Recyclable tension and compression composite type anchor rod in bag and its bearing capacity calculation method

Abstract

The application discloses a bag type recyclable pressure type anchor rod, which comprises an anchor head anchor, a rod body, a bearing body and an anchoring body. The rod body comprises a steel strand and a protective sleeve, the protective sleeve is sleeved on the periphery of the steel strand, the bearing body is connected with the steel strand at the end of the rod body, and the anchoring body comprises a cement soil anchoring body and a cement slurry anchoring body. The cement soil anchoring body is formed by high-pressure rotary jet grouting process of cement slurry and surrounding soil, and the cement slurry anchoring body is formed by injecting cement slurry into a bag around the rod body through a reserved grouting pipe. The anchor rod makes the shear stress distribution of the anchoring body and the soil interface more uniform, effectively prevents the cement soil anchoring body from being damaged under pressure, and fully plays the bearing performance of the anchoring body. The application also provides a bearing capacity calculation method of the bag type recyclable pressure type anchor rod, which can obtain the limit bearing capacity data of the anchor rod concisely, efficiently and accurately.

Description

Technical Field

[0001] This invention relates to a bag-type recyclable tension-compression composite anchor and its bearing capacity calculation method, which is mainly applied to foundation pit engineering, slope engineering and tunnel engineering. Background Technology

[0002] With the development of engineering construction and the utilization of underground space in my country, the number and scale of foundation pit projects are constantly expanding. Anchored retaining structures, by setting prestressed anchor rods to provide support points for the retaining structure, can actively reinforce the soil and rock mass compared to other support methods such as pile foundations and bracing in foundation pit support. This provides more space for subsequent foundation pit excavation and basement construction, saves time on support construction and dismantling, improves construction speed and efficiency, and is also economical. It is currently widely used in foundation pit support projects.

[0003] Traditional prestressed anchors are divided into tension anchors and compression anchors. Tension anchors transfer external loads to the soil and rock mass through the bond between the anchorage and the reinforcement. However, tension anchors tend to extend beyond the land boundary during use, and their reinforcement can become obstacles to subsequent underground space development, which greatly limits their practical application. Consequently, compression anchors were developed.

[0004] Pressure-type anchor bolts transfer the load directly to the bottom end (the end furthest from the free section) of the anchor bolt via sleeved steel strands or unbonded prestressed steel strands. This load-bearing body consists of the load-bearing component, the unlocking anchor, and its outer protective sleeve. Pressure-type anchor bolts can be retrieved using the unlocking device at the end of the reinforcement, allowing the anchor bolt to be recovered after its service life. This addresses the issue of anchor bolts exceeding the red line, preventing them from becoming underground obstacles for subsequent construction, aligning with sustainable development and "dual carbon" goals, saving resources, and being environmentally friendly. However, pressure-type anchor bolts can cause stress concentration at the load-bearing body location, making the anchor body at the front end of the load-bearing body susceptible to compressive failure and preventing the anchor body from fully utilizing its load-bearing capacity.

[0005] To overcome the application defects of tension and compression anchors, this invention develops a pocket-type recyclable tension-compression composite prestressed anchor (hereinafter referred to as a pocket-type recyclable tension-compression composite anchor). However, there is currently no calculation theory for pocket-type recyclable tension-compression composite anchors, either domestically or internationally. As a new type of anchor, the existing national standard anchor bearing capacity calculation formula is no longer applicable, and existing theories cannot calculate the bearing capacity of each load transfer interface. Therefore, this invention also provides a method for calculating the bearing capacity of pocket-type recyclable tension-compression composite anchors. By analyzing the stress mechanism of various parts of the pocket-type recyclable tension-compression composite anchor, the ultimate bearing capacity of the anchor is provided, providing a basis for engineering design. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a bag-type recyclable tension-compression composite anchor bolt. This anchor bolt makes the shear stress distribution at the interface between the anchor body and the soil more uniform, and can increase the area of ​​the compression zone of the cement-soil anchor body at its front end and reduce its stress level to effectively prevent the cement-soil anchor body from failing under pressure, thus fully utilizing the bearing capacity of the anchor body. This invention also provides a method for calculating the bearing capacity of the above-mentioned bag-type recyclable tension-compression composite anchor bolt. This method can obtain the ultimate bearing capacity data of the anchor bolt simply, efficiently and accurately.

[0007] To address this, the present invention provides a bag-type recyclable tension-compression composite anchor bolt, comprising an anchor head, a rod body, a bearing body, and an anchor body. The anchor body includes a cement-soil anchor body and a cement grout anchor body, with the cement grout anchor body located within the cement-soil anchor body and at its rear. The cement grout anchor body is formed by injecting cement grout into the bag. The bearing body is radially positioned within the cement grout anchor body in the bag. Multiple high-strength fiber reinforcements are laterally distributed within the bag and fixedly connected to the bearing body. The rod body includes steel strands and a sleeve, with the sleeve fitted onto the steel strands. The steel strands are located at the front of the bearing body and connected to it.

[0008] Preferably, the rear end of the rod is provided with an unlocking anchor and an unlocking anchor protective sleeve.

[0009] Preferably, the cement-soil anchor body is formed with the surrounding soil through a high-pressure jet grouting process, and the cement grout anchor body is formed by injecting cement grout into the bag surrounding the pole body through a pre-reserved grouting pipe.

[0010] This invention also provides a method for calculating the bearing capacity of the above-mentioned bag-type recyclable tension-compression composite anchor, comprising the following steps:

[0011] Step 1. Determine the critical anchorage length of the cement grout anchor in the pressure zone.

[0012] Its expression is:

[0013] (20)

[0014] In the formula: This refers to the critical anchorage length of the cement grout anchor body in the pressure zone; d 1 represents the diameter of the cement grout anchor body; The comprehensive elastic modulus of the cement grout anchor solid in the pressure-bearing zone; This refers to the shear modulus of the cement-soil anchor body.

[0015] The critical anchorage length of the cement grout anchor in the pressure zone can be determined using this formula.

[0016] Step 2. Determine the bearing capacity of the cement grout anchor in the pressure zone.

[0017] The cement grout anchor body in the pressure zone should not be damaged by pressure under normal working conditions, and should not slip off from the surrounding structure.

[0018] The bearing capacity of the cement grout anchor body in the pressure zone is the smaller of the compressive bearing capacity of the cement grout anchor body at the front end of the bearing body and the interfacial frictional resistance between the cement grout anchor body in the pressure zone and the surrounding cement-soil anchor body.

[0019] The compressive bearing capacity of the cement grout anchor body at the front end of the bearing body is calculated according to formula (21):

[0020] (twenty one)

[0021] In the formula: This represents the ultimate compressive stress that the cement grout anchor can withstand. The diameter of the cement grout anchor body.

[0022] The interfacial friction between the cement grout anchor body in the pressure zone and the surrounding structure is:

[0023] (twenty two)

[0024] In the formula: The shear strength of the interface between the cement grout anchor and the surrounding structure; The length of the cement grout anchor body in the pressure-bearing zone; This is the critical length of the cement grout anchor body in the pressure zone.

[0025] According to equations (21) and (22), the bearing capacity of the cement grout anchor solid in the pressure zone is:

[0026] (twenty three)

[0027] Step 3. Determine the critical anchorage length of the cement grout anchor in the tension zone.

[0028] Its expression is:

[0029] (twenty four)

[0030] In the formula: The critical anchorage length of the cement grout anchor body in the tension zone; The diameter of the cement grout anchor body; The comprehensive elastic modulus of the cement grout anchor solid in the tension zone; This refers to the shear modulus of the cement-soil anchor body.

[0031] The critical anchorage length of the cement grout anchor in the tension zone can be determined using this formula.

[0032] Step 4. Determine the bearing capacity of the cement grout anchor in the tension zone.

[0033] Under normal working conditions, the high-strength fiber reinforcement within the tension zone of the cement grout anchor should not slip off from the cement grout anchor, and the cement grout anchor in the tension zone should not slip off from the surrounding cement-soil anchor.

[0034] The bearing capacity of the cement grout anchor body in the tension zone is the smaller of the bond force between the high-strength fiber reinforcement and the reinforced soil within the cement grout anchor body area and the interfacial friction between the cement grout anchor body in the tension zone and the surrounding cement-soil anchor body.

[0035] Bonding force between high-strength fiber reinforcement and reinforced soil within the cement grout anchorage area:

[0036] (25)

[0037] In the formula: The interfacial shear strength between the high-strength fiber reinforcement and the cement grout anchor body; Take the smaller value of the length of the high-strength fiber reinforcement in the cement grout anchor body in the pressure zone and the cement grout anchor body in the tension zone; The diameter of the high-strength fiber reinforcement.

[0038] Interfacial friction between the cement grout anchor body in the tension zone and the surrounding cement-soil anchor body:

[0039] (26)

[0040] In the formula: The length of the cement grout anchor body in the tension zone; This is the critical length of the cement grout anchor body in the tension zone.

[0041] According to equations (25) and (26), the bearing capacity of the cement grout anchor solid in the tension zone is:

[0042] (27)

[0043] Step 5. Determine the overall bearing capacity of the cement grout anchor.

[0044] According to equations (23) and (27), the overall bearing capacity of the cement grout anchor is:

[0045] (28)

[0046] Step 6. Determine the critical anchorage length of the cement-soil anchorage in Zone I.

[0047] Its expression is:

[0048] (29)

[0049] In the formula: The critical anchorage length of the cement-soil anchorage body in Zone I; The diameter of the cement-soil anchor body; The comprehensive elastic modulus of the cement-soil anchor solid in Zone I; This is the shear modulus of the surrounding soil.

[0050] The critical anchorage length of the cement-soil anchorage body in Zone I can be determined using this formula.

[0051] Step 7. Determine the bearing capacity of the cement-soil anchorage in Zone I.

[0052] The bearing capacity of the cement-soil anchor body in Zone I is the smaller of the compressive bearing capacity of the cement-soil anchor body in Zone I at the front end of the cement grout anchor body and the interfacial frictional resistance between the cement-soil anchor body in Zone I and the surrounding rock and soil.

[0053] The compressive bearing capacity of the cement-soil anchor body in zone I at the front end of the cement grout anchor body is:

[0054] (30)

[0055] In the formula: This represents the ultimate compressive stress that the cement-soil anchor can withstand. The diameter of the cement-soil anchor body.

[0056] The interfacial friction between the cement-soil anchor body and the surrounding rock and soil in Zone I is:

[0057] (31)

[0058] In the formula: The shear strength of the interface between the cement-soil anchor and the surrounding rock and soil; The length of the cement-soil anchor in Zone I; This represents the critical length of the cement-soil anchor body in Zone I.

[0059] According to equations (30) and (31), the bearing capacity of the cement-soil anchor solid in Zone I is:

[0060] (32)

[0061] Step 8. Determine the critical anchorage length of the cement-soil anchorage in Zone II.

[0062] Its expression is:

[0063] (33)

[0064] In the formula: The critical anchorage length of the cement-soil anchorage body in Zone II; The diameter of the cement-soil anchor body; The comprehensive elastic modulus of the cement-soil anchor solid in Zone II; This is the shear modulus of the surrounding soil.

[0065] The critical anchorage length of the cement-soil anchorage in Zone II can be determined using this formula.

[0066] Step 9. Determine the bearing capacity of the cement-soil anchor in Zone II.

[0067] When the cement-soil anchor body in Zone II is in normal working condition, there should be no slippage between the cement-soil anchor body in Zone II and the surrounding rock and soil. At the same time, the cement grout anchor body inside the cement-soil anchor body in Zone II should also be in normal working condition.

[0068] The bearing capacity of the cement-soil anchor body in Zone II is the smaller value between the interfacial frictional resistance between the cement-soil anchor body in Zone II and the surrounding rock and soil, and the bearing capacity of the cement grout anchor body inside the cement-soil anchor body in Zone II.

[0069] In practical engineering applications, the anchorage length of cement grout anchors is much shorter than their critical anchorage length. Therefore, the shear stress distribution at the interface between the cement grout anchor and the cement-soil anchor tends to be uniform. The anchorage length of the cement-soil anchor in Zone II is also much shorter than its critical anchorage length. Therefore, the shear stress distribution at the interface between the cement-soil anchor and the surrounding soil and rock in Zone II can be simplified to a uniform distribution. For safety, the ultimate shear stress at the interface is multiplied by a corresponding reduction factor. .

[0070] The interfacial friction between the cement-soil anchor body and the surrounding rock and soil in Zone II is:

[0071] (34)

[0072] In the formula: The length of the cement-soil anchor in Zone II.

[0073] According to equations (28) and (34), the bearing capacity of the cement-soil anchor solid in Zone II is:

[0074] (35)

[0075] Step 10. Determine the overall bearing capacity of the anchor body.

[0076] According to equations (32) and (33), the bearing capacity of the bag-type recyclable tension-compression composite anchor is:

[0077] (36)

[0078] Step 11. Determine the bearing capacity of the bag-type recyclable tension-compression composite anchor bolt.

[0079] The overall bearing capacity of the bag-type recyclable tension-compression composite anchor should be the smaller value among the overall bearing capacity of the anchor body, the bearing capacity of the steel strand, and the normal working limit bearing capacity of the unlocking anchor.

[0080] The load-bearing capacity of the steel strand is:

[0081] (37)

[0082] In the formula: The strength reduction factor for steel strands can be taken as 0.80~0.95; This refers to the design value of the tensile strength of the steel strand; This represents the effective cross-sectional area of ​​the steel strand.

[0083] The overall bearing capacity of the bag-type recyclable tension-compression composite anchor bolt is:

[0084] (38)

[0085] In the formula: The manufacturer's test report is required to determine the maximum bearing capacity of the anchorage under normal working conditions.

[0086] Technical effects of the present invention:

[0087] 1. The bag-type recyclable tension-compression composite anchor bolt provided by this invention has reinforcements at both the front and rear ends of the bearing body. The front reinforcement is a steel strand with a sleeve, and the rear reinforcement is a high-strength fiber reinforcement or basalt fiber reinforcement. High-strength fiber reinforcement and basalt fiber reinforcement have characteristics such as high strength and brittleness, exhibiting excellent tensile properties. However, due to their brittle nature, their shear resistance is poor, making them easy to cut. Therefore, when used in underground spaces, after fulfilling their function, they can be easily cut through without becoming an obstacle in later construction of railways, underground passages, or other tunnels. A bag is placed over the rear reinforcement, the bearing body, and part of the front steel strand. After high-pressure jet grouting, the bolt and the bag are placed together in cement soil, and cement grout is filled into the bag to form a double anchoring structure of cement grout and cement soil. Cement grout anchors not only increase the pressure zone area of ​​the cement-soil anchor at its front end and reduce its stress level, making the cement-soil anchor less prone to compressive failure, but also ensure a uniform distribution of interfacial shear stress between the cement-soil anchor and the soil, thereby improving the ultimate bearing capacity of the anchor.

[0088] 2) In this invention, by analyzing the stress mechanism of each part of the bag-type recyclable tension-compression composite anchor and calculating the bearing capacity of each part, the ultimate bearing capacity data of the anchor can be obtained simply, efficiently and accurately. This overcomes the deficiency that there is currently no calculation method for bag-type recyclable tension-compression composite anchors at home and abroad, and can provide a reliable basis for engineering design, which is conducive to saving material costs and improving safety. Attached Figure Description

[0089] Figure 1 This is a structural diagram of a bag-type recyclable tension-compression composite anchor bolt.

[0090] Figure 2 This is a cross-sectional view of various positions of a bag-type recyclable tension-compression composite anchor bolt.

[0091] Figure 3 This is a schematic diagram of the cement-soil anchor solid zone.

[0092] Figure 4 This is a schematic diagram of the cement grout anchor solid zone.

[0093] Figure 5 This is a schematic diagram showing the tensile failure of the cement grout anchor at the location of the load-bearing body.

[0094] Figure 6 This is a diagram illustrating the force mechanism of a tension-type anchor bolt.

[0095] Figure 7 This is a diagram showing the shear displacement model of the soil around a tension anchor.

[0096] Figure 8 This is a diagram showing the shear stress distribution pattern within the critical anchorage length.

[0097] Figure 9 A simplified diagram for calculating the damage.

[0098] Figure 10 This is the force diagram of region ① of the damaged body.

[0099] Figure 11 This is the force diagram of region ② of the damaged body.

[0100] Figure 12 The force diagram is shown for a small segment of the damaged body ②.

[0101] Figure 13 This diagram illustrates the stress mechanism of a bag-type recyclable tension-compression composite anchor bolt cement-soil anchor body.

[0102] Figure 14 This diagram illustrates the stress mechanism of the cement grout anchor body in a bag-type recyclable tension-compression composite anchor bolt.

[0103] Figure 15 This diagram illustrates the stress mechanism of high-strength fiber reinforcement inside the cement grout anchor body of a bag-type recyclable tension-compression composite anchor bolt.

[0104] Figure 16 This is a diagram showing the shear stress distribution at the cement-soil anchor interface of a bag-type recyclable tension-compression composite anchor bolt.

[0105] Figure 17 This is a diagram showing the shear stress distribution at the cement grout anchor body interface of a bag-type recyclable tension-compression composite anchor bolt.

[0106] Reference numerals: 1 Anchor head; 2 Steel strand; 3 Sleeve; 4 Cement-soil anchor body; 5 Bag; 6 High-strength fiber reinforcement; 7 Bearing body; 8 Unlocking anchor protective sleeve; 9 Cement grout anchor body. Detailed Implementation

[0107] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0108] Reference Figure 1-5 As shown, the bag-type recyclable tension-compression composite anchor bolt provided by the present invention includes an anchor head and anchorage 1, a rod body, a bearing body 7, and an anchor body. The bearing body 7 is a metal plate, preferably circular. The anchor body includes a cement-soil anchor body 4 and a cement grout anchor body 9. The cement-soil anchor body 4 is formed with the surrounding soil through a high-pressure jet grouting process. The cement grout anchor body 9 is formed by injecting cement grout into a bag 5 surrounding the rod body through a pre-reserved grouting pipe. The cement grout anchor body 9 is located inside the cement-soil anchor body 4 and is located on the rear side. The cement grout anchor body 9 is formed by injecting cement grout into the bag 5. The bearing body 7 is radially arranged in the cement grout anchor body 9 in the bag 5. Multiple high-strength fiber reinforcements 6 are transversely distributed in the bag 5 and are connected to the bearing body. The support body 7 is fixedly connected. The rod body includes a steel strand 2 and a sleeve 3. The sleeve 3 is sleeved on the steel strand 2. The inner end of the sleeve 3 is fixed to the support body 7. The joint between the two is sealed to ensure that no grout enters. The steel strand 2 is located on the front side of the support body 7 and is connected to the support body 7. The rear end of the rod body is provided with an unlocking anchor and an unlocking anchor protective sleeve 8. The unlocking anchor is located inside the support body 7 at the end of the steel strand 2, connecting the steel strand 2 to the support body 7. It is a component that can be detached from the support body 7 through unlocking. The unlocking anchor protective sleeve 8 is located outside the unlocking anchor and is connected to the support body 7. It should have good sealing performance to prevent grout from leaking into the unlocking device during grouting, which would make the anchor rod unrecoverable later.

[0109] The high-strength fiber reinforcement 6 in the aforementioned bag-type recyclable tension-compression composite anchor bolt is made of glass fiber or basalt fiber. High-strength fiber reinforcement 6 is characterized by high strength and brittleness, exhibiting excellent tensile properties. However, due to its brittle nature, its shear resistance is poor, making it easy to cut. Therefore, when used in underground spaces and its function completed, it can be easily cut through without becoming an obstacle in later construction of railways, underground passages, or other tunnels. A bag 5 is placed over the high-strength fiber reinforcement 6, the load-bearing body 7, and part of the front steel strand 2. After high-pressure jet grouting, the bolt body, along with the bag 5, is placed into the cement-soil mixture. Cement grout is then filled into the bag 5, forming a double anchoring structure of cement grout and cement-soil. The cement grout anchor body 9 not only increases the pressure zone area of ​​the front cement-soil anchor body 4 and reduces its stress level, making the cement-soil anchor body 4 less prone to compressive failure, but also ensures a uniform distribution of interfacial shear stress between the cement-soil anchor body 4 and the soil, improving the ultimate bearing capacity of the anchor bolt.

[0110] Reference Figure 1-17 As shown, when the aforementioned bag-type recyclable tension-compression composite anchor is subjected to an external load, the external load is ultimately transferred to the soil mass through the interfacial shear stress between the anchor body and the soil. This interfacial shear stress decreases along the length of the anchor, reaching zero after a certain length. Therefore, the shear stress of the anchor is only distributed within a certain length, and the length from the peak shear stress point to the zero shear stress point is the critical anchorage length. Within the critical anchorage length range, the shear stress distribution pattern is triangular, as shown in the figure. Figure 6 .

[0111] Within the critical anchorage length range, any point around the anchor body at a distance from the top... The magnitude of the shear stress at that point is:

[0112] (1)

[0113] (2)

[0114] In the formula: The critical anchorage length of the anchor body; The diameter of the anchor body; The load at the front end of the anchor body; The distance from the load-bearing end of the anchor body; This represents the interfacial shear stress between the top of the anchor body and the surrounding soil.

[0115] According to equation (1), the axial force of the anchor body is obtained as follows:

[0116] (3)

[0117] According to equation (3) and Hooke's law, the displacement at the top of the anchor body is:

[0118] (4)

[0119] In the formula: This represents the displacement at the end of the anchor body where the load is applied. The elastic modulus of the anchor body; Let be the cross-sectional area of ​​the anchor body.

[0120] Based on the similarity between anchor bolts and tension piles in terms of tension bearing mechanism and deformation characteristics, and without considering the vertical stress growth of the surrounding soil, the surrounding soil can adopt a shear displacement model similar to that of tension piles. (See...) Figure 7 .

[0121] According to the shear displacement model, the distance from the top of the anchor body... Distance from anchor body axis The soil shear stress at the location is:

[0122] (5)

[0123] The corresponding shear strain at this location is:

[0124] (6)

[0125] In the formula: This represents the soil displacement along the axis of the anchor body. This represents the soil displacement along the diameter of the anchor body. This is the shear modulus of the soil.

[0126] According to equations (5) and (6), we can obtain:

[0127] (7)

[0128] In the formula: The radius of influence of the anchor bolt.

[0129] when , hour:

[0130] (8)

[0131] According to the deformation compatibility condition, the displacement of the anchor body's front end is equal to the displacement of the surrounding soil, that is:

[0132] (9)

[0133] Based on engineering experience, take The critical anchorage length of the anchor body is obtained as follows:

[0134] (10)

[0135] When calculating the critical anchorage length, a simplified model of shear stress distribution is used, which is more uniform than the actual distribution pattern. Therefore, the critical anchorage length obtained from equation (10) is less than the actual value. To be on the safe side, a correction factor is multiplied. ,get:

[0136] (11)

[0137] Based on the calculation formula for the critical anchorage length and the distribution pattern of shear stress, the interfacial friction between the anchor body and the surrounding structure can be calculated.

[0138] The failure mode of the cement grout anchor body at the front end of the bearing body and the cement-soil anchor body at the front end of the cement grout anchor body (hereinafter referred to as the failure body) under compression is similar to the failure mode of the circular shallow foundation rock mass foundation, which is overall shear failure. A simplified force diagram of the failure body under compression failure is shown below. Figure 9 The cement grout anchor or cement-soil anchor at the point of failure can be divided into three parts: ①, ②, and ③. The force analysis diagrams for parts ① and ② are shown below. Figure 10 , Figure 11 , Figure 12 .

[0139] An axial equilibrium analysis of the forces acting in region ① yields the following results:

[0140] (12)

[0141] (13)

[0142] In the formula: The compressive bearing capacity of the damaged body; The sidewall pressure experienced by the damaged body; The normal stress between the damaged parts in regions ① and ②; The shear stress between the damaged parts in regions ① and ②; The angle between the failure edge of the shear failure body ① and the horizontal direction; It is the cohesive force of the destructive body; The internal friction angle of the destructive body; The diameter of the damaged body; The diameter of the pressure zone.

[0143] An axial equilibrium analysis of the forces acting in region ② yields the following results:

[0144] (14)

[0145] In the formula: The normal stress between the damaged parts in zones ② and ③; The shear stress is between the damaged parts in zones ② and ③.

[0146] The force exerted on point C by region ② is: We can obtain:

[0147] (15)

[0148] In the formula: The distance is AC; The distance to EC;

[0149] Using the elasticity of a cylinder and the generalized Hooke's law, and based on the deformation compatibility conditions of the anchor body and the sidewall soil, we can obtain:

[0150] (16)

[0151] In the formula: ; The elastic modulus of the structure surrounding the damaged body; The Poisson's ratio of the structures surrounding the damaged body; The elastic modulus of the broken body; The Poisson's ratio of the destructive body.

[0152] According to equations (12)-(16), we can obtain:

[0153] (17)

[0154] In the formula: ; ;

[0155] According to equations (12) and (17), the compressive bearing capacity of the damaged body can be determined as follows:

[0156] (18)

[0157] (19)

[0158] The present invention targets a bag-type recyclable tension-compression composite anchor bolt. The tension section of the anchor body is made of high-strength fiber reinforcement, whose tensile strength is much greater than the bond strength with the surrounding anchor body. The high-strength fiber reinforcement slips off from the surrounding anchor body before being subjected to tension, i.e., it fails to bear the load. Therefore, the tensile failure of the high-strength fiber reinforcement is not considered.

[0159] Reference Figure 1-17 As shown, the method for calculating the bearing capacity of the bag-type recyclable tension-compression composite anchor provided by the present invention includes the following steps:

[0160] Step 1. Determine the critical anchorage length of the cement grout anchor in the pressure zone.

[0161] Its expression is:

[0162] (20)

[0163] In the formula: This refers to the critical anchorage length of the cement grout anchor body in the pressure zone; d 1 represents the diameter of the cement grout anchor body; The comprehensive elastic modulus of the cement grout anchor solid in the pressure-bearing zone; This refers to the shear modulus of the cement-soil anchor body.

[0164] The critical anchorage length of the cement grout anchor in the pressure zone can be determined using this formula.

[0165] Step 2. Determine the bearing capacity of the cement grout anchor in the pressure zone.

[0166] The cement grout anchor body in the pressure zone should not be damaged by pressure under normal working conditions, and should not slip off from the surrounding structure.

[0167] The bearing capacity of the cement grout anchor body in the pressure zone is the smaller of the compressive bearing capacity of the cement grout anchor body at the front end of the bearing body and the interfacial frictional resistance between the cement grout anchor body in the pressure zone and the surrounding cement-soil anchor body.

[0168] The compressive bearing capacity of the cement grout anchor body at the front end of the bearing body is calculated according to formula (21):

[0169] (twenty one)

[0170] In the formula: This represents the ultimate compressive stress that the cement grout anchor can withstand. The diameter of the cement grout anchor body.

[0171] The interfacial friction between the cement grout anchor body in the pressure zone and the surrounding structure is:

[0172] (twenty two)

[0173] In the formula: The shear strength of the interface between the cement grout anchor and the surrounding structure; The length of the cement grout anchor body in the pressure-bearing zone; This is the critical length of the cement grout anchor body in the pressure zone.

[0174] According to equations (21) and (22), the bearing capacity of the cement grout anchor solid in the pressure zone is:

[0175] (twenty three)

[0176] Step 3. Determine the critical anchorage length of the cement grout anchor in the tension zone.

[0177] Its expression is:

[0178] (twenty four)

[0179] In the formula: The critical anchorage length of the cement grout anchor body in the tension zone; The diameter of the cement grout anchor body; The comprehensive elastic modulus of the cement grout anchor solid in the tension zone; This refers to the shear modulus of the cement-soil anchor body.

[0180] The critical anchorage length of the cement grout anchor in the tension zone can be determined using this formula.

[0181] Step 4. Determine the bearing capacity of the cement grout anchor in the tension zone.

[0182] Under normal working conditions, the high-strength fiber reinforcement within the tension zone of the cement grout anchor should not slip off from the cement grout anchor, and the cement grout anchor in the tension zone should not slip off from the surrounding cement-soil anchor.

[0183] The bearing capacity of the cement grout anchor body in the tension zone is the smaller of the bond force between the high-strength fiber reinforcement and the reinforced soil within the cement grout anchor body area and the interfacial friction between the cement grout anchor body in the tension zone and the surrounding cement-soil anchor body.

[0184] Bonding force between high-strength fiber reinforcement and reinforced soil within the cement grout anchorage area:

[0185] (25)

[0186] In the formula: The interfacial shear strength between the high-strength fiber reinforcement and the cement grout anchor body; Take the smaller value of the length of the high-strength fiber reinforcement in the cement grout anchor body in the pressure zone and the cement grout anchor body in the tension zone; The diameter of the high-strength fiber reinforcement.

[0187] Interfacial friction between the cement grout anchor body in the tension zone and the surrounding cement-soil anchor body:

[0188] (26)

[0189] In the formula: The length of the cement grout anchor body in the tension zone; This is the critical length of the cement grout anchor body in the tension zone.

[0190] According to equations (25) and (26), the bearing capacity of the cement grout anchor solid in the tension zone is:

[0191] (27)

[0192] Step 5. Determine the overall bearing capacity of the cement grout anchor.

[0193] According to equations (23) and (27), the overall bearing capacity of the cement grout anchor is:

[0194] (28)

[0195] Step 6. Determine the critical anchorage length of the cement-soil anchorage in Zone I.

[0196] Its expression is:

[0197] (29)

[0198] In the formula: The critical anchorage length of the cement-soil anchorage body in Zone I; The diameter of the cement-soil anchor body; The comprehensive elastic modulus of the cement-soil anchor solid in Zone I; This is the shear modulus of the surrounding soil.

[0199] The critical anchorage length of the cement-soil anchorage body in Zone I can be determined using this formula.

[0200] Step 7. Determine the bearing capacity of the cement-soil anchorage in Zone I.

[0201] The bearing capacity of the cement-soil anchor body in Zone I is the smaller of the compressive bearing capacity of the cement-soil anchor body in Zone I at the front end of the cement grout anchor body and the interfacial frictional resistance between the cement-soil anchor body in Zone I and the surrounding rock and soil.

[0202] The compressive bearing capacity of the cement-soil anchor body in zone I at the front end of the cement grout anchor body is:

[0203] (30)

[0204] In the formula: This represents the ultimate compressive stress that the cement-soil anchor can withstand. The diameter of the cement-soil anchor body.

[0205] The interfacial friction between the cement-soil anchor body and the surrounding rock and soil in Zone I is:

[0206] (31)

[0207] In the formula: The shear strength of the interface between the cement-soil anchor and the surrounding rock and soil; The length of the cement-soil anchor in Zone I; This represents the critical length of the cement-soil anchor body in Zone I.

[0208] According to equations (30) and (31), the bearing capacity of the cement-soil anchor solid in Zone I is:

[0209] (32)

[0210] Step 8. Determine the critical anchorage length of the cement-soil anchorage in Zone II.

[0211] Its expression is:

[0212] (33)

[0213] In the formula: The critical anchorage length of the cement-soil anchorage body in Zone II; The diameter of the cement-soil anchor body; The comprehensive elastic modulus of the cement-soil anchor solid in Zone II; This is the shear modulus of the surrounding soil.

[0214] The critical anchorage length of the cement-soil anchorage in Zone II can be determined using this formula.

[0215] Step 9. Determine the bearing capacity of the cement-soil anchor in Zone II.

[0216] When the cement-soil anchor body in Zone II is in normal working condition, there should be no slippage between the cement-soil anchor body in Zone II and the surrounding rock and soil. At the same time, the cement grout anchor body inside the cement-soil anchor body in Zone II should also be in normal working condition.

[0217] The bearing capacity of the cement-soil anchor body in Zone II is the smaller value between the interfacial frictional resistance between the cement-soil anchor body in Zone II and the surrounding rock and soil, and the bearing capacity of the cement grout anchor body inside the cement-soil anchor body in Zone II.

[0218] In practical engineering applications, the anchorage length of cement grout anchors is much shorter than their critical anchorage length. Therefore, the shear stress distribution at the interface between the cement grout anchor and the cement-soil anchor tends to be uniform. The anchorage length of the cement-soil anchor in Zone II is also much shorter than its critical anchorage length. Therefore, the shear stress distribution at the interface between the cement-soil anchor and the surrounding soil and rock in Zone II can be simplified to a uniform distribution. For safety, the ultimate shear stress at the interface is multiplied by a corresponding reduction factor. .

[0219] The interfacial friction between the cement-soil anchor body and the surrounding rock and soil in Zone II is:

[0220] (34)

[0221] In the formula: The length of the cement-soil anchor in Zone II.

[0222] According to equations (28) and (34), the bearing capacity of the cement-soil anchor solid in Zone II is:

[0223] (35)

[0224] Step 10. Determine the overall bearing capacity of the anchor body.

[0225] According to equations (32) and (33), the bearing capacity of the bag-type recyclable tension-compression composite anchor is:

[0226] (36)

[0227] Step 11. Determine the bearing capacity of the bag-type recyclable tension-compression composite anchor bolt.

[0228] The overall bearing capacity of the bag-type recyclable tension-compression composite anchor should be the smaller value among the overall bearing capacity of the anchor body, the bearing capacity of the steel strand, and the normal working limit bearing capacity of the unlocking anchor.

[0229] The load-bearing capacity of the steel strand is:

[0230] (37)

[0231] In the formula: The strength reduction factor for steel strands can be taken as 0.80~0.95; This refers to the design value of the tensile strength of the steel strand; This represents the effective cross-sectional area of ​​the steel strand.

[0232] The overall bearing capacity of the bag-type recyclable tension-compression composite anchor bolt is:

[0233] (38)

[0234] In the formula: The manufacturer's test report is provided to unlock the anchor's normal operating limit bearing capacity. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for calculating the bearing capacity of a bag-type recyclable tension-compression composite anchor bolt, wherein the bag-type recyclable tension-compression composite anchor bolt includes an anchor head, an anchor body, a bearing body, and an anchor body. The anchor body includes a cement-soil anchor body and a cement grout anchor body. The cement grout anchor body is located inside the cement-soil anchor body and at the rear side. The cement grout anchor body is formed by injecting cement grout into the bag. The bearing body is radially arranged in the cement grout anchor body within the bag. Multiple high-strength fiber reinforcements are laterally distributed within the bag and fixedly connected to the bearing body. The rod body includes steel strands and a sleeve. The sleeve is fitted onto the steel strands. The steel strands are located at the front side of the bearing body and connected to the bearing body. An unlocking anchor and an unlocking anchor protective sleeve are provided at the rear end of the rod body. The cement-soil anchor body is formed with the surrounding soil through a high-pressure jet grouting process. The cement grout anchor body is formed by injecting cement grout into the bag surrounding the rod body through a pre-reserved grouting pipe. Its characteristics are: The method for calculating bearing capacity includes the following steps: Step 1. Determine the critical anchorage length of the cement grout anchor in the pressure zone. Its expression is: （20） In the formula: This refers to the critical anchorage length of the cement grout anchor body in the pressure zone; The diameter of the cement grout anchor body; The comprehensive elastic modulus of the cement grout anchor solid in the pressure-bearing zone; The shear modulus of the cement-soil anchor body; The critical anchorage length of the cement grout anchor body in the pressure zone is determined based on this expression; Step 2. Determine the bearing capacity of the cement grout anchor in the pressure zone. The cement grout anchor body in the pressure zone should not be damaged by pressure under normal working conditions, and should not slip off from the surrounding structure. The bearing capacity of the cement grout anchor body in the pressure zone is the smaller value between the compressive bearing capacity of the cement grout anchor body at the front end of the bearing body and the interfacial frictional resistance between the cement grout anchor body in the pressure zone and the surrounding cement-soil anchor body. The compressive bearing capacity of the cement grout anchor body at the front end of the bearing body is calculated according to formula (21): （21） In the formula: This represents the ultimate compressive stress that the cement grout anchor can withstand. The diameter of the cement grout anchor body; The interfacial friction between the cement grout anchor body in the pressure zone and the surrounding structure is: （22） In the formula: The shear strength of the interface between the cement grout anchor and the surrounding structure; The length of the cement grout anchor body in the pressure-bearing zone; This refers to the critical anchorage length of the cement grout anchor body in the pressure zone; According to equations (21) and (22), the bearing capacity of the cement grout anchor solid in the pressure zone is: （23） Step 3. Determine the critical anchorage length of the cement grout anchor in the tension zone. Its expression is: （24） In the formula: The critical anchorage length of the cement grout anchor body in the tension zone; The diameter of the cement grout anchor body; The comprehensive elastic modulus of the cement grout anchor solid in the tension zone; The shear modulus of the cement-soil anchor body; The critical anchorage length of the cement grout anchor body in the tension zone is determined based on this expression; Step 4. Determine the bearing capacity of the cement grout anchor in the tension zone. Under normal working conditions, the high-strength fiber reinforcement within the tension zone of the cement grout anchor should not slip off from the cement grout anchor, and the cement grout anchor in the tension zone should not slip off from the surrounding cement-soil anchor. The bearing capacity of the cement grout anchor body in the tension zone is the smaller value between the bond force between the high-strength fiber reinforcement and the reinforced soil within the cement grout anchor body range and the interfacial friction between the cement grout anchor body in the tension zone and the surrounding cement-soil anchor body. Bonding force between high-strength fiber reinforcement and reinforced soil within the cement grout anchorage area: （25） In the formula: The interfacial shear strength between the high-strength fiber reinforcement and the cement grout anchor body; Take the smaller value of the length of the high-strength fiber reinforcement in the cement grout anchor body in the pressure zone and the cement grout anchor body in the tension zone; The diameter of the high-strength fiber reinforcement; Interfacial friction between the cement grout anchor body in the tension zone and the surrounding cement-soil anchor body: （26） In the formula: The length of the cement grout anchor body in the tension zone; The critical length of the cement grout anchor body in the tension zone; According to equations (25) and (26), the bearing capacity of the cement grout anchor solid in the tension zone is: （27） Step 5. Determine the overall bearing capacity of the cement grout anchor. According to equations (23) and (27), the overall bearing capacity of the cement grout anchor is: （28） Step 6. Determine the critical anchorage length of the cement-soil anchorage in Zone I. Its expression is: （29） In the formula: The critical anchorage length of the cement-soil anchorage body in Zone I; The diameter of the cement-soil anchor body; The comprehensive elastic modulus of the cement-soil anchor solid in Zone I; The shear modulus of the surrounding soil; The critical anchorage length of the cement-soil anchorage body in zone I is determined based on this expression; Step 7. Determine the bearing capacity of the cement-soil anchorage in Zone I. The bearing capacity of the cement-soil anchor body in Zone I is the smaller of the compressive bearing capacity of the cement-soil anchor body in Zone I at the front end of the cement grout anchor body and the interfacial frictional resistance between the cement-soil anchor body in Zone I and the surrounding rock and soil. The compressive bearing capacity of the cement-soil anchor body in zone I at the front end of the cement grout anchor body is: （30） In the formula: This represents the ultimate compressive stress that the cement-soil anchor can withstand. The diameter of the cement-soil anchor solid; The interfacial friction between the cement-soil anchor body and the surrounding rock and soil in Zone I is: （31） In the formula: The shear strength of the interface between the cement-soil anchor and the surrounding rock and soil; The length of the cement-soil anchor in Zone I; The critical length of the cement-soil anchor body in Zone I; According to equations (30) and (31), the bearing capacity of the cement-soil anchor solid in Zone I is: （32） Step 8. Determine the critical anchorage length of the cement-soil anchorage in Zone II. Its expression is: （33） In the formula: The critical anchorage length of the cement-soil anchorage body in Zone II; The diameter of the cement-soil anchor body; The comprehensive elastic modulus of the cement-soil anchor solid in Zone II; The shear modulus of the surrounding soil; The critical anchorage length of the cement-soil anchorage body in Zone II is determined based on this expression; Step 9. Determine the bearing capacity of the cement-soil anchor in Zone II. When the cement-soil anchor body in Zone II is in normal working condition, there should be no slippage between the cement-soil anchor body in Zone II and the surrounding rock and soil. At the same time, the cement grout anchor body inside the cement-soil anchor body in Zone II should also be in normal working condition. The bearing capacity of the cement-soil anchor body in Zone II is the smaller value between the interfacial frictional resistance between the cement-soil anchor body in Zone II and the surrounding rock and soil and the bearing capacity of the cement grout anchor body inside the cement-soil anchor body in Zone II. In practical engineering applications, the anchorage length of the cement grout anchor is much smaller than its critical anchorage length. Therefore, the shear stress distribution at the interface between the cement grout anchor and the cement-soil anchor tends to be uniform. The anchorage length of the cement-soil anchor in Zone II is also much smaller than its critical anchorage length. The shear stress distribution at the interface between the cement-soil anchor and the surrounding rock and soil in Zone II is simplified to a uniform distribution. To be on the safe side, the ultimate shear stress at the interface is multiplied by a corresponding reduction factor. ; The interfacial friction between the cement-soil anchor body and the surrounding rock and soil in Zone II is: （34） In the formula: The length of the cement-soil anchor in Zone II; According to equations (28) and (34), the bearing capacity of the cement-soil anchor solid in Zone II is: （35） Step 10. Determine the overall bearing capacity of the anchor body. According to equations (32) and (35), the overall bearing capacity of the anchor body is: （36） Step 11. Determine the bearing capacity of the bag-type recyclable tension-compression composite anchor bolt. The overall bearing capacity of the bag-type recyclable tension-compression composite anchor bolt should be the smaller value among the overall bearing capacity of the anchor body, the bearing capacity of the steel strand, and the normal working limit bearing capacity of the unlocking anchor. The load-bearing capacity of the steel strand is: （37） In the formula: The strength reduction factor for steel strands is taken as 0.80~0.95; This refers to the design value of the tensile strength of the steel strand; This is the effective cross-sectional area of ​​the steel strand; The overall bearing capacity of the bag-type recyclable tension-compression composite anchor bolt is: （38） In the formula: The manufacturer's test report is required to determine the maximum bearing capacity of the anchorage under normal working conditions.

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