Optimization design method for protective net of tunnel construction rack

Abstract

The invention discloses a tunnel construction rack protective net optimization design method, which belongs to the field of tunnel construction, and comprises the following steps: S1, determining the vertical bearing maximum stress of the current tunnel construction rack protective net; s2, determining the maximum transverse tensile stress of the protective net of the current tunnel construction rack; s3, according to the steps S1 and S2, determining the elastic coefficient of the protective net of the current tunnel construction rack; s4, the material of the tunnel construction rack protective net is replaced, the steps S1 to S3 are repeated, and the elastic coefficient of the replaced protective net is determined; s5, the step S4 is repeated, and the elastic coefficients of the multiple sets of protective nets made of different materials are obtained; s6, comparing the elastic coefficients of the protective nets made of different materials, selecting the protective net with the maximum elastic coefficient as the optimal scheme of the protective net of the tunnel construction rack, determining the optimal scheme of the protective net of the tunnel construction rack by analyzing and calculating the elastic coefficients of the protective nets made of different materials, and meanwhile, evaluating whether the current protective net meets the requirement or not. The method is simple and high in optimization reliability.

Description

Technical Field

[0001] The invention relates to the field of tunnel construction, and in particular to an optimization design method for a tunnel construction stand protection net. Background Art

[0002] Tunnel engineering is a common type of engineering project in daily life. With the rise of underground engineering in my country, more and more people and places need us to build tunnels. However, at the construction site, tunnel excavation projects are always faced with the risk of sudden falling debris. At present, protective nets are mostly used for protection against such debris. Due to the unique structural characteristics of tunnels and the extreme complexity of geological conditions, the structural form of the protective net lacks a specific design basis, and its structural form and construction have not been well combined with the design and construction process of the tunnel. Summary of the invention

[0003] In view of the above problems, the present invention provides a method for optimizing the design of a tunnel construction platform protection net, which can effectively guide the design of the tunnel protection net.

[0004] The technical solution of the present invention is:

[0005] A tunnel construction platform protection net optimization design method comprises the following steps:

[0006] S1. Determine the maximum vertical bearing stress of the protection net of the current tunnel construction platform;

[0007] S2. Determine the maximum transverse tensile stress of the current tunnel construction platform protection net;

[0008] S3, the elastic coefficient of the current tunnel construction platform protection net determined according to steps S1 and S2;

[0009] S4, replace the material of the tunnel construction platform protection net, repeat steps S1-S3, and determine the elastic coefficient of the replaced protection net;

[0010] S5. Repeat step S4 to obtain elastic coefficients of multiple groups of protective nets made of different materials;

[0011] S6. Compare the elastic coefficients of various protective nets made of different materials, and select the protective net with the largest elastic coefficient as the optimal solution for the tunnel construction platform protective net.

[0012] The method also includes verification of the elasticity coefficient of the scheme, and the elasticity coefficient verification method is to take an average value by repeated tests.

[0013] The conditions for judging the maximum vertical bearing stress of the protection net are as follows:

[0014]

[0015] Among them: Fmax is the maximum vertical stress of the protection net, F0 is the average force on the protection net, m0 is the mass of the gravel, v0 is the initial velocity of the gravel hitting the protection net, g is the acceleration of gravity, k is the elastic coefficient, and v is the velocity at any time during the impact.

[0016] The calculation formula of the average force F0 of the protection net is as follows:

[0017]

[0018]

[0019]

[0020]

[0021] F0*T=m0v0

[0022]

[0023]

[0024] Where m0 is the mass of the gravel, v0 is the speed of the gravel hitting the protective net, g is the acceleration of gravity, k is the elastic coefficient, v is the speed at any time during the impact, T is the total time, t is the time, and l0 is the maximum vertical deformation of the protective net.

[0025] The judgment conditions for the maximum transverse tensile stress of the protective net are as follows:

[0026]

[0027] Where: x0 is the minimum distance between the impacted area of ​​the protective net and the outermost part of the protective net before the impact, E is the transverse elastic modulus of the protective net, σ max is the maximum lateral tensile stress of the protective net, v0 is the speed of the gravel hitting the protective net, g is the acceleration of gravity, and k is the elastic coefficient.

[0028] The calculation formula of the transverse tensile stress of the protective net is as follows:

[0029]

[0030]

[0031] σ0≤σ max

[0032]

[0033] where σ maxis the maximum lateral tensile stress of the protective net, σ0 is the lateral tensile stress of the protective net, l0 is the maximum vertical deformation of the protective net, k is the elastic coefficient, E is the lateral elastic modulus of the protective net, g is the gravitational acceleration, and x0 is the minimum value from the outermost edge of the protective net before being hit.

[0034] The beneficial effects of the present invention are:

[0035] By analyzing and calculating the elastic coefficients of protective nets made of different materials, the optimal solution for the protective net of the tunnel construction scaffold can be determined. At the same time, it can be evaluated whether the current protective net meets the requirements. The method is simple and has high optimization reliability. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are further described below.

[0037] Example:

[0038] A tunnel construction platform protection net optimization design method comprises the following steps:

[0039] S1. Determine the maximum vertical bearing stress of the protection net of the current tunnel construction platform;

[0040] S2. Determine the maximum transverse tensile stress of the current tunnel construction platform protection net;

[0041] S3, the elastic coefficient of the current tunnel construction platform protection net determined according to steps S1 and S2;

[0042] S4, replace the material of the tunnel construction platform protection net, repeat steps S1-S3, and determine the elastic coefficient of the replaced protection net;

[0043] S5. Repeat step S4 to obtain elastic coefficients of multiple groups of protective nets made of different materials;

[0044] S6. Compare the elastic coefficients of various protective nets made of different materials, and select the protective net with the largest elastic coefficient as the optimal solution for the tunnel construction platform protective net.

[0045] The method also includes verification of the elasticity coefficient of the scheme, and the elasticity coefficient verification method is to take an average value by repeated tests.

[0046] The conditions for judging the maximum vertical bearing stress of the protection net are as follows:

[0047]

[0048] Among them: F max is the maximum vertical stress of the protection net, F0 is the average force on the protection net, m0 is the mass of the gravel, v0 is the initial velocity of the gravel hitting the protection net, g is the acceleration of gravity, k is the elastic coefficient, and v is the velocity at any time during the impact.

[0049] The calculation formula of the average force F0 of the protection net is as follows:

[0050]

[0051]

[0052]

[0053]

[0054] F0*T=m0v0

[0055]

[0056]

[0057] Where m0 is the mass of the gravel, v0 is the speed of the gravel hitting the protective net, g is the acceleration of gravity, k is the elastic coefficient, v is the speed at any time during the impact, T is the total time, t is the time, and l0 is the maximum vertical deformation of the protective net.

[0058] The judgment conditions for the maximum transverse tensile stress of the protective net are as follows:

[0059]

[0060] Where: x0 is the minimum distance between the impacted area of ​​the protective net and the outermost part of the protective net before the impact, E is the transverse elastic modulus of the protective net, σ max is the maximum lateral tensile stress of the protective net, v0 is the speed of the gravel hitting the protective net, g is the acceleration of gravity, and k is the elastic coefficient.

[0061] The calculation formula of the transverse tensile stress of the protective net is as follows:

[0062]

[0063]

[0064] σ0≤σ max

[0065]

[0066] where σ max is the maximum lateral tensile stress of the protective net, σ0 is the lateral tensile stress of the protective net, l0 is the maximum vertical deformation of the protective net, k is the elastic coefficient, E is the lateral elastic modulus of the protective net, g is the gravitational acceleration, and x0 is the minimum value from the outermost edge of the protective net before being hit.

[0067] At present, the most common protective net in tunnels is steel mesh. If during the excavation process, an explosion occurs somewhere above the operating table, causing gravel to fall and fly towards the operating table, the vertically falling stones are the most dangerous. Assume that the stone falling at the blasting point has an initial velocity of v0 and a direction of an angle θ0 with the vertical direction (the vertical downward direction is considered to be the positive direction at this time). Assume that the height of the blasting point from the operating table is h0. Since the protective net is connected between the two operating tables, the vertical distance from the blasting point to the protective net is also h0. Since the distance and time of the stone from the blasting to falling on the protective net are very short, it can be considered that there is no loss of mechanical energy during the movement of the stone from the blasting to falling on the protective net. The gravitational potential energy is converted into kinetic energy, and the equation listed for this is

[0068]

[0069] Where v1 refers to the speed at which the stone collides with the protective net.

[0070] Since gravity does work throughout the process, the horizontal velocity remains constant at v0*sinθ0, so the vertical velocity is Since the impact speed v1 is a constant when v0 is fixed, the greater the impact speed, the greater the pressure on the protective net caused by the speed.

[0071] Because when an object hits, only the vertical direction will have an additional gravity effect, which will bring danger to the protective net. Therefore, when all the impact speed is concentrated in the vertical direction, the destructive force on the protective net is the greatest.

[0072] Now consider the entire process of movement and function of the gravel in the process of vertically hitting the protective net. Here we only consider the first collision between the gravel and the protective net. Even if the gravel bounces up and falls down after the first collision, the energy at this time is less than the energy at the first contact. If the protective net can hold up during the first collision, it can also hold up during the second collision.

[0073] Throughout the entire movement of the gravel, its speed will first decrease to 0, then accelerate in the opposite direction until it leaves the protective net. Obviously, if the protective net breaks in the middle, it will happen when the speed of the gravel decreases to 0 (the process of the speed of the gravel decreasing to 0 is symmetrical to the process of accelerating from 0). So we only consider the movement of this process. And from common sense in physics, when an object with a mass of m collides completely with another object at a speed of v, the rebound force it will receive is mkv 2 , k is a constant related to the properties of the two colliding objects.

[0074] When the stone hits the protective net, the corresponding k value is changed by changing the hardness and other characteristics of the iron wire on the protective net.

[0075] Based on this, the motion equation for the whole process is established.

[0076] According to Newton's second law, for the gravel with mass m0, in the whole process, we always have:

[0077]

[0078] Simplify

[0079] Integrating both sides simultaneously, we get Through separate mathematical analysis, we can know that under general realistic conditions The value of will decrease as k increases.

[0080] In this process, considering the average force of the protection net to be F0,

[0081] According to the momentum theorem,

[0082] F0*T=m0v0,

[0083] T is the total time it takes for the stone to slow down from impact to zero.

[0084] Integrating dt and dv, we get

[0085]

[0086]

[0087] In the formula, l0 represents the distance the stone moves from the beginning of impact to the time when the speed reaches 0.

[0088] For the protective net, l0 is its maximum vertical deformation. Assuming that the minimum distance from the outermost periphery of the protective net to the impacted area before the impact is x0, the minimum distance from the impact point corresponding to this minimum value to the outermost periphery after the impact becomes The deformation before and after this period is

[0089] Since the deformation is small, according to Hooke's law, the tensile stress in this section is Where E is the elastic modulus of the protective net in the transverse direction. Assume that the ultimate tensile stress is σ max , then it must be ensured in the design that σ0≤σ max , substitute

[0090] Right now As k increases, the value on the left side of the inequality increases.

[0091] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A tunnel construction platform protection net optimization design method, characterized in that: The steps include: S1. Determine the maximum vertical bearing stress of the protection net of the current tunnel construction platform; S2. Determine the maximum transverse tensile stress of the current tunnel construction platform protection net; S3, the elastic coefficient of the current tunnel construction platform protection net determined according to steps S1 and S2; S4, replace the material of the tunnel construction platform protection net, repeat steps S1-S3, and determine the elastic coefficient of the replaced protection net; S5. Repeat step S4 to obtain elastic coefficients of multiple groups of protective nets made of different materials; S6. Compare the elastic coefficients of various protective nets made of different materials, and select the protective net with the largest elastic coefficient as the optimal solution for the tunnel construction platform protective net.

2. The method for optimizing the design of a tunnel construction platform protection net according to claim 1, characterized in that: The method also includes verification of the elasticity coefficient of the scheme, and the elasticity coefficient verification method is to take an average value by repeated tests.

3. The method for optimizing the design of a tunnel construction platform protection net according to claim 1, characterized in that: The conditions for judging the maximum vertical bearing stress of the protection net are as follows: Among them: F max is the maximum vertical stress of the protection net, F0 is the average force on the protection net, m0 is the mass of the gravel, v0 is the speed of the gravel hitting the protection net, g is the acceleration of gravity, k is the elastic coefficient, and v is the speed at any time during the impact process.

4. The method for optimizing the design of a tunnel construction platform protection net according to claim 3 is characterized in that: The calculation formula of the average force F0 of the protection net is as follows: F0*T=m0v0 Where m0 is the mass of the gravel, v0 is the speed of the gravel hitting the protective net, g is the acceleration of gravity, k is the elastic coefficient, v is the speed at any time during the impact, t is the time, T is the total time, and l0 is the maximum vertical deformation of the protective net.

5. The method for optimizing the design of a tunnel construction platform protection net according to claim 1, characterized in that: The judgment conditions for the maximum transverse tensile stress of the protective net are as follows: Where: x0 is the minimum distance between the impacted area of ​​the protective net and the outermost part of the protective net before the impact, E is the transverse elastic modulus of the protective net, σ max is the maximum lateral tensile stress of the protective net, v0 is the speed of the gravel hitting the protective net, g is the acceleration of gravity, and k is the elastic coefficient.

6. The method for optimizing the design of a tunnel construction platform protection net according to claim 5, characterized in that: The calculation formula of the transverse tensile stress of the protective net is as follows: σ0≤σ max where σ max is the maximum lateral tensile stress of the protective net, σ0 is the lateral tensile stress of the protective net, l0 is the maximum vertical deformation of the protective net, k is the elastic coefficient, E is the lateral elastic modulus of the protective net, g is the gravitational acceleration, and x0 is the minimum value from the outermost edge of the protective net before being hit.

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