Hydrophobic soil breakthrough head measurement system and method

Abstract

The application discloses a kind of hydrophobic soil breakthrough water head measuring system and method, belong to geotechnical engineering technical field, including sample cabin, first metal pressure chamber and second metal pressure chamber, sample cabin is placed in second metal pressure chamber, first metal pressure chamber and second metal pressure chamber top are connected by first pipeline, bottom is connected by second pipeline, air pressure control device is connected with first metal pressure chamber and second metal pressure chamber by first pipeline, flowmeter is arranged on second pipeline, data acquisition device and air pressure control device and flowmeter are electrically connected;The application adopts the above-mentioned hydrophobic soil breakthrough water head measuring system and method, realizes pressure accurate regulation and control and breakthrough water head automatic identification by synergic control, and effectively overcomes sidewall seepage and bubble interference by means of all-around infiltration structure, improves the accuracy and repeatability of measurement.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a system and method for measuring breakthrough water head in hydrophobic soil. Background Technology

[0002] With the continuous advancement of transportation infrastructure construction in cold regions, roadbeds are prone to water damage and frost heave under freeze-thaw cycles and moisture migration, severely affecting the stability and durability of road structures. Preventing moisture infiltration and inhibiting capillary water rise are key technical issues in roadbed design for cold regions. Traditional waterproofing and frost protection methods often employ materials such as geotextiles, coarse-grained cushion layers, or waterproof membranes. While these measures can block moisture migration to some extent, they suffer from high construction costs, poor environmental adaptability, easy aging, and easy failure, and cannot achieve a long-term, uniform water-blocking effect from within the soil.

[0003] In recent years, artificially hydrophobic modified soil has attracted attention as a novel impermeable and antifreeze material. This material transforms the soil from hydrophilic to hydrophobic by introducing hydrophobic groups or low surface energy coatings onto the surface of soil particles. This significantly inhibits capillary water rise and the attraction of water by freezing fronts, exhibiting excellent potential for impermeability and frost heave prevention. In cold-region roadbeds, hydrophobic modified soil can form a "water barrier," effectively blocking the migration channels of surface water, groundwater, and capillary water, reducing water supply, and thus lowering the risk of frost heave and roadbed collapsibility.

[0004] In engineering design, the critical breakthrough head is a crucial indicator for evaluating the water-blocking performance of hydrophobic modified soil. It represents the minimum pressure head required for water to overcome the hydrophobic barrier and infiltrate the soil. This parameter directly reflects the reliability of hydrophobic soil in seepage prevention and frost heave prevention applications, and is an important basis for determining the thickness, location, and dosage of the water-repellent layer. Therefore, accurately measuring the breakthrough head of hydrophobic soil is of significant engineering importance for evaluating its seepage prevention performance and designing water-repellent structures for roadbeds in cold regions.

[0005] However, current methods for testing the breakthrough head of hydrophobic modified soils still rely on those used for natural hydrophobic soils. These methods generally suffer from large testing errors, high result dispersion, and difficulty in reflecting actual water-blocking capacity, thus limiting the widespread application of hydrophobic soils in cold-region engineering projects. Therefore, it is necessary to develop a high-precision breakthrough head measurement system suitable for artificial hydrophobic soils to meet their parameter testing requirements in seepage prevention and frost heave prevention design.

[0006] Currently, the determination of breakthrough water head in hydrophobic soils mainly employs capillary rise method, pressure osmosis method, water droplet infiltration time method (WDPT), and contact angle measurement method. These methods were initially used to study the wetting characteristics of natural hydrophobic soils, and their theoretical basis and device structure are mainly based on unidirectional capillary infiltration. They are not suitable for testing the water-blocking performance of artificially hydrophobic modified soils in the fields of seepage prevention and frost heave prevention.

[0007] While the capillary rise method is simple to operate, in strongly hydrophobic media, water struggles to rise along capillary channels, often resulting in localized channel flow or false infiltration, leading to low test results and poor repeatability. Although the pressure osmosis method is the mainstream approach, existing devices are mostly based on modified pressure plates or tensiometer structures, with a single loading direction and uneven water pressure distribution. This easily creates seepage channels between the sample and the container wall, causing water to preferentially infiltrate along the wall, failing to accurately reflect the overall water-blocking performance. The droplet infiltration time method and contact angle measurement method can only qualitatively characterize the strength of hydrophobicity, making it difficult to obtain quantitative breakthrough head suitable for engineering design. While methods such as gas pressure displacement and CT imaging can indirectly observe the infiltration process, the equipment is expensive, the operation is complex, and it is difficult to accurately identify the breakthrough point under dynamic pressurization conditions.

[0008] Furthermore, most existing testing systems only focus on single pressure data at the breakthrough point, lacking continuous monitoring of the entire hydraulic response of the soil sample, and cannot achieve multi-dimensional synchronous acquisition of parameters such as water pressure, volume, and humidity. Insufficient system sealing leads to frequent gas retention and pressure leakage problems; tiny annular gaps exist between the sample and the container wall, allowing water to easily seep along the wall and infiltrate prematurely, reducing measurement accuracy. Existing technologies generally struggle to stably measure the breakthrough head under constant pressure conditions with high precision and small step sizes, and also fail to effectively eliminate error sources such as air bubbles and lateral seepage during experiments. Currently, there is a lack of a high-precision measurement system capable of simulating multi-directional water pressure, achieving omnidirectional infiltration, and accurately identifying the breakthrough head. Summary of the Invention

[0009] The purpose of this invention is to provide a system and method for measuring the critical breakthrough water head of hydrophobic soil, so as to solve the problems of low loading accuracy, large error and poor repeatability of traditional methods. It can accurately measure the critical breakthrough water head of artificial hydrophobic soil, and provide reliable experimental basis for evaluating its seepage prevention and frost heave resistance performance.

[0010] To achieve the above objectives, the present invention provides a system for measuring breakthrough water head in hydrophobic soil, comprising: The sample chamber is used to hold hydrophobic soil samples to be tested. A first metal pressure chamber and a second metal pressure chamber, wherein the first metal pressure chamber is used to contain the infiltration medium and the second metal pressure chamber is used to place the sample chamber, the tops of the first metal pressure chamber and the second metal pressure chamber are connected by a first pipe and the bottoms of the first metal pressure chamber and the second metal pressure chamber are connected by a second pipe; A pneumatic pressure control device is connected to the first metal pressure chamber and the second metal pressure chamber through the first pipeline, and is used to evacuate the first metal pressure chamber and apply positive pressure, and to evacuate the second metal pressure chamber. A flow meter is installed on the second pipeline to measure the volumetric flow rate of the infiltration medium entering the second metal pressure chamber in real time. The data acquisition device is electrically connected to the air pressure control device and the flow meter, and is used to collect and record pressure, volume and flow data in real time, and automatically identify the over-head based on the collected data.

[0011] Preferably, the sample chamber is a cylindrical metal cavity with a top opening and water-permeable side walls and bottom. The sample chamber is supported in the second metal pressure chamber by a bottom support, and an annular cavity is formed between the water-permeable side wall of the sample chamber and the inner wall of the second metal pressure chamber.

[0012] Preferably, a first check valve is provided near the second metal pressure chamber in the first pipeline, and a barometer is provided near the air pressure control device in the first pipeline.

[0013] Preferably, a second check valve is provided on the second pipeline, and the conduction direction of the second check valve is configured to flow from the bottom of the first metal pressure chamber to the bottom of the second metal pressure chamber.

[0014] Preferably, the air pressure control device includes a touch LCD screen and a pressurization control feedback unit.

[0015] A method for measuring breakthrough water head in hydrophobic soil includes the following steps: S1. Load the hydrophobic soil sample into the sample chamber and place the sample chamber in the second metal pressure chamber; S2. Inject the permeation medium into the first metal pressure chamber and evacuate the system using the air pressure control device; S3. Inject the infiltration medium from the first metal pressure chamber into the second metal pressure chamber until the infiltration medium fills the annular cavity and bottom cavity around the sample chamber, surrounding the sample from all sides and bottom. S4. The system is pressurized in stages by the air pressure control device, and the data acquisition device simultaneously records the pressure data of the air pressure control device and the volume data collected by the flow meter, and automatically plots the pressure-volume-time curve. S5. By identifying abrupt changes in the volume data of the infiltrating medium on the pressure-volume-time curve, the corresponding critical pressure value is automatically determined as the breakthrough head of the sample.

[0016] Therefore, the present invention employs the above-mentioned hydrophobic soil breakthrough water head measurement system and method, which has the following beneficial effects: (1) By adopting an all-around infiltration structure, the infiltration medium is applied uniformly from the outer periphery of the sample, which helps to reduce interference such as preferential seepage on the sidewall that is common in traditional unidirectional infiltration, and provides support for obtaining more reliable breakthrough head data.

[0017] (2) The system integrates a high-precision pressure control and data acquisition unit, which can realize stable pressure loading, synchronous monitoring of multiple parameters and automatic identification of breakthrough points, reducing manual intervention and helping to improve test efficiency and the objectivity of results.

[0018] (3) The measurement system can adapt to the testing needs of hydrophobic soils with different characteristics. Its structural design also provides potential for integrated visualization and other extended functions, which helps to support more in-depth mechanism research and application.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a structural layout diagram of a hydrophobic soil breakthrough water head measurement system according to the present invention; Figure 2 This is a flowchart of a method for measuring breakthrough water head in hydrophobic soil according to the present invention; Reference numerals: 1. Sample chamber; 2. First metal pressure chamber; 3. Second metal pressure chamber; 4. Second check valve; 5. First check valve; 6. Barometer; 7. Pressure control device; 8. Bottom support; 9. Data acquisition device; 10. Flow meter; 11. First pipeline; 12. Second pipeline. Detailed Implementation

[0021] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0022] Example like Figure 1 As shown, this invention provides a hydrophobic soil breakthrough water head measurement system, including a sample chamber 1, a first metal pressure chamber 2, a second metal pressure chamber 3, a pressure control device 7, a data acquisition device 9, and a flow meter 10. Sample chamber 1 is a cylindrical metal cavity with an open top, permeable side walls and bottom, and a pressure rating of MPa. Its internal dimensions are Ø39.1mm*80mm. It is used to hold the hydrophobic soil sample to be tested. The sample can be compacted to the target compaction degree within sample chamber 1. Sample chamber 1 is suspended within the second metal pressure chamber 3 via a bottom support 8, thus connecting the bottom of sample chamber 1 with the bottom cavity of the second metal pressure chamber 3. An annular cavity is formed between the permeable side wall of sample chamber 1 and the inner wall of the second metal pressure chamber 3, avoiding preferential infiltration caused by direct pressure on the bottom. This ensures that during the test, the infiltration medium can apply pressure simultaneously and uniformly from the bottom and circumference of the sample, achieving omnidirectional infiltration. The physical structure eliminates the preferential seepage path on the side walls caused by uneven water pressure distribution, providing a basis for accurate measurement.

[0023] The first metal pressure chamber 2 and the second metal pressure chamber 3 are cylindrical sealed metal containers capable of withstanding pressures of several megapascals, ensuring the safety and stability of the system under high-pressure testing. The first metal pressure chamber 2 is used to hold the infiltration medium. In the preparation stage, air in the infiltration medium is removed by evacuating the vacuum environment in the first metal pressure chamber 2. In the testing stage, the infiltration medium is pressurized and forced into the second metal pressure chamber 3, where the sample is infiltrated. The second metal pressure chamber 3 is used to hold the sample chamber 1. In the preparation stage, air in the sample pores of the sample chamber 1 is removed by evacuating the vacuum environment. In the pressurization stage, the infiltration medium is pressurized to infiltrate the sample to be tested through the sample chamber 1. In the pressurization testing stage, the top air chamber is in a sealed state. The top of the first metal pressure chamber 2 and the second metal pressure chamber 3 is connected by the first... A pipeline 11 is connected, and a first one-way valve 5 is installed on the first pipeline 11. During the system vacuuming stage, the first one-way valve 5 is opened to ensure that the gas pressure control device can simultaneously extract the gas from the first metal pressure chamber 2 and the second metal pressure chamber 3 to discharge the gas in the top space of the two metal pressure chambers and the sample pores. The bottoms of the first metal pressure chamber 2 and the second metal pressure chamber 3 are connected through a second pipeline 12, and a second one-way valve 4 is installed on the second pipeline 12. The conduction direction of the second one-way valve 4 is configured to flow from the bottom of the first metal pressure chamber 2 to the bottom of the second metal pressure chamber 3. During the pressurization stage, the second one-way valve 4 is opened to allow the infiltration medium to flow from the first metal pressure chamber 2 into the second metal pressure chamber 3 under gas pressure and infiltrate the sample in the second metal pressure chamber 3, while preventing the medium from flowing backward.

[0024] The pneumatic control device 7 is connected to the first metal pressure chamber 2 and the second metal pressure chamber 3 through the first pipeline 11. It is used to evacuate the first metal pressure chamber 2 and apply positive pressure, and to evacuate the second metal pressure chamber 3. The pressure control range of the pneumatic control device 7 is -0.1MPa ~ 1.4MPa, with a resolution of no more than 1kPa and an absolute accuracy of no more than 3kPa. It can evacuate air to a vacuum state and can also pressurize the infiltration medium into the sample pores. In the preparation stage, a vacuum environment is evacuated to remove air from the sample pores and the infiltration medium. In the pressurization stage, the first one-way valve 5 is closed to ensure that the pressurization can smoothly pressurize the infiltration medium into the first metal pressure chamber 2, allowing the infiltration medium to infiltrate the sample. It is equipped with a touch LCD screen and a pressurization control feedback unit. A barometer 6 is installed near the pneumatic control device 7 on the first pipeline 11 for real-time monitoring of the system vacuum degree and loading pressure. The flow meter 10 is installed on the second pipeline 12 and is used to measure the volumetric flow rate of the infiltration medium entering the second metal pressure chamber 3 in real time. It can be a high-precision electromagnetic flow sensor with a range of 0 to 10 L / min, a resolution of no more than 0.01 L / min, and a measurement error of no more than ±0.5%.

[0025] The data acquisition device 9 is electrically connected to the air pressure control device 7 and the flow meter 10. It is used to collect and record pressure, volume and flow data in real time, and automatically identify the over-head based on the collected data.

[0026] like Figure 2 As shown, a method for measuring breakthrough water head in hydrophobic soil includes the following steps: S1. Weigh a predetermined mass of hydrophobic soil sample, load the hydrophobic soil sample into sample chamber 1, and compact it in layers in sample chamber 1 to the target density. To prevent fine particles from clogging the permeable pores of sample chamber 1 during compaction, lay a layer of filter paper on the inner wall and bottom of sample chamber 1 as protection. After the sample is filled, place sample chamber 1 in the second metal pressure chamber 3.

[0027] S2. Inject the permeation medium into the first metal pressure chamber 2, ensuring that there are no residual air bubbles in the permeation medium. Close the second one-way valve 4 and open the first one-way valve 5. Set the target vacuum degree to -0.1MPa through the touch screen of the air pressure control device 7 and start the vacuuming program. When the air pressure gauge 6 displays that the system vacuum degree has reached -0.1MPa, stop the air pumping and maintain this vacuum state for 1 to 2 hours. This operation is to use the negative pressure environment to fully dissolve and remove the tiny air bubbles remaining in the sample pores, pipelines and permeation medium, and eliminate the interference of air bubbles on subsequent measurements.

[0028] S3. Close the first one-way valve 5 and open the second one-way valve 4. Slowly apply positive pressure to the first metal pressure chamber 2 through the air pressure control device 7 to inject the infiltration medium from the first metal pressure chamber 2 into the second metal pressure chamber 3 until the infiltration medium fills the annular cavity and bottom cavity around the sample chamber 1, surrounding the sample from all sides and bottom. During this process, the operator needs to observe the change in the reading of the flow meter 10. When the flow rate approaches zero, it can be determined that the infiltration medium has completely filled the bottom cavity of the second metal pressure chamber 3 and the annular cavity around the sample chamber 1, surrounding the sample from all sides and bottom. At this point, a sealed, near-vacuum low-pressure air cavity is formed at the top of the second metal pressure chamber 3.

[0029] S4. Keep the first check valve 5 closed and the second check valve 4 open. Pressurize the first metal pressure chamber 2 in stages through the pneumatic control device 7. Each stage is maintained for a sufficient time to stabilize the system. Pressurization causes the infiltrating medium to generate controlled hydraulic pressure. This pressure is transmitted to the second metal pressure chamber 3 through the second pipeline 12, thereby forming a stable infiltrating confining pressure at the bottom and sides of the sample. The data acquisition device 9 simultaneously records the pressure data of the pneumatic control device 7 and the volume data collected by the flow meter 10, and automatically plots the pressure-volume-time curve. S5. Analyze the pressure-volume-time curve. When the applied confining pressure is lower than the breakthrough head of the sample, the cumulative infiltration volume changes very slowly with time (the curve is flat). When the confining pressure reaches and exceeds the breakthrough head, the curve shows an obvious inflection point, and the cumulative infiltration volume begins to increase significantly. The data acquisition device 9 automatically determines the corresponding critical pressure value as the breakthrough head of the sample by identifying the abrupt change point of the infiltration medium volume data on the pressure-volume-time curve.

[0030] Therefore, the present invention employs the above-mentioned hydrophobic soil breakthrough head measurement system and method, which can achieve continuous and steady-state pressure adjustment and use a data acquisition system to monitor pressure and water inflow in real time to automatically identify breakthrough head; at the same time, the omnidirectional infiltration structure adopted by the system ensures uniform water pressure distribution, effectively eliminates sidewall seepage and bubble interference, thereby improving the accuracy and repeatability of measurement.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A hydrophobic soil breakthrough head measurement system, characterized by, include: The sample chamber is used to hold hydrophobic soil samples to be tested. A first metal pressure chamber and a second metal pressure chamber, wherein the first metal pressure chamber is used to contain the infiltration medium and the second metal pressure chamber is used to place the sample chamber, the tops of the first metal pressure chamber and the second metal pressure chamber are connected by a first pipe and the bottoms of the first metal pressure chamber and the second metal pressure chamber are connected by a second pipe; The sample chamber is a cylindrical metal cavity with a top opening and water-permeable side walls and bottom. The sample chamber is supported in the second metal pressure chamber by a bottom support. An annular cavity is formed between the water-permeable side wall of the sample chamber and the inner wall of the second metal pressure chamber. A pneumatic pressure control device is connected to the first metal pressure chamber and the second metal pressure chamber through the first pipeline, and is used to evacuate the first metal pressure chamber and apply positive pressure, and to evacuate the second metal pressure chamber. A flow meter is installed on the second pipeline to measure the volumetric flow rate of the infiltration medium entering the second metal pressure chamber in real time. The data acquisition device is electrically connected to the air pressure control device and the flow meter, and is used to collect and record pressure, volume and flow data in real time, and automatically identify the over-head based on the collected data.

2. A hydrophobic soil breakthrough head measurement system according to claim 1, wherein: A first check valve is installed near the second metal pressure chamber in the first pipeline, and a barometer is installed near the air pressure control device in the first pipeline.

3. The hydrophobic soil breakthrough water head measurement system according to claim 1, characterized in that: A second check valve is provided on the second pipeline, and the conduction direction of the second check valve is configured to flow from the bottom of the first metal pressure chamber to the bottom of the second metal pressure chamber.

4. The hydrophobic soil breakthrough water head measurement system according to claim 1, characterized in that: The air pressure control device includes a touch LCD screen and a pressurization control feedback unit.

5. A method for measuring breakthrough water head in hydrophobic soil, applied to a hydrophobic soil breakthrough water head measurement system as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Load the hydrophobic soil sample into the sample chamber and place the sample chamber in the second metal pressure chamber; S2. Inject the permeation medium into the first metal pressure chamber and evacuate the system using the air pressure control device; S3. Inject the infiltration medium from the first metal pressure chamber into the second metal pressure chamber until the infiltration medium fills the annular cavity and bottom cavity around the sample chamber, surrounding the sample from all sides and bottom. S4. The system is pressurized in stages by the air pressure control device, and the data acquisition device simultaneously records the pressure data of the air pressure control device and the volume data collected by the flow meter, and automatically plots the pressure-volume-time curve. S5. By identifying abrupt changes in the volume data of the infiltrating medium on the pressure-volume-time curve, the corresponding critical pressure value is automatically determined as the breakthrough head of the sample.

Images