, the inclination angle and the penetration depth are demodulated in real time.

[0055] In summary, the embodiment provides an effective stress static cone penetrometer based on a fiber Bragg grating, which comprises a probe 10, a probe rod 20 and an integrated fiber sensing assembly 30 distributed in the probe 10 and the probe rod 20, and the probe 10 and the probe rod 20 are connected to each other; the probe comprises a cone head 11 and a cone head deformation column 12; the probe rod 20 comprises an effective stress ring column 21, an inclinometer ring column 22, a sidewall friction cylinder 23, a demodulation ring column 24, a grating demodulation module 25 arranged in the cavity of the demodulation ring column 24, a damping cylinder 26 and a built-in optical fiber channel 27; the integrated fiber sensing assembly 30 comprises a fiber cone tip resistance sensing module 31, a fiber sidewall friction resistance sensing module 32, a fiber inclinometer sensing module 33 and a fiber effective stress sensing module 34, and the built-in optical fiber channel 27 is connected to the grating demodulation module 25, wherein the fiber cone tip resistance sensing module 31 is arranged in the probe 10, the fiber sidewall friction resistance sensing module 32 is arranged on the upper side of the inside of the sidewall friction cylinder 23, the fiber inclinometer sensing module 33 is arranged at the center of the inclinometer ring column 22, and the fiber effective stress sensing module 34 is arranged on the outside of the effective stress ring column 21. The effective stress static cone penetrometer based on a fiber Bragg grating provided in the embodiment solves the problems that there is no penetrometer based on a fiber Bragg grating for directly measuring the effective stress of a soil body in an in-situ test in the prior art, and the measurement error of the current static cone penetrometer is significant and the anti-electromagnetic interference capability is weak. Based on the effective stress static cone penetrometer based on a fiber Bragg grating provided in the embodiment, the effective stress in the static cone penetration can be directly measured, which is more convenient than the pore pressure static cone penetration, and in the embodiment, the fiber Bragg grating sensor based on the thin plate theory is adopted to realize the measurement of the cone tip resistance, the sidewall friction resistance, the effective stress and the inclination direction and angle of the probe rod in the static cone penetration process in different arrangement forms, the data acquisition and analysis system is unified, and the soil body parameter detection efficiency and precision are significantly improved.

[0056] In the description of the application, unless otherwise clearly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection or can communicate with each other; can be directly connected, can also be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0057] In the description of the application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application.

[0058] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the application, the meaning of "multiple" is at least two, for example, two, three, etc., unless otherwise clearly specified and limited.

[0059] It should be noted that: in the present application, unless otherwise clearly specified and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0060] The terms "first", "second", "third", "fourth" and the like in the description and in the claims of the present application, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the use of these terms herein is to be construed to cover the embodiments of the application whether or not the embodiments are described using the same term. Furthermore, these terms can be used interchangeably in different examples of the application. The terms "comprise", "comprising", "include", "including" and "has", "having", "contain", "containing" as used herein are intended to cover the respective terms whether or not used in the above sense. The terms "comprise", "comprising", "include", "including" and "has", "having", "contain", "containing" are used in their open-ended, conventional sense, that is, they are used to include "including but not limited to".

[0061] In the description of the application, the description of the terms "one embodiment", "some embodiments", "certain embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the description of the present disclosure, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0062] Finally, it should be noted that the above embodiments are merely used to illustrate the technical solutions of the present application, rather than limit the technical solutions of the present application; even though the above embodiments of the present application have been described in detail, those skilled in the art should understand that modifications can be made to the technical solutions recorded in the above embodiments, or equivalent replacements can be made to some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An effective stress static cone penetrometer based on fiber Bragg grating, characterized in that, The effective stress static cone penetrometer based on fiber Bragg grating comprises a probe, a probe rod and an integrated fiber sensing assembly distributed in the probe and the probe rod, and the probe and the probe rod are connected with each other; The probe comprises a cone head and a cone head deformation column; The probe rod comprises an effective stress ring column, an inclinometer ring column, a side wall friction cylinder, a demodulation ring column, a grating demodulation module arranged in a cavity of the demodulation ring column, a damping cylinder and an embedded fiber channel; The integrated fiber sensing assembly comprises a fiber cone tip resistance sensing module, a fiber side wall friction resistance sensing module, a fiber inclinometer sensing module and a fiber effective stress sensing module, and is connected to the grating demodulation module based on the embedded fiber channel, wherein the fiber cone tip resistance sensing module is arranged in the probe, the fiber inclinometer sensing module is arranged at the center of the inclinometer ring column, the fiber side wall friction resistance sensing module is arranged above the inner side of the side wall friction cylinder, and the fiber effective stress sensing module is arranged outside the effective stress ring column.

2. The fiber Bragg grating based active stress cone penetrometer according to claim 1, characterized in that, The fiber cone tip resistance sensing module comprises a first rectangular base, a first fiber strain sensor, a first fiber temperature sensor, a first deformation sheet and a first connecting member; The first deformation sheet is a rectangular steel sheet which will be deformed when subjected to the action of the cone head deformation column; The first fiber strain sensor is arranged at the center of the inner wall of the first deformation sheet and is used for measuring the deformation at the center of the sheet; The first fiber temperature sensor is arranged in the cavity of the first rectangular base and is used for measuring the temperature change in the process of penetration; The first rectangular base is used for fixing the fiber cable, the first fiber strain sensor and the first fiber temperature sensor in the fiber cone tip resistance sensing module; The first connecting member is used for connecting the first rectangular base and the first deformation sheet.

3. The fiber Bragg grating based active stress cone penetrometer of claim 2, wherein, The first deformation sheet is a rectangular sheet, the first fiber strain sensor is arranged at the center of the inner wall of the rectangular sheet, and when the effective stress static cone penetrometer based on fiber Bragg grating measures the effective stress of the soil body, the resistance borne by the probe is calculated based on the cone tip resistance formula, and the cone tip resistance formula is: ； wherein, is the tip drag, D is the bending stiffness of the first deformed sheet, is the thickness of the first deformed sheet, a and b are the length and width, respectively, of the first deformed sheet, is the tip surface area, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the strain-induced wavelength change, is the fiber thermal expansion coefficient, is the fiber thermal expansion coefficient, is the temperature change.

4. The fiber Bragg grating based active stress cone penetrometer of claim 1, wherein, The fiber side wall friction resistance sensing module comprises a second rectangular base, a second fiber strain sensor, a second fiber temperature sensor, a second deformation sheet and a second connecting member; The second deformation sheet is a rectangular steel sheet which will be deformed when subjected to the action of the friction deformation column; The second fiber strain sensor is arranged at the center of the inner wall of the second deformation sheet and is used for measuring the deformation at the center of the sheet; The second fiber temperature sensor is arranged in the cavity of the second rectangular base and is used for measuring the temperature change in the process of penetration; The second rectangular base is used for fixing the fiber cable, the second fiber strain sensor and the second fiber temperature sensor of the fiber side wall friction resistance sensing module; The second connecting member is used for connecting the second rectangular base and the second deformation sheet.

5. The fiber Bragg grating based active stress cone penetrometer of claim 1, wherein, The fiber inclinometer sensing module comprises a cylindrical counterweight, a third connecting member and an inclinometer sensor; The cylindrical weight is used to apply load on the sensor in the optical fiber inclinometer sensor module when the probe rod is inclined, so as to determine the inclination direction and angle of the probe rod; The third connecting member is a connecting spring, which is used to connect the cylindrical weight and the inclinometer sensor and transmit the load to the inclinometer sensor; The inclinometer sensor comprises a third optical fiber strain sensor and a third optical fiber temperature sensor, and a plurality of the inclinometer sensors are arranged around the cylindrical weight, and the inclination direction and angle of the probe rod are measured by the plurality of inclinometer sensors working together.

6. The fiber Bragg grating based active stress cone penetrometer of claim 1, wherein, The optical fiber effective stress sensor module is a hollow cylinder, comprising a side wall deformation sheet, an annular perforated base, a fourth optical fiber strain sensor, a fourth optical fiber temperature sensor and a fourth connecting member: The outer surface of the side wall deformation sheet is used to bear the effective stress and pore water pressure in the soil, and the inner side wall is used to bear the pore water pressure; The annular perforated base is used to conduct the pore water in the soil, so that the pore water enters the inside of the optical fiber effective stress sensor module to act on the pore water pressure in the inside of the side wall deformation sheet; The fourth optical fiber strain sensor is arranged at the axial center point of the inner wall of the side wall deformation sheet to measure the strain of the side wall deformation sheet; The fourth optical fiber temperature sensor is arranged in the cavity of the optical fiber effective stress sensor module to measure the temperature change in the process of penetration; The fourth connecting member is used to connect the side wall deformation sheet and the annular perforated base into a hollow cylindrical cavity.

7. The fiber Bragg grating based active stress cone penetrometer of claim 6, wherein, When the optical fiber Bragg grating based effective stress static sounding instrument is used to detect the soil, the effective stress of the soil is calculated based on the effective stress formula and the thin plate theory, and the effective stress formula is: ； wherein, is the effective stress of the soil, r is the inner wall radius of the side wall deformed sheet, is the elastic modulus of the side wall deformed sheet, is the thickness of the side wall deformed sheet, is the effective photoelastic coefficient, is the initial Bragg wavelength, is the wavelength change caused by the strain, is the thermal expansion coefficient of the optical fiber, is the thermal expansion coefficient of the optical fiber, is the temperature change amount.

8. The fiber Bragg grating based active stress cone penetrometer of claim 6, wherein, The water inlet of the optical fiber effective stress sensor module adopts water-permeable stone to prevent the entry of external particles, and adopts gradient aperture one-way water-permeable fiber membrane to form pore water film, so as to establish hydraulic connection between the water in the optical fiber effective stress sensor module and the pore water in the soil; The hydrophilic membrane and the hydrophobic membrane are arranged on the two sides of the fiber membrane respectively, so as to increase the amount of pore water entering while reducing the water diversion out of the optical fiber effective stress sensor module.

9. The fiber Bragg grating based active stress cone penetrometer of claim 6, wherein, Before the static sounding operation is performed, the optical fiber effective stress sensor module is placed in the still distillation water, and the internal cavity of the optical fiber effective stress sensor module is saturated to ensure that there is no residual gas in the hydraulic transmission channel of the optical fiber effective stress sensor module, so that the saturation state is achieved.

10. The effective stress static cone penetrometer based on fiber Bragg grating according to claim 1, characterized in that, The grating demodulation module is located in the internal cavity of the demodulation ring column, and comprises a broadband light source, a coupler, an optical fiber F-P tunable filter, a photodetector, a signal amplifier and a data acquisition card; The broadband light source is used to emit broadband light of a fixed wavelength to provide optical signals for the integrated optical fiber sensing assembly; The coupler transmits the light signal emitted by the broadband light source to the integrated optical fiber sensing assembly, and transmits the reflected light signal back to the grating demodulation module; The optical fiber F-P tunable filter is used to perform wavelength scanning on the reflected light signal transmitted by the coupler, so as to separate and screen different wavelength light signals; The photodetector is used to convert the filtered and separated light signal into an electrical signal to complete the photoelectric conversion process; The signal amplifier is used for amplifying the electric signal output by the photodetector, improving signal signal-to-noise ratio and measurement accuracy. The data acquisition card is used for collecting the amplified electric signal, converting the amplified electric signal into a digital signal and transmitting the digital signal to the upper computer, so as to obtain accurate measurement values of various physical parameters in real time.

Images