Impact load dynamic seepage device and method

Abstract

The present invention discloses a dynamic seepage device and method under impact load, the device comprises a loading device, a device body, and a water supply system, wherein the loading device is arranged in the device body, and the water supply system is connected to the device body. The present invention aims at solving the technical requirements of how to solve the current problem of sand liquefaction, which is completed under vibration load or large shear displacement conditions, and most of the studies maintain an undrained state, and rarely consider the liquefaction response of the bottom of saturated sand after being impacted. A dynamic seepage device and method under impact load are proposed, which can better observe the sand sample changes and liquefaction response of the sand when the bottom is impacted, and analyze the changes in the speed of seepage under dynamic load by recording data through sensors. The present invention can observe the sand sample changes and its liquefaction response when the bottom is impacted, and can also observe the changes in the speed of seepage under different dynamic loads.

Description

Technical Field

[0001] The invention relates to an impact load dynamic seepage device and method, belonging to the technical field of geotechnical engineering and geological engineering. Background Art

[0002] Liquefaction response mechanism of saturated sand under bottom impact: When the bottom of the sand sample is subjected to different impact pressures and different impact frequencies, the saturated sand will form different pore water pressures. When the pore water pressure at the same height is equal to the total pressure of the sand, the saturated sand will liquefy (even if the impact pressure is small, the saturated sand will not liquefy, but the pore water pressure will increase). Therefore, the equipment determines the relationship between impact load and sand liquefaction by determining the relationship between pore water pressure and total pressure.

[0003] Saturated sand will liquefy under the action of vibration, impact, explosion and other forms of dynamic loads, accompanied by the settlement of the sand surface, and in severe cases, sand blasting and water bubbling. As a result, it causes serious damage to geotechnical structures such as mines, dams, and docks, resulting in serious casualties and property losses. At present, there are few studies on equipment that causes liquefaction of upper sand due to underground shock waves. This device is conducive to simulating the study of liquefaction of saturated sand due to impact from the bottom.

[0004] At present, most of the research on sand liquefaction is completed under vibration load or large shear displacement conditions, and most of the research maintains an undrained state, and rarely considers the liquefaction response of saturated sand after the bottom is impacted. The impact device proposed in this patent can better observe the changes in sand samples and liquefaction response when the sand is impacted at the bottom.

[0005] At present, most of the research on seepage is completed under static load conditions, and the impact of the impact on sand on its seepage is rarely considered. However, this experimental device can record data through sensors to analyze the changes in the speed of seepage under dynamic loads. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art and to provide a device with low cost and simple structure for performing impact test under seepage state in view of the deficiencies in the existing equipment. The device can not only solve the problem of liquefying the sample by impacting the sample with a specific frequency and size, but also can make use of the device to further study the dynamic seepage problem under impact, and provide an impact load dynamic seepage device and method.

[0007] In order to solve the above technical problems, the present invention provides an impact load dynamic seepage device, including a loading device, a device body, and a water supply system, wherein the loading device is arranged in the device body, and the water supply system is connected to the device body.

[0008] As a preferred embodiment, the loading device includes an adjustable speed motor, a crankshaft, a connecting rod, and an impact rod. The output end of the adjustable speed motor is connected to the crankshaft, and the adjustable speed motor drives the crankshaft to rotate. One end of the connecting rod is connected to the crankshaft, and the other end of the connecting rod is connected to the impact rod. An impact head is provided at the head of the impact rod, and a detachable spring is placed on the impact head, and a copper cap is installed above the spring.

[0009] As a preferred embodiment, the device body includes a sample tube, a box base, and a threaded rod. The bottom of the box base is fixedly connected to the threaded rod to form an integral bracket, and an optical axis for placing a counterweight is arranged in the box base; a steel hoop matching the outer diameter of the sample tube is installed on the upper part of the integral bracket; an upper flange and a lower flange symmetrically distributed up and down are arranged on the integral bracket, and the upper flange and the lower flange are moved and adjusted on the threaded rod by the first nut and the second nut through the upper and lower cooperation of the first nut and the second nut to adjust the positioning height, and the side of the lower flange is externally connected to the water inlet pipe; the lower end of the sample tube is connected to the upper flange, and a filter box is arranged at the inner bottom of the sample tube.

[0010] As a preferred embodiment, a box base slide rail is installed at the upper opening of the box base to ensure that the copper cap in the loading device moves up and down smoothly.

[0011] As a preferred embodiment, the apertures of the reserved threaded holes in the sample tube match the diameters of the sensor and drainage pipe used in the experiment, the threaded hole reserved at the top of the sample tube is connected to the drainage pipe, and the hole pressure sensor is inserted into one side of the remaining highly symmetrical threaded holes on the sample tube, and the pressure sensor is inserted into the other side.

[0012] As a preferred embodiment, a mesh copper cap is installed outside the probe of the pore pressure sensor.

[0013] As a preferred embodiment, the interior of the filter box is composed of a layer of glass beads and a screen, which not only ensures that the sand sample does not fall into the upper flange, but also ensures that the water flows evenly over the sand surface.

[0014] As a preferred embodiment, the steel hoop is used to prevent the upper part of the sample tube from shaking due to being too high. The interior of the steel hoop is designed with a rubber cushion layer to increase the friction between the steel hoop and the sample tube and increase stability.

[0015] As a preferred embodiment, the water supply system includes an adjustable speed water pump, a flow meter, and a needle valve. The left end of the needle valve is connected to the adjustable speed water pump through an inlet pipe, and the right end of the needle valve is connected to the flow meter. The flow meter is connected to the device body through an inlet pipe.

[0016] The present invention also proposes an impact load dynamic seepage method, comprising the following steps:

[0017] Step SS1: using a circular knife to prepare sand samples at a field sampling point, screening different types of sand, and drying and storing them;

[0018] Step SS2: The dry density of sand is measured according to the geotechnical test procedures, and the required sand volume is calculated according to the inner diameter of the sample tube and the highest position height of the pore pressure sensor arranged on the sample tube. The required dry sand mass is calculated according to the dry density of sand. The formula is:

[0019] m=ρ d v=ρπr 2 h

[0020] In the formula, m is the mass of dry sand required for sample preparation, ρ d is the dry density of natural sand, v is the required volume of dry sand, π is the pi, r is the inner radius of the sample tube, and h is the highest position height of the pore pressure sensor arranged on the sample tube;

[0021] Step SS3: Connect the pore pressure sensor and the pressure sensor to the reserved threaded holes on the side wall of the sample tube respectively, place the filter box at the bottom of the sample tube, load the weighed sand samples into the sample tube in batches through the funnel, then open the needle valve, fill water into the sample tube until the water level reaches the reserved threaded hole position at the top of the sample tube, block the reserved threaded holes at the two symmetrical positions at the top, and stop the water flow;

[0022] Step SS4: Turn on the adjustable speed motor, and the impact rod impacts the lower flange. The sensor probe data at each position is recorded by the computer. The total pressure of the sensor and the pore water pressure at each position after the impact are compared. According to the effective stress principle, it is determined whether the sand sample is liquefied, and the hydraulic gradient i between the two holes at this time is calculated. n , the relevant formula is:

[0023] σ′ n =σ n -u n

[0024] In the formula, σ n is the total stress displayed by the pressure sensor at the nth reserved hole position, u n The pore water pressure displayed by the pore pressure sensor at the nth reserved hole, σ′ n is the effective stress at the position of the nth reserved hole. When it is equal to 0, liquefaction occurs;

[0025]

[0026] In the formula, h n = excess pore water pressure head at the nth reserved hole position, h n+1 = excess pore water pressure head at the position of the n+1th reserved hole, H nis the height between the nth and n+1th reserved threaded holes, i n is the hydraulic gradient between the two holes;

[0027] Step SS5: Open the needle valve, remove the rubber plugs of the reserved holes at the two symmetrical positions at the top of the side wall of the sample tube, connect the drainage pipe to the reserved threaded hole at the top, keep the other parts of the sample tube running, and then adjust the water flow rate to keep the water level in the sample tube at the height of the top threaded hole;

[0028] Step SS6: Read the current seepage velocity v through the flow meter, and record the pore water pressure u′ of the sensor at the nth reserved hole position and the n+1th reserved hole position when the seepage state is maintained through the computer again n , and calculate the dynamic hydraulic gradient i′ at this time n According to Darcy's law, the dynamic seepage coefficient k at this time is calculated, and the relevant formula is:

[0029] k=v / (i′ n -i n )

[0030] Beneficial effects achieved by the present invention: The present invention aims at solving the technical demand that most of the current research on sand liquefaction is completed under vibration load or large shear displacement conditions, and most of the research maintains an undrained state, and rarely considers the liquefaction response of the bottom of saturated sand after being impacted. A dynamic seepage device and method under impact load are proposed, which can better observe the sand sample changes and liquefaction response of the sand when the bottom is impacted. The present invention aims at solving the technical demand that most of the current research on seepage is completed under static load conditions, and rarely considers the impact of the sand on its seepage. The sensor records data to analyze the changes in the speed of seepage under dynamic load. The present invention can observe the sand sample changes and its liquefaction development process when the sand is impacted at the bottom as a whole, and can also observe the changes in the speed of seepage under different dynamic loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of the loading device of the present invention;

[0032] Figure 2 It is a schematic structural diagram of the sample loading device of the present invention;

[0033] Figure 3 It is a structural schematic diagram of the box base of the present invention;

[0034] Figure 4 It is a structural schematic diagram of the impact loading test under seepage conditions of the present invention.

[0035] The meaning of the marks in the figure: 1-adjustable speed motor, 2-impact rod, 3-connecting rod, 4-crankshaft, 5-spring, 6-copper cap, 7-counterweight, 8-impact head, 9-box base, 10-steel hoop, 11-pore pressure sensor, 12-pressure sensor, 13-threaded rod, 14-sample cylinder, 15-filter box, 16-upper flange, 17-lower flange, 18-box base slide rail, 19-water inlet pipe, 20-drainage pipe, 21-first nut, 22-second nut, 23-bolt, 24-adjustable speed water pump, 25-needle valve, 26-flow meter. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0037] Example 1: Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the present invention proposes a dynamic seepage device under impact load, including a loading device, a device body and a water supply system.

[0038] Combination Figure 1 The loading device is placed in the base 9 of the box body, and includes an adjustable speed motor 1, a crankshaft 4, a connecting rod 3, and an impact rod 2. The adjustable speed motor 1 drives the crankshaft 4 to rotate. One end of the connecting rod 3 is connected to the crankshaft 2, and the other end is connected to the impact rod 2. The head of the impact rod is designed with a wider impact head 8, on which a detachable spring 5 is placed, and a replaceable copper cap 6 is installed above the spring 5.

[0039] Combination Figure 3 The device body includes a sample tube 14, a box base 9, and a threaded rod 13. The selected box base 9 can be waterproof and discharge-proof to ensure the safety of the device body. The bottom of the box base 9 is provided with a threaded hole and fixedly connected with the threaded rod 13 to form an integral bracket. The box base 9 is designed with an optical axis to place a counterweight 7 to increase the stability of the device body; a steel hoop 10 matching the outer diameter of the sample tube 14 is installed on the upper part of the integral bracket; the upper flange 16 and the lower flange 17 are provided with a light hole to connect with the integral bracket, and the positioning height is adjusted by moving on the threaded rod 13 through the first nut 21, and the overall sealing of the device body is ensured by the upper and lower cooperation of the first nut 21 and the second nut 22. At the same time, a threaded hole is provided on the side of the lower flange 17 to connect with the water inlet pipe 19; the sample tube 14 is transparent, and the lower end of the sample tube 14 is connected to the upper flange 16. The tube wall of the sample tube 14 has two rows of symmetrical reserved threaded holes along the busbar, and a filter box 15 is placed at the bottom position of the sample tube 14.

[0040] Combination Figure 4The water supply system includes an adjustable speed water pump 24, a flow meter 26, and a needle valve 25, wherein the left end of the needle valve 25 is connected to the adjustable speed water pump 24 through an inlet pipe 19, and the right end of the needle valve 2 is connected to the flow meter 26, and the flow meter 26 is connected to the device body through the inlet pipe 19.

[0041] Optionally, the sample tube 14 is made of organic glass, and the lower flange 17, the threaded rod 13 and the box base 9 are made of stainless steel.

[0042] Optionally, a box base slide rail 18 is installed at the box upper opening position of the box base 9 to ensure that the copper cap 6 in the loading device moves up and down smoothly.

[0043] Optionally, the copper material used for the copper cap 6 is softer than the material of the lower flange 17 , and can protect the bottom surface of the lower flange 17 .

[0044] Optionally, the apertures of the reserved threaded holes in the sample tube 14 are matched with the diameters of the sensors and drainage pipes used in the experiment, and are sealed with rubber plugs during the sample loading process. During the experiment, the threaded holes reserved at the top of the sample tube are connected to the drainage pipe 20, and the pore pressure sensor 11 is inserted on one side of the remaining highly symmetrical threaded holes, and the pressure sensor 12 is inserted on the other side.

[0045] Optionally, the drainage pipe 20 can ensure that the water level in the sample tube 14 remains unchanged.

[0046] Optionally, the filter box 15 is made of stainless steel on the outside and consists of a layer of glass beads and a screen on the inside, which can ensure that the sand sample does not fall into the upper flange 16 and ensure that the water flows evenly through the sand surface.

[0047] Optionally, the steel hoop 10 can prevent the sample tube 14 from shaking due to its upper part being too high, and a rubber cushion layer is designed inside to increase the friction between the steel hoop 10 and the sample tube 14, thereby increasing stability.

[0048] Optionally, the spring 5 can play a buffering role during the impact loading process to prevent the loading device from getting stuck.

[0049] Optionally, a mesh copper cap is installed on the outside of the probe of the pore pressure sensor 11 , which is different from the pressure sensor 12 .

[0050] Optionally, the adjustable speed water pump 24 can adjust the water flow speed and water flow size to ensure that the flow rate remains unchanged during the experiment.

[0051] Optionally, the adjustable speed motor 1 can adjust the magnitude and frequency of the impact load to ensure that the load remains constant during the experiment.

[0052] Embodiment 2: The present invention also discloses an impact load dynamic seepage method, comprising the following steps:

[0053] (1) Use a circular knife to prepare sand samples at the field sampling point, screen different types of sand, and dry and store them;

[0054] (2) The dry density of sand is measured according to the geotechnical test regulations. The required volume of sand is calculated according to the inner diameter of the sample tube 14 and the highest position height of the pore pressure sensor 11 arranged on the sample tube 14. The required dry sand mass is calculated according to the dry density of sand. The formula is:

[0055] m=ρ d v=ρπr 2 h;

[0056] In the formula, m is the mass of dry sand required for sample preparation, ρ d is the dry density of natural sand, v is the required volume of dry sand, π is the pi, r is the inner radius of the sample tube 14, and h is the highest position height of the pore pressure sensor 11 arranged on the sample tube;

[0057] (3) Connect the pore pressure sensor 11 and the pressure sensor 12 to the reserved threaded holes on the side wall of the sleeve respectively according to the aforementioned connection method, place the filter box 15 at the bottom of the sample tube 14, and then load the weighed sand samples into the sample tube 14 in batches through the funnel. Then open the needle valve 25, and fill water into the sample tube 14 until the water level reaches the reserved threaded hole position at the top of the sample tube 14, block the reserved threaded holes at the two symmetrical positions at the top, and stop the water flow;

[0058] (4) Turn on the adjustable speed motor 1, and the impact rod 2 impacts the lower flange 17. The sensor probe data at each position is recorded by the computer. The total pressure of the sensor and the pore water pressure at each position after the impact are compared. According to the effective stress principle, it is determined whether the sand sample is liquefied, and the hydraulic gradient i at this time is calculated. n , the relevant formula is:

[0059] σ′ n =σ n -u n ;

[0060] In the formula, σ n is the total stress displayed by the pressure sensor at the nth reserved hole position, u n The pore water pressure displayed by the pore water pressure sensor at the nth reserved hole, σ′ n is the effective stress at the position of the nth reserved hole. When it is equal to 0, liquefaction occurs;

[0061]

[0062] In the formula, h n = excess pore water pressure head at the nth reserved hole position, hn+1 = excess pore water pressure head at the position of the n+1th reserved hole, H n is the height between the nth and n+1th reserved threaded holes, i n is the hydraulic gradient between the two holes; (5) Open the needle valve 25, remove the rubber plugs of the reserved holes at the two symmetrical positions at the top of the side wall of the sample tube 14, connect the drainage pipe 20 to the reserved threaded hole at the top, keep the other parts of the instrument running, and then adjust the water flow rate to keep the water level in the sample tube 14 at the height of the top threaded hole;

[0063] (6) The current seepage velocity v is read out by the flow meter 26, and the pore water pressure u′ of the sensor at the nth reserved hole position and the n+1th reserved hole position is recorded by the computer again while the seepage state is maintained. n , and calculate the dynamic hydraulic gradient i′ at this time n According to Darcy's law, the dynamic seepage coefficient k at this time can be calculated, and the relevant formula is:

[0064] k=v / (i′ n -i n )

[0065] Through this experiment, the relationship between the total pressure and pore water pressure of the sand sample under impact loads of different sizes can be effectively measured. At the same time, the relationship between the liquefaction of the sand sample and the impact load can also be established. At the same time, the dynamic seepage coefficient k value under impact load can also be calculated.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A dynamic seepage method for impact load, characterized in that: The impact load dynamic seepage device comprises a loading device, a device body, and a water supply system, wherein the loading device is arranged in the device body, and the water supply system is connected to the device body; The loading device comprises an adjustable speed motor (1), a crankshaft (4), a connecting rod (3), and an impact rod (2); the output end of the adjustable speed motor (1) is connected to the crankshaft (4); the adjustable speed motor (1) drives the crankshaft (4) to rotate; one end of the connecting rod (3) is connected to the crankshaft (4); the other end of the connecting rod (3) is connected to the impact rod (2); an impact head (8) is provided at the head of the impact rod (2); a detachable spring (5) is placed on the impact head (8); a copper cap (6) is installed above the spring (5); The device body comprises a sample tube (14), a box base (9), and a threaded rod (13); the bottom of the box base (9) is fixedly connected to the threaded rod (13) to form an integral bracket; an optical axis for placing a counterweight (7) is arranged in the box base (9); a steel hoop (10) matching the outer diameter of the sample tube (14) is arranged on the upper part of the integral bracket; an upper flange (16) and a lower flange (17) symmetrically distributed up and down are arranged on the integral bracket; the upper flange (16) and the lower flange (17) are matched up and down on the threaded rod (13) through a first nut (21) and a second nut (22) to move and adjust the positioning height; the side of the lower flange (17) is externally connected to a water inlet pipe (19); the lower end of the sample tube (14) is connected to the upper flange (16); and a filter box (15) is arranged at the inner bottom of the sample tube (14); The diameters of the reserved threaded holes of the sample tube (14) are respectively matched with the diameters of the sensor and the drainage pipe (20) used in the experiment; the threaded hole reserved at the top of the sample tube (14) is connected to the drainage pipe (20); the pore pressure sensor (11) is inserted into one side of the remaining highly symmetrical threaded holes on the sample tube (14), and the pressure sensor (12) is inserted into the other side; The water supply system comprises an adjustable-speed water pump (24), a flow meter (26), and a needle valve (25); the left end of the needle valve (25) is connected to the adjustable-speed water pump (24) via a water inlet pipe (19); the right end of the needle valve (25) is connected to the flow meter (26); and the flow meter (26) is connected to the device body via the water inlet pipe (19); The impact load dynamic seepage method based on the impact load dynamic seepage device comprises: Step SS1: using a circular knife to prepare sand samples at a field sampling point, screening different types of sand, and drying and storing them; Step SS2: The dry density of the sand is measured according to the geotechnical test regulations, and the required volume of the sand is calculated according to the inner radius of the sample tube (14) and the highest position height of the pore pressure sensor (11) arranged on the sample tube (14), and the required dry sand mass is calculated according to the dry density of the sand. The calculation formula is: ， In the formula, m is the mass of dry sand required for sample preparation, ρ d is the dry density of natural sand, v is the required volume of dry sand, π is the pi, r is the inner radius of the sample tube (14), and h is the highest position height of the pore pressure sensor (11) arranged on the sample tube (14); Step SS3: Connect the pore pressure sensor (11) and the pressure sensor (12) to the reserved threaded holes on the side wall of the sample tube (14), respectively, place the filter box (15) at the bottom of the sample tube (14), load the weighed sand sample into the sample tube (14) in batches through the funnel, then open the needle valve (25), and fill water into the sample tube (14) until the water level reaches the reserved threaded hole position at the top of the sample tube (14), block the reserved threaded holes at the two symmetrical positions at the top, and stop the water flow; Step SS4: Turn on the adjustable speed motor (1), and the impact rod (2) impacts the lower flange (17). The sensor probe data at each position is recorded by the computer, and the total pressure of the sensor and the pore water pressure at each position after the impact are compared. According to the effective stress principle, it is determined whether the sand sample is liquefied, and the hydraulic gradient i at this time is calculated. n , the relevant formula is: ， In the formula, σ n is the total stress displayed by the pressure sensor at the nth reserved hole position, u n The pore water pressure displayed by the pore pressure sensor at the nth reserved hole, σ´ n is the effective stress at the position of the nth reserved hole. When it is equal to 0, liquefaction occurs; ， In the formula, h n = excess pore water pressure head at the nth reserved hole position, h n+1 = excess pore water pressure head at the n+1th reserved hole position, H n is the height between the nth and n+1th reserved threaded holes, i n is the hydraulic gradient between the two holes; Step SS5: Open the needle valve (25), remove the rubber plugs of the reserved holes at the two symmetrical positions at the top of the side wall of the sample tube (14), connect the drainage pipe (20) to the reserved threaded hole at the top, keep the other parts of the sample tube (14) running, and then adjust the water flow rate to keep the water level in the sample tube (14) at the height of the threaded hole at the top unchanged; Step SS6: The current seepage velocity v is read out by the flow meter (26), and the pore water pressure u´ of the sensor at the nth reserved hole position and the n+1th reserved hole position is recorded by the computer again when the seepage state is maintained. n , and calculate the dynamic hydraulic gradient i´ between the two holes at this time n， According to Darcy's law, the dynamic seepage coefficient k at this time is calculated, and the relevant formula is: 。 2. The impact load dynamic seepage method according to claim 1, characterized in that: The box base (9) is provided with a box base slide rail (18) at the upper opening of the box body to ensure that the copper cap (6) in the loading device can move up and down smoothly.

3. The impact load dynamic seepage method according to claim 1, characterized in that: A mesh copper cap is installed outside the probe of the pore pressure sensor (11).

4. The impact load dynamic seepage method according to claim 1, characterized in that: The interior of the filter box (15) is composed of a layer of glass beads and a screen, which not only ensures that the sand sample does not fall into the upper flange (16), but also ensures that the water flows evenly over the sand surface.

5. The impact load dynamic seepage method according to claim 1, characterized in that: The steel hoop (10) is used to prevent the upper part of the sample tube (14) from shaking due to being too high. A rubber cushion layer is designed inside the steel hoop (10) to increase the friction between the steel hoop (10) and the sample tube (14) and increase stability.

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