Coarse-grained soil lateral confinement dynamic compressor and experimental method thereof

Abstract

The invention relates to the technical field of geotechnical experiment equipment, and discloses a coarse-grained soil lateral confinement dynamic compression instrument and an experiment method thereof. The electric cylinder is longitudinally arranged above the test piece bin, the pressing plate is arranged on a movable rod of the electric cylinder, the pressing plate is located in the test piece bin, and a water injection opening is formed in the pressing plate; the displacement sensor is arranged on a reaction frame of the pressure piece and used for measuring the axial deformation of the test piece, the force sensor is arranged on the test piece and used for measuring the load applied to the test piece, and the multiple pore pressure sensors are all arranged in the test piece and used for measuring the pressure distribution of the inner wall of the test piece; the coarse-grained soil lateral confinement dynamic compression instrument can reveal a deformation mechanism of a soil-rock mixture under the action of lateral confinement compression cyclic loading, and explores plastic cumulative deformation and excess pore water pressure change rules of a sample under different stone contents and loading amplitudes.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical experimental equipment, and in particular to a coarse-grained soil confined dynamic compression instrument and an experimental method thereof. Background Art

[0002] In high-fill airports in mountainous areas, soil-rock mixture is the main filling material for airport runways. The mechanical response of soil-rock mixture under complex stress paths is the main internal cause of the deformation of the fill body.

[0003] During takeoff, landing and taxiing, aircraft will generate impact loads and cyclic loads on the airport runway, resulting in dynamic strain and dynamic pore pressure in the lower foundation, and causing uneven settlement deformation. In-depth research on the dynamic response of soil-rock mixture under dynamic load is of great significance for the post-construction foundation settlement control of high-fill airports in mountainous areas.

[0004] In the existing technology, the research on the mechanical behavior of soil-rock mixture mainly focuses on the strength and deformation characteristics under static load. The commonly used test methods include consolidation test, direct shear test and triaxial compression test. The main factors considered are particle content, initial moisture content, stress level, etc. The existing experimental equipment cannot study the evolution law of the cumulative plastic deformation and excess pore water pressure of soil-rock mixture under traffic load. Summary of the invention

[0005] The present invention proposes a coarse-grained soil confined dynamic compression instrument to solve the shortcomings of the above-mentioned prior art. The coarse-grained soil confined dynamic compression instrument can reveal the deformation mechanism of soil-rock mixture under confined compression cyclic load, and explore the plastic cumulative deformation and excess pore water pressure change law of samples under different stone contents and loading amplitudes.

[0006] The technical solution of the present invention is: a coarse-grained soil confined dynamic compression instrument, comprising:

[0007] The test piece bin is in a hollow column shape, the bottom end of the test piece bin is a bell mouth, and a valve is provided at the bell mouth of the test piece bin;

[0008] The pressure piece includes a reaction frame, an electric cylinder and a pressure plate, wherein the electric cylinder is longitudinally arranged on the reaction frame, the pressure plate is arranged on the movable rod of the electric cylinder, the pressure plate is located in the specimen chamber, a water injection port is arranged on the pressure plate, and the pressure plate is used to provide a periodic load to the specimen in the specimen chamber under the drive of the electric cylinder;

[0009] The detection component includes: a displacement sensor, a force sensor and a plurality of pore pressure sensors, wherein the displacement sensor is arranged on a reaction frame, and the displacement sensor is used to measure the axial deformation of the specimen, the force sensor is arranged on the specimen, and the force sensor is used to measure the load applied to the specimen, and the plurality of pore pressure sensors are arranged in the specimen, and the pore pressure sensors are used to measure the pressure distribution on the inner wall of the specimen.

[0010] In at least one embodiment of the present invention, a seepage system is further included, and the seepage system includes:

[0011] A clean water tank connected to the water inlet of the pressing plate through a first connecting pipe;

[0012] A servo constant pressure water pump is arranged on the first connecting pipe;

[0013] An inlet pressure sensor is arranged on the first connecting pipe;

[0014] A flow sensor is arranged on the first connecting pipe;

[0015] The return water tank is connected with the bell mouth of the test piece chamber through a second connecting pipe;

[0016] The outlet pressure sensor is arranged on the second connecting pipe.

[0017] In at least one embodiment of the present invention, the return water tank is provided with a return water pipe connected to the clean water tank, and the return water pipe is provided with a return water pump.

[0018] In at least one embodiment of the present invention, the specimen chamber is a plexiglass cylinder, and a plurality of mounting holes for mounting pore pressure sensors are provided on a side wall of the specimen chamber.

[0019] In at least one embodiment of the present invention, a base is provided at the bottom of the specimen chamber, the reaction frame includes a plurality of columns and a top plate, the plurality of columns are longitudinally arranged on the base, the top plate is horizontally arranged at the top ends of the plurality of columns, the electric cylinder is arranged on the top plate, and the movable rod of the electric cylinder passes through the top plate.

[0020] In at least one embodiment of the present invention, a pulley is provided at the bottom of the specimen chamber, a guide rail is installed on the base, and the pulley is arranged on the guide rail.

[0021] The present invention also discloses a coarse-grained soil confined dynamic compression test method, comprising the following steps:

[0022] S1: Place a permeable stone at the bell mouth of the specimen chamber;

[0023] S2: Layered sample preparation: add the sample layer by layer into the specimen chamber, place the force sensor in the middle of the specimen chamber, and install the pore pressure sensor. After completion, compact the sample;

[0024] S3: Cover the sample with a pressure plate, add an appropriate amount of clean water through the water injection port to immerse the sample, maintain a low seepage state to prevent fine particles from flowing, then stop the water inlet, and let the sample stand for 8 to 12 hours to saturate;

[0025] S4: Connect the data acquisition instrument to the displacement sensor, the force sensor and multiple pore pressure sensor signals respectively, control the electric cylinder to apply an axial static load of 0 kN to 0.1 kN for pre-tightening, and adjust the position of the displacement sensor so that the displacement sensor can measure the axial deformation of the sample;

[0026] S5: According to the specific experimental requirements, static load, dynamic load or static and dynamic combined load is selected, vertical load is applied at 0kN / S~0.1kN / S, the electric cylinder accurately applies 0kN~10kN force, and the upper and lower peak values ​​of the vertical load are input periodically. The input force ranges from 0kN to 10kN, and the loading frequency is 0Hz~5Hz;

[0027] S6: After the experiment is completed, clean the specimen chamber, turn off all power supplies, and clean the specimen chamber in layers.

[0028] In at least one embodiment of the present invention, the pore pressure sensor is immersed in clean water for 30 minutes to 40 minutes before step S1.

[0029] In at least one embodiment of the present invention, vaseline is evenly applied on the inner wall of the specimen chamber before step S1.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention provides a specimen bin for loading soil-rock mixture, an electric cylinder and a pressing plate for providing a periodic load to the specimen, and a displacement sensor, a force sensor and a pore pressure sensor arranged on the specimen. During the experiment, water is injected into the specimen through a water injection port arranged on the pressing plate. After the specimen is saturated and static, static load, dynamic load or dynamic and static combined load is applied through the electric cylinder and the pressing plate according to specific experimental requirements. The experimental data finally obtained can reveal the deformation mechanism of the soil-rock mixture under the action of the lateral confined compression cyclic load, and explore the plastic cumulative deformation and excess pore water pressure change law of the specimen under different stone contents and loading amplitudes.

[0032] 2. The use of the coarse-grained soil confined dynamic compression instrument proposed in the present invention can establish the confined compression model and dynamic pore pressure model of the soil-rock mixture based on the final experimental data, and explore the relationship between key mechanical indicators such as cumulative plastic deformation and maximum excess pore water pressure and factors such as stone content, loading frequency and loading amplitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0034] Figure 2 It is a schematic diagram of the main structure of the present invention;

[0035] Figure 3 This is a schematic diagram of the seepage principle of the present invention.

[0036] Figure 4 It is a schematic diagram of the experimental structure of the present invention;

[0037] Description of reference numerals:

[0038] 1. Test piece chamber; 2. Pressure piece; 21. Electric cylinder; 22. Pressure plate; 23. Reaction frame; 231. Column; 232. Top plate; 3. Detection component; 31. Displacement sensor; 32. Force sensor; 33. Pore pressure sensor; 4. Seepage system; 41. Clean water tank; 411. First connecting pipe; 42. Servo constant pressure water pump; 43. Inlet pressure sensor; 44. Flow sensor; 45. Return water tank; 451. Second connecting pipe; 452. Return water pipe; 46. Outlet pressure sensor; 47. Return water pump; 6. Base. DETAILED DESCRIPTION

[0039] The drawings in the present invention are not drawn strictly according to the actual scale, and the specific size and quantity of each structure can be determined according to actual needs. The drawings described in the present invention are only schematic diagrams of the structures.

[0040] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. The words "include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Inside", "outside", "up", "down", "far", "near", "front", "back" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0042] In the existing technology, the research on the mechanical behavior of soil-rock mixtures mainly focuses on the strength and deformation characteristics under static loads. Commonly used test methods include consolidation test, direct shear test and triaxial compression test. The main factors considered include particle content, initial moisture content, stress level, etc.

[0043] At present, the research foundation for the evolution law of the accumulated plastic deformation and excess pore water pressure of soil-rock mixture under traffic load is relatively weak. During the take-off and landing and taxiing process, the aircraft will generate impact loads and cyclic loads on the airport runway, resulting in dynamic strain and dynamic pore pressure in the lower foundation, and causing uneven settlement deformation. In-depth research on the dynamic response of soil-rock mixture under dynamic load is of great significance for the post-construction foundation settlement control of high-fill airports in mountainous areas.

[0044] Combination Figures 1 to 3 As shown, a coarse-grained soil confined dynamic compression instrument comprises:

[0045] The specimen chamber 1 is in a hollow column shape, and the bottom end of the specimen chamber 1 is a bell mouth, and a valve is provided at the bell mouth of the specimen chamber 1;

[0046] The pressure piece 2 includes a reaction frame 23, an electric cylinder 21 and a pressure plate 22. The electric cylinder 21 is longitudinally arranged on the reaction frame, and the pressure plate 22 is arranged on the movable rod of the electric cylinder 21. The pressure plate 22 is located in the specimen chamber 1. The pressure plate 22 is provided with a water injection port and an exhaust valve. The pressure plate 22 is used to provide a periodic load to the specimen in the specimen chamber 1 under the drive of the electric cylinder 21. The pressure plate 22 is made of 304 stainless steel, which can effectively prevent rust in a water environment. The electric cylinder 21 is a servo motor loading device, and its motor adopts the A6 series servo motor of Panasonic, Japan. The servo motor has a power of 750W, and the servo motor has a built-in encoder, which can measure the displacement of the servo motor loading device. It adopts Taiwan TBI ball screw, NSK bearing, reduction ratio of 1:10, and the front and rear ends have travel limit protection. The maximum output is 10KN, the maximum movement speed is 1200mm / min, the amplitude can reach ±1mm at 5Hz, and the life span of full stroke reciprocation is 20 million times.

[0047] The detection component 3 includes: a displacement sensor 31, a force sensor 32 and a plurality of pore pressure sensors 33. The displacement sensor 31 is arranged on the reaction frame 23. The displacement sensor 31 is used to measure the axial deformation of the specimen. The force sensor 32 is arranged on the specimen. The force sensor 32 is used to measure the load applied to the specimen. The plurality of pore pressure sensors 33 are all arranged in the specimen. The pore pressure sensors 33 are used to measure the pressure distribution on the inner wall of the specimen.

[0048] Specifically, the force sensor 32 adopts a strain sensor. The internal circuit structure of this sensor is a strain full-bridge structure with high measurement accuracy and good stability. It is a widely used measurement sensor. The working principle of the metal resistance strain gauge is that the strain resistor adsorbed on the base material produces a phenomenon of change in resistance with mechanical deformation, commonly known as the resistance strain effect. The strain gauges are connected into a Wheatstone bridge. Due to the piezoresistance effect of the varistor, the bridge generates a highly linear voltage signal that is proportional to the pressure and proportional to the excitation voltage. According to the needs of the device, a force sensor with a range of 30KN is selected.

[0049] As an alternative embodiment, it also includes a seepage system 4, which includes:

[0050] The clean water tank 41 is connected to the water inlet of the pressing plate 22 through the first connecting pipe 411;

[0051] The servo constant pressure water pump 42 is arranged on the first connecting pipe 411;

[0052] The inlet pressure sensor 43 is arranged on the first connecting pipe 411;

[0053] The flow sensor 44 is arranged on the first connecting pipe 411;

[0054] The return water tank 45 is connected to the bell mouth of the specimen chamber 1 through a second connecting pipe 451;

[0055] The outlet pressure sensor 46 is disposed on the second communication pipe 451 .

[0056] The setting of the seepage system can not only study the variation law of excess pore water pressure, but also explore the mud-boiling phenomenon under the action of periodic load under the seepage state.

[0057] Specifically, the inlet pressure sensor 43 and the outlet pressure sensor 46 can control the magnitude of the water pressure of the inlet and outlet water, so that the seepage system can exert a stable seepage field.

[0058] As an alternative embodiment, the return water tank 45 is provided with a return water pipe 452 connected to the clean water tank 41, and the return water pipe 452 is provided with a return water pump 47; the setting of the return water pipe 452 and the return water pump enables the device to complete the entire experimental work using a small amount of water.

[0059] As an alternative embodiment, the specimen chamber 1 is a plexiglass cylinder, and the side wall of the specimen chamber 1 is provided with four mounting holes for mounting the pore pressure sensor 33 . The pore pressure sensors 33 on the specimen chamber 1 are each provided with a sealing nut for sealing the mounting holes on the specimen chamber 1 .

[0060] As an alternative embodiment, a base 6 is provided at the bottom of the specimen chamber 1, and the reaction frame 23 includes a plurality of columns 231 and a top plate 232. The plurality of columns 231 are longitudinally arranged on the base 6, and the top plate 232 is horizontally arranged at the top of the plurality of columns 231. The electric cylinder 21 is arranged on the top plate 232, and the movable rod of the electric cylinder 21 passes through the top plate; a support frame for supporting the specimen chamber 1 is also provided on the base 6 to ensure the stability of the specimen chamber 1 during the experiment; the base 6 is welded from Q235 material; the top plate 232 is finely machined from 45# steel; the four columns 231 are bright rods with threads at both ends, and the base and the top plate are locked with nuts. The base 6 is spray-painted, and the top plate 232 and the columns 231 are electroplated with chrome, which is both beautiful and rust-proof.

[0061] As an alternative embodiment, the specimen bin 1 has a pulley at the bottom, the base 6 is provided with a guide rail, and the pulley is arranged on the guide rail; since the specimen bin 1 is heavy, the specimen bin 1 must be installed directly below the electric cylinder 21 after the sample is loaded, and the specimen bin 1 must be moved out when the sample is cleaned. During the process, it is difficult to move the specimen bin 1 without roller skates and guide rails. Therefore, the setting of the pulley and guide rail facilitates the movement of the specimen bin 1 and the cleaning of the specimen bin 1.

[0062] The present invention also discloses a coarse-grained soil confined dynamic compression test method, comprising the following steps:

[0063] S1: Place a permeable stone at the bell mouth of the specimen chamber 1 to prevent soil samples, gravel, etc. from falling into the bell mouth of the specimen chamber 1; when using this device to conduct a seepage experiment, place a filter screen in the specimen chamber 1;

[0064] S2: Layered sample preparation: add the sample into the sample chamber 1, put in the force sensor 32 and the pore pressure sensor 33, the force sensor 32 is required to be placed in the middle of the sample chamber 1, tighten the nut to compact the sample, and prepare samples for other layers in turn;

[0065] S3: After the sample is prepared, cover the pressing plate 22, open the water inlet valve, add an appropriate amount of clean water, immerse the sample, maintain a low seepage state to prevent fine particles from flowing, close the water inlet valve, and let the sample stand for 8 to 12 hours to saturate;

[0066] S4: After saturation is completed, the acquisition instrument is connected to the displacement sensor 31, the force sensor 32 and the plurality of pore pressure sensors 33 respectively, and the electric cylinder 21 is controlled to apply an axial static load of 0kN to 0.1kN for pre-tightening, and the position of the displacement sensor 31 is adjusted so that the displacement sensor 31 can measure the axial deformation of the sample; the axial position of the displacement sensor 31 on the reaction frame can be adjusted. During the experiment, the sample is subjected to an axial load, which causes the sample to be axially compressed. The displacement sensor 31 extends downward into the specimen chamber 1 as the sample is compressed, thereby measuring the axial deformation of the sample. When cleaning the sample, the position of the displacement sensor 31 needs to be adjusted upward so that it is not in the specimen chamber 1, and the specimen chamber 1 can be removed for cleaning. After the sample is loaded, the position of the sensor also needs to be adjusted so that it can measure the axial deformation of the sample;

[0067] S5: According to the specific experimental requirements, static load, dynamic load or static and dynamic combined load is selected, and the vertical load is applied at 0kN / S~0.1kN / S. The electric cylinder 21 accurately applies a force of 0kN~10kN, and the upper peak and lower peak of the vertical load are periodically loaded. The input force ranges from 0kN to 10kN, and the loading frequency is 0Hz~5Hz;

[0068] S6: After the experiment is completed, clean the specimen chamber 1, turn off all power supplies, and clean the specimen chamber 1 in layers.

[0069] As an alternative embodiment, the pore pressure sensor 33 is immersed in clean water for 30 to 40 minutes before step S1. Immersing the pore pressure sensor 33 can make the pore pressure sensor 33 saturated with water, thereby improving the accuracy of data collection.

[0070] As an alternative embodiment, vaseline is evenly applied on the inner wall of the specimen chamber 1 before step S1; applying vaseline can prevent the specimen chamber 1 from being damaged by soil and stone particles, making it easier to clean the specimen.

[0071] The above embodiments are only specific implementation methods of the patent of the present invention, which are used to illustrate the technical solution of the patent of the present invention rather than to limit it. The protection scope of the patent of the present invention is not limited thereto. Although the patent of the present invention is described in detail with reference to the above embodiments, ordinary technicians in this field should understand that any technician familiar with the technical field can still modify the technical solution recorded in the above embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solution for implementing the patent of the present invention, and should be covered within the protection scope of the present invention.

Claims

1. A coarse-grained soil confined dynamic compression instrument, characterized in that: include: The specimen chamber (1) is in the shape of a hollow column, and the bottom end of the specimen chamber (1) is a bell mouth; The pressure piece (2) comprises a reaction frame (23), an electric cylinder (21) and a pressure plate (22), wherein the electric cylinder (21) is longitudinally arranged on the reaction frame, and the pressure plate (22) is arranged on a movable rod of the electric cylinder (21). The pressure plate (22) is located in the specimen chamber (1), and a water injection port is arranged on the pressure plate (22). The pressure plate (22) is used to provide a periodic load to the specimen in the specimen chamber (1) under the drive of the electric cylinder (21); A detection component (3) comprises: a displacement sensor (31), a force sensor (32) and a plurality of pore pressure sensors (33); the displacement sensor (31) is arranged on a reaction frame (23); the displacement sensor (31) is used to measure the axial deformation of a test piece; the force sensor (32) is arranged on the test piece; the force sensor (32) is used to measure the load applied to the test piece; the plurality of pore pressure sensors (33) are arranged in the test piece; the pore pressure sensors (33) are used to measure the pressure distribution on the inner wall of the test piece.

2. A coarse-grained soil confined dynamic compression instrument as claimed in claim 1, characterized in that: It also includes a seepage system (4), wherein the seepage system (4) includes: A clean water tank (41) is connected to the water inlet of the pressing plate (22) through a first connecting pipe (411); A servo constant pressure water pump (42) is arranged on the first connecting pipe (411); An inlet pressure sensor (43) is arranged on the first connecting pipe (411); A flow sensor (44) is arranged on the first connecting pipe (411); The return water tank (45) is connected to the bell mouth of the test piece chamber (1) through a second connecting pipe (451); The outlet pressure sensor (46) is arranged on the second connecting pipe (451).

3. A coarse-grained soil confined dynamic compression instrument as claimed in claim 1, characterized in that: The return water tank (45) is provided with a return water pipe (452) which is connected with the clean water tank (41), and the return water pipe (452) is provided with a return water pump (47).

4. A coarse-grained soil confined dynamic compression instrument as claimed in claim 1, characterized in that: The test piece chamber (1) is a plexiglass cylinder, a side wall of the test piece chamber (1) is provided with a plurality of mounting holes, and the pore pressure sensors (33) are respectively arranged in the mounting holes.

5. The coarse-grained soil confined dynamic compression instrument according to claim 1, characterized in that: A base (6) is provided at the bottom of the specimen chamber (1); the reaction frame (23) comprises a plurality of columns (231) and a top plate (232); the plurality of columns (231) are longitudinally arranged on the base (6); the top plate (232) is horizontally arranged on the tops of the plurality of columns (231); the electric cylinder (21) is arranged on the top plate (232); and a movable rod of the electric cylinder (21) passes through the top plate.

6. A coarse-grained soil confined dynamic compression instrument as claimed in claim 4, characterized in that: The bottom of the specimen chamber (1) is provided with a pulley, the base (6) is provided with a guide rail, and the pulley is arranged on the guide rail.

7. A coarse-grained soil confined dynamic compression test method, based on the coarse-grained soil confined dynamic compression instrument according to claim 1, characterized in that: The steps include: S1: Place a permeable stone at the bell mouth of the test specimen chamber (1); S2: preparing the sample in layers, adding the sample layer by layer into the sample chamber (1), placing the force sensor (32) in the middle of the sample chamber (1), and installing the pore pressure sensor (33), and then compacting the sample; S3: Cover the sample with a pressing plate (22), add an appropriate amount of clean water through the water injection port to immerse the sample, maintain a low seepage state to prevent fine particles from flowing, and then stop the water injection, and let the sample stand for 8 to 12 hours to saturate; S4: connecting the data acquisition instrument to the displacement sensor (31), the force sensor (32) and the plurality of pore pressure sensors (33) respectively, controlling the electric cylinder (21) to apply an axial static load of 0 kN to 0.1 kN for pre-tightening, and adjusting the position of the displacement sensor (31) so that the displacement sensor (31) can measure the axial deformation of the sample; S5: According to specific experimental requirements, static load, dynamic load or static and dynamic combined load is selected, vertical load is applied at 0 kN / S to 0.1 kN / S, the electric cylinder (21) accurately applies a force of 0 kN to 10 kN, and the upper peak value and the lower peak value of the vertical load are periodically loaded, the input force ranges from 0 kN to 10 kN, and the loading frequency is from 0 Hz to 5 Hz; S6: After the experiment is completed, clean the specimen chamber (1), turn off all power supplies, and clean the specimen chamber (1) in layers.

8. A coarse-grained soil confined dynamic compression test method as claimed in claim 6, characterized in that: Before step S1, the pore pressure sensor (33) is soaked in clean water for 30 to 40 minutes.

9. A coarse-grained soil confined dynamic compression test method as claimed in claim 6, characterized in that: Before step S1, vaseline is evenly applied on the inner wall of the specimen chamber (1).

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