Sludge geology inclined anchor rod detection method

Abstract

The invention provides a sludge geology inclined anchor rod detection method, and belongs to the technical field of civil construction, the method comprises the following steps: welding I-shaped steel to form a base and a high stand column, then welding an inclined beam forming a 45-degree angle with the base and an end plate with an opening, and ensuring that the drawing direction is consistent with the embedding direction of an anchor rod; sleeving the hollow self-resetting hydraulic cylinder into the anchor rod and placing the hollow self-resetting hydraulic cylinder on the end plate, applying a pulling force by utilizing a hydraulic oil pump, and analyzing actually measured data by adopting an anchor rod drawing mechanical equation set; loading to a design load step by step according to a recovery deviation degree measurement standard, continuously increasing to 1.5 times of the design load after keeping stable, and monitoring the displacement of the anchor rod in the whole process; when the displacement exceeds a critical value or reaches a limit value, recording the maximum drawing force, and calculating a sludge rigidity coefficient; and finally, analyzing the data and issuing a detection report. The technical problem that the detection result is inaccurate due to inaccurate control of the pulling detection direction of the inclined anchor rod is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of civil engineering construction, and more specifically, relates to a method for detecting inclined anchor bolts in silt geological conditions. Background Art

[0002] In geotechnical engineering, underground engineering, and slope reinforcement engineering, anchor bolts, as important support and reinforcement structures, are closely related to engineering safety. Traditional anchor bolt pull-out tests mainly target vertical anchor bolts, and a pull-out instrument is used to apply a vertical upward pulling force to measure the bond strength and ultimate pull-out force between the anchor bolt and the anchor body. This method has formed a relatively mature test system in practical engineering applications and provides an important basis for engineering quality assessment.

[0003] However, when inclined anchor bolts are used in engineering, the traditional pull-out test method has obvious defects. Since it is difficult to keep the pull-out direction of the inclined anchor bolt consistent with the axis of the anchor bolt, problems such as eccentric pull-out and unstable direction often occur during the test, resulting in additional bending stress and shear stress on the anchor bolt. This not only causes deviation in the measurement results but also may damage the anchor bolt. Especially in silt geological conditions, due to the soft foundation and poor stability of the support system, the difficulty of controlling the pull-out direction is further exacerbated.

[0004] Currently, there is a lack of a precise pull-out test method specifically for inclined anchor bolts in silt geological conditions in engineering practice. The existing temporarily built scaffolds or simple pull-out devices are difficult to ensure that the pull-out force is completely consistent with the axis of the anchor bolt, and the accuracy and reliability of the test results cannot meet the engineering requirements. How to precisely control the pull-out direction of inclined anchor bolts under soft foundation conditions to ensure that the test results truly reflect the bearing capacity of the anchor bolts has become a technical problem that needs to be solved urgently. That is to say, there is a technical problem in the prior art that inaccurate control of the pull-out test direction of inclined anchor bolts leads to inaccurate test results. Summary of the Invention

[0005] In view of this, the present invention provides a method for detecting inclined anchor bolts in silt geological conditions, which can solve the technical problem in the prior art that inaccurate control of the pull-out test direction of inclined anchor bolts leads to inaccurate test results.

[0006] The present invention is implemented as follows: The present invention provides a method for detecting inclined anchor rods in silt geological conditions, which includes: establishing a rigid support structure for anchor rod pulling, including a base, a column, and an inclined beam at a 45-degree angle to the base, with an open end plate provided at the end of the inclined beam; passing the anchor rod through the opening of the end plate along the inclined beam from the base, determining the deflection index of the anchor rod pulling direction to ensure that the pulling direction is consistent with the embedding direction of the anchor rod; sleeving a hollow self-resetting hydraulic cylinder onto the anchor rod and positioning it at the end plate, adjusting the axis of the hydraulic cylinder to coincide with the axis of the anchor rod to ensure that the pulling force is applied along the axial direction of the anchor rod; applying hydraulic oil to the hydraulic cylinder using a hydraulic oil pump, establishing a monitoring system for the anchor rod pulling jump index, and using the mechanical equations for anchor rod pulling to fit and optimize the measured data to form an accurate force-displacement curve; gradually increasing the pulling force to the design load value according to the determination standard of the recovery deviation degree; continuing to increase the pulling force to 1.5 times the design load, and recording the displacement of the anchor rod; when the displacement of the anchor rod exceeds the critical value, recording the maximum pulling force value and calculating the rigidity coefficient of the anchor solid in silt; after the detection is completed, issuing an anchor rod pulling detection report.

[0007] Among them, specifically establishing the rigid support structure for anchor rod pulling is as follows: Four No. 25 I-beams are welded to form the base, the size of the base is 1700×1700 mm, two No. 25 I-beam columns are welded, and the height of the columns is 1346 mm; Two No. 25 I-beams are welded obliquely from the base as the inclined beam, the inclined beam forms a 45-degree angle with the base, the inclined beam rests on two steel columns, and a 30-mm-thick end plate is welded at the end of the inclined beam, and an opening of 50×50 mm is provided at the end plate.

[0008] Among them, the deflection index of the anchor rod pulling direction refers to the angle deviation coefficient between the anchor rod pulling direction and the embedding axis of the anchor rod. In an ideal state, the deflection index of the anchor rod pulling direction is zero, indicating that the pulling direction coincides completely with the axis of the anchor rod, avoiding the generation of shear stress and affecting the accuracy of the detection results; The recovery deviation degree refers to the degree of displacement recovery of the anchor rod when unloading after bearing a certain load. The calculation method is the ratio of the residual displacement after unloading to the maximum displacement. The smaller the recovery deviation degree, the closer the combination of the anchor rod and the silt geological condition, and the better the anchoring effect.

[0009] Among them, the anchor rod pulling jump index refers to the non-linear relationship parameter between the displacement and the pulling force change of the anchor rod during the pulling process, which is used to describe the critical point where the displacement of the anchor rod suddenly increases during the loading process. The change of the anchor rod pulling jump index reflects the bonding strength between the anchor solid and the surrounding silt medium.

[0010] Among them, the rigidity coefficient of silt refers to the deformation resistance ability of the silt geological condition under the action of the pulling force, which is related to the water content, density, and cohesion of the silt. The larger the rigidity coefficient of the silt, the greater the anchoring resistance provided by the silt geological condition, and the stronger the anti-pulling ability of the anchor rod.

[0011] Among them, the mechanical equations for bolt pull - out include a tensile force transfer equation, a displacement prediction equation, a deformation response equation, and a critical state equation.

[0012] Among them, the tensile force transfer equation is used to calculate the force distribution of each cross - section of the bolt. The inputs include the bolt diameter, the elastic modulus of the bolt material, the silt friction coefficient, the bolt embedding depth, and the applied tensile force value, and the output is the force distribution function of each point along the bolt axis.

[0013] Among them, the displacement prediction equation is used to predict the displacement of the bolt under different tensile forces. The inputs include the elastic modulus of the bolt material, the cross - sectional area of the bolt, the effective length of the bolt, the silt rigidity coefficient, and the applied tensile force value, and the output is the theoretical displacement.

[0014] Among them, the deformation response equation is used to describe the interaction relationship between the bolt and the surrounding silt medium. The inputs include the surface roughness of the bolt, the silt cohesion, the bolt embedding angle, the length of the anchorage zone, and the groundwater level height, and the output is the stress distribution at the interface of the anchor body.

[0015] Among them, the critical state equation is used to judge the stability change during the bolt pull - out process. The inputs include the applied tensile force value, the bolt displacement, the displacement increment, the tensile force increment, and the time increment, and the output is the bolt pull - out jump index value.

[0016] Through designing an I - beam support structure and an inclined beam guiding device, and combining with the mathematical model analysis of the mechanical equations for bolt pull - out, the present invention realizes the precise control of the inclined bolt pull - out direction and the scientific evaluation of the detection data. This method adopts a rigid support structure and an inclined beam guiding structure to ensure that the pull - out direction is consistent with the bolt embedding axis, effectively avoiding the detection error caused by eccentric pull - out.

[0017] Compared with the traditional technology, the present invention solves the problem that the inclined bolt pull - out direction is not easy to control. By obliquely welding an I - beam inclined beam on the support base and using the opening on the end plate of the inclined beam to guide the bolt, the precise control of the pull - out direction is realized; at the same time, by setting the hollow self - reset hydraulic cylinder to coincide with the bolt axis, it is ensured that the tensile force is applied along the bolt axis, eliminating the influence of eccentric tensile stress on the detection result. In addition, introducing the mechanical equations for bolt pull - out to conduct mathematical processing on the detection data improves the scientificity and reliability of the detection result.

[0018] The fundamental reason for the present invention to solve the core technical problem is as follows: on the one hand, an inclined support system matching the bolt embedding angle is designed from the mechanical structure to ensure the consistency between the direction of the pulling force and the bolt axis; on the other hand, a complete mechanical model is established from the theoretical analysis, which can accurately evaluate the true stress state of the bolt in the silt geology. This method combining structural design and theoretical analysis fundamentally solves the technical problem of inaccurate control of the inclined bolt pull - out detection direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flowchart of the method of the present invention.

[0020] Figure 2 This is a schematic diagram of the rigid support structure for bolt pull-out in Example 2.

[0021] Figure 3 This is a schematic diagram of the bolt placement position in Example 2.

[0022] Figure 4 This is a practical usage diagram of the rigid support structure for bolt pull-out and the bolt in Example 2. Detailed implementation manners

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0024] As Figure 1 shown, this is a flowchart of a method for detecting inclined bolts in silt geology provided by the present invention. This method includes the following steps:

[0025] S01. Establish a rigid support structure for bolt pull-out according to the silt geological characteristics. Use four No. 25 I-beams to weld into a base, the size of the base is 1700×1700 mm, weld two No. 25 I-beam columns, and the height of the columns is 1346 mm;

[0026] S02. Weld two No. 25 I-beams obliquely from the base as inclined beams. The inclined beams form a 45-degree angle with the base and rest on the two steel columns. Weld end plates with a thickness of 30 mm at the ends of the inclined beams, and openings of 50×50 mm are opened at the end plates;

[0027] S03. Determine the deflection index of the bolt pull-out direction, and make the bolt pass through the end plate opening along the two inclined beams from the base, ensuring that the pull-out direction is consistent with the bolt embedding direction to reduce the eccentric tensile stress;

[0028] S04. Sleeve the hollow self-resetting hydraulic cylinder onto the bolt and automatically position it at the end plate. Adjust the axis of the hydraulic cylinder to coincide with the axis of the bolt to ensure that the pulling force is applied along the axial direction of the bolt;

[0029] S05. Use a hydraulic oil pump to apply hydraulic oil to the hydraulic cylinder, establish a monitoring system for the bolt pull-out jump index, record the relationship between the pressure gauge reading and the bolt displacement, use the bolt pull-out mechanical equations to fit and optimize the measured data, form an accurate force-displacement curve, and calculate the critical state parameters of the bolt in real time;

[0030] S06. According to the restoration deviation measurement standard, gradually increase the pulling force to the design load value, keep the load stable for no less than 5 minutes, and observe whether there is any obvious displacement of the anchor rod;

[0031] S07. If there is no obvious displacement of the anchor rod, continue to increase the pulling force to 1.5 times the design load, keep the load stable for no less than 15 minutes, and record the displacement of the anchor rod;

[0032] S08. When the displacement of the anchor rod exceeds the critical value or the pulling force reaches the design limit value, record the maximum pulling force value, calculate the rigidity coefficient of the anchor solid in the silt, and evaluate the pull-out resistance of the anchor rod in the silt geology;

[0033] S09. After the detection is completed, slowly unload and remove the detection device, analyze and process the detection data, and issue an anchor rod pull-out detection report.

[0034] The anchor rod pull-out mechanical equations include a tensile force transfer equation, a displacement prediction equation, a deformation response equation, and a critical state equation;

[0035] The tensile force transfer equation is used to calculate the force distribution of each section of the anchor rod. The inputs include the anchor rod diameter, the elastic modulus of the anchor rod material, the silt friction coefficient, the buried depth of the anchor rod, and the applied tensile force value. The output is the force distribution function of each point along the axis of the anchor rod;

[0036] The displacement prediction equation is used to predict the displacement of the anchor rod under different tensile forces. The inputs include the elastic modulus of the anchor rod material, the cross-sectional area of the anchor rod, the effective length of the anchor rod, the silt rigidity coefficient, and the applied tensile force value. The output is the theoretical displacement;

[0037] The deformation response equation is used to describe the interaction relationship between the anchor rod and the surrounding silt medium. The inputs include the surface roughness of the anchor rod, the silt cohesion, the buried angle of the anchor rod, the length of the anchorage zone, and the groundwater level height. The output is the stress distribution at the interface of the anchor solid;

[0038] The critical state equation is used to judge the stability change during the pull-out of the anchor rod. The inputs include the applied tensile force value, the displacement of the anchor rod, the displacement increment, the tensile force increment, and the time increment. The output is the pull-out jump index value of the anchor rod.

[0039] Among them, the anchor rod pull-out rigid support structure refers to the support structure system established to ensure the accuracy of the anchor rod pull-out detection under the silt geological conditions. It is a geometric structure formed by welding I-beams and can withstand multi-directional stresses and maintain the overall stability of the support system.

[0040] Among them, the anchor rod pull-out direction deviation index refers to the angle deviation coefficient between the anchor rod pull-out direction and the buried axis of the anchor rod. In the ideal state, the anchor rod pull-out direction deviation index is zero, indicating that the pull-out direction coincides completely with the axis of the anchor rod, avoiding the generation of shear stress and affecting the accuracy of the detection results.

[0041] Among them, the bolt pull-out jump index refers to the non-linear relationship parameter between the bolt displacement and the tensile force change during the pull-out process, which is used to describe the critical point where the bolt displacement suddenly increases during the stress process. The change of the bolt pull-out jump index can reflect the bonding strength between the anchor solid and the surrounding silt medium.

[0042] Among them, the recovery deviation degree refers to the degree of displacement recovery when the bolt is unloaded after bearing a certain load. The calculation method is the ratio of the residual displacement after unloading to the maximum displacement. The smaller the recovery deviation degree, the closer the bolt is bonded to the silt geology and the better the anchoring effect.

[0043] Among them, the silt rigidity coefficient refers to the deformation resistance ability of the silt geology under the action of the pull-out force, which is related to the silt moisture content, density, and silt cohesion. The larger the silt rigidity coefficient, the greater the anchoring resistance provided by the silt geology and the stronger the bolt pull-out resistance.

[0044] Among them, the bolt diameter refers to the diameter size of the bolt cross-section, thereby determining the bearing capacity of the bolt.

[0045] Among them, the elastic modulus of the bolt material refers to the ratio of stress to strain of the bolt material in the elastic deformation stage, reflecting the ability of the material to resist elastic deformation.

[0046] Among them, the silt friction coefficient refers to the ratio of the frictional force between the silt and the bolt surface to the normal pressure, which affects the bonding force between the bolt and the silt.

[0047] Among them, the bolt burial depth refers to the vertical distance from the ground surface to the anchoring end of the bolt, which determines the geological environment where the anchor solid is located.

[0048] Among them, the applied tensile force value refers to the magnitude of the axial tensile force applied to the bolt through the hydraulic oil pump, which is the control parameter for bolt pull-out detection.

[0049] Among them, the force distribution function of each point along the axis of the bolt refers to the force magnitude distribution of each point of the bolt from the free end to the anchoring end, reflecting the stress transfer characteristics of the bolt in the silt.

[0050] Among them, the bolt cross-sectional area refers to the size of the bolt cross-section area, which is related to the bolt diameter and affects the bearing capacity of the bolt.

[0051] Among them, the effective length of the bolt refers to the length part of the bolt that actually participates in the force, excluding the exposed part and the ineffective anchoring part of the bolt.

[0052] Among them, the theoretical displacement amount refers to the ideal displacement value of the bolt under different tensile forces calculated according to the displacement prediction equation, which is used for comparative analysis with the measured displacement amount.

[0053] Among them, the surface roughness of the anchor rod is a quantitative index reflecting the degree of micro unevenness of the anchor rod surface, which affects the bonding performance between the anchor rod and the surrounding silt.

[0054] Among them, the embedding angle of the anchor rod is the included angle between the anchor rod and the horizontal plane, which affects the stress direction and anchoring performance of the anchor rod.

[0055] Among them, the length of the anchorage zone is the actual length of the part where the anchor rod plays an anchoring role, which is the key area for the anchor rod to effectively exert its uplift resistance.

[0056] Among them, the height of the groundwater level is the vertical distance from the groundwater surface to the ground surface, which affects the water content of the silt and the physical and mechanical properties of the silt.

[0057] Among them, the stress distribution at the interface of the anchor solid is the stress distribution state on the contact surface between the anchor solid and the surrounding silt, which reflects the interaction between the anchor solid and the silt.

[0058] Among them, the displacement of the anchor rod is the axial displacement distance of the anchor rod under the action of the pulling force, which is an important index for evaluating the anchoring performance of the anchor rod.

[0059] Among them, the displacement increment is the increase in the displacement of the anchor rod between two adjacent measurements, which is used to analyze the change trend of the anchor rod displacement.

[0060] Among them, the tension increment is the increase in the tension between two adjacent loadings, which is the control parameter for the pull-out test of the anchor rod.

[0061] Among them, the time increment is the time interval between two adjacent measurements, which is used to analyze the time effect of the anchor rod displacement.

[0062] The specific implementation manners of the above steps are described in detail below. The specific implementation manner of step S01 is to first perform structural design calculations according to the geological characteristics of the silt, and determine the geometric dimensions and material strengths of the support structure by using the static equilibrium principle of structural mechanics. In the specific implementation process, first select the No. 25 I-beam made of national standard Q235B material, and its elastic modulus is 2.1×10 5MPa, the yield strength is 235 MPa to ensure that the support structure has sufficient stiffness and strength. Then, four No. 25 I-beams are used to form a square base by full welding. The size of the base is precisely controlled at 1700×1700 mm. The weld uses E4303 welding electrodes, and the weld height is not less than 8 mm. Then, two No. 25 I-beam columns are vertically welded at symmetric positions on both sides of the base. The height of the columns is precisely controlled at 1346 mm. The connection between the columns and the base is reinforced with triangular stiffeners. The thickness of the stiffeners is 12 mm, and the side length is 150 mm. The purpose of this step is to establish a support structure with sufficient stiffness to ensure that the support structure does not undergo obvious deformation during the anchor rod pulling process, and the self-deformation of the support structure is controlled within 0.5 mm, thereby ensuring the accuracy of the measurement data.

[0063] The specific implementation method of step S02 is to design the inclined beam structure using the principle of mechanical vector decomposition so that it can withstand the inclined pulling force of the anchor rod and transfer the force to the entire support structure. During the specific implementation process, first calculate the designed embedding angle of the anchor rod, usually 45 degrees. According to this angle, two No. 25 I-beams are welded obliquely from the base as inclined beams. The inclined beams are precisely at a 45-degree angle with the base to ensure that the angle error does not exceed ±1 degree. Then, the upper ends of the inclined beams are placed on the two steel columns and fixed by full circumferential full welding. The weld thickness is not less than 8 mm. Then, end plates made of Q235B steel plates with a thickness of 30 mm are welded at the ends of the inclined beams. The size of the end plates is 300×300 mm, meeting the bearing capacity requirements. Finally, a 50×50 mm square opening is opened at the center position of the end plate, and the chamfer radius of the opening edge is 5 mm to avoid stress concentration. The purpose of this step is to provide a pulling channel consistent with the embedding direction of the anchor rod. The design basis for the opening size of the end plate is that it is 25 - 40 mm larger than the common anchor rod diameter, leaving enough operating space, and at the same time ensuring that the end plate can withstand the maximum designed pulling force. The design strength safety factor of the end plate usually takes 2.0.

[0064] The specific implementation of step S03 is to ensure the consistency between the anchor rod pulling direction and the embedding direction of the anchor rod through precise measurement and adjustment, reducing the influence of eccentric tensile stress on the test results. During the specific implementation process, first use a total station to measure the spatial coordinates of the exposed part of the anchor rod, establish a three-dimensional coordinate system, and calculate the axial direction vector of the anchor rod. Then, according to the axial direction of the anchor rod, adjust the position of the support structure so that the anchor rod can pass through the end plate opening along the two inclined beams from the base. Next, use a laser level and an inclinometer to measure the angle between the axial line of the anchor rod and the pulling direction, and calculate the deflection index of the anchor rod pulling direction, the value of which is equal to the sine value of the angle between the pulling direction and the axial line of the anchor rod. Finally, by adjusting the position of the support structure, the deflection index of the anchor rod pulling direction is controlled within 0.02, which is equivalent to an angular deviation of about 1.15 degrees or less. This step uses the principles of spatial geometry and vector analysis methods to ensure that the pulling force is applied along the axial direction of the anchor rod, reducing the influence of the lateral component force generated by eccentric tension on the test accuracy, and the lateral component force generated by eccentric tension does not exceed 2% of the pulling force.

[0065] The specific implementation of step S04 is to use adaptive centering technology to achieve precise alignment between the hydraulic cylinder and the anchor rod, ensuring that the pulling force is evenly applied along the axial direction of the anchor rod. During the specific implementation process, first select a hollow self-resetting hydraulic cylinder with a rated pressure of 63 MPa and a rated thrust of 1000 kN. The inner diameter of the hydraulic cylinder is not less than 200 mm, the piston rod stroke is not less than 200 mm, and the central hole diameter is 60 mm. Then, after putting the hollow self-resetting hydraulic cylinder on the anchor rod, it automatically locates at the end plate under its own weight. The bottom of the hydraulic cylinder is designed with a hemispherical contact surface, which can achieve an automatic adjustment function of ±3 degrees. Next, use a precision level to detect the inclination angle of the hydraulic cylinder axis, and finely adjust the position of the hydraulic cylinder through adjustment bolts so that the angle between the hydraulic cylinder axis and the anchor rod axis does not exceed 0.5 degrees. Finally, install a high-precision displacement sensor with an accuracy of 0.01 mm and a measurement range of 0 - 50 mm to monitor the displacement of the anchor rod in real time. The purpose of this step is to ensure that the pulling force is applied along the axial direction of the anchor rod through precise alignment, avoid the additional bending moment caused by eccentric load, and improve the accuracy and reliability of the test data.

[0066] The specific implementation of step S05 is to establish a monitoring system based on a non-linear mechanical model, and collect and analyze the mechanical parameters during the anchor rod pulling process in real time. During the specific implementation process, first connect the hydraulic system, including a high-pressure oil pump, high-pressure oil pipes, precision pressure gauges, flow control valves and safety valves. The rated pressure of the hydraulic oil pump is 70 MPa, the range of the precision pressure gauge is 0 - 100 MPa, and the accuracy class is 0.5 level. Then write the monitoring software for the anchor rod pulling jump index, and use a data acquisition card to collect the signals of the pressure sensor and displacement sensor simultaneously at a frequency of 100 Hz, and calculate the relationship between the tensile force and displacement in real time. Next, use the least squares method combined with non-linear regression analysis to fit and optimize the measured data, and control the fitting accuracy within a relative error of 3%, forming an accurate tensile force-displacement curve. Finally, based on the theory of elastic-plastic mechanics, calculate the critical state parameters of the anchor rod in real time, including the elastic limit, yield point and ultimate strength. The critical state determination threshold is set as the displacement rate mutation point. Generally, when the displacement rate increases to more than 3 times that of the previous stable stage, it can be considered that the critical state is reached. The purpose of this step is to monitor the stress state of the anchor rod in real time, capture the critical point when the anchor rod transitions from the elastic stage to the plastic stage, and provide data support for evaluating the anchoring performance of the anchor rod.

[0067] The specific implementation of step S06 is to use the graded loading method to test the load stability of the anchor rod and evaluate the working performance of the anchor rod under the design load. During the specific implementation process, first set the graded loading scheme according to the design load value of the anchor rod. Generally, it is divided into 5 - 8 loading levels, and the load increment for each level is 10% - 20% of the design load. Then gradually increase the pulling force through the hydraulic system. After each level of load is reached, keep the pressure constant, observe the displacement change of the anchor rod, record the readings of the displacement sensor, and the sampling frequency is 1 Hz. Next, under the condition that the stable time for each level of load is not less than 5 minutes, judge whether there is obvious displacement of the anchor rod. The determination criterion for obvious displacement is that the displacement increment exceeds 0.1 mm / min. Finally, record the final stable displacement value of the anchor rod under each level of load, and calculate the recovery deviation degree. The recovery deviation degree threshold is usually set to 0.2. A value lower than this indicates that the anchor rod is well combined with the silt. This step is based on the material creep theory, and the purpose is to evaluate the stable performance of the anchor rod under the design load, verify whether the anchor rod meets the engineering use requirements, and ensure that the anchor rod will not undergo excessive deformation or failure during use.

[0068] The specific implementation of step S07 is to use the overloading test method to evaluate the ultimate bearing capacity and safety reserve of the anchor bolt, and verify the reliability of the anchor bolt. During the specific implementation process, first, on the basis of the qualified design load verification, continue to increase the pulling force according to the graded loading scheme, and the loading increment is 10% of the design load until it reaches 1.5 times the design load. Then, under 1.5 times the design load of the maximum load, keep the load stable for no less than 15 minutes, observe the displacement change trend of the anchor bolt, and increase the sampling frequency to 5 Hz to capture possible sudden change phenomena. Next, record the displacement process curve of the anchor bolt within 15 minutes, calculate the displacement rate, and the displacement rate should gradually decrease and tend to be stable. The stability judgment criterion is that the displacement increment within the last 5 minutes is less than 0.05 mm. Finally, record the maximum stable displacement under the overloaded state. Under normal circumstances, this value should not exceed 1% of the anchor bolt diameter. For a 25-mm diameter anchor bolt, the maximum allowable displacement is 0.25 mm. This step is based on the structural reliability theory, aiming to evaluate the working performance of the anchor bolt under extreme conditions, determine the safety reserve coefficient of the anchor bolt, and provide a reliable basis for engineering design.

[0069] The specific implementation of step S08 is to use the ultimate state analysis method to determine the ultimate bearing capacity of the anchor bolt and evaluate the uplift resistance of the anchor bolt in the silt geological formation. During the specific implementation process, first, continue to increase the pulling force until the displacement of the anchor bolt increases rapidly or the pulling force cannot be increased further. At this time, record the maximum pulling force value, which is the ultimate uplift resistance of the anchor bolt. Then, according to the displacement-tension curve, determine the yield point of the anchor bolt. The yield point is usually defined as the point where the tension-displacement curve changes from linear to non-linear, and can be determined by the double tangent method. Next, calculate the silt rigidity coefficient of the anchor solid, and its calculation formula is that the silt rigidity coefficient is equal to the yield point tension divided by the corresponding displacement, with the unit of kN / mm. The silt rigidity coefficient is usually between 20 and 100 kN / mm. A value lower than 20 kN / mm indicates poor silt anchoring performance and reinforcement measures need to be taken. Finally, calculate the safety factor according to the ratio of the ultimate uplift force to the design load. The safety factor should not be less than 2.0, otherwise, the number of anchor bolts needs to be increased or the anchoring method needs to be improved. This step is based on the foundation bearing capacity theory and the structural ultimate state design theory, aiming to determine the actual working ability of the anchor bolt and provide a basis for engineering design and construction.

[0070] The specific implementation of step S09 is to adopt the system unloading process and data mining technology to complete the evaluation of the bolt performance and form a test report. In the specific implementation process, first, perform hierarchical unloading in the reverse order of loading. The stabilization time after each level of unloading is not less than 3 minutes, and record the displacement recovery during the unloading process. Then calculate the elastic deformation and plastic deformation ratios under each level of load. The higher the elastic deformation ratio, the better the working state of the bolt. Under normal circumstances, the elastic deformation ratio should not be less than 70%. Next, remove the test device, including the hydraulic cylinder, sensor, and support structure. During the removal process, pay attention to protecting the bolt to avoid damage to the bolt. Finally, use the least squares fitting method combined with nonlinear regression analysis to process all the test data, establish a mathematical model of the bolt mechanical properties, control the model accuracy within a relative error of 5%, and issue a bolt pull-out test report. The report content includes the ultimate pull-out force of the bolt, the bonding strength between the bolt and the silt, the mechanical properties in the elastic stage and plastic stage, the recommended working load, and the safety factor. This step is based on the experimental data statistical analysis theory, aiming to comprehensively evaluate the bolt performance and provide a scientific basis for project acceptance and subsequent use.

[0071] The following details the mathematical models or calculation processes involved in the present invention.

[0072] In step S01, the design of the bolt pull-out rigid support structure involves structural mechanics calculations. Specifically, it is expressed as follows:

[0073]

[0074] In the formula, F is the force distribution matrix of the support structure; F xi , F yi , F zi are the force components of the i-th support point in three directions respectively, with the unit of kN; the value range of i is from 1 to 4, corresponding to the four I-beam support points.

[0075] The stiffness matrix of the support structure is expressed as:

[0076]

[0077] In the formula, K is the stiffness matrix of the support structure; k ij is the stiffness coefficient, indicating the displacement generated at the i-th point when a unit force is applied at the j-th point, with the unit of mm / kN; the value ranges of both i and j are from 1 to 4.

[0078] The calculation method of the stiffness coefficient k ij is:

[0079]

[0080] In the formula, L ijis the distance from the i-th point to the j-th point, with the unit of mm; E is the elastic modulus of the I-beam, taking the value of 2.1×10 5 MPa; I ij is the moment of inertia of the I-beam. For the No. 25 I-beam, I ij takes the value of 5.73×10 6 mm 4 .

[0081] In step S03, the calculation of the skew index of the anchor bolt pulling direction involves vector analysis. The vector of the anchor bolt axis direction is expressed as:

[0082]

[0083] In the formula, is the vector of the anchor bolt axis direction; a x , a y , a z are the components of the direction vector on the three coordinate axes respectively, dimensionless; the two-point coordinates (x1, y1, z1) and (x2, y2, z2) of the exposed part of the anchor bolt are obtained by total station measurement, and then calculated:

[0084]

[0085] The pulling direction vector is expressed as:

[0086]

[0087] In the formula, is the pulling direction vector; b x , b y , b z are the components of the direction vector on the three coordinate axes respectively, dimensionless; it is determined by measuring the axis of the hydraulic cylinder.

[0088] The calculation formula of the skew index of the anchor bolt pulling direction is:

[0089]

[0090] In the formula, D 偏 is the skew index of the anchor bolt pulling direction, dimensionless; θ is the angle between the anchor bolt axis and the pulling direction, with the unit of degree; is the dot product of the two vectors, and the calculation formula is:

[0091]

[0092] When D 偏 ≤0.02, it is considered that the pulling direction is close enough to the anchor bolt axis to meet the test requirements. The angle corresponding to this threshold is about 1.15 degrees, which is the allowable error range determined according to engineering experience.

[0093] In step S05, the mechanical equations for bolt pull - out involve multiple equations. The tensile force transfer equation is specifically expressed as:

[0094] P(x) = P0e -βx ;

[0095] In the formula, P(x) is the axial tensile force of the cross - section at a distance x from the free end of the bolt, with the unit of kN; P0 is the applied pull - out force value, with the unit of kN; β is the tensile force attenuation coefficient, with the unit of mm -1 ; x is the distance from the free end of the bolt, with the unit of mm.

[0096] The calculation method of the tensile force attenuation coefficient β is:

[0097]

[0098] In the formula, μ f is the friction coefficient between the silt and the bolt surface, dimensionless, and usually takes values in the range of 0.3 - 0.6, which is obtained through direct shear tests; d a is the bolt diameter, with the unit of mm; k s is the silt rigidity coefficient, with the unit of kN / mm 3 ; E a is the elastic modulus of the bolt material, with the unit of MPa. For the commonly used HRB400 - grade steel bars, E a takes a value of 2.0×10 5 MPa.

[0099] The displacement prediction equation is specifically expressed as:

[0100]

[0101] In the formula, δ is the theoretical displacement of the bolt, with the unit of mm; L e is the effective length of the bolt, with the unit of mm; A a is the cross - sectional area of the bolt, with the unit of mm 2 , L a is the length of the anchorage zone, with the unit of mm; α is the anchorage characteristic coefficient, with the unit of mm -1 , and the calculation formula is:

[0102]

[0103] The first term of the equation represents the elastic deformation of the bolt itself, and the second term represents the relative slip deformation at the bolt - silt interface. This equation is based on the composite material interface shear theory and takes into account two main factors: the elastic deformation of the bolt and the interface slip.

[0104] The deformation response equation is specifically expressed as:

[0105]

[0106] In the formula, τ(x) is the shear stress at the interface of the anchor body at a distance x from the free end of the anchor rod, with the unit of MPa; τ max is the maximum shear stress at the interface, with the unit of MPa; γ is the interface characteristic coefficient, with the unit of mm -1 ; δ r (x) is the relative slip at this location, with the unit of mm.

[0107] The calculation method of the maximum shear stress τ max at the interface is as follows:

[0108] τ max = c + σ n tanφ;

[0109] In the formula, c is the cohesive force of the silt, with the unit of MPa, obtained through triaxial compression tests; σ n is the normal stress, with the unit of MPa; φ is the internal friction angle of the silt, with the unit of degrees, obtained through triaxial compression tests.

[0110] The calculation method of the normal stress σ n at the interface is as follows:

[0111] σ n = γ m hcos 2 θ + K0γ m hsin 2 θ;

[0112] In the formula, γ m is the unit weight of the silt, with the unit of kN / m 3 ; h is the thickness of the overlying soil, with the unit of m; θ is the installation angle of the anchor rod, with the unit of degrees; K0 is the coefficient of the at-rest lateral earth pressure, dimensionless, and K0 = 1 - sinφ.

[0113] The calculation method of the relative slip δ r (x) is as follows:

[0114]

[0115] In the formula, P(x) is the axial tension at the cross-section at a distance x from the free end of the anchor rod calculated in the tensile force transfer equation. <x

[0116] The critical state equation is specifically expressed as:

[0117]

[0118] In the formula, I 跳is the bolt pull-out jump index, dimensionless; Δδ is the displacement increment, in mm; Δt is the time increment, in s; ΔP is the tensile force increment, in kN; P0 is the currently applied pull-out force value, in kN; P cr is the critical pull-out force value, in kN. The initial value can be taken as 1.2 times the design load and is updated during the testing process.

[0119] The update method of the critical pull-out force value P cr is as follows:

[0120] P cr = P cr，0 ·(1 + λ·I 跳 );

[0121] In the formula, P cr，0 is the estimated value of the initial critical pull-out force, in kN; λ is the adjustment coefficient, dimensionless, with a value range of 0.1 to 0.3.

[0122] When I 跳 > I 临 , it is considered that the bolt reaches the critical state. I 临 is the critical jump index threshold, usually with a value of 3.0. This equation is based on the jump condition theory in plastic mechanics and is used to capture the critical point of the bolt's transition from a stable state to an unstable state.

[0123] In step S06, the calculation formula for the recovery deviation degree is:

[0124]

[0125] In the formula, D 恢 is the recovery deviation degree, dimensionless; δ r is the residual displacement after unloading, in mm; δ max is the maximum displacement, in mm. When D 恢 < 0.2, it indicates that the bolt is well combined with the silt and the anchoring effect meets the requirements.

[0126] In step S08, the calculation formula for the silt rigidity coefficient is:

[0127]

[0128] In the formula, k s is the silt rigidity coefficient, in kN / mm 3 ; P y is the yield point tensile force, in kN; δ y is the yield point displacement, in mm; d a is the bolt diameter, in mm; L a is the anchoring zone length, in mm.

[0129] The yield point is determined by the double tangent method. The specific steps are as follows:

[0130] 1. Draw a tangent line in the tensile force - displacement curve for the initial loading stage, that is, the tangent line in the elastic stage;

[0131] 2. Draw a tangent line in the tensile force - displacement curve for the rapid deformation stage, that is, the tangent line in the plastic stage;

[0132] 3. The tensile force value corresponding to the intersection point of the two tangent lines is the yield point tensile force P y , and the corresponding displacement value is the yield point displacement δ y .

[0133] The formula for determining the yield point value is:

[0134]

[0135] In the formula, P0 is the initial tensile force, with the unit of kN; P max is the maximum test tensile force, with the unit of kN; k1 is the stiffness in the elastic stage, with the unit of kN / mm; k2 is the stiffness in the plastic stage, with the unit of kN / mm.

[0136] The calculation methods for the stiffness in the elastic stage and the stiffness in the plastic stage are:

[0137]

[0138] In the formula, ΔP1 and Δδ1 are the tensile force increment and displacement increment in the elastic stage respectively; ΔP2 and Δδ2 are the tensile force increment and displacement increment in the plastic stage respectively.

[0139] The calculation formula for the safety factor is:

[0140]

[0141] In the formula, F s is the safety factor, dimensionless; P max is the maximum pulling force value, with the unit of kN; P d is the design load, with the unit of kN.

[0142] In step S09, the calculation formula for the elastic deformation ratio is:

[0143]

[0144] In the formula, η e is the elastic deformation ratio, dimensionless; δ e is the elastic deformation amount, with the unit of mm; δ total is the total deformation amount, with the unit of mm.

[0145] The calculation methods for the elastic deformation amount and the total deformation amount are:

[0146] δ e = δ total -δ r ;

[0147] δ total = δ max ;

[0148] In the formula, δ r is the residual displacement after unloading, with the unit of mm; δ max is the maximum displacement, with the unit of mm.

[0149] The mathematical model of the bolt anchoring performance adopts a power function expression:

[0150] P = a·δ b ;

[0151] In the formula, P is the pulling force, with the unit of kN; δ is the displacement, with the unit of mm; a and b are undetermined parameters, which are obtained by fitting the measured data through the least square method.

[0152] The solution of parameters a and b involves a non - linear optimization problem, which is solved by the least square method:

[0153]

[0154] In the formula, P i and δ i are respectively the pulling force and displacement measured at the i - th measurement; n is the number of measurement data points.

[0155] By taking the logarithm of the function, the non - linear optimization can be transformed into a linear optimization problem:

[0156] lnP = lna + b·lnδ;

[0157] Let Y = lnP, X = lnδ, A = lna, then there is:

[0158] Y = A + b·X.

[0159] The estimated values of parameters A and b can be obtained through linear regression:

[0160]

[0161] Then calculate a = e A , thus obtaining the mathematical model of the bolt anchoring performance.

[0162] These equations and formulas are constructed based on multiple principles: The tensile force transfer equation is based on the stress attenuation theory and adopts an exponential function form to reflect the attenuation law of the tensile force along the axial direction of the anchor rod; the displacement prediction equation is based on the superposition principle, considering the contributions of the elastic deformation of the anchor rod itself and the interfacial slip deformation respectively; the deformation response equation is based on the nonlinear interfacial constitutive relationship to reflect the nonlinear mechanical properties of the interface between the silt and the anchor rod; the critical state equation is based on the instability criterion, introducing a jump index to quantify the transition process of the anchor rod from a stable state to an unstable state. These equations comprehensively consider various factors such as the geological characteristics of the silt, the material characteristics of the anchor rod, and the interfacial interaction characteristics, forming a complete mechanical theory system for anchor rod pulling tests, providing a theoretical basis and calculation method for anchor rod pulling tests under silt geological conditions.

[0163] Specifically, the principle of the present invention is: The technical principle of the present invention is based on the mechanical equilibrium principle and the material deformation theory. By combining a rigid support structure with a mathematical model, precise control of the pulling direction of the inclined anchor rod and scientific analysis of the test results are achieved. First, according to the principle of action and reaction, the pulling device must have sufficient stiffness and stability to resist the pulling reaction force of the anchor rod. The I-beam support structure designed in the present invention provides high-strength structural support to prevent deformation or inclination of the support system under silt geological conditions.

[0164] Secondly, the core of the anchor rod pulling test lies in ensuring that the pulling force direction is consistent with the axis of the anchor rod to truly reflect the axial pulling resistance of the anchor rod. The present invention, through the design of the inclined beam guiding structure and a 45-degree angle, makes the acting direction of the pulling force consistent with the embedding direction of the anchor rod, avoiding the common eccentric pulling problem in traditional tests. From the perspective of vector decomposition, ensuring that the pulling force is applied along the axis of the anchor rod eliminates the additional stress caused by the transverse component force on the anchor rod, reducing the result deviation and the risk of anchor rod damage.

[0165] Analyzed from the perspective of material mechanics, the anchor rod shows linear elastic deformation characteristics under pure axial tensile force. Once eccentric pulling occurs, it will lead to a complex composite stress state, causing the relationship between displacement and pulling force to deviate from the ideal linear model. The present invention guides the anchor rod through an end plate opening and uses a hollow self-resetting hydraulic cylinder arranged coaxially with the anchor rod axis to ensure the application of pure axial tensile force and maintain an ideal stress state.

[0166] More importantly, the present invention introduces a system of mechanical equations for anchor rod pulling to systematically analyze the test data. This system of equations comprehensively considers the material characteristics of the anchor rod, the silt geological conditions, and the interfacial interaction, establishing a complete theoretical framework. By analyzing the axial force distribution of the anchor rod through the tensile force transfer equation, evaluating the theoretical displacement through the displacement prediction equation, describing the interfacial stress state through the deformation response equation, and judging the stability change through the critical state equation, a complete theoretical support from mechanical principles to practical applications is formed, ensuring the scientific nature and reliability of the test results.

[0167] A specific Embodiment 1 of the present invention is provided below. The specific implementation of each step in this Embodiment 1 is described in detail as follows.

[0168] The specific implementation of step S01 is to design and construct the rigid support structure for bolt pulling based on the static equilibrium principle of structural mechanics. First, use No. 25 I-beams made of Q235B material, with an elastic modulus of 2.1×10 5 MPa and a yield strength of 235 MPa. A base is formed by welding four I-beams, and the size of the base is 1700×1700 mm. Determine the force conditions at each support point by calculating the force distribution matrix of the support structure:

[0169]

[0170] In the formula, F is the force distribution matrix of the support structure; F xi , F yi , F zi are the force components of the i-th support point in three directions respectively, with the unit of kN; the value range of i is from 1 to 4. At the same time, determine the stiffness matrix of the support structure:

[0171]

[0172] In the formula, K is the stiffness matrix of the support structure; k ij is the stiffness coefficient, with the unit of mm / kN. The stiffness coefficient is calculated by the following formula:

[0173]

[0174] In the formula, L ij is the distance from the i-th point to the j-th point, with the unit of mm; E is the elastic modulus of the I-beam; I ij is the moment of inertia of the I-beam, and for No. 25 I-beam, the value is 5.73×10 6 mm 4 . Then, vertically weld two No. 25 I-beam columns at symmetric positions on both sides of the base. The height of the columns is 1346 mm. The connection between the columns and the base is reinforced with triangular stiffening plates, with a thickness of 12 mm and a side length of 150 mm. The purpose of this step is to establish a support structure with sufficient stiffness to ensure that the support structure does not undergo obvious deformation during the bolt pulling process, and the self-deformation amount of the support structure is controlled within 0.5 mm to ensure the accuracy of the measurement data.

[0175] The specific implementation of step S02 is to design the inclined beam structure using the principle of mechanical vector decomposition. First, calculate the designed embedding angle of the anchor rod, usually 45 degrees. According to this angle, weld two No. 25 I-beams obliquely from the base as the inclined beams. The inclined beams are precisely at a 45-degree angle with the base, and the angle error is controlled within ±1 degree. The upper ends of the inclined beams rest on two steel columns and are fixed by full-circumference full welding, with the weld thickness not less than 8 mm. Weld end plates made of Q235B steel plates with a thickness of 30 mm at the ends of the inclined beams. The size of the end plates is 300×300 mm. Open a 50×50 mm square opening at the center of the end plate, and the chamfer radius at the edge of the opening is 5 mm to avoid stress concentration. This step provides a pulling channel consistent with the embedding direction of the anchor rod. The opening size of the end plate is 25 - 40 mm larger than the diameter of the commonly used anchor rod, leaving enough operating space to ensure that the end plate can withstand the maximum designed pulling force, and the design strength safety factor of the end plate is taken as 2.0.

[0176] The specific implementation of step S03 is to ensure the consistency between the pulling direction of the anchor rod and the embedding direction of the anchor rod through precise measurement and vector analysis. First, use a total station to measure the spatial coordinates of the exposed part of the anchor rod, establish a three-dimensional coordinate system, and calculate the direction vector of the anchor rod axis:

[0177]

[0178] In the formula, is the direction vector of the anchor rod axis; a x , a y , a z are the components of the direction vector on the three coordinate axes respectively, dimensionless. By measuring the coordinates of two points (x1, y1, z1) and (x2, y2, z2) of the exposed part of the anchor rod, calculate:

[0179]

[0180] The pulling direction vector is expressed as:

[0181]

[0182] In the formula, is the pulling direction vector; b x , b y , b z are the components of the direction vector on the three coordinate axes respectively, dimensionless. Then, according to the direction of the anchor rod axis, adjust the position of the support structure so that the anchor rod can pass through the opening of the end plate along the two inclined beams from the base. Use a laser level and an inclinometer to measure the angle between the axis of the anchor rod and the pulling direction, and calculate the skewness index of the pulling direction of the anchor rod:

[0183]

[0184] In the formula, D偏 is the deviation index of the bolt pulling direction, dimensionless; θ is the angle between the bolt axis and the pulling direction, in degrees; is the dot product of two vectors, and the calculation formula is:

[0185]

[0186] By adjusting the position of the support structure, the deviation index of the bolt pulling direction is controlled within 0.02, which is equivalent to an angular deviation of about 1.15 degrees or less. This step ensures that the pulling force is applied along the bolt axis, reducing the influence of the lateral component force generated by eccentric pulling on the test accuracy, and the lateral component force generated by eccentric pulling does not exceed 2% of the pulling force.

[0187] The specific implementation of step S04 is to use adaptive centering technology to achieve precise alignment between the hydraulic cylinder and the bolt. First, a hollow self-resetting hydraulic cylinder with a rated pressure of 63 MPa and a rated thrust of 1000 kN is selected. The inner diameter of the hydraulic cylinder is not less than 200 mm, the piston rod stroke is not less than 200 mm, and the central hole diameter is 60 mm. After the hollow self-resetting hydraulic cylinder is sleeved onto the bolt, it automatically locates at the end plate under its own weight. The bottom of the hydraulic cylinder is designed with a hemispherical contact surface, which can achieve an automatic adjustment function of ±3 degrees. Use a precision level to detect the inclination angle of the hydraulic cylinder axis, and finely adjust the position of the hydraulic cylinder through adjustment bolts so that the angle between the hydraulic cylinder axis and the bolt axis does not exceed 0.5 degrees. Install a high-precision displacement sensor with an accuracy of 0.01 mm and a measurement range of 0 - 50 mm to monitor the bolt displacement in real time. This step ensures that the pulling force is applied along the bolt axis through precise alignment, avoiding the additional moment caused by eccentric load and improving the accuracy and reliability of the test data.

[0188] The specific implementation of step S05 is to establish a monitoring system based on a non-linear mechanical model. First, connect the hydraulic system, including a high-pressure oil pump, high-pressure oil pipes, a precision pressure gauge, a flow control valve, and a safety valve. The rated pressure of the hydraulic oil pump is 70 MPa, the range of the precision pressure gauge is 0 - 100 MPa, and the accuracy class is 0.5. Then write the bolt pulling jump index monitoring software, and use a data acquisition card to simultaneously collect the signals of the pressure sensor and the displacement sensor at a frequency of 100 Hz. Implement the tensile force transfer equation:

[0189] P(x) = P0e -βx ;

[0190] In the formula, P(x) is the axial tensile force at the cross-section at a distance x from the free end of the bolt, in kN; P0 is the applied pulling force value, in kN; β is the tensile force attenuation coefficient, in mm -1 ; x is the distance from the free end of the bolt, in mm. The calculation method of the tensile force attenuation coefficient β is:

[0191]

[0192] Wherein, μ f is the friction coefficient between the silt and the surface of the anchor rod, dimensionless, and usually takes values in the range of 0.3 to 0.6; d a is the diameter of the anchor rod, in mm; k s is the rigidity coefficient of the silt, in kN / mm 3 ; E a is the elastic modulus of the anchor rod material, in MPa. At the same time, the displacement prediction equation is realized:

[0193]

[0194] Wherein, δ is the theoretical displacement of the anchor rod, in mm; L e is the effective length of the anchor rod, in mm; A a is the cross-sectional area of the anchor rod, in mm 2 , L a is the length of the anchorage zone, in mm; α is the anchorage characteristic coefficient, in mm -1 , and the calculation formula is:

[0195]

[0196] The deformation response equation also needs to be realized:

[0197]

[0198] Wherein, τ(x) is the shear stress of the anchor solid interface at a distance x from the free end of the anchor rod, in MPa; τ max is the maximum shear stress of the interface, in MPa; γ is the interface characteristic coefficient, in mm -1 ; δ r (x) is the relative slip at this place, in mm. The calculation method of the maximum shear stress τ max of the interface is:

[0199] τ max = c + σ n tanφ;

[0200] Wherein, c is the cohesion of the silt, in MPa; σ n is the normal stress, in MPa; φ is the internal friction angle of the silt, in degrees. Finally, the critical state equation is realized:

[0201]

[0202] Wherein, I 跳is the bolt pulling jump index, dimensionless; Δδ is the displacement increment, with the unit of mm; Δt is the time increment, with the unit of s; ΔP is the tensile force increment, with the unit of kN; P0 is the currently applied pulling force value, with the unit of kN; P cr is the critical pulling force value, with the unit of kN. The least squares method combined with non-linear regression analysis is used to fit and optimize the measured data, and the fitting accuracy is controlled within 3% of the relative error to form an accurate tensile force-displacement curve. This step monitors the stress state of the bolt in real time, captures the critical point when the bolt transitions from the elastic stage to the plastic stage, and provides data support for evaluating the anchoring performance of the bolt.

[0203] The specific implementation of step S06 is to use the graded loading method to test the load stability of the bolt. First, set the graded loading scheme according to the designed load value of the bolt. Usually, it is divided into 5 - 8 loading levels, and the load increment for each level is 10% - 20% of the designed load. The pulling force is increased step by step through the hydraulic system. After each level of load is reached, keep the pressure constant, observe the displacement change of the bolt, record the readings of the displacement sensor, and the sampling frequency is 1 Hz. Under the condition that the stable time for each level of load is not less than 5 minutes, judge whether there is obvious displacement of the bolt. The criterion for obvious displacement is that the displacement increment exceeds 0.1 mm / minute. Record the final stable displacement value of the bolt under each level of load, and calculate the recovery deviation degree:

[0204]

[0205] In the formula, D 恢 is the recovery deviation degree, dimensionless; δ r is the residual displacement after unloading, with the unit of mm; δ max is the maximum displacement, with the unit of mm. The threshold of the recovery deviation degree is set to 0.2. A value lower than this indicates good bonding between the bolt and the silt. This step evaluates the stable performance of the bolt under the designed load based on the material creep theory and verifies whether the bolt meets the engineering use requirements.

[0206] The specific implementation of step S07 is to use the overloading test method to evaluate the ultimate bearing capacity and safety reserve of the anchor bolt. First, on the basis of passing the design load verification, continue to increase the pulling force according to the graded loading scheme, with the loading increment being 10% of the design load, until 1.5 times the design load is reached. At 1.5 times the maximum design load, keep the load stable for no less than 15 minutes, observe the change trend of the anchor bolt displacement, and increase the sampling frequency to 5 Hz to capture possible sudden change phenomena. Record the displacement process curve of the anchor bolt within 15 minutes, calculate the displacement rate, and the displacement rate should gradually decrease and tend to be stable. The stability judgment criterion is that the displacement increment within the last 5 minutes is less than 0.05 mm. Record the maximum stable displacement under the overloaded state. Under normal circumstances, this value should not exceed 1% of the anchor bolt diameter. For a 25-mm diameter anchor bolt, the maximum allowable displacement is 0.25 mm. This step is based on the structural reliability theory to evaluate the working performance of the anchor bolt under extreme conditions and determine the safety reserve coefficient of the anchor bolt.

[0207] The specific implementation of step S08 is to use the limit state analysis method to determine the ultimate bearing capacity of the anchor bolt. First, continue to increase the pulling force until the displacement of the anchor bolt increases rapidly or the pulling force cannot be increased further. At this time, record the maximum pulling force value. According to the displacement-tension curve, use the double tangent method to determine the yield point of the anchor bolt. The formula for determining the yield point value is:

[0208]

[0209] In the formula, P0 is the initial tension, with the unit of kN; P max is the maximum test tension, with the unit of kN; k1 is the stiffness in the elastic stage, with the unit of kN / mm; k2 is the stiffness in the plastic stage, with the unit of kN / mm. The calculation methods for the stiffness in the elastic stage and the stiffness in the plastic stage are:

[0210]

[0211] In the formula, ΔP1 and Δδ1 are the tension increment and displacement increment in the elastic stage respectively; ΔP2 and Δδ2 are the tension increment and displacement increment in the plastic stage respectively. Calculate the rigidity coefficient of the anchor solid silt:

[0212]

[0213] In the formula, k s is the silt rigidity coefficient, with the unit of kN / mm 3 ; P y is the yield point tension, with the unit of kN; δ y is the yield point displacement, with the unit of mm; d a is the anchor bolt diameter, with the unit of mm; L a is the length of the anchorage zone, with the unit of mm. Calculate the safety factor:

[0214]

[0215] wherein, F s is the safety factor, dimensionless; P max is the maximum pulling force value, with the unit of kN; P d is the design load, with the unit of kN. The rigidity coefficient of silt is usually between 20 and 100 kN / mm 3 When it is lower than 20 kN / mm 3 it indicates that the anchoring performance of silt is poor and reinforcement measures need to be taken. The safety factor should not be less than 2.0, otherwise the number of anchor rods needs to be increased or the anchoring method needs to be improved. This step is based on the foundation bearing capacity theory and the structural ultimate limit state design theory to determine the actual working capacity of the anchor rods, providing a basis for engineering design and construction.

[0216] The specific implementation of step S09 is to adopt the system unloading process and data mining technology to complete the evaluation of the anchor rod performance and form a test report. First, perform graded unloading in the reverse order of loading, with a stable time of not less than 3 minutes after each level of unloading, and record the displacement recovery during the unloading process. Calculate the elastic deformation ratio:

[0217]

[0218] wherein, η e is the elastic deformation ratio, dimensionless; δ e is the elastic deformation amount, with the unit of mm; δ total is the total deformation amount, with the unit of mm. The calculation methods of the elastic deformation amount and the total deformation amount are:

[0219] δ e = δ total - δ r ;

[0220] δ total = δ max ;

[0221] wherein, δ r is the residual displacement after unloading, with the unit of mm; δ max is the maximum displacement, with the unit of mm. The elastic deformation ratio should not be lower than 70%, otherwise it indicates that the anchoring effect of the anchor rod is not good. Remove the test device, including the hydraulic cylinder, sensor and support structure, and pay attention to protecting the anchor rod during the removal process to avoid damaging the anchor rod. Use the least squares method combined with non-linear regression analysis to process all the test data and establish a mathematical model for the anchoring performance of the anchor rod:

[0222] P = a·δ b ;

[0223] Wherein, P is the drawing force in kN; δ is the displacement in mm; a and b are undetermined parameters. The least squares method is used to solve the parameters a and b:

[0224]

[0225] Taking the logarithm to transform the non - linear optimization into a linear optimization problem:

[0226] lnP = lna + b·lnδ;

[0227] Let Y = lnP, X = lnδ, A = lna, then we have:

[0228] Y = A + b·X.

[0229] The estimated values of parameters A and b can be obtained through linear regression, and then calculate a = e A , thus obtaining the mathematical model of the bolt anchoring performance. The model accuracy is controlled within a relative error of 5%. An anchor bolt pull - out test report is issued, and the report content includes the ultimate pull - out force of the anchor bolt, the bond strength between the anchor bolt and the silt, the mechanical properties in the elastic stage and plastic stage, the recommended working load and safety factor. This step is based on the theory of statistical analysis of experimental data, comprehensively evaluating the performance of the anchor bolt, and providing a scientific basis for project acceptance and subsequent use.

[0230] To better understand and implement the present invention, Example 2 of a specific application scenario of the present invention is provided below: An anchor bolt pull - out test is carried out in a silt geological area of a certain project. Geological exploration of this area shows that the thickness of the silt layer is about 15 meters, the moisture content of the silt is 38% - 45%, the average unit weight is 17.5 kN / m 3 , the cohesion is 0.025 MPa, and the internal friction angle is 12.5 degrees. To ensure the slope stability, it is necessary to detect the pull - out capacity of the anchor bolt and verify whether it meets the design requirements.

[0231] First, an anchor bolt pull - out rigid support structure is established according to the silt geological characteristics. As Figure 2 shown, a base is formed by welding four No. 25 I - beams. The size of the base is 1700×1700 mm, and two No. 25 I - beam columns are welded. The height of the columns is 1346 mm. The force distribution analysis of the support structure is shown in Table 1:

[0232] Table 1 Force distribution analysis of the support structure

[0233]

[0234] Two No. 25 I - beams are welded obliquely from the base as diagonal beams. The diagonal beams form a 45 - degree angle with the base and rest on two steel columns. A 30 - mm - thick end plate is welded at the end of the diagonal beam, and an opening of 50×50 mm is provided at the end plate. As Figure 3As shown in the figure, the anchor rod is made of HRB400 grade steel bar, with a diameter of 32 mm, a burial angle of 45 degrees, a burial depth of 12 m, and an effective anchorage length of 5 m.

[0235] As Figure 4 shown, use a total station to measure the coordinates of the exposed part of the anchor rod, and calculate the axial direction vector of the anchor rod as (0.7036, 0.0152, -0.7104). According to the vector calculation results, adjust the position of the support structure so that the anchor rod passes through the end plate opening along the two inclined beams from the base. Use a laser level and an inclinometer to measure the angle between the axis of the anchor rod and the pulling direction, and calculate the deviation index of the anchor rod pulling direction as shown in Table 2:

[0236] Table 2 Calculation of the deviation index of the anchor rod pulling direction

[0237]

[0238] After sleeving the hollow self-resetting hydraulic cylinder onto the anchor rod, it automatically falls into place at the end plate. Adjust the axis of the hydraulic cylinder to coincide with the axis of the anchor rod, and install a high-precision displacement sensor. The parameters of the hydraulic cylinder are shown in Table 3:

[0239] Table 3 Parameters of the hydraulic system

[0240] Parameter Name Value Rated Pressure of Hydraulic Cylinder 63 MPa Rated Thrust of Hydraulic Cylinder 1000 kN Inner Diameter of Hydraulic Cylinder 240 mm Piston Rod Stroke 200 mm Diameter of Center Hole 60 mm Range of Pressure Gauge 0 - 100 MPa Accuracy Class of Pressure Gauge Grade 0.5 Accuracy of Displacement Sensor 0.01 mm Range of Displacement Sensor 0 - 50 mm

[0241] Apply hydraulic oil to the hydraulic cylinder using a hydraulic oil pump, establish a monitoring system for the pulling jump index of the anchor rod, and record the relationship between the pressure gauge reading and the displacement of the anchor rod. According to the characteristics of the silt geology, calculate the tensile decay coefficient β = 0.0032 mm - 1, the anchorage characteristic coefficient α = 0.0245 mm - 1, the interface characteristic coefficient γ = 0.1837 mm - 1. Load according to the graded loading scheme. The design load is 250 kN, divided into 8 loading levels. The stabilization time after each level of loading is 5 minutes, and record the displacement data of the anchor rod as shown in Table 4:

[0242] Table 4 Displacement data of the anchor rod under graded loading

[0243] Loading Level Load Value (kN) Stable Displacement (mm) Displacement Rate (mm / min) Jump Index 1 50 0.18 0.003 0.21 2 100 0.41 0.005 0.35 3 150 0.68 0.008 0.52 4 200 1.03 0.015 0.79 5 250 1.46 0.023 1.28 6 300 2.05 0.035 1.87 7 350 2.89 0.058 2.76 8 375 3.87 0.083 4.25

[0244] When the load reaches 375 kN, the pulling jump index of the anchor rod exceeds the critical value of 3.0, indicating that the anchor rod reaches the critical state. Continue to increase the pulling force until the displacement of the anchor rod increases rapidly, and record the maximum pulling force value as 406 kN. Determine the yield point of the anchor rod as 352 kN by the double tangent method, corresponding to a displacement of 2.73 mm. Calculate the rigidity coefficient of the silt as shown in Table 5:

[0245] Table 5 Calculation of the rigidity coefficient of the silt

[0246] Parameter Value Tensile Force at Yield Point 352 kN Displacement at Yield Point 2.73 mm Diameter of Anchor Bolt 32 mm Length of Anchorage Zone 5000 mm Rigidity Coefficient of Silt <![CDATA[0.0129kN / mm 3 >

[0247] After the detection is completed, the staged unloading is carried out in the reverse order of loading. The stabilization time after each stage of unloading is 3 minutes. The displacement recovery during the unloading process is recorded as shown in Table 6:

[0248] Table 6 Unloading Displacement Recovery Data

[0249] Unloading Level Load Value (kN) Displacement Value (mm) Recovery Amount (mm) Recovery Rate (%) 1 300 3.62 0.25 6.47 2 225 3.27 0.35 9.04 3 150 2.83 0.44 11.37 4 75 2.21 0.62 16.02 5 0 1.43 0.78 20.16

[0250] The calculated recovery deviation degree is 0.37, which is higher than the threshold of 0.2, indicating that the bonding condition between the anchor rod and the silt is average. The calculated elastic deformation ratio is 63.05%, which is lower than the standard value of 70%, further confirming that the bonding condition between the anchor rod and the silt is average. The least squares method combined with non-linear regression analysis is used to process the detection data, and a mathematical model of the anchor rod anchoring performance P = 145.7·δ 0.856 is established, and the relative error of the model fitting accuracy is 3.85%. The calculated safety factor is 1.62, which is lower than the requirement of 2.0, indicating that the number of anchor rods needs to be increased or the anchoring method needs to be improved.

[0251] Traditional anchor rod detection methods usually adopt the vertical pulling method, which requires building a large reaction frame above the anchor rod and using a special anchor rod connection device to deflect the pulling force. This method is difficult to implement under the silt geological conditions. It is not only complex in operation, but also prone to additional bending moments due to eccentric pulling, resulting in distorted test data. In addition, traditional methods often only focus on the maximum pulling force value and lack in-depth analysis of the interaction process between the anchor rod and the silt medium.

[0252] The inclined anchor rod detection method of the present invention has significant advantages compared with the traditional method: First, the pulling is realized in the same direction as the embedding direction of the anchor rod through a rigid support structure, effectively reducing the eccentric pulling stress and improving the accuracy of the test data; Second, a complete set of mechanical equations for anchor rod pulling is established, including the pulling force transfer equation, displacement prediction equation, deformation response equation and critical state equation, which can comprehensively analyze the stress state and deformation characteristics of the anchor rod in the silt; Third, new parameters such as the anchor rod pulling jump index and recovery deviation degree are introduced, providing a more detailed judgment basis for the evaluation of the anchor rod anchoring performance; Fourth, non-linear regression analysis and the least squares method are used to fit and optimize the measured data, and a more accurate mathematical model of the anchor rod anchoring performance is established, providing reliable theoretical support and data basis for engineering design and construction.

[0253] It should be noted that the detailed explanations of the variables involved in the present invention are shown in Tables 7 and 8 below.

[0254] Table 7 Variable Explanation Table (Part 1)

[0255]

[0256]

[0257] Table 8 Explanation Table of Variables (Second Part)

[0258]

[0259] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A detection method for inclined anchor rods in silt geological conditions, characterized in that, Including: Establish a rigid support structure for bolt pull-out, including a base, columns, and inclined beams at a 45-degree angle to the base. The end of the inclined beam is provided with an open end plate. Pass the bolt from the base along the inclined beam through the opening of the end plate, determine the deviation index of the bolt pull-out direction, and ensure that the pull-out direction is consistent with the bolt embedding direction. Sleeve the hollow self-resetting hydraulic cylinder onto the bolt and position it at the end plate. Adjust the axis of the hydraulic cylinder to coincide with the axis of the bolt to ensure that the pulling force is applied along the axial direction of the bolt. Apply hydraulic oil to the hydraulic cylinder using a hydraulic oil pump, establish a monitoring system for the bolt pull-out jump index, and use the bolt pull-out mechanical equations to fit and optimize the measured data to form an accurate force-displacement curve. Gradually increase the pull-out force to the design load value according to the recovery deviation determination standard. Continue to increase the pull-out force to 1.5 times the design load, and record the bolt displacement. When the bolt displacement exceeds the critical value, record the maximum pull-out force value and calculate the rigidity coefficient of the anchor solid silt. After the inspection, issue a bolt pull-out inspection report.

2. The method for detecting inclined anchor rods in silt geological conditions according to claim 1, wherein Specifically, the rigid support structure for bolt pull-out is established as follows: Four No. 25 I-beams are welded to form the base, with the base size being 1700×1700 mm. Two No. 25 I-beam columns are welded, with the column height being 1346 mm. Two No. 25 I-beams are welded obliquely from the base as inclined beams, with the inclined beams at a 45-degree angle to the base. The inclined beams rest on the two steel columns, and a 30-mm-thick end plate is welded at the end of the inclined beam, with an opening of 50×50 mm at the end plate.

3. The method for detecting inclined anchor rods in silt geological conditions according to claim 2, wherein, The deviation index of the bolt pull-out direction refers to the angle deviation coefficient between the bolt pull-out direction and the bolt embedding axis. In an ideal state, the deviation index of the bolt pull-out direction is zero, indicating that the pull-out direction coincides completely with the bolt axis, avoiding the generation of shear stress and affecting the accuracy of the test results. The recovery deviation refers to the displacement recovery degree of the bolt when unloading after bearing a certain load. The calculation method is the ratio of the residual displacement after unloading to the maximum displacement. The smaller the recovery deviation, the closer the bolt is combined with the silt geology and the better the anchoring effect.

4. The method for detecting inclined anchor rods in silt geological strata according to claim 3, characterized in that, The bolt pull-out jump index refers to the non-linear relationship parameter between the bolt displacement and the tensile force change during the pull-out process, which is used to describe the critical point where the bolt displacement suddenly increases during the loading process. The change in the bolt pull-out jump index reflects the bonding strength between the anchor solid and the surrounding silt medium.

5. The method for detecting inclined anchor rods in silt geological conditions according to claim 1, characterized in that The silt rigidity coefficient refers to the deformation resistance of the silt geology under the action of the pull-out force, which is related to the silt moisture content, density, and silt cohesion. The larger the silt rigidity coefficient, the greater the anchoring resistance provided by the silt geology and the stronger the bolt anti-pull-out ability.

6. The method for detecting inclined anchor rods in silt geological conditions according to claim 1, characterized in that, The bolt pull-out mechanical equations include a tensile force transfer equation, a displacement prediction equation, a deformation response equation, and a critical state equation.

7. The method for detecting inclined anchor rods in silt geological conditions according to claim 6, wherein The tensile force transfer equation is used to calculate the force distribution of each cross-section of the bolt. The inputs include the bolt diameter, the elastic modulus of the bolt material, the silt friction coefficient, the bolt embedding depth, and the applied tensile force value, and the output is the force distribution function of each point along the axial direction of the bolt.

8. The method for detecting inclined anchor rods in silt geological conditions according to claim 1, characterized in that, The displacement prediction equation is used to predict the displacement of the bolt under different tensile forces. The inputs include the elastic modulus of the bolt material, the cross-sectional area of the bolt, the effective length of the bolt, the silt rigidity coefficient, and the applied tensile force value, and the output is the theoretical displacement.

9. The method for detecting inclined anchor rods in silt geological conditions according to claim 1, characterized in that, The deformation response equation is used to describe the interaction relationship between the anchor rod and the surrounding silt medium. The inputs include the surface roughness of the anchor rod, the cohesion of the silt, the embedding angle of the anchor rod, the length of the anchorage zone, and the groundwater level height, and the output is the stress distribution at the interface of the anchor solid.

10. The method for detecting inclined anchor rods in silt geological conditions according to claim 1, characterized in that The critical state equation is used to judge the stability change during the pulling process of the anchor rod. The inputs include the applied tensile force value, the displacement of the anchor rod, the displacement increment, the tensile force increment, and the time increment, and the output is the pulling jump index value of the anchor rod.

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