CN113720870A - Testing device and testing method for researching local deformation characteristics of frozen soil - Google Patents
Testing device and testing method for researching local deformation characteristics of frozen soil Download PDFInfo
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- G01N25/00—Investigating or analyzing materials by the use of thermal means
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Abstract
The invention provides a testing device and a testing method for researching local deformation characteristics of frozen soil, belonging to the technical field of experimental equipment. The testing device and the testing method for researching the local deformation characteristics of the frozen soil can track the local deformation of the frozen soil in real time. The problem that the original PIV technology cannot be applied to frozen soil tests is effectively solved. The provided sample texture construction method effectively enhances the surface texture characteristics of frozen soil, reduces the gray scale correlation error caused by ice-water phase change, and enables the PIV method to be applied to frozen soil testing; the defect that the traditional experiment can only obtain the total deformation of the sample and cannot obtain the local deformation is overcome; the decoupling analysis of the frost heaving process of the quantitative angle under the load effect is realized. The temperature field, the moisture field and the displacement field are decoupled, and the respective quantification of various factors influencing frost heaving is realized.
Description
Technical Field
The invention belongs to the technical field of experimental equipment, and particularly relates to a testing device and a testing method for researching local deformation characteristics of frozen soil.
Background
Frozen soil generally refers to various soil bodies which have a temperature below 0 ℃ and contain ice. Because the frozen soil is a complex ice, water, gas and solid four-phase body, the original pores in the frozen soil are redistributed due to the repeated phase change of the ice water under the action of external load, and macroscopically, the large plastic deformation of the frozen soil is shown. Therefore, frozen earth has more complicated deformation characteristics than ordinary earth. Pore ice freezing-thawing segregation is a main cause of diseases generated in engineering in a freezing region, frozen soil bodies caused by freezing-thawing of the segregation ice are more harmful to linear engineering such as railways, highways and the like in the freezing region, and the safety and stability of buildings are seriously threatened. The frozen soil is widely distributed in China and spans half of the territory of China. With the rapid development of the transportation in China, the engineering construction in cold areas in China is briskly rising. According to investigation and statistics, the soil body in the seasonal freezing area can generate uneven frost heaving due to uneven soil quality, moisture and freezing conditions. The development of frost heaving not only can cause a series of engineering diseases such as uneven uplift of buildings, unsmooth tracks, frost cracks on road surfaces and the like, but also can cause repeated change of the internal structure of the soil body, thereby causing the change of the internal mechanical property of the soil body; in addition, the phenomena of heavy train and overload are serious, the disasters such as slurry turning, mud pumping, hot melt collapse and the like of the roadbed in the seasonal frozen soil area under the synergistic action of freeze-thaw cycle and heavy-load vehicles are more serious than the disasters in the past, the reasons are more complicated, the economic loss is more serious, and the operation safety of the train is seriously threatened. Therefore, it is important to study the frost heaving deformation characteristics of the frozen soil.
At present, frost heaving deformation research of soil bodies mainly focuses on frozen soil or melted soil after freeze-thaw cycle, and the deformation rule of the frozen soil is researched rarely. The research on the soil body frost heaving under the load effect only comprises the change processes of temperature, water supply and the whole frost heaving amount of the sample at present, and cannot be organically combined with the local deformation (the frost heaving process of a frozen area and the compression process of an unfrozen area) and the whole refrigeration structure evolution in the sample frost heaving process. The deformation of one-dimensional frozen earth can be generally divided into three stages over time: an initial rapid expansion phase, a retarded expansion phase and a tendency to stabilize phase. In the initial rapid expansion stage, the freezing frontal surface gradually moves downwards, and the frost heaving mainly takes the in-situ frost heaving of pore water as the main component; in the deceleration expansion section, the freezing frontal surface is gradually stabilized, and the frost heaving form is gradually transited from in-situ frost heaving to segregation frost heaving; in the stabilization phase, the frost heave pattern is mainly migration frost heave of pore water. Different cold-growing sections can be formed in the three stages, a testing device is not available at present, and the local deformation characteristics of soil bodies with different depths can be quantitatively measured in the one-dimensional deformation process of the frozen soil under different load working conditions.
Disclosure of Invention
The invention aims to provide a test device and a test method for researching local deformation characteristics of frozen soil, and aims to solve the problem that the existing frozen soil deformation test equipment cannot conveniently and visually measure the local deformation characteristics of soil bodies with different depths in a one-dimensional deformation process of the frozen soil under different load working conditions.
In order to achieve the purpose, the invention adopts the technical scheme that: the test device for researching the local deformation characteristics of the frozen soil comprises:
the temperature adjusting box body is used for maintaining a constant experimental environment;
the temperature control box comprises a temperature control box body, a sample cylinder and a control device, wherein the temperature control box body is internally provided with a temperature control box body, a measuring scale arranged along the length direction of the sample cylinder is arranged on the side wall of the sample cylinder, a plurality of small holes of sensing units for measuring sample data are arranged on the side wall of the sample cylinder, and the sensing units are sequentially arranged at intervals along the height direction of the sample cylinder;
the bottom plate is arranged in the temperature adjusting box body and positioned at the bottom of the sample cylinder, and a first temperature control structure for maintaining the temperature change of the sample is also arranged in the bottom plate;
the water replenishing plate body is attached to the upper part of the bottom plate and is positioned at the end part of the sample cylinder close to the bottom plate, and a water replenishing pipeline communicated with a water replenishing system through a pipeline is further arranged in the water replenishing plate body;
the top plate is arranged in the sample cylinder, is positioned at the top of the sample cylinder, covers the top of the sample in the sample cylinder and is used for pressing the sample in a region between the water supplementing plate body and the top plate, and a second temperature control structure for maintaining the temperature change of the sample is also arranged in the top plate;
the pressure unit is arranged in the temperature adjusting box body, and the driving end of the pressure unit is positioned above the top plate and used for applying pressure to the sample in the sample cylinder through the top plate;
the image acquisition unit is arranged on the side surface of the sample cylinder and used for monitoring the deformation of the sample;
and the data processing unit is electrically connected with the image acquisition unit, electrically connected with the plurality of sensing units on the sample cylinder and used for receiving and processing signals acquired by the image acquisition unit and the sensing units.
As another embodiment of this application, first control by temperature change structure is the serpentine channel who sets up in the bottom plate inside, second control by temperature change structure is also the serpentine channel who sets up in the roof inside, serpentine channel all passes through the pipeline intercommunication with outside cold bath device.
As another embodiment of this application, the moisturizing plate body is in including supporting the basic unit and setting the supporting the basic unit is close to the reservoir stratum on sample one side, the moisturizing pipeline all sets up supporting on the basic unit and running through supporting the basic unit setting.
As another embodiment of this application, the inner wall of sample section of thick bamboo with still be provided with seal ring between the moisturizing plate body, seal ring cover is established the week of moisturizing plate body, still be provided with on the week of moisturizing plate body and hold the recess.
As another embodiment of the application, the pressure unit comprises a base, a support frame body arranged on the base, a load actuator movably arranged on the support frame body, and a loading device for driving the load actuator to move.
As another embodiment of this application, still be provided with four on the base with sample cylinder parallel arrangement's bracing piece, the top of sample cylinder still is provided with the flange that is used for fixed sample cylinder, two bracing piece one end runs through the flange and sets up the other end and pass the base setting, the tip of bracing piece is provided with the stop nut who is used for hold-down flange and base.
As another embodiment of the present application, a displacement sensor for monitoring macroscopic deformation of the sample is further disposed above the sample cylinder, the displacement sensor is disposed on the flange, and the displacement sensor is electrically connected to the data processing unit.
The test device for researching the local deformation characteristics of the frozen soil provided by the invention has the beneficial effects that: when the experiment for measuring the local deformation of the frozen soil is carried out, a sample is firstly placed on a water supplementing plate body positioned in a temperature adjusting box body, the sample is compacted in a sample cylinder in a layering mode, then tracer particles with certain thickness and width are paved on the collection side surface of the sample, the compaction and particle paving of a lower-layer soil sample are carried out until the height of the sample is required, the prepared sample is compacted in a layering mode, and the tracer particles are paved in a layering mode. And finally, placing the top plate above the sample in the sample cylinder to finish installation. Then the pressure unit can apply a certain load to the sample through the top plate according to the experiment requirements, the image acquisition unit takes pictures at intervals and transmits the taken images to the data processing unit, and the acquired tracer particle image area is subjected to image convolution through a normalized image cross-correlation algorithm. The displacement field (unit: pixel) of the measuring surface is inversely calculated through the result of the position of the correlation peak obtained by image convolution. And converting the original displacement field according to the measurement results of the graduated scale and the displacement meter to obtain the full-field deformation results of the frozen soil at different times and different depths. The water supplementing plate body and the water supplementing system can supplement water lost by upward migration of the water at the lower part of the sample under the action of negative temperature suction force in the freezing process, and the stability of the water in the sample is ensured. The testing device for researching the local deformation characteristics of the frozen soil is used for constructing the surface texture of the soil body, taking pictures at intervals by the image acquisition unit, analyzing the change rule of the surface texture of the sample, and tracking the local deformation of the frozen soil in real time by the correlation analysis of the interval picture sequence. The problem that the original PIV technology cannot be applied to frozen soil tests is effectively solved. The provided sample texture construction method can effectively enhance the surface texture characteristics of frozen soil and reduce the gray scale correlation error caused by ice-water phase change, so that the PIV method can be applied to frozen soil testing; the defect that the traditional experiment can only obtain the total deformation of the sample and cannot obtain the local deformation is overcome; the decoupling analysis of the frost heaving process of the quantitative angle under the load effect is realized. The temperature field, the moisture field and the displacement field are decoupled, and the respective quantification of various factors influencing frost heaving is realized. The local deformation characteristics of soil bodies with different depths in the one-dimensional deformation process of the frozen soil under different load working conditions can be conveniently and visually measured.
The invention also provides a test method for researching the local deformation characteristics of frozen soil, which uses the test device for researching the local deformation characteristics of frozen soil as claimed in any one of claims 1 to 8, and comprises the following steps:
preparing a sample, namely preparing a soil sample with a certain water content according to the requirement of the experimental design, placing the prepared soil sample in a sealed container, standing the soil sample for 22-26 hours, and taking out the soil sample from the sealed container for later use;
mounting a sample cylinder, namely mounting a water replenishing disc body at the bottom of the sample cylinder, maintaining the seal between the sample cylinder and the water replenishing disc body, placing the sample cylinder on a bottom plate, and paving filter paper at the bottom of the sample cylinder;
the method comprises the following steps of compacting a soil sample in a layering manner, taking a certain amount of soil sample and trace particles, firstly placing the soil sample in a sample cylinder, compacting the soil sample in the sample cylinder in the layering manner through a compaction hammer, then paving the trace particles with a certain thickness and width on the acquisition side surface of the sample, and then sequentially compacting the soil sample at the lower layer and paving the particles until the required sample height is reached, wherein the prepared sample is compacted in a layering manner, and the trace particles are paved in a layering manner;
fixing a sample cylinder, placing a layer of filter paper on the top of the compacted soil sample, covering a top plate on the top of the soil sample, pressing a fixing flange on the end part of the sample cylinder and fixing the sample cylinder through a limiting nut;
the external equipment is connected, and the cold bath equipment is respectively connected with the top plate and the mounting base to form refrigeration cycle; connecting the March's flask with a water replenishing port of a water replenishing plate body, opening a water replenishing valve to adjust the height of the March's flask so that the liquid level in the March's flask and the bottom of the soil sample are positioned on the same plane, and then fixing the March's flask and closing the valve;
and data acquisition and recording, and adjusting the positions of the image acquisition unit and the illumination unit so as to clearly capture the change of the surface texture of the soil body. Simultaneously starting the cold bath device and the freeze-thaw test chamber, setting the temperature in the freeze-thaw test chamber at 5 ℃ for temperature control, and opening a valve of the Mariotte bottle when the internal temperature of the soil body is stabilized at 5 ℃; applying a load with specified frequency and amplitude by an actuating device of a loading instrument; meanwhile, the cold bath device connected with the top plate is adjusted to-10 ℃, data of the temperature sensor, the moisture sensor and the image acquisition unit are acquired once every 10min through the data acquisition instrument and are transmitted to the data processing unit, and the water level change of the Martensity bottle is recorded once every 2 h;
and (3) data calculation, wherein the data processing unit is used for sorting the data collected by the image acquisition unit, the temperature sensing unit and the moisture sensing unit and carrying out image convolution on the acquired tracer particle image area through a normalized image cross-correlation algorithm. The displacement field (unit: pixel) of the measuring surface is inversely calculated through the result of the position of the correlation peak obtained by image convolution. According to the measuring results of the graduated scale and the displacement meter, the original displacement field is converted, the full-field deformation results of the frozen soil at different depths at different moments can be obtained, and then the results are displayed through a display device.
In another embodiment of the present application, in the step of compacting the soil sample by layers, the trace particles are black quartz sand and white quartz sand.
Compared with the prior art, the test method for researching the local deformation characteristics of the frozen soil provided by the invention has the advantages that the change rule of the surface texture of the sample is analyzed by constructing the surface texture of the soil body and taking pictures at intervals by the image acquisition unit, and the local deformation of the frozen soil can be tracked in real time by analyzing the correlation of the interval picture sequence. The problem that the original PIV technology cannot be applied to frozen soil tests is effectively solved. The provided sample texture construction method can effectively enhance the surface texture characteristics of frozen soil and reduce the gray scale correlation error caused by ice-water phase change, so that the PIV method can be applied to frozen soil testing; the defect that the traditional experiment can only obtain the total deformation of the sample and cannot obtain the local deformation is overcome; the decoupling analysis of the frost heaving process of the quantitative angle under the load effect is realized. The temperature field, the moisture field and the displacement field are decoupled, and the respective quantification of various factors influencing frost heaving is realized. The local deformation characteristics of soil bodies with different depths in the one-dimensional deformation process of the frozen soil under different load working conditions can be conveniently and visually measured.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a testing device for studying local deformation characteristics of frozen soil according to an embodiment of the present invention;
fig. 2 is a cross-sectional structural view of the base plate and the water supplement plate body according to the embodiment of the present invention.
FIG. 3 is a schematic structural diagram of a base plate used in an embodiment of the present invention;
FIG. 4 is a schematic diagram of a sample cartridge used in an embodiment of the present invention;
FIG. 5 is a schematic structural view of a top plate employed in an embodiment of the present invention;
FIG. 6 is a schematic cross-sectional view of a top plate used in an embodiment of the present invention;
in the figure: 1. a temperature regulating box body; 2. a base; 3. a lighting unit; 4. a support bar; 5. a base plate; 6. a water supplementing plate body; 61. a support base layer; 62. a water storage layer; 7. a moisture sensor; 8. a temperature sensor; 9. a sample; 10. an image acquisition unit; 11. a water replenishing system; 12. a sample cartridge; 13. a heat-insulating layer; 14. a top plate; 15. a flange; 16. a limit nut; 17. a displacement sensor; 18. a load actuator; 19. a support frame body; 20. a first temperature control structure; 21. a second temperature control structure; 22. a serpentine channel; 23. a data processing unit; 24. a data acquisition unit; 25. a cold bath device; 26. and (4) loading the device.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Referring to fig. 1 and fig. 2 together, the testing device for studying local deformation characteristics of frozen soil according to the present invention will now be described. The testing device for researching the local deformation characteristics of the frozen soil comprises a temperature adjusting box body 1, a bottom plate 5, a sample cylinder 12, a water supplementing plate body 6, a top plate 14, a pressure unit, a data processing unit 23 and an image acquisition unit 10. The temperature adjusting box body 1 is used for maintaining a constant experimental environment; the sample cylinder 12 is arranged in the temperature adjusting box body 1, a measuring scale arranged along the length direction of the sample cylinder 12 is arranged on the side wall of the sample cylinder 12, a plurality of small holes of sensing units for measuring data of a sample 9 are arranged on the side wall of the sample cylinder 12, and the sensing units are sequentially arranged at intervals along the height direction of the sample cylinder 12; the bottom plate 5 is arranged in the temperature adjusting box body 4 and is positioned at the bottom of the sample cylinder 12, and a first temperature control structure 20 for maintaining the temperature change of the sample is also arranged in the bottom plate 5; the water supplementing plate body 6 is attached to the upper side of the bottom plate 5 and is positioned at the end part, close to the bottom plate 5, of the sample cylinder 12, and a water supplementing pipeline communicated with the water supplementing system 11 through a pipeline is further arranged inside the water supplementing plate body 6; the top plate 14 is arranged in the sample cylinder 12, is positioned at the top of the sample cylinder 12, and covers the top of the sample 9 in the sample cylinder 12, and is used for pressing the sample 9 in the area between the water supplementing plate body 6 and the top plate 14; a second temperature control structure 21 for maintaining the temperature change of the sample is also arranged in the top plate 14, the pressure unit is arranged in the temperature adjusting box body 1, and the driving end of the pressure unit is positioned above the top plate 14 and is used for applying pressure to the sample 9 in the sample cylinder 12 through the top plate 14; the image acquisition unit 10 is arranged on the side surface of the sample cylinder 12 and is used for monitoring the deformation of the sample 9; the data processing unit 23 is electrically connected to the image capturing unit 10, and electrically connected to the plurality of sensing units on the sample barrel 12, and is configured to receive and process signals captured by the image capturing unit 10 and the sensing units.
Compared with the prior art, the testing device for researching the local deformation characteristics of the frozen soil provided by the embodiment is characterized in that when a local deformation measurement experiment of the frozen soil is carried out, a certain amount of soil sample and trace particles are taken, the soil sample is firstly placed in a sample cylinder, the sample cylinder is subjected to layered compaction through a compaction hammer, then the trace particles with certain thickness and width are paved on the acquisition side surface of a sample 9, then compaction and particle paving of the soil sample on the lower layer are sequentially carried out until the required sample height is reached, the prepared sample is subjected to layered compaction, the trace particles are paved in layers, and finally a top plate 14 is placed above the sample 9 in the sample cylinder 12 to complete installation. Then, after a certain load is applied to the sample 9 through the top plate 14 according to experimental requirements through the pressure unit, pictures are taken at intervals through the image acquisition unit 10, the shot images are transmitted to the data processing unit 23, and image convolution is performed on the acquired tracer particle image area through a normalized image cross-correlation algorithm. The displacement field (unit: pixel) of the measuring surface is inversely calculated through the result of the position of the correlation peak obtained by image convolution. And converting the original displacement field according to the measurement results of the graduated scale and the displacement meter to obtain the full-field deformation results of the frozen soil at different times and different depths. The water supplementing plate body 6 and the water supplementing system 11 can supplement water lost due to the fact that water at the bottom of the sample 9 migrates upwards under the action of negative temperature suction, the stability of the water at the bottom of the sample 9 is guaranteed, and frost heaving deformation of a soil body under groundwater replenishment can be simulated. The testing device for researching the local deformation characteristics of the frozen soil comprises a testing device and an image acquisition unit 10, wherein the testing device is used for constructing the surface texture of the soil body, taking pictures at intervals by the image acquisition unit 10, analyzing the change rule of the surface texture of a sample 9, and tracking the local deformation of the frozen soil in real time by the correlation analysis of an interval picture sequence. The problem that the original PIV technology cannot be applied to frozen soil tests is effectively solved. The provided pattern method can effectively enhance the surface texture characteristics of frozen soil, reduce the gray scale correlation error caused by ice-water phase change, and enable the PIV method to be applied to frozen soil testing; the defect that the traditional experiment can only obtain the total deformation of the sample 9 and cannot obtain the local deformation is overcome; the decoupling analysis of the frost heaving process of the quantitative angle under the load effect is realized. The temperature field, the moisture field and the displacement field are decoupled, and the respective quantification of various factors influencing frost heaving is realized. The local deformation characteristics of soil bodies with different depths in the one-dimensional deformation process of the frozen soil under different load working conditions can be conveniently and visually measured.
In this embodiment, as a preferred embodiment, the temperature adjustment box 1 generally adopts a freeze-thaw test chamber, and the whole experimental apparatus is located in the freeze-thaw test chamber during the experiment, so as to prevent the interference of the external environment and maintain the temperature stability in the experimental environment. The image acquisition unit 10 preferably adopts an adjusting industrial camera, and the model is MV-EM510C industrial camera, so that interval photographing can be performed for a long time, the photographing definition is higher, the photographing effect of the image is improved, and the detected data is more accurate.
In this embodiment, as a preferred embodiment, the sensing unit includes a temperature sensor 8 and a moisture sensor 7, and the temperature sensor 8 and the moisture sensor 7 both penetrate into the sample 9 to a certain depth through a mounting hole provided in a sidewall of the sample tube 12. The change and the relation of a displacement field, a temperature field, a moisture field and a cold growing structure of the soil body can be monitored in real time. The number of the temperature sensors is multiple, the temperature sensors 8 are sequentially arranged at intervals along the length direction of the sample cylinder 12, and the interval between the two temperature sensors 8 is 2 cm. The plurality of temperature sensors 8 are spirally arranged on the outer wall of the sample tube 12. The number of the moisture sensors 7 is plural, the moisture sensors 7 are sequentially provided at intervals in the longitudinal direction of the sample tube 12, and the moisture sensors 7 are spirally distributed on the outer wall of the sample tube 12. The diameter of the prepared sample 9 is 15cm, the height is 20cm, two temperature sensors 8 are arranged in the center of the sample 9 at intervals of 2cm from top to bottom, and two moisture sensors 7 are arranged on a sample cylinder 12 at intervals of 4 cm. The temperature sensor 8 is a platinum thermistor type PT100 sensor; the displacement sensor 17 is a split type displacement meter with high precision. The data processing unit 23 is a computer, data acquisition is arranged between the data processing unit 23 and each electrical element, and the type of the data acquisition instrument is preferably dataTaker DT 85.
In the present embodiment, as a preferred embodiment, the illumination unit 3 is further provided on the side surface of the sample tube 12, and the number of the illumination units 3 is two, and the two illumination units are respectively provided at the upper end and the lower end of the sample tube 12.
The PIV (particle image velocimetry) technology is a non-contact full-field displacement measurement technology based on array image correlation analysis. Originally, it was widely used for flow field measurements. Some researchers consider the soil as a low velocity fluid and measure PIV geotechnical engineering. Although the PIV technology is widely applied to geotechnical engineering, the PIV technology is applied to a small number of frozen soil deformation measurement test devices, particularly the deformation measurement of frozen soil under the action of load. The reason for analyzing the method mainly comprises the following steps: (1) for soil with a single color, selecting proper tracer particles to construct surface textures of the sample 9; (2) the ice water phase change effect can change the gray scale range of the image before and after freeze thawing, reduce the gray scale correlation of the image and cause the search failure of the displacement correlation; (3) under the coupling action of a stress field and a temperature field, freezing and thawing segregation of pore ice and migration and freezing of pore water can cause large plastic deformation of a soil body. The deformation of the soil body is more complex, and the local deformation state of the frozen soil is difficult to capture. By means of the PIV technology, the local deformation characteristics of the soil body can be accurately analyzed, and the deformation characteristics of the frozen soil under the load effect can be visually displayed. In order to further explore the local deformation mechanism of the frozen soil, it is necessary to develop a visual deformation measurement test device and method for researching the frozen soil under the action of load.
Referring to fig. 3 together, a first temperature control structure 20 for maintaining the temperature of the sample 9 in the sample cylinder 12 is disposed in the bottom plate 5, a second temperature control structure 21 for maintaining the temperature of the sample 9 in the sample cylinder 12 is also disposed in the top plate 14, and the first temperature control structure 20 and the second temperature control structure 21 are both in communication with the cold bath device 25 through a pipeline. The first temperature control structure 20 and the second temperature control structure 21 are communicated with the cold bath device 25 through pipelines to form a temperature control system, so that the temperature constancy of the two ends of the sample 9 in the sample cylinder 12 can be ensured, the influence of temperature change on data in the experimental process is eliminated, the measurement of the local deformation characteristic of frozen soil is more accurate, and the temperature regulation is more convenient.
Referring to fig. 2 and 3, as an embodiment of the testing device for studying local deformation characteristics of frozen soil provided by the present invention, the first temperature control structure 20 is a serpentine channel 22 disposed inside the bottom plate 5, the second temperature control structure 21 is also a serpentine channel 22 disposed inside the top plate 14, and the serpentine channels 22 are all in pipeline communication with the cooling bath device 25. The preferred cold bath machine that adopts of cold bath device 25, serpentine channel 22 is through communicating with the cold bath machine, can make the coolant liquid in the cold bath machine enter into serpentine channel 22 inside, can be convenient the temperature of regulation bottom plate 5 and roof 14 department, further simulate the one-way freezing of the soil body.
In this embodiment, as a preferable embodiment, the top plate 14 and the bottom plate 5 are both made of an aluminum alloy material, and have the characteristics of large thermal conductivity, light weight, and large rigidity. The size of the top plate 14 is a disc with the diameter of 148mm and the height of 40mm, and the serpentine channels 22 are all serpentine grooves, so that the circulating refrigeration of the refrigerating fluid is ensured. A boss is centrally provided on the upper surface of the top plate 14 to apply different types of loads by means of the pressure unit. Four pipe orifices are arranged on the bottom plate 5, wherein two pipe orifices are respectively a water inlet and an air outlet, and the other two pipe orifices are connected with a cold bath machine, so that the circulating refrigeration is ensured, and the temperature of the bottom of the sample 9 can be conveniently kept constant.
In the present embodiment, the top plate 14 is a double-layer plate structure, and a serpentine groove is formed on the top surface of the bottom plate by machining the serpentine groove, and then the top plate is covered on the top surface of the bottom plate and fastened by screws, so that the groove forms the sealed serpentine channel 22. Communication holes for communicating the serpentine channel 22 with the outside are also provided on the top plate, and rubber packing is also provided for sealing between the top plate and the bottom plate. The presence of the load boss on the top plate facilitates the attachment of the top plate 14 to the load actuator 18.
In this embodiment, can carry out the moisturizing for the sample bottom through water charging system 11 and moisturizing pipeline intercommunication each other, the replenishment of better simulation groundwater. A water permeable plate is further paved at the bottom of the sample cylinder 12, and soil particles can be prevented from blocking a water replenishing hole to influence the water replenishing effect of the sample when the sample 9 is prepared by the water permeable plate.
As a specific embodiment of the testing apparatus for studying the local deformation characteristics of the frozen soil provided by the present invention, please refer to fig. 2 and 3, a sealing gasket is further disposed between the inner wall of the sample cylinder 12 and the water supplement plate body 6, the sealing gasket is sleeved on the periphery of the water supplement plate body 6, and a receiving groove is further disposed on the periphery of the water supplement plate body 6. The sealing gasket is arranged to ensure the sealing performance of the contact surface of the water supplementing plate body 6 and the sample cylinder 12.
Referring to fig. 2 and 3, the pressure unit includes a base 2, a support frame 19 disposed on the base 2, a load actuator 18 movably disposed on the support frame 19, and a loading device 26 for driving the load actuator 18 to move. The base 2 and the support frame body 19 are arranged to enable the load actuator 18 to be more convenient to install, wherein the loading device 26 can apply loads in different forms through the load actuator 18, the loads are carried out through control force or displacement, the load actuator 18 of the loading system is provided with a displacement element, macroscopic deformation of the test sample 9 can be further tested, and the layered frost heaving deformation measuring system of the soil body can be further verified and corrected. The loading device consists of a 20kN host, a 10L oil source 22, a microcomputer system and a control system. The load control mode is powerful, displacement, speed, deformation and the like, and meanwhile, information is fed back to a computer, so that smooth undisturbed switching of any control mode can be realized. And load of different forms can be exerted through loading device 26, and soil body frost heaving and load effect coupling link together, and the atress condition of actual road bed is better simulated, makes the measurement of experimental data more diversified.
Referring to fig. 2 and 3, the base 2 is further provided with four support rods 4 arranged parallel to the sample cylinder 12, the end of the sample cylinder 12 is further provided with a flange 15 for fixing the sample cylinder 12, one end of each support rod 4 penetrates through the flange 15, the other end of each support rod 4 penetrates through the base 2, and the end of each support rod 4 is further provided with a limit nut 16 for pressing the flange 15 and the base 2. Before carrying out experimental measurement, place bottom plate 5 on base 2, then place sample cylinder 12 and moisturizing plate body 6 on bottom plate 5, then set up flange 15 lid on the oral area of sample cylinder 12, make bracing piece 4 pass the via hole on the flange 15, then use stop nut 16 to compress tightly flange 15 fixedly, make the installation of sample cylinder 12 fixed more firm.
Referring to fig. 2 and 3, as a specific embodiment of the testing device for studying local deformation characteristics of frozen soil provided by the present invention, a displacement sensor 17 for monitoring a displacement of a sample is further disposed above the sample cylinder 12, the displacement sensor 17 is located on a side surface of the driving end, and the displacement sensor 17 is electrically connected to the data processing unit 23. The displacement sensor 17 is fixed on the flange 15, can accurately read the frost heaving deformation of the soil body, can test the macroscopic frost heaving of the sample 9, further verifies and corrects the layered frost heaving deformation measuring system of the soil body, ensures the accuracy of experimental data, and greatly improves the efficiency in the experiment and the accuracy of the experiment.
Referring to fig. 2 and 3, as a specific embodiment of the testing apparatus for studying local deformation characteristics of frozen soil provided by the present invention, a sample cylinder 12 is made of a transparent material, and an insulating layer 13 is further disposed on an outer periphery of the sample cylinder 12. The heat insulation material is arranged outside the sample cylinder 12 for heat insulation, so that the influence of the external environment temperature on the test result is avoided, and the test error is reduced. The sample cylinder 12 is made of transparent materials, so that the image acquisition unit 10 can conveniently shoot and monitor the sample 9 in the sample cylinder 12, the acquisition side facing the camera is not paved with a heat insulation layer, and the heat insulation layer 13 can also adopt transparent heat insulation materials to carry out heat insulation, so that the influence of the external environment temperature on the test result is avoided, the test error is reduced, and the test data are more accurate.
Referring to fig. 2 and 3, as a specific embodiment of the testing device for studying local deformation characteristics of frozen soil provided by the present invention, the water replenishing system 11 is a mahalanobis bottle, and the mahalanobis bottle is communicated with the water replenishing pipeline through a water replenishing pipe. One end of the water replenishing pipe is connected with a water inlet on the bottom plate 5, and the other end of the water replenishing pipe is connected with the Ma bottle which is provided with a ball valve for controlling a water replenishing switch. Because the moisture migration of the sample 9 can be generated in the freezing process, the moisture on the lower part of the sample 9 migrates to the freezing area under the action of the negative temperature suction force. In order to better simulate the migration of actual underground water to the sample, the position of the Mariotte bottle is adjusted to supplement water to the sample 9 under no pressure.
The invention also provides a test method for researching the local deformation characteristics of frozen soil, which uses the test device for researching the local deformation characteristics of frozen soil as claimed in any one of claims 1 to 8, and comprises the following steps:
preparing a sample, namely preparing a soil sample with a certain water content according to the requirement of the experimental design, placing the prepared soil sample in a sealed container, standing the soil sample for 22-26 hours, and taking out the soil sample from the sealed container for later use;
mounting a sample cylinder, namely mounting a water replenishing disc body at the bottom of the sample cylinder, maintaining the sealing between the sample cylinder and the water replenishing disc body, placing the sample cylinder on a bottom plate, and paving filter paper at the bottom of the sample cylinder;
preparing a sample, namely taking a certain amount of soil sample and trace particles, firstly placing the soil sample in a sample cylinder, compacting the soil sample in the sample cylinder in a layering manner through a compaction hammer, then paving the trace particles with certain thickness and width on the acquisition side surface of the sample, and then sequentially compacting the soil sample at the lower layer and paving the particles until the height of the sample is required, wherein the prepared sample is compacted in a layering manner, and the trace particles are paved in a layering manner;
fixing a sample cylinder, placing a layer of filter paper on the top of the compacted soil sample, covering a top plate on the top of the soil sample, pressing a fixing flange on the end part of the sample cylinder and fixing the sample cylinder through a limiting nut;
the external equipment is connected, and the cold bath equipment is respectively connected with the top plate and the mounting base to form refrigeration cycle; connecting the March's flask with a water replenishing port of a water replenishing plate body, opening a water replenishing valve to adjust the height of the March's flask so that the liquid level in the March's flask and the bottom of the soil sample are positioned on the same plane, and then fixing the March's flask and closing the valve;
and data acquisition and recording, and adjusting the positions of the image acquisition unit and the illumination unit so as to clearly capture the change of the surface texture of the soil body. Simultaneously starting the cold bath device and the freeze-thaw test chamber, setting the temperature in the freeze-thaw test chamber at 5 ℃ for temperature control, and opening a valve of the Mariotte bottle when the internal temperature of the soil body is stabilized at 5 ℃; applying a load with specified frequency and amplitude by an actuating device of a loading instrument; meanwhile, the cold bath device connected with the top plate is adjusted to-10 ℃, data of the temperature sensor, the moisture sensor and the image acquisition unit are acquired once every 10min through the data acquisition instrument and are transmitted to the data processing unit, and the water level change of the Martensity bottle is recorded once every 2 h;
and (3) data calculation, wherein the data processing unit is used for sorting the data collected by the image acquisition unit, the temperature sensing unit and the moisture sensing unit and carrying out image convolution on the acquired tracer particle image area through a normalized image cross-correlation algorithm. The displacement field (unit: pixel) of the measuring surface is inversely calculated through the result of the position of the correlation peak obtained by image convolution. According to the measuring results of the graduated scale and the displacement meter, the original displacement field is converted, the full-field deformation results of the frozen soil at different depths at different moments can be obtained, and then the results are displayed through a display device.
In another embodiment of the present application, in the step of compacting the soil sample by layers, the trace particles are black quartz sand and white quartz sand.
Compared with the prior art, the test method for researching the local deformation characteristics of the frozen soil provided by the invention has the advantages that the change rule of the surface texture of the sample is analyzed by constructing the surface texture of the soil body and taking pictures at intervals by the image acquisition unit, and the local deformation of the frozen soil can be tracked in real time by analyzing the correlation of the interval picture sequence. The problem that the original PIV technology cannot be applied to frozen soil tests is effectively solved. The provided sample texture construction method can effectively enhance the surface texture characteristics of frozen soil and reduce the gray scale correlation error caused by ice-water phase change, so that the PIV method can be applied to frozen soil testing; the defect that the traditional experiment can only obtain the total deformation of the sample and cannot obtain the local deformation is overcome; the decoupling analysis of the frost heaving process of the quantitative angle under the load effect is realized. The temperature field, the moisture field and the displacement field are decoupled, and the respective quantification of various factors influencing frost heaving is realized. The local deformation characteristics of soil bodies with different depths in the one-dimensional deformation process of the frozen soil under different load working conditions can be conveniently and visually measured.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A testing device for studying local deformation characteristics of frozen soil, comprising:
the temperature adjusting box body is used for maintaining a constant experimental environment;
the temperature control box comprises a temperature control box body, a sample cylinder and a control device, wherein the temperature control box body is internally provided with a temperature control box body, a measuring scale arranged along the length direction of the sample cylinder is arranged on the side wall of the sample cylinder, a plurality of small holes of sensing units for measuring sample data are arranged on the side wall of the sample cylinder, and the sensing units are sequentially arranged at intervals along the height direction of the sample cylinder;
the bottom plate is arranged in the temperature adjusting box body and positioned at the bottom of the sample cylinder, and a first temperature control structure for maintaining the temperature change of the sample is also arranged in the bottom plate;
the water replenishing plate body is attached to the upper part of the bottom plate and is positioned at the end part of the sample cylinder close to the bottom plate, and a water replenishing pipeline communicated with a water replenishing system through a pipeline is further arranged in the water replenishing plate body;
the top plate is arranged in the sample cylinder, is positioned at the top of the sample cylinder, covers the top of the sample in the sample cylinder and is used for pressing the sample in a region between the water supplementing plate body and the top plate, and a second temperature control structure for maintaining the temperature change of the sample is also arranged in the top plate;
the pressure unit is arranged in the temperature adjusting box body, and the driving end of the pressure unit is positioned above the top plate and used for applying pressure to the sample in the sample cylinder through the top plate;
the image acquisition unit is arranged on the side surface of the sample cylinder and used for monitoring the deformation of the sample;
and the data processing unit is electrically connected with the image acquisition unit, electrically connected with the plurality of sensing units on the sample cylinder and used for receiving and processing signals acquired by the image acquisition unit and the sensing units.
2. The testing device for studying the local deformation characteristics of frozen soil of claim 1, wherein the first temperature control structure is a serpentine channel disposed inside the bottom plate and the second temperature control structure is a serpentine channel disposed inside the top plate, the serpentine channels being in communication with an external cold bath device pipe.
3. The testing apparatus for studying local deformation characteristics of frozen soil according to claim 1, wherein a sealing gasket is further disposed between the inner wall of the sample cylinder and the moisturizing plate body, the sealing gasket is sleeved on the periphery of the moisturizing plate body, and a receiving groove is further disposed on the periphery of the moisturizing plate body.
4. The testing apparatus for studying local deformation characteristics of frozen soil according to claim 1, wherein the pressure unit comprises a base, a support frame disposed on the base, a load actuator movably disposed on the support frame, and a loading device for driving the load actuator to move.
5. The testing apparatus for studying local deformation characteristics of frozen soil according to claim 4, wherein the base is further provided with four support rods arranged in parallel with the sample cylinder, the top of the sample cylinder is further provided with a flange for fixing the sample cylinder, one end of each support rod penetrates through the flange and the other end penetrates through the base, and the end parts of the support rods are provided with limit nuts for pressing the flange and the base.
6. The testing device for researching the local deformation characteristics of the frozen soil as claimed in claim 5, wherein a displacement sensor for monitoring the macroscopic deformation of the sample is further arranged above the sample cylinder, the displacement sensor is arranged on the flange, and the displacement sensor is electrically connected with the data processing unit.
7. An examination method for studying the local deformation characteristics of frozen soil, which uses the examination device for studying the local deformation characteristics of frozen soil according to any one of claims 1 to 6, and is characterized by comprising the following steps:
preparing a sample, namely preparing a soil sample with a certain water content according to the requirement of the experimental design, placing the prepared soil sample in a sealed container, standing the soil sample for 22-26 hours, and taking out the soil sample from the sealed container for later use;
mounting a sample cylinder, namely mounting a water replenishing disc body at the bottom of the sample cylinder, maintaining the sealing between the sample cylinder and the water replenishing disc body, placing the sample cylinder on a bottom plate, and paving filter paper at the bottom of the sample cylinder;
the method comprises the following steps of compacting a soil sample in a layering manner, taking a certain amount of soil sample and trace particles, firstly placing the soil sample in a sample cylinder, compacting the soil sample in the sample cylinder in the layering manner through a compaction hammer, then paving the trace particles with a certain thickness and width on the acquisition side surface of the sample, and then sequentially compacting the soil sample at the lower layer and paving the particles until the required sample height is reached, wherein the prepared sample is compacted in a layering manner, and the trace particles are paved in a layering manner;
fixing a sample cylinder, placing a layer of filter paper on the top of the compacted soil sample, covering a top plate on the top of the soil sample, pressing a fixing flange on the end part of the sample cylinder and fixing the sample cylinder through a limiting nut;
the external equipment is connected, and the cold bath equipment is respectively connected with the top plate and the mounting base to form refrigeration cycle; connecting the March's flask with a water replenishing port of a water replenishing plate body, opening a water replenishing valve to adjust the height of the March's flask so that the liquid level in the March's flask and the bottom of the soil sample are positioned on the same plane, and then fixing the March's flask and closing the valve;
data acquisition and recording, namely adjusting the positions of the image acquisition unit and the illumination unit so as to clearly capture the change of the surface texture of the soil body; simultaneously starting the cold bath device and the freeze-thaw test chamber, setting the temperature in the freeze-thaw test chamber at 5 ℃ for temperature control, and opening a valve of the Mariotte bottle when the internal temperature of the soil body is stabilized at 5 ℃; applying a load with specified frequency and amplitude by an actuating device of a loading instrument; meanwhile, the cold bath device connected with the top plate is adjusted to-10 ℃, data of the temperature sensor, the moisture sensor and the image acquisition unit are acquired once every 10min through the data acquisition instrument and are transmitted to the data processing unit, and the water level change of the Martensity bottle is recorded once every 2 h;
data calculation, wherein the data processing unit is used for sorting the data collected by the image acquisition unit, the temperature sensing unit and the moisture sensing unit and carrying out image convolution on the acquired tracer particle image area through a normalized image cross-correlation algorithm; inversely calculating the displacement field (unit: pixel) of the measuring surface through the position result of the correlation peak obtained by image convolution; according to the measuring results of the graduated scale and the displacement meter, the original displacement field is converted, the full-field deformation results of the frozen soil at different depths at different moments can be obtained, and then the results are displayed through a display device.
8. The test method for studying local deformation characteristics of frozen soil according to claim 7, wherein in the step of compacting the soil sample in layers, the trace particles are black quartz sand and white quartz sand.
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