High-precision model soil saturation measuring device and method

Abstract

The invention discloses a high-precision model soil saturation measuring device and method. The soil body model is placed in the saturation box, the target is placed on the soil body model, the monitoring assembly is installed at the top of the saturation box and used for collecting liquid level information of the soil body model and pressure of the saturation box, and then the saturation degree of the soil body model in the saturation box is measured; the method comprises the steps that a model is placed in a saturation box, a target is placed on the surface of the model, and a laser displacement meter is installed above the target; then sealing the saturation box to saturate the model in vacuum, gradually releasing vacuum after the saturation is completed, and automatically recording the pressure and the liquid level height change measured by the laser displacement meter by using a portable data acquisition instrument; and finally, calculating the saturation of the model according to the recorded liquid level change height and pressure change. Compared with methods such as compression wave measurement, the saturation measuring device and the saturation measuring method have the advantages of simple system, high precision, high automation degree, low cost and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of physical model test monitoring, and in particular relates to a high-precision model soil saturation determination device and method. Background Art

[0002] The saturation of soil is a key physical parameter in soil mechanics and engineering. The saturation directly reflects the degree of water saturation in the soil and has an important influence on various characteristics and engineering behaviors of the soil. Saturation has a significant effect on the shear strength of the soil. Soil saturation is a key parameter connecting soil mechanics, hydraulics, geological engineering and environmental engineering. Its changes affect the mechanical properties, permeability characteristics and environmental behavior of the soil. In engineering practice, accurate evaluation and control of soil saturation not only helps to improve the scientificity and safety of the design, but also reduces potential risks and ensures the long-term stability of the project. Geotechnical engineering model test technology is a research method that simulates the actual working state of rock and soil and engineering structures by scale. Through model tests, theoretical calculation results can be verified, engineering design schemes can be optimized, the complex mechanical mechanisms inside the rock and soil can be revealed, and a reliable basis can be provided for engineering practice. At the same time, this technology also provides important calibration parameters and verification data for numerical simulation, and is an indispensable and important method in geotechnical engineering research. Since the saturation of soil is an important indicator, it is crucial to accurately determine the saturation of the model before conducting the test.

[0003] In the field of geotechnical engineering, the most commonly used method is the B-value method for determining saturation. However, for low-saturation soils, gas dissolution and bubble compression may introduce complex nonlinear responses, affecting the detection accuracy; secondly, it can only indirectly infer saturation and cannot obtain specific moisture distribution information. The most important point is that in model tests, it is difficult to monitor the changes in pore water pressure inside the model after pressurization, so it is mostly used in unit tests and is difficult to generalize to model tests.

[0004] At present, theoretical calculation, conductivity and compression wave velocity are commonly used in model tests to determine the saturation of the model. The accuracy of the results of the theoretical calculation method depends on the accurate measurement of the void volume and the volume of the saturated fluid entering, while the calculation or measurement of the saturated fluid volume is often uncertain, especially in complex soils or heterogeneous materials, the error may be large. The conductivity method is highly dependent on electrolytes, the calibration process is complicated, and the non-uniformity of the conductivity distribution inside the soil (such as cracks, bubbles, etc.) may lead to measurement errors. The measurement results of the compression wave method for determining the saturation of the model may have large errors, the principle is complex, the measurement system is complex, the system reliability is low, and the equipment cost is high. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a high-precision model soil saturation determination device and method to solve the technical difficulties existing in model saturation measurement in existing physical model tests.

[0006] 1. A high-precision model soil saturation measurement device:

[0007] It includes a saturation box, a target, a soil model and a monitoring component; the soil model to be tested is placed in the saturation box, the target is placed on the upper surface of the soil model, and the monitoring component is installed on the top of the saturation box. The monitoring component is used to collect the liquid level information of the liquid in the soil model and the pressure in the saturation box, and then measure the saturation of the soil model to be tested in the saturation box.

[0008] The monitoring component includes a laser displacement meter, a portable data acquisition instrument and a vacuum pressure gauge; the laser displacement meter and the vacuum pressure gauge are electrically connected to the portable data acquisition instrument, and the portable data acquisition instrument is located outside the saturation box, the laser displacement meter and the vacuum pressure gauge are installed on the top of the saturation box, and the laser displacement meter is located directly above the target. The laser emitted by the laser displacement meter irradiates the middle of the target. The laser displacement meter is used to collect the distance change of the target in the vertical direction and send the position information of the target to the portable data acquisition instrument. The vacuum pressure gauge is used to collect the pressure in the saturation box and send the pressure information of the saturation box to the portable data acquisition instrument.

[0009] The measurement resolution of the laser displacement meter is greater than 10 μm.

[0010] The target adopts a flat plate capable of floating on the surface of liquid in the soil model, and the target floats up and down as the liquid level rises and falls.

[0011] 2. A high-precision model soil saturation determination method includes the following steps:

[0012] Step S1, first prepare a soil model and place the prepared soil model to be tested horizontally in a saturation box;

[0013] Step S2, then fix the laser displacement meter and the vacuum pressure gauge, and then place the target on the surface of the soil model so that the bull's eye of the target is directly below the laser displacement meter;

[0014] Step S3, saturating the soil model, measuring the pressure and liquid level data of the saturated soil model, and obtaining the saturation of the soil model using the pressure and liquid level data.

[0015] The step S3 is specifically as follows:

[0016] Step S3.1, saturating the soil model. After the soil model is saturated, connecting the laser displacement meter and the vacuum pressure gauge to the portable data acquisition instrument;

[0017] Step S3.2, start the portable data acquisition instrument, gradually reduce the vacuum degree in the saturation box, and record the pressure data in the saturation box and the height data of the liquid level in the soil model;

[0018] Step S3.3, using the pressure data of the saturation box and the height data of the liquid surface of the soil model to obtain the saturation of the soil model.

[0019] In step S3.3, the saturation of the soil model is obtained according to the following formula:

[0020]

[0021] Among them, S r represents the saturation of the soil model; p1 represents the real-time pressure in the saturation box recorded by the portable data acquisition instrument; Δh represents the height difference of the liquid surface of the soil model under the pressure p1 compared with the initial pressure p0 of the saturation box; A represents the bottom area of ​​the soil model; p a Indicates standard atmospheric pressure; V v Represents the volume of voids in the soil model.

[0022] The measurement accuracy of the present invention can reach 0.1% or higher. Since the measurement accuracy is only related to the gas pressure and vertical displacement, and the measurement accuracy of the digital pressure gauge for measuring gas pressure is usually around 0.1%, and the accuracy of the laser displacement meter can reach micrometer or even nanometer level, the measurement error can be ignored. The accuracy of the traditional theoretical calculation method and wave velocity method is usually only 1%-5%, and may be lower in some special cases. The present invention significantly improves the test accuracy, reaching an improvement of two orders of magnitude over the prior art.

[0023] The implementation of the present invention only requires adding a laser displacement meter for measuring the change in liquid level height and a portable data acquisition instrument to the existing model saturation system for recording and saving data, so as to complete the high-precision measurement of saturation, and the system modification cost is low. In contrast, the compression wave velocity law requires the use of complex and expensive equipment such as oscilloscopes, function generators, charge amplifiers, and piezoelectric elements. The present invention not only greatly simplifies the measurement system and reduces the measurement cost, but also effectively improves the stability and reliability of the system.

[0024] The principle of the present invention is simple, and it does not need to rely on complex theoretical foundations or cumbersome preliminary calibration test processes, which greatly reduces the technical threshold and operational difficulty of saturation measurement. Its high efficiency and convenience enable users to quickly obtain accurate results, while avoiding the decrease in accuracy that may be caused by model complexity or test process errors in traditional methods, significantly improving the practicality and promotion value of measurement work.

[0025] The invention has strong applicability and a wide range of applications. Its core principle is based on the ideal state gas equation and directly measures the gas volume in the model. Compared with traditional methods, the measurement results of the invention are not affected by complex factors such as ion concentration, mineral composition or saturation in the soil. It can still maintain high measurement accuracy under high saturation conditions, has stronger stability and reliability, and is suitable for the precise testing needs of model saturation in a variety of complex environments.

[0026] The data post-processing process of the present invention is simple and efficient. It only needs to perform linear fitting on the measured data to directly calculate the final saturation of the model. In contrast, the compression wave velocity method needs to accurately judge the wave velocity propagation time based on complex signal processing principles, and usually requires the operator to have professional signal processing knowledge. Similarly, the conductivity method also requires cumbersome post-data processing to obtain results. These complex processes undoubtedly increase the difficulty of operation and professional threshold. In comparison, the present invention significantly simplifies the data processing process, making the measurement of saturation more convenient and practical.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention uses a high-precision laser displacement meter, and the measurement accuracy of saturation can reach 0.1% or higher. The present invention significantly improves the test accuracy, achieving an improvement of two orders of magnitude over the prior art.

[0029] 2. The present invention not only greatly simplifies the measurement system and reduces the measurement cost, but also effectively improves the stability and reliability of the system, is simple to operate, and significantly improves the practicality and promotion value of the measurement work.

[0030] 3. The present invention has strong applicability and a wide range of applications. The measurement results are not affected by complex factors such as ion concentration, mineral composition or saturation in the soil. It can still maintain high measurement accuracy under high saturation conditions and has stronger stability and reliability.

[0031] 4. The present invention significantly simplifies the data processing process, making the saturation measurement more convenient and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall composition of the device of the present invention;

[0033] Figure 2 It is the data collected and processed by the embodiment of the present invention.

[0034] In the figure: 1-saturation box; 2-laser displacement meter; 3-target; 4-portable data acquisition instrument; 5-vacuum pressure gauge; 6-soil model. DETAILED DESCRIPTION

[0035] The device of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

[0036] like Figure 1 As shown, the device includes a saturation box 1, a target 3, a soil model 6 and a monitoring component; the soil model 6 to be tested is placed in the saturation box 1, the target 3 is placed on the upper surface of the soil model 6, and the monitoring component is installed on the top of the saturation box 1. The monitoring component is used to collect the position information of the soil model 6 and the pressure in the saturation box 1, and then measure the saturation of the soil model 6 to be tested in the saturation box 1.

[0037] The monitoring component includes a laser displacement meter 2, a portable data acquisition instrument 4 and a vacuum pressure gauge 5; the laser displacement meter 2 and the vacuum pressure gauge 5 are electrically connected to the portable data acquisition instrument 4, and the portable data acquisition instrument 4 is located outside the saturation box 1, the laser displacement meter 2 and the vacuum pressure gauge 5 are both installed on the top of the saturation box 1, and the laser displacement meter 2 is located directly above the target 3, and the laser emitted by the laser displacement meter 2 irradiates the middle of the target 3. The laser displacement meter 2 is used to collect the distance change of the target 3 in the vertical direction, and then obtain the height data of the liquid level in the soil model 6, and send the position information of the target 3 to the portable data acquisition instrument 4, and the vacuum pressure gauge 5 is used to collect the pressure in the saturation box 1, and send the pressure information of the saturation box 1 to the portable data acquisition instrument 4.

[0038] The signal line of the laser displacement meter 2 is connected to the portable data acquisition instrument 4 located outside the saturation box 1 through the opening of the saturation box 1, and the vacuum pressure gauge 5 is used to monitor the pressure change in the saturation box 1. The laser displacement meter 2 is an instrument made by the laser reflection principle for measuring the vertical distance change of the target 3, and the measurement resolution is 10μm or higher. The portable data acquisition instrument 4 uses a device that can record the signal of the laser displacement meter 2.

[0039] The measurement resolution of the laser displacement meter 2 is greater than 10 μm.

[0040] The target 3 is a flat plate that can float on the surface of the liquid in the soil model 6. The target 3 can float up and down with the rise and fall of the liquid level and cannot be fixed on the surface of the soil in the soil model 6. The target 3 needs to have strong reflectivity to facilitate measurement by the laser displacement meter 2. The position where the target 3 is placed on the surface of the soil model 6 is below the laser displacement meter 2.

[0041] An embodiment of the present invention comprises the following steps:

[0042] Step S1, first prepare a soil model 6 and place the prepared soil model 6 to be tested horizontally in a saturation box 1;

[0043] Step S2, then fix the laser displacement meter 2 and the vacuum pressure gauge 5, and then place the target 3 on the surface of the soil model 6 so that the bull's eye of the target 3 is located directly below the laser displacement meter 2;

[0044] Step S3, saturating the soil model 6, measuring the pressure and liquid level data of the saturated soil model 6, and obtaining the saturation of the soil model 6 using the pressure and liquid level data.

[0045] Specifically, step S3 is as follows:

[0046] Step S3.1, saturating the soil model 6. After the soil model 6 is saturated, connecting the laser displacement meter 2 and the vacuum pressure gauge 5 to the portable data acquisition instrument 4;

[0047] Step S3.2, start the portable data acquisition instrument 4, gradually reduce the vacuum degree in the saturation box 1, and record the pressure change data in the saturation box 1 and the height change data of the liquid level in the soil model 6;

[0048] Step S3.3, using the pressure data of the saturation box 1 and the height data of the liquid level of the soil model 6 to obtain the saturation of the soil model 6.

[0049] The principle of step S3.3 is to determine the gas volume of the soil model 6 using the ideal gas state equation, and then calculate the gas volume and saturation of the soil model 6.

[0050] In step S3.3, the saturation of the soil model 6 is obtained according to the following formula:

[0051]

[0052] Among them, S rrepresents the saturation of the soil model 6; p1 represents the real-time pressure in the saturation box 1 recorded by the portable data acquisition instrument 4 (i.e., the pressure data collected by the vacuum pressure gauge 5; Δh represents the height difference of the liquid surface of the soil model 6 under the pressure p1 compared with the initial pressure p0 of the saturation box 1. In the specific implementation, the initial pressure p0 = -90 kPa; A represents the bottom area of ​​the soil model 6; p a Indicates standard atmospheric pressure; V v Represents the volume of the voids in the soil model 6.

[0053] In step S3.3, a pressure-liquid level curve can be drawn based on the pressure-liquid level data collected at different times: the horizontal coordinate of the pressure-liquid level curve is (p a -p1), the ordinate is (p1Δh), for each moment (p a -p1)-(p1Δh) data points are fitted to obtain the pressure-liquid level curve, and then the saturation S of the soil model 6 is obtained using the pressure-liquid level curve. r :

[0054]

[0055] Where k is the slope of the pressure-liquid level curve;

[0056] like Figure 1 As shown in the figure, in the model test, the soil model is 74cm long, 34cm wide and 40cm high. Therefore, the bottom area of ​​the soil model can be obtained as A = 2516cm 2 , the volume is V = 100640 cm 3 Model dry density ρ d =1570kg / m 3 The specific gravity of the soil is G s =2.65. The model is saturated with air-free water, and the density of water is ρ w =1570kg / m 3 According to the following soil mechanics formula, the porosity ratio of the soil can be obtained as e=0.688:

[0057]

[0058] The void ratio of the soil is obtained by calculation. According to the definition of void ratio, the void volume in the soil can be obtained as V according to the following formula v =41019cm 3 :

[0059]

[0060] The model is first placed in the saturation box 1, and then the laser displacement meter 2 is installed on the top cover of the saturation box 1. Subsequently, the target 3 is placed under the laser displacement meter 2, and finally the saturation box 1 is closed.

[0061] When saturated, the saturation box 1 is first evacuated to a vacuum of -90 kPa using a vacuum pump, and then saturated with silicone oil in a vacuum environment. After 72 hours, the model is saturated. After the model is saturated, the laser displacement meter 2 and the vacuum pressure gauge 5 are connected to the portable data acquisition instrument 4, and the portable data acquisition instrument 4 is turned on to ensure that the data acquisition is normal. It is assumed that the gas present in the model conforms to the ideal gas hypothesis and satisfies the following state equation:

[0062] pV g =nRT

[0063] In the formula, n is the amount of gas; T is the temperature; p is the real-time pressure of the gas; V g is the volume of the gas; R is the universal gas constant; during the test, it can be assumed that the temperature remains unchanged, so the volume of the gas is inversely proportional to the current pressure. If the vacuum equipment is slowly controlled to make the pressure in the saturated box 1 gradually rise from the initial p0=-90kPa, then if there is gas in the model, it will shrink, causing the liquid level to drop, and the lower the model saturation, the more gas there is, the greater the drop in the liquid level. The drop in the liquid level can be obtained by monitoring the vertical displacement change of the target 3 through the laser displacement meter 2. The measurement accuracy of the laser displacement meter 2 can usually reach the micron level or even the nanometer level. It has extremely high resolution and accuracy, can capture tiny displacements or deformations, and is insensitive to environmental factors (such as temperature, humidity, vibration). It is particularly suitable for monitoring tiny parameters such as liquid level changes, displacements, and deformations. After the laser displacement meter 2 obtains the settlement Δh under a certain pressure p1, it can be obtained according to the following formula:

[0064]

[0065] In the formula, p a is standard atmospheric pressure, equal to 101 kPa. p1 represents the real-time pressure in the saturation box (1) recorded by the portable data acquisition instrument 4; V1 represents the volume of the gas under the pressure of p1; the gas volume V can be solved by the following formula g The expression is:

[0066]

[0067] Combined with the definition of saturation, we can finally get the expression of saturation S r for:

[0068]

[0069] Among them, V wRepresents the volume of the saturated fluid in the model; V v Represents the volume of the void in the model;

[0070] Therefore, the real-time pressure p1 and settlement Δh collected by the portable data acquisition instrument 4 are (p1Δh)-(p a -p1) coordinates, it will be approximately a straight line. The larger the slope of the straight line, the lower the saturation of the model, and the higher the saturation, the smaller the slope. Figure 2 The experimental data are shown in the example. It can be seen that the experimental data points are similar to those derived theoretically. a -p1) coordinates will resemble a straight line with a slope of k = 0.2025. Substituting this slope into the above formula, we can get:

[0071]

[0072] The bottom area A = 2516cm 2 After substitution, the final model saturation was determined to be 98.76%.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision model soil saturation determination device, characterized in that: The invention comprises a saturation box (1), a target (3), a soil model (6) and a monitoring component; the soil model (6) to be tested is placed in the saturation box (1), the target (3) is placed on the upper surface of the soil model (6), and the monitoring component is installed on the top of the saturation box (1); the monitoring component is used to collect liquid level information of the liquid in the soil model (6) and the pressure in the saturation box (1), and then measure the saturation of the soil model (6) to be tested in the saturation box (1).

2. A high-precision model soil saturation determination device according to claim 1, characterized in that: The monitoring component comprises a laser displacement meter (2), a portable data acquisition instrument (4) and a vacuum pressure gauge (5); the laser displacement meter (2) and the vacuum pressure gauge (5) are both electrically connected to the portable data acquisition instrument (4), and the portable data acquisition instrument (4) is located outside the saturation box (1), the laser displacement meter (2) and the vacuum pressure gauge (5) are both installed on the top of the saturation box (1), and the laser displacement meter (2) is located directly above the target (3), and the laser emitted by the laser displacement meter (2) irradiates the middle of the target (3), and the laser displacement meter (2) is used to collect the distance change of the target (3) in the vertical direction, and send the position information of the target (3) to the portable data acquisition instrument (4); The vacuum pressure gauge (5) is used to collect the pressure in the saturation tank (1) and send the pressure information of the saturation tank (1) to the portable data acquisition instrument (4).

3. A high-precision model soil saturation determination device according to claim 1, characterized in that: The measurement resolution of the laser displacement meter (2) is greater than 10 μm.

4. The high-precision model soil saturation determination device according to claim 1 is characterized in that: The target (3) is a flat plate capable of floating on the surface of the liquid in the soil model (6), and the target (3) floats up and down as the liquid level rises and falls.

5. A high-precision model soil saturation determination method applied to the device described in any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1, firstly prepare a soil model (6) and place the prepared soil model to be tested (6) horizontally in a saturation box (1); Step S2, then fix the laser displacement meter (2) and the vacuum pressure gauge (5), and then place the target (3) on the surface of the soil model (6) so that the bull's eye of the target (3) is located directly below the laser displacement meter (2); Step S3, saturating the soil model (6), measuring the pressure and liquid level data of the saturated soil model (6), and obtaining the saturation of the soil model (6) using the pressure and liquid level data.

6. A high-precision model soil saturation determination method according to claim 5, characterized in that: The step S3 is specifically as follows: Step S3.1, saturating the soil model (6). After the soil model (6) is saturated, connecting the laser displacement meter (2) and the vacuum pressure gauge (5) to the portable data acquisition device (4); Step S3.2, start the portable data acquisition instrument (4), gradually reduce the vacuum degree in the saturation box (1), and record the pressure data in the saturation box (1) and the height data of the liquid level in the soil model (6); Step S3.3, using the pressure data of the saturation box (1) and the height data of the liquid level of the soil model (6), the saturation of the soil model (6) is obtained.

7. A high-precision model soil saturation determination method according to claim 6, characterized in that: In step S3.3, the saturation of the soil model (6) is obtained according to the following formula: Among them, S r represents the saturation of the soil model (6); p1 represents the real-time pressure in the saturation box (1) recorded by the portable data acquisition device (4); Δh represents the height difference of the liquid surface of the soil model (6) under the pressure p1 compared with the initial pressure p0 of the saturation box (1); A represents the bottom area of ​​the soil model (6); p a Indicates standard atmospheric pressure; V v represents the volume of voids in the soil model (6).

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