A double-layer composite protective net and its optimization method

Abstract

The present invention discloses a double-layer composite protection net and an optimization method thereof, belonging to the field of protection nets for rockfall impact. It includes support piles and a double-layer protection net structure fixed on both sides of the support piles. The double-layer protection net structure includes an inner protection net arranged facing the rockfall impact side and an outer protection net facing away from the rockfall impact side. The inner protection net is an annular net woven by steel strands, and the outer protection net is a grid net composed of transverse NPR steel strands and longitudinal NPR steel strands. The aperture of the grid net is smaller than that of the annular net, and the strength of the annular net is higher than that of the grid net. Both ends of the inner protection net and the outer protection net are sequentially fixed on the slope through tension plates and ground anchors, and the support piles are fixed on the ground through prestressed anchor cables. By adopting the above double-layer composite protection net and its optimization method, through the adoption of the double-layer protection net structure, it is possible to intercept both boulders and crushed stones while improving the protection safety level.

Description

Technical Field

[0001] The present invention relates to the technical field of protective nets for rockfall impact, and in particular to a double-layer composite protective net and an optimization method thereof. Background Art

[0002] Rockfall refers to the sudden downward collapse of dangerous rock masses or boulders on a slope after exceeding the critical balance point, and then rolling downward along the slope through one or several combinations of rolling, collision, rebound, jumping or sliding movement modes until it stops moving on flat ground, rivers, reservoirs or obstacles, etc. When there are human activity areas such as residential areas and construction sites below the rockfall, it may cause huge casualties and property losses. The passive protective net can form a surface protection for the protected area, thereby preventing the falling of collapsed rock masses and soil bodies and cushioning the impact of rockfall on the protected area to a certain extent. Therefore, it is necessary to set up protective measures to intercept rockfall in actual engineering.

[0003] The structure of the existing protective net is as follows:

[0004] CN202410130285.4 discloses a high-position and high-steep rockfall protection structure applicable to a rockfall impact energy level of 8000 KJ, which includes a protective net arranged on one side of the entrance and exit of a mountain tunnel or on the slope side of a mountain body. The protective net is fixed to the ground by multiple support columns; the protective net is a grid structure composed of multiple transverse NPR steel strands and multiple longitudinal NPR steel strands that intersect vertically and horizontally. The two ends of the transverse NPR steel strands pass through the outermost support columns and continue to extend, and the extended parts are anchored to the mountain slope or the ground after applying prestress.

[0005] It can be seen that the existing protective net is a single-layer structure, which can only intercept large boulders and has a poor interception effect on crushed stones. Summary of the Invention

[0006] The purpose of the present invention is to provide a double-layer composite protective net and an optimization method thereof to solve the above technical problems.

[0007] To achieve the above purpose, the present invention provides a double-layer composite protective net, which includes support piles and a double-layer protective net structure fixed on both sides of the support piles. The double-layer protective net structure includes an inner protective net arranged facing the rockfall impact side and an outer protective net facing away from the rockfall impact side. The inner protective net is an annular net woven from steel strands, and the outer protective net is a square grid composed of transverse NPR steel strands and longitudinal NPR steel strands. The aperture of the square grid is smaller than that of the annular net, and the strength of the annular net is higher than that of the square grid;

[0008] Both ends of the inner protective net and the outer protective net are sequentially fixed to the slope through tension plates and ground anchors, and the support piles are fixed to the ground through prestressed anchor cables.

[0009] Preferably, a plurality of spring buffer members are provided between the outer protective net and the inner protective net.

[0010] An optimization method for a double-layer composite protective net includes the following steps:

[0011] S1. Based on a double-layer composite protective net and a polyhedron rockfall model, construct an obstruction model under rockfall impact conditions;

[0012] S2. Dynamically analyze the constructed obstruction model through numerical simulation software to evaluate the performance of the double-layer composite protective net under different rockfall speeds, rockfall masses, and impact angles;

[0013] S3. Parameter adjustment: respectively adjust the sizes of the outer protective net and the inner protective net, the distance between the outer protective net and the inner protective net, the number and position distribution of the spring buffer members, and re-enter the adjusted parameters into step S2 for simulation, compare the performance after each adjustment, and determine the optimal parameter combination;

[0014] S4. Based on the optimal parameter combination, produce experimental samples and conduct actual tests under laboratory conditions to verify whether their protection effectiveness reaches the expected goal. If the expected indicators are met, output the final solution; otherwise, return to step S3;

[0015] S5. Construct according to the final solution.

[0016] Preferably, step S1 specifically includes the following steps:

[0017] S11. Determine the geometric parameters of the double-layer composite protective net: set the aperture of the inner protective net as , and the strength as ; and set the aperture of the outer protective net as , and the strength as ; where , ; at the same time, set the cross-sectional area of the support pile as , and the distance between the outer protective net and the inner protective net as ; set the number of spring buffer members as , and the elastic coefficient as ;

[0018] S12. Establish a polyhedron rockfall model: determine the coordinates of each vertex of the rockfall, use geometric modeling software, draw each face of the polyhedron according to the determined vertex coordinates to obtain a polyhedron model, and then import the polyhedron model into physical simulation software, set the material properties of the rockfall, the mass of the rockfall as , the initial velocity and the impact angle as ,

[0019] S13. Construct the mechanical model of the double-layer composite protection net: Consider both the inner protection net and the outer protection net as flexible structures, and establish the total stiffness calculation formula of the double-layer composite protection net:

[0020] ;

[0021] ;

[0022] ;

[0023] ;

[0024] ;

[0025] ;

[0026] In the formula, represents the total stiffness of the double-layer composite protection net; represents the stiffness of the outer protection net; represents the stiffness of the inner protection net; represents the stiffness of the spring buffer; represents the number of steel strands of the inner protection net; represents the elastic modulus of the steel strand; represents the cross-sectional area of the steel strand; represents the length of the steel strand; and respectively represent the stiffness of the transverse NPR steel strand and the longitudinal NPR steel strand; and respectively represent the number of the transverse NPR steel strand and the longitudinal NPR steel strand; and respectively represent the elastic modulus of the transverse NPR steel strand and the longitudinal NPR steel strand; and respectively represent the cross-sectional area of the transverse NPR steel strand and the longitudinal NPR steel strand; and respectively represent the length of the transverse NPR steel strand and the longitudinal NPR steel strand; represents the number of spring buffers; represents the elastic coefficient of the spring buffer;

[0027] S14. Set the contact conditions between the falling rock and the double-layer composite protection net to obtain the contact model;

[0028] S15. Simulate the contact force between the falling rock and the double-layer composite protection net, and calculate the normal force and the tangential force :

[0029] ;

[0030] ;

[0031] wherein, and respectively represent the spring constants in the normal and tangential directions; and respectively represent the displacement amounts in the normal and tangential directions; and respectively represent the velocity components in the normal and tangential directions; and respectively represent the normal viscous damping coefficient and the tangential viscous damping coefficient;

[0032] S16. Optimize the contact conditions described in step S14 using the simulation results of step S15, and loop steps S14 - S15 until the end condition is met, and output the obstacle model.

[0033] Preferably, in step S14, the falling rock is regarded as a rigid body, and the double - layer composite protection net is regarded as a flexible structure, and the contact type is determined to be rigid - flexible body contact, and it is surface - surface contact;

[0034] And set the static friction coefficient and the dynamic friction coefficient of the contact interface to describe the friction behavior of the contact interface;

[0035] Meanwhile, consider the energy dissipation when the falling rock impacts the double - layer composite protection net. The energy dissipation includes elastic energy , sliding energy and plastic energy , and their expressions are as follows:

[0036] ;

[0037] ;

[0038] ;

[0039] wherein, represents the cross - sectional area of the steel strand at the impact position of the falling rock; represents the elastic modulus of the steel strand at the impact position of the falling rock; represents the deformation amount at the impact position of the falling rock; represents the force - displacement relationship function; represents the displacement of the double - layer composite protection net at the impact position of the falling rock; is a random number within the range; Represents the force-displacement curve; Represents the length of the steel strand at the rockfall impact position.

[0040] Preferably, in step S2, input the polyhedron rockfall model and the double-layer composite protection net parameters into the finite element software, perform the simulation, and record the deformation, stress distribution, and energy absorption of the double-layer composite protection net during the rockfall impact as the performance indicators.

[0041] Therefore, the present invention adopts the above-mentioned double-layer composite protection net and its optimization method, and the beneficial effects are as follows:

[0042] 1. Multi-level protection: The inner ring net (woven with steel strands) and the outer grid net (composed of NPR steel strands) are adopted. The inner and outer two-layer protection nets form a double barrier, which can effectively disperse and absorb the rockfall impact energy, and improve the overall protection performance; and the high-strength characteristic of the inner protection net ensures reliable protection even in extreme cases, while the small aperture design of the outer protection net can block small gravel or objects from passing through;

[0043] 2. Application of spring buffer members: A plurality of spring buffer members are arranged between the inner and outer protection nets, which further enhances the shock absorption capacity of the system and reduces the impact force directly transmitted to the support piles and fixed structures; and the number and distribution positions of the spring buffer members can be adjusted according to the actual situation to flexibly adapt to different terrain and environmental requirements;

[0044] 3. Optimization process based on numerical simulation: Starting from constructing the obstacle model, through multiple simulation analyses and parameter adjustments until the optimal design scheme is found, which ensures the scientificity and reliability of the final scheme;

[0045] Using advanced finite element analysis software to accurately simulate the actual working conditions can accurately predict the performance of the protection net under various conditions, providing solid data support for engineering applications;

[0046] 4. Comprehensive consideration of influencing factors: Not only pay attention to the static parameters such as the geometric dimensions and material properties of the protection net itself, but also fully consider the dynamic factors such as the speed, mass, and impact angle of the rockfall, making the optimization result closer to the real scenario; at the same time, in-depth research is carried out on the friction behavior of the contact interface and the energy dissipation mechanism, which helps to improve the ability of the system to resist complex external loads;

[0047] 5. Experimental verification link: Making experimental samples under laboratory conditions and conducting actual tests to verify the effectiveness of the simulation results, further ensuring the feasibility and safety of the design scheme; at the same time, continuously improving and perfecting the design according to the experimental feedback, forming a closed-loop optimization system, and improving the success rate and technical level of the project.

[0048] In summary, the double-layer composite protection net and its optimization method of the present invention have the characteristics of reasonable structure, excellent performance, and scientific optimization, and have broad application prospects in the field of slope protection and other fields.

[0049] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is one layout diagram of a double-layer composite protection net of the present invention;

[0051] Figure 2 It is another layout diagram of a double-layer composite protection net of the present invention;

[0052] Figure 3 It is a flowchart of an optimization method of a double-layer composite protection net of the present invention.

[0053] BRIEF DESCRIPTION OF THE DRAWINGS: 1. Outer protection net; 2. Inner protection net; 3. Tie plate; 4. Ground anchor; 5. Prestressed anchor cable; 6. Support pile; 7. Spring buffer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of this application. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions throughout.

[0055] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or server that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0056] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] As Figure 1 and Figure 2As shown in the figure, a double - layer composite protection net includes support piles and a double - layer protection net structure fixed on both sides of the support piles. The double - layer protection net structure includes an inner protection net 2 arranged facing the side of rockfall impact and an outer protection net 1 facing away from the side of rockfall impact. The inner protection net 2 is an annular net woven from steel strands, and the outer protection net 1 is a square grid net composed of transverse NPR steel strands and longitudinal NPR steel strands. The aperture of the square grid net is smaller than that of the annular net, and the strength of the annular net is higher than that of the square grid net. Both ends of the inner protection net 2 and the outer protection net 1 are fixed to the slope through tension plates 3 and ground anchors 4 in sequence, and the support piles 6 are fixed to the ground through prestressed anchor cables 5.

[0058] And a plurality of spring buffer members 7 are arranged between the outer protection net 1 and the inner protection net 2.

[0059] As Figure 2 shown, an optimization method for a double - layer composite protection net includes the following steps:

[0060] S1. Based on a double - layer composite protection net and a polyhedron rockfall model, construct an obstacle model under rockfall impact conditions;

[0061] Step S1 specifically includes the following steps:

[0062] S11. Determine the geometric parameters of the double - layer composite protection net: Set the aperture of the inner protection net as , the strength as ; and set the aperture of the outer protection net as , the strength as ; where , ; At the same time, set the cross - sectional area of the support pile as , the distance between the outer protection net and the inner protection net as ; Set the number of spring buffer members as , and the elastic coefficient as ;

[0063] S12. Establish a polyhedron rockfall model: Determine the coordinates of each vertex of the rockfall. In a geometric modeling software, draw each face of the polyhedron according to the determined vertex coordinates to obtain a polyhedron model, and then import the polyhedron model into a physical simulation software. Set the material properties of the rockfall, the mass of the rockfall as , the initial velocity and the impact angle as ,

[0064] S13. Construct a mechanical model of the double - layer composite protection net: Consider both the inner protection net and the outer protection net as flexible structures, and establish a total stiffness calculation formula for the double - layer composite protection net:

[0065] ;

[0066] ;

[0067] ;

[0068] ;

[0069] ;

[0070] ;

[0071] In the formula, represents the total stiffness of the double-layer composite protection net; represents the stiffness of the outer protection net; represents the stiffness of the inner protection net; represents the stiffness of the spring buffer; represents the number of steel strands of the inner protection net; represents the elastic modulus of the steel strand; represents the cross-sectional area of the steel strand; represents the length of the steel strand; and represent the stiffness of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the number of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the elastic modulus of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the cross-sectional area of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the length of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; represents the number of spring buffers; represents the elastic coefficient of the spring buffer;

[0072] S14. Set the contact conditions between the falling rock and the double-layer composite protection net to obtain the contact model;

[0073] S15. Simulate the contact force between the falling rock and the double-layer composite protection net, and calculate the normal force and the tangential force at each time step according to the contact conditions:

[0074] ;

[0075] ;

[0076] In the formula, and represent the spring constants in the normal and tangential directions respectively; and represent the displacement amounts in the normal and tangential directions respectively; and represent the velocity components in the normal and tangential directions respectively; and represent the normal viscous damping coefficient and the tangential viscous damping coefficient respectively;

[0077] S16. Optimize the contact conditions described in step S14 using the simulation results of step S15, and loop steps S14 - S15 until the end condition is met, then output the hindrance model.

[0078] Preferably, in step S14, the falling rock is regarded as a rigid body, and the double - layer composite protection net is regarded as a flexible structure. Determine the contact type as rigid - flexible body contact, and it is surface - surface contact;

[0079] And set the static friction coefficient and the dynamic friction coefficient of the contact interface to describe the friction behavior of the contact interface;

[0080] Meanwhile, consider the energy dissipation when the falling rock impacts the double - layer composite protection net. The energy dissipation includes elastic energy , sliding energy and plastic energy , and their expressions are as follows:

[0081] ;

[0082] ;

[0083] ;

[0084] In the formula, represents the cross - sectional area of the steel strand at the impact position of the falling rock; represents the elastic modulus of the steel strand at the impact position of the falling rock; represents the deformation amount at the impact position of the falling rock; represents the force - displacement relationship function; represents the displacement of the double - layer composite protection net at the impact position of the falling rock; is a random number within the range; represents the force - displacement curve; represents the length of the steel strand at the impact position of the falling rock.

[0085] S2. Dynamically analyze the constructed obstacle model through numerical simulation software to evaluate the performance of the double-layer composite protection net under different rockfall speeds, rockfall masses, and impact angles;

[0086] In step S2, input the polyhedral rockfall model and the parameters of the double-layer composite protection net into the finite element software, perform the simulation, and record the deformation, stress distribution, and energy absorption of the double-layer composite protection net during the rockfall impact as the performance indicators.

[0087] S3. Parameter adjustment: Adjust the sizes of the outer protection net and the inner protection net, the distance between the outer protection net and the inner protection net, the number and position distribution of the spring buffers respectively, and re-enter the adjusted parameters into step S2 for simulation. Compare the performance after each adjustment to determine the optimal parameter combination;

[0088] S4. Based on the optimal parameter combination, make experimental samples and conduct actual tests under laboratory conditions to verify whether their protection efficiency reaches the expected goal. If it reaches the expected indicators, output the final solution; otherwise, return to step S3;

[0089] S5. Construct according to the final solution.

[0090] The parameters involved in the final solution obtained by using the optimization method of the present invention are as follows: the aperture of the inner protection net is 0.08 m; the aperture of the outer protection net is 0.02 m; the cross-sectional area of the support pile is 2 m * 3 m; the distance between the holes of the inner protection net and the outer protection net is 3 m; the number of spring buffers is 50; the elastic coefficient of the spring buffer is 2000; the static friction coefficient is 0.6; the dynamic friction coefficient is 0.4; the total stiffness of the protection net obtained by adopting the above final solution is 180,000 N / m, and it can intercept gravel with a particle size of more than 0.02 m.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for optimizing a double-layer composite protective net, the double-layer composite protective net comprising supporting piles and a double-layer protective net structure fixed on both sides of the supporting piles, the double-layer protective net structure comprising an inner protective net arranged facing the rockfall impact side and an outer protective net away from the rockfall impact side, wherein the inner protective net is an annular net woven from steel strands, and the outer protective net is a grid net composed of transverse NPR steel strands and longitudinal NPR steel strands, the aperture of the grid net is smaller than the aperture of the annular net, and the strength of the annular net is higher than the strength of the grid net; both ends of the inner protective net and the outer protective net are fixed to the slope via tension plates and ground anchors in turn, the supporting piles are fixed to the ground via prestressed anchor cables, and a plurality of spring buffers are arranged between the outer protective net and the inner protective net; the characteristics are as follows: The optimization method includes the following steps: S1. Based on the double-layer composite protection net and the polyhedron rockfall model, construct an obstacle model under rockfall impact conditions; Step S1 specifically includes the following steps: S11. Determine the geometric parameters of the double-layer composite protection net: Set the aperture of the inner protection net , with a strength of ; and set the aperture of the outer protection net , with a strength of ; where , ; At the same time, set the cross-sectional area of the support pile to , and the distance between the outer protection net and the inner protection net to ; Set the number of spring buffers to , and the elastic coefficient to ; S12. Establish a polyhedron rockfall model: Determine the coordinates of each vertex of the rockfall. In a geometric modeling software, draw each face of the polyhedron according to the determined vertex coordinates to obtain a polyhedron model. Then import the polyhedron model into a physical simulation software and set the material properties of the rockfall, the mass of the rockfall to be , the initial velocity and the impact angle to be ; S13. Construct the mechanical model of the double-layer composite protection net: regard both the inner protection net and the outer protection net as flexible structures, and establish the total stiffness calculation formula of the double-layer composite protection net; ； ； ； ； ； ； Wherein, represents the total stiffness of the double-layer composite protective net; represents the stiffness of the outer protective net; represents the stiffness of the inner protective net; represents the stiffness of the spring buffer; represents the number of steel strands of the inner protective net; represents the elastic modulus of the steel strand; represents the cross-sectional area of the steel strand; represents the length of the steel strand; and represent the stiffness of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the number of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the elastic modulus of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the cross-sectional area of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; and represent the length of the transverse NPR steel strand and the longitudinal NPR steel strand respectively; represents the number of spring buffers; represents the elastic coefficient of the spring buffer; S14. Set the contact conditions between the rockfall and the double-layer composite protection net to obtain the contact model; S15. Simulate the contact force between the simulated falling rock and the double-layer composite protection net, and calculate the normal force and tangential force at each time step according to the contact conditions. and tangential force : ； ； Wherein, and respectively represent the spring constants in the normal and tangential directions; and respectively represent the displacement amounts in the normal and tangential directions; and respectively represent the velocity components in the normal and tangential directions; and respectively represent the normal viscous damping coefficient and the tangential viscous damping coefficient; S16. Use the simulation results of step S15 to optimize the contact conditions described in step S14, and cycle steps S14 - S15 until the end condition is met, and output the obstacle model; S2. Perform dynamic analysis on the constructed obstacle model through numerical simulation software to evaluate the performance of the double-layer composite protection net under different rockfall speeds, rockfall masses, and impact angles; S3. Parameter adjustment: respectively adjust the sizes of the outer protection net and the inner protection net, the distance between the outer protection net and the inner protection net, the number and position distribution of the spring buffers, and re-enter the adjusted parameters into step S2 for simulation, compare the performance after each adjustment, and determine the optimal parameter combination; S4. Based on the optimal parameter combination, produce experimental samples and conduct actual tests under laboratory conditions to verify whether their protection effectiveness reaches the expected goal. If the expected indicators are met, output the final solution; otherwise, return to step S3; S5. Carry out construction according to the final solution.

2. The optimization method of a double-layer composite protection net according to claim 1, characterized in that: In step S14, regard the rockfall as a rigid body and the double-layer composite protection net as a flexible structure, determine the contact type as rigid-flexible body contact, and it is surface-surface contact; And set the static friction coefficient of the contact interface and the dynamic friction coefficient , to describe the friction behavior of the contact interface; Meanwhile, considering the energy dissipation when a falling rock impacts the double-layer composite protection net, the energy dissipation includes elastic energy , sliding energy and plastic energy , and its expression is as follows: ； ； ； In the formula, represents the cross-sectional area of the steel strand at the rockfall impact position; represents the elastic modulus of the steel strand at the rockfall impact position; represents the deformation amount at the rockfall impact position; represents the force-displacement relationship function; represents the displacement of the double-layer composite protection net at the rockfall impact position; is a random number within the range; represents the force-displacement curve; represents the length of the steel strand at the rockfall impact position.

3. The optimization method of a double-layer composite protection net according to claim 2, wherein: In step S2, input the polyhedron rockfall model and the double-layer composite protection net parameters into the finite element software, execute the simulation, and record the deformation, stress distribution, and energy absorption of the double-layer composite protection net during the rockfall impact process as the performance index.

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