Concrete and rock mass bonding interface mechanical property in-situ test device and test method

Abstract

The invention relates to a concrete and rock mass bonding interface mechanical property in-situ test device and a test method. 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

Technical Field

[0001] The present invention relates to an in-situ test device and test method for the mechanical properties of the bonding interface between concrete and rock mass, and is applicable to the technical field of geotechnical engineering. Background Art

[0002] As a common building material, concrete is widely used in the fields of water conservancy and hydropower engineering, traffic tunnel engineering, mine engineering, etc. For the mechanical properties of concrete itself, the current research results are very mature. However, for the mechanical properties of the bonding interface between concrete and rock mass or soil, the current research results are relatively few, and no unified understanding has been formed.

[0003] The mechanical properties of the bonding interface between concrete and rock mass are important indicators for evaluating the co-working performance of concrete structures and rock masses, and are of great significance for aspects such as the design of underground engineering concrete lining structures, the stability calculation of concrete dam foundations, and the evaluation of the anti-sliding performance of retaining structures such as retaining walls. Especially during the simulation process using numerical methods, the strength characteristics (shear strength, tensile strength) and deformation characteristics (normal stiffness, shear stiffness) of the bonding interface between concrete and rock mass are important input parameters, which have an important impact on the rationality and reliability of the calculation results. However, currently, engineering experience methods are mostly used for value taking, with poor accuracy. Overestimating the bonding interface strength and anti-deformation ability may bring certain risks to the project, while underestimating may lead to reduced project economy.

[0004] At present, the research on the mechanical properties of the bonding interface between concrete and rock mass at home and abroad mainly adopts indoor test methods, while in-situ test research is relatively less. However, there are significant differences between indoor tests and the field in terms of scale and working environment. Appendix M of the Technical Code for Rock and Soil Anchor and Shotcrete Support Engineering GB 50086-2015 gives an in-situ test method for the bonding strength of shotcrete. By conducting a pull-out test on the concrete specimens isolated by coring on-site, the tensile strength of the bonding interface can be obtained, but this method cannot obtain parameters such as the shear strength and deformation characteristics of the bonding interface.

[0005] The Chinese patent with the patent publication number CN 112098236 B, "An in-situ test device and test method for the shear strength of the concrete-rock mass-shotcrete contact surface", proposes a simple in-situ test device for shear strength, which can apply normal pressure and tangential shear force to the concrete-rock mass-shotcrete contact surface under horizontal or vertical conditions. However, this method has the following deficiencies: 1. It cannot obtain the tensile strength and deformation characteristics of the bonding interface; 2. It is not applicable to the state where the bonding interface is inclined (such as the foundation of a concrete dam); 3. The influence of the self-weight of the test device on the test results cannot be eliminated during the test process. Especially when the shear strength of the bonding interface is low, the test results may have large errors; 4. The influence of the friction between the metal pressing plate and the concrete on the test results is not considered.

[0006] When conducting the lining design of underground chambers and the anti-sliding stability analysis of dam foundations, the inventor found that in the existing engineering design process, the mechanical properties of the bonding interface between concrete and rock mass are rarely accurately considered. Especially in the numerical simulation process, currently, either the concrete and rock mass are considered as co-nodes without relative deformation, or an inaccurate empirical value is assigned based on relevant specifications. This is mainly because the in-situ test conditions are poor, the device is complex, the cost is high, and it is difficult to promote and use, resulting in difficulties in obtaining the mechanical properties of the bonding interface between concrete and rock mass on-site. Therefore, there is an urgent need to invent a simple, economical, and effective in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: in view of the above problems, to provide an in-situ test device and test method for the mechanical properties of the bonding interface between concrete and rock mass.

[0008] The technical solution adopted by the present invention is: an in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass, comprising: A concrete test block, cast on the rock mass; A test box, arranged around the concrete test block and fixed on the rock mass; A shear force loading mechanism, installed on the test box for applying a shear force in the front-back direction to the concrete test block; A shear displacement acquisition mechanism for acquiring the shear displacement of the concrete test block; A normal force loading mechanism, installed on the test box for applying a normal force to the concrete test block through a pressing plate mechanism; The pressing plate mechanism includes an upper pressing plate and a lower pressing plate. The upper pressing plate is connected to the normal force loading mechanism, and the upper pressing plate presses on the lower pressing plate through a low-friction mechanism and can move in the front-back direction. The lower pressing plate is bonded to the upper surface of the concrete test block; A normal displacement acquisition mechanism for acquiring the normal displacement of the concrete test block; A data acquisition instrument, connected to the shear displacement acquisition mechanism and the normal displacement acquisition mechanism through a data line.

[0009] The shear force loading mechanism includes a first hydraulic jack, a shear plate, a shear pull rod, and a shear force bearing plate; Among them, the axis direction of the shear pull rod is parallel to the front-back direction, and the shear pull rod passes through the circular hole on the test box. The front end of the shear pull rod is connected to the shear force bearing plate, and a first hydraulic jack is installed between the shear force bearing plate and the test box; the rear end of the shear pull rod is connected to the shear plate located behind the concrete test block.

[0010] The shear displacement acquisition mechanism includes a connecting rod and a slider-type displacement sensor. The axis direction of the connecting rod is parallel to the front-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-type displacement sensor. The slider-type displacement sensor is installed on the test box.

[0011] A circular ring is made at the front end of the connecting rod. The circular ring is sleeved on a round rod, and the round rod is fixedly connected to the shear bearing plate.

[0012] The normal force loading mechanism includes a second hydraulic jack and a normal bearing plate. The normal bearing plate is fixed on the test box, and the second hydraulic jack is arranged between the upper pressure plate and the normal bearing plate.

[0013] 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 on the test box. The normal threaded rod is arranged parallel to the up-down direction and passes through a round hole on 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 a second hydraulic jack is arranged between the third nut and the normal bearing plate.

[0014] A groove is made on the upper surface of the lower pressure plate. The axis direction of the groove is parallel to the front-back direction, and guiding grooves parallel to the front-back direction are made on the two side walls of the groove; protrusions adapted to the guiding grooves are made on the left and right sides of the upper pressure plate.

[0015] The low-friction mechanism includes a plurality of rolling rods arranged between the upper pressure plate and the lower pressure plate. The rolling rods are arranged perpendicular to the front-back direction.

[0016] An in-situ test method for the mechanical properties of the bonding interface between concrete and rock mass, based on the in-situ test device, to carry out the mechanical shear test on the bonding interface between concrete and rock mass, includes: 1) Select the test position; 2) Pour the concrete test block and cure it; 3) Fix the test box on the rock mass surface to ensure that the concrete test block is located at the middle position inside the test box; 4) Bond the lower pressure plate of the pressure plate mechanism to the upper surface of the concrete test block through an adhesive, and install the normal force loading mechanism on the test box; 5) Set up the shear force loading mechanism corresponding to the concrete test block and install the shear force loading mechanism on the test box; 6) Conduct multiple groups of parallel tests; Shear strength test of the bonding interface: i. Apply a normal pressure to apply a certain pressure P1 to the upper surface of the concrete test block; ii. Apply a pre-shear force; iii. Install the monitoring instruments; iv. Shear force is applied in a way of increasing the load step by step until the bond interface between the concrete and the rock mass fails, and record the shear force T and the shear displacement u under each level of load; v. Data processing. During the test, the normal stress on the bond interface remains constant, σ1 = P1 / A The shear stress τ on the bond interface under each level of load i is calculated as follows: τ i = T / A where A is the area of the bond interface; Taking the shear displacement u as the abscissa and the shear stress τ as the ordinate to plot a curve, and the slope of the initial straight line segment of the curve is the shear stiffness K of the bond interface between the concrete and the rock mass S : K S =Δτ / Δu 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 ; vi. Change the normal pressure and repeat the test steps of i~v to obtain multiple groups of test results, and respectively obtain the normal stress σ corresponding to each group of tests i and the shear strength τ fi , plot the relationship curve between the shear strength τ fi and the normal stress σ i , and according to the relationship of τ f =c+σ*tanφ, obtain the cohesion c and the friction angle φ of the bond interface.

[0017] An in-situ test method for the mechanical properties of the bond interface between concrete and rock mass, based on the in-situ test device, to carry out the mechanical pull-out test of the bond interface between concrete and rock mass, including: 1) Select the test location; 2) Pour the concrete test block and cure it; 3) Fix the test box to the rock mass surface to ensure that the concrete test block is located at the middle position inside the test box; 4) Bond the lower pressing plate of the pressing plate mechanism to the upper surface of the concrete test block with an adhesive, and install the normal force loading mechanism on the test box; 5) Conduct multiple groups of parallel tests; Tensile strength test of the bond interface: i. Install the monitoring instrument; ii. Apply the initial normal tensile force; iii. Apply the normal tensile force in a way of increasing the load step by step until the bond interface between the concrete and the rock mass fails, and record the tensile force F and the normal displacement s under each level of load; iv. Data processing.

[0018] The tensile stress σ on the bonding interface under each level of load ti is calculated as follows: σ ti = F / A Taking the normal displacement s as the abscissa and the tensile stress σ t as the ordinate to plot a curve, the slope of the initial straight line segment of the curve is the normal stiffness of the concrete-rock mass bonding interface: K n =Δσ t / Δs The peak tensile stress on the tensile stress-normal displacement curve is the tensile strength σ of the bonding interface tf ; v. Repeat the test steps of i~iv to obtain multiple groups of test results, and take the average value of multiple groups as the tensile strength of the concrete-rock mass bonding interface.

[0019] The beneficial effects of the present invention are as follows: By setting a low-friction mechanism (such as a roller) between the upper pressure plate and the lower pressure plate, the present invention 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 test block and the lower pressure plate undergo shear displacement, so that the normal pressure can be ensured to be constant during the test process, improving the test accuracy.

[0020] The test device of the present invention is simple in structure, convenient to operate, and good in economy. It can effectively make up for the deficiencies of the current in-situ test methods, facilitate popularization and large-scale on-site testing, and provide a basis for the design of concrete structures in projects such as underground caverns, dams, and slopes.

[0021] The present invention is equipped with a shear test method for the concrete-rock mass bonding interface. By real-time monitoring of the shear force and shear displacement during the shear test, the shear strength and shear stiffness of the bonding interface can be obtained simultaneously.

[0022] The present invention is equipped with a pull-out test method for the concrete-rock mass bonding interface, which can be operated integrally with the shear test. By real-time monitoring of the tensile force and normal displacement during the pull-out test, the tensile strength and normal stiffness of the bonding interface can be obtained simultaneously. Description of the Drawings

[0023] Figure 1 It is a three-dimensional view of the in-situ test device in the embodiment.

[0024] Figure 2 It is a top view of the in-situ test device in the embodiment.

[0025] Figure 3 It is a schematic diagram of the in-situ test device when carrying out the shear test in the embodiment.

[0026] Figure 4Schematic diagram of the in-situ test device during the pulling test in the embodiment.

[0027] Figure 5 Schematic diagram of the structure of the test box in the embodiment.

[0028] Figure 6 Schematic diagram of the structure of the shear plate in the embodiment.

[0029] Figure 7 Schematic diagram of the connection of the slider type displacement sensor in the embodiment.

[0030] Figure 8 Schematic diagram of the structure of the normal bearing plate in the embodiment.

[0031] Figure 9 Schematic diagram of the structure of the pressing plate mechanism in the embodiment.

[0032] Figure 10 Shear stress - shear displacement relationship curve in the embodiment.

[0033] Figure 11 Shear strength - normal stress relationship curve in the embodiment.

[0034] Figure 12 Tensile stress - normal displacement relationship curve in the embodiment.

[0035] In the figure: 1 - rock mass; 2 - concrete test block; 3 - test box; 31 - side plate; 32 - top plate; 33 - fixed wing plate; 34 - expansion bolt; 35 - screw rod; 41 - first hydraulic jack; 42 - shear plate; 43 - shear tension rod; 44 - shear force bearing plate; 45 - round rod; 51 - second hydraulic jack; 52 - normal bearing plate; 53 - normal threaded rod; 54 - upper pressing plate; 55 - lower pressing plate; 56 - adhesive; 57 - roller; 58 - protrusion; 59 - screw hole; 61 - slider type displacement sensor; 62 - displacement meter; 63 - data acquisition instrument; 64 - connecting rod. Detailed implementation manners

[0036] For a better understanding of the technical solution of the present application, the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0037] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms of "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0038] It should be understood that the term "and / or" used herein is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " in this text generally indicates that the associated objects before and after are in an "or" relationship.

[0039] It should be noted that the orientation terms such as "upper", "lower", "left", and "right" described in the embodiments of this application are described from the angles shown in the drawings and should not be construed as limitations on the embodiments of this application. In addition, in the context, it should also be understood that when it is mentioned that one component is connected "above" or "below" another component, it can not only be directly connected "above" or "below" another component, but also be indirectly connected "above" or "below" another component through an intermediate component.

[0040] As Figures 1 - 9 shown, this embodiment is an in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass, which mainly includes a test box 3, a shear force loading mechanism, a shear displacement acquisition mechanism, a normal force loading mechanism, a normal displacement acquisition mechanism, a data acquisition instrument 63, etc.

[0041] In this example, the in-situ test device cooperates with the concrete test block 2 for the test. The concrete test block 2 is cast on-site. The concrete test block 2 is located inside the test box 3 and keeps a certain distance from the side wall of the test box 3. The concrete test block 2 is in contact with the surface of the rock mass 1 to form a bonding interface for the test.

[0042] In this embodiment, the test box 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 portal arrangement. Fixed wing plates 33 are vertically arranged at the bottom of the side plates 31. Screw holes are provided on the fixed wing plates 33 for fixing the test box 3 to the surface of the rock mass 1 through expansion bolts 34.

[0043] In this embodiment, the shear force loading mechanism includes a first hydraulic jack 41, a shear plate 42, shear tie rods 43, a shear force bearing plate 44, and a second nut 102. Among them, the shear plate 42 is arranged behind the concrete test block 2 and is arranged parallel to the left and right directions. Both ends of the shear plate 42 are connected to two shear tie rods 43. The axial direction of the shear tie rods 43 is parallel to the front and back directions. And the front end of the shear tie rod 43 sequentially passes through the round holes on the test top plate and the round holes on the trademark of the shear force bearing plate 44 and then installs the second nut 102. The second nut 102 restricts the shear force bearing plate 44 to move parallel to the left and right directions. The axis of the first hydraulic jack 41 is parallel to the front and back directions, and the front end of the first hydraulic jack 41 is connected to the shear force bearing plate 44, and the rear end is connected to the top plate 32.

[0044] In this example, the shear plate 42 is placed outside the concrete specimen 2 and together with the shear tie rod 43, the shear bearing plate 44 and the first hydraulic jack 41, they jointly form a shear force loading mechanism. During the test, an external force is applied to the shear bearing plate 44 by the first hydraulic jack 41 and transmitted to the shear plate 42 through the shear tie rod 43, and finally acts on the concrete specimen 2.

[0045] In this embodiment, the shear displacement acquisition mechanism is used to acquire the shear displacement of the concrete specimen, and includes a connecting rod 64 and a slider displacement sensor 61. The axis direction of the connecting rod 64 is parallel to the front-back direction. A ring is made at the front end of the connecting rod 64 and is sleeved on the round rod 45 through the ring. The round rod 45 is arranged parallel to the left-right direction and is fixed on the shear bearing plate 44. The rear end of the connecting rod 64 is connected to the slider displacement sensor 61, and the slider displacement sensor 61 is installed on the side plate 31 of the test box 3.

[0046] 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.

[0047] In this embodiment, the normal force loading mechanism is installed on the test box 3 and can apply a normal force to the concrete specimen 2 through the pressing plate mechanism.

[0048] In this example, the pressing plate mechanism includes an upper pressing plate 54 and a lower pressing plate 55. The lower pressing plate 55 is bonded to the upper surface of the concrete specimen 2 by an adhesive 56. A groove adapted to the upper pressing plate 54 is made on the upper surface of the lower pressing plate 55. The axis direction of the groove is parallel to the front-back direction, and guide grooves parallel to the front-back direction are made on the two side walls of the groove. Protrusions 58 adapted to the left and right guide grooves of the groove are made on the left and right sides of the upper pressing plate 54.

[0049] The upper pressing plate 54 is placed in the groove of the lower pressing plate 55, and the protrusions 58 are placed in the guide grooves of the lower pressing plate 55. The upper pressing plate 54 can move relative to the lower pressing plate 55 in the front-back direction. The protrusions 58 cooperate with the guide grooves to transfer the tensile force to the concrete specimen 2 through the lower pressing plate during the tensile test process.

[0050] In this embodiment, a low friction mechanism is provided between the upper pressing plate 54 and the lower pressing plate 55. The low friction mechanism has a number of roller bars 57. The roller bars 57 are arranged parallel to the left-right direction and are rotatably installed on the bottom of the groove of the lower pressing plate 55 around their own axes. Lubricant is applied to the roller bars 57 to reduce the friction force between the upper pressing plate 54 and the lower pressing plate 55 during the shear test process.

[0051] When conducting a shear test, the normal force loading mechanism includes a second hydraulic jack 51 and a normal bearing plate 52. There are screw holes on both sides of the normal bearing plate 52, and it is fixedly connected to the upper end of the side plate 31 of the test box 3 through a screw rod 35 and a first nut 101. The second hydraulic jack 51 is arranged 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 thus reacted onto the upper surface of the concrete test block 2.

[0052] 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 up-and-down direction and passes through the round 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. The third nut 103 is located above the normal bearing plate 52. A 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 test block 2 through the third nut 103, the normal threaded rod 53, and the pressure plate mechanism.

[0053] In this embodiment, the normal displacement acquisition mechanism uses a displacement gauge 62, which contacts the upper surface of the upper pressure plate 54. When conducting a pull-out test, the normal displacement of the concrete test block 2 during the pull-out test is monitored through the displacement gauge 62.

[0054] In this embodiment, both the slider-type displacement sensor 61 and the displacement gauge 62 are connected to the data acquisition instrument 63 through data lines, and all monitoring data can be collected in real time.

[0055] The method for conducting an in-situ test on the mechanical properties of the bonding interface between concrete and rock mass using the in-situ test device in this embodiment is as follows: I. The steps for conducting a shear test on the mechanical properties of the bonding interface between concrete and rock mass are as follows: 1) Select the test position. Select a suitable test position according to needs. The surface of the rock mass at the test position can be horizontal, vertical, or an inclined plane with a certain angle. Try to ensure that the surface of the rock mass at the test position is smooth.

[0056] 2) Pour and cure the concrete test block. The size of the concrete test block is preferably 200mm×200mm×150mm (length×width×height). Before pouring, first clean and dry the rock mass at the test site with clean water, fix the formwork and pour the concrete, vibrate the concrete thoroughly. Before pouring, ensure that the surface of the rock mass and the formwork are wet. Cure the concrete until the strength reaches the design requirements, and then remove the formwork.

[0057] 3) Secure the test chamber to the rock surface with expansion bolts, ensuring the concrete test block is centered inside the chamber and its sides are parallel to the chamber's side panels. If the rock surface is inclined or vertical, ensure the chamber's top panel is positioned above the concrete test block to eliminate the influence of the device's own weight on the test results. Secure the slider-type displacement sensor to the outer surface of the chamber's side panels with the fourth nut.

[0058] 4) Bond the lower platen to the upper surface of the concrete test block with adhesive, apply lubricant to the roller in the groove of the lower platen, and then insert the protrusion of the upper platen into the groove of the upper platen and align them, as shown in the attached figure. Figure 9 The normal pressure plate is fixed to the screw on the side plate of the test box through the first nut, so that the test box and the normal pressure plate are connected as a whole. The second hydraulic jack is placed between the upper pressure plate and the normal pressure plate to provide normal pressure, as shown in the attached figure. Figure 3 .

[0059] 5) Place the shear plate under the concrete test block, and insert the shear rod through the side of the concrete test block, the circular hole on the top plate of the test box, and the circular hole on the shear pressure plate in sequence. Place the first hydraulic jack between the top plate of the test box and the shear pressure plate, and screw the second nut into the shear rod on the outside of the shear pressure plate to complete the installation of the shear force application device.

[0060] 6) Preferably, multiple parallel tests should be conducted to meet the test requirements. It is recommended to set up 3 to 4 groups.

[0061] Bonding interface shear strength test: i. Apply normal pressure. Use the second hydraulic jack to apply a certain pressure P1 to the upper surface of the concrete specimen. Maintain the pressure P1 constant during the test.

[0062] ii. Pre-shear force: Use the first hydraulic jack to apply a small initial shear force to the side of the concrete specimen so that the shear plate fits tightly against the side of the concrete specimen.

[0063] iii. Install the monitoring instrument. Install the connecting rod into the slider displacement sensor and secure it to the round rods on both sides of the shear bearing plate. Connect the slider displacement sensor to the data acquisition instrument via a data cable and reset the initial data to zero. During the test, monitor the shear displacement in real time and take the average of the shear displacement values from the two instruments.

[0064] iv. Shear force application. A stepwise load increase of 5 kN was used until the concrete-rock interface failed. The shear force T and shear displacement u at each load level were recorded.

[0065] v. Data processing. During the test, the normal stress on the bonding interface remains constant σ1 = P1 / A The shear stress τ on the bonding interface under each load level i is calculated as follows: τ i = T / A where A is the bonding interface area.

[0066] Taking the shear displacement u as the abscissa and the shear stress τ as the ordinate to plot a curve, as shown in the appendix Figure 10 , the slope of the initial straight line segment of the curve is the shear stiffness K of the concrete-rock mass bonding interface S : K S =Δτ / Δu The peak shear stress on the shear stress-shear displacement curve is the shear strength τ of the bonding interface under the normal stress σ1 f1 .

[0067] vi. Change the normal pressure and repeat the test steps of i~v to obtain multiple groups of test results, and respectively obtain the normal stress σ corresponding to each group of tests i and the shear strength τ fi , plot the relationship curve of the shear strength τ fi and the normal stress σ i . According to the relationship of τ f =c+σ*tanφ, the cohesion c and friction angle φ of the bonding interface can be obtained, as shown in the appendix Figure 11 .

[0068] II. The steps for carrying out the mechanical pull-out test of the concrete-rock mass bonding interface are as follows: 1) Select the test position. Select a suitable test position according to needs. The surface of the rock mass at the test position can be horizontal, vertical or an inclined plane with a certain angle. Try to ensure that the surface of the rock mass at the test position is smooth.

[0069] 2) Pour and cure the concrete test block. The size of the concrete test block is recommended to be 200mm×200mm×150mm (length×width×height). Before pouring, first clean and dry the rock mass at the test part with clean water, fix the formwork and pour the concrete, vibrate the concrete thoroughly. Before pouring, ensure that the surface of the rock mass and the formwork are wet. Cure the concrete until the strength reaches the design requirements, and then remove the formwork.

[0070] 3) Fix the test box to the surface of the rock mass with expansion bolts, ensure that the concrete test block is located in the middle of the test box, and the side of the concrete test block is parallel to the side plate of the test box. When the surface of the rock mass is an inclined plane or vertical, ensure that the top plate of the test box is located above the concrete test block to eliminate the influence of the self-weight of the device on the test results. Fix the slider displacement sensor to the outer surface of the side plate of the test box with the fourth nut.

[0071] 4) Bond the lower pressing plate to the upper surface of the concrete specimen with an adhesive. Apply lubricant to the rollers in the groove of the lower pressing plate, and then insert the protrusion of the upper pressing plate into the groove of the upper pressing plate and align them. Fix the normal bearing plate to the screw rod on the side plate of the test box through the first nut, thus connecting the test box and the normal bearing plate as a whole. Place the second hydraulic jack on the normal bearing plate. The normal threaded rod passes through the second hydraulic jack and the normal bearing plate in sequence and is fixed to the screw hole at the center of the upper pressing plate. Screw the third nut onto the normal threaded rod outside the second hydraulic jack, as shown in the appendix Figure 4 .

[0072] 5) Preferably, to meet the test requirements, multiple sets of parallel tests should be carried out, and it is recommended to set 3 - 4 sets.

[0073] Tensile strength test of the bonding interface: i. Installation of monitoring instruments. Fix the displacement gauge and make it contact with the upper surface of the upper pressing plate, ensuring that the axis direction of the displacement gauge is perpendicular to the upper pressing plate. Connect the displacement gauge to the data acquisition instrument through the data cable and zero the initial data. Monitor the normal displacement in real time during the test.

[0074] ii. Pre - application of tensile force. Apply a small initial tensile force to the concrete specimen through the second hydraulic jack.

[0075] iii. Application of tensile force. Adopt the method of increasing the load in stages. Each time the load is increased by 5 kN until the bonding interface between the concrete and the rock mass fails. Record the tensile force F and the normal displacement s under each stage of load.

[0076] iv. Data processing.

[0077] The tensile stress σ on the bonding interface under each stage of load ti is calculated as follows: σ ti = F / A Take the normal displacement s as the abscissa and the tensile stress σ t as the ordinate to make a curve, as shown in the appendix Figure 12 . The slope of the initial straight - line segment of the curve is the normal stiffness of the bonding interface between the concrete and the rock mass: K n =Δσ t / Δs The peak tensile stress on the tensile - stress - normal - displacement curve is the tensile strength σ tf of the bonding interface.

[0078] v. Repeating the test steps from i to iv can obtain multiple sets of test results. Take the average value of multiple sets of tests as the tensile strength of the bonding interface between the concrete and the rock mass.

[0079] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various modifications and changes can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. An in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass, characterized in that, Comprising: Concrete test blocks, cast on the rock mass; Test box, arranged around the concrete test blocks and fixed to the rock mass; Shear loading mechanism, installed on the test box for applying a shear force in the front - rear direction to the concrete test blocks; Shear displacement acquisition mechanism, for acquiring the shear displacement of the concrete test blocks; Normal force loading mechanism, installed on the test box for applying a normal force to the concrete test blocks through a pressing plate mechanism; The pressing plate mechanism includes an upper pressing plate and a lower pressing plate. The upper pressing plate is connected to the normal force loading mechanism, and the upper pressing plate presses on the lower pressing plate through a low - friction mechanism and can move in the front - rear direction. The lower pressing plate is bonded to the upper surface of the concrete test blocks; Normal displacement acquisition mechanism, for acquiring the normal displacement of the concrete test blocks; Data acquisition instrument, connected to the shear displacement acquisition mechanism and the normal displacement acquisition mechanism through data lines.

2. The in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass 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; Among them, the axis direction of the shear tie rod is parallel to the front - rear direction, and the shear tie rod passes through the circular hole on the test box. The front end of the shear tie rod is connected to the 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 the shear plate located behind the concrete test blocks.

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

4. The in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass according to claim 3, characterized in that: A circular ring is made at the front end of the connecting rod, and the circular ring is sleeved on a 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 bonding interface between concrete and rock mass according to claim 1, characterized in that: The normal force loading mechanism includes a second hydraulic jack and a normal bearing plate. The normal bearing plate is fixed to the test box, and the second hydraulic jack is arranged between the upper pressing plate and the normal bearing plate.

6. The in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass 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 box. The normal threaded rod is arranged parallel to the up - down direction and passes through the circular hole on the normal bearing plate. The lower end of the normal threaded rod is connected to the upper pressing plate, 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 a second hydraulic jack is arranged between the third nut and the normal bearing plate.

7. The in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass according to claim 1, characterized in that: A groove is made on the upper surface of the lower pressing plate. The axis direction of the groove is parallel to the front - rear direction, and guiding grooves parallel to the front - rear direction are made on the two side walls of the groove; protrusions adapted to the guiding grooves are made on the left and right sides of the upper pressing plate.

8. The in-situ test device for the mechanical properties of the bonding interface between concrete and rock mass according to claim 1 or 7, characterized in that: The low - friction mechanism includes a number of rollers arranged between the upper pressing plate and the lower pressing plate, and the rollers are arranged perpendicular to the front - rear direction.

9. An in-situ test method for the mechanical properties of the bonding interface between concrete and rock mass, characterized in that, Based on the in - situ test device according to any one of claims 1 - 8, conducting a mechanical shear test on the bonding interface between concrete and rock mass, including: 1) Selecting the test position; 2) Casting and curing the concrete test blocks; 3) Fixing the test box to the surface of the rock mass to ensure that the concrete test blocks are located at the middle position inside the test box; 4) Bond the lower platen of the platen mechanism to the upper surface of the concrete specimen using an adhesive, and install the normal force loading mechanism on the test box; 5) Set up a shear force loading mechanism corresponding to the concrete specimen and install it on the test box; 6) Conduct multiple groups of parallel tests; Bond interface shear strength test: i. Apply a normal pressure to apply a certain pressure P1 to the upper surface of the concrete specimen; ii. Apply a pre-shear force; iii. Install monitoring instruments; iv. Apply the shear force. Adopt a method of 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 at each stage of the load; v. Data processing. During the test, the normal stress on the bond interface remains constant, σ1 = P1 / A The shear stress τ on the bonding interface under each level of load i is calculated as follows: τ i = T / A where A is the bond interface area; Taking the shear displacement u as the abscissa and the shear stress τ as the ordinate to plot a curve, the slope of the initial straight-line segment of the curve is the shear stiffness K of the concrete-rock mass bonding interface S [[ID= K S = Δτ / Δu The peak shear stress on the shear stress-shear displacement curve is the shear strength τ of the bonding interface under the normal stress σ1 f1 ; vi. By changing the normal pressure and repeating the test steps from i to v, multiple sets of test results can be obtained, and the normal stress σ corresponding to each set of tests can be obtained respectively. i and the shear strength τ fi , plot the relationship curve between the shear strength τ fi and the normal stress σ i . According to the relationship of τ f = c + σ * tanφ, the cohesion c and friction angle φ of the bonding interface can be obtained.

10. An in-situ test method for the mechanical properties of the bonding interface between concrete and rock mass, characterized in that, Based on the in-situ test device described in any one of claims 1 to 8, conduct a mechanical pull-out test on the bond interface between concrete and rock mass, including: 1) Select the test location; 2) Pour the concrete specimen and cure it; 3) Fix the test box to the rock mass surface to ensure that the concrete specimen is located at the middle position inside the test box; 4) Bond the lower platen of the platen mechanism to the upper surface of the concrete specimen using an adhesive, and install the normal force loading mechanism on the test box; 5) Conduct multiple groups of parallel tests; Bond interface tensile strength test: i. Install monitoring instruments; ii. Apply a pre-normal tensile force; iii. Apply the normal tensile force. Adopt a method of 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 at each stage of the load; iv. Data processing, the tensile stress σ on the bonding interface under each level of load ti is calculated as follows: σ ti = F / A Taking the normal displacement s as the abscissa and the tensile stress σ t as the ordinate to plot a curve, the slope of the initial straight line segment of the curve is the normal stiffness of the concrete-rock mass bonding interface: K n = Δσ t / Δs The peak tensile stress on the tensile stress - normal displacement curve is the tensile strength σ of the bonding interface tf ; v. Repeat the test steps of i to iv to obtain multiple groups of test results, and take the average value of multiple groups of tests as the tensile strength of the bond interface between concrete and rock mass.

Images