CN115340319A

CN115340319A - Engineering rock mass heterogeneous simulation test piece based on rock-like resin material and preparation method and application thereof

Info

Publication number: CN115340319A
Application number: CN202210894012.8A
Authority: CN
Inventors: 付金伟; 程慧香; 雒翔宇; 李彤
Original assignee: North China University of Water Resources and Electric Power
Current assignee: North China University of Water Resources and Electric Power
Priority date: 2022-07-27
Filing date: 2022-07-27
Publication date: 2022-11-15
Anticipated expiration: 2042-07-27
Also published as: CN115340319B

Abstract

The invention discloses an engineering rock mass heterogeneity simulation test piece and preparation and application thereof, and aims to solve the problem of rock mass heterogeneity caused by difficulty in simulation of mineral particles of the conventional test piece. The test piece comprises a rock-like body formed by mixing and casting a transparent resin material and an aggregate, and a joint surface embedded in the rock-like body. The quartz sand aggregate test piece has good rock-like characteristics at the temperature of-15 to-10 ℃, the compression strength ratio and the tensile strength ratio are as high as 9.12, and the compression strength ratio and the tensile strength ratio are obviously enhanced compared with the test piece without quartz sand; the castable is prepared from CY-39 type resin, YS-T31 type curing agent and accelerant according to the weight ratio of 100:34:4 in a mass ratio; the quartz sand is transparent particles with the particle size of 0.6-0.8 mm; the joint surface is made of mica sheets. In addition, the material, the form and the addition of test piece aggregate can be changed according to the rock that is simulated to produce same inner structure and mechanical properties, and the test piece is high transparent, can clearly observe inside crack evolution process, can effectively be used for the influence research of aggregate size and form to the rock mechanism.

Description

Engineering rock mass heterogeneous simulation test piece based on rock-like resin material and preparation method and application thereof

Technical Field

The invention relates to the technical field of geotechnical engineering, in particular to an engineering rock mass heterogeneous simulation test piece and a preparation method and application thereof.

Background

Natural rock is a heterogeneous material with a large number of mineral particles, the size and morphology of which have a significant effect on the mechanical and deformation properties of the rock. The problems of instability and damage of the rock material, the problem of heat points such as shear bands and the like can not be solved without researching the complexity of the rock material, particularly the heterogeneity. Therefore, the method has important academic value and engineering significance for the research on the heterogeneous structural characteristics and the failure mechanism of the rock material. In addition, the engineering rock mass generally contains a plurality of macroscopic weak joint surfaces, the deformation and strength characteristics of the rock mass are also strongly influenced, and the research on the expansion and evolution rule of the three-dimensional fracture is also one of the key contents of rock mechanics.

The indoor test is an important means for carrying out geotechnical engineering research, and the currently commonly used rock simulation materials comprise cement mortar, ceramics, gypsum, organic glass, photosensitive resin and the like, but the materials have great difficulty in manufacturing aggregate-containing heterogeneous simulation test pieces and presetting joint cracks in the test pieces, and cannot be consistent with engineering rock masses. In addition, cement mortar, ceramics and gypsum have the disadvantages of being opaque and not allowing the propagation and evolution process of internal cracks to be observed; the organic glass has the defects of too great difference from the rock characteristics and extremely low representativeness; photosensitive resin is a raw material of a 3D printing technology, and has the defects that a test piece is manufactured in a layer-by-layer printing and curing mode, so that the integrity of the test piece is poor, the plasticity degree of the photosensitive resin is high, and the similarity with rocks is poor.

Therefore, how to search for a transparent rock-like material, the heterogeneous pore structure characteristics consistent with the rock structure are manufactured in the transparent rock-like material, the damage and crack propagation process in the transparent rock-like material is directly observed by naked eyes, and the three-dimensional crack can be preset to carry out indoor experimental research on the instability mechanism of the engineering rock mass, so that the transparent rock-like material has important academic value and engineering significance.

The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is known to a person skilled in the art.

Disclosure of Invention

The invention aims to provide a simulation test piece for the heterogeneity of an engineering rock mass and preparation and application thereof, and aims to solve the technical problem that the existing rock-like material is difficult to effectively simulate the high brittleness and the heterogeneity of real rock.

In order to solve the technical problem, the invention adopts the following technical scheme:

designing a heterogeneous rock-like test piece, which comprises a rock-like body formed by mixing and casting high-brittleness transparent resin and quartz sand and a joint surface embedded in the rock-like body; the high-brittleness transparent resin is prepared by mixing CY-39 type resin, YS-T31 type curing agent and dithiodibenzothiazole curing accelerator according to the weight ratio of 100:34:4 in a mass ratio; the joint surface is made of transparent mica sheets with corresponding shapes.

For example, fig. 1 (a) is a cross section of the heterogeneous rock-like test piece, fig. 1 (b) is a cross section of a real rock in nature, and it can be seen that the two are consistent in the dimension and distribution of microscopic aggregate/mineral particles, which illustrates the effectiveness of the test piece in simulating the internal structure of the real rock.

The quartz sand is transparent particles with the particle size of 0.6-0.8 mm, and the particle density is different from that of the liquid resin.

The preparation method for designing the heterogeneous rock-like test piece comprises the following specific steps:

(1) Preparing a resin casting material: taking CY-39 type resin, YS-T31 type curing agent and dithiodibenzothiazole curing accelerator, and mixing the components in a proportion of 100:34:4, uniformly mixing and removing bubbles;

(2) Mixing aggregate: adding quartz sand into the mixture according to 5% of the mass of the mixture obtained in the previous step, placing the mixture on a centrifugal table for treatment for 2 minutes after the mixture is sufficiently vibrated, and then carrying out bubble removal treatment after the mixture is uniformly stirred;

(3) Laying a joint surface: arranging and fixing joint surfaces required by the test in corresponding test piece casting molds;

(4) Pouring and maintaining the test piece for molding: and (3) draining and pouring the resin casting material into a test piece casting mold after the joint surface is arranged, removing bubbles, curing at the constant temperature of 20 ℃ for 35 h, demolding, and curing at the constant temperature of 70-80 ℃ for 48 h. A completed test piece is shown in fig. 2.

The test piece pouring mold is an organic polymer silica gel (HTV) mold; as shown in fig. 3.

The joint surface is a circular or oval sheet punched by a mica sheet with the thickness of 0.1 mm, and FIG. 4 is a structural drawing and a physical drawing of a steel mould for processing the mica sheet; fig. 5 shows a finished mica sheet joint face.

The transparent quartz sand with the particle size of 0.6-0.8 mm is prepared by long searching process on the color, performance and body shape of aggregate in the early stage, and dozens of materials and different particle sizes are tried. Since the particle density of the quartz sand is different from that of the liquid resin, the quartz sand can precipitate, float or gather (see the failure example in fig. 6), and cannot be effectively distributed in the test piece, which results in failure of the experiment. In addition to the conventional treatment measures such as vibration, centrifugation, stirring and the like, the adopted method is to add a dithiodibenzothiazyl curing accelerator into the mixture to accelerate the initial setting speed of the mixture and ensure that the initial setting is finished within 30 min; in the subsequent slow solidification process, the disease phenomenon can not occur any more.

In the step (4), after demolding, drying and curing at a constant temperature of 70 ℃ for 24 h, and a test piece with a compressive strength of 96.7 MPa can be obtained.

Compared with the prior art, the invention has the main beneficial technical effects that:

(1) The transparent rock-like resin test piece has important significance for researching the influence mechanism of heterogeneity on the mechanical properties of rock materials.

(2) The transparent rock-like resin test piece prepared based on the aggregate brittleness and toughness increasing has similar internal structure and mechanical property with real rock and has good brittleness and transparency at a lower temperature; the heterogeneity caused by the defects of uneven distribution of mineral particles, pores, joints and the like in the rock can be effectively simulated; furthermore, the transparent quartz sand is further selected as the aggregate, so that the high transparency of the test piece is not influenced, the deformation and crack expansion of the test piece are not influenced, the test piece is closer to real rock compared with a pure resin rock test piece, and the brittleness is also obviously improved (reaching 9.12); compared with 3D printing photosensitive resin, the photosensitive resin has stronger integrity and closer mechanical property to real rocks.

(3) The heterogeneous internal structure of the heterogeneous rock test piece can be adjusted and changed according to the material, the addition amount and the body shape parameters of the aggregate according to the actual conditions of different engineering rock masses, as shown in figure 7, so as to keep consistent with the heterogeneous structure, the shape and the elastic modulus of the simulated rock.

The aggregate addition amount calculation method is as follows: when the density of the particle defects is the same as or within 10 percent of the density of the rock main body framework, acquiring the mesoscopic particle/aggregate mass percentage information (marked as omega) in the real rock (the cement mortar test piece can also be used) firstly ₁ ) If the amount of the aggregate added in step 2 is ω ₂ =138ω ₁ /(1-ω ₁ ) The aggregate content omega can be directionally prepared by the method ₁ The rock-like test piece of (1). In the aspect of aggregate shape parameters, information such as circularity, sphericity and flatness of particle defects in natural rocks is obtained by CT scanning, then consistent aggregate shapes and mixing amount are obtained for manufacturing test pieces, and aggregates can be firmly bonded by glue and then placed in a mold for distribution when necessary. FIG. 8 shows the completed test pieces with different aggregate additions and form parameters.

When the density difference between the particle defects and the rock main body skeleton is more than 10%, the addition amount of the aggregate is as follows:

(1)，

in the formula: the volume ratio content of the aggregate, the elastic modulus of the resin material, the elastic modulus of the simulated rock, the body shape parameter of the aggregate and the Poisson ratio of the resin material.

Wherein, as a function of the aggregate shape parameter and the poisson's ratio of the resin material, the following is calculated:

(2)；

in the formula: is the minimum value of the tangent angle in the geometric profile of the aggregate.

(4) In the invention, a pouring test piece mold made of silica gel is further selected, and compared with a mold made of glass, stainless steel, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC) and the like which are conventionally used, bubbles are not easily attached to the inner wall of the mold, as shown in fig. 9, the mold is a partial sample example of failed preparation caused by the problem of the mold material; the test piece is easier to demould after being formed; the high transparency of the material can clearly observe the curing process of the test piece; the soft silica gel facilitates the positioning of joint positions by drilling and bracing wires, joint surfaces under various conditions are easy to preset, the research on crack expansion of joint sizes, positions, inclination angles and the like, the influence of the number, relative positions, relative angles and the like of a plurality of joint surfaces on crack expansion, the interaction among the joint surfaces and the like is developed.

Drawings

FIG. 1 is a cross-sectional comparison diagram of a test piece and a natural real rock in an embodiment of the present application; wherein a is the test piece of the invention, and b is basalt.

Fig. 2 shows the test pieces manufactured in the embodiment of the present application, including the test piece without the prefabricated joint and the prefabricated joint test piece.

Fig. 3 shows an organic polymer silicone (HTV) mold for casting a test piece according to an embodiment of the present disclosure.

FIG. 4 is a steel mold for processing the mica sheet joints in the present invention; wherein a is a structural diagram and b is a real object diagram.

FIG. 5 is a joint plane of transparent mica plate prepared in an embodiment of the present application; wherein a is a 12 (minor axis) × 17 mm (major axis) ellipse, b is a φ 15 mm circle, c is a 15 × 20 mm ellipse, and d is a 13 × 20 mm ellipse.

FIG. 6 is a test piece of an embodiment of the present application, wherein improper selection of aggregate results in a failed preparation; wherein, a is the sinking caused by the excessive density of the aggregate, and b is the expansion of the test piece caused by the cementing reaction of the aggregate and the raw materials such as resin and the like.

FIG. 7 is a schematic representation of aggregate materials of different body shape parameters in an embodiment of the present application.

FIG. 8 shows a sample prepared according to the embodiment of the present disclosure with different amounts of aggregate and different body shape parameters; wherein a is 2 mm particle size blue rubber particles, and b is 1.2 mm particle size polyethylene plastic particles.

FIG. 9 is a sample of an embodiment of the present disclosure, wherein the sample failed to be prepared due to a mold material problem; wherein, a is dense bubbles formed on the surface of the test piece after the mold is demolded, and b is distorted and deformed by heat generated in the curing process of the test piece because the mold is not resistant to high temperature.

FIG. 10 is a diagram illustrating the phenomenon of the crack growth early stage of the built-in single joint specimen according to another embodiment of the present application, wherein a is a front view of the specimen, and b is a side view of the specimen.

FIG. 11 shows a phenomenon of a crack growth late stage of a built-in single joint test piece according to another embodiment of the present application; wherein a is the front view of the test piece and b is the side view of the test piece.

Detailed Description

The following examples are intended to illustrate the present application in detail and should not be construed as limiting the scope of the invention in any way.

The instruments and devices referred to in the following examples are conventional instruments and devices unless otherwise specified; the raw materials are all conventional raw materials which are sold in the market if not specifically indicated; the detection method and the test method are conventional methods unless otherwise specified.

The existence of a large amount of mineral particles, pores, cracks and joints in the rock mass has extremely complicated internal structure and has great influence on the practical engineering application; and is therefore very important for the study of fractures and the like in rock masses. In order to simulate the heterogeneity of the rock and improve the mechanical property of the rock-like material, transparent quartz sand is added on the basis of pure resin materials, a three-dimensional built-in joint surface is preset, and the rock-like test piece is manufactured by integral casting for indoor experiments. The heterogeneity of the rock is simulated by selecting proper aggregate through experiments, the material, the particle size, the physical and chemical properties, the mechanical property and the like of the aggregate need to be considered, and the selection of the material and the particle size of the aggregate is a major difficulty to be solved. The macroscopic crack in the rock mass is simulated by embedding a three-dimensional built-in crack in a mold in advance, and the key to successful experiment is the material selection, cutting and positioning of the prefabricated three-dimensional crack.

The first embodiment is as follows: the preparation method of the transparent rock-like resin material test piece based on the aggregate brittleness increasing and toughness reducing specifically comprises the following steps:

(1) Preparation of resin, curing agent and curing accelerator

1000 g of CY-39 type resin, 340 g of YS-T31 type curing agent and 40 g of dithiodibenzothiazole curing accelerator are weighed and poured into a stirring barrel, the materials are continuously stirred by a glass rod to be fully mixed to form a mixture, the resin on the side wall and the bottom of the container is also fully mixed, and then the container is placed into a vacuum box for degassing.

The CY-39 type resin is tasteless and harmless, and has the advantages of good stability, strong binding power, high curing speed, high strength after curing reaction and the like; after the curing agent YS-T31 is added, a cross-linking reaction can occur to generate a thermosetting material with a three-dimensional network, the strength is greatly improved, and the mechanical property of a cured test piece is very similar to that of rock. The selection and amount of the curing agent are the largest factors affecting the mechanical properties.

(2) Mixing of aggregate

And (2) adding aggregate accounting for 5% of the mass of the mixture into the mixture subjected to the defoaming treatment in the step (1), vibrating the mixture fully, placing the mixture on a centrifugal table for treatment for 2 minutes, stirring the mixture uniformly, and then performing the defoaming treatment for 4 minutes.

For the selection of aggregate material in the rock-like test piece, carry out a large amount of experimental quests, including the experiment of choosing the multiple materials of uniform particle diameter to seek, for example polyethylene plastic granule, acrylic solid ball, PVC injection moulding granule, sky blue acrylic microballon, transparent quartz sand etc. the result shows: the density of the transparent quartz sand is close to that of the mixture, the transparent quartz sand can be uniformly distributed in the mixture after being mixed, the reaction with the resin raw material cannot occur, and the transparency of a test piece is not influenced due to the transparent color; when other selected materials are used for casting a test piece, the aggregate with too light weight can be easily aggregated and cannot be uniformly distributed in the resin mixture, and the requirement on pore distribution characteristics cannot be met; too high or too low density can cause the aggregate to be unevenly distributed, so that the aggregate sinks to the bottom or floats on the upper part of the test piece, and the requirements on the uniformity and the compactness of the aggregate distribution cannot be met (see figure 9); too deep a color may affect the transparency of the test piece, making it inconvenient to observe the curing process and the crack propagation process of the test piece.

In the meantime, the influence of the particle size of the aggregate on the mechanical properties of the test piece is further studied, for example, 6 groups of quartz sand with different particle sizes (0.1-0.2 mm, 0.2-0.4 mm, 0.4-0.85 mm, 0.85-2 mm, 2-3.5 mm and 3.5-5 mm) are selected as the aggregate, 6 groups of rock-like test pieces with different particle sizes are prepared, and a plurality of mechanical experiments are carried out on the rock-like test pieces to study the influence of the particle size of the aggregate on the mechanical properties of the test piece; the results show that: along with the increase of the particle size, the compressive strength of the test piece shows a trend of increasing and gradually changes into brittle failure; when the particle size of the aggregate is smaller, the mechanical property of the test piece is not obviously improved, the observation is not facilitated, the cementation degree of the test piece is lower under the condition of overlarge particle size, the pores are increased, the test piece is close to tension damage, and the condition that the particle size of the quartz sand is 0.6-0.8 mm is determined to be more appropriate. After the particle size of the aggregate is determined, the result is obtained through further experiments and analysis: the aggregate is made into a hollow structure, which is closer to the internal structure of natural rock, the mechanical property of the aggregate is improved, and the aggregate structure requirement is better met. The prepared test piece has high strength, the distribution of aggregate particles on the section of the test piece can be clearly observed, the deformation characteristic of the test piece is not influenced, and the mechanical property is closer to that of various rocks.

(3) Embedding of prefabricated joints

Determining projection points of joint surfaces on two sides of a silica gel mold, drilling holes, and positioning the joint surfaces by using cotton thread traction, wherein the joint surfaces are pre-embedded in the center of a test piece, and the joint surfaces form an included angle of 45 degrees with the horizontal plane.

In the embodiment, the prefabricated joint surface is made of a mica sheet with the thickness of 0.1 mm, and the mica sheet is used as a layered rock, so that compared with materials such as metal, plastic, resin, stainless steel sheet and the like, the strength and deformation of a test piece cannot be influenced due to low rigidity; the chemical property is stable, and the resin and the curing agent can not react; the positioning is convenient to simulate the hollow fracture existing in the natural rock. And (3) stamping the mica sheet by using a customized steel die, and cutting the mica sheet into oval prefabricated cracks with fixed sizes. The cracks with different sizes are manufactured, and the influence of the size, the inclination angle, the position and the like of the crack on the strength and the crack expansion of the test piece can be researched; the expansion can research the influence of the number, the distance, the relative position, the relative opening degree and the like of multiple fractures on the fracture expansion and the rock mass damage.

The steel die for processing and prefabricating the three-dimensional crack consists of a metal base and an impact column, and the impact column can freely move in the oval hole. Oval steel dies with three sizes are manufactured and used for stamping mica sheets, and the problem that burrs, sharp corners and rough sections can cause stress concentration in the conventional manual cutting of the mica sheets is solved. The mica sheet cut by the steel mould has accurate size and smooth section, the size of the mica sheet can be accurately controlled, and the manual error is reduced.

The silica gel mold for preparing the test piece is a square box body with an opening at the upper part, and is sealed by the organic insulating silicone grease to form a whole, so that the corresponding size can be customized according to the test requirement. Compared with the moulds of glass, stainless steel, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC) and the like used by the predecessors, the silica gel has stable chemical property, the inner wall is not easy to be attached with bubbles, and the silica gel is soft and easy to demould. In addition, the silica gel has high transparency, and the curing process of the test piece can be clearly observed. In addition, the three-dimensional joint surface arranged in the silica gel mold is drilled, the thin lines are pulled and positioned more conveniently, and the test pieces with different quantities, different angles and different relative positions can be manufactured by drilling at different positions on two sides of the mold.

(4) Pouring of test piece

Placing the silica gel mold with the pre-embedded joint surface on a workbench, and guiding the mixture added with the aggregate in the step (2) into the mold by using a glass rod for casting and molding; after pouring, the mould is placed into a vacuum box for bubble removal treatment for 25 minutes, and then is placed into a constant-temperature drying air box at 18 ℃ for maintenance for 40 hours, so that the mould can be removed.

(5) Maintenance of test pieces

Then placing the test piece into a constant-temperature drying air box, setting different curing temperatures and curing times for curing, wherein the curing temperature is set to be 70 ℃ and the curing time is set to be 24 hours in the example, so that the transparent rock-like resin test piece with the brittleness-increasing and toughness-reducing function of the aggregate which is very similar to the brittleness characteristic of the rock is obtained, the brittleness of the transparent rock-like resin test piece reaches 9.12 at the temperature of between 15 ℃ below zero and 10 ℃ below zero, the brittleness is greatly improved compared with a pure resin rock test piece prepared by the prior art and a 3D printing photosensitive resin test piece, and the mechanical property is closer to that of the rock; compared with cement mortar rock materials, the strength is improved, and the transparency and the visibility thereof are incomparable advantages; the mechanical property of the rock is closer to that of various real rocks. The main mechanical parameters of the resin material of the invention at-15 to-10 ℃ are shown in Table 1, besides, the experimental temperature of Dyskin and Wong is-50 ℃, and the experimental temperature of Song is-20 ℃.

TABLE 1 comparison of the physico-mechanical parameters of the heterogeneous resin test piece of the present invention with other transparent rock-like materials and some real rocks

。

As can be seen from Table 1, the mechanical parameters of the heterogeneous resin sample are relatively close to those of real rocks, so that the rocks can be simulated to a certain extent, and the test piece obtained by the method has the characteristics of high transparency, easiness in direct observation by naked eyes and the like.

Example two: verification test

The test piece prepared by the invention is easy to prepare and strong in repeatability, a group of rock-like test pieces with completely identical built-in cracks are prepared, a plurality of mechanical experiments are carried out on the rock-like test pieces, such as uniaxial compression, brazilian splitting and the like, the rock-like test pieces are respectively loaded to a certain state and then unloaded, and the whole process of built-in crack expansion evolution can be obtained through photographing and recording, for example, fig. 10 shows the phenomenon of the early stage of crack development obtained by unloading after the pressure is increased to 20 MPa, and fig. 11 shows the phenomenon of the later stage of crack development obtained by unloading after the pressure is increased to 90 MPa. The global stress-strain curve can be obtained from a test piece through a global compression process.

And pressurizing the test piece containing the single-joint rock resin, observing the crack expansion evolution process, and analyzing the rock damage rule. The crack propagation evolution of the test piece under the pressurization condition goes through an initial stage, then an elastic deformation stage is started, the upper end of the prefabricated joint at the stage has wing cracks to be generated, then the upper end and the lower end of the prefabricated crack generate the wing cracks, and the propagation scales are approximately synchronous. And (2) entering a crack propagation stage along with the increase of the pressure, wherein 1 and 2 particularly obvious spot-shaped cracks are respectively arranged near two sides of the wrapped type wing crack at the upper end of the prefabricated crack, and 1 relatively small spot-shaped crack is respectively arranged at the lower end of the prefabricated crack and is closely adjacent to two sides of the wrapped type wing crack. And finally, entering a crack accelerating and expanding stage, continuously expanding the petal-shaped cracks and the vertical cracks along the loading direction, reducing the bearing capacity of the test piece, hearing intensive crack sound of the test piece, and finally splitting the test piece to show brittle fracture damage after the vertical large cracks form a macroscopic fracture surface.

While the invention has been described in detail with reference to the drawings and examples, it will be understood by those skilled in the art that various changes in the details of construction and materials may be made therein without departing from the spirit of the invention, and it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A heterogeneous rock-like test piece is characterized in that the test piece is highly transparent, can clearly observe the whole-course evolution law of internal cracks and damages by naked eyes, and is applied to the simulation experiment research of various engineering rock masses; the method is realized by adding quantitative aggregate into a transparent resin material to prepare an engineering rock mass simulation test piece with heterogeneous characteristics; taking a quartz sand aggregate test piece as an example, the test piece specifically comprises a quasi-rock body formed by mixing and pouring brittle transparent resin and quartz sand, and a macroscopic soft joint surface embedded in the quasi-rock body; by means of the effects of increasing brittleness and reducing toughness of the aggregate, the rock-like property of the test piece is obviously enhanced compared with that of a homogeneous pure resin test piece without the aggregate, the brittleness, namely the ratio of the compressive strength to the tensile strength, is greatly improved from 6.6 to 9.12, and compared with 2.98 of the prior transparent rock-like test piece of the same type, the brittleness reaches the standard of a plurality of real rocks in the nature.

2. The heterogeneous rock test piece of claim 1, wherein the heterogeneity of the engineering rock is due to the fact that a large number of microscopic particle defects exist inside the engineering rock, and the simulation implementation method is to use transparent quartz sand and the like as pouring aggregates of the pure resin test piece;

because the particle density of the quartz sand is different from that of the liquid resin, the phenomena of precipitation, floating or aggregation and the like can be generated, and the quartz sand cannot be effectively distributed in a test piece, so that the experiment fails; in addition to the measures of conventional vibration, centrifugation, repeated stirring and the like, the dithiodibenzothiazyl curing accelerator is added into the mixture to accelerate the initial setting speed and ensure that the initial setting is completed within 30 min; in the subsequent slow solidification process, the phenomenon of uneven distribution can not occur any more;

the addition amount of the curing accelerator is 4% of the mass of the liquid resin, too much of the curing accelerator influences the mechanical parameters of a cured test piece, and too little of the curing accelerator does not achieve the effect of accelerating initial curing;

in addition, the test piece used for the rock mechanical test needs to contain a macroscopic soft joint surface consistent with real rock except homogeneity so as to meet the requirements of various mechanical tests; the transparent mica sheet is adopted to simulate a joint surface, the thickness of the transparent mica sheet is 0.1 mm, the transparent mica sheet is punched by a steel die to form round and oval sheets, and the edges of the round and oval sheets are neat so as to avoid stress concentration caused by burrs and size defects.

3. The preparation method of the heterogeneous rock-like test piece is characterized by comprising the following steps:

(1) Preparing a resin casting material: taking CY-39 type resin, YS-T31 type curing agent and dithiodibenzothiazole curing accelerator, and mixing the components in a proportion of 100:34:4, uniformly mixing, and vacuumizing to remove bubbles;

(2) Mixing aggregate: adding the quartz sand of claim 2 into the mixture according to 5 percent of the mass of the mixture obtained in the previous step, placing the mixture on a centrifugal table for processing for 2 minutes after fully vibrating, and then carrying out bubble removal processing for 4 minutes after uniformly stirring;

(3) Laying a macroscopic joint surface: the method is characterized in that a perforation and line drawing mode is adopted in a test piece die, soft joint surfaces required by a fixed test are arranged and stuck before a mixture is poured, and three-dimensional arrangement combinations with different numbers, different angles and different positions are formed so as to meet the requirements of various mechanical experiments;

(4) Pouring and curing the test piece: pouring the resin casting material into a test piece mold with the joint surfaces arranged, maintaining at the constant temperature of 20 ℃ for 35 h, then demolding, and maintaining at the constant temperature of 70-80 ℃ for 48 h to finish the manufacture of the test piece; before the test, the test piece was placed in a freezer at-20 ℃ in advance at 24 h.

4. The heterogeneous rock-like test piece of claim 3, wherein in the step (2), the material, form and addition amount of the aggregate are variable, and the form of the aggregate is consistent with the form of the particle defect in the natural rock, and the addition amount of the aggregate is calculated according to the following two conditions in order to make the macroscopic elastic modulus of the test piece consistent with the simulated rock:

(1) when the density of the particle defect is the same as or within 10 percent of that of the main skeleton of the rock, acquiring the mass percent information omega of microscopic particles in the real rock by a digital image or CT scanning technology ₁ If the amount of the aggregate added in the step (2) is ω ₂ =138ω ₁ /(1-ω ₁ ) The aggregate content omega is prepared by the orientation ₁ The rock-like test piece of (1);

(2) when the density difference between the particle defects and the rock main body skeleton is more than 10%, the addition amount of the aggregate is as follows:

(1)；

in the formula: the volume ratio content of the aggregate, the elastic modulus of the resin material, the elastic modulus of the simulated rock, the body shape parameter of the aggregate and the Poisson ratio of the resin material are shown;

(2)；

5. The method for preparing the heterogeneous rock-like test piece according to claim 3, wherein the test piece casting mold in the step (3) is an organic polymer silica gel mold which has strong thermal stability, does not react with the casting material, is convenient to demold, can ensure the test piece to be intact to the maximum extent, and can be reused.