A dynamic characteristics testing system and method based on chemical electroosmosis solidified soft soil

Abstract

The present invention discloses a dynamic characteristic testing system and method for soft soil solidification based on chemical electroosmosis. The testing system includes a pressure chamber, a sample placed in the pressure chamber, an excitation system, and a chemical electroosmosis system. The chemical electroosmosis system includes a sample end electrode, a drainage device, and a chemical grouting device. The sample end electrode includes a top cap provided above the sample and a base provided below the sample. The chemical grouting device is connected to the base, and the drainage device is connected to the top cap. The excitation system is connected to the sample for applying axial and torsional excitation to the sample. A pressure chamber for measuring sample deformation is provided on the outside of the sample. The present invention can fully utilize the advantages of the chemical electroosmosis method for treating soft soil, effectively shorten the soft soil consolidation time, and improve test efficiency. At the same time, silicate substances in the soil and cations in the grouting liquid react chemically under the action of the electric field to generate a gel substance that fills soil gaps, cements soil particles, and enhances soil strength.

Description

Technical Field

[0001] The present invention relates to the technical field of rapid consolidation and dynamic characteristics testing of geotechnical engineering soil, and in particular to a dynamic characteristics testing system and method based on chemical electroosmosis solidified soft soil. Background Art

[0002] Soft soil generally has the characteristics of high water content, large porosity, low strength, thixotropy and structural properties. Under the action of seismic loads, its dynamic pore pressure and shear strength change, and the soil shows obvious strain softening phenomenon.

[0003] Currently, research on the mechanical properties of soft soil after electroosmotic solidification has primarily focused on its bearing capacity and shear strength, while little research has been conducted on its dynamic properties. Research on the dynamic properties of soil can extend the traditional study of soil properties under static loads to include the study of its dynamic properties and stability under dynamic loads, linking the dynamic properties and stability of soil with dynamic loads and time. The dynamic shear modulus and damping ratio of soil are important mechanical properties of soil, reflecting the response of this type of geotechnical material to dynamic loads such as earthquakes and vibration impacts. They are fundamental parameters for the seismic design and dynamic analysis of many geotechnical structures and are crucial for evaluating soil site effects.

[0004] The traditional dynamic characteristics test method requires a long time for sample consolidation, and the consolidation causes changes in sample size, which affects the accuracy of the dynamic characteristics test results. Summary of the Invention

[0005] Purpose of the invention: The present invention aims to provide a soft soil dynamic characteristics testing system and method that can shorten the curing time and improve the test accuracy.

[0006] Technical solution: The present invention relates to a dynamic characteristics testing system for soft soil solidification based on chemical electroosmosis, comprising a pressure chamber, a sample placed in the pressure chamber, an excitation system and a chemical electroosmosis system; the chemical electroosmosis system comprises a sample end electrode, a drainage device and a chemical grouting device, the sample end electrode comprises a top cap provided above the sample and a base below the sample, the chemical grouting device is connected to the base, the drainage device is connected to the top cap, the excitation system is connected to the sample for applying axial excitation and torsional excitation to the sample, and a pressure chamber for measuring sample deformation is provided outside the sample.

[0007] Preferably, the excitation system includes a torsional excitation device and an axial excitation device; the torsional excitation device includes a driving plate, a magnet and a coil, the driving plate is connected to the top cap, the magnet is fixed on the driving plate, and the coil is sleeved outside the magnet.

[0008] Preferably, an acceleration sensor is provided on the driving board, and a small mass block with the same mass as that of the acceleration sensor is provided at a central symmetrical position of the driving board.

[0009] Preferably, the axial excitation device is an axial exciter, and an LVDT axial displacement sensor is provided on the top of the axial exciter.

[0010] Preferably, a copper metal electrode is embedded below the top cap and above the base, and the surface of the copper metal electrode is provided with eight rows of raised blades with equal spacing and four rows of circular holes with equal spacing.

[0011] Preferably, a power supply is further included, wherein the anode of the power supply is connected to the base via a wire, and the cathode of the power supply is connected to the top cap via a wire.

[0012] Preferably, a grouting hole is provided at the lower part of the base, which is connected to the chemical grouting device through a grouting pipe. The grouting pipe is provided with a water stop valve for controlling the slurry injection time and amount. The grouting hole is connected to the pore pressure detection device.

[0013] Preferably, the edge of the top cap is provided with a drainage hole, which is connected to a drainage device through a drainage pipe. The drainage device is provided with a water level detection element for monitoring the consolidation degree of the soil sample and the drainage volume.

[0014] Preferably, the pressure chamber is connected to a water injection device via a water injection pipe, and the water injection device is provided with a liquid level gauge. Water is injected into the pressure chamber before consolidation, and the size of the sample after chemical electroosmosis consolidation is measured by combining the water volume change and the LVDT axial displacement sensor.

[0015] The testing method of the dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to the present invention comprises the following steps:

[0016] (a) Specimen installation: Install the base on the support, prepare a cylindrical specimen, cover the specimen with a rubber membrane using a sleeve, press the specimen into the raised blade on the top of the base and secure it tightly. Install the top cap so that the blade at the bottom of the cap cuts into the surface of the soil specimen and secures it tightly.

[0017] (b) For torsional vibration, install the torsional excitation device, horizontally secure the accelerometer to the driver board and symmetrically mount the small mass blocks, and connect the driver board to the top cap. For axial vibration, secure the accelerometer vertically to the driver board and connect the upper end of the driver board to the axial exciter and the lower end to the top cap. Connect the coil to the power amplifier and the accelerometer to the electrical signal amplifier. Assemble the instrument, connect the wires, and connect it to the computer operating system.

[0018] (c) Remove the split mold, inject water into the pressure chamber, lower the pressure chamber cover, apply pressure to the pressure chamber, and monitor the changes in the height and diameter of the specimen;

[0019] (d) Turning on the power supply, opening the drainage device and the chemical grouting device, injecting grout into the specimen, draining the water through the electrodes at the end of the specimen and collecting the water discharged from the specimen, and detecting the drainage volume through the water level detection element until the specimen is completely consolidated;

[0020] (e) Opening the computer operating system, setting the test conditions, turning on the torsional vibration excitation device, power amplifier, electrical signal amplifier, and digital-to-analog converter, conducting a vibration test, recording the vibration process of the specimen and obtaining the specimen's natural vibration attenuation curve, calculating the specimen's dynamic modulus and damping ratio based on the natural vibration attenuation curve, repeatedly increasing the excitation force step by step to obtain sufficient test data for analyzing the specimen's dynamic characteristics, and then using an acceleration sensor to collect and process the acceleration values ​​of the specimen during vibration;

[0021] (f) After the test is completed, shut down the system, remove the components, and organize the system data based on the test results of the specimen height and diameter.

[0022] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: 1. It gives full play to the advantages of chemical electroosmosis in treating soft soil, effectively shortens the consolidation time of soft soil, and improves the test efficiency; at the same time, the silicate substances in the soil react chemically with the cations in the grouting liquid under the action of the electric field to generate gel substances, which fill the gaps in the soil, cement the soil particles, and enhance the strength of the soil; 2. Taking into account the sample size effect, the height diameter of the sample is measured to improve the accuracy of the dynamic characteristics test results; 3. Setting different dynamic conditions and collecting various parameters of the soil are helpful to explore the dynamic characteristics of the soil after chemical electroosmosis treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the present invention;

[0024] Figure 2 This is a structural diagram of the driving plate of the present invention;

[0025] Figure 3 It is a structural diagram of the top cap and base of the present invention.

[0026] In the figure, 1. pressure chamber; 2. sample end electrode; 21. top cap; 22. base; 23. blade; 24. circular hole; 3. drainage device; 31. drainage pipe; 4. chemical grouting device; 41. grouting pipe; 42. water stop valve; 5. pressure chamber; 6. torsional excitation device; 61. drive plate; 62. magnet; 63. coil; 64. acceleration sensor; 65. small mass block; 7. axial excitation device; 8. LVDT axial displacement sensor; 9. water injection device; 91. water injection pipe; 10. power supply; 11. pore pressure detection device; 12. base. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0028] like Figure 1 As shown, the dynamic characteristics testing system of soft soil solidified by chemical electroosmosis according to the present invention includes a pressure chamber 1, a sample placed in the pressure chamber, an excitation system and a chemical electroosmosis system. The excitation system is connected to the sample for applying axial excitation and torsional excitation to the sample, and a pressure chamber 5 for measuring the deformation of the sample is provided outside the sample.

[0029] The chemical electroosmosis system includes a sample end electrode 2, a drainage device 3, a chemical grouting device 4 and a power supply 10. The sample end electrode 2 includes a top cap 21 arranged above the sample and a base 22 below the sample. A copper metal electrode is embedded below the top cap 21 and above the base 22. The surface of the copper metal electrode is provided with eight rows of raised equidistant blades 23 with a center spread out, which can make the sample in close contact with the top cap 21 and the base 22. The copper metal electrode is provided with four rows of equidistant circular holes 24 with a center spread out, which makes the grouting and drainage process more uniform. Figure 3 The anode of the power supply 10 is connected to the base 22 via a wire, and the cathode of the power supply is connected to the top cap 21 via a wire.

[0030] The base 22 has a grouting hole at the bottom, which is connected to the chemical grouting device 4 via a grouting pipe 41. The grouting pipe 41 is equipped with a water stop valve 42 for controlling the slurry injection time and amount. The grouting hole is connected to the pore pressure detection device 11. The top cap 21 has a drainage hole at the edge, which is connected to the drainage device 3 via a drainage pipe 31. The drainage device 3 is equipped with a water level detection element to monitor the degree of soil consolidation and drainage volume.

[0031] The excitation system includes a torsional excitation device 6 and an axial excitation device 7. The torsional excitation device 6 includes a drive plate 61, a magnet 62, and a coil 63. The drive plate 61 has a reserved hole, which is connected to the top cap 21 via a screw to fix the synthetic mass block. The magnet 62 is fixed to the drive plate 61, and the coil 63 is sleeved outside the magnet 62. The drive plate 61 is equipped with an acceleration sensor 64, which is connected to the electrical signal amplifier via a lead wire. A small mass block 65 with the same mass as the acceleration sensor 64 is installed symmetrically at the center of the drive plate. The axial excitation device 7 is an axial exciter, and an LVDT axial displacement sensor 8 is installed on its top.

[0032] The pressure chamber 5 is connected to the water injection device 9 through the water injection pipe 91. The water injection device 9 is provided with a liquid level gauge. Water is injected into the pressure chamber 5 before consolidation. The size of the sample after chemical electroosmosis consolidation is measured by combining the water volume change and the LVDT axial displacement sensor 8. The influence of the size effect caused by the sample consolidation on the accuracy of the dynamic characteristics test results is considered.

[0033] Compared with the traditional electroosmosis method, the chemical electroosmosis method for treating soft soil can effectively shorten the electroosmosis treatment time. At the same time, due to chemical grouting, ion exchange and cementation hardening are promoted under the action of the electric field, gel material is generated, soil voids are filled, and clay particles are cemented, which can increase the strength of the soft soil after consolidation.

[0034] The testing method of the dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to the present invention comprises the following steps:

[0035] (a) Specimen installation: Install the base 22 on the pedestal 12, prepare a cylindrical specimen, cover the specimen with a rubber membrane using a sleeve, and press the specimen into the raised blade 23 on the top of the base 22. Fold up the lower rubber membrane to clamp the base and tighten it with a rubber band to ensure the bottom of the rubber membrane is sealed. Then, turn the upper rubber membrane outward and remove the sleeve. Install the split mold on the outside of the specimen, turn the upper rubber membrane outward to press it against the split mold, tighten the middle of the split mold with a rubber band, and then tighten the bottom of the split mold with a stainless steel tie to ensure that the soft soil specimen does not collapse during consolidation. Install the top cap 21 so that the blade 23 at the bottom of the top cap 21 contacts the surface of the soil specimen. Apply appropriate force to make the blade better cut into the top of the specimen to prevent the driving plate and the specimen from slipping when the excitation force is large during the test, which may not accurately reflect the specimen's natural vibration attenuation process. Slowly pull a rubber band on the split mold to the contact position between the rubber membrane and the mass block to ensure the contact position is sealed.

[0036] (b) For torsional vibration, fix the accelerometer 64 horizontally to the drive plate 61. During installation, the coils must be suspended in the air, otherwise the free vibration of the drive plate 61 and the specimen will be affected. Install the drive plate 61 connected to the top cap 21 directly above the top of the specimen. According to the coil holder number, insert the corresponding coil 63 into the outer pole of the magnet 62 and place it in the H-shaped groove on the top surface of the coil holder. Tighten the coil fixing thread. The distance from the center of the magnetic pole to the upper and lower ends of the coil 63 is equal, and the height of the two pairs of coils is consistent. The gaps on both sides of the coils are equal and symmetrical with the coil holder.

[0037] For axial vibration, fix the acceleration sensor 64 vertically on the driver 61 and connect the upper end of the driver plate 61 to the axial exciter 7. When the driver plate 61 can move freely up and down, install it just above the top of the sample. Connect the coil 63 to the power amplifier and the acceleration sensor 64 to the electrical signal amplifier. Assemble the instrument, connect the wires, and connect it to the computer operating system.

[0038] (c) Loosen the split mold tie, remove the split mold, inject water into the pressure chamber 5 through the water injection pipe 91, lower the outer cover of the pressure chamber 1, pressurize the pressure chamber 1, and monitor the changes in the height and diameter of the sample;

[0039] (d) Turning on the power supply, opening the drainage device 3 and the chemical grouting device 4, injecting grout into the sample through the grouting pipe 41, performing chemical electroosmotic drainage through the electrodes at the end of the sample, collecting the water discharged from the sample, and detecting the drainage volume through the water level detection element until the sample is completely consolidated;

[0040] (e) Opening the computer operating system, setting the test conditions, turning on the torsional excitation device, power amplifier, electrical signal amplifier, and digital-to-analog converter, and conducting a vibration test. The computer issues corresponding instructions, and the current in the coil 63 generates a certain magnetic force, causing torsional shear deformation at the top of the sample, or the axial exciter 7 causes the sample to undergo axial deformation. Then, the current disappears, and the sample vibrates freely. The mass block sensor 64 mounted on the drive plate 61 records the vibration process of the sample and obtains the sample's self-vibration attenuation curve. The dynamic modulus and damping ratio of the sample are calculated based on the self-vibration attenuation curve. The excitation force is repeatedly increased step by step to obtain sufficient test data to analyze the dynamic characteristics of the sample. The acceleration sensor then collects and processes the acceleration value of the sample during the vibration process.

[0041] (f) After the test is completed, shut down the system, remove the components, and organize the system data based on the test results of the specimen height and diameter.

Claims

1. A dynamic characteristics testing system based on chemical electroosmosis solidified soft soil, characterized in that: The invention comprises a pressure chamber (1), a sample placed in the pressure chamber, an excitation system and a chemical electroosmosis system; the chemical electroosmosis system comprises a sample end electrode (2), a drainage device (3) and a chemical grouting device (4); the sample end electrode (2) comprises a top cap (21) arranged above the sample and a base (22) below the sample; the chemical grouting device (4) is connected to the base (22); the drainage device (3) is connected to the top cap (21); the excitation system is connected to the sample for applying axial excitation and torsional excitation to the sample; a pressure chamber (5) for measuring the deformation of the sample is provided outside the sample; a pressure chamber (5) is embedded below the top cap (21) and above the base (22); A copper metal electrode, wherein the surface of the copper metal electrode is provided with eight rows of raised equally spaced blades (23) spread out from the center of a circle and four rows of equally spaced circular holes (24) spread out from the center of a circle; a grouting hole is provided at the lower part of the base (22), the grouting hole is connected to the chemical grouting device (4) through a grouting pipe (41), a water stop valve (42) for controlling the slurry injection time and amount is provided on the grouting pipe (41), and the grouting hole is connected to the pore pressure detection device (11); a drainage hole is provided at the edge of the top cap (21), the drainage hole is connected to the drainage device (3) through a drainage pipe (31), and the drainage device (3) is provided with a water level detection element for monitoring the consolidation degree of the soil sample and the drainage amount.

2. The dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to claim 1 is characterized in that: The excitation system includes a torsional excitation device (6) and an axial excitation device (7); the torsional excitation device (6) includes a driving plate (61), a magnet (62) and a coil (63), the driving plate (61) is connected to the top cap (21), the magnet (62) is fixed on the driving plate (61), and the coil (63) is sleeved outside the magnet (62).

3. The dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to claim 2, characterized in that: An acceleration sensor (64) is provided on the driving plate (61), and a small mass block (65) having the same mass as the acceleration sensor (64) is provided at a central symmetrical position of the driving plate.

4. The dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to claim 2, characterized in that: The axial excitation device (7) is an axial exciter, and an LVDT axial displacement sensor (8) is provided on the top of the axial exciter.

5. The dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to claim 1 is characterized in that: It also includes a power supply (10), wherein the anode of the power supply is connected to the base (22) through a wire, and the cathode of the power supply is connected to the top cap (21) through a wire.

6. The dynamic characteristics testing system based on chemical electroosmosis solidified soft soil according to claim 1, characterized in that: The pressure chamber (5) is connected to a water injection device (9) via a water injection pipe (91). A liquid level gauge is provided in the water injection device (9). Water is injected into the pressure chamber (5) before consolidation, and the size of the sample after chemical electroosmosis consolidation is measured by combining the water volume change and the LVDT axial displacement sensor (8).

7. A testing method for a dynamic characteristics testing system based on chemical electroosmotic solidification of soft soil according to any one of claims 1 to 6, characterized in that: The following steps are involved: (a) Sample installation: Install the base (22) on the base (12), prepare a cylindrical sample, cover the sample with a rubber film using a sleeve, press the sample into the raised blade (23) on the top of the base (22) and fix it tightly. Install the top cap (21) so that the blade (23) at the bottom of the top cap cuts into the surface of the soil sample and fixes it tightly. (b) For torsional vibration, a torsional excitation device (6) is installed, an acceleration sensor (64) is fixed horizontally on a driving plate (61) and a small mass block (65) is installed symmetrically, and the driving plate (61) is connected to a top cap (21); for axial vibration, an acceleration sensor (64) is fixed vertically on a driving plate (61), and the upper end of the driving plate (61) is connected to an axial exciter (7) and the lower end is connected to a top cap (21); the coil (63) is connected to a power amplifier and the acceleration sensor (64) is connected to an electrical signal amplifier; Assemble the instrument, connect the wires, and access the computer operating system; (c) Remove the split mold, inject water into the pressure chamber (5), lower the outer cover of the pressure chamber (1), pressurize the pressure chamber (1), and monitor the changes in the height and diameter of the sample; (d) Turn on the power supply, open the chemi-electroosmotic system, inject grout into the sample, drain water through the sample end electrode (2) by chemi-electroosmotic method, collect the water discharged from the sample, and detect the drainage volume through the water level detection element until the sample is completely consolidated; (e) Open the computer operating system, set the test conditions, turn on the torsional vibration device, power amplifier, electrical signal amplifier, and digital-to-analog converter, conduct the vibration test, record the vibration process of the specimen and obtain the specimen's natural vibration attenuation curve, calculate the specimen's dynamic modulus and damping ratio based on the natural vibration attenuation curve, repeatedly increase the excitation force step by step, obtain sufficient test data to analyze the specimen's dynamic characteristics, and then use the acceleration sensor to collect and process the acceleration value of the specimen during the vibration process; (f) After the test is completed, shut down the system, remove the components, and organize the system data based on the test results of the specimen height and diameter.

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