Layered filling construction method of transparent similar model based on vacuum negative pressure

Abstract

The invention discloses a transparent similar model layered filling construction method based on vacuum negative pressure, and belongs to the field of geotechnical engineering. According to the technical scheme, an unsaturated transparent similar material and a cementing solution which are used for carrying out a simulation experiment are firstly loaded into a model box with a sealing effect, meanwhile, the appearance of a simulation object is molded by using a 3D printing mold, then vacuumizing is carried out through sealing operation, so that the interior of the model box is in a vacuum negative pressure state, and when the vacuum expression number is 0, the simulation object is obtained. The transparent adhesive solution can fully permeate into the unsaturated transparent similar material, and the model becomes a completely transparent state through fusion and consolidation of the transparent adhesive solution and the unsaturated transparent similar material, so that layered filling and construction of the transparent similar model are realized. The operation process is simple, the model implementation efficiency is high, and the method has wide practicability in the field of transparent similar simulation experiments.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical engineering, and in particular relates to a layered filling construction method of a transparent similarity model based on vacuum negative pressure. Background Art

[0002] Soil deformation measurement is a crucial foundation for soil mechanics research. Traditional indoor model tests use sensors embedded within the soil to obtain localized monitoring information, which is affected by sensor size, as well as deformation at soil boundaries. To enable visual observation of internal soil deformation, seepage, and other parameters, transparent soil testing technology has been developed.

[0003] Transparent soil is made of transparent solid particles and pore liquid with matching refractive index. Using transparent soil and adopting modern optical observation technology and image capture and processing technology can realize the visualization study of soil deformation, seepage, temperature effect and other problems. It is of great significance for in-depth study of the internal deformation laws and mechanisms of soil under various engineering geological conditions and improving the understanding of the essence of soil mechanics and geotechnical engineering problems.

[0004] Due to the repeatability and operability of similarity model testing, it is possible to realistically reproduce the deformation characteristics of geotechnical engineering structures such as slopes during catastrophic events. Building on existing inventions, the consolidation method is being used to simulate similar geotechnical engineering structures such as transparent slopes, demonstrating promising research value and development prospects. Transparent soil produced using the consolidation method exhibits certain advantages in simulating the physical and mechanical properties of natural clay, demonstrating a high degree of similarity in terms of particle grading, permeability, and consolidation properties, thus meeting the requirements for simulating the physical and mechanical properties of rock (or soil).

[0005] The transparent similar material rock (soil) produced by the consolidation method needs to go through steps such as mixing and solidification. The rock formation process is relatively complex, and the control of experimental operations is particularly demanding. The formation and molding of saturated transparent materials require cyclic compaction and exhaust operations. In actual operation, the entire process is limited by the weight of the model box and the internal mixture. It is difficult for the transparent cementing solution to penetrate the unsaturated transparent material well. The operation is time-consuming and labor-intensive, and it is usually difficult to achieve the desired transparency. The shear strength of transparent similar material rock (soil) is mainly characterized by cohesion and internal friction angle. The strength and stiffness of transparent similar material rock (soil) increase with the increase of silica powder content. After the silica powder content reaches a peak, the strength and stiffness of the transparent similar material rock (soil) gradually weaken when the content is increased. The cementing solution is used to increase the bonding effect between quartz sand and silica powder. The amount of cementing solution used is positively correlated with the quality of silica. In the prior art CN113248188A, an unsaturated transparent similar material is first added to a binder solution and stirred and mixed, then compacted, and then placed in a vacuum box to exhaust air and adjust the density, which directly affects the bite effect between the particles; this prior art only disperses the binder solution to the surface of the silica powder by stirring, and it is difficult to ensure that the silica surface is evenly adsorbed with the binder solution. The internal friction angle reflects the friction resistance and bite effect between the particles. The internal friction angle of the transparent similar material rock (soil) of this prior art is low, and the material is more prone to shear deformation. It cannot be used to simulate soil in scenarios such as slope engineering with high anti-slip ability and foundation reinforcement. There is an urgent need to solve the problem of low internal friction angle of the transparent similar material rock (soil) of this prior art. Summary of the Invention

[0006] Based on the related invention "A preparation method, product and application of a soft rock transparent similar material" (application publication number: CN113248188A, application publication date: 2021.08.13), in order to solve the above problems, the present invention discloses a layered filling and construction method of a transparent similar model based on vacuum negative pressure. After the transparent binder solution and the unsaturated transparent similar material are initially prepared, the unsaturated transparent similar material is laid in layers in the model box; after the unsaturated transparent similar material is initially compacted, the transparent binder solution is poured into it, and then the cover plate is placed and the vacuum operation is performed to allow the internal gas of the unsaturated soil to exchange with the transparent binder solution, so that the unsaturated transparent similar material and the transparent binder solution are fully integrated to reach a saturated state; while laying the unsaturated transparent similar material, the boundary conditions of the similar model are restricted by a 3D printed mold to shape the shape of the simulation object, and a simulated physical model of the soft rock transparent similar material is prepared, which specifically includes:

[0007] A layered filling construction method of a transparent similarity model based on vacuum negative pressure includes the following steps:

[0008] (1) Add unsaturated transparent similar material to the model box, compact it after laying, pour in an appropriate amount of transparent cementing solution, and after most of the transparent cementing solution enters the unsaturated transparent similar material, use a 3D printed mold to cover the mixture;

[0009] (2) Seal the model box, close the exhaust valve, open the exhaust valve, and extract the air inside the model box until the air pressure reaches -80kPa to -90kPa. Use the negative pressure in the model box to slowly force out the air in the unsaturated transparent similar material;

[0010] (3) Repeat step (2) until a small amount of transparent binder solution remains on the surface of the unsaturated transparent similar material, close the exhaust valve and the vacuum pump, open the exhaust valve, and use the pressure difference between the inside and outside of the box to press the residual transparent binder solution on the surface of the unsaturated transparent similar material into the unsaturated transparent similar material. When the air pressure reading is 0 MPa, the transparent binder solution can fully penetrate into the unsaturated transparent similar material to reach saturation, thereby obtaining a saturated transparent similar material.

[0011] Furthermore, in the construction method, the unsaturated transparent similar material is laid multiple times, and operations (1)-(3) are performed after each layer of the unsaturated transparent similar material is laid; a plurality of 3D printing molds are provided accordingly, and the outline of each 3D printing mold is a rectangular parallelepiped with one end beveled, and the width and height of each 3D printing mold are the same, but the length is different. All 3D printing molds are stacked from the bottom layer to the top in order of length from small to large, so that the two ends of each layer of 3D printing molds can be aligned with the two ends of the 3D printing mold of the previous layer to form a trapezoidal mold, and a cross bar is provided inside each mold for easy extraction. The height and length of the 3D printing mold are designed according to the set slope shape and the slope layering scheme.

[0012] Furthermore, the unsaturated transparent similar material includes fused quartz sand with three particle sizes of 0.2-0.5 mm, 0.5-1.0 mm, and 1.0-2.0 mm, and nano-hydrophobic fumed silica powder, and the mass ratio of the sum of the three particle sizes of fused quartz sand to the nano-hydrophobic fumed silica powder is 125:4;

[0013] The weight ratio of the three particle sizes of fused quartz sand is 2:2:1. The dry density of the fused quartz sand with a particle size of 0.2-0.5 mm is 1.40 g / cm 3 The porosity is 36%, and the dry density of fused quartz sand with a particle size of 0.5 to 1.0 mm is 1.25 g / cm 3 The porosity is 43%, and the dry density of fused quartz sand with a particle size of 1.0 to 2.0 mm is 1.10 g / cm 3 , porosity is 50%;

[0014] The particle size of nano-scale hydrophobic fumed silica powder is ≤15nm, and the density in its natural state is 70g / L.

[0015] Furthermore, the transparent binder solution is obtained by mixing n-dodecane and 15# white oil in a mass ratio of 1:4 at 25°C.

[0016] Furthermore, the model box includes a semi-open box body and a cover plate composed of a U-shaped acrylic plate and two rectangular acrylic plates. A U-shaped metal plate is fixed to the bottom of the box body for fixing the model box on the loading platform. A vacuum gauge and several exhaust valves integrated with the vacuum gauge are arranged above the cover plate, and a rubber sealing ring is arranged under the cover plate.

[0017] A vacuum device is also provided, which is connected to a vacuum gauge above the cover plate through an air suction pipe, and an air extraction valve is provided on the air suction pipe; vacuuming and exhausting operations are achieved through the vacuum device, the air extraction valve and the exhaust valve.

[0018] During the above operations, it is necessary to prevent temperature changes from causing changes in the refractive index of the transparent similar cementing solution.

[0019] Compared with the prior art, this application has the following advantages and beneficial effects:

[0020] (1) The present invention provides a method and experimental device for constructing a layered filling of a transparent similar model based on gas-liquid exchange under vacuum negative pressure. A vacuum pump is used to perform internal negative pressure operation at the air valve connected to the model box, which can accelerate the replacement of air between the transparent binder solution and the unsaturated transparent similar material; the remaining four air valves arranged at the top can balance the equipment air pressure, thereby further accelerating the formation of saturated transparent similar material.

[0021] (2) The cohesion of the transparent similar material was measured to be 38.778 kPa and the internal friction angle was 46.277° through the quadruple direct shear test, which can be used to simulate soft rock experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of the model experiment of the present invention;

[0023] Figure 2 This is a structural diagram of a transparent similarity model experimental device for vacuum negative pressure gas-liquid exchange according to the present invention;

[0024] Figure 3 This is the appearance diagram of the 3D printing mold required for layered filling in the present invention;

[0025] Figure 4 This is a transparent similar model forming diagram of the gas-liquid exchange based on vacuum negative pressure in Example 3;

[0026] Figure 5is the direct shear stress-displacement curve of the transparent similar material in the model prepared in Example 3;

[0027] Figure 6 This is a straight line graph of the strength fitting of the transparent similar material in the model prepared in Example 3. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0029] Example 1 Preparation of unsaturated transparent similar materials

[0030] Preparation of unsaturated transparent similar materials:

[0031] According to the mechanical parameter values of the soft rock transparent similar material, the particle size and gradation of the skeleton material and the content of the binder are determined to obtain the composition ratio of the unsaturated transparent similar material.

[0032] In the embodiment of the present invention, based on the physical properties of the simulated soft rock and soil, the skeleton material is selected from fused quartz sand with three particle sizes of 0.2-0.5mm, 0.5-1.0mm, and 1.0-2.0mm, with a mass ratio of 2:2:1. The dry density of fused quartz sand with a particle size of 0.2-0.5mm is 1.40g / cm 3 The porosity is 36%. The dry density of fused quartz sand with a particle size of 0.5 to 1.0 mm is 1.25 g / cm 3 The porosity is 43%, and the dry density of fused quartz sand with a particle size of 1.0 to 2.0 mm is 1.10 g / cm 3 , porosity is 50%; the specific gravity of fused quartz sand is 2.2g / cm 3 , and the refractive index is 1.4585.

[0033] The binder is nano-scale hydrophobic fumed silica powder, which is white powder with a particle size of ≤15nm, a density of 70g / L in its natural state, and a refractive index of 1.4585.

[0034] Example 2

[0035] A transparent similar model device for gas-liquid exchange based on vacuum negative pressure, the transparent similar model device comprising a model box and a vacuum device;

[0036] The model box includes a semi-open box body and a cover plate made of a U-shaped acrylic plate and two rectangular acrylic plates. A U-shaped metal plate is fixed to the bottom of the box body to fix the model box to the loading platform. A vacuum gauge and several exhaust valves integrated with the vacuum gauge are installed above the cover plate (five are provided in this embodiment). A rubber sealing ring is arranged below the cover plate. In this embodiment, the external dimensions of the box body are: 35 cm high, 21 cm wide, and 66 cm long. The internal dimensions of the box body are: 32 cm high, 15 cm wide, and 60 cm long.

[0037] The vacuum device (in the specific embodiment, the vacuum device is a vacuum pump) is connected to the vacuum gauge above the cover plate through an air suction pipe, and an air suction valve is provided on the air suction pipe.

[0038] The transparent similar model device also includes a matching 3D printing mold. In this embodiment, five 3D printing molds with consistent heights and different lengths are provided. The outline of each 3D printing mold is a cuboid with one end beveled. The width and height of each 3D printing mold are the same, but the length is different. All 3D printing molds are stacked from the bottom layer to the top in order of length from small to large, so that the two ends of each layer of 3D printing molds can be aligned with the two ends of the 3D printing mold of the previous layer to form a trapezoidal mold. A crossbar is provided inside each mold for easy extraction. The height and length of the 3D printing mold are designed according to the set slope shape and slope layering scheme.

[0039] Example 3 A layered filling construction method for a transparent similarity model based on gas-liquid exchange under vacuum negative pressure, the specific steps are as follows:

[0040] After the model box is fixed, the material is added to the box body and filled into the model box layer by layer for compaction. According to the actual model test plan, in combination with the 3D printing mold, the unsaturated transparent similar material prepared in Example 1 is filled into the model box layer by layer and compacted, and then the mold is taken out to obtain a transparent similar material. In this embodiment, the unsaturated transparent similar material is laid in six layers. After each layer of unsaturated transparent similar material is laid, a compaction operation is performed to initially reduce the porosity. Each layer of unsaturated similar material needs to be laid in combination with five slope molds in sequence. Each layer is an independent process, specifically:

[0041] (1) After adding unsaturated transparent similar material and compacting it, pour in an appropriate amount of cementing solution. After most of the transparent cementing solution has entered the unsaturated transparent similar material, use a 3D printing mold to shape the model outline. At the same time, use a heavy object to cover the mixture to prevent the solution from seeping into the model and causing the model volume to expand.

[0042] The cementing solution is a mixture of n-dodecane and 15# white oil. At 25°C, the mass ratio of n-dodecane and 15# white oil is 1:4, so that the refractive index of the transparent cementing solution reaches 1.4585.

[0043] In this embodiment, the weight ratio of fused quartz sand: transparent cementing solution: SiO2 powder is 125:25:4, and the silicon dioxide powder accounts for 2.6%.

[0044] (2) Cover the cover, close the exhaust valve, open the exhaust valve, and extract the air inside the sealed model box until the air pressure reaches -80kPa to -90kPa. Use the negative pressure in the sealed model box to slowly force out the air in the unsaturated transparent similar material. The air exchange between the transparent similar glue solution and the unsaturated transparent similar material can be clearly observed.

[0045] (3) The operation of step (2) is continued until a small amount of transparent binder solution remains on the surface of the soil. The exhaust valve and the vacuum pump are closed, and the exhaust valve is opened. The residual transparent binder solution on the surface of the soil is pressed into the soil by using the pressure difference between the inside and outside of the box. When the pressure reading is 0 MPa, the transparent binder solution is fully infiltrated into the transparent similar material to reach saturation, thereby obtaining a saturated transparent similar material.

[0046] During the test, the indoor temperature must be controlled at around 25°C (to prevent temperature changes from causing changes in the refractive index of the transparent similar cementing solution).

[0047] Four saturated transparent similar material samples were prepared according to the above steps. The sample diameter was 61.8 mm and the height was 20 mm. The sample was subjected to a quick shear test using a ZJ strain-controlled direct shear tester. The standard ring knife volume was 60 cm 3 The shear displacement of the direct shear tester was set to 8 mm, the shear rate was set to 0.8 mm / min, and the axial pressures applied in the four tests were respectively 50 kPa, 100 kPa, 200 kPa and 300 kPa. During the test, the indoor temperature was controlled at about 25 ° C (to prevent the temperature change from causing the refractive index change of the transparent similar cementing solution). The cohesion of the saturated transparent similar material (please verify whether it is accurate here) was measured to be 38.778 kPa, and the internal friction angle was 46.277 °, which can be used to simulate soft rock experiments. The compaction degree of the saturated transparent similar material is 92%, the saturation is 100%, and the density is 1.76 g / cm 3 .

[0048] In step (1) of this embodiment, the method of directly stirring and mixing the binding solution with the unsaturated transparent similar material and then compacting is not adopted. On the one hand, the problem of large density difference between quartz sand and fumed silica, which causes segregation of fumed silica after pouring the binding solution, is avoided. On the other hand, step (1) mixes quartz sand and fumed silica by dry method, and then pours the binding solution and compacts with a heavy object, which avoids the density of the binding solution being greater than the density of some particles, resulting in an increase in the gaps between the particles and the expansion of the model volume. The friction resistance and bite force between the particles are also increased through compaction.

[0049] After the air pressure in the sealed model box reaches negative pressure in step (2), the air pressure in the gaps of the unsaturated transparent similar material that has infiltrated the cementing solution is greater than the air pressure in the sealed model box, so that the bubbles in the unsaturated transparent similar material are discharged into the sealed model box, reducing the resistance of the cementing solution to infiltrate the gaps in the unsaturated transparent similar material, and the cementing solution further infiltrates into the gaps in the unsaturated transparent similar material.

[0050] In step (3), when a small amount of transparent cementing solution still remains on the surface of the unsaturated transparent similar material soil, after the exhaust valve of the model device is opened, the unsaturated transparent similar material is under negative pressure, and the pressure above the transparent cementing solution is atmospheric pressure. The atmospheric pressure is used to press the residual transparent cementing solution on the surface of the soil into the soil, so that the transparent cementing solution fully penetrates into the transparent similar material to reach saturation.

[0051] Figure 5 and Figure 6 The direct shear stress-displacement curve and strength fitting straight line diagram of the transparent similar material in the prepared model are respectively obtained, which can simulate the displacement of rock and soil under greater shear stress.

[0052] Comparative Example 1: The layered filling construction method of the transparent similar model in CN113248188A has the following specific steps:

[0053] D1. Add an unsaturated transparent similar material to the cementing solution and stir thoroughly to form a mixture. The weight ratio of fused silica sand: transparent cementing solution: SiO2 powder is 125:25:4. The particle size distribution of the fused silica sand is 0.2-0.5 mm, 0.5-1.0 mm, and 1.0-2.0 mm, with a mass ratio of 2:2:1.

[0054] D2. The mixture prepared in step D1 is compacted layer by layer to a specified thickness and compaction degree to obtain an unsaturated soft rock-like transparent material. This means that the transparent soil blocks are compacted layer by layer, and the surface is scraped after each layer is compacted before the next layer is compacted. The compaction height of each layer should not exceed 3 cm. This can produce a soft rock-like material with a maximum compaction degree of 92%. At this point, the saturation of the mixture is 80%. Since it is not fully saturated, the mixture is light milky white or colorless and translucent, and has a density of 1.39 g / cm 3 .

[0055] D3. The unsaturated soft rock transparent material prepared in step D2 was placed in a vacuum chamber and degassed for 5-6 hours. A cementing solution was then added to the chamber to achieve back pressure saturation, thereby producing a fully saturated soft rock transparent material. This transparent material was subjected to an unconsolidated, undrained triaxial shear test, revealing mechanical parameters corresponding to a confining pressure of 50-200 kPa: cohesion of 38.8 kPa, internal friction angle of 29.5°, compression modulus of 7-20 MPa, and maximum elastic strain of 0.5-1.2%.

Claims

1. A layered filling construction method for a transparent similarity model based on vacuum negative pressure, comprising the following steps: (1) Add unsaturated transparent similar material to the model box, compact it after laying, pour in an appropriate amount of transparent cementing solution, and after most of the transparent cementing solution enters the unsaturated transparent similar material, use a 3D printed mold to cover the mixture; (2) Seal the model box, close the exhaust valve, open the exhaust valve, and extract the air inside the model box until the air pressure reaches -80kPa to -90kPa. Use the negative pressure in the model box to slowly force out the air in the unsaturated transparent similar material; (3) Repeat step (2) until a small amount of transparent binder solution remains on the surface of the unsaturated transparent similar material, close the exhaust valve and the vacuum pump, open the exhaust valve, and use the pressure difference between the inside and outside of the box to press the residual transparent binder solution on the surface of the unsaturated transparent similar material into the unsaturated transparent similar material. When the air pressure display number is 0 MPa, the transparent binder solution can fully penetrate into the unsaturated transparent similar material to reach saturation.

2. The layered filling construction method according to claim 1, characterized in that: In the construction method, the unsaturated transparent similar material is laid multiple times, and operations (1)-(3) are performed after each layer of the unsaturated transparent similar material is laid; a plurality of 3D printing molds are provided accordingly, and the outline of each 3D printing mold is a rectangular parallelepiped with one end beveled, and the width and height of each 3D printing mold are the same, but the length is different. All 3D printing molds are stacked from the bottom layer to the top in order of length from small to large, so that the two ends of each layer of 3D printing molds can be aligned with the two ends of the 3D printing mold of the previous layer to form a trapezoidal mold. A cross bar is provided inside each mold for easy extraction, and the height and length of the 3D printing mold are designed according to the set slope shape and the slope layering scheme.

3. The layered filling construction method according to claim 1, characterized in that: The unsaturated transparent similar material includes fused quartz sand with three particle sizes of 0.2-0.5 mm, 0.5-1.0 mm, and 1.0-2.0 mm and nano-scale hydrophobic fumed silica powder, and the mass ratio of the sum of the three particle sizes of fused quartz sand to the nano-scale hydrophobic fumed silica powder is 125:4; The weight ratio of the three particle sizes of fused quartz sand is 2:2:

1. The dry density of the fused quartz sand with a particle size of 0.2-0.5 mm is 1.40 g / cm 3 The porosity is 36%, and the dry density of fused quartz sand with a particle size of 0.5 to 1.0 mm is 1.25 g / cm 3 The porosity is 43%, and the dry density of fused quartz sand with a particle size of 1.0 to 2.0 mm is 1.10 g / cm 3 , porosity is 50%; The particle size of nano-scale hydrophobic fumed silica powder is ≤15nm, and the density in its natural state is 70g / L.

4. The layered filling construction method according to claim 1, characterized in that: The transparent binder solution is a mixture of n-dodecane and 15# white oil in a mass ratio of 1:

4.

5. The layered filling construction method according to claim 1, characterized in that: The model box includes a semi-open box body and a cover plate formed by splicing a U-shaped acrylic plate and two rectangular acrylic plates. A U-shaped metal plate is fixed to the bottom of the box body for fixing the model box on the loading platform. A vacuum gauge and several exhaust valves integrally provided with the vacuum gauge are provided above the cover plate, and a rubber sealing ring is arranged below the cover plate. A vacuum device is also provided, which is connected to a vacuum gauge above the cover plate through an air suction pipe, and an air extraction valve is provided on the air suction pipe.

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