A deep rock mass displacement monitoring method based on segmented temperature compensation

Abstract

The application relates to a deep rock mass displacement monitoring method based on segmented temperature compensation and relates to the technical field of geotechnical engineering monitoring.The deep rock mass displacement meter (single-point or multi-point displacement meter) is arranged in a borehole, a hollow measuring rod is adopted, and a temperature sensor is arranged in the hollow measuring rod to realize real-time collection of multiple points of temperature along the length direction of the measuring rod; the measuring rod is divided into multiple monitoring sections, the temperature deformation of each section of the measuring rod is calculated according to the measured temperature of the corresponding depth of each section of the measuring rod, the displacement measurement value of each measuring point is compensated by the segmented temperature deformation, the true displacement of the bedrock is obtained after the temperature influence is eliminated, and thus the quantitative description of the bedrock creep process is realized.The application overcomes the system error caused by the uneven distribution of the ground temperature gradient, significantly improves the deep displacement monitoring precision, is compatible with the existing deep rock mass displacement meter structure, is easy to implement, and is suitable for the bedrock creep mechanism research and long-term safety monitoring of major projects.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering monitoring technology, specifically to a high-precision displacement monitoring device and system that uses a temperature sensing unit built into a measuring rod for segmented compensation and is used for quantitative research on creep in deep bedrock. Background Technology

[0002] In major engineering projects such as water conservancy, transportation, and energy, the long-term creep characteristics of deep bedrock directly affect the overall stability and service safety of the project. Deep rock mass displacement monitoring devices (single-point or multi-point displacement gauges) are key instruments for acquiring the temporal characteristics of deep rock mass deformation and revealing its creep patterns. Typically, due to the thermal expansion and contraction characteristics of the measuring rod material, displacement measurements must be corrected for temperature deformation. Traditional deep rock mass displacement monitoring devices usually only deploy a single temperature sensing unit at the borehole opening, using the borehole opening temperature as a reference to uniformly compensate for temperature deformation of the measuring rod throughout the entire borehole length.

[0003] However, in actual deep-hole monitoring, the surface and subsurface temperature fields within the borehole are not uniformly distributed along the depth direction. This is especially true in deep bedrock, long-term service projects, and conditions where the temperature field varies significantly with the seasons or environment. The borehole opening temperature (largely affected by ambient temperature, exhibiting significant fluctuations) differs significantly from the actual temperature at various depths within the borehole (where temperature variation decreases with depth, remaining relatively stable year-round). Using a single, highly variable borehole opening temperature to compensate for the entire measuring rod, which can be tens of meters long, introduces substantial systematic errors. Particularly in bedrock creep monitoring, the actual creep deformation of the rock mass is often extremely small. This error is often on the same order of magnitude as the actual displacement, meaning that displacement measurements cannot accurately reflect the long-term, minute creep deformation process of the bedrock. This makes it difficult to meet the high precision and stability requirements of monitoring data for safety assessments of major projects and quantitative analysis of the bedrock creep causal mechanism.

[0004] Currently, most existing technologies for improving the accuracy of displacement gauges in deep rock masses are limited to improving the structure of the displacement gauge, optimizing the material of the measuring rod (such as using materials with low thermal expansion coefficients, but these have problems such as easy corrosion and high cost), or improving the installation process. They have not formed a complete method and system for "segmented temperature measurement and segmented temperature compensation along the depth of the measuring rod", which has resulted in a long-standing technical bottleneck in the accuracy of quantitative monitoring of creep in deep bedrock. Summary of the Invention

[0005] This invention addresses the problem that existing deep rock mass displacement gauges, which rely solely on single-orifice temperature compensation, introduce significant systematic errors, resulting in insufficient monitoring accuracy and failing to meet the accuracy requirements for quantitative analysis of bedrock creep. The invention aims to provide a deep rock mass displacement monitoring device and system based on segmented temperature compensation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for monitoring displacement in deep rock masses based on segmented temperature compensation, characterized by the following steps:

[0008] S1, Install a deep rock mass displacement monitoring device in a deep borehole in the bedrock to be monitored;

[0009] S2, Temperature measuring points are set up at multiple different locations along the length of the measuring rod to collect the actual temperature at each location;

[0010] S3, the measuring rod is divided into multiple sections along its length, and the temperature deformation of each section of the measuring rod is calculated segment by segment based on the actual temperature of the corresponding depth of each section of the measuring rod;

[0011] S4 uses segmented temperature deformation to perform segmented temperature compensation on the displacement measurements of each measuring point, eliminating the true displacement of the bedrock affected by temperature, and is used for quantitative analysis of the bedrock creep process.

[0012] The formula for calculating segmented temperature compensation in step S4 is as follows:

[0013] ;

[0014] In the formula:

[0015] This represents the actual displacement increment (mm) of the probe anchor end relative to the initial test time after temperature compensation correction.

[0016] This is the direct measured value (mm) of the displacement at the anchor end of the measuring rod.

[0017] The initial measured value (mm) of the displacement at the anchor end of the measuring rod;

[0018] This represents the number of segments in the temperature measurement area.

[0019] The coefficient of thermal expansion of the measuring rod (1 / ℃);

[0020] The length (mm) of the i-th temperature measuring section of the measuring rod;

[0021] This is the temperature measurement value (°C) of the i-th temperature measurement section during this measurement.

[0022] The initial temperature measurement value (°C) for the i-th temperature measurement zone.

[0023] Furthermore, the inner diameter of the measuring rod is larger than the outer diameter of the temperature sensing unit to ensure that the temperature sensing unit can be smoothly inserted. The wall thickness of the measuring rod should ensure the structural strength and buckling resistance requirements of the measuring rod, so as to ensure that it has sufficient strength and buckling stability under all expected load conditions.

[0024] Furthermore, a thermally conductive filling layer is provided between the temperature sensing unit and the inner wall of the measuring rod to ensure that the temperature sensing unit is in close contact with the inner wall of the measuring rod, thus ensuring temperature response and measurement accuracy. For multi-point displacement gauges, since the temperature changes slowly inside the measuring hole, the temperature of each measuring rod at the same depth is almost identical. Only the temperature sensing unit needs to be installed along the longest measuring rod, and all measuring rods share a set of temperature measurements. The data of the corresponding measuring points are selected according to the coverage range of the measuring rod length, which greatly simplifies the system layout and improves the overall reliability.

[0025] A monitoring device used in a deep rock mass displacement monitoring method based on segmented temperature compensation is a rock mass displacement gauge. The longest measuring rod of the rock mass displacement gauge is a hollow protective tube. A temperature sensing and processing unit is installed inside the protective tube, and a heat-conducting filling layer is installed between the protective tube and the temperature sensing and processing unit.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. This invention uses distributed temperature measurement along the measuring rod to replace the traditional single temperature measurement at the borehole opening. Through segmented temperature compensation, it significantly reduces the systematic error caused by ignoring the uneven temperature field distribution due to single temperature measurement at the borehole opening, eliminates the deformation of the measuring rod caused by changes in ambient temperature and borehole temperature, and significantly improves the accuracy of quantitative monitoring of bedrock creep.

[0028] 2. The method does not rely on displacement gauges with specific structures and is compatible with existing deep rock mass displacement monitoring devices such as vibrating wire and inductive types, making it highly applicable;

[0029] 3. By segmented temperature measurement and segmented compensation for the temperature deformation of the measuring rod, the minute creep deformation at the anchoring end of the measuring rod can be accurately reproduced, providing reliable data support for long-term bedrock creep mechanism research and engineering safety evaluation;

[0030] 4. The system has a simple structure, with the temperature sensor built into the hollow measuring rod. The overall structure is simple and reliable, and only the distributed temperature acquisition and segmented calculation logic is added to the existing monitoring system. The engineering implementation is convenient and low-cost, and it is easy to implement and promote. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a deep rock mass displacement monitoring device based on segmented temperature compensation.

[0032] Figure 2 This is the AA section view of the measuring rod.

[0033] In the diagram: 1-measuring rod; 2-anchor head; 3-support plate; 4-displacement sensing unit; 5-protective tube; 6-temperature sensing unit; 7-thermal conductive filling layer; 8-observation cable. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0035] Example 1:

[0036] like Figures 1 to 2 As shown, taking the deep bedrock deformation monitoring of a certain water conservancy and hydropower project as an example, this paper illustrates a deep rock mass displacement monitoring method based on segmented temperature compensation. The specific implementation of this method includes the following steps:

[0037] S1. A deep rock mass displacement monitoring device is installed in a deep borehole in the bedrock. This device is a three-point displacement gauge with three anchor heads set along the borehole depth, with anchoring depths of 50m, 30m, and 10m respectively. The casing material is 316 stainless steel, whose coefficient of thermal expansion is [missing information]. =1.6×10 -5 The diameter φ is 8mm. The numbering of the measuring rod and its anchor head is based on the number closest to the borehole opening. # 1, and arranged sequentially into measuring rods as they deepen. # 1. Measuring rod # 2. Measuring rod # 3;

[0038] S2, the longest measuring rod # The measuring rod is 50m long, with a 4mm inner diameter protective tube containing a built-in temperature sensing unit, specifically an FBG temperature sensor. The protective tube effectively protects the sensor and divides it into 10 temperature monitoring sections, each 5m long. Temperature measuring points are set every 5m, starting 2.5m from the borehole opening, for a total of 10 measuring points. The temperature measuring point is numbered with the one closest to the borehole opening as the measuring point. # 1. And sequentially arranged deeper into the temperature measurement point. # 10;

[0039] measuring rod # 1. # 2 and # 3. The temperature at the same depth is almost identical, so it is only necessary to follow the measuring rod. # 3. Deploy temperature sensing units at the same depth, measuring rods # 1. # 2. Selection of measuring rod # The measured temperature value is sufficient;

[0040] S3, synchronously acquire the displacement value of the anchor end of the j-th measuring rod using a data acquisition instrument. Temperature measurement value of the i-th temperature measurement section The displacement of the measuring rod is defined as positive in the direction extending out of the orifice, and the initial measured value is... and The temperature deformation compensation values ​​for each segment are as follows: The calculated temperature values ​​at each measuring point and the segmented compensation results are shown in Table 1.

[0041] Table 1 Initial and current measurements at each temperature measuring point, and results of segmented compensation for temperature deformation of the measuring rod.

[0042]

[0043] S3, measuring rod # 1. Use temperature measuring points # 1 and # 2. Correct the sum of the temperature deformation segment compensation values, and then apply the correction to the measuring rod. # 2. Temperature measurement points # 1- # The sum of the temperature deformation segment compensation values ​​is used for correction, and the measuring rod is then used for correction. # 3. Use temperature measuring points # 1- # The sum of the temperature deformation segment compensation values ​​was corrected, and the displacement values ​​of each measuring rod, the compensation correction values, and the results before and after correction are shown in Table 2.

[0044] Table 2 Initial displacement values, current displacement values, and results before and after compensation correction for each probe.

[0045]

[0046] As shown in Table 2, for deep bedrock deformation monitoring with small displacement and excessively long measuring rods, the extension and retraction of the measuring rod caused by temperature changes are on the same order of magnitude as the actual displacement. Therefore, it is essential to improve the accuracy of temperature deformation compensation.

[0047] If, using existing traditional methods, the orifice temperature (in this embodiment, the initial orifice temperature and the measured value are 25.9℃ and 18.1℃ respectively) is used to uniformly compensate for temperature deformation of the measuring rod within the entire length of the hole, the measurement rod... # 1. # 2. # The temperature deformation compensation correction values ​​for the three probes are 1.25 mm, 3.74 mm, and 6.24 mm, respectively. Since the temperature variation at the borehole opening fluctuates significantly due to environmental influences, it is usually much greater than the temperature variation deep within the borehole. Correcting solely based on the borehole opening temperature severely exaggerates the temperature deformation of the deep probe, leading to overcompensation. This traditional correction method is not suitable for creep monitoring of long probes in deep holes.

[0048] In this embodiment, if a commonly packaged FBG temperature sensor (with a measurement accuracy of ±0.5℃) is used, the compensation error generated by the segmented temperature compensation method on a 50m long 316 stainless steel measuring rod is ±0.4mm, which can basically meet the monitoring accuracy requirements of quantitative analysis of long-term creep in bedrock.

[0049] The temperature sensor should meet the requirements of multiple measurement points, long distance, high precision, and small outer diameter. If higher creep accuracy is required, a measuring rod made of a material with a low coefficient of thermal expansion can be used to obtain better displacement monitoring accuracy, such as Invar steel, whose coefficient of thermal expansion is less than 1 / 10 of that of 316 stainless steel. However, it is prone to corrosion and requires special measures. Alternatively, a high-precision temperature sensor, such as a fiber optic grating (FBG), can be used. A single fiber can connect more than 10 measurement points. In this embodiment, the FBG temperature sensor has an accuracy of ±0.5℃ and an outer diameter of 0.9–1.5 mm, and can be inserted into the measuring rod. A high-precision FBG temperature sensor with enhanced sensitivity packaging can achieve an accuracy of ±0.05℃ and is used in scenarios requiring high-precision temperature compensation. The FBG system consists of a sensor and a demodulator (reading device). The demodulator accounts for a large proportion of the cost. Multiple monitoring lines in the entire monitoring area can share a single demodulator through an optical switch to significantly reduce the overall cost.

[0050] In this embodiment, the displacement monitoring device is a rock mass displacement gauge, which consists of an anchor head 2, a measuring rod 1, a support plate 3, an observation cable 8, and a displacement sensing unit 4.

[0051] The measuring rod 1 of the rock mass displacement gauge includes a hollow protective tube 5, a temperature sensing and processing unit 6 is installed inside the protective tube 5, and a heat-conducting filling layer 7 is provided between the protective tube 5 and the temperature sensing and processing unit 6.

[0052] One end of the measuring rod 1 is fixedly connected to the anchor head 2, and the other end is connected to the displacement sensing unit 4; the measuring rods are fixed to each other by the support plate 3.

[0053] The temperature sensing unit is divided into multiple temperature measurement sections along the length of the measuring rod, and corresponding temperature sensor measuring points are arranged to collect the actual temperature at different depths. The measured temperature is processed by the data processing unit and then transmitted through the observation cable 8. At the same time, the displacement sensing unit 4 collects the displacement of the measuring rod.

[0054] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for monitoring displacement in deep rock masses based on segmented temperature compensation, characterized in that, The method includes the following steps: S1, Install a deep rock mass displacement monitoring device in a deep borehole in the bedrock to be monitored; S2, Temperature measuring points are set up at multiple different locations along the length of the measuring rod to collect the actual temperature at each location; S3, the measuring rod is divided into multiple sections along its length, and the temperature deformation of each section of the measuring rod is calculated segment by segment based on the actual temperature of the corresponding depth of each section of the measuring rod; S4 uses segmented temperature deformation to perform segmented temperature compensation on the displacement measurements of each measuring point, eliminating the true displacement of the bedrock affected by temperature, and is used for quantitative analysis of the bedrock creep process. The formula for calculating segmented temperature compensation in step S4 is as follows: ； In the formula: This represents the actual displacement increment (mm) of the probe anchor end relative to the initial test time after temperature compensation correction. This is the direct measured value (mm) of the displacement at the anchor end of the measuring rod. The initial measured value (mm) of the displacement at the anchor end of the measuring rod; This represents the number of segments in the temperature measurement area. The coefficient of thermal expansion of the measuring rod (1 / ℃); The length (mm) of the i-th temperature measuring section of the measuring rod; This is the temperature measurement value (°C) of the i-th temperature measurement section during this measurement. The initial temperature measurement value (°C) for the i-th temperature measurement zone.

2. The monitoring device used in the deep rock mass displacement monitoring method based on segmented temperature compensation as described in claim 1, characterized in that, The device is a rock mass displacement gauge. The longest measuring rod of the rock mass displacement gauge is a hollow protective tube. A temperature sensing and processing unit is installed inside the protective tube, and a heat-conducting filling layer is installed between the protective tube and the temperature sensing and processing unit.

3. The deep rock mass displacement monitoring device based on segmented temperature compensation as described in claim 2, characterized in that, The inner diameter of the measuring rod is larger than the outer diameter of the temperature sensing unit, and the wall thickness of the measuring rod should ensure the structural strength and buckling resistance of the measuring rod.

4. The deep rock mass displacement monitoring device based on segmented temperature compensation as described in claim 2, characterized in that, The temperature sensing unit should meet the requirements of multiple measurement points, long distance, high precision, and small outer diameter.

5. The deep rock mass displacement monitoring device based on segmented temperature compensation as described in claim 2, characterized in that, A thermally conductive filling layer is provided between the temperature sensing unit and the inner wall of the measuring rod to ensure that the temperature sensing unit is in close contact with the inner wall of the measuring rod.

6. The deep rock mass displacement monitoring device based on segmented temperature compensation as described in claim 1, characterized in that, When the deep rock mass displacement gauge has multiple measuring points, the temperature sensing unit needs to be installed along the longest measuring rod. Other measuring rods at the same depth level reuse the temperature measurement value corresponding to that depth to calculate their respective temperature deformation.

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