A layered rock mass-mortar anchoring interface bonding test and strength prediction method

Abstract

The present application belongs to the technical field of geotechnical engineering, and relates to a layered rock mass-mortar anchoring interface bonding test and strength prediction method, comprising the following steps: obtaining layered rock mass-mortar anchoring interface direct shear test samples corresponding to multiple bedding dip angles under each mortar strength grade; obtaining a data set; constructing a layered rock mass-mortar anchoring interface bonding strength prediction model; obtaining a verified layered rock mass-mortar anchoring interface bonding strength prediction model; and determining the optimal anchoring angle value that maximizes the interface peak bonding strength. The present application can uniformly and quantitatively characterize the combined influence of normal stress, bedding dip angle and material strength on the interface peak bonding-shear strength, describe the nonlinear evolution law of the interface bonding strength with the bedding dip angle, determine the optimal anchoring angle that maximizes the interface peak bonding strength, thereby realizing effective evaluation of the real bearing capacity of the anchoring interface under the condition of the change of the bedding dip angle, and improving the interface bonding strength prediction accuracy and the supporting design reliability.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology and relates to a test method and strength prediction method for the bonding of layered rock mass-mortar anchoring interface. Background Technology

[0002] As transportation and underground engineering construction expands into mountainous and complex geological formations, underground structures often traverse layered rock masses such as carbonaceous slate and shale. These rock masses exhibit significant bedding structures and anisotropic mechanical characteristics. The strength, deformation, and failure modes of the surrounding rock are controlled by the bedding dip angle and the interlayer bonding state. After tunnel excavation, engineering disasters such as surrounding rock spalling, rib spalling, and roof collapse are prone to occur, posing a continuous threat to the stability of the support structure.

[0003] Currently, in engineering projects, a combination of anchor bolts, grouting mortar, and shotcrete is commonly used to control large deformations of the surrounding rock. The layered rock mass and mortar form an anchoring interface in the borehole, which becomes a key structural surface for load transfer and stress coordination. Research on the mechanical behavior of this type of interface is still relatively limited. Most of the relevant results focus on homogeneous rock masses, conventional structural surfaces, or single-material interfaces, forming a structural surface shear strength evaluation system represented by the Barton structural surface shear strength model, which is widely used in the calculation of shear strength of rock mass structural surfaces.

[0004] However, since the existing structural shear strength evaluation system is based on the assumption of homogeneous medium and only covers a few extreme working conditions such as horizontal and vertical bedding, the mechanical response of the mortar anchorage interface of layered rock mass deviates significantly from the actual engineering state. This makes it difficult to effectively evaluate the true bearing capacity of the anchorage interface under the condition of varying bedding dip angle, which reduces the accuracy of interface bond strength prediction and the reliability of support design. Summary of the Invention

[0005] The purpose of this invention is to provide a test and strength prediction method for the bonding interface of layered rock mass-mortar anchorage, which can accurately reflect the true characteristics of the interface mechanical behavior under complex layered structure conditions, and improve the accuracy of interface bonding strength prediction and the reliability of support design.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: A method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface includes the following steps: Layered rock specimens with different bedding dip angles were prepared, and mortar of different strength grades was combined with layered rock specimens with different bedding dip angles to obtain direct shear samples of layered rock mass-mortar anchoring interface with multiple bedding dip angles corresponding to each mortar strength grade. Shear tests were conducted on each specimen under different normal stress conditions to obtain a dataset including the full-process curve of shear stress-shear displacement and peak bond-shear strength under different bedding angles and different mortar strengths. Based on the Barton structural shear strength model, the equivalent wall strength and equivalent friction angle are corrected by bedding dip angle, and an enhancement term reflecting the contribution of mortar strength to bond strength is superimposed to construct a prediction model for the bond strength of the layered rock mass-mortar anchorage interface. The undetermined parameters in the prediction model of the bond strength of the layered rock mass-mortar anchoring interface are determined. The values ​​of the undetermined parameters are obtained by fitting from the dataset. The values ​​of the undetermined parameters are used to verify the prediction model of the bond strength of the layered rock mass-mortar anchoring interface, and the verified prediction model of the bond strength of the layered rock mass-mortar anchoring interface is obtained. Extreme value analysis was performed based on the validated layered rock mass-mortar anchorage interface bond strength prediction model to determine the optimal anchorage angle value that maximizes the interface peak bond strength.

[0007] The invention is further characterized by: When preparing layered rock specimens with different bedding dip angles, a modular mold is used to first prefabricate a matrix slab, and then a soft cementing material is used to bond multiple matrix slabs together to form a layered rock mass module with an alternating matrix layer and joint layer structure. Finally, the layered rock mass module is cut and cored vertically to obtain layered rock specimens with different bedding dip angles.

[0008] The different bedding angles are multiple angle values ​​within the range of 0° to 90°, the different strength grades of mortar are multiple grades within the range of M10 to M20, and the different normal stresses are multiple stress values ​​within the range of 0.5MPa to 2MPa.

[0009] The prediction model for the bond strength at the layered rock mass-mortar anchoring interface is as follows: , In the formula, τ p The interfacial peak bond-shear strength, σ n For normal stress, ϕ i ( β The effective friction angle is related to the bedding dip angle. JRC 0 represents the basic roughness coefficient of the interface. JRS eq ( β The equivalent wall strength considering the effect of bedding dip angle, m This represents the strengthening coefficient of mortar strength on interfacial bond strength. σ b This represents the uniaxial compressive strength of the mortar under actual working conditions. σ b0 As a reference mortar strength, β The bedding dip angle, ϕ 0 is the inherent friction angle of the interface.n This is the nonlinear adjustment exponent of the bedding dip angle on the friction angle. A and B These are all correction factors for the equivalent friction angle based on the bedding dip angle. K ( β ) represents the strength weighting coefficient related to the bedding dip angle. JCS a ( β () represents the compressive strength of the sidewall of the layered rock mass. JCS b It represents the compressive strength of the wall surface on the mortar side.

[0010] The undetermined parameters in the prediction model for the bond strength of the layered rock mass-mortar anchoring interface include the correction coefficient of the bedding dip angle to the equivalent friction angle, the nonlinear adjustment index of the bedding dip angle to the friction angle, the strength weighting coefficient related to the bedding dip angle, the wall compressive strength of the layered rock mass side, the interface foundation roughness coefficient, and the strengthening coefficient of the mortar strength to the interface bond strength.

[0011] When fitting the dataset to obtain the values ​​of the undetermined parameters, the least squares method is used to fit the dataset to obtain the values ​​of the undetermined parameters.

[0012] When determining the optimal anchoring angle value that maximizes the peak bond strength at the interface, an extreme value analysis is performed on the verified layered rock mass-mortar anchoring interface bond strength prediction model to obtain the optimal anchoring angle value that maximizes the peak bond strength at the interface.

[0013] This also includes: using the validated layered rock mass-mortar anchorage interface bond strength prediction model to obtain the interface bond strength corresponding to different bedding dip angles, screening out the interface bond strength corresponding to the preset bedding dip angle interval, and determining the anchorage length by combining the distribution law of the interface bond strength corresponding to the preset bedding dip angle interval.

[0014] The preset bedding dip angle range is [60°, 90°].

[0015] The method for testing and predicting the bond strength at the layered rock mass-mortar anchoring interface of the present invention has the following advantages: This invention systematically considers the bonding characteristics of the anchorage interface under the coupled effects of multiple factors such as bedding angle, normal stress, and mortar strength. By preparing direct shear specimens covering different combinations of bedding angle and mortar strength and conducting systematic shear tests, it comprehensively obtains full-process data on the interface bonding-shear behavior. Based on this, a bonding strength prediction model integrating bedding angle correction and mortar strength enhancement terms is constructed. This model can uniformly and quantitatively characterize the combined influence of normal stress, bedding angle, and material strength on the interface peak bonding-shear strength, accurately describe the nonlinear evolution law of interface bonding strength with bedding angle, and determine the optimal anchorage angle that maximizes the interface peak bonding strength. Thus, it enables effective assessment of the true bearing capacity of the anchorage interface under varying bedding angle conditions, improving the prediction accuracy of interface bonding strength and the reliability of support design. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall process of the present invention.

[0017] Figure 2 This is a top view of the mold structure in this invention.

[0018] Figure 3 This is a schematic diagram of the side plate structure of the mold in this invention.

[0019] Figure 4 This is a schematic diagram of the insert plate structure of the mold in this invention.

[0020] Figure 5 This is a schematic diagram of layered rock specimens with different bedding angles in this invention.

[0021] Figure 6 This is a schematic diagram of a direct shear test sample of the layered rock mass-mortar anchorage interface corresponding to multiple bedding dip angles under various mortar strength grades in this invention.

[0022] Figure 7 (a) shows the original support scheme, and (b) shows the optimized support scheme.

[0023] Figure 8 (a) shows the numerical simulation results of the surrounding rock displacement under the unsupported state, (b) shows the numerical simulation results of the surrounding rock displacement under the original support scheme, and (c) shows the numerical simulation results of the surrounding rock displacement under the optimized support scheme. Detailed Implementation

[0024] The technical solutions of the present invention will now be described clearly and in detail with reference to the accompanying drawings. In the description of the embodiments of the present invention, unless otherwise stated, " / " indicates "or," for example, A / B can mean A or B. "And / or" in the text 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 alone, A and B simultaneously, and B alone. Furthermore, in the description of the embodiments of the present invention, "multiple" refers to two or more. The terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0025] like Figure 1 As shown, this invention provides a method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface, comprising the following steps: Layered rock specimens with different bedding dip angles were prepared, and mortar of different strength grades was combined with layered rock specimens with different bedding dip angles to obtain direct shear samples of layered rock mass-mortar anchoring interface corresponding to multiple bedding dip angles under each mortar strength grade.

[0026] Shear tests were conducted on each specimen under different normal stress conditions to obtain a dataset including the full-process curves of shear stress-shear displacement and peak bond-shear strength under different bedding angles and mortar strengths.

[0027] Based on the Barton structural shear strength model, the equivalent wall strength and equivalent friction angle are corrected by bedding dip angle, and an enhancement term reflecting the contribution of mortar strength to bond strength is superimposed to construct a predictive model for the bond strength of the layered rock mass-mortar anchorage interface.

[0028] The undetermined parameters in the prediction model of the bond strength of the layered rock mass-mortar anchoring interface are determined. The values ​​of the undetermined parameters are obtained by fitting from the dataset. The prediction model of the bond strength of the layered rock mass-mortar anchoring interface is verified using the values ​​of the undetermined parameters, and the verified prediction model of the bond strength of the layered rock mass-mortar anchoring interface is obtained.

[0029] Extreme value analysis was performed based on the validated layered rock mass-mortar anchorage interface bond strength prediction model to determine the optimal anchorage angle value that maximizes the interface peak bond strength.

[0030] In summary, this invention systematically considers the bonding characteristics of the anchorage interface under the coupled effects of multiple factors such as bedding angle, normal stress, and mortar strength. By preparing direct shear specimens covering different combinations of bedding angle and mortar strength and conducting systematic shear tests, it comprehensively obtains full-process data on the interface bonding-shear behavior. Based on this, a bonding strength prediction model integrating bedding angle correction and mortar strength enhancement is constructed. This model can uniformly and quantitatively characterize the combined influence of normal stress, bedding angle, and material strength on the interface peak bonding-shear strength, accurately describe the nonlinear evolution law of interface bonding strength with bedding angle, and determine the optimal anchorage angle that maximizes the interface peak bonding strength. Thus, it enables effective assessment of the true bearing capacity of the anchorage interface under varying bedding angle conditions, improving the prediction accuracy of interface bonding strength and the reliability of support design.

[0031] In the preparation of layered rock-like specimens with different bedding dip angles, a modular mold is used to prefabricate a matrix slab. Then, a soft cementing material is used to bond multiple matrix slabs together to form a layered rock mass module with an alternating matrix layer and joint layer structure. Finally, the layered rock mass module is cut and cored vertically to obtain layered rock-like specimens with different bedding dip angles. The modular mold prefabrication of matrix slabs and layer-by-layer bonding can precisely control the bedding dip angle, the thickness ratio of the matrix layer and joint layer, and the interlayer bonding state, thus realizing the parametric and standardized preparation of layered rock mass specimens.

[0032] like Figure 2 , Figure 3 , Figure 4 As shown, the modular mold consists of a base plate, two side plates, and multiple insert plates. The two side plates are respectively located on both sides of the base plate, and the multiple insert plates are located between the two side plates. The multiple insert plates are evenly arranged along the length of the two side plates. Positioning grooves are formed on the opposite surfaces of the two side plates near each insert plate along their width direction. The two ends of each insert plate are located in the two positioning grooves respectively. The base plate is 670mm long and 220mm wide. Each side plate is 650mm long. The distance between the two side plates is 170mm. The width of each positioning groove is 10mm. The distance between two adjacent positioning grooves is 9mm. The distance between the outermost positioning groove and the end of the corresponding side plate is 35mm. Each insert plate is 178mm long and 10mm wide, that is, the depth of the positioning groove is 8mm. The two side plates are made of high-strength aluminum alloy material, and the base plate and insert plates are made of POM engineering plastic.

[0033] Among them, the different bedding dip angles are multiple angle values ​​in the range of 0° to 90°, preferably 0°, 30°, 45°, 60° and 90°; the different strength grades of mortar are multiple grades in the range of M10 to M20, preferably 10MPa, 15MPa and 20MPa; and the different normal stresses are multiple stress values ​​in the range of 0.5MPa to 2MPa, preferably 0.5MPa, 1MPa and 2MPa.

[0034] like Figure 5 , Figure 6 As shown, the precast matrix slab uses PC42.5 composite silicate cement as the binder, 40-70 mesh quartz sand as the aggregate, and calcined gypsum powder as the modifier. The preferred mass ratio is water:cement:quartz sand:calcined gypsum powder = 6:10:5:2. The specific steps for preparing layered rock-like specimens with different bedding dip angles are as follows: The matrix material was weighed and mixed strictly according to the mixing ratio, then injected between multiple insert plates spaced 9mm apart. It was compacted using a vibrating table, allowed to stand for 24 hours, and then demolded to obtain a 9mm thick matrix slab. This slab was then cured for 7 days. The surface of the cured matrix slab was roughened and wiped until saturated and dry, then immersed in a soft cementitious grout and stacked sequentially. By controlling the total height of every 15 layers to 150mm, the joint thickness of each layer was indirectly ensured to be approximately 1mm, forming a layered structure of "9mm matrix + 1mm joint". After standing for 24 hours, it was cured for 28 days. The cured layered rock mass module was then cut to obtain... Figure 5 The images shown are layered rock-like structures with different bedding angles, measuring 100mm × 100mm × 100mm. Figure 5 From left to right, the rock formations are layered rock at angles of 0°, 30°, 45°, 60°, and 90°. These layered rock formations with different bedding angles are fixed below a water-cooled core drill, and cylindrical cores with a diameter of 50mm are drilled. The angle between the axis and the bedding plane is the required test angle. The end faces are ground smooth to obtain the desired result. Figure 6 The specimens shown are layered rock samples with different bedding dip angles, measuring 100mm×100mm×50mm.

[0035] For the weak cementing material, PC32.5 composite silicate cement with added fly ash was selected. The preferred mix ratio was water:cement:fly ash = 7:9:1, used to simulate weak cemented joint surfaces. Three different strength grades of mortar (M10, M15, M20) were designed. For example, the mix ratio for M15 mortar was cement:sand:water = 1:6.2:1.21.

[0036] The specific steps for combining mortars of different strength grades with layered rock specimens with different bedding angles are as follows: The prepared 100mm×100mm×50mm layered rock specimens with different bedding angles were placed on one side of the mold. A well-mixed mortar was poured into the other side of the mold and compacted to ensure close contact between the mortar and the rock interface. The specimens were demolded 24 hours after molding and placed in a standard curing room for 28 days. After curing, the observation surfaces of the specimens were finely polished using a double-end grinder to meet the requirements for DIC observation.

[0037] In the shear test of each sample under different normal stress conditions, the TAW-1000 microcomputer-controlled high-temperature rock direct shear apparatus from Jinan Mineral Testing Instruments Co., Ltd. was used. Combined with the VIC-2D digital image correlation (DIC) acquisition system, the direct shear apparatus provides high-precision constant normal load (6kN~300kN) and displacement-controlled shear (0.001mm / min~50mm / min). The DIC system realizes the full-process observation of the surface deformation field during the shear process.

[0038] In this study, based on the Barton structural shear strength model, when correcting the equivalent wall strength and equivalent friction angle for the bedding dip angle, a weighted average of the wall strengths on both sides is adopted, considering the strength differences between the materials on both sides of the heterogeneous interface and the influence of the bedding dip angle on the rock mass side strength. An anisotropic function of the uniaxial compressive strength of the layered rock mass as a function of the bedding dip angle is also introduced. Simultaneously, the internal friction angle of the interface varies with the bedding dip angle, exhibiting a maximum at 45° and minimums at 0° and 90°. The internal friction angle is constructed as a function of the bedding dip angle. Substituting the corrected equivalent wall strength and equivalent friction angle into the Barton formula yields the corrected Barton friction strength.

[0039] When superimposing the strengthening term reflecting the contribution of mortar strength to bond strength, considering the positive correlation between mortar strength improvement and the weakening effect of the increase in peak shear strength at the interface, a logarithmic function is used to characterize the bond strengthening effect.

[0040] The prediction model for the bond strength at the layered rock mass-mortar anchoring interface is as follows: .

[0041] In the formula, τ p The interfacial peak bond-shear strength, σ n For normal stress, ϕ i ( β The effective friction angle is related to the bedding dip angle. JRC 0 represents the basic roughness coefficient of the interface. JRS eq ( β The equivalent wall strength considering the effect of bedding dip angle, mThis represents the strengthening coefficient of mortar strength on interfacial bond strength. σ b This represents the uniaxial compressive strength of the mortar under actual working conditions. σ b0 As a reference mortar strength, β The bedding dip angle, ϕ 0 is the inherent friction angle of the interface. n This is the nonlinear adjustment exponent of the bedding dip angle on the friction angle. A and B These are all correction factors for the equivalent friction angle based on the bedding dip angle. K ( β ) represents the strength weighting coefficient related to the bedding dip angle. JCS a ( β () represents the compressive strength of the sidewall of the layered rock mass. JCS b It represents the compressive strength of the wall surface on the mortar side.

[0042] Among them, the undetermined parameters in the prediction model of the bond strength of the layered rock mass-mortar anchoring interface include the correction coefficient of the bedding dip angle to the equivalent friction angle, the nonlinear adjustment index of the bedding dip angle to the friction angle, the strength weighting coefficient related to the bedding dip angle, the wall compressive strength of the layered rock mass side, the interface foundation roughness coefficient, and the strengthening coefficient of the mortar strength to the interface bond strength.

[0043] When fitting the values ​​of the undetermined parameters from the dataset, the least squares method is used to fit the dataset to obtain the values ​​of the undetermined parameters.

[0044] Specifically, the extreme value analysis involves using the bedding dip angle... β Using this as the independent variable, we substitute it into the validated prediction model for the bond strength of the layered rock mass-mortar anchorage interface to obtain the peak bond-shear strength at the interface. τ p With bedding angle β Given a single-variable function that changes; find the first derivative of this function and set the derivative to zero, then solve for the extreme points. β Value, that β The value is the value that makes the interfacial peak bond-shear strength... τ p To achieve the maximum optimal bedding dip angle, the optimal anchorage angle value is determined.

[0045] This invention provides a method for testing and predicting the bond strength of layered rock mass-mortar anchorage interfaces. The method further includes: using a validated layered rock mass-mortar anchorage interface bond strength prediction model to obtain the interface bond strength corresponding to different bedding dip angles; screening out interface bond strengths lower than those corresponding to preset bedding dip angle intervals; and determining the anchorage length based on the distribution pattern of interface bond strengths within the preset bedding dip angle intervals. Specifically: Under the condition that other parameters are the same, for the high-strength section (interfacial peak bond-shear strength) τ p High) and low strength sections (interfacial peak bond-shear strength) τ p (For lower anchorages) Different anchorage lengths need to be calculated, and the matching anchorage lengths should be calculated separately for each. The anchorage length is determined by the following formula: N d ≤(τ p1 / K)·π·D·L a ·ψ.

[0046] In the formula, N d L is the design value of the axial tensile force of the anchor bolt or unit anchor bolt. a τ is the length of the anchorage section. p1 The standard value of the ultimate bond strength between the grout in the anchoring section and the stratum can be determined by test. D is the diameter of the borehole in the anchoring section of the anchor bolt, K is the safety factor for the pull-out resistance of the bond between the grout in the anchoring section and the stratum, and ψ is the influence coefficient of the anchoring section length on the ultimate bond strength.

[0047] Based on the analysis results of the verified prediction model of the bond strength of the layered rock mass-mortar anchoring interface, it can be concluded that when the anchoring angle and the dip angle of the surrounding rock bedding are in the range of [60°, 90°], the distribution law of the interface bond strength is that the overall shear strength of the anchoring interface is the lowest. Therefore, in this range, the anchoring length is increased to effectively improve the overall anchoring stability of the layered surrounding rock.

[0048] Furthermore, in locations with low bond strength, the insufficient bond performance of the anchoring interface itself can be compensated by increasing the anchor diameter or optimizing the thread shape on the anchor surface, such as increasing the height of the helical ribs or adjusting the pitch parameters.

[0049] Furthermore, in areas with low bond strength, local grouting is carried out using high-grade special mortar or fiber-modified mortar, which effectively improves the bonding ability of the mortar material in weak areas and directly enhances the bond strengthening contribution of the mortar at that location to the anchorage interface.

[0050] The preset bedding dip angle range is [60°, 90°]. The interfacial bond strength is approximately symmetrically distributed with the bedding dip angle. The interfacial bond strength reaches its peak when the bedding dip angle is 45°. When the bedding dip angle is [0°, 30°] and [60°, 90°], the corresponding interfacial bond strength is at a low level. However, in the layered rock mass, the anchoring reinforcement effect is not obvious in the area where the angle between the anchor and the bedding is small ([0°, 30°]). Therefore, the preset bedding dip angle range corresponding to the interfacial bond strength is set to [60°, 90°], which is taken as the key reinforcement range.

[0051] Example 1 Based on the differences in interfacial bond strength across different bedding dip angles, this invention optimizes parameters such as anchor length, anchor diameter, and grouting intensity. This invention achieves a non-uniform anchor design for layered surrounding rock based on the distribution of interfacial bond strength along the path. To verify the effectiveness of this non-uniform anchor design for layered surrounding rock based on the distribution of interfacial bond strength along the path, a layered rock tunnel project was used as a case study. The original support scheme and the optimized support scheme based on the non-uniform anchor design of this invention were compared. The numerical simulation comparison results are as follows: Figure 7 , Figure 8 As shown.

[0052] Figure 7 Here are schematic diagrams of the anchor bolt arrangement for two support schemes: Figure 7 (a) is the original support scheme, which adopts a uniform and equal-length anchor bolt arrangement, with the anchor bolt length, diameter and grouting intensity all being consistent; Figure 7 (b) To achieve the optimized support scheme obtained by using the non-uniform anchor design of the present invention, targeted reinforcement support is achieved for the weak interface bonding strength area in the bedding dip angle range [60°, 90°] by increasing the anchor length, optimizing the rod structure parameters, and using high-strength modified mortar for local grouting.

[0053] Figure 8 The numerical simulation results of surrounding rock displacement under different working conditions are shown. The displacement U is expressed in meters (m). The more red the color, the greater the displacement. Figure 8 (a) is in an unsupported state, with significant displacement of the surrounding rock around the tunnel, with a maximum displacement of 0.77m, and obvious development of cracks in the surrounding rock, resulting in extremely poor stability; Figure 8 (b) is the original support scheme, in which the displacement is controlled to a certain extent, with a maximum displacement of about 0.34m, but there is still a large deformation in the weak area; Figure 8 (c) The optimized support scheme obtained by adopting the non-uniform anchor design of the present invention significantly reduces the overall displacement of the surrounding rock, with the maximum displacement being only 0.11m. The crack propagation is effectively suppressed, and the support effect is significantly improved.

[0054] As can be seen from the comparison, the non-uniform anchor design method proposed in this invention can achieve differentiated support based on the distribution characteristics of the interface bond strength along the path. This effectively controls the deformation and crack propagation of the layered surrounding rock, avoids the material waste of traditional uniform support, and achieves a balance between stability and economy.

[0055] The method for testing and predicting the bond strength at the layered rock mass-mortar anchoring interface according to the present invention has the following other advantages: First, this invention proposes a systematic test method for the layered rock mass-mortar anchoring interface, which can comprehensively consider multiple coupling factors such as normal stress, mortar strength and bedding dip angle, and obtain more comprehensive and accurate data on the bonding characteristics of the anchoring interface under complex geological conditions.

[0056] Second, this invention constructs a bond strength prediction model based on the classic Barton theory, which is modified and extended. This model successfully introduces the equivalent wall strength and equivalent friction angle terms modulated by the bedding angle, and superimposes the mortar strength additional strengthening term, realizing the multi-factor coupled prediction of the bond strength of the anchorage interface, filling the gap of existing models in this field.

[0057] Third, this invention, combined with DIC technology, intuitively reveals the crack evolution path and failure mode (pure interface slip, interface-matrix composite tensile shear, interface-internal joint surface slip) of the anchoring interface during the shearing process, deepening the understanding of the interaction mechanism between layered surrounding rock and anchoring structure.

[0058] Fourth, this invention has important engineering guiding significance and academic reference value for clarifying the interaction mechanism between layered surrounding rock and anchored support structure, improving the design theory of underground engineering (especially tunnel anchored support) under complex geological conditions, and enhancing the pertinence and reliability of support system.

[0059] Fifth, this invention can stably prepare rock-like structures with controllable bedding, ensuring the reliability of the experimental results; while retaining the classical theoretical framework, the model improves the prediction accuracy and applicability by introducing innovative correction terms.

[0060] Sixth, this invention realizes the design of non-uniform anchor bolts for layered surrounding rock based on the distribution of interfacial bond strength along the path. It can optimize parameters such as anchor length, anchor bolt diameter and grouting intensity according to the differences in interfacial bond strength in different bedding dip angle ranges, avoiding the drawbacks of the "one-size-fits-all" approach in traditional uniform anchor bolt design, and achieving differentiated and precise support. This effectively ensures the stability of anchor bolts in layered surrounding rock, while reasonably controlling support costs and improving the scientific and economical nature of anchor bolt design.

[0061] It is understood that this invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this invention are within the protection scope of this invention.

Claims

1. A method for testing and predicting the bond strength at the layered rock mass-mortar anchoring interface, characterized in that, Includes the following steps: Layered rock specimens with different bedding dip angles were prepared, and mortar of different strength grades was combined with layered rock specimens with different bedding dip angles to obtain direct shear samples of layered rock mass-mortar anchoring interface with multiple bedding dip angles corresponding to each mortar strength grade. Shear tests were conducted on each specimen under different normal stress conditions to obtain a dataset including the full-process curve of shear stress-shear displacement and peak bond-shear strength under different bedding angles and different mortar strengths. Based on the Barton structural shear strength model, the equivalent wall strength and equivalent friction angle are corrected by bedding dip angle, and an enhancement term reflecting the contribution of mortar strength to bond strength is superimposed to construct a prediction model for the bond strength of the layered rock mass-mortar anchorage interface. The undetermined parameters in the prediction model of the bond strength of the layered rock mass-mortar anchoring interface are determined. The values ​​of the undetermined parameters are obtained by fitting from the dataset. The values ​​of the undetermined parameters are used to verify the prediction model of the bond strength of the layered rock mass-mortar anchoring interface, and the verified prediction model of the bond strength of the layered rock mass-mortar anchoring interface is obtained. Extreme value analysis was performed based on the validated layered rock mass-mortar anchorage interface bond strength prediction model to determine the optimal anchorage angle value that maximizes the interface peak bond strength.

2. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 1, characterized in that, When preparing layered rock-like specimens with different bedding dip angles, a modular mold is used to first prefabricate a matrix slab, and then a soft cementing material is used to bond multiple matrix slabs together to form a layered rock mass module with an alternating matrix layer and joint layer structure. Finally, the layered rock mass module is cut and cored vertically to obtain layered rock-like specimens with different bedding dip angles.

3. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 1, characterized in that, The different bedding angles are multiple angle values ​​within the range of 0° to 90°, the different strength grades of mortar are multiple grades within the range of M10 to M20, and the different normal stresses are multiple stress values ​​within the range of 0.5MPa to 2MPa.

4. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 1, characterized in that, The prediction model for the bond strength at the layered rock mass-mortar anchoring interface is as follows: ， In the formula, τ p The interfacial peak bond-shear strength, σ n For normal stress, ϕ i ( β The effective friction angle is related to the bedding dip angle. JRC 0 represents the basic roughness coefficient of the interface. JRS eq ( β The equivalent wall strength considering the effect of bedding dip angle, m This represents the strengthening coefficient of mortar strength on interfacial bond strength. σ b This represents the uniaxial compressive strength of the mortar under actual working conditions. σ b0 As a reference mortar strength, β The bedding dip angle, ϕ 0 is the inherent friction angle of the interface. n This is the nonlinear adjustment exponent of the bedding dip angle on the friction angle. A and B These are all correction factors for the equivalent friction angle based on the bedding dip angle. K ( β ) represents the strength weighting coefficient related to the bedding dip angle. JCS a ( β () represents the compressive strength of the sidewall of the layered rock mass. JCS b It represents the compressive strength of the wall surface on the mortar side.

5. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 4, characterized in that, The undetermined parameters in the layered rock mass-mortar anchoring interface bond strength prediction model include the correction coefficient of bedding dip angle to equivalent friction angle, the nonlinear adjustment index of bedding dip angle to friction angle, the strength weighting coefficient related to bedding dip angle, the wall compressive strength of the layered rock mass side, the interface foundation roughness coefficient, and the strengthening coefficient of mortar strength to interface bond strength.

6. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 1, characterized in that, When fitting the dataset to obtain the values ​​of the undetermined parameters, the least squares method is used to fit the dataset to obtain the values ​​of the undetermined parameters.

7. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 1, characterized in that, It also includes: using the validated layered rock mass-mortar anchorage interface bond strength prediction model to obtain the interface bond strength corresponding to different bedding dip angles, screening out the interface bond strength corresponding to the preset bedding dip angle interval, and determining the anchorage length by combining the distribution law of the interface bond strength corresponding to the preset bedding dip angle interval.

8. The method for testing and predicting the bond strength of layered rock mass-mortar anchoring interface according to claim 7, characterized in that, The preset bedding angle range is [60°, 90°].

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