Preparation of homogeneous frozen gravel and dynamic testing method under low temperature environment

Abstract

The present invention discloses a method for preparing homogeneous frozen gravel and a dynamic testing method under low environmental temperature, and relates to the technical field of preparation, processing and detection of rock-like materials in rock engineering. The method comprises: S1, sample preparation step: preparing a homogeneous frozen gravel sample; S2, sample placement step: clamping the sample between an incident rod and a transmission rod; S3, incident wave application step: applying an incident wave to the incident rod and recording experimental data. The present invention solves the defects of the existing system by optimizing the system equipment and process flow, realizes process optimization, and further realizes qualitative and quantitative analysis of the physical and mechanical properties related to real engineering geological materials in high-cold mountainous areas.

Description

Technical Field

[0001] The invention relates to the technical field of preparation, processing and detection of rock-like materials in rock engineering, and in particular to a method for preparing homogeneous frozen gravel and a dynamic testing method under low environmental temperature. Background Art

[0002] Due to its special geographical environment, the alpine mountainous areas are characterized by high altitude, strong weathering and frequent earthquakes. The rock and soil on its surface and inside form a complex multi-media composite rock and soil with ice under the low temperature coupling effect. In order to further develop and construct the alpine mountainous areas, it is necessary to study the dynamic mechanical properties of the special rock and soil in its environment.

[0003] At present, the main method for studying the properties of related materials in the field of rock engineering in alpine areas is to use rock samples with similar lithology and simulate low-temperature environments, and dynamically load the samples with relevant detection devices and Hopkinson pressure bars. In the test, rock samples are mostly processed by freeze-thaw cycles, low temperature, saturation, and drying in order to approach the real state of geotechnical materials in specific engineering environments. However, geotechnical materials in real engineering environments are mostly multi-media composite materials, especially in alpine mountainous environments. The original geotechnical materials are cemented with ice under long-term low temperatures to form special composite geotechnical materials. The corresponding material physical and mechanical properties and related mechanical responses have changed greatly compared with simple rock materials. The samples and detection methods currently used cannot simulate the actual situation well, so this has hindered the relevant research and engineering construction in alpine mountainous areas. Based on this situation, it is necessary to develop a test sample and test method that can truly simulate alpine mountain geological materials to further study the relevant fields of rock engineering in alpine mountainous areas.

[0004] Therefore, it is an urgent problem for those skilled in the art to propose a method for preparing homogeneous frozen gravel and a dynamic testing method under low temperature to solve the difficulties existing in the prior art. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing homogeneous frozen gravel and dynamically testing it under low environmental temperature. In response to the current need to simulate real rock materials in high-altitude and cold mountainous areas and conduct in-depth research, a dynamic testing method combining an environmental low-temperature box and a Hopkinson pressure bar is provided at the same time, aiming to simulate the real engineering environment and detect the relevant mechanical responses of ice-rock cementing materials.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme: a method for preparing homogeneous frozen gravel and dynamically testing it under low temperature environment, comprising the following steps:

[0007] S1. Sample preparation steps: preparing a homogenized frozen gravel sample;

[0008] S2, sample placement step: clamp the sample between the incident rod and the transmission rod;

[0009] S3, incident wave application step: the incident rod applies the incident wave and records the experimental data.

[0010] In the above method, optionally, the sample preparation step in S1 includes:

[0011] S101, determining relevant dimensions of the frozen gravel sample;

[0012] S102, crushing and sieving the gravel based on the relevant size of the frozen gravel sample obtained in S101 to obtain sieved debris;

[0013] S103, dyeing the gravel debris obtained in S102 to obtain dyed tracer rock debris particles;

[0014] S104, preparing a saturated gravel sample;

[0015] S105. Prepare frozen gravel samples.

[0016] In the above method, optionally, the gravel debris pretreatment in S103 includes:

[0017] Part of the debris obtained after screening in S102 is selected and dyed with a dark acrylic paint that is resistant to low temperature, wear and water, to obtain dyed tracer rock debris particles that are different from the color of the original rock debris particles.

[0018] In the above method, optionally, S104, preparing a saturated gravel sample comprises:

[0019] The original rock debris particles of the same particle size are placed in the sample mold in layers to prepare standard dynamic, static compression and tensile specimens. When placing, a small amount of dyed and labeled rock debris particles are mixed in layers with the standard sample. After the gravel fills the mold, pure water is added. The water-filled mold is placed on a vibration table and vibrated for 60 seconds to allow the bubbles to fully dissipate, and then left to stand for 48 hours to obtain a saturated gravel sample.

[0020] The above method, optional, the relationship between saturation and parameters such as temperature, time, and size during rock saturation:

[0021]

[0022] Where S(t,T,D) is the rock saturation at time t, temperature T and typical size D of the rock sample; S max— is the maximum saturation of the rock; k is the rate constant of the saturation process, which is related to the pore structure of the rock and the fluid properties; D is the typical size of the rock sample, such as diameter or thickness; α is the temperature coefficient, which describes the effect of temperature change on saturation; T0 is the reference temperature, usually the starting temperature or ambient temperature of the experiment.

[0023] In the above method, optionally, frozen gravel samples are prepared in S105: saturated gravel samples are frozen at different low temperatures for more than 24 hours to obtain frozen gravel samples, and the end faces of the samples are polished at ambient low temperatures to ensure that the flatness and verticality of the prepared samples meet the ISRM requirements, so that the contact surface with the loading end is not pure ice, and a uniform sample that meets the continuous medium assumption is obtained.

[0024] In the above method, optionally, the formula for calculating the proportion of water-ice gravel in the frozen gravel sample is as follows:

[0025] w i =a·(1-e -b·T )+c

[0026] Where:

[0027] w i — percentage by weight of ice;

[0028] T—ambient temperature, in °C;

[0029] a, b and c—constants obtained by fitting the experimental data, representing the changing trend of ice content at different ambient temperatures.

[0030] In the above method, optionally, the experimental data recorded in S3 includes:

[0031] The first incident strain pulse received by the strain gauge of the incident rod and the reflected strain pulse after the stress wave is reflected are recorded, the transmitted strain pulse received by the strain gauge on the transmission rod is recorded, and the acoustic emission signal received by the acoustic emission sensor is recorded.

[0032] It can be seen from the above technical solution that, compared with the prior art, the preparation method of homogeneous frozen gravel and the dynamic testing method under low temperature environment of the present invention have the following beneficial effects:

[0033] 1. The preparation method of homogeneous frozen gravel in the present invention can obtain a sample that meets the assumption of continuous medium mechanics and thus meets the basic premise of dynamic mechanics testing and can simulate the real engineering geological material in high-cold mountainous areas;

[0034] 2. The preparation method of homogenized frozen gravel in the present invention can be used to obtain rock-like material dynamic test specimens that are repeatable and meet the requirements of the dynamic test method of the International Society for Rock Mechanics and Engineering (ISRM);

[0035] 3. The dynamic testing method under low temperature in the present invention can further realize the qualitative and quantitative analysis of the physical and mechanical properties of real engineering geological materials in high-cold mountainous areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0037] Figure 1 A flow chart of a method for preparing homogeneous frozen gravel and a dynamic testing method under low temperature provided by the present invention;

[0038] Figure 2 A schematic diagram of a frozen gravel sample provided by the present invention;

[0039] Figure 3 The internal schematic diagram of the combination of the frozen gravel sample and the Hopkinson pressure bar test system with an environmental low temperature box in the present invention is shown;

[0040] Among them, 1- gravel, 2- water, 3- ice, 4- incident rod, 5- frozen gravel sample, 6- transmission rod. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In this application, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0043] Reference Figure 1 As shown, the present invention discloses a method for preparing homogeneous frozen gravel and a dynamic testing method under low temperature environment, comprising the following steps:

[0044] S1. Sample preparation steps: preparing a homogenized frozen gravel sample;

[0045] S2, sample placement step: clamp the sample between the incident rod and the transmission rod;

[0046] S3, incident wave application step: the incident rod applies the incident wave and records the experimental data.

[0047] Furthermore, the sample preparation step in S1 includes:

[0048] S101, determining relevant dimensions of the frozen gravel sample;

[0049] S102, crushing and sieving the gravel based on the relevant size of the frozen gravel sample obtained in S101 to obtain sieved debris;

[0050] S103, dyeing the gravel debris obtained in S102 to obtain dyed tracer rock debris particles;

[0051] S104, preparing a saturated gravel sample;

[0052] S105. Prepare frozen gravel samples.

[0053] Specifically, determine the relevant size of the frozen gravel sample: first use a cutting machine to cut the original rock sample and drill the core, and select fine-grained granite (particle size 0.2-1mm) with an overall grayish white color as the gravel base material in the sample. According to the method recommended by the International Society for Rock Mechanics and Engineering (ISRM), when using a 50mm diameter SHPB for impact testing, the gravel size should be less than 5mm. Therefore, gravel particles with rock fragment particle sizes of 2mm, 3mm, and 4mm were prepared.

[0054] Crushing gravel and screening debris: Use a crusher to break the fine-grained granite into fragments, and use screening to select fragments with particle sizes of approximately 4mm, 5mm, and 6mm; then use a grinder to process the gravel into three groups of rock fragments with particle sizes of 2mm, 3mm, and 4mm, and an aspect ratio of close to 1:1.

[0055] Furthermore, the gravel debris pretreatment in S103 includes:

[0056] Part of the debris obtained after screening in S102 is selected and dyed with a dark acrylic paint that is resistant to low temperature, wear and water, to obtain dyed tracer rock debris particles that are different from the color of the original rock debris particles.

[0057] Furthermore, S104, preparing a saturated gravel sample includes:

[0058] The original rock debris particles of the same particle size are placed in the sample mold in layers to prepare standard dynamic, static compression and tensile specimens. When placing, a small amount of dyed and labeled rock debris particles are mixed in layers with the standard sample. After the gravel fills the mold, pure water is added. The water-filled mold is placed on a vibration table and vibrated for 60 seconds to allow the bubbles to fully dissipate, and then left to stand for 48 hours to obtain a saturated gravel sample.

[0059] Furthermore, the relationship between saturation and parameters such as temperature, time, and size during rock saturation is as follows:

[0060]

[0061] Where S(t,T,D) is the rock saturation at time t, temperature T and typical size D of the rock sample; S max — is the maximum saturation of the rock; k is the rate constant of the saturation process, which is related to the pore structure of the rock and the fluid properties; D is the typical size of the rock sample, such as diameter or thickness; α is the temperature coefficient, which describes the effect of temperature change on saturation; T0 is the reference temperature, usually the starting temperature or ambient temperature of the experiment.

[0062] Furthermore, frozen gravel samples are prepared in S105: saturated gravel samples are placed at different low temperatures for freezing for more than 24 hours to obtain frozen gravel samples, and the sample end faces are polished at ambient low temperatures to ensure that the flatness and verticality of the prepared samples meet the ISRM requirements, so that the contact surface with the loading end is not pure ice, and a uniform sample that meets the continuous medium assumption is obtained. The schematic diagram of the frozen gravel sample is shown in Figure 2 .

[0063] Furthermore, the formula for calculating the proportion of water-ice gravel in the frozen gravel sample is as follows:

[0064] w i =a·(1-e -b·T )+c

[0065] Where:

[0066] W i — percentage by weight of ice;

[0067] T—ambient temperature, in °C;

[0068] a, b and c—constants obtained by fitting the experimental data, representing the changing trend of ice content at different ambient temperatures.

[0069] Furthermore, the experimental data recorded in S3 include:

[0070] The first incident strain pulse received by the strain gauge on the incident rod and the reflected strain pulse after the stress wave is reflected are recorded, and the transmitted strain pulse received by the strain gauge on the transmission rod is recorded.

[0071] In a specific embodiment, for a Hopkinson pressure bar test system with an environmental low temperature box, this embodiment only describes the incident rod and the transmission rod. During the test, the sample is located in the low temperature box throughout the test. The incident rod and the transmission rod penetrate into the box from both sides of the box and load the sample. The schematic diagram of the combination of the frozen gravel sample and the Hopkinson pressure bar test system with an environmental low temperature box is shown in FIG. Figure 3 .

[0072] Clamp the sample between the incident rod and the transmission rod: Apply an appropriate amount of lubricant on both ends of the sample to reduce the friction effect caused by the sample and the end faces of the test rod. Align the center axis of the sample with the center axis of the incident rod and the transmission rod, so that the incident rod, sample, and transmission rod are on the same axis.

[0073] The incident rod and the transmission rod are made of the same material and the same manufacturing process. Both rods are attached with strain gauges and connected to the data processing system to detect the strain pulses of the incident rod and the transmission rod and further calculate the strain. A launching device is set in front of the incident rod, so that the bullet can be used to apply stress waves to the incident rod and transmit them to the sample. In addition, a shaper is set at the front end of the incident rod for waveform shaping.

[0074] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0075] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing homogeneous frozen gravel and dynamically testing it at low ambient temperature, characterized in that: The following steps are involved: S1. Sample preparation steps: preparing a homogenized frozen gravel sample; S2, sample placement step: clamp the sample between the incident rod and the transmission rod; S3, incident wave application step: applying incident wave to the incident rod and recording experimental data; The sample preparation steps in S1 include: S101, determining relevant dimensions of the frozen gravel sample; S102, crushing and sieving the gravel based on the relevant size of the frozen gravel sample obtained in S101 to obtain sieved debris; S103, dyeing the gravel debris obtained in S102 to obtain dyed tracer rock debris particles; S104, preparing a saturated gravel sample; S105, preparing a frozen gravel sample; The gravel and debris pretreatment in S103 includes: Selecting some of the debris after screening in S102, dyeing them with a dark acrylic paint that is resistant to low temperature, wear and water, to obtain dyed tracer rock debris particles that are different from the color of the original rock debris particles; S104. Preparation of saturated gravel samples includes: The original rock debris particles of the same particle size are placed in the sample mold in layers to prepare standard dynamic, static compression and tensile specimens. When placing, a small amount of dyed and labeled rock debris particles are mixed in layers with the standard sample. After the gravel fills the mold, pure water is added. The water-filled mold is placed on a vibration table and vibrated for 60 seconds to allow the bubbles to fully dissipate, and then left to stand for 48 hours to obtain a saturated gravel sample.

2. The method for preparing homogeneous frozen gravel and dynamically testing it at low temperature according to claim 1, characterized in that: The relationship between saturation and temperature, time and size parameters during rock saturation: Where S(t,T,D) is the rock saturation at time t, temperature T and typical size D of the rock sample; S max — is the maximum saturation of the rock; k is the rate constant of the saturation process, which is related to the pore structure of the rock and the fluid properties; D is the typical size of the rock sample, such as diameter or thickness; α is the temperature coefficient, which describes the effect of temperature change on saturation; T0 is the reference temperature, usually the starting temperature or ambient temperature of the experiment.

3. The method for preparing homogeneous frozen gravel and dynamically testing it at low temperature according to claim 1, characterized in that: Prepare frozen gravel samples in S105: freeze the saturated gravel samples at different low temperatures for more than 24 hours to obtain frozen gravel samples, and grind the sample end faces at ambient low temperatures to ensure that the flatness and verticality of the prepared samples meet the ISRM requirements, so that the contact surface with the loading end is not pure ice, and obtain a uniform sample that meets the continuous medium assumption.

4. The method for preparing homogeneous frozen gravel and dynamically testing it at low temperature according to claim 3, characterized in that: The formula for calculating the proportion of water-ice gravel in the frozen gravel sample is as follows: w i =a·(1-e -b·T )+c Where: W i — percentage by weight of ice; T—ambient temperature, in °C; a, b and c—constants obtained by fitting the experimental data, representing the changing trend of ice content at different ambient temperatures.

5. The method for preparing homogeneous frozen gravel and dynamically testing it at low temperature according to claim 1, characterized in that: The experimental data recorded in S3 include: The first incident strain pulse received by the strain gauge of the incident rod and the reflected strain pulse after the stress wave is reflected are recorded, the transmitted strain pulse received by the strain gauge on the transmission rod is recorded, and the acoustic emission signal received by the acoustic emission sensor is recorded.

Images