TWI650574B - Tdr device and method for monitoring subsidence variation - Google Patents

Abstract

The invention relates to a time domain reflection type monitoring subsidence changing device and a method thereof, which comprise a time domain reflective sensing device installed in an environment to be tested to extract a measuring waveform. A data processor compares the reference band with one of the measured waveforms, and compares with one of the reference waveforms to obtain an error value, and compares the sinking band and the reference waveform with one of the measured waveforms. A reference sinking band is used to generate a sinking difference. Finally, according to the difference between the error value and the sinking difference, a waveform time difference is generated, and an actual sinking amount equation is taken to obtain an actual sinking amount. The present invention utilizes time domain reflection for multiple depths, and automatically detects the amount of sinking, and can filter out error values generated in the system to achieve accurate numerical measurements.

Description

Time domain reflective monitoring subsidence changing device and method thereof

The present invention relates to a technique for measuring formation subsidence, and more particularly to a time domain reflective monitoring subsidence changing device and method therefor.

As the demand for water resources increases, the water in rivers and reservoirs is in short supply, leading people to start pumping groundwater to make up for the shortage of water resources. As a result, the situation of over-pumping groundwater is becoming more and more serious. The result of continuous pumping of groundwater causes groundwater salinization and soil. Salinization and subsidence of the formation, so how to effectively monitor changes in soil subsidence to prevent soil subsidence and protect the environment has become a very important issue.

At present, the traditional method of measuring subsidence is to carry out large-scale or local leveling on the ground surface regularly to grasp the changes of topographic features. When measuring the amount of subsidence, it is necessary to set an appropriate amount of reference point, and the depression of the formation of each reference point can be used to draw the contour line of the depression amount, to find the center of the subsidence, and obtain the comparison results of multiple times to find out The formation is trapped under time. However, this method is quite labor-intensive and time-consuming, and the measurement interval is large, and the average side can be measured once every two to three months, and it is difficult to obtain continuous formation subsidence data.

In addition to the above-mentioned traditional surface detection methods, underground monitoring can be divided into single-point or multi-point, single-point refers to the measurement of the subsidence change in the fixed position in the monitoring well. In detail, the monitoring well is generally The bottom is used as a fixed measuring point, and the current depth of the stratum is measured by a monitoring instrument installed in the ground or measuring well to compare the sinking value generated by the original depth.

The multi-point type can be divided into two types, one of which is placed in the monitoring well by setting the extensometer, and is poured into the mixed slurry of cement and bentonite, and can be measured after consolidation. When the local layer is sunken, the elastic steel telescopic rod in the extension gauge slides in the nylon protective tube, and the displacement shows the compression amount from the point to the surface, and the displacement is measured on the surface by the vernier scale. The other one of the multi-point type uses a magnetic ring with a measuring tube placed at different depths in the ground, and then a magnetic detector is placed through the indium steel ruler to detect the position of the magnetic ring under the measuring tube, thereby confirming the position difference at different times. This is the sink value of the depth point.

However, whether it is a single-point or multi-point measurement method, the procedures required for the installation beforehand are quite complicated, and must be monitored by human operation. The instrument cannot be used to reflect the soil at each time point without interruption. The change of subsidence. Furthermore, in addition to the amount of soil subsidence, in addition to the amount of soil subsidence, the data on monitoring the water pressure in the well is also very important. At present, the way to measure the water pressure is to additionally drill a monitoring well and put it into the water pressure to measure the water pressure. Therefore, the traditional water pressure measurement method cannot measure the water pressure and the amount of soil subsidence at a place. The factors that may result in different data may be incomplete, and the collected parameters are incomplete, resulting in inaccurate data calculated by subsequent data.

In view of the above, the present invention has been directed to the absence of the above-mentioned prior art, and proposes a time domain reflective monitoring subsidence changing device and method thereof to effectively overcome the above problems.

The main object of the present invention is to provide a time domain reflection type monitoring subsidence changing device and a method thereof, which use the electromagnetic pulse wave reflected by the time domain to measure the soil subsidence at a multi-point depth, and can automatically detect the sinking amount, and can filter In addition to the error values generated in the original system to achieve accurate numerical measurements, it is a more reliable measurement technique.

Another object of the present invention is to provide a time domain reflection type monitoring subsidence changing device and a method thereof, which can utilize the electromagnetic pulse wave measurement to achieve the advantages of rapid measurement and accurate measurement data, and can simultaneously measure the amount of subsidence. In the same place, the parameters of the water pressure can avoid errors in the measurement of different places, which is beneficial to improve the calculation accuracy of the subsidence of the formation.

To achieve the above object, the present invention provides a time domain reflective monitoring subsidence changing device installed in an environment to be tested to monitor the amount of soil subsidence change of the environment to be tested, wherein the time domain reflective monitoring subsidence changing device includes At least one transmission line, an inner conductor of the transmission line is connected to at least one coaxial cable, and an outer conductor of the transmission line is connected to a conductive tube body, and the transmission line can transmit an electromagnetic pulse wave to the coaxial cable and the conductive tube body; wherein the conductive tube body is disposed In the environment to be tested, the coaxial cable is disposed in the conductive tube body, so that the electromagnetic pulse wave transmitted by the transmission line flows in the conductive tube body, and at least one sensing device is further disposed in the conductive tube body, and the outer surface of the sensing device is The anchoring device is provided with at least one anchoring device, and the anchoring device is disposed to fix the sensing device to the soil of the environment to be monitored; and the conductive tube body is further provided with at least one water pressure gauge to detect the environment to be monitored. The liquid generates a water pressure signal; at least one data processor is electrically connected to the water pressure gauge and the transmission line, and the data processor can receive the water pressure signal and control the transmission line to emit electromagnetic pulse waves, and The material processor can sense the electromagnetic pulse wave touches the sensing device and the water pressure gauge through the transmission line, and generates a measurement waveform, and the data processor compares the measurement waveform with a reference waveform in the data processor. After obtaining a waveform time difference, the waveform time difference is brought into an actual sinking amount equation, and the waveform time difference is converted into an actual sinking amount.

In addition, the present invention also provides a time domain reflective monitoring subsidence variation method, which includes the following steps: first, a measurement waveform is selected, and the measurement waveform includes a measurement reference band and a measurement subsidence band; and then the comparison measurement The reference band of the waveform is measured, and one of the reference waveforms is referenced to the reference band to obtain an error value; the measured sinking band is compared with the measured waveform, and one of the reference waveforms is referenced to the sinking band to generate a sinking difference Finally, according to the difference between the error value and the sinking difference, a waveform time difference is generated and brought into an actual sinking amount equation to obtain an actual sinking amount. The actual subsidence equation is: △S is the actual amount of subsidence; (△ T ₂ -△ T ₁ ) is the waveform time difference; Δ T ₂ detector detects the difference in subsidence; △ T ₁ is the error quality of the water pressure gauge; c is the speed of light; ε _m is the dielectric of the medium in the conductive tube; a is the measurement efficiency proportional coefficient; ε _c is the dielectric of the insulating layer of the coaxial cable.

The purpose, technical content, features and effects achieved by the present invention will be more readily understood by the detailed description of the embodiments.

Referring to the first figure and the second figure, the time domain reflection type monitoring subsidence changing device 1 of the present invention is installed in a to-be-monitored environment. In this embodiment, the environment to be tested is a groundwater monitoring well 60 to monitor the soil subsidence. The change amount and the water pressure change in the monitoring well 60, in the present embodiment, a monitoring well 60 is drilled in the soil 62, and a cover 66 is provided on the opening of the monitoring well 60 for installing the time domain reflective monitoring subsidence changing device 1 . The time domain reflective monitoring subsidence changing device 1 includes a data processor 10, a conductive tube body 20, at least one time domain reflective sensing device 30, and a water pressure gauge 40. The data processor 10 is disposed on the cover 66 of the monitoring well 60 and electrically connected to at least one transmission line 12; the conductive tube 20 is disposed on the cover 66 and extends into the monitoring well 60 and directly inserted into the monitoring well 60. In the soil 62, the groundwater in the soil 62 can be infiltrated into the conductive pipe body 20. The conductive pipe body 20 is electrically connected to the transmission line 12. The conductive pipe body 20 is further provided with a coaxial cable 22, which includes a conductor 222. The surface is further covered with an insulating layer 224, which can effectively alleviate the problem of electromagnetic wave energy attenuation caused by groundwater. The coaxial cable 22 is also electrically connected to the transmission line 12. Please refer to the third figure for further detailed description of the conductive tube body 20. The conductive tube body 20 can be a metal tube or a conductive material tube body such as an aluminum tube or a copper tube, and the conductive tube body 20 is further provided with a slot 24 on at least one side thereof, so that the groundwater in the soil 62 can also be slotted. It penetrates into the conductive tube body 20.

Next, please refer to the first and fourth figures to explain in detail the connection relationship between the conductive tube body 20, the coaxial cable 22, and the transmission line 12. As shown, the transmission line 12 of the data processor 10 connects an inner conductor 122 of the transmission line 12 to the conductor 222 of the coaxial cable 22 through a fixing ring 142 of a connector 14 disposed on the cover 66. The transmission line 12 The outer conductor 124 is connected to the conductive tube body 20, so that the data processor 10 can control the transmission line 12 to transmit an electromagnetic pulse wave between the coaxial cable 22 and the conductive tube body 20, so that the electromagnetic pulse wave flows in the conductive tube body 20.

Referring to the first and second figures, the sensing device 30 is disposed in the conductive tube body 20, and the present invention can serially connect the plurality of sensing devices 30 in the conductive tube body 20. This embodiment only uses one sensing device. 30 is exemplified, but not limited by the provision of one sensing device 30. The coaxial cable 22 passes through the sensing device 30. The sensing device 30 is movable and can be moved within the conductive tube 20 to sense The device 30 includes an anchor 34. The anchor 34 can pass through the slot 24 of the conductive tube 20 to fix the sensing device 30 to the soil 62. Since the sensing device 30 can be in the conductive tube 20 Moving and fixed on the soil 62, the sensing device 30 can be sunk together with the soil 62 when the soil 62 sinks, so that the current position of the sensing device 30 can be used as a reference for measuring the subsidence; the conductive tube body 20 A centering device 26 is further disposed to allow the coaxial cable 22 to pass through the centering device 26, and the coaxial cable 22 and the sensing device 30 are centered in the conductive tube body 20 to improve the stability of the measured waveform. In this embodiment, the sensing device 30 includes a metal sensor 36 and a non-metal sensor 38. The material of the metal sensor 36 is aluminum, copper or other conductive material, and the material of the non-metal sensor 38. The material is plastic, polystyrene or non-conductive material; the metal sensor 36 is connected in series with the non-metal sensor 38, and the metal sensor 36 is located above the non-metal sensor 38, when the conductive tube When the electromagnetic pulse wave in the body 20 touches the metal sensor 36 and the non-metal sensor 38, different waveform changes can be generated to utilize the change of the waveform as a feature point to obtain the metal sensor 36 and the non-metal sensor 36 Metal sensor 38 is in position in monitoring well 60.

The water pressure gauge 40 is also disposed in the conductive tube body 20 to detect the groundwater pressure in the conductive tube body 20 from the soil, and the water pressure gauge 40 is electrically connected to the analog converter 42, the analog converter 42. Re-electrically connected to the data processor 10. The water pressure gauge 40 can detect the water pressure of the liquid in the environment, generate a water pressure signal, and transmit the water pressure signal to the analog converter 42 for signal conversion, and then to the data processor 10. When the electromagnetic pulse wave in the conductive pipe body 20 touches the water pressure gauge 40, different waveform changes can also be generated, and the present invention can use the change of the waveform as a feature point to obtain the position of the water pressure gauge 40.

The structure of the data processor 10 is further described in detail with reference to the first and second figures. The data processor 10 further includes a time domain reflectometer 16 and a computer 18, wherein the time domain reflectometer 16 is electrically connected to the transmission line 12. To emit an electromagnetic pulse wave to the transmission line 12 and receive the measurement waveform through the transmission line 12. The computer 18 is electrically connected to the time domain reflectometer 16 and the analog converter 42. The computer 18 can receive the measurement waveform of the time domain reflectometer 16 and the water pressure signal of the water pressure gauge 40 converted by the analog converter 42 and display The water pressure signal is referenced to a user in a display 19 of the electrical connection computer 18; the computer 18 further stores a reference waveform and an actual sinking amount equation, and the computer senses the electromagnetic pulse wave through the transmission line 12 to touch the sensing device. 30 and the measurement waveform generated by the water pressure gauge 40, to compare the measurement waveform with the reference waveform, obtain a waveform time difference, and then bring it into the actual sinking amount equation, and convert the waveform time difference into an actual sinking amount. And the actual amount of sinking is displayed in the display 19.

Having explained the above structure, the method of monitoring the sink value of the present invention will be described. Referring to the first, second and fifth figures. Before measuring the subsidence value, the reference waveform of the monitoring well 60 where the soil 62 has not been collapsed must be obtained as a reference for comparing the actual subsidence amount in the backward direction. The reference waveform is extracted at the beginning of the time domain reflection. When the monitoring subsidence changing device 1 is in the environment to be monitored, the control time domain reflectometer 16 emits a measuring electromagnetic pulse wave into the conductive pipe body 20, and the electromagnetic pulse wave touches the water pressure gauge 40 in the conductive pipe body 20 and senses After the measurement device 30, a change in waveform is generated and reflected back into the reference waveform time domain reflectometer 16, which in turn stores the reference waveform into the computer 18. The reference waveform includes a reference reference band 50 and a reference sink band 52. The reference reference band 50 is a band in which the electromagnetic pulse wave touches the water pressure gauge 40, and the reference sink band 52 is the electromagnetic pulse wave touches the sensing device 30. The reason for the fact that the reference sinking band 52 exhibits a wave shape is that the sensing device 30 of the present embodiment includes the metal sensor 36 of different materials and the non-metal sensor 38, so that the electromagnetic pulse wave touches the metal. When the sensor 36 and the non-metal sensor 38 are used, different waveforms are generated. As shown in the fifth figure, referring to the upper half of the sinker band 52, the band protruding to the left is a touch of the metal sensor. The waveform of 36, the waveform protruding to the right in the lower half, touches the waveform of the non-metallic sensor 38.

After obtaining the reference waveform, please refer to the first, second and sixth figures in detail to explain in detail how the computer 18 of the data processor 10 uses the reference waveform to compare the measured waveforms to calculate the actual sinking amount. First, in step S10, the time domain reflectometer 16 of the data processor 10 sends an electromagnetic pulse wave to the conductive tube body 20 and the coaxial cable 22, so that the electromagnetic pulse wave in the conductive tube body 20 touches the water pressure gauge 40 and the sense After the measuring device 30, the reflected measurement waveform is taken by the time domain reflectometer 16. Please refer to the sixth and seventh figures, wherein the measurement waveform includes a measurement reference band 54 and a measurement subsidence band 56, and the measurement reference band 54 refers to the band of the electromagnetic pulse wave touching the hydrometer 40. The measurement subsidence band 56 is a band in which the electromagnetic pulse wave in the conductive tube touches the sensing device 30. The reason why the measurement subsidence band 56 exhibits a wave shape is the same as that of the reference sink band 52, so the description is not repeated.

Next, referring to step S12, after the computer 18 obtains the measurement waveform through the time domain reflectometer 16, the reference measurement band 54 and the reference reference band 50 of the reference waveform are compared to obtain an error value. Please cooperate with the eighth figure. Since the sensing device 30 is fixed to the soil 62 through the anchor 34, the sensing device 30 is also collapsed when the soil 62 is sunk, so the measured waveform is measured when it is not collapsed. The reference waveform will also vary, but the measured waveform may also have an error value. In detail, as shown in the eighth figure, the water pressure gauge 40 in the present embodiment is in a state of not moving, but the measurement waveform taken by the data processor 10 represents the measurement of the position of the water pressure gauge 40. The position of the reference band 54 is decreased, indicating that the measurement waveform may be subject to errors due to certain factors, so the computer 18 must capture the reference reference band 50 of the reference waveform and the measurement reference band 54 of the measurement waveform for comparison. Get an error value , as a parameter for correction.

Next, referring to step S14, the computer 18 compares the measured waveform waveform with the measured sinking band 56 and the reference sinking reference band 52 to generate a sinking difference. Subsidence difference The cross-correlation is used to compare the sinking band of the measured waveform with the sinking band of the reference waveform. The correlation analysis method is calculated by a correlation analysis equation. The correlation analysis equation (1) is as follows Shown as follows: (1)

among them Is a reference waveform, Is a measurement waveform, For time, It is a time difference. In addition to the above-mentioned mutual correlation analysis method to determine the difference in subsidence In addition, a comparison can be made directly on the measurement subsidence band 56 and the reference subsidence band 52 to obtain a relative feature point. For example, the reference sink band 52 can be used to represent the metal sensor 36 and the non-metal sensing. The intersection of the device 38 serves as the feature point a, and the intersection of the representative metal sensor 36 and the non-metal sensor 38 in the measurement subsidence band 56 is taken as the feature point b, between the feature point a and the feature point b. Difference is the difference .

Finally, proceeding to step S16, the computer 18 can compare the error value calculated in step S12. And the difference in sinking calculated in step S14 Difference in waveform, resulting in a waveform time difference Waveform time difference Then bring in an actual subsidence equation to obtain an actual subsidence . The actual subsidence equation (2) is as follows: (2) where Is the actual amount of subsidence; Is the waveform time difference; For the subsidence difference; Is the error value; For the speed of light; The dielectric of the medium in the conductive tube; Measuring the performance ratio factor for a quantity; It is the dielectric of the insulating layer of the coaxial cable.

In summary, the present invention can utilize the electromagnetic pulse wave reflected by the time domain to measure the subsidence of the soil at a multi-point depth, and can automatically, quickly and continuously detect the sinking amount at each time point, and at the same time, can filter out the original The error values generated in the system to achieve accurate numerical measurements are a more reliable measurement technique. In addition, the present invention can simultaneously obtain the parameters of the water pressure in the same place where the amount of subsidence is measured, avoiding numerical errors in different places, and is advantageous for improving the calculation accuracy of the formation subsidence.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Therefore, any changes or modifications of the features and spirits of the present invention should be included in the scope of the present invention.

1‧‧‧ Time Domain Reflective Monitoring Subsidence Change Device

10‧‧‧data processor

12‧‧‧ transmission line

122‧‧‧ Inner conductor

124‧‧‧Outer conductor

14‧‧‧Adapter

142‧‧‧Fixed ring

16‧‧‧Time Domain Reflectometer

18‧‧‧ computer

19‧‧‧ Display

20‧‧‧Electrical tube body

22‧‧‧ coaxial cable

222‧‧‧ conductor

224‧‧‧Insulation

24‧‧‧ slotting

26‧‧‧ centering device

30‧‧‧Sensing device

34‧‧‧ anchor

36‧‧‧Metal sensor

38‧‧‧Non-metal sensor

40‧‧‧Hydraulic pressure gauge

42‧‧‧ analog converter

50‧‧‧Reference reference band

52‧‧‧Refer to the subsidence band

54‧‧‧Measured reference band

56‧‧‧Measure the subsidence band

60‧‧‧Monitoring well

62‧‧‧ soil

66‧‧‧ cover

a‧‧‧Feature points

b‧‧‧Feature points

The first figure is a schematic diagram of the installation of the time domain reflective monitoring subsidence changing device of the present invention.

The second figure is a block diagram of the time domain reflective monitoring subsidence changing device of the present invention.

The third figure is a three-dimensional schematic view of the conductive tube body of the present invention.

The fourth figure is a schematic diagram of the connection relationship of the conductive tube body, the coaxial cable and the transmission line of the present invention.

The fifth figure is a schematic waveform diagram of the present invention.

The sixth figure is a flow chart of the steps of calculating the actual sinking amount according to the present invention.

The seventh figure is a schematic diagram of the measurement waveform of the present invention.

The eighth figure is a schematic diagram of the method for calculating the actual sinking amount according to the present invention.

Claims (13)

A time domain reflective monitoring subsidence changing device is installed in a to-be-monitored environment to monitor a change in soil subsidence, the time domain reflective monitoring subsidence changing device comprising: at least one transmission line, an inner conductor connected to at least one coaxial a cable, an outer conductor is connected to a conductive tube body for transmitting an electromagnetic pulse wave to the coaxial cable and the conductive tube body, wherein the conductive tube body is disposed in the environment to be tested, and the coaxial cable is disposed In the conductive tube body, the electromagnetic pulse wave flows in the conductive tube body; at least one sensing device is disposed in the conductive tube body, and at least one anchor is disposed on an outer surface of the sensing device, the anchoring The conductive tube is disposed to fix the sensing device to the soil in the environment to be monitored; at least one water pressure gauge is disposed in the conductive tube to detect the liquid in the environment to be monitored, and generate a a water pressure signal; and at least one data processor electrically connected to the water pressure gauge and the transmission line, the data processor can receive the water pressure signal, and control the transmission line to emit the electromagnetic pulse wave, the data processor can The transmission line senses that the electromagnetic pulse wave touches the sensing device and a measurement waveform generated by the water pressure gauge, and is compared with one of the measurement reference band and a reference waveform in the measurement waveform. The reference band is obtained to obtain an error value, and the subsidence band is measured by one of the measurement waveforms, and one of the reference waveforms is referenced to the subsidence band to generate a subsidence difference, and the difference between the error value and the subsidence difference is A quantity, a waveform time difference is generated and brought into an actual sinking amount equation, and the waveform time difference is converted into an actual sinking quantity, wherein the actual sinking quantity equation is: △ S wherein the system for the actual amount of settlement; the _{(△ T 2 - △ T 1} ) for the waveform of the time difference; △ T ₂ for the difference between a sinker; △ T ₁ is a system error value; the c The speed of light; the ε _m is the dielectric of the medium in the conductive tube; the a is a measured performance proportional coefficient; the ε _c is the dielectric of the coaxial cable insulation layer. The time domain reflective monitoring subsidence changing device of claim 1, wherein the data processor further comprises: a time domain reflectometer electrically connected to the transmission line to emit the electromagnetic pulse wave and receive the measurement waveform; a computer electrically connecting the time domain reflectometer and the water pressure gauge, the computer storing the reference waveform and the actual sinking amount equation, and receiving the measured waveform transmitted by the time domain reflectometer to calculate the actual sinking amount . The time domain reflective monitoring subsidence changing device according to claim 1, wherein the measuring reference band and the reference reference band are bands in which the electromagnetic pulse wave touches the water pressure gauge; the measuring subsidence band and the Referring to the sinking band, the electromagnetic pulse wave touches the band of the sensing device. The time domain reflective monitoring subsidence changing device of claim 1, wherein the coaxial cable further comprises a conductor, and the outer surface of the conductor is further covered with an insulating layer. The time domain reflective monitoring subsidence changing device of claim 1, wherein the sinking difference is a cross-correlation comparing the sinking band of the measuring waveform with a sinking band of the reference waveform. The time domain reflective monitoring subsidence changing device of claim 1, wherein the time domain reflective sensing device further comprises a metal sensor and a non-metal sensor. The time domain reflective monitoring subsidence changing device according to claim 6, wherein the material of the metal sensor is aluminum, copper or other conductive material. The time domain reflective monitoring subsidence changing device according to claim 6, wherein the non-metal sensing The material of the device is plastic, polystyrene or non-conductive material. The time domain reflective monitoring subsidence changing device of claim 1, further comprising a centering device disposed in the conductive tube body, wherein the coaxial cable is disposed in the centering device to enable the coaxial cable and the coaxial cable A sensing device can be centered in the conductive tube. The time domain reflective monitoring subsidence changing device of claim 1, wherein the conductive tube system is a metal tube body, which may be an aluminum tube or a copper tube. The time domain reflective monitoring subsidence changing device of claim 1, wherein one side of the conductive tube body is further provided with at least one slot for the anchor to pass through the slot of the conductive tube body. And fixing the sensing device to the soil in the environment to be monitored. A time domain reflective monitoring subsidence variation method includes the following steps: capturing a measurement waveform, the measurement waveform includes a measurement reference band and a measurement subsidence band; and the measurement reference band of the measurement waveform And one of the reference waveforms is referenced to the reference band to obtain an error value; the measured subsidence band is compared to the measurement waveform, and one of the reference waveforms refers to the subsidence band to generate a subsidence difference; and according to the error The difference between the value and the subsidence difference produces a waveform time difference and is brought into an actual subsidence equation to obtain an actual subsidence amount, wherein the actual subsidence equation is: Wherein the ΔS is the actual sinking amount; the (Δ T ₂ - Δ T ₁ ) is the waveform time difference; the Δ T ₂ the sinking difference; Δ T ₁ is the error value; the c is the speed of light The ε _m is the dielectric of the medium in the conductive tube; the a is a measured performance ratio coefficient; the ε _c is the dielectric of the insulating layer of the coaxial cable. The time domain reflective monitoring subsidence variation method of claim 12, wherein the sinking difference is a cross-correlation comparing the sinking band of the measured waveform with a sinking band of the reference waveform.