In-situ test device for mechanical properties of bonding interface of concrete and rock mass

Abstract

The utility model relates to an in-situ test device for mechanical properties of a concrete and rock mass bonding interface. The method is suitable for the technical field of geotechnical engineering. According to the technical scheme, a concrete test block is poured on a rock mass; the test box is arranged around the concrete test block, and the test box is fixed on the rock mass; the shearing force loading mechanism is used for applying shearing force to the concrete test block in the front-back direction; the shear displacement acquisition mechanism is used for acquiring the shear displacement of the concrete test block; the normal force loading mechanism is used for applying normal force to the concrete test block through the pressing plate mechanism; the pressing plate mechanism comprises an upper pressing plate and a lower pressing plate, the upper pressing plate is connected with the normal force loading mechanism, the upper pressing plate can be movably pressed on the lower pressing plate along the front-back direction through a low-friction mechanism, and the lower pressing plate is adhered to the upper surface of the concrete test block; the normal displacement acquisition mechanism is used for acquiring the normal displacement of the concrete test block; and the data acquisition instrument is connected with the shear displacement acquisition mechanism and the normal displacement acquisition mechanism through data lines.

Description

In-situ test apparatus for mechanical properties of concrete-rock bond interface Technical Field

[0001] This utility model relates to an in-situ testing device for the mechanical properties of the bond interface between concrete and rock mass. It is applicable to the field of geotechnical engineering technology. Background Technology

[0002] Concrete, as a common building material, is widely used in water conservancy and hydropower projects, transportation tunnel projects, mining projects, and other fields. While research on the mechanical properties of concrete itself is quite mature, research on the mechanical properties of the interface between concrete and rock or soil is relatively limited, and a unified understanding has not yet been reached.

[0003] The mechanical properties of the concrete-rock interface are crucial indicators for evaluating the performance of concrete structures working together with rock masses. They are significant for the design of underground concrete lining structures, stability calculations of concrete dam foundations, and the evaluation of the anti-sliding performance of retaining walls and other support structures. Particularly in numerical simulations, the strength characteristics (shear strength, tensile strength) and deformation characteristics (normal stiffness, shear stiffness) of the concrete-rock interface are critical input parameters, significantly impacting the rationality and reliability of the calculation results. However, current methods often rely on empirical engineering approaches, resulting in poor accuracy. Overestimating the interface strength and deformation resistance may introduce risks to the project, while underestimating it could reduce its economic viability.

[0004] Currently, research on the mechanical properties of the concrete-rock bond interface, both domestically and internationally, mainly employs laboratory testing methods, while in-situ testing is relatively limited. However, laboratory testing differs significantly from field testing in terms of scale and working environment. Appendix M of the "Technical Specification for Rock and Soil Anchors and Shotcrete Support Engineering" GB 50086-2015 provides an in-situ test method for shotcrete bond strength. In the field, pull-out tests on core-isolated concrete specimens can yield the tensile strength of the bond interface, but this method cannot obtain parameters such as the shear strength and deformation characteristics of the bond interface.

[0005] Chinese patent CN 112098236 B, entitled "An In-situ Testing Device and Method for Shear Strength of Concrete-Rock-Shotcrete Interface," proposes a simple in-situ shear strength testing device that can apply normal pressure and tangential shear force to the concrete-rock-shotcrete interface under horizontal or vertical conditions. However, this method has the following shortcomings: 1. It cannot obtain the tensile strength and deformation characteristics of the bonding interface; 2. It is not suitable for the state of inclined bonding interface (such as the foundation of concrete dams); 3. It cannot eliminate the influence of the self-weight of the testing device on the test results during the test, especially when the shear strength of the bonding interface is low, the test results may have large errors; 4. It does not consider the influence of the friction between the metal pressure plate and the concrete on the test results.

[0006] In designing underground cavern linings and analyzing the anti-sliding stability of dam foundations, researchers have found that existing engineering designs rarely accurately consider the mechanical properties of the concrete-rock interface, especially in numerical simulations. Currently, either the concrete and rock are considered as common nodes without relative deformation, or inaccurate empirical values ​​are assigned based on relevant specifications. This is mainly due to poor conditions, complex equipment, high costs, and limited applicability for in-situ testing, making it difficult to obtain the mechanical properties of the concrete-rock interface on-site. Therefore, a simple, economical, and effective in-situ testing device for the mechanical properties of the concrete-rock interface is urgently needed. Summary of the Invention

[0007] The technical problem to be solved by this utility model is: to provide an in-situ test device for the mechanical properties of the bond interface between concrete and rock mass, in view of the above-mentioned problems.

[0008] The technical solution adopted in this utility model is: an in-situ test device for the mechanical properties of the bond interface between concrete and rock mass, comprising:

[0009] Concrete test blocks were poured onto the rock mass.

[0010] A test chamber is arranged around the concrete test block and is fixed to the rock mass;

[0011] A shear loading mechanism, installed on the test chamber, is used to apply a shear force along the front-to-back direction to the concrete specimen.

[0012] A shear displacement acquisition mechanism is used to acquire the shear displacement of the concrete test block;

[0013] A normal force loading mechanism, installed on the test chamber, is used to apply a normal force to the concrete test block via a pressure plate mechanism;

[0014] The pressure plate mechanism includes an upper pressure plate and a lower pressure plate, wherein the upper pressure plate is connected to the normal force loading mechanism, and the upper pressure plate is pressed onto the lower pressure plate in the back-and-forth direction via a low-friction mechanism, and the lower pressure plate is bonded to the upper surface of the concrete test block;

[0015] A normal displacement acquisition mechanism is used to acquire the normal displacement of the concrete test block;

[0016] The data acquisition device is connected to the shear displacement acquisition mechanism and the normal displacement acquisition mechanism via a data cable.

[0017] The shear loading mechanism includes a first hydraulic jack, a shear plate, a shear tie rod, and a shear bearing plate;

[0018] The shear tie rod has its axis parallel to the front-to-back direction and passes through a circular hole in the test box. The front end of the shear tie rod is connected to a shear bearing plate, and a first hydraulic jack is installed between the shear bearing plate and the test box. The rear end of the shear tie rod is connected to a shear plate located behind the concrete test block.

[0019] The shear displacement acquisition mechanism includes a connecting rod and a slider displacement sensor. The axis of the connecting rod is parallel to the front-to-back direction. The front end of the connecting rod is connected to the shear bearing plate, and the rear end of the connecting rod is connected to the slider displacement sensor, which is installed on the test chamber.

[0020] The connecting rod has a ring at its front end, which is fitted onto the round rod, and the round rod is fixedly connected to the shear bearing plate.

[0021] The normal force loading mechanism includes a second hydraulic jack and a normal bearing plate, wherein the normal bearing plate is fixed on the test chamber, and the second hydraulic jack is disposed between the upper pressure plate and the normal bearing plate.

[0022] The normal force loading mechanism includes a second hydraulic jack, a normal bearing plate, and a normal threaded rod. The normal bearing plate is fixed to the test chamber. The normal threaded rod is arranged parallel to the vertical direction and passes through a circular hole in the normal bearing plate. The lower end of the normal threaded rod is connected to the upper pressure plate, and the upper part of the normal threaded rod is connected to a third nut. The third nut is located above the normal bearing plate, and the second hydraulic jack is provided between the third nut and the normal bearing plate.

[0023] The upper surface of the lower pressure plate has a groove, the axis of which is parallel to the front-to-back direction, and guide grooves parallel to the front-to-back direction are formed on the groove walls on both sides; the left and right sides of the upper pressure plate have protrusions that are adapted to the guide grooves.

[0024] The low-friction mechanism includes a plurality of rollers disposed between the upper pressure plate and the lower pressure plate, the rollers being arranged perpendicular to the front-back direction.

[0025] An in-situ test method for the mechanical properties of the concrete-rock bond interface, based on the aforementioned in-situ test apparatus, includes conducting mechanical shear tests on the concrete-rock bond interface, comprising:

[0026] 1) Select the test location;

[0027] 2) Pour concrete test blocks and cure them;

[0028] 3) Fix the test chamber to the surface of the rock mass, ensuring that the concrete specimen is located in the middle of the test chamber;

[0029] 4) Bond the lower pressure plate of the pressure plate mechanism to the upper surface of the concrete specimen using adhesive, and install the normal force loading mechanism on the test chamber;

[0030] 5) Set up a shear loading mechanism for the concrete test block and install the shear loading mechanism on the test chamber;

[0031] 6) Conduct multiple sets of parallel experiments;

[0032] Bond interface shear strength test:

[0033] i. Apply normal pressure, apply a certain pressure P1 to the upper surface of the concrete specimen;

[0034] ii. Pre-applied shear force;

[0035] iii. Installation of monitoring instruments;

[0036] iv. Apply shear force by increasing the load in stages until the bond interface between the concrete and the rock mass fails, and record the shear force T and shear displacement u under each load stage;

[0037] v. Data processing. During the experiment, the normal stress at the bond interface remained constant: σ1 = P1 / A

[0038] The shear stress τ at the bond interface under each load level i Calculate as follows:

[0039] τ i = T / A

[0040] In the formula, A is the bonding interface area;

[0041] Plot a curve with shear displacement u as the abscissa and shear stress τ as the ordinate. The slope of the initial straight segment of the curve is the shear stiffness K of the concrete-rock bond interface. S :

[0042] K S =Δτ / Δu

[0043] The peak shear stress on the shear stress-shear displacement curve is the shear strength τ of the bond interface under the normal stress σ1. f1 ;

[0044] vi. By changing the normal pressure and repeating the experimental steps i~v, multiple sets of experimental results can be obtained, and the normal stress σ corresponding to each set of tests can be obtained. i and shear strength τ fi Plot the shear strength τ fi With normal stress σ i Relationship curve, based on τ f The relationship =c + σ*tanφ is used to obtain the cohesive force c and friction angle φ at the bonding interface.

[0045] An in-situ test method for the mechanical properties of the concrete-rock bond interface, based on the aforementioned in-situ test apparatus, includes conducting a mechanical pull-out test of the concrete-rock bond interface, comprising:

[0046] 1) Select the test location;

[0047] 2) Pour concrete test blocks and cure them;

[0048] 3) Fix the test chamber to the surface of the rock mass, ensuring that the concrete specimen is located in the middle of the test chamber;

[0049] 4) Bond the lower pressure plate of the pressure plate mechanism to the upper surface of the concrete specimen using adhesive, and install the normal force loading mechanism on the test chamber;

[0050] 5) Conduct multiple parallel experiments;

[0051] Bond interface tensile strength test:

[0052] i. Installation of monitoring instruments;

[0053] ii. Pre-applied normal tension;

[0054] iii. Apply normal tensile force by increasing the load in stages until the bond interface between the concrete and the rock mass fails, and record the tensile force F and normal displacement s under each load level;

[0055] iv. Data processing.

[0056] Tensile stress σ at the bond interface under each load level ti Calculate as follows:

[0057] σ ti = F / A

[0058] With normal displacement s as the abscissa and tensile stress σ t Plot a curve with the vertical axis as the ordinate. The slope of the initial straight segment of the curve represents the normal stiffness of the concrete-rock bond interface.

[0059] K n =Δσ t / Δs

[0060] The peak tensile stress on the tensile stress-normal displacement curve is the tensile strength σ of the bond interface. tf ;

[0061] v. Repeat the test steps i to iv to obtain multiple sets of test results, and take the average value of multiple sets of tests as the tensile strength of the bond interface between concrete and rock mass.

[0062] The beneficial effects of this utility model are: by setting a low-friction mechanism (such as a roller) between the upper and lower pressure plates, this utility model reduces the influence of friction on the shear test results; during the shear test, the upper pressure plate can remain stationary, and only the concrete specimen and the lower pressure plate undergo shear displacement, thereby ensuring that the normal pressure remains constant during the test and improving the test accuracy.

[0063] This experimental device is simple in structure, easy to operate, and economical. It can effectively make up for the deficiencies and shortcomings of current in-situ testing methods, facilitate its promotion and large-scale field testing, and provide a basis for the design of concrete structures in underground caverns, dams, slopes and other engineering projects.

[0064] This invention is equipped with a shear test method for the bond interface between concrete and rock mass. By monitoring the shear force and shear displacement during the shear test in real time, the shear strength and shear stiffness of the bond interface can be obtained simultaneously.

[0065] This invention provides a pull-out test method for the bond interface between concrete and rock mass, which can be integrated with the shear test. By monitoring the tensile force and normal displacement during the pull-out test in real time, the tensile strength and normal stiffness of the bond interface can be obtained simultaneously. Attached Figure Description

[0066] Figure 1 is a perspective view of the in-situ test device in the embodiment.

[0067] Figure 2 is a top view of the in-situ test apparatus in the embodiment.

[0068] Figure 3 is a schematic diagram of the in-situ testing device used in the embodiment for conducting shear tests.

[0069] Figure 4 is a schematic diagram of the in-situ testing device used in the pull-out test in the embodiment.

[0070] Figure 5 is a schematic diagram of the test chamber in the embodiment.

[0071] Figure 6 is a schematic diagram of the shear plate in the embodiment.

[0072] Figure 7 is a schematic diagram of the connection of the slider displacement sensor in the embodiment.

[0073] Figure 8 is a schematic diagram of the normal bearing plate in the embodiment.

[0074] Figure 9 is a schematic diagram of the pressure plate mechanism in the embodiment.

[0075] Figure 10 shows the shear stress-shear displacement relationship curve in the embodiment.

[0076] Figure 11 shows the shear strength-normal stress relationship curve in the embodiment.

[0077] Figure 12 shows the tensile stress-normal displacement relationship curve in the embodiment.

[0078] In the diagram: 1-Rock mass; 2-Concrete test block; 3-Test chamber; 31-Side plate; 32-Top plate; 33-Fixed wing plate; 34-Expansion bolt; 35-Threaded rod; 41-First hydraulic jack; 42-Shear plate; 43-Shear tie rod; 44-Shear bearing plate; 45-Round rod; 51-Second hydraulic jack; 52-Normal bearing plate; 53-Normal threaded rod; 54-Upper pressure plate; 55-Lower pressure plate; 56-Adhesive; 57-Roller; 58-Protrusion; 59-Threaded hole; 61-Slider displacement sensor; 62-Displacement gauge; 63-Data acquisition instrument; 64-Connecting rod. Detailed Implementation

[0079] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0080] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0081] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0082] It should be noted that the directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this application are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this application. Furthermore, in the context, it should be understood that when it is mentioned that an element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0083] As shown in Figures 1-9, this embodiment is an in-situ test device for the mechanical properties of the bond interface between concrete and rock mass, which mainly includes a test chamber 3, a shear loading mechanism, a shear displacement acquisition mechanism, a normal force loading mechanism, a normal displacement acquisition mechanism, and a data acquisition instrument 63.

[0084] In this example, the in-situ testing device is used in conjunction with concrete specimen 2 for testing. Concrete specimen 2 is cast on site and is located inside test chamber 3 at a certain distance from the side wall of test chamber 3. Concrete specimen 2 is in contact with the surface of rock mass 1 to form a bonding interface for testing.

[0085] In this embodiment, the test chamber 3 includes two side plates 31 located on the left and right sides of the concrete test block 2 and a top plate 32 located in front of the concrete test block 2. The two side plates and the top plate form a door-shaped arrangement. A fixed wing plate 33 is vertically arranged at the bottom of the side plate 31. The fixed wing plate 33 is provided with screw holes for fixing the test chamber 3 to the surface of the rock mass 1 by means of expansion bolts 34.

[0086] In this embodiment, the shear loading mechanism includes a first hydraulic jack 41, a shear plate 42, a shear tie rod 43, a shear bearing plate 44, and a second nut 102. The shear plate 42 is located behind the concrete test block 2 and is arranged parallel to the left and right directions. Two shear tie rods 43 are connected to both ends of the shear plate 42. The axis of the shear tie rods 43 is parallel to the front and back directions. The front end of the shear tie rods 43 passes through the round hole on the test top plate and the round hole of the shear bearing plate 44 in sequence before the second nut 102 is installed. The second nut 102 restricts the shear bearing plate 44 to be parallel to the left and right directions. The axis of the first hydraulic jack 41 is parallel to the front and back directions. The front end of the first hydraulic jack 41 is connected to the shear bearing plate 44, and the rear end is connected to the top plate 32.

[0087] In this example, the shear plate 42 is placed on the outside of the concrete specimen 2, and together with the shear tie rod 43, the shear bearing plate 44 and the first hydraulic jack 41, it forms a shear loading mechanism. During the test, an external force is applied to the shear bearing plate 44 through the first hydraulic jack 41, and then transmitted to the shear plate 42 through the shear tie rod 43, and finally applied to the concrete specimen 2.

[0088] In this embodiment, the shear displacement acquisition mechanism is used to acquire the shear displacement of the concrete test block. It includes a connecting rod 64 and a slider displacement sensor 61. The axis of the connecting rod 64 is parallel to the front-back direction. The front end of the connecting rod 64 has a ring, which is fitted onto a round rod 45. The round rod 45 is arranged parallel to the left-right direction and fixed to the shear bearing plate 44. The rear end of the connecting rod 64 is connected to the slider displacement sensor 61, which is installed on the side plate 31 of the test chamber 3.

[0089] In this example, during the shear test, the shear bearing plate 44 and the shear plate 42 behind the concrete specimen 2 move synchronously. The slider displacement sensor 61 obtains the displacement of the shear bearing plate 44, and thus obtains the shear displacement of the concrete specimen 2.

[0090] In this embodiment, the normal force loading mechanism is installed on the test chamber 3, and can apply normal force to the concrete test block 2 through the pressure plate mechanism.

[0091] In this example, the pressure plate mechanism includes an upper pressure plate 54 and a lower pressure plate 55. The lower pressure plate 55 is bonded to the upper surface of the concrete test block 2 by an adhesive 56. The upper surface of the lower pressure plate 55 has a groove with a size that matches the upper pressure plate 54. The axis of the groove is parallel to the front-back direction. Guide grooves parallel to the front-back direction are formed on the groove walls on both sides. The upper pressure plate 54 has protrusions 58 on its left and right sides that match the left and right guide grooves of the groove.

[0092] The upper pressure plate 54 is placed in the groove of the lower pressure plate 55, and the protrusion 58 is placed in the guide groove of the lower pressure plate 55. The upper pressure plate 54 can move relative to the lower pressure plate 55 in the front-back direction. The protrusion 58 cooperates with the guide groove to transfer the tensile force to the concrete specimen 2 through the lower pressure plate during the tensile test.

[0093] In this embodiment, a low-friction mechanism is provided between the upper pressure plate 54 and the lower pressure plate 55. The low-friction mechanism has several rollers 57. The rollers 57 are arranged in parallel left and right directions and can rotate around their own axis. They are installed at the bottom of the groove of the lower pressure plate 55. The rollers 57 are coated with lubricant to reduce the friction between the upper pressure plate 54 and the lower pressure plate 55 during the shear test.

[0094] When a shear test is performed, the normal force loading mechanism includes a second hydraulic jack 51 and a normal bearing plate 52. The normal bearing plate 52 has screw holes on both sides and is fixedly connected to the upper end of the side plate 31 of the test box 3 by screws 35 and first nuts 101. The second hydraulic jack 51 is set between the upper pressure plate 54 and the normal bearing plate 52. By applying an upward pressure to the normal bearing plate 52, the pressure is reacted onto the upper surface of the concrete specimen 2.

[0095] When conducting a pull-out test, the normal force loading mechanism includes a second hydraulic jack 51, a normal bearing plate 52, and a normal threaded rod 53. The normal bearing plate 52 is fixed to the test box 3. The normal threaded rod 53 is arranged parallel to the vertical direction and passes through the circular hole on the normal bearing plate 52. The lower end of the normal threaded rod is connected to the screw hole 59 at the center of the upper surface of the upper pressure plate 54. The upper part of the normal threaded rod 53 is connected to a third nut 103, which is located above the normal bearing plate 52. The second hydraulic jack 51 is provided between the third nut 103 and the normal bearing plate 52. The second hydraulic jack 51 can transmit the tensile force to the upper surface of the concrete specimen 2 through the third nut 103, the normal threaded rod 53, and the pressure plate mechanism.

[0096] In this embodiment, the normal displacement acquisition mechanism uses a displacement meter 62, which is in contact with the upper surface of the upper pressure plate 54. When a pull-out test is performed, the normal displacement of the concrete specimen 2 is monitored by the displacement meter 62 during the pull-out test.

[0097] In this embodiment, both the slider displacement sensor 61 and the displacement gauge 62 are connected to the data acquisition instrument 63 via data cables, enabling real-time acquisition of all monitoring data.

[0098] The basic steps of the in-situ test method for the mechanical properties of the concrete-rock bond interface using the in-situ test device in this embodiment are as follows:

[0099] The steps for conducting mechanical shear tests at the concrete-rock bond interface are as follows:

[0100] 1) Select the test location. Choose a suitable test location as needed. The rock surface at the test location can be horizontal, vertical, or inclined at a certain angle. The surface of the rock at the test location should be as smooth as possible.

[0101] 2) Pour and cure concrete test blocks. The recommended dimensions for the concrete test blocks are 200mm × 200mm × 150mm (length × width × height). Before pouring, clean the rock mass at the test site with clean water and allow it to dry. Fix the formwork and pour in the concrete, then vibrate it to ensure it is compacted. Before pouring, ensure the surface of the rock mass and the formwork are moist. Cure the concrete until it reaches the design strength, then remove the formwork.

[0102] 3) Secure the test chamber to the rock surface using expansion bolts, ensuring the concrete specimen is positioned in the center of the chamber and its side is parallel to the side plate of the chamber. When the rock surface is sloped or vertical, ensure the top plate of the test chamber is above the concrete specimen to eliminate the influence of the device's weight on the test results. Secure the slider displacement sensor to the outer surface of the test chamber's side plate using the fourth nut.

[0103] 4) Adhere the lower pressure plate to the upper surface of the concrete test block using adhesive. Apply lubricant to the roller in the groove of the lower pressure plate. Then, insert the protrusion of the upper pressure plate into the groove of the upper pressure plate and align it, as shown in Figure 9. Secure the normal bearing plate to the screw on the side plate of the test chamber using the first nut, thereby connecting the test chamber and the normal bearing plate into a whole. Place the second hydraulic jack between the upper pressure plate and the normal bearing plate to provide normal pressure, as shown in Figure 3.

[0104] 5) Place the shear plate under the concrete test block, and pass the shear tie rod through the round hole on the side of the concrete test block, the round hole on the top plate of the test chamber, and the round hole on the shear bearing plate in sequence. Place the first hydraulic jack between the top plate of the test chamber and the shear bearing plate, and screw the second nut into the shear tie rod on the outside of the shear bearing plate to complete the installation of the shear force application device.

[0105] 6) Preferably, in order to meet the test requirements, multiple parallel tests should be conducted, and it is recommended to set up 3 to 4 sets.

[0106] Bond interface shear strength test:

[0107] i. Apply normal pressure. Apply a certain pressure P1 to the upper surface of the concrete specimen using a second hydraulic jack, and maintain the pressure P1 constant during the test.

[0108] ii. Pre-applied shear force. A small initial shear force is applied to the side of the concrete specimen using the first hydraulic jack, ensuring that the shear plate fits tightly against the side of the concrete specimen.

[0109] iii. Installation of monitoring instruments. Install the connecting rod into the slider-type displacement sensor and connect and fix it to the round rods on both sides of the shear bearing plate. Connect the slider-type displacement sensor to the data acquisition instrument through the data cable and reset the initial data to zero. Monitor the shear displacement in real time during the test, and take the average value of the two instruments.

[0110] iv. Shear force application. The load was increased in stages by 5 kN each time, until the bond interface between the concrete and the rock mass failed. The shear force T and shear displacement u under each load stage were recorded.

[0111] v. Data processing. During the experiment, the normal stress at the bond interface remained constant: σ1 = P1 / A

[0112] The shear stress τ at the bond interface under each load level i Calculate as follows:

[0113] τ i = T / A

[0114] In the formula, A represents the area of ​​the bonding interface.

[0115] Plot a curve with shear displacement u as the abscissa and shear stress τ as the ordinate, as shown in Figure 10. The slope of the initial straight segment of the curve is the shear stiffness K of the concrete-rock bond interface. S :

[0116] K S =Δτ / Δu

[0117] The peak shear stress on the shear stress-shear displacement curve is the shear strength τ of the bond interface under the normal stress σ1. f1 .

[0118] vi. By changing the normal pressure and repeating the experimental steps i~v, multiple sets of experimental results can be obtained, and the normal stress σ corresponding to each set of tests can be obtained. i and shear strength τ fi Plot the shear strength τ fi With normal stress σ i Relationship curve, based on τ f The relationship =c + σ*tanφ can be used to calculate the cohesive force c and friction angle φ at the bonding interface, as shown in Figure 11.

[0119] II. The steps for conducting mechanical pull-out tests at the concrete-rock bond interface are as follows:

[0120] 1) Select the test location. Choose a suitable test location as needed. The rock surface at the test location can be horizontal, vertical, or inclined at a certain angle. The surface of the rock at the test location should be as smooth as possible.

[0121] 2) Pour and cure concrete test blocks. The recommended dimensions for the concrete test blocks are 200mm × 200mm × 150mm (length × width × height). Before pouring, clean the rock mass at the test site with clean water and allow it to dry. Fix the formwork and pour in the concrete, then vibrate it to ensure it is compacted. Before pouring, ensure the surface of the rock mass and the formwork are moist. Cure the concrete until it reaches the design strength, then remove the formwork.

[0122] 3) Secure the test chamber to the rock surface using expansion bolts, ensuring the concrete specimen is positioned in the center of the chamber and its side is parallel to the side plate of the chamber. When the rock surface is sloped or vertical, ensure the top plate of the test chamber is above the concrete specimen to eliminate the influence of the device's weight on the test results. Secure the slider displacement sensor to the outer surface of the test chamber's side plate using the fourth nut.

[0123] 4) Adhere the lower pressure plate to the upper surface of the concrete test block using adhesive. Apply lubricant to the roller in the groove of the lower pressure plate, then insert the protrusion of the upper pressure plate into the groove of the upper pressure plate and align it. Fix the normal bearing plate to the screw on the side plate of the test chamber using the first nut, thus connecting the test chamber and the normal bearing plate into a whole. Place the second hydraulic jack on the normal bearing plate, and pass the normal threaded rod through the second hydraulic jack and the normal bearing plate in sequence, fixing it in the screw hole in the center of the upper pressure plate. Screw the third nut into the normal threaded rod on the outside of the second hydraulic jack, as shown in Figure 4.

[0124] 5) Preferably, in order to meet the test requirements, multiple parallel tests should be conducted, and it is recommended to set up 3 to 4 sets.

[0125] Bond interface tensile strength test:

[0126] i. Installation of monitoring instruments. Fix the displacement gauge in place and make it contact with the upper surface of the upper pressure plate, ensuring that the axis of the displacement gauge is perpendicular to the upper pressure plate. Connect the displacement gauge to the data acquisition instrument via the data cable and reset the initial data to zero. Monitor the normal displacement in real time during the test.

[0127] ii. Pre-tension. A small initial tension is applied to the concrete specimen using a second hydraulic jack.

[0128] iii. Tensile force application. The load was increased in stages, with each increase being 5 kN, until the bond interface between the concrete and the rock mass failed. The tensile force F and normal displacement s under each load stage were recorded.

[0129] iv. Data processing.

[0130] Tensile stress σ at the bond interface under each load level ti Calculate as follows:

[0131] σ ti = F / A

[0132] With normal displacement s as the abscissa and tensile stress σ t Plot a curve with the vertical axis as shown in Figure 12. The slope of the initial straight segment of the curve represents the normal stiffness of the concrete-rock bond interface.

[0133] K n =Δσ t / Δs

[0134] The peak tensile stress on the tensile stress-normal displacement curve is the tensile strength σ of the bond interface. tf .

[0135] v. Repeating the test steps i to iv can yield multiple sets of test results. The average value of the multiple sets of tests is taken as the tensile strength of the bond interface between concrete and rock mass.

[0136] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An in-situ test device for the mechanical properties of the concrete-rock bond interface, characterized in that, include: Concrete test blocks were poured onto the rock mass. A test chamber is arranged around the concrete test block and is fixed to the rock mass; A shear loading mechanism, installed on the test chamber, is used to apply shear force to the concrete specimen in the front-to-back direction; a shear displacement acquisition mechanism is used to acquire the shear displacement of the concrete specimen; a normal force loading mechanism, installed on the test chamber, is used to apply normal force to the concrete specimen via a pressure plate mechanism; the pressure plate mechanism includes an upper pressure plate and a lower pressure plate, wherein the upper pressure plate is connected to the normal force loading mechanism, and the upper pressure plate is pressed onto the lower pressure plate in the front-to-back direction via a low-friction mechanism, and the lower pressure plate is bonded to the upper surface of the concrete specimen; a normal displacement acquisition mechanism is used to acquire the normal displacement of the concrete specimen; a data acquisition instrument is connected to the shear displacement acquisition mechanism and the normal displacement acquisition mechanism via a data cable.

2. The in-situ test device for the mechanical properties of the concrete-rock bonding interface according to claim 1, characterized in that: The shear loading mechanism includes a first hydraulic jack, a shear plate, a shear tie rod, and a shear bearing plate; wherein, the axis of the shear tie rod is parallel to the front-back direction, and the shear tie rod passes through a circular hole on the test box; the front end of the shear tie rod is connected to the shear bearing plate, and the first hydraulic jack is installed between the shear bearing plate and the test box; the rear end of the shear tie rod is connected to the shear plate located behind the concrete test block.

3. The in-situ test device for the mechanical properties of the concrete-rock bonding interface according to claim 2, characterized in that: The shear displacement acquisition mechanism includes a connecting rod and a slider displacement sensor. The axis of the connecting rod is parallel to the front-to-back direction. The front end of the connecting rod is connected to the shear bearing plate, and the rear end of the connecting rod is connected to the slider displacement sensor, which is installed on the test chamber.

4. The in-situ test device for the mechanical properties of the concrete-rock bonding interface according to claim 3, characterized in that: The connecting rod has a ring at its front end, which is fitted onto the round rod, and the round rod is fixedly connected to the shear bearing plate.

5. The in-situ test device for the mechanical properties of the concrete-rock bond interface according to claim 1, characterized in that: The normal force loading mechanism includes a second hydraulic jack and a normal bearing plate, wherein the normal bearing plate is fixed on the test chamber, and the second hydraulic jack is disposed between the upper pressure plate and the normal bearing plate.

6. The in-situ test apparatus for the mechanical properties of the concrete-rock bond interface according to claim 1, characterized in that: The normal force loading mechanism includes a second hydraulic jack, a normal bearing plate, and a normal threaded rod. The normal bearing plate is fixed to the test chamber. The normal threaded rod is arranged parallel to the vertical direction and passes through a circular hole in the normal bearing plate. The lower end of the normal threaded rod is connected to the upper pressure plate, and the upper part of the normal threaded rod is connected to a third nut. The third nut is located above the normal bearing plate, and the second hydraulic jack is provided between the third nut and the normal bearing plate.

7. The in-situ test device for the mechanical properties of the concrete-rock bond interface according to claim 1, characterized in that: The upper surface of the lower pressure plate has a groove, the axis of which is parallel to the front-to-back direction, and guide grooves parallel to the front-to-back direction are formed on the groove walls on both sides; the left and right sides of the upper pressure plate have protrusions that are adapted to the guide grooves.

8. The in-situ test apparatus for the mechanical properties of the concrete-rock bond interface according to claim 1 or 7, characterized in that: The low-friction mechanism includes a plurality of rollers disposed between the upper pressure plate and the lower pressure plate, the rollers being arranged perpendicular to the front-back direction.

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