Method for preparing columnar jointed rock samples with different connectivity rates

Abstract

The invention discloses a method for preparing columnar jointed rocks with different connectivity rates. After a cylindrical sample formed by columnar joints is prepared by adopting a mold, in order to obtain rock samples with different connectivity rates, the adhesion areas of the upper and lower inclined surfaces and the left and right vertical end surfaces of the columnar joints in the cylindrical rock samples are firstly solved at the set connectivity rate k of the rock samples, and the adhesion areas of the columnar joints in the cylindrical rock samples are calculated according to the obtained areas under each connectivity rate. Therefore, the adhesion length L1 is further solved to guide the adhesion of each independent columnar joint into the cylindrical rock sample with the required connectivity rate. The mold structurally comprises a cylindrical shell composed of two symmetrical semicircular cylinders, an upper cover plate, a lower cover plate and an internal columnar joint mold, wherein the upper cover plate and the lower cover plate are matched with openings in the top and the bottom of the cylindrical shell. The device meets the requirement for preparing columnar jointed rocks in laboratories, and is suitable for the requirement for preparing rocks with different connectivity rates in various laboratories.

Description

Technical Field

[0001] The present invention relates to the field of rock preparation in the geotechnical direction, and particularly to a method for preparing columnar jointed rocks with different connectivity rates. Background Art

[0002] Columnar jointed rock masses are widely distributed in China, especially in the southwestern regions of Yunnan, Guizhou, and Sichuan. In the southwestern region of China, there is abundant water resources, and it is located at the junction of the first and second steps of China, with a large drop, rich water energy resources, and is suitable for the construction of large-scale water conservancy project facilities. However, the complex geological structure in the southwestern region restricts the construction of projects. The Baihetan Hydropower Station located downstream of the Jinsha River is the second largest hydropower station in China. Its diversion tunnel is built in the columnar jointed rock mass zone, and its safety and stability are seriously threatened. With the advancement of water conservancy and hydropower development in the southwestern region, a large number of columnar jointed rock masses have been exposed in the project. Their mechanical properties and permeability have important impacts on project safety and stability. Therefore, it has important engineering application value to study the water-hydro-mechanical anisotropic characteristics, macroscopic equivalent elastic modulus size effect, etc. of columnar jointed rock masses.

[0003] In order to study columnar jointed rock masses and ensure the smooth progress of projects, researchers often carry out on-site tests around the rock masses. However, limited by the huge project volume and the application of equipment, researchers have started to carry out laboratory experiments and make specimens in the laboratory.

[0004] In recent years, the research progress of columnar jointed rock masses includes in-depth discussions on their mechanical behavior, permeability model, anisotropic characteristics, etc. During the excavation process of columnar rocks, there are a large number of irregular vertical joints and horizontal joints developed in the rock mass. There is also the phenomenon that due to the unloading (removing the load) effect, the joint surfaces of columnar rock masses gradually open, and rock mass shedding and instability will occur. The existing methods usually only consider the effect of dip angle, without considering that with the excavation, different connectivity rates will be formed due to the opening of columnar jointed rocks. In order to better study the opening degree of columnar jointed rock masses, it is necessary to propose a method for preparing columnar jointed rock masses with different penetration degrees indoors. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing columnar jointed rocks with different connectivity rates in view of the deficiencies of the prior art, so as to obtain columnar jointed rock masses with different penetration degrees.

[0006] The method for preparing columnar jointed rocks with different connectivity rates provided by the present invention includes the following contents:

[0007] (1) Sample preparation

[0008] Sample preparation is carried out using a mold. The structure of the mold includes a cylindrical outer shell composed of two symmetric semi-cylindrical tubes, upper and lower cover plates that match the openings at the top and bottom of the cylindrical outer shell, and an internal columnar joint mold. The columnar joint mold is composed of vertical partitions and inclined partitions. The vertical partitions are parallel to each other. The inclined partitions form a certain angle with the horizontal plane and are perpendicular to the vertical partitions. The inclined partitions penetrate the entire vertical partitions at equal intervals and are parallel to each other, and are integrated with the vertical partitions. The overall external contour of the columnar joint mold is a cylinder that matches the inner diameter of the cylindrical outer shell. The two side edges of the vertical partitions are clamped in the matching card slots provided on the inner wall surface of the cylindrical outer shell, and the entire columnar joint is installed inside the cylindrical outer shell. The upper and lower cover plates are connected to the cylindrical outer shell by being clamped in the matching card slots provided inside the cylindrical outer shell, covering the upper and lower end faces of the columnar joint mold.

[0009] First, assemble and connect one semi-cylindrical tube of the outer shell and the internal columnar joint, then install the upper and lower cover plates. Then, pour the sample preparation slurry into the mold. After pouring, assemble the other semi-cylindrical tube of the outer shell. Cure at room temperature. After curing, remove the outer shell and continue curing. After curing, demold the columnar joint rock sample to obtain multiple independent columnar joints. Number each columnar joint and place it in a curing box for curing. The obtained rock sample is a cylindrical sample with prismatic joints with a quadrilateral cross-section inside.

[0010] (2) Calculate the adhesion area and adhesion length of the upper and lower surfaces of the columnar joints at the set connectivity rate

[0011] The cylindrical rock sample prepared according to step (1) has columnar joints inside. To obtain rock samples with different connectivity rates, at the set connectivity rate k of the rock sample, by calculating the adhesion area of the upper and lower inclined surfaces and the left and right vertical end surfaces of the columnar joints inside the cylindrical rock sample (only need to calculate the adhesion area of two complete columns of columnar joints inside, without calculating the adhesion area of the joints on the cylindrical surface of the cylinder), and then calculating the adhesion length L1, to guide the bonding of each independent columnar joint into a cylindrical rock sample with the required connectivity rate.

[0012] The connectivity rate refers to the ratio of the total area of the structural planes in a cross-section in a certain direction within the studied rock mass range to the entire cross-sectional area.

[0013] The adhesion area refers to the contact area between two columnar joints, that is, the non-connected area.

[0014] The adhesion length refers to the maximum vertical distance between the boundary line of connectivity and non-penetration and the cylindrical surface of the cylindrical sample within the adhesion area.

[0015] The calculation process of the adhesion length L1 of the upper and lower inclined surfaces and the left and right vertical end surfaces of the columnar joints is as follows:

[0016] Set the connectivity rate of the inclined plane of the rock specimen as k. Take an inclined cross-section inside the cylindrical rock specimen along the extension direction of the columnar joints (i.e., the cross-section formed by the inclined partition in the mold in the rock specimen), and the inclination angle of this inclined plane (the angle with the horizontal plane) is θ. When a plane makes a certain angle with the horizontal plane, there is a relationship between the projection of the plane and the actual area of the plane. The projections of the inclined plane and the corresponding columnar joints on the horizontal plane are as shown in Figure 2 , and for the projection of the surface of each corresponding columnar joint on the horizontal plane, the following relationship is satisfied with the area of the columnar joint surface,

[0017]

[0018] A is the area of the inclined surface of a single columnar joint

[0019] A0 is the horizontal projected area of a single columnar joint-like rock

[0020] θ is the angle between the inclined surface of the columnar joint and the horizontal plane (the dip angle of the columnar joint-like rock)

[0021] Among them, A0 is the projected area of the upper and lower surfaces of a single columnar joint-like rock on the horizontal plane.

[0022] Let the adhesion length of a single columnar joint be L1, and L be the projected length on the horizontal plane of the adhesion length of the upper and lower surfaces of the columnar joints on the inclined cross-section. The relationship between L1 and L satisfies the following formula,

[0023]

[0024] Establish the coordinates of the projected circle of the inclined cross-section on the plane. The coordinate origin is the intersection point of two tangents that are tangent to the circle and perpendicular to each other. The shaded area is the projection of the upper and lower surfaces of a certain columnar joint. Calculate the area A0 of this projected surface by using integration, and obtain

[0025]

[0026] Deform formula (3) to get,

[0027]

[0028] Combining formulas (4) and (5) gives:

[0029]

[0030] In the formula:

[0031] K is the connectivity rate of the designed rock test;

[0032] a and b are the vertical coordinates of the projections of the columnar joints in the Y-axis direction respectively. The distance between a and b is the width d of the upper and lower parts of the columnar joint, that is, b - a = d, as Figure 4 ;

[0033] R is the radius of the horizontal projection circle of the inclined section;

[0034] L is the projected length on the horizontal plane of the adhesion length of the upper and lower surfaces of the columnar joints on the inclined section.

[0035] L1 is the actual adhesion length

[0036] The actual adhesion length L1 of each columnar joint is obtained through formula (6), and the adhesion area of the upper and lower surfaces is controlled by the adhesion length L1.

[0037] (3) Calculate the adhesion area and adhesion length of the front and rear sides of the columnar joints under the set connectivity rate

[0038] When the connectivity rate is k, since the side shapes of the columnar joints in the inclined section under different inclination angles are all regular figures (such as triangles, parallelograms, trapezoids), the area of each side can be obtained only by following the basic area calculation method, and further converted into the adhesion length L1 through the following formula (7).

[0039] L1 = D × (1 - k) (7)

[0040] D is the diameter of the cylindrical specimen, in mm;

[0041] k is the connectivity rate;

[0042] (4) After calculating the adhesion lengths of the upper and lower inclined surfaces and the front and rear vertical sides of the columnar joints, bond each columnar joint into a cylindrical specimen according to the number and the corresponding position in the mold, and complete the production of the rock test under the connectivity rate of this setting, so as to realize the rock tests with different connectivity rates.

[0043] In the above method, further, the sample-making slurry in step (1) is cement mortar, where cement: sand: water = 0.55: 0.55: 1, and the cement is preferably P.C42.5 cement.

[0044] In the above method, further, in step (3), the columnar joint specimens are bonded with white cement slurry, and the water-cement ratio of the white cement slurry is 0.45.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The sample-making mold of the present invention can better construct the internal columnar joints, which can not only obtain single individuals required for the columnar joints, but also facilitate the subsequent setting of the connectivity rate.

[0047] 2. In existing scientific research, no method has been proposed for preparing columnar rock masses with different connectivity rates and inclinations indoors. The present invention meets the requirements for preparing columnar jointed rocks in the laboratory and is applicable to the needs of preparing various types of rocks with different connectivity rates in the laboratory.

[0048] 3. In the method of the present invention, since the areas obtained at each connectivity rate are not convenient to apply to actual operations, the adhesion length L1 is used to control the bonding area, so that the connectivity rate can be easily controlled, the sample preparation efficiency is high, the integrity of the rock-like specimens is high, and the condition requirements are low, meeting the experimental standards and making standard specimens. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic structural view of the mold of the present invention, where a is the internal columnar joint mold and b is the outer shell;

[0050] Figure 2 It is a schematic view of the inclined plane and horizontal projection plane of the columnar joint;

[0051] Figure 3 It is a schematic view of the projected area of the inclined plane of a single columnar jointed rock specimen;

[0052] Figure 4 It is a schematic view of the adhesion length of the present invention.

[0053] Figure 5 It is a schematic view of the adhesion length of Example 1.

[0054] Figure 6 It is the adhesion length of the front and rear vertical sides of Example 1 (D is the diameter of the cylindrical specimen): DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention will be further described below through examples. It should be noted that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art make some non-essential improvements and adjustments to the present invention based on the above-mentioned invention content and carry out specific implementations, which still fall within the protection scope of the invention.

[0057] Example 1

[0058] (1) Sample preparation is carried out using a mold. The structure of the mold includes a cylindrical outer shell composed of two symmetric semi-cylindrical tubes, upper and lower cover plates that match the openings at the top and bottom of the cylindrical outer shell, and an internal columnar joint mold. The columnar joint mold is composed of vertical partitions and inclined partitions. The vertical partitions are parallel to each other. The inclined partitions are inclined at a certain angle to the horizontal plane and perpendicular to the vertical partitions. The inclined partitions penetrate the entire vertical partitions at equal intervals and are parallel to each other, and are integrated with the vertical partitions. The overall outer contour of the columnar joint mold is a cylinder that matches the inner diameter of the cylindrical outer shell. The two side edges of the vertical partitions are clamped in the matching slots provided on the inner wall surface of the cylindrical outer shell, and the entire columnar joint is installed inside the cylindrical outer shell. The upper and lower cover plates are connected to the cylindrical outer shell by being clamped in the matching slots provided inside the cylindrical outer shell, covering the upper and lower end faces of the columnar joint mold. The inclination angle of the inclined plate is 60°.

[0059] The sample prepared in this embodiment is a cylindrical rock sample with a height of 100 mm and a diameter of 50 mm, and the size of the mold is made accordingly.

[0060] First, evenly apply Vaseline to all the inner surfaces of the mold. After the application is completed, install and connect the outer shell and the internal joint mold along the pre-reserved slots, and then install the upper and lower cover plates.

[0061] (2) Prepare the sample-making material, cement mortar. Weigh the cement, sand, and water according to the mass ratio of cement:sand:water = 0.55:0.55:1, put them into the mixing container, and place the mixing container into the mixer for stirring. After stirring evenly, pour the obtained cement mortar along the direction of the inclined partition with an inclination angle. After pouring is completed, vibrate to discharge the internal air bubbles, then use a soil-scraping knife to scrape and level the outer surface of the cylindrical sample, and finally cover the other half of the outer shell to ensure good sealing.

[0062] (3) Place the poured cylindrical mold vertically. After curing at room temperature for two hours, remove the two outer shells to expose the internal columnar-like rock, and continue to cure for four hours.

[0063] (4) After curing for four hours, push out the columnar rock sample along the direction of the joint inclination angle, number it, place it on a tray and then put it into the curing box for curing. According to the requirements of the experimental plan, the curing time can be set to 7 days and 28 days.

[0064] (5) According to the inclination angle, first calculate the adhesion area of each face of a single columnar joint-like rock according to formulas (1) - (4), and then convert it into the adhesion length to calculate the adhesion lengths of each face at different connectivity rates. Make a columnar joint-like rock sample with a width of 15 mm and a connectivity rate of 0.4. The height H of the sample is 100 mm, the diameter D is 50 mm, and the inclination angle is 60°. Establish the projection line of the inclined section as Figure 5The coordinates shown

[0065] The adhesion length of the upper and lower surfaces of the columnar joints:

[0066]

[0067] The adhesion length of the front and rear vertical side surfaces of the columnar joints:

[0068] L1 = 50*(1 - k) = 30 mm

[0069] (6) On the third day of curing, take out the individual columnar specimens and bond them with white cement slurry with a mix ratio of 0.45. During the bonding process, control the connectivity rate by the bonding area and bond according to the bonding length obtained in step 5 above.

[0070] (7) Take out the specimens from the curing box, measure the bonding length L on the individual columnar specimens, and mark them with a white marker pen. Then apply the prepared white cement slurry (water-cement ratio of 0.45) to the marked areas, and try to ensure that the bonding thickness is within 1 mm to reduce the influence on the error. After applying one surface, bond it with another surface, and ensure that the corresponding surfaces fit during the bonding process.

[0071] (8) Continuously repeat the above seventh step to bond all the individual columnar specimens in the whole specimen into a whole. After the white cement slurry starts to set (30 minutes), place the specimens vertically and continue to cure them in the curing box.

[0072] (9) When the curing time required by the test plan is reached, it can be taken out for a series of physical experiments.

Claims

1. A method for preparing columnar jointed rocks with different connectivity rates, characterized in that, The following contents are included: (1) Specimen preparation Specimens are prepared using a mold. The structure of the mold includes a cylindrical outer shell composed of two symmetric semi-cylindrical tubes, upper and lower cover plates that match the openings at the top and bottom of the cylindrical outer shell, and an internal columnar joint mold. The columnar joint mold is composed of vertical partitions and inclined partitions. The vertical partitions are parallel to each other. The inclined partitions form a certain angle with the horizontal plane and are perpendicular to the vertical partitions. The inclined partitions penetrate through the entire vertical partitions at equal intervals and are parallel to each other, being integrated with the vertical partitions. The overall external contour of the columnar joint mold is a cylinder that matches the inner diameter of the cylindrical outer shell. The two side edges of the vertical partitions are clamped in the matching slots provided on the inner wall surface of the cylindrical outer shell, installing the entire columnar joint inside the cylindrical outer shell. The upper and lower cover plates are connected to the cylindrical outer shell by being clamped in the matching slots provided inside the cylindrical outer shell, covering the upper and lower end faces of the columnar joint mold. First, assemble and connect one semi-cylindrical tube of the outer shell and the internal columnar joint, then install the upper and lower cover plates. Then, pour the specimen preparation slurry into the mold. After pouring is completed, assemble the other semi-cylindrical tube of the outer shell. Cure at room temperature. After curing is completed, remove the outer shell and continue curing. After curing is completed, demold the columnar joint rock specimen to obtain multiple independent columnar joints. Number each columnar joint and place it in a curing box for curing. (2) Calculate the adhesion area and adhesion length of the upper and lower surfaces of the columnar joints at a set connectivity rate The obtained is a cylindrical rock specimen with internal columnar joints according to step (1). To obtain rock specimens with different connectivity rates, at the set connectivity rate k of the rock specimen, by finding the adhesion area of the upper and lower inclined surfaces and the left and right vertical end surfaces of the columnar joints inside the cylindrical rock specimen, and then finding the adhesion length L1, to guide the bonding of each independent columnar joint into a cylindrical rock specimen with the required connectivity rate. The connectivity rate refers to the ratio of the total area of the structural planes in a cross-section in a certain direction within the studied rock mass range to the area of the entire cross-section. The adhesion area refers to the contact area between two columnar joints, that is, the non-connected area. The adhesion length refers to the maximum perpendicular distance between the boundary line of connectivity and non-penetration and the cylindrical surface of the cylindrical specimen within the adhesion area. The calculation process of the adhesion length L1 of the upper and lower inclined surfaces and the left and right vertical end surfaces of the columnar joints is as follows: Set the connectivity rate of the inclined surface of the rock specimen as k. Take an inclined cross-section inside the cylindrical rock specimen along the extension direction of the columnar joint. The inclination angle of this inclined surface is θ. Then, the projection of the surface of each columnar joint on the horizontal plane and the area of this columnar joint surface satisfy the following relationship. A is the area of the inclined surface of a single columnar joint A0 is the horizontal projection area of a single columnar joint-like rock θ is the angle between the inclined surface of the columnar joint and the horizontal plane Among them, A0 is the projection area of the upper and lower surfaces of a single columnar joint-like rock on the horizontal plane Let the adhesion length of a single columnar joint be L1, and L be the projection length of the adhesion length of the upper and lower surfaces of the columnar joints on the inclined cross-section on the horizontal plane. The relationship between L1 and L satisfies the following formula. Establish the coordinates of the projection circle of the inclined section on the plane. The coordinate origin is the intersection of two tangents that are tangent to the circle and perpendicular to each other. The area of the shaded part is the projection of the upper and lower parts of a certain columnar joint. Calculate the area A0 of this projection surface by using integration, and obtain By transforming formula (3), we get Combining formulas (4) and (5), we have In the formula: K is the connectivity rate of the designed rock test; a and b are the vertical coordinates of the projection of the columnar joint in the Y-axis direction respectively. The distance between a and b is the width d of the upper and lower parts of the columnar joint, that is, b - a = d, as shown in Figure 4; R is the radius of the horizontal projection circle of the inclined section; L is the projection length of the adhesion length of the upper and lower surfaces of the columnar joint on the inclined section on the horizontal plane; L1 is the actual adhesion length; Calculate the actual adhesion length L1 of each columnar joint through formula (6), and control the adhesion area of the upper and lower surfaces through the adhesion length L1; (3) Calculate the adhesion area and adhesion length of the front and rear sides of the columnar joint under the set connectivity rate When the connectivity rate is k, it is further transformed into the adhesion length L1 through the following formula (7) L1 = D×(1 - k) (7) D is the diameter of the cylindrical specimen, with the unit of mm; k is the connectivity rate; (4) After calculating the adhesion lengths of the upper and lower inclined surfaces and the front and rear vertical sides of the columnar joint, bond each columnar joint into a cylindrical specimen according to the number and the corresponding position in the mold, and complete the production of the rock test under the connectivity rate of this setting, so as to realize the rock tests with different connectivity rates.

2. The method according to claim 1, wherein The sample-making slurry described in step (1) is cement mortar, where cement: sand: water = 0.55: 0.55: 1, and the cement is preferably P.C42.5 cement.

3. The method according to claim 1, wherein In step (3), the columnar joint specimens are bonded with white cement slurry, and the water-cement ratio of the white cement slurry is 0.45:1.

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