An optimization design method for underwater tunnel excavation face support

Abstract

The present invention relates to the field of geotechnical engineering technology, and specifically to an optimization design method for underwater tunnel excavation face support, comprising: step 1, establishing a three-dimensional mechanical model of tunnel excavation face destruction according to initial parameter settings; step 2, determining the tensile strength parameters of the soil in front of the tunnel, and calculating the external force power and internal force power affected by tensile truncation based on the functional principle of limit analysis, and defining the safety factor according to the external force power and internal force power; step 3, optimizing the independent variables corresponding to the initial parameters using the Harris Eagle algorithm, seeking the optimal upper limit solution of the safety factor, and obtaining the optimal solution for the tunnel excavation face support design. The solution rate of the safety factor is greatly improved, and a new and convenient method is provided for the collaborative optimization design of tunnel excavation face support.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to an optimization design method for underwater tunnel excavation face support. Background Art

[0002] With the acceleration of global urbanization, urban traffic pressure is increasing. As an effective means to alleviate urban traffic congestion, the scale of subway construction is expanding rapidly around the world. In the extensive construction of urban subway tunnels, in order to minimize the negative impact on surface activities, ground subsidence and existing buildings, shield tunneling machines have become the mainstream technology for underground tunnel construction due to their high efficiency and low disturbance. However, although shield tunneling technology has advantages, in the process of tunnel excavation, especially in the face of complex geological conditions, how to ensure the stability of the tunnel excavation surface, prevent collapse and groundwater intrusion, has become the key to ensuring construction safety and controlling surface subsidence.

[0003] At present, the assessment of tunnel excavation face stability mostly relies on the traditional linear Mohr-Coulomb failure criterion, that is, the failure of the soil is determined by the relationship between the shear stress and the normal stress on the two surfaces. Specifically, when the shear stress in the soil reaches a certain critical value, the soil will fail. This critical shear stress has a linear relationship with the normal stress, which can be expressed as the following formula:

[0004] ,in: represents the shear stress on the soil; c is the inherent shear strength, that is, the cohesion of the soil; is the normal stress, is the internal friction angle.

[0005] This formula can be viewed as an equation that describes the maximum shear stress that a material can withstand before breaking. It represents the shear resistance of the material, indicating the strength of the internal friction of the material, and is a constant; c represents the shear strength of the material without considering the normal stress, also known as shear strength, which represents the shear strength of the material without lateral stress. The size of c is affected by some influencing factors of the soil layer in geotechnical engineering, such as soil particle compressive strength, water content, load verticality, etc. represents the normal stress inside the material, which has an important influence on the shear strength of the material. Correspondingly, different materials provide different compressive strengths before failure, which is also the key difference in the function of materials under different stresses. Although this criterion has a certain universality in describing soil strength, it has significant limitations.

[0006] Specifically, this criterion often fails to fully consider the weak or even missing characteristics of the actual tensile strength of the soil, as well as the dynamic impact of environmental factors such as groundwater seepage on soil strength, resulting in an optimistic assessment of the stability of the tunnel excavation face, which is difficult to accurately reflect the safety risks under actual working conditions. Summary of the invention

[0007] In order to solve the problems of inaccurate tunnel excavation face stability assessment and difficulty in adapting to complex geological conditions in the prior art, the present invention proposes an underwater tunnel excavation face support optimization design method, which aims to improve the safety level of subway tunnel construction and reduce construction costs through technological innovation, so as to provide strong support for underground infrastructure construction in the process of rapid urbanization.

[0008] The technical means adopted by the present invention to solve its technical problems are: an underwater tunnel excavation face support optimization design method, the improvement of which is that it includes: step 1, establishing a three-dimensional mechanical model of tunnel excavation face destruction according to initial parameter settings; step 2, determining the tensile strength parameters of the soil in front of the tunnel, and calculating the external force power and internal force power affected by the tensile cutoff based on the functional principle of limit analysis, and defining the safety factor according to the external force power and the internal force power; step 3, using the Harris Eagle algorithm to optimize the independent variables corresponding to the initial parameters to seek the optimal upper limit solution of the safety factor.

[0009] Step 1 in the above technical solution includes: establishing a local rectangular coordinate system at the top of the tunnel excavation surface, and rotating around an axis passing through a certain point to form a three-dimensional rotating destruction mechanism, according to the initial parameters C, H, W, H W Establish the three-dimensional mechanical model of tunnel excavation surface destruction; the parameter C is the distance between the top of the tunnel and the ground, the parameter H is the height of the tunnel, the parameter W is the width of the tunnel, and the parameter H W is the distance between the tunnel top and the groundwater.

[0010] The tensile strength of the soil in front of the tunnel described in the above technical solution includes uniaxial tensile strength and triaxial tensile strength. The uniaxial tensile strength and triaxial tensile strength of the soil are calculated respectively according to the modified Mohr-Coulomb parameter. The formula is as follows:

[0011] Formula (1);

[0012] in, is the reduction factor, c is the cohesion, that is, the attraction or "bonding" strength between the particles inside the soil material, It is the internal friction angle, that is, the angle between the shear plane and the normal stress direction when the soil material is subjected to shear failure.

[0013] The above technical solution determines the tensile strength parameters of the soil in front of the tunnel, and calculates the external force power and internal force power affected by the tensile cutoff based on the functional principle of limit analysis, including:

[0014] The calculation process of the external force power includes gravity power, and the formula is as follows:

[0015] Formula (2);

[0016] in, is the density of the soil, and v is the volume of the soil.

[0017] The calculation process of the internal force power includes the power consumed on the velocity discontinuity surface when the soil undergoes shear sliding. The calculation formula is as follows:

[0018] Formula (3);

[0019] Among them, S t The volume of fill earth.

[0020] The functional principle based on limit analysis in the above technical solution calculates the external force power and internal force power affected by the tensile cutoff respectively, and defines the safety factor according to the external force power and the internal force power, including:

[0021] Using internal force power With external force power The ratio is taken as the safety factor, denoted as F S , defined as follows:

[0022] Formula (4);

[0023] The support force unloading method is adopted to determine the safety factor by gradually reducing the support force and iteratively calculating the ratio of internal force power to external force power until it approaches the critical state.

[0024] The iteration termination condition of the critical state in the above technical solution is that the difference between two consecutive calculation results is less than 10 -3 .

[0025] In the above technical solution, in step 301, a number of Harris Hawks are randomly generated in the search space as candidate solutions, and their fitness is calculated; in step 302, the Harris Hawks in the search space are searched, and the optimal individual position in the population is iteratively updated as the prey position; in step 303, the state is converted according to the escape energy E of the prey, and a global search is performed when |E|≥1, and a local development is performed when |E|<1; in step 304, the prey position is updated according to the escape energy E and a random number r, and the predation behavior of the Harris Hawk is simulated; the range of the random number r is 0-1; in step 305, formula (4) is used as the fitness function, the specific geometric shape of the tunnel excavation face destruction mechanism is determined by four independent variables, and the Harris Hawk algorithm is used for rapid optimization to determine the optimal upper limit solution of the safety factor;

[0026] Formula (5).

[0027] The above technical solution describes searching the Harris hawk in the search space, including: using two strategies with equal probability to find prey, one is that the Harris hawk will inhabit according to the positions of other members and prey, and the other is that the Harris hawk will randomly inhabit a tree within the activity range of the population.

[0028] The method of updating the prey position described in the above technical solution includes one or more of gentle siege, tough siege, gentle siege with gradual and rapid dive, and tough encirclement with gradual and rapid dive.

[0029] Step 305 in the above technical solution includes: determining the optimization range of the independent variables, giving initial values ​​to the initial geometric parameters such as the rotation center and the tension zone boundary of the rotation failure mechanism according to the design requirements; under the condition that each support force unloading coefficient is given, using formula (4) as the fitness function, It is introduced as an independent variable into the Harris Eagle algorithm for rapid optimization to determine the optimal upper limit solution of the safety factor; it is judged whether the optimal upper limit solution of the safety factor meets the design requirements. If so, the calculation is stopped to obtain a set of design schemes; if it does not meet the design requirements, a set of design parameters is replaced and recalculated until the design requirements are met.

[0030] The beneficial effects of the present invention are as follows: under the framework of the upper limit theory of limit analysis, a three-dimensional tunnel excavation face safety factor evaluation model under the limit failure state is constructed in combination with the tensile strength cutoff failure criterion; for given hydraulic conditions and tensile strength cutoff conditions, the seepage influence and the tensile strength cutoff influence are calculated, and the overall safety factor of the tunnel excavation face corresponding to a series of non-uniform support forces is solved through algorithm optimization, and finally the most appropriate support design is determined to achieve a safe and economical support design. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A flow chart of an underwater tunnel excavation face support optimization design method shown in an embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of a three-dimensional discrete destruction mechanism of a tunnel excavation face according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0034] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection / connection relationships involved in the patent do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0035] like Figure 1 As shown, the present invention provides an optimization design method for underwater tunnel excavation face support, comprising:

[0036] Step 1: Establish a three-dimensional mechanical model of tunnel excavation face failure based on the initial parameter settings.

[0037] Assume that the failure surface of the tunnel under three-dimensional conditions is a logarithmic spiral shape, such as Figure 2 As shown in the figure, a local rectangular coordinate system is established at the top of the tunnel excavation surface and rotated around the axis passing through point F to form a three-dimensional rotating destruction mechanism. W A three-dimensional mechanical model of tunnel excavation surface destruction is established; the parameter C is the distance between the top of the tunnel and the ground, the parameter H is the height of the tunnel, the parameter W is the width of the tunnel, and the parameter H is the distance between the top of the tunnel and the groundwater.

[0038] Step 2: determine the tensile strength parameters of the soil in front of the tunnel, and calculate the external force power and internal force power affected by the tensile cutoff based on the functional principle of limit analysis, and define the safety factor according to the external force power and internal force power.

[0039] In a possible implementation, the tensile strength of the soil in front of the tunnel includes uniaxial tensile strength and triaxial tensile strength. The uniaxial tensile strength and triaxial tensile strength of the soil are calculated respectively according to the modified Mohr-Coulomb parameter, and the formula is as follows:

[0040] Formula (1);

[0041] in, is the reduction factor, c is the cohesion, that is, the attraction or "bonding" strength between the particles inside the soil material, It is the internal friction angle, that is, the angle between the shear plane and the normal stress direction when the soil material is subjected to shear failure.

[0042] In a possible implementation, the calculation process of the external force power includes gravity power, and the calculation formula of gravity power is as follows:

[0043] Formula (2);

[0044] in, is the density of the soil, and v is the volume of the soil.

[0045] The calculation process of the internal force power includes:

[0046] Formula (3);

[0047] Among them, S t The volume of fill earth.

[0048] According to the internal force power With external force power The ratio is taken as the safety factor, denoted as F S , defined as follows:

[0049] Formula (4);

[0050] The support force unloading method is adopted to determine the safety factor by gradually reducing the support force and iteratively calculating the ratio of internal force power to external force power until it approaches the critical state.

[0051] Since the tunnel excavation face support power is linearly related to the support force. S When the reduction is performed, the corresponding support force power will also be reduced to equal the internal force power. At this time, the tunnel excavation face is in a critical state. From a certain coefficient At the beginning, the support force is gradually reduced with a fixed gradient. External force power Iteratively calculate the ratio of internal power to external power until it approaches the critical state (i.e. equal to 1), at which point the coefficient This is the required safety factor.

[0052] In a possible implementation, the critical state iteration termination condition is that the difference between two consecutive calculation results is less than 10 -3 .

[0053] By setting this iteration termination condition, it can be ensured that the iteration process stops when two adjacent calculation results are very close, thereby improving the accuracy of the calculation results; at the same time, unnecessary iteration processes are avoided, thereby saving computing resources.

[0054] Step 3: Use the Harris Eagle algorithm to optimize the independent variables corresponding to the initial parameters, seek the optimal upper limit solution of the safety factor, and obtain the optimal solution for the tunnel excavation face support design.

[0055] The Harris Hawk Optimization (HHO) algorithm is a new swarm intelligence optimization algorithm proposed by Ali Asghar Heidari et al. in 2019. The algorithm mathematically models the different processes of cooperative hunting by Harris Hawks. First, the prey to be hunted is assumed to be the optimal solution, and the Harris Hawk group represents the candidate solution. Therefore, based on this setting, the Harris Hawk group (candidate solution) in the algorithm encircles the prey (optimal solution). The encirclement process is mainly divided into two stages: the first stage is the prey search (exploration) stage; the second stage is the prey capture (exploitation) stage. In the prey search stage, the Harris Hawk group will randomly search around the prey or around other Harris Hawks in the hope of finding new prey. In the prey capture stage, the Harris Hawk group adopts four different strategies to capture the prey according to the four different states of the prey. The Harris Hawk Optimization (HHO) algorithm does not require additional adjustment parameters, has the characteristics of few adjustment parameters, and does not require the gradient mathematical information of the optimization problem, and has a wide range of applicability.

[0056] In a possible implementation, step 3 described in the present application may include the following steps:

[0057] Step 301: randomly generate several Harris Hawks as candidate solutions in the search space, and calculate their fitness.

[0058] In one possible implementation, the present application adopts two strategies with equal probability to find prey. One is that the Harris Hawk will roost according to the positions of other members and prey, and the other is that the Harris Hawk will randomly roost on a tree within the activity range of the population.

[0059] Step 302, searching the Harris hawks in the search space, and iteratively updating the optimal individual position in the population as the prey position;

[0060] Step 303: Perform state transition according to the escape energy E of the prey. When |E|≥1, perform global search; when |E|<1, perform local development.

[0061] The formula for variable E is as follows:

[0062] Formula (6);

[0063] In formula (6), E 0 is a random number between (-1, 1) representing the initial energy state, t is the current number of iterations, T is the maximum number of iterations, and the value of E approaches 0 from the range of (-1, 1) as the number of iterations increases.

[0064] In the global search phase, the reverse logarithmic spiral strategy is used to update the position of the Harris Hawk, as shown in formula (7):

[0065] Formula (7);

[0066] Formula (8);

[0067] Where X best is the optimal solution position in the current iteration, X reverse_best is the reverse solution of the current optimal solution obtained according to formula (7); X next is the new position after the Harris Hawk is updated, l is a random value between (-1, 1), and b=1 is a constant.

[0068] The Harris Hawk's exploration position is randomly updated according to the above reverse logarithmic spiral formula, hoping to find the area with the possible optimal solution.

[0069] In one possible implementation, two strategies are used with equal probability to find prey during the local exploitation phase. One is that the Harris's Hawk will roost according to the locations of other members and prey, and the other is that the Harris's Hawk will randomly roost on a tree within the activity range of the population.

[0070] Step 304: Update the prey position according to the escape energy E and the random number r to simulate the predation behavior of Harris's hawk; the random number r ranges from 0 to 1.

[0071] In a possible implementation, the method of updating the prey position includes one or more of gentle siege, tough siege, gentle siege with gradual and rapid dives, and tough encirclement with gradual and rapid dives.

[0072] Step 305: Under the condition that each support force unloading coefficient is given, formula (4) is used as the fitness function to transform the specific geometric shape of the tunnel excavation face failure mechanism from four independent variables: Determine, through the Harris Eagle algorithm to quickly optimize and determine the optimal upper limit solution of the safety factor;

[0073] Identify the independent variables The optimization range is given by giving initial values ​​to initial geometric parameters such as the rotation center and the tension zone limit of the rotation failure mechanism according to the design requirements;

[0074] Determine whether the optimal upper limit solution of the safety factor meets the design requirements. If so, stop the calculation and obtain a set of design solutions. If not, replace a set of design parameters and recalculate until the design requirements are met.

[0075] The above process steps have all been converted into corresponding FLAC3D-MATLAB codes, which can be used for coupled calculations in the MATLAB environment. Since the Harris Hawk algorithm simulates the predation behavior of the Harris Hawk very realistically, has a strong global search capability, and has the advantage of requiring fewer parameters to be adjusted, it can greatly speed up the solution of the safety factor of the tunnel excavation face under the influence of groundwater seepage and tensile strength cutoff.

[0076] Through the above embodiments, this application, under the framework of the upper limit theory of limit analysis, combines the tensile strength cutoff failure criterion to construct a three-dimensional tunnel excavation face safety factor assessment model under the limit failure state; for given hydraulic conditions and tensile strength cutoff conditions, the seepage influence and the tensile strength cutoff influence are calculated, and the overall safety factor of the tunnel excavation face corresponding to a series of non-uniform support forces is solved through algorithm optimization, and the final support design is determined to achieve a safe and economical support design.

[0077] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for optimizing the design of underwater tunnel excavation face support, characterized in that: The following steps are involved: Step 1: According to the initial parameters C, H, W, H W Establish the three-dimensional mechanical model of tunnel excavation surface destruction; the parameter C is the distance between the top of the tunnel and the ground, the parameter H is the height of the tunnel, the parameter W is the width of the tunnel, and the parameter H w is the distance between the tunnel top and the groundwater; Step 2: Determine the tensile strength parameters of the soil in front of the tunnel, and calculate the external force power and internal force power affected by the tensile cutoff based on the functional principle of limit analysis, and define the safety factor according to the external force power and internal force power, including: According to the modified Mohr-Coulomb parameters, the uniaxial tensile strength and triaxial tensile strength of the soil are calculated respectively. The tensile strength calculation formula is as follows: Formula (1): in, is the reduction factor, c is the cohesion, which is the attraction or "bonding" strength between the particles inside the soil material. is the internal friction angle; The calculation process of the external force power includes gravity power, and the calculation formula of gravity power is as follows: Formula (2): in, is the weight of the soil, v is the volume of the soil; The calculation process of the internal force power includes the power consumed on the velocity discontinuity surface when the soil undergoes shear sliding. The calculation formula is as follows: Formula (3): Among them, S t is the volume of earth filling; is the internal friction angle; Using internal force power With external force power The safety factor is defined as follows: Formula (4): The support force unloading method is used to gradually reduce the support force and iteratively calculate the ratio of internal force power to external force power until it approaches the critical state to determine the safety factor; Step 3: Use the Harris Eagle algorithm to optimize the independent variables corresponding to the initial parameters, seek the optimal upper limit solution of the safety factor, and obtain the optimal solution for the tunnel excavation face support design, including: Step 301: randomly generate several Harris Hawks as candidate solutions in the search space, and calculate their fitness; Step 302, searching the Harris hawks in the search space, and iteratively updating the optimal individual position in the population as the prey position; Step 303: Perform state transition according to the escape energy E of the prey, perform global search when |E|≥1, and perform local development when |E|<1; Step 304: updating the prey position according to the escape energy E and the random number r, simulating the predation behavior of Harris's hawk; the random number r ranges from 0 to 1; Step 305: Under the condition that each support force unloading coefficient is given, formula (4) is used as the fitness function to transform the specific geometric shape of the tunnel excavation face failure mechanism from four independent variables: Determine, through the Harris Eagle algorithm to quickly optimize and determine the optimal upper limit solution of the safety factor; Identify the independent variables The optimization range is given by giving initial values ​​to the initial geometric parameters of the rotation center and the tension zone boundary of the rotation failure mechanism according to the design requirements; Determine whether the optimal upper limit solution of the safety factor meets the design requirements. If so, stop the calculation; if not, replace a set of design parameters and recalculate until the design requirements are met; solve the overall safety factor of the tunnel excavation face corresponding to a series of non-uniform support forces through algorithm optimization to determine the final support design.

2. The underwater tunnel excavation face support optimization design method according to claim 1, characterized in that: The critical state iteration termination condition in step 2 is that the difference between two consecutive calculation results is less than 10 -3 .

3. The underwater tunnel excavation face support optimization design method according to claim 1, characterized in that: The searching of the Harris Hawk in the search space includes: There are two strategies with equal probability to find prey. One is that Harris's Hawk will roost according to the location of other members and prey, and the other is that Harris's Hawk will randomly roost on a tree within the activity range of the population.

4. The underwater tunnel excavation face support optimization design method according to claim 1, characterized in that: The method of iteratively updating the optimal individual position in the population as the prey position includes one or more of gentle siege, tough siege, gentle siege with gradual and rapid dives, and tough encirclement with gradual and rapid dives.

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