A method for preparing jointed rock samples based on 3D scanning and 3D printing

Abstract

The present invention proposes a method for preparing jointed rock samples based on three-dimensional scanning and 3D printing. The present invention uses a handheld three-dimensional scanner to perform multi-section scanning on the jointed rock sampled on site, obtains the spatial relative position of the cross-section joint fissures, reconstructs and partitions the three-dimensional model, and simulates and produces jointed rock samples based on the partitioning situation and the gaps between printed materials of different particle sizes based on the similarity ratio criterion to characterize the joint fissure situation, and then simulates the weakening effect of the filling in the joint fissures on the jointed rock under different confining pressure conditions through a weak filling migration simulation device. Through this method, samples of jointed rock containing fillings under different confining pressure conditions are simulated and produced, which provides a new idea for the study of the mechanical properties of rocks and a new method for artificially restoring the internal structure of jointed rock masses.

Description

Technical Field

[0001] The invention belongs to the field of rock mechanics, and in particular relates to a method for preparing a jointed rock mass sample based on three-dimensional scanning and 3D printing. Background Art

[0002] Due to geological tectonic action, natural rock mass shows obvious heterogeneity and anisotropy in mechanical properties, and a large number of structural planes with significant differences from the surrounding rock mass are generated in the rock mass. The structural planes with no obvious displacement of the rock mass on both sides are called joints. The rock walls on both sides of some joints can fit tightly, while some have certain gaps. Under the influence of groundwater migration under different confining pressure conditions, these gaps are filled with more or less soft rock and soil materials. Most joint fissure rock masses are filled with loess. Under the influence of these weak fillings, the mechanical properties of the jointed rock mass will be significantly weakened. When subjected to engineering disturbance, the rock mass will first shear and slip along the filling joints, and then the destruction will continue to grow and evolve until the entire rock mass becomes unstable. At present, the instability and destruction of many engineering rock masses are caused by the inadequate understanding of the mechanical properties of joints containing weak fillings. Therefore, the study of the mechanical properties of rock masses with different weak fillings in joints under different confining pressures is of great significance to underground engineering.

[0003] So far, many experts and scholars have proposed many methods for making specimens of jointed rock masses in order to study the mechanical properties of jointed rock masses.

[0004] For example, the Chinese invention patents with announcement numbers CN105651570B and CN105651572B disclose a method for preparing a columnar jointed rock mass sample containing unfilled hidden joints and a method for preparing a columnar jointed rock mass sample containing filled hidden joints, providing a method for preparing hidden joints and simulating components using water-soluble materials, and on this basis, solving the problem of preparing joint samples containing different types of fillers. However, there are the following deficiencies in the production process: (1) The similarity ratio between the joint fissures of similar simulated samples and the actual joint fissures is not considered; (2) When the joints of the 3D-printed water-soluble material are dissolved in water, the effect of water on the strength of the sample is ignored; (3) The sample needs to be prepared using materials such as molds and cement mortar, which is a complicated process.

[0005] The Chinese invention patent with announcement number CN109001237B discloses a method for producing the internal structure of a rock mass based on CT scanning and 3D printing. It provides a method for partitioning multiple two-dimensional tomography images through CT scanning of rock mass samples, reconstructing three-dimensional structural models of the partitioned images, and 3D printing and spraying three different partitions with different particle size mineral sands. However, the similarity ratio between the joints and fissures of similar simulated samples and the actual joints and fissures was not considered in the production process, and the joints and fissures formed by the space gaps between adjacent mineral sands were ignored.

[0006] The Chinese invention patent with announcement number CN106908289B discloses a method for preparing a columnar jointed rock mass sample with filled pores on the column surface, and provides a method for constructing a three-dimensional model of a columnar jointed rock mass using Revit software and based on the similarity ratio criterion; and a method for 3D printing using basalt powder and secondary yellow mud as double nozzle materials. However, there are the following deficiencies in the production process: (1) When determining the cross-sectional geometry, rock formation occurrence, joint width, and columnar morphological characteristics of a single column of basalt columnar jointed rock mass, an in-situ geological survey method is used; (2) The amount of filling in the columnar pores is not considered.

[0007] Through the above analysis, the existing methods of making jointed rock samples with fillings all have more or less defects. How to quickly and efficiently make samples that can reflect the real jointed rock with fillings under different confining pressure conditions has become an urgent problem to be solved in the research of jointed rock. Summary of the invention

[0008] In order to solve this problem, the present invention proposes a method for preparing jointed rock samples based on three-dimensional scanning and 3D printing. The present invention uses a handheld three-dimensional scanner to perform multi-section scanning on the jointed rock sampled on site, obtains the spatial relative position of the cross-section joints and fissures, reconstructs and partitions the three-dimensional model, and simulates and produces jointed rock samples based on the partition situation based on the similarity ratio criterion by characterizing the joints and fissures with the gaps between printed materials of different particle sizes, and then simulates the weakening effect of the fillings in the joints and fissures on the jointed rock under different confining pressure conditions through a weak filling migration simulation device. Through this method, samples of jointed rock containing fillings under different confining pressure conditions are simulated and produced, which provides a new idea for the study of the mechanical properties of rocks and a new method for artificially restoring the internal structure of jointed rock masses.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions to solve it.

[0010] A method for preparing a jointed rock sample based on three-dimensional scanning and 3D printing comprises the following steps:

[0011] Step 1: Use a handheld 3D scanner to perform multi-section scanning on the jointed rock mass sampled on site to obtain the width and relative position of the cross-section joint fissures. According to the cross-section scanning results of the handheld 3D scanner, the rock mass is divided into joint fissure development zone, transition zone and non-destructive zone, and the 3D model is reconstructed based on the multi-section zoning results.

[0012] Step 2: According to the joint fissure width and similarity ratio criteria, the gap between printing materials with different particle sizes is used to characterize the joint fissure width, the particle size of sandstone printing materials used in different partitions is determined, the relevant materials required for sample 3D printing are prepared, and joint rock sample printing is carried out.

[0013] Step 3: Prepare a certain concentration of yellow mud slurry to simulate the weak filling material that migrates with groundwater into the joint structure of the rock mass. Place the printed jointed rock mass sample into the weak filling material migration simulation device, and then pour in the prepared yellow mud slurry to simulate the situation where the joint cracks are filled with weak rock and soil materials under the influence of groundwater migration under different confining pressures, so that the joint structure in the jointed rock mass sample is fully filled.

[0014] Step 4: After the filling is completed, take out the jointed rock sample, remove the excess yellow mud on the surface, and put it into a drying oven for drying.

[0015] Furthermore, in step 2, the joint and fissure development zone uses a large-size sandstone printing material determined according to the joint and fissure width and the similarity ratio criterion, the non-destructive zone uses a determined small-size sandstone printing material, and the transition zone uses a mixed printing material of large-size and small-size sandstone.

[0016] Furthermore, in step 3, the soft filling material migration simulation device is composed of an air pump, a pressurized cylinder, a pressurized cylinder sealing cover, and a pressure gauge, wherein the air pump provides pressure for simulating confining pressures at different depths, the pressurized cylinder and the pressurized cylinder sealing cover are used to maintain the confining pressure environment, and at the same time provide a place for the yellow mud to be transported by water to the joints of the sample, and the pressure gauge is used to display the real-time air pressure in the cylinder to reflect the simulated confining pressure value.

[0017] Furthermore, in step 4, the temperature of the drying oven is 60 degrees Celsius and the drying time is 10 hours.

[0018] Compared with the prior art, the beneficial effects of the present invention are: providing a method for quickly and efficiently preparing samples of rock mass with joints containing fillings under different confining pressure conditions. Rock-like samples are made using advanced handheld 3D scanners and 3D printers, and the gaps between printed materials with different particle sizes are creatively proposed to characterize the joint fracture conditions based on the joint crack width and similarity ratio criteria obtained by different handheld 3D scanners. At the same time, the influence of hydraulic transport on the fillings in the joints under different burial depths and confining pressures is taken into account, which has the advantages of being close to the actual site and being simple and efficient to make. It provides a new method for studying the mechanical properties of rock masses with different weak fillings in the joints under different confining pressures. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 The present invention is a flowchart of the steps of a method for preparing a jointed rock sample based on three-dimensional scanning and 3D printing.

[0021] Figure 2 Schematic diagram of the soft filling migration simulation device. DETAILED DESCRIPTION

[0022] The embodiments of the present invention will be described in detail below with reference to the examples. Figure 1 and Figure 2 The present invention provides a method for preparing a jointed rock sample based on three-dimensional scanning and 3D printing, comprising the following steps:

[0023] Step 1: Use a handheld 3D scanner to perform multi-section scanning on the jointed rock mass sampled on site to obtain the width and relative position of the cross-section joint fissures. According to the cross-section scanning results of the handheld 3D scanner, the rock mass is divided into joint fissure development zone, transition zone and non-destructive zone, and the 3D model is reconstructed based on the multi-section zoning results.

[0024] Step 2: According to the joint crack width and similarity ratio criteria, the gap between printing materials of different particle sizes is used to characterize the joint crack width, and the particle size of the sandstone printing material used in different partitions is determined. The joint crack development zone uses large-size sandstone printing materials determined according to the joint crack width and similarity ratio criteria, the non-destructive zone uses small-size sandstone printing materials, and the transition zone uses large-size and small-size sandstone mixed printing materials. Prepare the relevant materials required for sample 3D printing, use the "vertical molding" process, the printing layer thickness is 0.2 mm, the printing accuracy is 0.2 mm, and the jointed rock mass sample is printed. The sample preparation process mainly generates a processing code file from the three-dimensional reconstructed model, and imports the instruction code file into the printer through a computer. The print head prints layer by layer from bottom to top according to the computer instructions, and finally obtains the printed sample.

[0025] Step 3: Prepare a certain concentration of yellow mud slurry to simulate the weak fillings that migrate with groundwater into the joint structure of the rock mass. Place the printed jointed rock mass sample into a weak filling migration simulation device consisting of an air pump, a pressurized cylinder, a pressurized cylinder sealing cover, and a pressure gauge, then pour the prepared yellow mud slurry into the pressurized cylinder to submerge the top of the printed jointed rock mass sample, cover the pressurized cylinder sealing cover, use the air pump to pressurize the pressurized container, and read the air pressure value in the pressurized container through the pressure gauge to simulate the confining pressure at different burial depths. Simulate the situation where the joints and fissures are filled with weak rock and soil materials under the influence of groundwater migration under different confining pressures, so that the joint structure in the jointed rock mass sample is fully filled.

[0026] Step 4: After filling is completed, take out the jointed rock sample, remove the excess yellow mud on the surface, and put it into a drying oven for drying. The temperature in the drying oven is 60 degrees Celsius and the drying time is 10 hours.

Claims

1. A method for preparing jointed rock samples based on three-dimensional scanning and 3D printing technology, characterized in that: The following steps are involved: Step 1: Use a handheld 3D scanner to perform multi-section scanning on the jointed rock mass sampled on site to obtain the width and relative position of the cross-section joint fissures. According to the cross-section scanning results of the handheld 3D scanner, the rock mass is divided into a joint fissure development zone, a transition zone, and a non-destructive zone. A 3D printing model is then built based on the multi-section zoning results. Step 2: According to the joint crack width and similarity ratio criteria, the gap between printing materials of different particle sizes is used to characterize the joint crack width, the particle size of sandstone printing materials used in different partitions is determined, and the relevant materials required for sample 3D printing are prepared to print the jointed rock mass sample; the joint crack development zone uses the large-size sandstone printing material determined according to the joint crack width and similarity ratio criteria, the non-destructive zone uses the determined small-size sandstone printing material, and the transition zone uses the large-size and small-size sandstone mixed printing material; Step 3: Prepare yellow mud slurry of a certain concentration to simulate the weak filling material that migrates to the joint structure of the rock mass with groundwater, put the printed jointed rock mass sample into the weak filling material migration simulation device, and then pour the prepared yellow mud slurry into it to simulate the situation that the joint fissures are filled with weak rock and soil materials under the influence of groundwater migration under different confining pressures, so that the joint structure in the jointed rock mass sample is fully filled; the weak filling material migration simulation device consists of an air pump, a pressurized cylinder, a pressurized cylinder sealing cover, and a pressure gauge, wherein the air pump provides pressure for simulating confining pressures at different depths, the pressurized cylinder and the pressurized cylinder sealing cover are used to maintain the confining pressure environment, and at the same time provide a place for the yellow mud slurry to be affected by the migration of water to the joints of the sample, and the pressure gauge is used to display the real-time air pressure in the cylinder to reflect the simulated confining pressure value; Step 4: After the filling is completed, take out the jointed rock sample, remove the excess yellow mud on the surface, and put it into a drying oven for drying. The temperature of the drying oven is 60 degrees Celsius and the drying time is 10 hours.

Images