A method for testing the strength recovery degree of disturbed soil

Abstract

The application discloses a kind of test methods of disturbed soil strength recovery degree, and test device includes vibration hammer, connecting shaft, liftable vibration rod, vibration hammer fixed support, vibration plate and support table frame;Vibration hammer is installed above vibration hammer fixed support and is connected with hydraulic power device;Connecting shaft is installed on vibration hammer and is connected with liftable vibration rod, liftable vibration rod vertically penetrates support table frame, vibration plate is installed at the top of liftable vibration rod, and leveling support leg is arranged at the bottom of vibration plate;Lower layer sample box and upper layer sample box are installed on vibration plate.Firstly, the leveling support leg at the bottom of vibration plate is adjusted, and the cone penetration depth of undisturbed soil sample is detected using cone liquid plastic limit instrument;Then, liftable vibration rod is raised to lift vibration plate, simulate the disturbance effect of soil body in field construction, and detect the cone penetration depth after the strength recovery of disturbed soil;Then, disturbed soil sample is placed in constant temperature and humidity box for curing, and the cone penetration depth after the strength recovery of disturbed soil is detected;Finally, the strength recovery degree of disturbed soil is calculated.

Description

A method for testing the strength resilience of disturbed soil Technical Field

[0001] This invention relates to the field of geotechnical engineering testing technology, and in particular to a method for testing the strength resilience of disturbed soil. Background Technology

[0002] In geotechnical engineering construction, processes such as pile driving, foundation pit excavation, and dynamic compaction inevitably disturb the surrounding soil. When structural clay is disturbed during construction, its microstructure is damaged and its macroscopic strength is reduced. After resting, the soil strength will continue to recover. This thixotropic strength characteristic of structural soil poses a great challenge to engineering design and construction.

[0003] Currently, the on-site testing process for detecting the strength recovery of soil after construction disturbance is cumbersome and consumes a lot of manpower and resources; indoor tests mostly use the triaxial compression method, and the remolded soil samples used are obtained by completely destroying the original soil structure, but the soil on site is mostly not completely destroyed, which does not match the actual engineering situation.

[0004] Therefore, there is a need to develop a test device and test method that is easy to operate, fits actual working conditions, and can monitor test data in real time. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the strength recovery of disturbed soil, addressing the technical deficiencies in existing technologies.

[0006] The technical solution adopted to achieve the purpose of this invention is:

[0007] A method for testing the strength restorer of disturbed soil employs a testing device, which includes: a vibratory hammer, a connecting shaft, a liftable vibratory rod, a hydraulic power unit, a vibration control device, a vibratory hammer fixing bracket, leveling legs, a vibrating plate, a lower sample box, an upper sample box, a cone-type liquid and plastic limit meter, and a support table.

[0008] The vibratory hammer is installed directly above the vibratory hammer fixing bracket and connected to the hydraulic power unit, which provides power for the vibration of the vibratory hammer; the vibration control device is connected to the hydraulic power unit; the connecting shaft is installed on the vibratory hammer and connected to the liftable vibratory rod, which is used to drive the liftable vibratory rod to vibrate; the liftable vibratory rod vertically penetrates the central hollow part of the supporting table frame, and the vibration plate is installed on the top of the liftable vibratory rod;

[0009] The lower and upper sample boxes are mounted on the vibrating plate and used to hold disturbed soil samples; the cone-shaped liquid and plastic limit meter is mounted on the support frame; an internal threaded hole is provided at the center of the upper surface of the vibrating plate, which is a blind hole, and an external thread is provided on the peripheral wall of the lower sample box. The lower sample box is connected to the vibrating plate by a screw; the bottom of the upper sample box is provided with a cutting edge.

[0010] A bubble level is installed on the vibrating plate to determine whether the vibrating plate is stable based on the position of the bubble. Leveling legs are installed at the four corners of the bottom of the vibrating plate to ensure that the vibrating plate is placed horizontally on the support table.

[0011] A groove is provided at the center of the bottom surface of the vibrating plate to match the top of the liftable vibrating rod, and the top of the liftable vibrating rod is installed into the groove.

[0012] The test method using the aforementioned test apparatus includes the following steps:

[0013] Step 1: Place the upper sample box with the cutting edge facing down on the original soil sample. Apply even force to press the upper sample box vertically down until the soil sample exceeds the upper edge of the upper sample box. Use a soil cutter to cut away and level the excess soil at both ends. Then, gently and slowly place the upper sample box containing the soil sample into the lower sample box. Place the upper and lower sample boxes together on the vibrating plate and connect the external thread of the lower sample box with the internal thread hole of the vibrating plate.

[0014] Step 2: Adjust the leveling legs at the bottom of the vibrating plate so that the vibrating plate is placed horizontally on the support table and the cone tip is just in contact with the soil sample surface. Start the cone liquid limit meter and let the cone sink freely to read the cone penetration depth.

[0015] Rotate the upper sample box to change the contact position between the cone tip and the soil sample. Repeat the cone drop test twice and take the average value as the cone penetration depth of the undisturbed soil sample.

[0016] Retract the leveling legs of the vibrating plate, raise the height of the adjustable vibrating rod to a suitable position, and lift the vibrating plate; set the vibration frequency and time, turn on the vibration control switch, and simulate the disturbance of the soil during on-site construction; after the vibration is completed, lower the height of the adjustable vibrating rod, readjust the leveling legs of the vibrating plate to place the vibrating plate horizontally on the support table, and then turn on the liquid limit and plastic limit tester to conduct a cone drop test and repeat it at least twice, taking the average value as the cone penetration depth of the disturbed soil sample;

[0017] Rotate the lower sample box and place the upper sample box and disturbed soil sample together into a constant temperature and humidity chamber for curing. After curing for the specified time according to experimental requirements, take out the soil sample and conduct the drop cone test again to obtain the cone penetration depth after the disturbed soil strength has recovered.

[0018] Step 3: Based on the cone penetration depth of the undisturbed soil sample, the cone penetration depth of the disturbed soil sample, and the cone penetration depth after the disturbed soil strength is restored, calculate the undrained strength index and the degree of strength restoration of the disturbed soil under different degrees of restoration.

[0019] In the above technical solution, the upper sample box is cylindrical, with an inner diameter of 12cm and a height of 10cm.

[0020] In the above technical solution, legs are provided at the four corners of the lower part of the support table frame to support the testing equipment.

[0021] In the above technical solution, a cabinet door is installed at the lower part of the supporting table frame, and an operation panel is installed on the outside of the cabinet door. The operation panel is connected to a vibration control device and a liftable vibrating rod, and is used to send control commands to the hydraulic power device and the liftable vibrating rod. The vibration control device adjusts the vibration frequency and vibration time of the driving hydraulic power device according to the commands input on the operation panel. The liftable vibrating rod rises or falls according to the commands input on the operation panel.

[0022] In the above technical solution, a noise-reducing rubber ring is installed between the central hollow part of the liftable vibrating rod and the supporting table frame, and the noise-reducing rubber ring is tightly clamped to the liftable vibrating rod.

[0023] In the above technical solution, the hollow part in the middle of the noise reduction rubber ring has multiple layers of pleats, and the outer edge of the noise reduction rubber ring is a thickened rubber strip with holes for fixing bolts to be inserted. The outer edge of the noise reduction rubber ring is fixed to the support table frame with fixing bolts.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This invention simulates the disturbance state of undisturbed soil after it is subjected to vibration; through testing equipment, it reveals the change law of the undrained strength index of the soil after it is disturbed; by comparing the strength index of the disturbed soil after it recovers with the strength index of the undisturbed soil, it determines the strength recovery status of the soil.

[0026] 2. This invention combines a vibration device and a falling cone liquid limit meter into a testing device. Through the vibration control device, vibration conditions of different frequencies and durations can be simulated, so that the test soil sample is in a more realistic stress state, thereby improving the rationality and accuracy of the test.

[0027] 3. Under the premise of meeting the test requirements, the present invention combines the soil vibration test and the drop cone test into one, which simplifies the test device, reduces the space occupied, reduces the number of soil movements, and avoids the soil being affected by other interferences that affect the strength characteristic test results. Attached Figure Description

[0028] Figure 1 shows a schematic diagram of the overall structure of the disturbed soil strength recovery test device of the present invention.

[0029] Figure 2 shows a schematic diagram of the bottom cabinet door of the support table frame of the present invention.

[0030] Figure 3 shows a schematic diagram of the connection structure between the vibrating plate and the sample box of the present invention.

[0031] Figure 4 shows a schematic diagram of the bottom surface of the vibration plate of the present invention.

[0032] Figure 5 shows a schematic diagram of the connection between the noise-reducing rubber ring, the vibration rod, and the support table frame of the present invention.

[0033] Figure 6 shows a schematic diagram of the recovery law curve of the undrained strength index of disturbed soil according to the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific 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.

[0035] Example 1

[0036] A test device for the strength recovery of disturbed soil, as shown in Figures 1 and 2, includes: a vibratory hammer 1, a connecting shaft 2, a liftable vibratory rod 3, a hydraulic power unit 4, a vibration control device 5, a vibratory hammer fixing bracket 6, a noise-reducing rubber ring 8, a leveling leg 9, a vibrating plate 10, a lower sample box 11, an upper sample box 12, a bubble level 13, a drop cone 14, a cone-type liquid and plastic limit meter 15, a supporting table frame 16, support legs 17, an operation panel 18, a cabinet door 19, and a power supply 20.

[0037] The vibratory hammer 1 is installed directly above the vibratory hammer fixing bracket 6 and connected to the hydraulic power device 4, which provides power for the vibration of the vibratory hammer 1. The vibration control device 5 is connected to the hydraulic power device 4 and installed inside the cabinet door to drive the hydraulic power device. The connecting shaft 2 is installed on the vibratory hammer 1 and connected to the liftable vibratory rod 3 to drive the liftable vibratory rod 3 to vibrate. The liftable vibratory rod 3 vertically penetrates the central hollow part of the supporting table frame 16. The vibrating plate 10 is installed on the top of the liftable vibratory rod 3, and the vibratory plate 10 is driven to rise and fall by the liftable vibratory rod 3.

[0038] The lower sample box 11 and the upper sample box 12 are installed on the vibrating plate 10 and are used to hold disturbed soil samples. The cone-type liquid and plastic limit meter 15 is installed on the support table 16. The cone-type liquid and plastic limit meter 15 is used to measure the cone penetration depth of the soil sample by inserting the cone 14 of the cone-type liquid and plastic limit meter 15 into the disturbed soil sample in the sample box. Specifically, referring to Figure 3, an internal threaded hole 10-1 (which is a blind hole) is provided at the center of the upper surface of the vibrating plate 10, and an external thread 11-1 is provided on the peripheral wall of the lower sample box 11 (the lower sample box 11 is a box with a bottom), so that the lower sample box 11 and the vibrating plate 10 are spirally connected; the upper sample box is cylindrical, with an inner diameter preferably of 12cm and a height of 10cm, and a cutting edge 12-1 is provided at the bottom of the upper sample box 12, which facilitates pressing the upper sample box down into the undisturbed soil sample, making it easier to sample disturbed soil.

[0039] A bubble level 13 is set on the vibrating plate 10 to determine whether the vibrating plate 10 is stable based on the position of the bubble in the bubble level 13; leveling legs 9 are set at the four corners of the bottom of the vibrating plate 10 to make the vibrating plate 10 horizontally placed on the support table 16.

[0040] Furthermore, referring to Figure 4, a groove 10-2 is provided at the center of the bottom surface of the vibrating plate 10, which mates with the top of the liftable vibrating rod 3. The top of the liftable vibrating rod 3 is installed into the groove 10-2. In this way, when the liftable vibrating rod 3 vibrates, it can ensure that the vibrating plate 10 vibrates with the liftable vibrating rod 3, and it can also ensure that the vibrating plate 10 does not detach from the top of the liftable vibrating rod 3. In addition, when the liftable vibrating rod descends a certain distance, the vibrating plate 10 can detach from the liftable vibrating rod, and then the leveling legs 9 at the four corners of the bottom of the vibrating plate 10 can be adjusted so that the vibrating plate 10 is placed horizontally on the support table 16 (it is necessary to ensure that the vibrating plate 10 is placed horizontally so that data can be accurately collected when the falling cone 14 is measured).

[0041] Support legs 17 are provided at the four corners of the lower part of the support table frame 16 to support the testing equipment. The cabinet door 19 is installed below the support table frame 16, and an operation panel 18 is installed on the outside of the cabinet door 19. The operation panel 18 is connected to the vibration control device 5 and the liftable vibration rod 3, and is used to send control commands to the hydraulic power device 4 and the liftable vibration rod 3. The vibration control device 5 can adjust the vibration frequency and vibration time of the hydraulic power device 4 according to the commands input by the operation panel 18. The liftable vibration rod 3 can be raised or lowered according to the commands input by the operation panel 19, realizing two states: the vibration plate 10 is suspended in the air and placed on the support table frame 16. Specifically, the operation panel 18 includes a vibration control switch 18-1, a vibration frequency setting button 18-2, a vibration time setting button 18-3, a vibration rod raising button 18-4, a vibration rod lowering button 18-5, and an emergency stop button 18-6. The operation panel 18 also includes a display unit 18-7, which displays the vibration frequency and the vibration time.

[0042] Furthermore, referring to Figure 5, a noise-reducing rubber ring 8 is installed between the central hollow portion of the height-adjustable vibrating rod 3 and the supporting table frame 16. The noise-reducing rubber ring 8 is tightly fastened to the height-adjustable vibrating rod 3. The central hollow portion of the noise-reducing rubber ring 8 has multiple layers of pleats, which facilitates the free vibration of the vibrating rod and prevents it from colliding with the supporting table frame 16. The outer edge of the noise-reducing rubber ring 8 is a thickened rubber strip with holes for the insertion of fixing bolts 7. The outer edge of the noise-reducing rubber ring 8 is fixed to the supporting table frame with fixing bolts 7.

[0043] Example 2

[0044] A test method based on a disturbed soil strength restorer test device, the method comprising the following steps:

[0045] Step 1: Press the upper sample box down to the original soil sample to complete the soil sampling.

[0046] Apply a thin, even layer of Vaseline to the inside of the upper sample box to reduce frictional resistance. Place the upper sample box with the cutting edge facing down on the undisturbed soil sample. Apply even force to press the upper sample box vertically down until the soil sample exceeds the upper edge of the upper sample box. Use a soil cutter to trim and level the excess soil at both ends. Then, gently and slowly place the upper sample box containing the soil sample into the lower sample box. Place the upper and lower sample boxes together on the vibrating plate and connect the external thread of the lower sample box to the internal thread hole 10-1 of the vibrating plate.

[0047] Step 2: Insert the cone into the soil sample and measure the cone penetration depth of the undisturbed soil sample and the cone penetration depth of the disturbed soil sample.

[0048] Select and install an appropriate cone based on the soil hardness. Apply Vaseline to the cone surface before each penetration to ensure smoothness. Specifically, for silty clay, a 76g cone with a 60° or 45° cone angle can be used; for plastic soft clay, a 76g cone with a 30° cone angle or a 100g cone with a 60° cone angle can be used; and for hard clay, a 100g cone with a 45° or 30° cone angle can be used.

[0049] Adjust the leveling legs at the bottom of the vibrating plate so that it is placed horizontally on the support table (with the bubble in the leveling bubble in the middle position) and the cone tip just in contact with the soil sample surface. Start the cone liquid limit tester and allow the cone to sink freely for 5 seconds, then read the cone penetration depth. A cone penetration depth between 3 mm and 18 mm is considered a valid cone penetration depth; otherwise, select a different cone and repeat the test. Rotate the upper sample box to change the contact position between the cone tip and the soil sample, ensuring the distance between the two penetration points is not less than 1 cm. Repeat the cone penetration test twice and take the average value as the cone penetration depth d0 of the undisturbed soil sample.

[0050] Retract the leveling legs of the vibrating plate, raise the height of the adjustable vibrating rod to a suitable position, and lift the vibrating plate. Set the vibration frequency and time through the control panel, and turn on the vibration control switch to simulate the disturbance of the soil during on-site construction. Depending on the degree of disturbance, the vibration frequency can be set between 1 and 80 Hz, and the vibration time between 1 and 30 minutes. After vibration, lower the height of the adjustable vibrating rod, readjust the leveling legs of the vibrating plate, and place the vibrating plate horizontally on the support table. Then, turn on the liquid limit and plastic limit tester to conduct a cone penetration test and repeat it at least twice. Take the average value as the cone penetration depth d1 of the disturbed soil sample.

[0051] Rotate the lower sample box and place the upper sample box and disturbed soil sample together into a constant temperature and humidity chamber for curing. After curing for the specified time according to experimental requirements, remove the soil sample and conduct another cone drop test to obtain the cone penetration depth d2, d3...d after the disturbed soil strength has recovered. n The upper sample box and disturbed soil sample can be cured in a constant temperature and humidity chamber for 7, 21, 30, 60 and 90 days. The soil samples can then be removed to obtain the cone penetration depth d7 after the disturbed soil strength has recovered. 21 d 30 d 60 d 90 .

[0052] Step 3: Based on the cone penetration depth of the undisturbed soil sample and the cone penetration depth of the disturbed soil sample, calculate the undrained strength index and the strength recovery degree of the disturbed soil under different degrees of recovery.

[0053] According to the calculation formula C u =KW / d 2The undrained strength index of disturbed soil under different degrees of restoration is calculated. K is an empirical coefficient, mainly related to the angle of the cone and the smoothness. The value of K can be referenced. W represents the weight of the falling cone, and d represents the cone penetration depth. This allows us to obtain the undrained strength index (C) for days 1, 7, 21, 30, 60, and 90. u0 C u1 C u7 C u21 C u30 C u60 C u90 According to the calculation formula R = C un / C u0 Calculate the degree of strength recovery of disturbed soil, i.e., the undrained strength index C of the disturbed soil after recovery. un Compared with the undrained strength index C of the original soil u0 The ratio, especially when the drop cone was not replaced throughout the entire test. You can obtain the intensity recovery rate on days 1, 7, 21, 30, 60, and 90.

[0054] Referring to Figure 6, a curve showing the recovery pattern of the undrained strength index of disturbed soil is plotted with curing time on the horizontal axis and the degree of strength recovery of disturbed soil on the vertical axis. After the cone tip penetrates the soil sample, the degree of strength recovery of disturbed soil increases rapidly during the initial curing period, and then increases more gradually in the later curing period. Based on the disturbed soil strength recovery test device, the changing pattern of the undrained strength index of soil after disturbance is revealed, and the degree of soil strength recovery is determined by comparing the recovered index of disturbed soil with the undrained soil strength index.

[0055] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for testing the strength resilience of disturbed soil, characterized in that: A testing device is employed, comprising: a vibratory hammer, a connecting shaft, a height-adjustable vibratory rod, a hydraulic power unit, a vibration control device, a vibratory hammer mounting bracket, leveling legs, a vibrating plate, a lower sample box, an upper sample box, a cone-type liquid and plastic limit meter, and a supporting table. The vibratory hammer is mounted directly above the vibratory hammer mounting bracket and connected to the hydraulic power unit, which provides power for the vibration of the vibratory hammer. The vibration control device is connected to the hydraulic power unit. The connecting shaft is mounted on the vibratory hammer and connected to the height-adjustable vibratory rod, used to drive the height-adjustable vibratory rod to vibrate. The height-adjustable vibratory rod vertically penetrates the central hollow portion of the supporting table, and the vibrating plate is mounted on the top of the height-adjustable vibratory rod. The lower and upper sample boxes are mounted on... The device is mounted on a vibrating plate to hold disturbed soil samples; the cone-shaped liquid and plastic limit meter is mounted on a support frame; an internal threaded hole (blind hole) is provided at the center of the upper surface of the vibrating plate, and an external thread is provided on the peripheral wall of the lower sample box, which is spirally connected to the vibrating plate; a cutting edge is provided at the bottom of the upper sample box; a leveling bubble is provided on the vibrating plate to determine whether the vibrating plate is stable based on the position of the bubble; leveling legs are provided at the four corners of the bottom of the vibrating plate to ensure that the vibrating plate is placed horizontally on the support frame; a groove is provided at the center of the bottom surface of the vibrating plate to mate with the top of the adjustable vibrating rod, and the top of the adjustable vibrating rod is installed into the groove; the test method using the aforementioned testing device includes the following: Steps: Step 1: Place the upper sampling box with the cutting edge facing down on the undisturbed soil sample. Apply even force to press the upper sampling box vertically down until the soil sample exceeds the upper edge of the upper sampling box. Use a soil cutter to remove and level the excess soil at both ends. Gently and slowly place the upper sampling box containing the soil sample into the lower sampling box. Place the upper and lower sampling boxes together on the vibrating plate and connect the external thread of the lower sampling box to the internal thread hole of the vibrating plate. Step 2: Adjust the leveling legs at the bottom of the vibrating plate so that the vibrating plate is placed horizontally on the support table and the cone tip is just in contact with the soil sample surface. Start the cone liquid limit tester and let the cone sink freely, reading the cone penetration depth. Rotate the upper sampling box to change the contact position between the cone tip and the soil sample, and repeat the cone drop test twice. Take the average value as the cone penetration depth of the undisturbed soil sample; retract the leveling legs of the vibrating plate, raise the height of the adjustable vibrating rod to a suitable position, and lift the vibrating plate; set the vibration frequency and time, turn on the vibration control switch, and simulate the disturbance effect of on-site construction on the soil; after the vibration is completed, lower the height of the adjustable vibrating rod, readjust the leveling legs of the vibrating plate to place the vibrating plate horizontally on the support table, and then turn on the liquid limit and plastic limit tester to conduct a drop cone test and repeat it at least 2 times, taking the average value as the cone penetration depth of the disturbed soil sample; rotate the lower sample box, put the upper sample box and the disturbed soil sample together into the constant temperature and humidity chamber for curing, and after curing for the specified time according to the experimental requirements, take out the soil sample and conduct the drop cone test again to obtain the cone penetration depth after the disturbed soil strength has recovered;Step 3: Based on the cone penetration depth of the undisturbed soil sample, the cone penetration depth of the disturbed soil sample, and the cone penetration depth of the disturbed soil after strength recovery, calculate the undrained strength index and the degree of strength recovery of the disturbed soil under different degrees of recovery.

2. The method for testing the strength resilience of disturbed soil according to claim 1, characterized in that: The upper sample box is cylindrical, with an inner diameter of 12cm and a height of 10cm.

3. The method for testing the strength resilience of disturbed soil according to claim 1, characterized in that: Support legs are installed at the four corners of the lower part of the support table to support the testing equipment.

4. The method for testing the strength resilience of disturbed soil according to claim 1, characterized in that: A cabinet door is installed at the bottom of the supporting table frame, and an operation panel is installed on the outside of the cabinet door. The operation panel is connected to a vibration control device and a height-adjustable vibration rod, and is used to send control commands to the hydraulic power device and the height-adjustable vibration rod. The vibration control device adjusts the vibration frequency and vibration time of the driving hydraulic power device according to the commands input on the operation panel. The height-adjustable vibration rod rises or falls according to the commands input on the operation panel.

5. The method for testing the strength resilience of disturbed soil according to claim 1, characterized in that: A noise-reducing rubber ring is installed between the height-adjustable vibrating rod and the central hollow part of the supporting table frame, and the noise-reducing rubber ring is tightly clamped to the height-adjustable vibrating rod.

6. The method for testing the strength resilience of disturbed soil according to claim 5, characterized in that: The hollowed-out part in the middle of the noise-reducing rubber ring has multiple layers of pleats, and the outer edge of the noise-reducing rubber ring is a thickened rubber strip with holes for fixing bolts to be inserted. The outer edge of the noise-reducing rubber ring is fixed to the support table frame with fixing bolts.

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