Calcareous sand impact crushing test device and method

Abstract

The invention relates to the technical field of calcareous sand property research, and discloses a calcareous sand impact crushing test device which comprises a sample barrel, a supporting frame, a guide rod, a pressure applying hammer and a pressure bearing plate, the sample barrel is used for containing calcareous sand, the supporting frame is fixedly connected with the sample barrel, the guide rod is vertically arranged in the sample barrel, and the pressure applying hammer is fixedly connected with the supporting frame. The pressure applying hammer and the pressure bearing plate are arranged on the guide rod in a sleeving mode and can slide along the guide rod. Compared with the prior art, the device is simple and reliable in structure and easy to operate, the defects that an existing simple device is poor in impact precision and low in repeatability are overcome, the structure of the device can be rapidly adjusted through assembly and disassembly of a small number of components, then different tests are completed, and the device is particularly suitable for teaching, basic research and field application. The invention further provides a calcareous sand impact crushing test method, initial gradation of calcareous sand and impact parameters such as impact times and impact energy are coupled to form a model, and popularization research and teaching practice of calcareous sand impact crushing characteristics are facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of calcareous sand impact test, in particular to a calcareous sand impact crushing test device and method. BACKGROUND

[0002] In order to study the particle crushing degree, influencing factors and laws of calcareous sand under impact load, the prior art provides a variety of crushing devices capable of applying impact load, but these devices have certain defects and cannot achieve ideal test results. Specifically, the standard guide rod type drop hammer device has high impact precision and relatively small energy loss, but the structure of the guide rail is usually complex, heavy and high in cost, and the friction between the weight and the guide rail may introduce errors; the split Hopkinson pressure bar device is also expensive, and the size of the tested sample is usually small, which limits the applicability of the device for simulating the impact response of a large range of calcareous sand in the foundation; the simple unguided drop hammer device is not limited by the guide rail and falls freely, which has poor operation precision and cannot guarantee the accuracy of the impact point, resulting in large dispersion of the test results; other general devices have problems such as limited sample size and limited number of repetitions.

[0003] Therefore, how to provide a device that is simple in structure, low in cost, convenient to operate, can guarantee basic impact precision and test repeatability, and is specially used for impact crushing characteristic research of calcareous sand is a technical problem to be solved at present. SUMMARY

[0004] To solve the above technical problems, the purpose of the present application is to provide a calcareous sand impact crushing test device which is simple in structure, low in cost, convenient to operate, has good impact precision and repeatability, and is used for studying the particle crushing degree, influencing factors and laws of calcareous sand under impact load.

[0005] Based on this, the present application provides a calcareous sand impact crushing test device, which comprises: A sample barrel, the sample barrel comprises a barrel body and a barrel bottom, the barrel body and the barrel bottom are detachably connected, the barrel body is connected with a water inlet pipe, and the barrel bottom is connected with a water outlet pipe and a water level pipe; A support frame is arranged outside the sample barrel and fixedly connected with the sample barrel; A guide rod is vertically arranged, one end of the guide rod is detachably connected with the support frame, and the other end of the guide rod is detachably connected with the barrel bottom; A pressure applying hammer is movably sleeved on the guide rod, and the support frame is provided with a driving mechanism for driving the movement of the pressure applying hammer; A pressure receiving plate is sleeved on the guide rod and can slide along the guide rod; The pressure hammer can be lifted by the driving mechanism and free-fall along the guide rod to hammer the pressure plate, and the pressure plate impacts the calcareous sand in the barrel when subjected to the pressure hammer; The inner side of the barrel bottom is provided with a ring cutter detachably connected with the barrel bottom, and the side of the pressure plate facing the barrel bottom is provided with an impact block matched with the ring cutter. The pressure hammer can be lifted by the driving mechanism and free-fall along the guide rod to hammer the pressure plate, and the impact block impacts the calcareous sand in the ring cutter when the pressure plate is subjected to the pressure hammer.

[0006] In some embodiments of the present application, the ring cutter is provided with a plurality of groups, and at least one ring cutter is provided in each group, and the inner diameters of the ring cutters in each group are different.

[0007] In some embodiments of the present application, the barrel is made of transparent material, and a high-speed camera is provided outside the barrel, and the high-speed camera is electrically connected with the processor.

[0008] In some embodiments of the present application, a height scale parallel to the guide rod is provided outside the barrel.

[0009] In some embodiments of the present application, the driving mechanism includes a pulley block formed by a plurality of fixed pulleys and a traction rope arranged on the fixed pulleys, each fixed pulley is fixedly connected with the support frame, one end of the traction rope is connected with the pressure hammer, the other end of the traction rope is connected with the operating handle, and a limiting piece is arranged on the support frame to position the operating handle.

[0010] In some embodiments of the present application, the pulley block includes a first pulley, a second pulley and a third pulley, the first pulley and the second pulley are symmetrically arranged relative to the guide rod, and the third pulley is arranged away from the first pulley and the second pulley. One end of the traction rope is connected with the operating handle, and the other end of the traction rope is connected with the pressure hammer after being divided into two sections, one of which is arranged on the first pulley and the third pulley, and the other of which is arranged on the second pulley and the third pulley.

[0011] In some embodiments of the present application, the water level pipe is arranged in an L shape and is threadedly connected with the barrel bottom.

[0012] Another object of the present application is to provide a calcareous sand impact crushing test method, which is completed by using the above-mentioned calcareous sand impact crushing test device, and includes the following steps: S1, the sample barrel is fixedly connected with the support frame, and the guide rod is assembled; S2, the calcareous sand is prepared in the sample barrel, and the excess calcareous sand is taken for particle size distribution analysis to obtain the initial grading curve of the calcareous sand; S3, select a pressure hammer with a mass of m, place a pressure plate on the guide rod and the pressure hammer, use a driving mechanism to lift the pressure hammer to a predetermined height h and position the pressure hammer, and place the pressure plate in the sample barrel to cover the calcareous sand; S4, release the positioning of the pressure hammer, and the pressure hammer freely falls along the guide rod, impacting the pressure plate, so that the pressure plate impacts the calcareous sand in the sample barrel; S5, after the impact is completed, the calcareous sand in the sample barrel is taken out, and the debris is collected; S6, perform particle size distribution analysis on the calcareous sand taken out from the barrel to obtain a particle size distribution curve of particles with a particle size less than 0.074 mm after crushing, and set the Hardin crushing potential of the calcareous sand as B r , then: B t is the increase of fine particles, specifically the incremental area enclosed by the particle size distribution curve after crushing and the horizontal axis; B p is the total amount of initial particle distribution, specifically the total area enclosed by the initial grading curve and the horizontal axis; Set the relative crushing rate as B t , then: D io is the initial characteristic particle size, D fo is the final characteristic particle size, D max is the initial maximum particle size, D min is the final minimum particle size; Set the fractal dimension as D f , then: N(ε) is the number of particles smaller than the particle size ε, and ε is the characteristic particle size, with units of mm; S7, adjust the mass m of the pressure hammer, the lifting height h of the pressure hammer, the initial grading of the calcareous sand, the initial density, the water content, and the number of impacts, and repeat steps S1 to S7 to obtain a grading evolution prediction model: P(D) is the passing rate (%) of particles with a particle size of D; P0 is the initial grading parameter; Dmax is the initial maximum particle size, with units of mm; α is the initial fractal dimension, reflecting the coarse and fine distribution of the initial grading, usually between 1.5 and 2.5; β is the crushing sensitivity coefficient, with units of kJ -1 , indicating the sensitivity of the material to impact energy, and the size is between 0.05 and 0.2; E kE = impact kinetic energy k = mgh n = number of impacts

[0013] In some embodiments of the present application, in the step S2, after the calcareous sand is loaded into the sample barrel, the sand surface is leveled.

[0014] In some embodiments of the present application, in the step S3, after the pressure plate and the pressure hammer are arranged on the guide rod, the contact area of the guide rod and the pressure plate is checked, the contact area of the guide rod and the pressure hammer is checked, and whether the pressure plate and the pressure hammer are smoothly matched with the guide rod is confirmed.

[0015] The calcareous sand impact crushing test device provided by the embodiments of the present application has the beneficial effects that, compared with the prior art: The application provides a calcareous sand impact crushing test device, which comprises a support frame and a sample barrel arranged below the support frame and fixedly connected with the support frame, the sample barrel is used for containing calcareous sand, the sample barrel comprises a barrel body and a barrel bottom which are also made of rigid materials, the barrel body and the barrel bottom are connected through flanges arranged on the outer sides of the barrel body and the barrel bottom, that is, the barrel body and the barrel bottom are detachably connected; further, a guide rod is vertically arranged in the sample barrel, the top end of the guide rod is detachably connected with the support frame, the bottom end of the guide rod is detachably connected with the barrel bottom, a pressure hammer and a pressure plate are arranged on the guide rod, the pressure hammer is connected with the support frame through a driving mechanism, and the pressure hammer can be lifted and freely falls along the guide rod to hammer the pressure plate under the action of the driving mechanism, the pressure plate is located below the pressure hammer and directly applies force to the calcareous sand in the test cavity when subjected to the action of the pressure hammer to complete the impact crushing test; furthermore, the top surface of the barrel bottom is provided with a plurality of annular cutters which are detachably connected with the barrel bottom, the pressure plate is provided with a plurality of impact blocks corresponding to the annular cutters on the side facing the barrel bottom, the impact blocks are also detachably connected with the pressure plate, the operator can fill the annular cutters with calcareous sand and impact the pressure plate again by using the pressure hammer, and the pressure plate applies force to the calcareous sand in the annular cutters through the impact blocks to complete the impact crushing test. Based on the above structure, when in use, the driving mechanism is started to lift the pressure hammer to a certain height, then the pressure plate is lifted to be separated from the barrel body, the barrel body is filled with an appropriate amount of calcareous sand, the pressure plate is placed above the calcareous sand in the barrel, then the pressure hammer is released to freely fall along the guide rod, the pressure hammer impacts the pressure plate after falling, and the pressure plate impacts the calcareous sand in the barrel body based on the action of the pressure hammer, the pressure hammer and the pressure plate are lifted to observe the crushing degree of the calcareous sand in the device, experimental data are collected, then the experiment is repeated and recorded, and the impact crushing test of the calcareous sand in the barrel body can be completed; after the impact crushing test of the calcareous sand in the barrel body is completed, the barrel body is dismounted through the flanges, the annular cutters are installed on the top surface of the barrel bottom, the impact blocks are installed on the bottom surface of the pressure plate, the annular cutters and the impact blocks are coaxially calibrated, the pressure hammer and the pressure plate are lifted again, an appropriate amount of calcareous sand is filled into the annular cutters, the pressure plate is placed on the barrel bottom so that the impact blocks abut against the calcareous sand in the annular cutters, the pressure hammer is released again to freely fall along the guide rod, and the pressure plate and the impact blocks impact the calcareous sand in the annular cutters based on the action of the pressure hammer, the test data after impact are collected, then the experiment is repeated and recorded, and the impact crushing test of the calcareous sand in the annular cutters can be completed.

[0016] Thus, the calcium sand impact crushing test device of some embodiments of the present application is capable of completing the calcium sand impact crushing test in the barrel by the complete barrel cooperating with the pressure hammer and the pressure plate, and the calcium sand test in the ring knife by the ring knife cooperating with the impact block on the pressure plate. The present application simplifies the structure design of the test device while retaining the guide rod, effectively overcoming the defects of poor impact accuracy and low repeatability caused by the lack of guide mechanism in the previous simple device. The pressure hammer falls vertically, the impact point is accurate, and the falling hammer posture is stable, greatly reducing the error of the non-guiding device and ensuring the reliability and repeatability of the test results. The replaceable pressure hammer and pressure plate can simulate impact loads of different strengths, and the detachable barrel, ring knife and impact block can quickly adjust the size of the sample barrel, simulate different test environments, and are particularly suitable for teaching, basic research and field application. The device has simple and reliable structure, is easy to manufacture, and has low production cost.

[0017] In addition, the present application also provides a calcium sand impact crushing test method, which couples the initial gradation of calcium sand with impact parameters such as impact times and impact energy, forms a model, inputs the initial gradation and impact parameters, and can predict the gradation curve after impact, which is beneficial to the popularization of the impact crushing characteristics of calcium sand and teaching practice. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a structural schematic diagram of a calcium sand impact crushing test device of some embodiments of the present application; Figure 2 FIG. 2 is an operation schematic diagram of a calcium sand impact crushing test device of some embodiments of the present application, at this time the barrel body is assembled on the barrel bottom, and the barrel body cooperates with the pressure plate to perform the experiment; Figure 3 FIG. 3 is an operation schematic diagram of a calcium sand impact crushing test device of some embodiments of the present application, at this time the barrel body is detached, and the ring knife cooperates with the impact block to perform the test; Figure 4 FIG. 4 is a schematic diagram of the A-A section in FIG. 1; Figure 3 Figure 5 FIG. 5 is an assembly schematic diagram of the ring knife and the barrel bottom of some embodiments of the present application; Figure 6 FIG. 6 is an assembly schematic diagram of the impact block and the pressure plate of some embodiments of the present application; Figure 7 FIG. 7 is a flowchart of the calcium sand impact crushing test method of the present application.

[0019] In the figure, 1 is a support frame; 2 is a barrel body; 3 is a barrel bottom; 4 is a flange; 5 is a water level pipe; 6 is a water inlet pipe; 7 is a water outlet pipe; 8 is a ring knife; 9 is a guide rod; 10 is a pressure hammer; 11 is a pressure plate; 12 is an impact block; 13 is a first pulley; 14 is a second pulley; 15 is a third pulley; 16 is a traction rope; 17 is an operation handle; and 18 is a wiring hole.​ DETAILED DESCRIPTION

[0020] The specific embodiments of the present application will be further described in conjunction with the drawings and examples. The following examples are intended to illustrate the present application and are not intended to limit the scope of the present application.

[0021] It should be understood that the terms "front", "back", and the like are used to describe various information in the present application, but these information should not be limited to these terms, and these terms are only used to distinguish the same type of information from each other. For example, the "front" information can also be referred to as "back" information, and the "back" information can also be referred to as "front" information without departing from the scope of the present application.

[0022] As a special geological material in marine engineering, the crushing mechanism of calcareous sand under impact load is of key significance to the design of marine foundation, cross-sea bridge and other projects. Research shows that the crushing behavior of calcareous sand is affected by the coupling of mineral composition, particle characteristics, confining pressure, stress level and other factors, and the present application provides an experimental basis for mechanism research through controllable boundary conditions, and the specific situation is as follows: Based on the Mohr-Coulomb criterion, the present application discloses a multi-factor coupling crushing mechanism of calcareous sand under impact load, which provides an important theoretical basis for marine engineering design. The Mohr-Coulomb criterion is a classic theory in soil mechanics for describing the shear strength of granular materials (such as calcareous sand, soil), which was proposed by German scholar Otto Mohr and French scholar Charles Coulomb, and its core is to associate the shear strength of the material with the normal stress and internal friction characteristics, which is suitable for describing the fracture behavior of brittle materials. Specifically, the crushing of particles is related to the following situations: ① Particle crushing caused by critical compressive strength For non-cohesive calcareous sand, the shear strength formula is When C=0 (such as calcareous sand), the shear strength is simplified as: And the particle crushing strength (i.e. compressive strength) can be derived as: Where σ3 is the confining pressure of the particle ② Particle crushing caused by critical tensile strength Calcareous sand is mainly composed of calcium carbonate, and its tensile strength is very low, about 10-30 MPa, which belongs to typical brittle materials. According to linear elastic fracture mechanics, when the tensile stress generated by impact exceeds the tensile strength of the particle, the particle will initiate a crack where the impact stress is related to the kinetic energy of the hammer as ③ Critical shear strength-induced particle breakage Shear strength formula : Shear strength of the material (MPa); : Cohesion (MPa), representing the cementing ability between particles of the material (calcarenite's cohesion is approximately 0, as it has no cohesion); : Normal stress acting on the shear plane (MPa); : Internal friction angle (°), reflecting the friction characteristics between particles (calcarenite's internal friction angle is usually 30° to 40°).

[0023] The larger the normal stress in the formula, the greater the normal pressure between particles, and the greater the friction force (f) that needs to be overcome during sliding, resulting in a higher shear strength. Calcarenite particles have no cohesion between them ( ), and their shear strength completely depends on the friction and biting action between particles. When the shear stress acting on the material exceeds the shear strength , the material will undergo shear failure along a certain plane, and the angle between the failure plane and the direction of the principal stress is ④ Effect of confining pressure on breakage strength In the test device of the present application, the confining pressure in the sample barrel is related to the vertical stress through the lateral pressure coefficient , and the breakage strength of the particles is : When the stress level generated by the impact exceeds the breakage strength , the particles will break. When the value of η exceeds 1, the particles will break.

[0024] For example, when , : the breakage stress The value of η is much greater than 1, triggering the brittle breakage of calcarenite particles. ​​​

[0025] Further, it is necessary to clarify the influence of mineral composition and particle characteristics, which mainly include the following aspects: ① The breakage sensitivity of mineral composition Calcitic sand is mainly composed of calcium carbonate, which has very low tensile strength, about 10-30 MPa, and belongs to typical brittle materials. According to linear elastic fracture mechanics, when the tensile stress generated by impact exceeds the tensile strength of the particle, the particle will initiate a crack, and the impact stress The relationship between impact stress and hammer kinetic energy is ② The stress concentration effect of particle size and shape The particle group with a particle size of about 2.0 mm is broken most severely, and the reason can be explained by Hertz contact theory. For angular particles, the curvature radius R is small, which leads to stress concentration: The expression of contact radius a is: Further, the confining pressure in the test is generated by the lateral constraint of the sample barrel or the ring cutter, which is related to the vertical stress through the lateral pressure coefficient K0: For cohesionless soil, K0 can be calculated by Jaky formula The vertical stress σ1 is calculated by impact kinetic energy Stress level breakage σ1 / σ0=σ1 / σ0 It is necessary to emphasize that the calculation formula of Hardin breakage potential B r is: Where, B t is the incremental area surrounded by the particle size distribution curve of particles with a particle size less than 0.074 mm after breakage and the horizontal axis, representing the increase of fine particles; B p is the total area surrounded by the original particle size distribution curve and the horizontal axis, representing the total amount of initial particle distribution; B r The higher the value, the more the content of fine particles (i.e. particles with a particle size less than 0.074 mm) increases after impact, and the more severe the breakage of particles. The specific grading standard is as follows: , representing micro-fragmentation, when the particles are basically not broken; , representing primary fragmentation, when part of the coarse particles are cracked; , representing severe fragmentation, when a large number of particles are cracked into fine particles.

[0026] Fractal dimension D f For characterizing the complexity of the grading: N(ε) is the number of particles with a particle size less than the characteristic size ε; ε is the characteristic particle size, with the unit of mm.

[0027] Before the sample is impacted, the well-graded calcareous sand D f is small, about 2.1, and the difference between the coarse and fine particles is small; after the sample is impacted, the increase in fine particles makes the grading curve flatten, and D f increases to about 2.5, indicating that the particles are refined and the distribution is more complex; in fact, the closer D f is to 3, the closer the surface particle grading is to three-dimensional space filling, and the shape and size distribution of the broken particles are more disordered.

[0028] In addition, the inner diameter Φ of the sample barrel in the device is fixed at 150 mm, and the inner diameter Φ of the ring knife is fixed at 50 mm; accordingly, the lateral pressure coefficient K0 in the barrel is fixed at 0.35, and the lateral pressure coefficient K0 of the ring knife is fixed at 0.42; accordingly, the confining pressure σ3 in the barrel is 0.35σ1, and the confining pressure σ3 of the ring knife is 0.42σ1.

[0029] The stress level in the ring knife is about 17% lower than that in the barrel, resulting in a decrease in the degree of fragmentation.

[0030] In addition, the expression of the sliding friction force F f between particles is That is, under high confining pressure, the friction force increases significantly, inhibiting the relative movement of particles.

[0031] Based on the above data, the fractal model is modified to predict the grading after impact, and the specific formula is as follows: P(D) is the passing rate of particles with a particle size of D (%); P0 is the initial grading parameter, which is related to the maximum passing rate; D max is the initial maximum particle size (mm); α is the initial fractal dimension, reflecting the coarse and fine distribution of the initial grading, and the size is 1.5 to 2.5; β is the fragmentation sensitivity coefficient, with the unit of kJ-1 , which represents the sensitivity of the material to impact energy, and ranges from 0.05 to 0.2; E k is the impact kinetic energy, in kJ, E k = mgh; n is the number of impacts.

[0032] The power function term describes the fractal characteristics of the initial gradation, and the exponential term quantifies the cumulative effect of impact energy and number on fragmentation, the larger the value, the more severe the fragmentation under the same energy.

[0033] Based on the above model formula, by inputting the initial gradation (G0) ) and impact parameters (E ), the post-impact gradation curve can be predicted, thereby guiding the design of marine foundations, such as the prediction of sand layer fragmentation during pile foundation impact construction.

[0034] Specifically, as shown in Figures 1 to 3 , the embodiment of the present application provides a calcareous sand impact fragmentation test device, which comprises a "gate" shaped support frame 1 made of rigid material and a sample barrel arranged below the support frame 1 and fixedly connected with the support frame 1, the sample barrel is used for containing calcareous sand, and the sample barrel comprises a barrel body 2 and a barrel bottom 3 which are also made of rigid material, the barrel body 2 and the barrel bottom 3 are connected through flanges 4 arranged on the outer sides of the two, that is, the barrel body 2 and the barrel bottom 3 are detachably connected; further, a guide rod 9 is vertically arranged in the test cavity enclosed by the barrel body 2 and the barrel bottom 3, the top end of the guide rod 9 is detachably connected with the support frame 1, and the bottom end of the guide rod 9 is detachably connected with the barrel bottom 3, a pressure hammer 10 and a pressure plate 11 are arranged on the guide rod 9, the pressure hammer 10 is connected with the support frame 1 through a driving mechanism, and it can be lifted and free-fall along the guide rod 9 under the action of the driving mechanism to hammer the pressure plate 11, the pressure plate 11 is located below the pressure hammer 10 and directly applies force to the calcareous sand in the test cavity when subjected to the action of the pressure hammer 10 to complete the impact fragmentation test; further, the top surface of the barrel bottom 3 can be provided with a plurality of ring knives 8 which are detachably connected with the barrel bottom 3, correspondingly, the pressure plate 11 is provided with a plurality of impact blocks 12 corresponding to the ring knives 8 on the side facing the barrel bottom 3, the impact blocks 12 are also detachably connected with the pressure plate 11, the operator can fill the ring knives 8 with calcareous sand and then use the pressure hammer 10 to impact the pressure plate 11 again, and the pressure plate 11 applies force to the calcareous sand in the ring knives 8 through the impact blocks 12 to complete the impact fragmentation test.

[0035] Based on the above structure, when in use, the driving mechanism is started to lift the pressure hammer 10 to a certain height, then the pressure plate 11 is lifted to be separated from the barrel body 2, an appropriate amount of calcareous sand is filled into the barrel body 2, the pressure plate 11 is placed above the calcareous sand in the barrel, then the pressure hammer 10 is released to free fall along the guide rod 9, the pressure hammer 10 impacts the pressure plate 11 after falling, the pressure plate 11 impacts the calcareous sand in the barrel body 2 based on the action of the pressure hammer 10, the pressure hammer 10 and the pressure plate 11 are lifted to observe the crushing degree of the calcareous sand in the device, experimental data is collected and then repeated experiments are recorded, and the impact crushing test of the calcareous sand in the barrel body 2 can be completed; after the impact crushing test of the calcareous sand in the barrel body 2 is completed, the barrel body 2 is disassembled through the flange 4, the annular cutter 8 is installed on the top surface of the barrel bottom 3, the impact block 12 is installed on the bottom surface of the pressure plate 11, the annular cutter 8 and the impact block 12 are coaxially calibrated, the pressure hammer 10 and the pressure plate 11 are lifted again, an appropriate amount of calcareous sand is filled into the annular cutter 8, the pressure plate 11 is placed on the barrel bottom 3 so that the impact block 12 abuts against the calcareous sand in the annular cutter 8, the pressure hammer 10 is released again to free fall along the guide rod 9, the pressure plate 11 and the impact block 12 impact the calcareous sand in the annular cutter 8 based on the action of the pressure hammer 10, the experimental data after impact is collected and then repeated experiments are recorded, and the impact crushing test of the calcareous sand in the annular cutter 8 can be completed.

[0036] The complete sample barrel is matched with the pressure hammer 10 and the pressure plate 11 to complete the impact crushing of the calcareous sand in the barrel, and the barrel bottom 3 is matched with the annular cutter 8 and the impact block 12 on the pressure plate 11 to complete the impact crushing of the calcareous sand in the annular cutter 8. The application simplifies the structure design of the test device while retaining the guide rod 9, effectively overcomes the defects of poor impact accuracy and low repeatability of the previous simple device due to the lack of a guide mechanism, the pressure hammer 10 strictly vertically falls, the impact point is accurate, and the drop hammer posture is stable, which greatly reduces the error of the non-guiding device, ensures the reliability and repeatability of the test results, and the replaceable pressure hammer 10 and the pressure plate 11 can simulate impact loads of different strengths, and the detachable barrel body 2, the annular cutter 8 and the impact block 12 can quickly adjust the size of the sample barrel, simulate different test environments, and are particularly suitable for teaching, basic research and field application; the structure of the device is simple and reliable, easy to manufacture, and low in production cost.

[0037] Optionally, in order to quickly and clearly determine the lifting height h of the pressure hammer 10, a height scale (not shown in the figure) parallel to the guide rod 9 is arranged outside the barrel body 2. When in use, the operator can quickly confirm the lifting height h of the pressure hammer based on the height scale, and the impact kinetic energy of the pressure hammer 10 this time can be obtained according to the formula Ek=mgh combined with the mass m of the pressure hammer.

[0038] It should be noted that the pressure plate 11 is located in the barrel during the test, so the outer diameter of the pressure plate 11 matches the inner diameter of the barrel body 2, and the outer diameter of the central hole of the pressure plate 11 matches the outer diameter of the guide rod 9, thereby preventing the calcium sand in the barrel from splashing during the impact process; similarly, the outer diameter of the impact block 12 matches the inner diameter of the annular cutter 8 to prevent the calcium sand in the annular cutter 8 from splashing when the impact block 12 falls into the annular cutter 8.

[0039] Optionally, the outer side of the annular cutter 8 is formed with external threads (not shown in the figure), and the top surface of the barrel bottom 3 is provided with a plurality of annular cutter assembly holes (not shown in the figure) having internal threads. The annular cutter 8 of the present application is threadedly connected with the barrel bottom 3. Similarly, the outer side of the impact block 12 is also formed with external threads, and the side of the pressure plate 11 facing the barrel bottom 3 is provided with a plurality of impact block assembly holes having internal threads. The impact block 12 of the present application is threadedly connected with the pressure plate 11. The threaded connection makes the assembly structure of the annular cutter 8 and the barrel bottom 3, and the impact block 12 and the pressure plate 11 compact, occupies small space, is relatively simple to process, has lower cost, and is relatively convenient to install and disassemble. Of course, repeated impact vibration is the enemy of threaded connection. Even with anti-loosening measures, it may still fail under high-frequency and high-energy impact. Moreover, the root of the thread is a natural stress concentration point and is prone to fatigue fracture under high impact load. Insufficient tightening torque may cause loosening, and excessive torque may cause damage to the thread or breakage of the impact head. Therefore, the threaded connection needs to be protected accordingly.

[0040] For the annular cutter 8 of the present application, a plurality of annular cutters 8 are provided and divided into multiple groups. At least one annular cutter 8 is provided in any group, and the inner diameters of the annular cutters 8 in each group are different from each other. As shown in Figure 4 、 Figure 5 and Figure 6 , the barrel bottom 3 of the present embodiment is provided with six annular cutters 8, which are divided into three groups. The inner diameter of the annular cutters 8 in the first group is the largest, the inner diameter of the annular cutters 8 in the second group is the second largest, and the inner diameter of the annular cutters 8 in the third group is the smallest. During the test, the operator can change the confining pressure by assembling annular cutters 8 of different sizes on the barrel bottom 3, thereby adjusting the test parameters.

[0041] Optionally, in some embodiments of the present application, the barrel body 2 is made of transparent rigid material such as tempered glass. In this way, the operator can accurately and effectively observe the crushing condition of the calcium sand when the pressure hammer 10 impacts the pressure plate 11 to crush the calcium sand in the sample barrel. Further, a high-speed camera (not shown in the figure) is provided outside the barrel body 2, and the high-speed camera is electrically connected with the processor. Based on the transparent barrel body and the high-speed camera, the operator can record the crushing condition of the calcium sand when it is impacted.

[0042] It is also necessary to make clear that the barrel body 2 inner diameter of the present application should be significantly larger than the maximum particle size of calcareous sand, and in some embodiments of the present application, the inner diameter of the barrel body 2 is more than ten times the maximum particle size of calcareous sand. The large size of the sample barrel can accommodate enough particles to reflect the grading evolution, reduce the influence of boundary effects, and make the sample representative; at the same time, the large size of the rigid sample barrel ensures that the barrel body 2 has sufficient rigidity and strength to withstand impact without significant deformation or damage, ensuring the validity and comparability of the test results.

[0043] During the above experiment, if there is water in the calcareous sand, the short-term load will be borne by the water, and the external load will be instantaneously converted into hydrostatic pressure. As the water is removed, the hydrostatic pressure is gradually transferred to the solid particles, and then the compaction and crushing of the particles will occur. Therefore, the water level itself plays a decisive role in the stress transfer in calcareous sand after impact loading, and also has a direct influence on the macroscopic foundation settlement and the microscopic particle crushing. In addition, the water content in the unsaturated zone above the water level is also very critical. The higher the water content, the smaller the friction between solid particles, and the weaker the nesting effect, which will also affect the transfer of dynamic load in calcareous sand. In order to clarify the water level in the barrel body 2, in some embodiments of the present application, the barrel body 2 is connected with a water inlet pipe 6, and the barrel bottom 3 is connected with a water outlet pipe 7 and a water level pipe 5. The operator can add water to the sample barrel through the water inlet pipe 6, or remove the water in the sample barrel through the water outlet pipe 7 to adjust the water content of the calcareous sand. The water level pipe 5 is L-shaped and detachably connected with the barrel bottom 3 based on a threaded structure. Since the water level pipe 5 is connected with the space in the sample barrel, based on the principle of communicating vessels, the operator can observe the water level in the water level pipe 5 to know the water level in the sample barrel in time.

[0044] Furthermore, the sample barrel containing calcareous sand also needs to be provided with an optical fiber for measuring the deformation profile of calcareous sand, a sensor for measuring pore water pressure, and a frequency domain reflectometer for measuring water content. As shown in Figure 1 In order to ensure the signal transmission of the optical fiber, the barrel body 2 is provided with a wiring hole 18, and the optical fiber in the calcareous sand extends to the outside of the barrel body 2 through the wiring hole 18 and is electrically connected with the processor. The optical fiber can continuously record the compression deformation profile of the calcareous sand based on the Rayleigh scattering light time domain technology, thereby providing a basis for further study of the deformation of the calcareous sand.

[0045] Optionally, as shown in Figure 1 and Figure 2As shown, in some embodiments of the present application, the driving mechanism of the present application comprises a pulley block formed by a plurality of fixed pulleys and a traction rope 16 arranged on the fixed pulleys, each fixed pulley is fixedly connected with the support frame 1, one end of the traction rope 16 is connected with the pressure hammer 10, the other end of the traction rope 16 is connected with the operating handle 17, and the support frame 1 is provided with a limiting piece (not shown in the figure) to position the operating handle 17; specifically, the pulley block of the present application comprises a first pulley 13, a second pulley 14 and a third pulley 15, the first pulley 13 and the second pulley 14 are symmetrically arranged relative to the guide rod 9, and the third pulley 15 is arranged away from the first pulley 13 and the second pulley 14, one end of the traction rope 16 is connected with the operating handle 17, and the other end of the traction rope 16 is connected with the pressure hammer 10 after being divided into two sections, one of which is arranged on the first pulley 13 and the third pulley 15, and the other of which is arranged on the second pulley 14 and the third pulley 15. When in use, the operating handle 17 is pulled, the pressure hammer 10 is lifted to a predetermined height h based on the arrangement of the traction rope 16, then the pressure hammer 10 is positioned by the limiting piece, and after the pressure hammer 10 is stable, the limiting piece limits the operating handle 17, at this time the pressure hammer 10 freely falls along the guide rod 9 under the action of its own gravity, and the impact on the pressure plate 11 is completed. In this way, the present application provides a simple, labor-saving and low-cost lifting method, and the true "free fall" (initial state initial speed is zero) is ensured through the rapid release of the limiting piece. This greatly improves the convenience and reliability of operation, and is the core of low-cost implementation of precise free fall impact.

[0046] Specifically, the limiting piece of the present application is preferably an electromagnetic suction cup, which is started after the operating handle 17 lifts the pressure hammer 10 to a predetermined height h, and can adsorb the operating handle 17 to keep the pressure hammer 10 stable, then the electromagnetic suction cup is powered off to release the adsorption of the operating handle 17, so as to realize the free fall of the pressure hammer 10 without any external force, avoiding the disturbance or initial speed error caused by manual release. At the same time, it should be pointed out that in addition to the rapid release of the electromagnet, the limiting piece of the present application can also select a mechanical pin structure to cooperate with the operating handle 17 to realize the free fall of the pressure hammer 10, which will not be described here.

[0047] In addition, as shown, Figure 7 The present application also provides a calcareous sand impact crushing test method completed by using the above-mentioned calcareous sand impact crushing test device, comprising the following steps: S1, fixedly connecting the sample bucket with the support frame, and assembling the guide rod; S2, preparing the calcareous sand in the sample bucket, leveling the sand surface, taking the excess calcareous sand for particle size distribution analysis, and obtaining the initial grading curve of the calcareous sand; S3, select a pressure hammer with a mass of m, set a pressure plate on the guide rod and the pressure hammer, check the contact area of the guide rod and the pressure plate, check the contact area of the guide rod and the pressure hammer, confirm whether the pressure plate and the pressure hammer cooperate with the guide rod smoothly, use a driving mechanism to lift the pressure hammer to a predetermined height h and position the pressure hammer, and place the pressure plate in the sample barrel to cover the calcareous sand; S4, release the positioning of the pressure hammer, and the pressure hammer freely falls along the guide rod, impacting the pressure plate, so that the pressure plate impacts the calcareous sand in the sample barrel; S6, after the impact is completed, the calcareous sand in the sample barrel is taken out, and the debris is collected; S7, the calcareous sand taken out in the barrel is subjected to particle size distribution analysis, and a particle size distribution curve of particles with a particle size less than 0.074 mm after crushing is obtained, and the Hardin crushing potential of the calcareous sand is B r , then: B t is the increase of fine particles, specifically the increase area enclosed by the particle size distribution curve of particles with a particle size less than 0.074 mm after crushing and the horizontal axis; B p is the total amount of initial particle distribution, specifically the total area enclosed by the initial particle size distribution curve and the horizontal axis; Let the relative crushing rate be B g , then: D io is the initial characteristic particle size, D fo is the final characteristic particle size, D max is the initial maximum particle size, D min is the final minimum particle size; Let the fractal dimension be D f , then: N(ε) is the number of particles less than the particle size ε, and ε is the characteristic particle size, with a unit of mm; S8, adjust the mass m of the pressure hammer, the lifting height h of the pressure hammer, the initial particle size distribution of the calcareous sand, the initial density, the water content, and the number of impacts, repeat steps S1 to S7, and obtain a particle size distribution evolution prediction model: P(D) is the passing rate (%) of particles with a particle size of D; P0 is the initial particle size distribution parameter; D max is the initial maximum particle size, with a unit of mm; α is the initial fractal dimension, reflecting the coarse and fine distribution of the initial particle size distribution, usually 1.5 to 2.5; β is the crushing sensitivity coefficient, with a unit of kJ-1 The value represents the sensitivity of a material to impact energy, ranging from 0.05 to 0.2. E k For impact kinetic energy, E k =mgh; n represents the number of impacts.

[0048] Hardin's Breaking Momentum B r Used to quantify fine particle formation rate, relative breakage rate B g Fractal dimension D is used to reflect the degree of overall gradation shift. f This is used to reflect the complexity of the gradation after fragmentation, by inputting the initial gradation ( ) and impact parameters ( This allows for the prediction of the post-impact gradation curve, which can then guide the design of marine foundations.

[0049] More specifically, the core formulas guiding the experiment are shown in Table 1.

[0050] Table 1 Core Indicators of Impact Crushing Test Furthermore, the specific applications of the core formula are shown in Table 2.

[0051] Table 2 Application Instructions for Core Indicators of Impact Crushing Test In summary, this invention provides a calcareous sand impact crushing test apparatus, comprising a sample container, a support frame, a guide rod, a pressure hammer, and a pressure plate. The sample container holds the calcareous sand. The support frame is located outside the sample container and is fixedly connected to it. The guide rod is vertically positioned inside the sample container and is detachably connected to both the support frame and the sample container. The pressure hammer and pressure plate are fitted onto the guide rod and can slide along it to apply force to the calcareous sand in the sample container. Compared with existing technologies, this application simplifies the structural design of the test apparatus while effectively overcoming the shortcomings of previous simple apparatuses, such as poor impact accuracy and low repeatability due to the lack of a guiding mechanism. Furthermore, the apparatus structure can be quickly adjusted by installing and disassembling a small number of parts to complete different tests, making it particularly suitable for teaching, basic research, and field applications.

[0052] This invention also provides a method for impact crushing of calcareous sand, which couples the initial gradation of calcareous sand with impact parameters such as the number of impacts and impact energy to form a model. By inputting the initial gradation and impact parameters, the gradation curve after impact can be predicted, which is beneficial for the popularization of research and teaching practice on the impact crushing characteristics of calcareous sand.

[0053] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and replacements can be made without departing from the technical principles of the present application, and these improvements and replacements should also be considered as the protection scope of the present application.

Claims

1. A calcareous sand impact breakage test apparatus, characterised in that, The utility model relates to a kind of calcium carbonate production test device, including: Sample barrel, the sample barrel includes barrel body (2) and barrel bottom (3), the barrel body (2) is detachably connected with the barrel bottom (3), the barrel body (2) is connected with inlet pipe (6), the barrel bottom (3) is connected with outlet pipe (7) and water level pipe (5); Support frame (1) is located outside the sample barrel and is fixedly connected with the sample barrel; Guide rod (9) is vertically arranged, one end of the guide rod (9) is detachably connected with the support frame (1), the other end of the guide rod (9) is detachably connected with the barrel bottom (3); Pressure hammer (10) is movably arranged on the guide rod (9), the support frame (1) is provided with a driving mechanism for driving the pressure hammer (10) to move; Pressure plate (11) is movably arranged on the guide rod (9) and can slide along the guide rod (9); The pressure hammer (10) can be lifted by the driving of the driving mechanism and free-fall along the guide rod (9) to hammer the pressure plate (11), the pressure plate (11) is impacted by calcareous sand in the barrel body (2) when being acted on by the pressure hammer (10); The inner side of the barrel bottom (3) is provided with a cutter (8) detachably connected with the barrel bottom (3), one side of the pressure plate (11) facing the barrel bottom (3) is provided with an impact block (12) matched with the cutter (8), the pressure hammer (10) can be lifted by the driving of the driving mechanism and free-fall along the guide rod (9) to hammer the pressure plate (11), the impact block (12) impacts the calcareous sand in the cutter (8) when the pressure plate (11) is acted on by the pressure hammer (10).

2. The calcareous sand impact crushing test device according to claim 1, characterized in that, The cutter (8) is provided with a plurality of cutters (8) and is divided into a plurality of groups, at least one cutter (8) is provided in any group, and the inner diameters of the cutters (8) in each group are different.

3. The calcareous sand impact crushing test device according to claim 1, characterized in that, The barrel body (2) is made of transparent material, a high-speed camera is arranged outside the barrel body (2), and the high-speed camera is electrically connected with a processor.

4. The calcareous sand impact crushing test device according to claim 1, characterized in that, A height scale parallel to the guide rod (9) is arranged outside the barrel body (2).

5. The calcareous sand impact crushing test device according to claim 1, characterized in that, The driving mechanism includes a pulley block formed by a plurality of fixed pulleys and a traction rope (16) arranged on the fixed pulleys, each fixed pulley is fixedly connected with the support frame (1), one end of the traction rope (16) is connected with the pressure hammer (10), the other end of the traction rope (16) is connected with an operating handle (17), and a limiting piece is arranged on the support frame (1) to position the operating handle (17).

6. The calcareous sand impact crushing test device according to claim 5, characterized in that, The pulley block comprises a first pulley (13), a second pulley (14) and a third pulley (15), the first pulley (13) and the second pulley (14) are symmetrically arranged relative to the guide rod (9), the third pulley (15) is arranged away from the first pulley (13) and the second pulley (14), one end of the traction rope (16) is connected with the operating handle (17), the other end of the traction rope (16) is connected with the pressure hammer (10) after being divided into two sections, one section is arranged on the first pulley (13) and the third pulley (15), and the other section is arranged on the second pulley (14) and the third pulley (15).

7. The calcareous sand impact crushing test device according to claim 1, characterized in that, The water level pipe (5) is arranged in an L shape and is threadedly connected with the barrel bottom (3).

8. A calcareous sand impact breakage test method, which is performed using the calcareous sand impact breakage test device according to any one of claims 1 to 7, characterized by, The method comprises the following steps: S1, fixing and connecting the sample barrel with the support frame, assembling the guide rod; S2, preparing the calcareous sand in the sample barrel, taking the excess calcareous sand for particle size distribution analysis to obtain the initial grading curve of the calcareous sand; S3, selecting a pressure hammer with a mass of m, arranging the pressure plate and the pressure hammer on the guide rod, lifting the pressure hammer to a predetermined height h by using the driving mechanism and positioning the pressure hammer, and placing the pressure plate in the sample barrel to cover the calcareous sand; S4, releasing the positioning of the pressure hammer, allowing the pressure hammer to freely fall along the guide rod, and impacting the pressure plate to make the pressure plate impact the calcareous sand in the sample barrel; S5, taking out the calcareous sand in the sample barrel after the impact is completed, and collecting the debris; S6, the calcareous sand taken out in the barrel is analyzed for particle size distribution, and the particle size distribution curve of the particles with particle size less than 0.074 mm after crushing is obtained, and the Hardin crushing potential of the calcareous sand is set as B r Then: B t The increase amount B is the increase area surrounded by the particle size distribution curve of the fine particles after crushing and the horizontal axis, and specifically refers to the increase area surrounded by the particle size distribution curve of the fine particles after crushing and the horizontal axis. p The total amount A is the total area surrounded by the initial particle size distribution curve and the horizontal axis, and specifically refers to the total area surrounded by the initial particle size distribution curve and the horizontal axis. Let the relative breakage be B t Then: D io D0 is the initial characteristic particle diameter fo D is the final characteristic particle diameter max D0 is the initial maximum particle diameter min D is the final minimum particle diameter Let the fractal dimension be D f then: N(ε) is the number of particles smaller than the particle size ε, and ε is the characteristic particle size, in mm; S7, adjusting the mass m of the pressure hammer, the lifting height h of the pressure hammer, the initial grading, the initial density, the water content of the calcareous sand and the number of impacts, repeating steps S1 to S7 to obtain a grading evolution prediction model: P(D) is the passing rate (%) of particles with a particle size of D; P0 is the initial grading parameter; Dmax is the initial maximum particle size, in mm; α is the initial fractal dimension, reflecting the coarse and fine distribution of the initial grading, and is usually 1.5 to 2.5; β is the breakage sensitivity coefficient, in kJ -1 , which indicates the sensitivity of the material to impact energy, and has a size of 0.05 to 0.2; E k For the kinetic energy of impact, E k =mgh; n is the number of impacts.

9. The calcareous sand impact breakage test method according to claim 8, characterized in that, In the step S2, after the calcareous sand is loaded into the sample barrel, the sand surface is leveled.

10. The calcareous sand impact breakage test method according to claim 8, characterized in that, In the step S3, after the pressure plate and the pressure hammer are arranged on the guide rod, the contact area of the guide rod and the pressure plate is checked, the contact area of the guide rod and the pressure hammer is checked, and whether the pressure plate and the pressure hammer cooperate smoothly with the guide rod is confirmed.

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