In-situ measurement method for underground soil temperature, confining pressure and compression

Abstract

The invention provides an in-situ measurement method for underground soil temperature, confining pressure and compression, and belongs to the technical field of geodetic survey. According to the method, an optical fiber sensor comprising three kinds of optical fibers is pre-buried in underground soil, tracking measurement of the temperature, the confining pressure and the compression of the underground soil is carried out, and the method specifically comprises the steps of assembling and installing a measurement tool, reading initial data, setting real-time measurement parameters, carrying out real-time measurement, calculating the temperature, the confining pressure and the compression of the underground soil and the like. The measuring precision is high, the application range is wide, formula conversion is simple, the optical fiber sensor can be placed in the hole to be measured all the time, and long-term monitoring of underground soil temperature, confining pressure and compression can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of geodetic surveying, and particularly relates to an in-situ measurement method for underground soil temperature, confining pressure, and compression. Background Art

[0002] The measurement of underground soil parameters is an indispensable part of geological construction projects. The temperature, confining pressure, and compression that a building experiences in deep underground soil are crucial for the operating state of the building and directly affect the safety state of the building's operation. Therefore, accurately measuring the temperature, confining pressure, and compression of deep soil is of great significance, and there are currently some testing methods.

[0003] Chinese patent document CN118777368A discloses a distributed in-situ measurement system and method for soil heat flux based on DTS. This method uses a DTS measuring tube to collect and calculate the temperature, thermal conductivity, and moisture content distribution of the soil, but this method lacks the measurement of stress and compression.

[0004] Chinese patent document CN216669078U discloses a fully distributed formation stress compression sensor. This sensor monitors the temperature and stress compression of underground soil layers, rock layers, and fluids by configuring stress compression optical fibers and temperature optical fibers on a support body, but this device cannot measure the compression above the device.

[0005] Chinese patent document CN117074180A discloses a method for measuring the pressure change of underground soil of a building. This method calculates the internal pressure of underground soil by arranging soil pressure sensors at different depths, but this method requires layered construction and burial, with complex construction and high costs.

[0006] Chinese patent document CN117759229A discloses a dynamic monitoring and perception system and method for the temperature field of deep strata in a metal mine. This method collects temperature by setting temperature probes in each temperature monitoring borehole of the target roadway, but this probe can only collect temperature data.

[0007] Chinese patent document CN104897718A discloses a deep soil thermal parameter monitoring sensor and detection method. This method monitors the thermal parameters of the soil around the cable in real time. However, this unit cannot measure the stress around the cable.

[0008] Chinese patent document CN116242986A discloses a soil mechanics test rod and a system and method for determining the physical and mechanical state of the surface soil in a certain area. This method is used to measure parameters such as the shear strength, stress state, and pore water pressure of the soil in a certain area. This device requires the installation of multiple sensors of multiple types, with a complex structure, high operation difficulty, and high monitoring costs.

[0009] Chinese patent document CN117168340A discloses a monitoring system and monitoring data processing method for an experimental model of open-pit to underground mining. This method uses stereo cameras and pressure cells to observe the impact of chamber and pillar mining on changes in stress, displacement, and moisture content within the mine. This system requires the installation of multiple sensors of various types, resulting in a complex structure, difficult operation, and high monitoring costs.

[0010] In summary, existing monitoring equipment has problems such as incomplete monitoring parameters, high cost, and cumbersome operation. Based on this, the present invention proposes an in-situ measurement method for underground soil temperature, confining pressure and compression. Summary of the Invention

[0011] The technical problem to be solved by the present invention is the defects of the existing technology. The purpose is to achieve accurate measurement of underground soil temperature, confining pressure and compression in response to the defects of the existing technology.

[0012] In order to achieve the above-mentioned purpose, the present invention intends to adopt the following technical solutions.

[0013] An in-situ measurement method for underground soil temperature, confining pressure, and compression includes pre-buried in the underground soil an optical fiber sensor, the main body of the optical fiber sensor being hollow cylindrical and maintained in a vertical position in the underground soil; the head of the optical fiber sensor is connected to a main optical cable, the other end of which passes upward through the underground soil and is connected to an optical fiber demodulator; the in-situ measurement method comprises the following steps:

[0014] Step 1, Assembly of measuring tools

[0015] The measuring tool is an optical fiber sensor, comprising a main body, a telescopic column inserted in the hollow part of the main body and extending at both ends, a base and a pressure-bearing cover, wherein a vertical wire groove is opened on the outer wall of the telescopic column; the base is a semi-hollow cylindrical shape with an opening upward, the tail of the main body is inserted into and completely seated in the base, and the tail of the telescopic column is fixed to the screw hole at the center of the inner bottom surface of the base by screwing; the pressure-bearing cover is a semi-hollow cylindrical shape with an opening downward, the top of the telescopic column is fixed to the screw hole at the center of the inner bottom surface of the pressure cover by screwing, and a gap is left between the main body and the inner bottom surface of the pressure cover; one end of a compression optical fiber is connected to the main optical cable, and the other end passes through the side wall of the pressure cover into the hollow part of the pressure cover, and is embedded in the wire groove of the telescopic column and extends along the wire groove to the bottom of the telescopic column; one end of a sensing optical cable is connected to the main optical cable, and the other end is spirally wound on the outer surface of the main body from top to bottom in an equidistant manner, and the sensing optical cable includes a temperature measuring optical fiber and a confining pressure optical fiber;

[0016] Step 2, Drilling

[0017] Determine the site to be tested and the depth of the hole to be tested according to construction requirements;

[0018] Use a drill rig to drill a hole in the site to be measured, and the drilling depth is the depth of the hole to be measured; the outer diameters of the base and the pressure-bearing cover are the same, and the diameter of the hole to be measured is at least 8 cm - 10 cm larger than the outer diameter of the base.

[0019] Step 3, lowering of the measuring tool

[0020] Lower the fiber optic sensor to the bottom of the hole to be measured, and ensure that the main body of the fiber optic sensor is perpendicular to the bottom surface of the hole to be measured. Then lead the total optical cable through the hole to be measured to the ground surface.

[0021] Step 4, recording of initial values

[0022] Connect the temperature measurement optical fiber, confining pressure optical fiber, and compression optical fiber in the total optical cable to the corresponding interfaces of the fiber optic demodulator, read the initial wavelength of each optical fiber, and record them as the initial temperature measurement wavelength γ0, the initial confining pressure wavelength α0, and the initial compression wavelength β0 respectively.

[0023] Step 5, backfilling and compaction of undisturbed soil

[0024] Backfill the undisturbed soil taken out from the drilled hole into the hole to be measured until it is flush with the ground surface, and compact it while backfilling.

[0025] Step 6, setting of real-time measurement parameters

[0026] Set the interval time A and the number of recordings N. The interval time is the time difference between two rounds of measurements, and the number of readings N is the total number of times of reading measurement data in one round of measurement. Denote any reading in one round of measurement as the i-th reading, where i = 1, 2,..., N.

[0027] Denote the wavelength of the temperature measurement optical fiber obtained in the i-th reading as the real-time temperature measurement wavelength r i and the wavelength of the confining pressure optical fiber as the real-time confining pressure wavelength α i and the wavelength of the compression optical fiber as the real-time compression wavelength β i ;

[0028] Step 7, measurement and calculation of real-time data

[0029] In one round of measurement, read and record the data of the three real-time wavelengths through the fiber optic demodulator to obtain three sets of reading data of the real-time wavelengths.

[0030] Denote the temperature of the underground soil corresponding to the real-time temperature measurement wavelength r i as the temperature C i and the confining pressure of the underground soil corresponding to the real-time confining pressure wavelength α i as the confining pressure N i and the compression of the underground soil corresponding to the real-time compression wavelength β i as the compression M i ; Their calculation formulas are respectively:

[0031] C i = K iγ (r i - γ0)......(1)

[0032] N i = K iα (α i - α0)......(2)

[0033] M i = K iβ (β i - β0)......(3)

[0034] In the formula, K iγ is the ratio coefficient of temperature to wavelength change, with the unit of degrees Celsius per nanometer; K iα represents the ratio coefficient of confining pressure to wavelength change, with the unit of megapascals per nanometer; K iβ represents the ratio coefficient of compression to wavelength change, with the unit of millimeters per nanometer; the temperature C i is in degrees Celsius, the confining pressure N i is in megapascals, and the compression M i is in millimeters;

[0035] Substitute the read data of the three groups of real-time wavelengths into formulas (1), (2) and (3) for calculation to obtain the data of the three groups of temperature, confining pressure and compression for one round of measurement;

[0036] The unit of wavelength in each of the above steps is nanometer;

[0037] Step 8, according to the data of the three groups of temperature, confining pressure and compression obtained in Step 7, plot the time-temperature curve, time-confining pressure curve and time-compression curve in a plane coordinate system, and analyze and study the state of the underground soil through the three curves;

[0038] Step 9, perform multiple rounds of measurement at an interval of time A to achieve long-term in-situ monitoring of the underground soil.

[0039] Preferably, the inner diameter of the hollow part of the main body is adapted to the outer diameter of the telescopic column.

[0040] Preferably, the reserved length of the total optical cable is at least 5 meters longer than the depth of the hole to be measured.

[0041] Preferably, the ratio coefficient K iγ of temperature to wavelength change, the ratio coefficient K iα of confining pressure to wavelength change, and the ratio coefficient K iβ of compression to wavelength change are determined by indoor calibration.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (1) The present invention proposes an in-situ measurement method for underground soil temperature, confining pressure and compression. The temperature, confining pressure and compression of underground soil are measured by an optical fiber sensor, and the measurement accuracy is high.

[0044] (2) By changing the total length of the optical cable, this method can realize the measurement of temperature, confining pressure and compression of soil at various depths, and has a wide application range.

[0045] (3) This method only needs to lower the optical fiber sensor into the hole to be measured and then backfill it, and the temperature, confining pressure and compression data of the soil in this area can be converted through the wavelength change of the optical fiber demodulator. The operation is simple and the formula conversion is simple.

[0046] (4) The optical fiber sensor of this method can be always placed in the hole to be measured to realize the long-term monitoring of underground soil temperature, confining pressure and compression. Description of the Drawings

[0047] Figure 1 It is the installation schematic diagram of the measuring tool of the present invention.

[0048] Figure 2 It is the structural schematic diagram of the optical fiber sensor in the embodiment of the present invention.

[0049] Figure 3 It is the structural schematic diagram of the total optical cable in the embodiment of the present invention.

[0050] Figure 4 It is the temperature change curve diagram of measuring underground 73.4 meters in a test site in Ningbo in the embodiment of the present invention.

[0051] Figure 5 It is the schematic diagram of confining pressure change of measuring underground 73.4 meters in a test site in Ningbo in the embodiment of the present invention.

[0052] Figure 6 It is the schematic diagram of compression change of measuring underground 73.4 meters in a test site in Ningbo in the embodiment of the present invention.

[0053] Reference numerals: 1. Optical fiber sensor; 2. Hole to be measured; 3. Total optical cable; 4. Optical fiber demodulator; 5. Pressure-bearing cover; 6. Main body; 7. Telescopic column; 8. Compression optical fiber; 9. Sensing optical cable; 10. Cable groove; 11. Base; 12. Temperature-measuring optical fiber; 13. Confining-pressure optical fiber; 14. Lead hole. Detailed Embodiments

[0054] The present invention will be described in detail below with reference to the drawings and embodiments.

[0055] The present invention provides an in-situ measurement method for underground soil temperature, confining pressure, and compression. A fiber optic sensor 1 is embedded in the soil. The main body 6 of the fiber optic sensor 1 is hollow and cylindrical and remains vertical within the soil. The head of the fiber optic sensor 1 is connected to a main optical cable 3. The other end of the main optical cable 3 extends upward through the soil and connects to a fiber optic interrogator 4. The in-situ measurement method includes the following steps:

[0056] Step 1, Assembly of measuring tools

[0057] Figure 2 is a schematic structural diagram of an optical fiber sensor 1 according to an embodiment of the present invention, Figure 3 FIG. 3 is a schematic diagram of the structure of the total optical cable 3 in an embodiment of the present invention. Figure 2 and Figure 3 As can be seen, the measuring tool, or fiber optic sensor 1, comprises a main body 6, a telescopic column 7 embedded in the hollow portion of the main body 6 and extending at both ends, a base 11, and a pressure cover 5. A vertical cable groove 10 is defined in the outer wall of the telescopic column 7. The base 11 is a semi-hollow cylindrical structure with an upward opening. The rear end of the main body 6 is embedded and completely seated within the base 11. The rear end of the telescopic column 7 is screwed into a screw hole at the center of the inner bottom surface of the base 11. The pressure cover 5 is a semi-hollow cylindrical structure with a downward opening. The top of the telescopic column 7 is screwed into a screw hole at the center of the inner bottom surface of the pressure cover 5, with a gap between the main body 6 and the inner bottom surface of the pressure cover 5. A compression optical fiber 8 is connected to the main optical cable 3 at one end. The other end passes through the side wall of the pressure cover 5, enters the hollow portion of the pressure cover 5, and then is embedded in the cable groove 10 of the telescopic column 7 and extends along the cable groove 10 to the bottom of the telescopic column 7. One end of a sensing optical cable 9 is connected to the main optical cable 3, and the other end is spirally wound on the outer surface of the main body 6 at equal intervals from top to bottom. The sensing optical cable 9 includes a temperature measuring optical fiber 12 and a confining pressure optical fiber 13.

[0058] In this embodiment, the compressed optical fiber 8 is adhered to the cable groove 10 when embedded in the cable groove 10 .

[0059] In this embodiment, the inner diameter of the hollow portion of the main body 6 matches the outer diameter of the telescopic column 7. Specifically, the telescopic column 7 has external threads at both ends, and the base 11 and the pressure cover 5 have internal threaded holes at the center of the inner bottom surface that match the external threads.

[0060] In this embodiment, the inner diameters of the base 11 and the hollow portion of the pressure cover 5 are the same and match the outer diameter of the main body 6 .

[0061] In this embodiment, a lead-in hole 14 is opened on the side wall of the hollow portion of the pressure-bearing cover 5 , and the compressed optical fiber 8 passes through the lead-in hole 14 and enters the hollow portion of the pressure-bearing cover 5 .

[0062] Step 2, Drilling

[0063] Determine the depth of the site to be measured and the borehole 2 to be measured according to the construction requirements;

[0064] Use a drilling rig to drill a hole in the site to be measured, and the drilling depth is the depth of the borehole 2 to be measured; the outer diameters of the base 11 and the pressure-bearing cover 5 are the same, and the diameter of the borehole 2 to be measured is at least 8 cm - 10 cm larger than the outer diameter of the base 11.

[0065] Step 3, Lowering of the measuring tool

[0066] Lower the fiber optic sensor 1 to the bottom of the borehole 2 to be measured, and ensure that the main body 6 of the fiber optic sensor 1 is perpendicular to the bottom surface of the borehole 2 to be measured, and then lead the main optical cable 3 through the borehole 2 to the ground surface.

[0067] In this embodiment, the reserved length of the main optical cable 3 is at least 5 meters longer than the depth of the borehole 2 to be measured.

[0068] Figure 1 It is a schematic installation diagram of the measuring tool of the present invention.

[0069] Step 4, Recording the initial value

[0070] Connect the temperature-measuring optical fiber 12, the confining pressure optical fiber 13, and the compression optical fiber 8 in the main optical cable 3 to the corresponding interfaces of the fiber optic demodulator 4 respectively, read the initial wavelength of each optical fiber and record them as the initial temperature-measuring wavelength γ0, the initial confining pressure wavelength α0, and the initial compression wavelength β0 respectively.

[0071] Step 5, Backfilling and compaction of undisturbed soil

[0072] Backfill the undisturbed soil taken out from the borehole into the borehole 2 to be measured until it is flush with the ground surface, and compact it while backfilling.

[0073] Step 6, Setting of real-time measurement parameters

[0074] Set the interval time A and the number of records N. The interval time is the time difference between two rounds of measurements, and the number of readings N is the total number of measurement data read in one round of measurement. Any reading in one round of measurement is recorded as the i-th reading, i = 1, 2,..., N.

[0075] Record the wavelength of the temperature-measuring optical fiber 12 obtained in the i-th reading as the real-time temperature-measuring wavelength r i 、the wavelength of the confining pressure optical fiber 13 as the real-time confining pressure wavelength α i 、and the wavelength of the compression optical fiber 8 as the real-time compression wavelength β i .

[0076] Step 7, Measurement and calculation of real-time data

[0077] In a round of measurements, the data of three real-time wavelengths are read and recorded by the fiber optic demodulator 4, and three sets of read data of real-time wavelengths are obtained.

[0078] Let the temperature of the underground soil corresponding to the real-time temperature measurement wavelength r i be denoted as temperature C i , the confining pressure of the underground soil corresponding to the real-time confining pressure wavelength α i be denoted as confining pressure N i , and the compression of the underground soil corresponding to the real-time compression wavelength β i be denoted as compression M i ; their calculation formulas are respectively:

[0079] C i = K iγ (ri - γ0)......(1)

[0080] N i = K iα (α i - α0)......(2)

[0081] M i = K iβ (β i - β0)......(3)

[0082] In the formulas, K iγ is the ratio coefficient of temperature to wavelength change, with the unit of degrees Celsius per nanometer; K iα represents the ratio coefficient of confining pressure to wavelength change, with the unit of megapascals per nanometer; K iβ represents the ratio coefficient of compression to wavelength change, with the unit of millimeters per nanometer. The unit of temperature C i is degrees Celsius, the unit of confining pressure N i is megapascals, and the unit of compression M i is millimeters.

[0083] Substitute the read data of the three sets of real-time wavelengths into formulas (1), (2), and (3) for calculation to obtain three sets of data of temperature, confining pressure, and compression for a round of measurement.

[0084] The unit of wavelength in each of the above steps is nanometer.

[0085] Step 8, according to the three sets of data of temperature, confining pressure, and compression obtained in step 7 for a round of measurement, plot the time-temperature curve, time-confining pressure curve, and time-compression curve in the plane coordinate system, and analyze and study the state of the underground soil through the three curves.

[0086] Step 9, conduct multiple rounds of measurements at an interval of time A to achieve in-situ long-term monitoring of the underground soil.

[0087] In this embodiment, the ratio coefficient K of the temperature to wavelength change is iγ , the ratio coefficient K of the confining pressure and wavelength change iα The ratio coefficient K of compression and wavelength change iβ Determined by indoor calibration. Specifically, the indoor calibration is: K iγ =29.44, K iα =66.26, K iβ =126.38.

[0088] In order to verify the beneficial effects of the present invention, the measurement method was tested at a test site in Ningbo City, Zhejiang Province, and the depth of the hole 2 to be measured was 73.4 meters.

[0089] Figure 4 This graph shows the temperature variation at 73.4 meters underground at a test site in Ningbo, according to an embodiment of the present invention. The horizontal axis represents the time of data acquisition, and the vertical axis represents the underground soil temperature. As can be seen from the graph, the soil temperature at 73.4 meters underground remains stable within the range of 19-22 degrees Celsius. The optical fiber sensor 1 can monitor the daily soil temperature variation at a depth of 73.4 meters in real time.

[0090] Figure 5 This is a schematic diagram of the confining pressure changes at 73.4 meters underground at a test site in Ningbo City, according to an embodiment of the present invention. The horizontal axis represents the time of monitoring data acquisition, and the vertical axis represents the underground soil confining pressure. The figure shows that the confining pressure at 73.4 meters increases continuously with increasing backfill depth. At 60 minutes, when backfill reaches the surface, the confining pressure stabilizes at around 26.2 MPa. Furthermore, the two curves in the figure represent confining pressure tests conducted on two adjacent test holes 2. The two curves essentially overlap, indicating that the monitoring data from the optical fiber sensor 1 is highly stable.

[0091] Figure 6 This diagram shows the compression changes in soil at 73.4 meters below ground level at a test site in Ningbo City, according to an embodiment of the present invention. The horizontal axis represents the time of data acquisition, and the vertical axis represents the amount of compression of the underground soil. The figure shows that the compression at 73.4 meters is essentially stable at around 61.3 mm. The two curves in the figure represent compression tests conducted on two adjacent test holes 2. The two curves essentially overlap, indicating good stability in the monitoring data from the optical fiber sensor 1.

Claims

1. An in-situ measurement method for underground soil temperature, confining pressure and compression, characterized in that A fiber optic sensor is pre-buried in the underground soil. The main body of the fiber optic sensor is a hollow cylindrical shape and remains vertical in the underground soil. The head of the fiber optic sensor is connected to a main optical cable, and the other end of the main optical cable passes upward through the underground soil and is connected to a fiber optic demodulator. The in-situ measurement method comprises the following steps: Step 1, Assembly of measuring tools The measuring tool is an optical fiber sensor, comprising a main body, a telescopic column embedded in the hollow part of the main body and extending at both ends, a base and a pressure cover, wherein a vertical wire groove is opened on the outer wall of the telescopic column; the base is a semi-hollow cylindrical shape with an upward opening, the tail of the main body is embedded and completely seated in the base, and the tail of the telescopic column is fixed to the screw hole at the center of the inner bottom surface of the base by screwing; the pressure cover is a semi-hollow cylindrical shape with a downward opening, the top of the telescopic column is fixed to the screw hole at the center of the inner bottom surface of the pressure cover by screwing, and a gap is left between the main body and the inner bottom surface of the pressure cover; one end of a compression optical fiber is connected to the main optical cable, and the other end passes through the side wall of the pressure cover into the hollow part of the pressure cover, and is embedded in the wire groove of the telescopic column and extends along the wire groove to the bottom of the telescopic column; one end of a sensing optical cable is connected to the main optical cable, and the other end is spirally wound on the outer surface of the main body from top to bottom at equal intervals, and the sensing optical cable includes a temperature measuring optical fiber and a confining pressure optical fiber; Step 2, Drilling Determine the site to be tested and the depth of the hole to be tested according to construction requirements; Use a drilling rig to drill a hole at the site to be tested. The drilling depth is the depth of the hole to be tested. The outer diameters of the base and the pressure cover are the same. The diameter of the hole to be tested is at least 8cm-10cm larger than the outer diameter of the base. Step 3: Lowering the measuring tool Lower the fiber optic sensor to the bottom of the hole to be measured, and ensure that the main body of the fiber optic sensor is perpendicular to the bottom surface of the hole to be measured, and then lead the main optical cable through the hole to be measured to the ground surface; Step 4: Record the initial value Connect the temperature measurement fiber, confining pressure fiber, and compression fiber in the total optical cable to the corresponding interfaces of the optical fiber demodulator respectively, read the initial wavelength of each fiber and record them as the initial temperature measurement wavelength γ0, the initial confining pressure wavelength α0, and the initial compression wavelength β0 respectively; Step 5: Backfill and compaction of undisturbed soil Backfill the original soil taken out from the drilling hole into the hole to be tested until it is flush with the ground surface, and compact it while backfilling; Step 6: Setting real-time measurement parameters Set the interval time A and the number of records N, where the interval time is the time difference between two rounds of measurement, and the number of readings N is the total number of times measurement data is read in one round of measurement. Any reading in one round of measurement is recorded as the i-th reading, where i = 1, 2, ..., N; Denote the wavelength of the temperature-measuring optical fiber obtained by the i-th reading as the real-time temperature-measuring wavelength r i and denote the wavelength of the confining pressure optical fiber as the real-time confining pressure wavelength α i and denote the wavelength of the compression optical fiber as the real-time compression wavelength β i ; Step 7: Real-time data measurement and calculation In one round of measurement, the optical fiber demodulator reads and records the data of three real-time wavelengths, and obtains three sets of real-time wavelength reading data; Record the temperature of the corresponding underground soil at the real-time temperature measurement wavelength r as temperature C i i Record the confining pressure of the corresponding underground soil at the real-time confining pressure wavelength α as confining pressure N i i Record the compression of the corresponding underground soil at the real-time compression wavelength β as compression M i i ; Their calculation formulas are respectively:​​​ C i = K iγ (r i - γ0)……(1) N i = K iα (α i - α0)……(2) M i = K iβ (β i - β0)......(3) where K iγ is the ratio coefficient of temperature to wavelength change, with the unit of degrees Celsius per nanometer; K iα represents the ratio coefficient of confining pressure to wavelength change, with the unit of megapascals per nanometer; K iβ represents the ratio coefficient of compression to wavelength change, with the unit of millimeters per nanometer; the temperature C i is in degrees Celsius, the confining pressure N i is in megapascals, and the compression M i is in millimeters; Substitute the three sets of real-time wavelength reading data into formulas (1), (2) and (3) for calculation to obtain three sets of temperature, confining pressure and compression data for one round of measurement; The unit of wavelength in each of the above steps is nanometer; Step 8: Based on the three groups of temperature, confining pressure, and compression data obtained in one round of measurement in Step 7, plot the time-temperature curve, time-confining pressure curve, and time-compression curve in a plane coordinate system, and analyze and study the state of the underground soil through the three curves; Step 9: Conduct multiple rounds of measurement at an interval of time A to achieve long-term in-situ monitoring of the underground soil.

2. The in-situ test method for underground soil temperature, confining pressure and compression according to claim 1, characterized in that The inner diameter of the hollow part of the main body is adapted to the outer diameter of the telescopic column.

3. The in-situ test method for underground soil temperature, confining pressure and compression according to claim 1, characterized in that, The reserved length of the total optical cable is at least 5 meters longer than the depth of the hole to be measured.

4. An in-situ testing method for underground soil temperature, confining pressure and compression according to claim 1, characterized in that, The ratio coefficient K of the temperature to the wavelength change iγ , the ratio coefficient K of the confining pressure to the wavelength change iα and the ratio coefficient K of the compression to the wavelength change iβ are determined through indoor calibration.

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