A non-contact type method for testing horizontal uniaxial tensile properties of clay with gravel

Abstract

The application discloses a kind of non-contact gravelly clay horizontal single-axle tensile test methods, comprising step 1, gravelly clay preparation: according to the size of gravel amount, the clay of target water content is weighed, gravel is mixed into clay, and gravelly clay mixture is formed by fully stirring;Step 2, the assembly of dumbbell-shaped mould: fixed section, tension section and moving section are connected, and moving section, fixed section and tension section are smoothly transitioned detachable connection;Step 3, sample preparation: gravelly clay is filled into the cavity of dumbbell-shaped mould by using layering compaction method, and the dumbbell-shaped mould is sealed;Step 4, tensile test: the dumbbell-shaped mould and sample are suspended by using suspension ring, the shell of tension section is disassembled, and the sample is stretched;Step 5, n standard samples are prepared according to step 3, the n standard samples are stretched according to step 4, n groups of tension and displacement data are obtained, and the tension-displacement curve of gravelly clay is obtained by data fitting.

Description

Technical Field

[0001] The invention relates to a geotechnical test method, in particular to a non-contact gravel-mixed clay horizontal uniaxial tensile test method. Background Art

[0002] The main test methods for measuring soil tensile strength include uniaxial tension, triaxial tension, beam bending, hollow cylinder, radial fracturing, and Brazilian split tests. Uniaxial and triaxial tension tests measure tensile strength by directly applying axial tension to the specimen, and are considered direct tension tests. Beam bending, radial fracturing, axial fracturing, and hollow cylinder tests apply pressure or torque to the specimen and then calculate the tensile strength based on certain assumptions from the pressure or torque at failure. These are considered indirect tension tests.

[0003] According to the placement of the specimen, the uniaxial tensile test can be divided into vertical uniaxial tensile test and horizontal uniaxial tensile test. The vertical uniaxial tensile test is represented by patent CN202111004574.2. In this type of uniaxial tensile test, since the specimen is placed vertically, the weight of the upper half of the broken specimen will affect the measurement of the test tension during the stretching process. Therefore, more and more scholars have begun to choose the horizontal uniaxial tensile test.

[0004] Patent CN202010716525.0 designs the test mold into an hourglass shape, with a tension section located in the middle of the hourglass. The transition between the tension section and the clamping section is a straight line. However, this still creates certain problems, such as stress concentration at the ends of the tension section, which can easily cause specimen fracture at these ends, preventing the desired test results.

[0005] At the same time, the horizontal uniaxial tensile test device still has the problem of friction between the bottom of the tensile die and the tensile platform. Many scholars choose to use pulleys, rollers, sliding rollers and other methods to minimize friction, but the effect is still unsatisfactory. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a non-contact gravel-mixed clay horizontal uniaxial tensile test method to eliminate the influence of friction during the tensile process and effectively avoid stress concentration in the tensile section.

[0007] To solve the above technical problems, the present invention adopts a technical solution: a non-contact gravel-mixed clay horizontal uniaxial tensile test method, which specifically includes the following steps:

[0008] Step 1: Preparation of gravel-mixed clay: Weigh clay, water, and gravel according to the required gravel mixing amount, maximum gravel particle size, dry density, and moisture content, mix the gravel into the clay, and stir to form a gravel-mixed clay mixture;

[0009] Step 2, assembling the dumbbell-shaped mold: first, detachably connect the two arc-shaped semi-detachable parts to form the tension section of the cylindrical structure; then, detachably connect a trumpet-shaped member to each end of the cylindrical structure to form a dumbbell-shaped mold;

[0010] Step 3: Sample preparation, including the following steps:

[0011] Step 3-1, filling gravel-mixed clay into the cavity of a dumbbell-shaped mold, and compacting the gravel-mixed clay after filling;

[0012] Step 3-2, sealing the dumbbell-shaped mold;

[0013] Step 3-3: Install tie rods at both ends of the dumbbell-shaped mold, and install electromagnets on both tie rods;

[0014] Step 4: tensile test, specifically including the following steps:

[0015] Step 4-1, mold placement: Install two suspension ring lower halves on the work platform, and place the two tie rods of the dumbbell-shaped mold prepared in step 3 into the arc-shaped grooves of the two sets of suspension ring lower halves respectively;

[0016] Step 4-2, assembling the suspension rings: detachably install a suspension ring upper half on the top of each suspension ring lower half to form a suspension ring, thereby confining the corresponding pull rod; wherein each suspension ring upper half and each suspension ring lower half have a built-in magnet;

[0017] Step 4-3, Suspension: The electromagnets in the two tie rods are energized separately. The current is adjusted according to the gravity of the sample and the dumbbell-shaped mold. Under the combined action of the magnetic field formed by the electromagnets and the magnetic field inside the suspension ring, the dumbbell-shaped mold and the tie rods are suspended.

[0018] Step 4-4, mold axial limit: After the entire mold is stable, connect one of the tie rods to the fixing device and the other tie rod to the tensile loading device;

[0019] Step 4-5, dismantling the tension section: dismantle the two arc halves of the tension section in the dumbbell-shaped mold to expose the gravel-mixed clay corresponding to the tension section in the dumbbell-shaped specimen;

[0020] Step 4-6, specimen stretching: Start the tensile loading device, which drives the connected pull rod away from the fixing device and moves axially at a constant speed until the tensile section of the specimen breaks. During the stretching process, observe the specimen and record the fracture position.

[0021] Furthermore, in steps 4-6, a tensile force gauge and a displacement sensor are connected to the tensile loading device; wherein the tensile force gauge is used to measure and record the magnitude of the tensile force during the stretching process, and the displacement sensor is used to measure and record the axial displacement of the sample.

[0022] Furthermore, the method further includes step 5 of obtaining a tension-displacement curve, which specifically includes the following steps:

[0023] Step 5-1: Using gravel-mixed clay with the same parameters, use the sample preparation method of step 3 to prepare n standard samples; where n ≥ 5;

[0024] In step 5-2, the tensile test of step 4 is repeated for n standard specimens. During the tensile process, the tensile force is measured and recorded using a tensile dynamometer, and the displacement of the specimen is measured and recorded using a displacement sensor. This yields n sets of tensile force F and displacement S data. These n sets of tensile force F and displacement S data are then fitted to obtain the tensile force-displacement curve of the gravel-mixed clay.

[0025] Furthermore, the inner diameter of the cylinder in the tension section is 4-5 times the maximum particle size of the sample gravel. Therefore, when the inner diameter of the cylinder is D, the maximum particle size of the gravel is in the range of D / 5-D / 4.

[0026] Furthermore, in step 1, the clay is placed in an oven for drying and the dried clay is ground; water is then added according to the required moisture content to prepare clay with a target moisture content; gravels of various particle sizes are weighed, mixed, and then evenly mixed with the clay to ensure that each graded gravel is coated with clay.

[0027] Furthermore, in step 3, during the gravel-mixed clay filling process, the sample is filled and compacted in stages.

[0028] Furthermore, in step 3, during the multi-component compaction process, the connection between the two compactions should be far away from the joint between the tension section and the horn.

[0029] Furthermore, in step 3, after each compaction is completed, the upper surface of the previous layer of soil sample is scraped.

[0030] The present invention has the following beneficial effects:

[0031] (1) The dumbbell-shaped mold is suspended by a hanging ring, thereby eliminating the friction between the bottom of the mold and the platform during the stretching process, effectively reducing the influence of friction on the tensile test results during the test, and improving the accuracy of the tensile test;

[0032] (2) The dumbbell-shaped mold sample preparation and test are carried out in the same mold. During the test, only the tensile section mold needs to be disassembled, and the fixed section and the movable section do not need to be disassembled. This can avoid unnecessary demoulding and disassembly operations, effectively reduce the probability of damage to the sample, and reduce the influence of human operation factors on the test results. In addition, the middle tensile section and the movable section and the fixed section are connected by a curved surface with a smooth transition connection, which is more conducive to the compaction of the adobe during the sample preparation process of the gravel-mixed clay, and effectively prevent the problem of poor compaction effect of the gravel-mixed clay sample at the corners when the traditional hourglass-shaped test mold with sharp corners is used;

[0033] (3) The common hourglass-shaped test mold has an insufficient transition from both ends to the middle tensile section, which can easily cause the gravel-mixed clay sample to break at the end of the tensile section, and thus fail to achieve the ideal test effect. The dumbbell-shaped mold used in the present invention has a smooth transition between the tensile section and the fixed section and the movable section, and will not cause stress concentration in the tensile section, thus effectively ensuring the tensile test effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a structural schematic diagram of a horizontal uniaxial stretching device for gravel-mixed clay that eliminates friction during stretching.

[0035] Figure 2 It is a top view of the entire stretching device structure before the start of the test of the present invention.

[0036] Figure 3 Schematic diagram of the dumbbell-shaped mold of the present invention.

[0037] Figure 4 It is a front view of the fixed side suspended ring according to an embodiment of the present invention.

[0038] Figure 5 The connection between the upper half of the fixed side suspension ring and the lower half of the suspension ring in the embodiment of the present invention ( Figure 4 (A in the middle) Enlarged view.

[0039] Figure 6 It is a side view of a suspended ring according to an embodiment of the present invention.

[0040] Figure 7 It is a cross-sectional view of an electromagnet according to an embodiment of the present invention.

[0041] Figure 8 It is a schematic diagram of the process of assembling a dumbbell-shaped mold and preparing a sample according to an embodiment of the present invention.

[0042] Figure 8 (a) Shows the schematic diagram of the dumbbell-shaped mold before assembly.

[0043] Figure 8 (b) shows a schematic diagram of the completed dumbbell-shaped mold assembly.

[0044] Figure 8 (c) Schematic diagram showing the stepwise filling of gravel-mixed clay into a dumbbell-shaped mold.

[0045] Figure 8 (d) Schematic diagram showing the sealing of the dumbbell-shaped mold and the installation of tie rods at both ends.

[0046] Figure 9 The present invention is a schematic diagram of the tensile test process of the gravel-mixed clay horizontal uniaxial tensile device for eliminating friction during stretching.

[0047] Figure 9 (a) Schematic diagram showing the placement of the dumbbell-shaped mold filled with the specimen.

[0048] Figure 9 (b) Schematic diagram showing the assembly of the dangling ring.

[0049] Figure 9 (c) Schematic diagram showing the state of the dumbbell-shaped mold being suspended.

[0050] Figure 9 (d) shows the schematic diagram of the axial limit installation of the dumbbell-shaped mold.

[0051] Figure 9 (e) Schematic diagram showing the removal of the tension section in the dumbbell-shaped mold.

[0052] Figure 9 (f) Schematic diagram showing the state of the specimen being stretched.

[0053] Among them are:

[0054] 1. Work platform;

[0055] 2. Electromagnet;

[0056] 2-1. Electromagnet housing; 2-2. Coil above the electromagnet; 2-3. Coil to the right of the electromagnet; 2-4. Coil below the electromagnet; 2-5. Coil to the left of the electromagnet;

[0057] 3. Fixed side hanging ring;

[0058] 3-1. Upper half of the fixed-side suspension ring; 3-1-1. Upper half of the suspension ring; 3-1-2. Magnet above the fixed-side suspension ring; 3-1-3. Magnet on the right side of the fixed-side suspension ring; 3-1-4. Magnet on the left side of the fixed-side suspension ring; 3-1-5. Concave buckle on the upper half of the suspension ring; 3-1-6. Ear hole on the upper half of the suspension ring; 3-1-7. Plug on the fixed-side suspension ring

[0059] 3-2. Lower half of the fixed-side suspension ring; 3-2-1. Lower half of the suspension ring; 3-2-2. Magnet below the fixed-side suspension ring; 3-2-3. Convex buckle below the suspension ring; 3-2-4. Ear hole below the suspension ring;

[0060] 4. Dumbbell-shaped mold;

[0061] 4-1. Fixed section; 4-2. Fixed section ear hole; 4-3. Tension section lower arc half; 4-4. Tension section lower arc half ear hole; 4-5. Tension section upper arc half; 4-6. Tension section upper arc half ear hole; 4-7. Moving section ear hole; 4-8. Moving section; 4-9. Moving section cover plug; 4-10. Moving section cover;

[0062] 5. Sample;

[0063] 6. Mobile side suspension ring; 6-1. Mobile side suspension ring upper half; 6-2. Mobile side suspension ring lower half;

[0064] 7. Left lever;

[0065] 8. Right lever;

[0066] 9. Fixing plate; 9-1. Fixing plate limiting hole; 9-2. Bolt 1;

[0067] 10. Tensile loading device;

[0068] 10-1. Tension plate; 10-2. Tension plate limit hole; 10-3. Bolt 2; 10-4. Loading screw; 10-5. Loading base;

[0069] 11. Tensile force gauge. DETAILED DESCRIPTION

[0070] The present invention will be further described in detail below with reference to the accompanying drawings and specific preferred embodiments.

[0071] In the description of the present invention, it should be understood that the terms "left side," "right side," "upper," "lower," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Terms such as "first" and "second" do not indicate the importance of components and therefore should not be construed as limitations on the present invention. The specific dimensions used in this embodiment are intended only to illustrate the technical solution and do not limit the scope of protection of the present invention.

[0072] like Figure 1 、 Figure 2 and Figure 3 As shown, a gravel-mixed clay horizontal uniaxial stretching device for eliminating friction during stretching comprises a working platform 1, a dumbbell-shaped mold 4, a suspension component and a tension component;

[0073] The working platform 1 is fixed on a plane;

[0074] The dumbbell-shaped mold 4 is dumbbell-shaped and is sequentially provided with a fixed section 4-1, a tension section and a movable section 4-8;

[0075] The fixed section 4-1, the tension section and the movable section 4-8 together form a dumbbell-shaped mold cavity, which is used to load gravel-mixed clay to form a dumbbell-shaped specimen;

[0076] Both the fixed section 4-1 and the movable section 4-8 are trumpet-shaped, with a large trumpet end face and a small trumpet end face. The small trumpet end faces of both the fixed section 4-1 and the movable section 4-8 face the tension section, and the connection between them is smooth and removable. The smooth curved transition between the intermediate tension section, the fixed section 4-1, and the movable section 4-8 facilitates compaction during the gravel-incorporated clay sample preparation process, effectively preventing the poor compaction of gravel-incorporated clay samples at the corners encountered by conventional hourglass-shaped test molds.

[0077] The large end face of the fixed section 4-1 horn is a sealed structure; the large end face of the movable section 4-8 horn is an open design, and the opening is used to fill gravel-mixed clay into the dumbbell-shaped mold cavity; at the same time, a movable section sealing plate 4-10 matching the opening is provided, and when the dumbbell-shaped mold cavity is filled with gravel-mixed clay, the mold is sealed using the movable section sealing plate 4-10; bolt holes are provided on both sides of the movable section sealing plate 4-10 and on the side wall of the movable section opening, and the movable section sealing plate bolt 4-9 can be used to achieve a detachable connection between the movable section sealing plate 4-10 and the movable section 4-8.

[0078] The tension section is a cylindrical tube structure with a cylindrical cavity inside. The cylindrical tube structure is composed of a removable connection between the upper arc half 4-5 of the tension section and the lower arc half 4-3 of the tension section. The upper arc half 4-5 of the tension section is provided with an upper arc half ear hole 4-6 of the tension section, and the lower arc half ear hole 4-4 of the tension section is correspondingly provided on the lower arc half 4-3 of the tension section. The fixed section ear hole 4-2 is provided at the connection between the fixed section 4-1 and the tension section, and the movable section ear hole 4-7 is provided at the connection between the movable section 4-8 and the tension section. Thus, the tension section can be removably connected to the fixed section and the movable section using a bolt. After the specimen is produced in the dumbbell-shaped mold 4, there is no need to disassemble the fixed section and the movable end. Only the upper and lower arc halves of the tension section need to be disassembled. This can avoid unnecessary demolding and disassembly operations, effectively reduce the probability of damage to the specimen, and reduce the impact of human operation factors on the test results.

[0079] The suspension components include two groups, and both groups have the same structure and include a suspension ring and an electromagnet 2; the two suspension rings are arranged on the working platforms on both sides of the dumbbell-shaped mold 4;

[0080] The suspension ring includes a detachably connected upper and lower suspension ring halves, which are combined to form a cylindrical cavity. The fixed-side suspension ring 3 is provided on one side of the fixed section of the dumbbell-shaped mold, and the movable-side suspension ring 6 is provided on one side of the movable section. The fixed-side suspension ring 3 and the movable-side suspension ring 6 have the same structure. The following describes the structure of the fixed-side suspension ring in detail using the fixed-side suspension ring as an example:

[0081] like Figure 4 、 Figure 5 、 Figure 6 As shown, the fixed-side suspended ring 3 includes a fixed-side suspended ring upper half 3-1 and a fixed-side suspended ring lower half 3-2, which can be combined to form a cylindrical cavity; the fixed-side suspended ring upper half 3-1 is a semicircular double-layer sleeve structure, and the fixed-side suspended ring lower half 3-2 is a base plus a semicircular double-layer sleeve structure; the fixed-side suspended ring upper half 3-1 and the fixed-side suspended ring lower half 3-2 are both provided with a semicircular hollow ring cavity, and magnets are provided inside the semicircular hollow ring cavity, including the upper magnet 3-1-2 of the fixed-side suspended ring with an S pole on the upper side and an N pole on the lower side; the right magnet 3-1-3 of the fixed-side suspended ring has an S pole on the outer side and an N pole on the inner side; the left magnet 3-1-4 of the fixed-side suspended ring has an S pole on the outer side and an N pole on the inner side; the lower magnet 3-2-2 of the fixed-side suspended ring has an N pole on the upper side and an S pole on the lower side, so that a magnetic field can be formed inside the cylindrical cavity.

[0082] The upper half of the fixed-side suspension ring 3-1 is provided with a concave upper half buckle 3-1-5, and the lower half of the fixed-side suspension ring 3-2 is provided with a convex lower half buckle 3-2-3. The upper and lower halves 3-1 and 3-2 are detachably connected by the buckle. Furthermore, the outer wall of the upper half of the fixed-side suspension ring 3-1 is provided with an upper ear hole 3-1-6, and the outer wall of the lower half of the fixed-side suspension ring 3-2 is provided with a lower ear hole 3-2-4. A bolt is inserted through the upper ear hole 3-1-6 and the lower ear hole 3-2-4 to further connect the upper and lower halves 3-1 and 3-2.

[0083] like Figure 2 As shown, the tension assembly includes a left pull rod 7, a right pull rod 8, a fixing device and a tensile loading device 10;

[0084] One end of the left pull rod 7 is connected to the large end face of the speaker of the fixed section 4-1, and the other end passes through the fixed plate limiting hole 9-1 and is connected to the fixing device through bolt 1 9-2; one end of the right pull rod 8 is connected to the large end face of the speaker of the moving section 4-8, specifically, it is connected to the moving section sealing plate 4-10 of the moving section 4-8, and the other end passes through the tension plate limiting hole 10-2 and is connected to the tensile loading device through bolt 2 10-3;

[0085] The left pull rod 7 is provided with an electromagnet 2 and is placed in the cylindrical cavity of the fixed side suspension ring 3. The right pull rod 8 is also provided with an electromagnet 2 and is placed in the cylindrical cavity of the movable side suspension ring 6. The electromagnet 2 is surrounded by the cylindrical cavities of the fixed side suspension ring and the movable side suspension ring. The electromagnet 2 includes an electromagnet housing 2-1, inside which are provided an electromagnet upper coil 2-2, an electromagnet right coil 2-3, an electromagnet lower coil 2-4 and an electromagnet left coil 2-5. Figure 7 As shown, when electromagnet 2 is energized, the upper side of coil 2-2 above the electromagnet is an S pole, and the lower side is an N pole; the outer side of coil 2-3 to the right of the electromagnet is an N pole, and the inner side is an S pole; the upper side of coil 2-4 below the electromagnet is an S pole, and the lower side is an N pole; the outer side of coil 2-5 to the left of the electromagnet is an N pole, and the inner side is an S pole. Electromagnet 2 is connected to an external power source. When the electromagnet is energized, the magnetic field formed by electromagnet 2 and the magnetic field within the cylindrical cavity work together to suspend the dumbbell-shaped mold 4. In addition, the dumbbell-shaped mold 4 is preferably made of a high-strength, lightweight material to ensure the strength of the mold during the sample compaction process, while also ensuring that the weight of the mold, excluding the sample in the mold, is reduced as much as possible, making it easier for the entire mold to be suspended under the action of the electromagnetic force.

[0086] By setting up suspension rings on the working platforms on both sides of the dumbbell-shaped mold 4 and setting electromagnets on the left and right pull rods, the dumbbell-shaped mold is suspended, thereby eliminating the friction between the bottom of the mold and the stretching platform during the stretching process, effectively reducing the influence of friction on the stretching test results during the test, and improving the accuracy of the stretching test.

[0087] like Figure 1 and Figure 2 As shown, the fixing device includes a fixing plate 9 and a bolt 9-2.

[0088] A fixing plate limiting hole 9-1 with equal width at the top and bottom and semicircular ends is provided in the middle of the fixing plate 9 to adapt to the height of the electromagnet 2 after it is energized and suspended; a bolt 9-2 is connected to the left pull rod 7 through the fixing plate limiting hole 9-1 to limit and fix the position of one side of the fixed section of the dumbbell-shaped mold 4.

[0089] The tensile loading device 10 includes a tension plate 10-1, a second bolt 10-3, a loading base 10-5, and a loading screw 10-4 disposed within the loading base. The tension plate 10-1 is mounted on the loading base 10-5 and can move horizontally along the loading base 10-5 under the action of the loading screw 10-4, applying a horizontal tensile force to the specimen. A tension plate retaining hole 10-2 with equal widths at the top and bottom and semicircular at both ends is provided in the center of the tension plate 10-1. The second bolt 10-3 connects to the right tie rod 8 through the tension plate retaining hole 10-2, thereby securing one side of the moving section of the dumbbell-shaped mold 4.

[0090] The tensile loading device 10 is further connected to a tensile force measuring device 11 and a displacement sensor.

[0091] The tensile force gauge 11 is used to measure and record the magnitude of the tensile force, and the displacement sensor is used to measure and record the axial displacement of the sample.

[0092] A non-contact horizontal uniaxial tensile test method for gravel-mixed clay comprises the following steps:

[0093] Step 1, preparation of gravel-mixed clay:

[0094] Step 1-1, put the clay into the oven to dry. Since the clay blocks are large, they may not be able to be put into the grinder when taken out of the oven, so you need to use a small hammer to break the clay blocks first.

[0095] Step 1-2: Grind the dried clay, slowly add water and stir to adjust the moisture content to the target moisture content. During the stirring process, water should be added slowly to ensure that the water is in full contact with the clay particles to prevent the formation of large soil clumps.

[0096] Steps 1-3: Weigh gravels of different particle sizes according to the required gravel content and mix them together to ensure that gravel of each grade is included, simulating the particle distribution in the actual project as much as possible.

[0097] Step 1-4: weigh clay with a target moisture content according to the required gravel content, add gravel of the required grade into the clay, and stir thoroughly to form a gravel-clay mixture.

[0098] Steps 1-5 are placed in a sealed container for 24 hours to prevent the water from escaping and to allow the water to be evenly distributed in the gravel-mixed clay sample.

[0099] Step 2: Assembling the dumbbell-shaped mold 4.

[0100] Step 2-1 ( Figure 8 (a) Place the various structural parts of the dumbbell-shaped mold according to their positions:

[0101] Arrange the fixed section 4-1, the lower arc half 4-3 of the tension section, the upper arc half 4-5 of the tension section, and the movable section 4-8 as follows: Figure 8 (a) Arrange them in the order shown from bottom to top.

[0102] Step 2-2 ( Figure 8 (b) The dumbbell-shaped mold is assembled:

[0103] After the above-mentioned structural components are arranged, first, bolts are passed through the fixed section ear hole 4-2 and the upper arc-shaped half ear hole 4-6 of the tension section to fix the upper arc-shaped half 4-5 of the tension section to the fixed section 4-1. Then, bolts are passed through the fixed section ear hole 4-2 and the lower arc-shaped half ear hole 4-4 of the tension section to fix the lower arc-shaped half 4-3 of the tension section to the fixed section 4-1. Then, bolts are passed through the upper arc-shaped half ear hole 4-6 of the tension section and the ear hole 4-7 of the movable section to fix the upper arc-shaped half 4-5 of the tension section to the movable section 4-8. Finally, bolts are passed through the lower arc-shaped half ear hole 4-4 of the tension section and the ear hole 4-7 of the movable section to fix the lower arc-shaped half 4-3 of the tension section to the movable section 4-8. This completes the connection between the fixed section, the tension section, and the movable section. After the dumbbell-shaped mold is assembled, a dumbbell-shaped mold cavity is formed inside.

[0104] Step 3: Sample preparation.

[0105] Step 3-1 ( Figure 8 (c)) Compact the gravel-mixed clay in batches:

[0106] One-time compaction cannot ensure that the density of the surface layer of the soil sample is the same as that of the bottom layer of the soil sample, so the compaction method is adopted in batches.

[0107] First, weigh the gravel-clay mixture after 24 hours of stabilization and place it in a dumbbell-shaped mold, above the Layer 1 marking line shown in the diagram. Place the compacting hammer inside and compact the mixture, ensuring that the compacted height reaches approximately the Layer 1 marking line. Ensure that the marking line is 4-5 cm below the joint between the fixed section 4-1 and the tension section. This is because there may be a weak spot at the joint between the two compactions. If the compaction reaches the joint exactly, it is most likely to break during the test, which can easily affect the test results.

[0108] After compaction, use a sharp shovel to roughen the top surface of the first layer of soil sample to roughen the surface and loosen small gravels, facilitating bonding with the next layer of gravel-infused clay. Then, add the gravel-infused clay mixture to the top of the Layer 2 marking, ensuring the compacted height reaches the Layer 2 marking. After roughening the second layer, compact the third layer of gravel-infused clay again, completing the entire dumbbell-shaped mold cavity.

[0109] Step 3-2 ( Figure 8 (d)), seal the mold:

[0110] Place the moving section sealing plate 4-10 on the sample surface, align the plug holes on both sides of the moving section sealing plate with the plug holes on the open side wall of the large end face of the moving section 4-8 speaker, and screw the moving section sealing plate plug 4-9 into the plug hole to achieve the sealing of the dumbbell-shaped mold.

[0111] Connect the left pull rod 7 to the large end surface of the fixed section large speaker, connect the right pull rod 8 to the movable section sealing plate 4-10, and install the electromagnet 2 on the left pull rod 7 and the right pull rod 8.

[0112] Step 4, tensile test, specifically includes the following steps:

[0113] Step 4-1, mold placement ( Figure 9 (a)): Fix the fixed plate 9, the fixed side suspension ring lower half 3-2, the movable side suspension ring lower half 6-2, and the tensile loading device 10 on the working platform 1 in order from left to right, and then move the entire dumbbell-shaped mold 4 and the sample inside it to the top of the device, so that the left pull rod 7 and the right pull rod 8 fall on the fixed side suspension ring lower half 3-2 and the movable side suspension ring lower half 6-2 respectively, temporarily providing support, and at the same time, the electromagnets 2 fall into the fixed side suspension ring lower half 3-2 and the movable side suspension ring lower half 6-2.

[0114] Step 4-2, assemble the hanging ring ( Figure 9 (b) First, connect the concave buckle 3-1-5 of the upper half of the suspension ring with the convex buckle 3-2-3 of the lower half of the suspension ring, and then pass the fixed side suspension ring plug 3-1-7 through the upper ear hole 3-1-7 and the lower ear hole 3-2-4 of the suspension ring in sequence to fix them, further stabilizing the upper half 3-1 and the lower half 3-2 of the fixed side suspension ring to prevent the magnets inside the two from repelling each other and causing the buckle to open automatically.

[0115] The assembly process of the movable-side suspended ring 6 is the same as that of the fixed-side suspended ring 3 .

[0116] Step 4-3, suspension ( Figure 9 (c) : Simultaneously, energize the upper and lower coils of the electromagnet 2 in the fixed-side suspended ring 3 and the movable-side suspended ring 6, so that the current I gradually increases to ensure that the upper coil 2-2 of the electromagnet and the upper magnet of the suspended ring attract each other, and the lower coil 2-4 of the electromagnet and the lower magnet of the suspended ring repel each other, so that the electromagnet is suspended under the simultaneous attraction from above and repulsion from below, and after the electromagnet 2 reaches a relatively stable state in the vertical direction; energize the right coil 2-3 of the electromagnet and the left coil 2-5 of the electromagnet, so that the right coil 2-3 of the electromagnet and the right magnet of the suspended ring repel each other, and the left coil 2-5 of the electromagnet repel each other. The repulsive forces on the left and right sides can keep the electromagnet 2 in a relatively stable position in the horizontal direction.

[0117] Assuming the density of the gravel-mixed clay is ρ1, the weight of the entire sample is G1, and the weight of the dumbbell mold 4 is G. The total weight of the sample and the dumbbell mold is G + G1. To levitate the dumbbell mold, current must be passed through the coil in electromagnet 2 to generate an electromagnetic force between it and the suspended ring magnets, thereby offsetting G + G1. The electromagnetic force acting on the dumbbell mold 4 is the attractive force of the upper magnet on the upper coil. This is the force between the two electromagnets and the two suspended rings, which is F1 and F2. In addition, there is the repulsive force of the lower magnet on the lower coil. This is also the force between the two electromagnets and the two suspended rings, which is F3 and F4.

[0118] From the above, it can be concluded that the total gravity G+G1 of the sample and the dumbbell-shaped mold downward along the direction of gravity offsets the sum of F1, F2, F3 and F4 upward along the direction of gravity, that is, G+G1=F1+F2+F3+F4. At this time, the entire dumbbell-shaped mold 4 can be suspended.

[0119] When the density of the gravel-infused clay being tested changes, the current flowing through the coil needs to be changed, thereby changing F1, F2, F3, and F4. Assuming the density of the gravel-infused clay changes to ρ2, with ρ1 < ρ2, the weight of the entire specimen is now G2. At this point, G1 < G2, and the total weight of the specimen and the tensile die becomes G + G2. At this point, the current flowing through the coil in electromagnet 2 needs to be increased, increasing F1, F2, F3, and F4 individually, thereby increasing the sum of the four factors and ultimately balancing them with G + G2.

[0120] Step 4-4, mold axial limit ( Figure 9 (d)): The dumbbell-shaped mold 4 is fixed relative to the fixing device and the tensile loading device:

[0121] When the entire dumbbell-shaped mold 4 reaches a relatively balanced position, first, bolt 1 9-2 is passed through the fixing plate limiting hole 9-1 to fix the left pull rod 7 on the fixing plate 9, and the left pull rod 7 and the fixing plate 9 are kept in a relatively static fixed state;

[0122] Then, connect the tensile force gauge 11 to the right pull rod 8; and then pass the bolt 10-3 through the tension plate limit hole 10-2 to fix the right pull rod 8 on the tension plate 10-1, while keeping the two in a relatively static fixed state.

[0123] Step 4-5, remove the tension section ( Figure 9 (e)):

[0124] In the state of fixed and relatively static on both sides of the dumbbell-shaped mold, the lower arc-shaped half 4-3 of the tension section and the upper arc-shaped half 4-5 of the tension section are disassembled. The bolts in the ear holes of the tension section and the moving section are unscrewed, and then the lower arc-shaped half 4-3 of the tension section and the upper arc-shaped half 4-5 of the tension section are disassembled gently. During the disassembly process, the damage or interference to the sample is minimized.

[0125] Step 4-6, sample stretching Figure 9 (f):

[0126] Start the stretching loading device 10, and load the screw rod 10-4 to start rotating in the loading base 10-5, drive the tension plate 10-1 to move at a constant speed away from the sample, so as to drive the moving section 4-8 to move at a constant speed together, until the tension section sample is broken. During the stretching process, the sample is observed and the breaking position is recorded.

[0127] Step 5, obtaining the tension-displacement curve, specifically including the following steps:

[0128] Step 5-1, using the same parameters of the gravel clay, using the sample preparation method of step 3, 5 standard samples are prepared;

[0129] Step 5-2, repeating the stretching test of step 4 for the 5 standard samples respectively. During the stretching process, the tension force is measured and recorded by using the stretching force measuring device, and the displacement of the sample movement is measured and recorded by using the displacement sensor. Thus, 5 groups of tension F and displacement S data are obtained. Then, the 5 groups of tension F and displacement S data are fitted, and the tension-displacement curve of the gravel clay is obtained. Using the tension-displacement curve, the tensile strength of the gravel clay can be determined.

[0130] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above-described embodiments. Within the technical concept of the present application, various equivalent transformations of the technical solutions of the present application can be made, and these equivalent transformations all belong to the protection scope of the present application.

Claims

1. A non-contact horizontal uniaxial tensile test method for gravel-mixed clay, characterized by: The steps include: Step 1: Preparation of gravel-mixed clay: Weigh clay, water, and gravel according to the required gravel mixing amount, maximum gravel particle size, dry density, and moisture content, mix the gravel into the clay, and stir to form a gravel-mixed clay mixture; Step 2, assembling the dumbbell-shaped mold: first, detachably connect the two arc-shaped semi-detachable parts to form the tension section of the cylindrical structure; then, detachably connect a trumpet-shaped member to each end of the cylindrical structure to form a dumbbell-shaped mold; Step 3: Sample preparation, including the following steps: Step 3-1, filling gravel-mixed clay into the cavity of a dumbbell-shaped mold, and compacting the gravel-mixed clay after filling; Step 3-2, sealing the dumbbell-shaped mold; Step 3-3: Install tie rods at both ends of the dumbbell-shaped mold, and install electromagnets on both tie rods; Step 4: tensile test, specifically including the following steps: Step 4-1, mold placement: Install two suspension ring lower halves on the work platform, and place the two tie rods of the dumbbell-shaped mold prepared in step 3 into the arc-shaped grooves of the two sets of suspension ring lower halves respectively; Step 4-2, assembling the suspension rings: detachably install a suspension ring upper half on the top of each suspension ring lower half to form a suspension ring, thereby confining the corresponding pull rod; wherein each suspension ring upper half and each suspension ring lower half have a built-in magnet; Step 4-3, Suspension: The electromagnets in the two tie rods are energized separately. The current is adjusted according to the gravity of the sample and the dumbbell-shaped mold. Under the combined action of the magnetic field formed by the electromagnets and the magnetic field inside the suspension ring, the dumbbell-shaped mold and the tie rods are suspended. Step 4-4, mold axial limit: After the entire mold is stable, connect one of the tie rods to the fixing device and the other tie rod to the tensile loading device; Step 4-5, dismantling the tension section: dismantle the two arc halves of the tension section in the dumbbell-shaped mold to expose the gravel-mixed clay corresponding to the tension section in the dumbbell-shaped specimen; Step 4-6, specimen stretching: Start the tensile loading device, which drives the connected pull rod away from the fixing device and moves axially at a constant speed until the tensile section of the specimen breaks. During the stretching process, observe the specimen and record the fracture position.

2. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 1, characterized in that: In steps 4-6, a tensile force gauge and a displacement sensor are also connected to the tensile loading device; wherein the tensile force gauge is used to measure and record the magnitude of the tensile force during the stretching process, and the displacement sensor is used to measure and record the axial displacement of the sample.

3. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 2, characterized in that: The method further includes step 5 of obtaining a tension-displacement curve, which specifically includes the following steps: Step 5-1: Using gravel-mixed clay with the same parameters, use the sample preparation method of step 3 to prepare n standard samples; where n ≥ 5; In step 5-2, the tensile test of step 4 is repeated for n standard specimens. During the tensile process, the tensile force is measured and recorded using a tensile dynamometer, and the displacement of the specimen is measured and recorded using a displacement sensor. This yields n sets of tensile force F and displacement S data. These n sets of tensile force F and displacement S data are then fitted to obtain the tensile force-displacement curve of the gravel-mixed clay.

4. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 1, characterized in that: The inner diameter of the cylinder in the tension section is 4-5 times the maximum particle size of the sample gravel. Therefore, when the inner diameter of the cylinder is D, the maximum particle size of the gravel is in the range of D / 5-D / 4.

5. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 1, characterized in that: In step 1, the clay is placed in an oven to dry and the dried clay is ground; water is then added according to the required moisture content to prepare the clay with the target moisture content; gravel of various particle sizes is weighed, mixed and mixed with the clay to ensure that each grade of gravel is coated with clay.

6. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 1, characterized in that: In step 3, during the gravel-mixed clay filling process, the sample is compacted in stages.

7. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 6, characterized in that: In step 3, during the multi-component compaction process, the connection between the two compactions should be far away from the joint between the tension section and the horn.

8. The non-contact gravel-mixed clay horizontal uniaxial tensile test method according to claim 7, characterized in that: In step 3, after each compaction, the upper surface of the previous soil sample is scraped.

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