A method for phase transition control of a prefabricated stiffener conversion reinforcement system

Abstract

This invention discloses a stage transition control method for a prefabricated stiffened brace conversion reinforcement system. The method includes establishing an original support system model, dividing the construction into stages, identifying the impact zone of openings, generating candidate prefabricated stiffened brace schemes, calculating the stage transition safety factor, and optimizing the candidate schemes. By replacing multiple ordinary supports that need to be removed within the opening area with a small number of high-bearing-capacity, high-rigidity, and prefabricable stiffened supports, and combining a stage transition safety factor determination method and a minimum replacement support set optimization algorithm, the method achieves a safe transition of the underground structure from a conventional foundation pit support state to a deep and large opening construction state, and then to a complete basement structure state. This solves the problems of insufficient bearing capacity of ordinary steel supports, large space occupation and difficult removal of large-section concrete supports, lack of quantitative criteria for support conversion in deep and large opening areas, and difficulty in balancing construction space and support safety in existing underground structure connection construction.

Description

Technical Field

[0001] This invention relates to the field of foundation pit support technology, and in particular to a stage transition control method for a prefabricated stiffening support conversion reinforcement system. Background Technology

[0002] Connection construction is often required between existing basements, between newly built basements, or between existing basements and newly built underground spaces. Such projects typically require the creation of large temporary openings or working spaces within the basements, such as pipe jacking starting shafts, equipment hoisting shafts, starting openings for underground connecting passages, tunnel excavation openings, pipe roof construction openings, or freezing reinforcement work spaces.

[0003] For conventional basement construction, the excavation stage typically employs a support system consisting of diaphragm walls or other retaining structures combined with multiple horizontal internal bracing. As the basement structure is rebuilt from bottom to top, the internal bracing is gradually removed as the structural floor slabs are formed, ultimately leaving the permanent basement structure to bear the horizontal constraint. However, in areas with large temporary openings, the basement structure cannot be rebuilt completely in the conventional sequence due to extensive disruption of floor slabs, beams, partial walers, or partial support systems. Consequently, this area still requires temporary support systems to resist external soil and water pressure for a longer construction period.

[0004] Existing steel supports offer advantages in terms of ease of installation and dismantling, but their individual load-bearing capacity and overall rigidity are limited. In situations involving large temporary openings, deep openings, and significant soil and water pressure on the outer side of the retaining structure, multiple ordinary steel supports are often required to meet the load-bearing requirements. However, multiple steel supports significantly reduce the working space inside the opening, impacting the lowering of the pipe jacking machine, equipment hoisting, underground tunnel construction, and subsequent structural completion work.

[0005] While existing reinforced concrete supports have high load-bearing capacity, they typically have large cross-sectional dimensions, are heavy, require long on-site construction periods, and are difficult to dismantle later. The dismantling process also generates a large amount of construction waste, which is detrimental to green construction and efficient organization of underground spaces. For projects requiring gradual restoration of the basement structure later, large-section concrete supports can also affect the construction space for floor slabs and the installation of slabs to fill openings.

[0006] Furthermore, existing solutions typically rely on engineering experience for support system conversion, determining the timing of support removal, retention, and basement re-construction based on the construction sequence. This lacks a method for determining phased conversion that comprehensively considers factors such as load-bearing loss after ordinary support removal, stiffener replacement capacity, opening deformation control requirements, boundary bearing capacity, and construction clearance requirements. Due to the lack of quantitative criteria, problems such as premature support removal, insufficient support replacement, excessive opening deformation, or overly dense support arrangement affecting construction space are prone to occur during the formation of temporary openings at Shenzhen University. Summary of the Invention

[0007] The purpose of this invention is to provide a stage transition control method for a prefabricated rigid support conversion reinforcement system, in order to solve the problems of insufficient bearing capacity of ordinary steel supports, large-section concrete supports occupying a lot of space and being difficult to dismantle, lack of quantitative criteria for support conversion in deep and large opening areas, and difficulty in balancing construction space and support safety in existing underground structure connection construction.

[0008] To solve the above-mentioned technical problems, the technical solution provided by this invention is: a stage transition control method for a prefabricated stiffener transition reinforcement system, comprising:

[0009] Step S1: Establish the original support system model: Determine the initial force relationship between the ordinary internal support, the enclosure structure and the basement structure based on the original support system model;

[0010] Step S2: Divide the construction process into several stages: Divide the construction process of the deep and large temporary openings in the underground structure into several construction stages:

[0011] Step S3: Identify the impact zone of the opening: Based on the planar and vertical extent of the proposed deep temporary opening and the location of the ordinary internal supports, identify the area affected by the opening. A collection of ordinary supports that need to be dismantled, relocated, or replaced by prefabricated stiffened supports during each construction phase due to the influence of openings;

[0012] Step S4: Generate candidate prefabricated stiffener layout schemes: Based on the boundaries of the temporary opening at Shenzhen University, floor slab elevation avoidance requirements, construction clearance requirements, support force direction, and on-site installation conditions, generate several candidate prefabricated stiffener layout schemes:

[0013] (2);

[0014] In Equation 2, For the first The first construction phase Individual support candidate solutions For the first Root prefabricated rigid support, The number of stiffening supports in this candidate scheme;

[0015] Step S5: Calculate the safety factor for stage transition:

[0016] For each candidate scheme, calculate the bearing capacity substitution factor, stiffness substitution factor, opening deformation control factor, and boundary bearing pressure safety factor, and formulate the stage transition safety factor accordingly. ;

[0017] when When the candidate solution is determined to satisfy the first condition, it is determined that the first condition is met. The conditions for conversion during the construction phase allow for the removal of ordinary supports, the retention of prefabricated rigid supports, the formation of deep and large temporary openings, the backfilling of basements, or subsequent support removal operations.

[0018] when When the candidate solution does not meet the first requirement, it is determined that the candidate solution does not satisfy the requirement. The transition conditions during the construction phase require adjustments to the quantity, location, spacing, cross-sectional dimensions, or opening sequence of prefabricated rigid supports;

[0019] Step S6, optimize candidate solutions for prefabricated stiffening supports:

[0020] Based on meeting the safety factor requirements for phase transition, the optimal solution is determined from multiple feasible candidate solutions by using the minimum alternative support set optimization algorithm, which minimizes the number of prefabricated stiffeners, maximizes the clearance release at the opening, achieves a more balanced support layout, and minimizes construction interference.

[0021] Furthermore, the method for phase transition control of the prefabricated stiffening brace transition reinforcement system provided by the present invention, in step S5, includes the following method for forming the phase transition safety factor:

[0022] Step S51: Calculate the load-bearing substitution factor:

[0023] (3);

[0024] In Equation 3:

[0025] For the first The candidate solution is in the... The carrying capacity substitution coefficient of the stage;

[0026] For the first The design axial bearing capacity of the prefabricated stiffening brace;

[0027] For the first The design axial force of the root is replaced by that of ordinary support;

[0028] For the first The load reduction factor of prefabricated stiffened supports during the construction phase;

[0029] For the first Contribution coefficient of ordinary support to the influence zone of the tunnel entrance;

[0030] For the first Additional horizontal load requirements arising from the formation of openings, missing floor slabs, or boundary transitions at each stage;

[0031] Step S52: Calculate the stiffness substitution factor:

[0032] (4);

[0033] In Equation 4:

[0034] For the first The candidate solution is in the... Stiffness substitution factor for each stage;

[0035] For the first The horizontal equivalent stiffness of the prefabricated stiffening brace;

[0036] For the first The horizontal equivalent stiffness of the root replacing the ordinary support;

[0037] Step S53: Calculate the deformation control coefficient at the opening:

[0038] (5);

[0039] In Equation 5:

[0040] For the first The candidate solution is in the... The deformation control coefficient of the opening at each stage;

[0041] This refers to the maximum allowable deformation value for the enclosure structure, opening boundary, or basement structure.

[0042] For the first The candidate solution is in the... The maximum deformation value obtained from stage calculations or monitoring;

[0043] Step S54: Calculate the boundary bearing capacity safety factor:

[0044] (6);

[0045] In Equation 6:

[0046] For the first The candidate solution is in the... The boundary bearing capacity safety factor of the stage;

[0047] The bearing capacity of the opening boundary components, walers, hidden beams, hidden columns, enclosure structures, or other pressure-bearing parts;

[0048] The design reaction force transmitted from the prefabricated stiffening support to the boundary structure;

[0049] Step S55, calculate the stage transition safety factor:

[0050] (7);

[0051] In Equation 7:

[0052] For the first The candidate solution is in the... Safety factor for phase transition;

[0053] To bear the safety control coefficient;

[0054] This is the stiffness safety control factor;

[0055] This is the deformation safety control coefficient;

[0056] This is the boundary pressure safety control coefficient.

[0057] Furthermore, the stage transition control method for the prefabricated stiffener conversion reinforcement system provided by the present invention, and the method for optimizing candidate prefabricated stiffener schemes, include:

[0058] Step S61, calculate the air release coefficient:

[0059] (8);

[0060] In Equation 8:

[0061] For the first The candidate solution is in the... The net air release coefficient for the stage;

[0062] This refers to the usable net clearance area of ​​the tunnel entrance area under this scheme;

[0063] The target is a large temporary tunnel opening area;

[0064] Step S62, calculate the support offset influence coefficient:

[0065] (9);

[0066] In Equation 9:

[0067] For the first The candidate solution is in the... The support bias influence coefficient of the stage;

[0068] The eccentricity of the line of action of the resultant force of the prefabricated stiffening support in this scheme relative to the center line of the opening;

[0069] This refers to the width of the opening or the dimension controlling the direction.

[0070] Step S63: Determine the degree of operational conflict based on the construction interference coefficient.

[0071] Construction interference coefficient Judge the first The candidate solution is in the... The degree of conflict between the stage and floor slab construction, hoisting path, equipment access, and underground connecting work space;

[0072] Step S64, calculate the comprehensive evaluation function:

[0073] (10);

[0074] In Equation 10:

[0075] For the first The candidate solution is in the... The overall evaluation value of the stage;

[0076] ;

[0077] This is the net air release coefficient;

[0078] To support the bias influence coefficient;

[0079] This is the construction interference coefficient;

[0080] These are the weighting coefficients;

[0081] In all satisfied Among the candidate solutions, the solution with the smallest comprehensive evaluation function is selected as the optimal alternative support set:

[0082]

[0083] And it satisfies:

[0084]

[0085] Therefore, the first The optimal number, planar location, elevation, retention range, and removal sequence of prefabricated stiffeners in each construction stage.

[0086] Furthermore, the stage transition control method for the prefabricated stiffener transition reinforcement system provided by the present invention further includes:

[0087] Step S64, Output stage conversion construction sequence:

[0088] According to the optimal alternative support set Output the corresponding construction sequence for each construction stage, including:

[0089] Sequence of removal of ordinary supports;

[0090] The order of prefabricated stiffening supports should be retained.

[0091] The sequence of reconstructing the basement area (excluding openings);

[0092] The sequence of formation of the temporary tunnel entrance at Shenzhen University;

[0093] Sequence of underground connections or specialized construction projects;

[0094] Sequence of removal for prefabricated rigid supports in later stages;

[0095] The order of completing the basement structure in the opening area.

[0096] Furthermore, the prefabricated stiffened bracing conversion reinforcement system stage conversion control method provided by the present invention obtains the basic parameters of the underground structure engineering, including the planar dimensions of the foundation pit, the form of the retaining structure, the location of the ordinary internal bracing, the spacing of the ordinary internal bracing, the elevation of the ordinary internal bracing, the design axial force of the ordinary internal bracing, the elevation of the basement floor slab, the arrangement of the basement beams and slabs, the planar dimensions and vertical range of the proposed deep and large temporary opening, and establishes the original support system model based on the basic parameters of the underground structure engineering.

[0097] Furthermore, the prefabricated stiffened bracing conversion reinforcement system stage conversion control method provided by the present invention refers to a prefabricated steel-concrete composite support component formed by internal steel sections, steel pipes, steel boxes or other steel components and external concrete under joint stress.

[0098] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0099] First, the phase transition control method of the prefabricated stiff bracing conversion reinforcement system provided by the present invention uses prefabricated stiff bracing to replace multiple ordinary supports that need to be removed within the scope of deep and large temporary openings. This can reduce the number of supports while meeting the requirements of high bearing capacity and stiffness, and free up construction space inside the opening.

[0100] Secondly, the stage transition control method of the prefabricated stiffening brace conversion reinforcement system provided by the present invention allows the prefabricated stiffening brace to be prefabricated in the factory and assembled on site, which can reduce the amount of cast-in-place concrete support construction, reduce demolition difficulty, reduce construction waste, and has good green construction and reuse value.

[0101] Third, the stage transition control method of the prefabricated stiffened bracing conversion reinforcement system provided by the present invention coordinates the elevation of the prefabricated stiffened bracing with the elevation of the ordinary bracing and avoids the elevation of the basement floor slab, so that the basement floor slab can be constructed while the bracing is retained, avoiding the temporary support risk caused by removing the bracing before constructing the floor slab.

[0102] Fourth, the stage transition control method of the prefabricated stiffened brace conversion reinforcement system provided by the present invention establishes a stage transition safety factor and incorporates the load-bearing replacement capacity, stiffness replacement capacity, opening deformation control capacity and boundary bearing capacity into the judgment system, so that the stage transitions such as ordinary support removal, stiffened brace retention, opening formation and basement completion have clear quantitative basis.

[0103] Fifth, the prefabricated stiffened support conversion reinforcement system provided by this invention proposes a minimum replacement support set optimization algorithm. Under the premise of meeting the stage conversion safety conditions, it comprehensively considers the number of supports, the release of the opening clearance, support offset, and construction interference to determine the optimal stiffened support layout scheme, balancing support safety and construction efficiency. By replacing multiple ordinary supports that need to be removed within the opening range with a small number of high-bearing-capacity, high-rigidity, and prefabricable stiffened supports, and combining the stage conversion safety factor determination method and the minimum replacement support set optimization algorithm, the underground structure can safely transition from the conventional foundation pit support state to the deep and large opening construction state, and then to the complete basement structure state. This solves the problems of insufficient bearing capacity of ordinary steel supports, large space occupation and difficult removal of large-section concrete supports, lack of quantitative judgment criteria for support conversion in deep and large opening areas, and difficulty in balancing construction space and support safety in existing underground structure connection construction.

[0104] Sixth, the stage transition control method of the prefabricated stiffened support conversion reinforcement system provided by the present invention has a wide range of applications. It is not only applicable to the construction of pipe jacking starting shafts, but also to engineering scenarios in urban renewal where deep and large temporary openings need to be formed, such as connecting existing basements, adding new underground passages, equipment hoisting shafts, tunneling, pipe sheds, and freezing method construction. Attached Figure Description

[0105] Figure 1 This is a flowchart of a phase transition control method for a prefabricated stiffened bracing conversion reinforcement system for deep and large temporary openings in underground structures;

[0106] Figure 2This is a schematic diagram of the prefabricated rigid support reinforcement system installed when the deep temporary opening of the pipe jacking starting shaft is in the state of preparing for pipe jacking construction.

[0107] Figure 3 This is a vertical cross-sectional schematic diagram of the prefabricated stiffened support conversion and reinforcement system when the deep temporary opening of the pipe jacking starting shaft is in the state of preparing for pipe jacking construction.

[0108] Figure 4 This is a schematic diagram of the prefabricated rigid support reinforcement system installed when the deep temporary opening of the pipe jacking starting shaft is in the foundation pit construction state.

[0109] Figure 5 This is a vertical cross-sectional schematic diagram of a prefabricated stiffened support conversion and reinforcement system when the deep temporary opening of the pipe jacking starting shaft is in the state of foundation pit construction.

[0110] 1. Enclosure structure; 2. Deep temporary opening of the pipe jacking starting shaft; 3. Floor structure in non-pipe jacking areas; 4. Prefabricated rigid support; 5. Column; 6. Edge sealing beam; 7. Hidden column; 8. Hidden beam; 9. Force transfer plate; 10. Backing structural column; 11. Backing structural beam; 12. Waler; 13. Steel support; 14. Concrete support; 15. Crown beam; 16. Base slab; 17. Floor slab; 18. Ground wall opening. Detailed Implementation

[0111] The present invention will now be described in detail with reference to the accompanying drawings. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0112] This invention provides a prefabricated stiffened bracing conversion and reinforcement system for deep and large temporary openings in underground structures, including an enclosure structure, ordinary internal bracing, prefabricated stiffened bracing, a basement structure, and a deep and large temporary opening area.

[0113] The retaining structure is set outside the foundation pit or underground structure to withstand the water and soil pressure from outside the pit. The retaining structure can be a diaphragm wall, pile wall, interlocking pile, SMW method pile, or other foundation pit retaining structures.

[0114] Ordinary internal supports are arranged according to conventional support design during the excavation stage of the foundation pit, and are used to form a temporary support system for the foundation pit together with the retaining structure. Ordinary internal supports can be steel supports, concrete supports, structural steel supports, or other temporary support components.

[0115] Prefabricated rigid supports are installed on both sides, around, or at locations requiring enhanced support capacity where deep and large temporary openings are to be formed. The support direction of the prefabricated rigid supports is consistent with or substantially consistent with the main stress direction of the ordinary internal supports, and their elevation is preferably consistent with, close to, or corresponding to the elevation of the ordinary internal supports. This allows the prefabricated rigid supports to participate in the support work together with the ordinary internal supports during the excavation stage, and to replace some or all of the ordinary internal supports in the subsequent formation stage of the deep and large temporary openings, fulfilling the horizontal support function. The elevation of the prefabricated rigid supports avoids the basement floor slab elevation, allowing the basement floor slab to be constructed while the prefabricated rigid supports are retained. Once a floor slab in the basement is completed and reaches its design strength, the supports near that floor or at the corresponding stage are removed, ensuring effective horizontal support for the deep and large temporary opening area throughout the entire process. The prefabricated rigid supports can be steel-concrete composite supports, steel-tube concrete supports, steel-box concrete supports, or other steel-concrete composite support components.

[0116] The term "deep-scale temporary opening area" refers to a large temporary opening area created during underground structure construction or renovation for underground connections, pipe jacking, equipment hoisting, tunneling, pipe roofing, freezing construction, or other underground operations. Basement floor slabs, beams, or some ordinary internal supports within this area are not yet formed or need to be removed during the construction phase; therefore, prefabricated rigid supports are required to provide temporary support. Boundary components, such as retained partial walers, concealed beams, concealed columns, edge sealing beams, or temporary boundary beams, can be installed around the deep-scale temporary opening to form a temporary stress path around the opening together with the prefabricated rigid supports. These boundary components can be installed according to different project needs and are not limited to the above-mentioned limitations.

[0117] Please refer to Figure 1 This invention also provides a method for controlling the stage transition of a prefabricated stiffener conversion reinforcement system, comprising:

[0118] Step S1: Establish the original support system model:

[0119] Obtain the basic parameters of the underground structure project, that is, input the basic parameters of the project, including the plan dimensions of the foundation pit, the form of the retaining structure, the location of the ordinary internal supports, the spacing of the ordinary internal supports, the elevation of the ordinary internal supports, the design axial force of the ordinary internal supports, the elevation of the basement floor slab, the layout of the basement beams and slabs, and the plan dimensions and vertical range of the proposed deep and large temporary opening.

[0120] Based on the above parameters, an original support system model is established to determine the initial force relationship between the ordinary internal support, the enclosure structure, and the basement structure.

[0121] Step S2: Divide the construction phases:

[0122] The construction process of deep and large temporary openings in underground structures is divided into several construction stages, including at least:

[0123] Excavation and support stage of foundation pit;

[0124] Backfilling stage in non-opening areas of the basement;

[0125] The formation stage of the temporary tunnel entrance at Shenzhen University;

[0126] Underground connection or special construction phase;

[0127] The structural completion stage of the tunnel entrance area.

[0128] The stress states of ordinary supports, prefabricated stiffened supports, and basement structures differ at different construction stages, requiring separate stage transition determinations.

[0129] Step S3: Identify the affected area of ​​the opening:

[0130] Based on the planar and vertical dimensions of the proposed deep temporary opening and the location of the ordinary internal supports, the first... The set of ordinary supports that need to be dismantled, relocated, or replaced by prefabricated stiffened supports during each construction phase due to the influence of openings:

[0131] (1);

[0132] In Equation 1, For the first The set of ordinary supports that need to be replaced during each construction phase For the first Root ordinary support, This represents the number of ordinary supports that need to be replaced.

[0133] Step S4: Generate candidate solutions for prefabricated stiffeners:

[0134] Based on the Shenzhen University temporary opening boundary, floor slab elevation avoidance requirements, construction clearance requirements, support stress direction, and on-site installation conditions, several candidate layout schemes for prefabricated rigid supports are generated:

[0135] (2);

[0136] In Equation 2, For the first The first construction phase Individual support candidate solutions For the first Root prefabricated rigid support, This represents the number of stiffening supports in the candidate scheme.

[0137] Each candidate scheme should include at least the planar location, elevation, quantity, spacing, cross-sectional dimensions, design axial bearing capacity, and horizontal equivalent stiffness of the prefabricated stiffeners.

[0138] Step S5: Calculate the safety factor for stage transition:

[0139] For each candidate scheme, calculate the bearing capacity substitution coefficient, stiffness substitution coefficient, opening deformation control coefficient, and boundary bearing pressure safety factor, and form a stage transition safety factor accordingly.

[0140] Step S51: Calculate the load-bearing substitution factor:

[0141] (3);

[0142] In Equation 3:

[0143] For the first The candidate solution is in the... The carrying capacity substitution coefficient of the stage;

[0144] For the first The design axial bearing capacity of the prefabricated stiffening brace;

[0145] For the first The design axial force of the root is replaced by that of ordinary support;

[0146] For the first The load reduction factor of prefabricated stiffened supports during the construction phase;

[0147] For the first Contribution coefficient of ordinary support to the influence zone of the tunnel entrance;

[0148] For the first Additional horizontal load requirements arising from the formation of openings, missing floor slabs, or boundary transitions during the phase.

[0149] when If the load-bearing safety control requirement is not less than the preset load-bearing requirement, the candidate solution is deemed to meet the load-bearing substitution requirement.

[0150] in: The ratio of the j-th prefabricated stiffener to its design axial bearing capacity after being affected by connection structure, installation deviation, end bearing conditions, and construction quality inspection status during the construction phase can be determined by the following formula:

[0151] (3.1)

[0152] In Equation 3.1, μ c,j To construct the reduction factor for the connection, μ e,j μ is the installation deviation reduction factor. b,j μ is the reduction factor for end bearing pressure or boundary conditions. q,j This refers to the reduction factor for construction quality and inspection status. Each factor can be determined according to Table 1 below:

[0153] Partial factor Physical meaning Range of values ​​and determination principles <![CDATA[μ c,j ]]> Connection reduction factor For integral welded or reliable cast-in-place connections, the value is 0.98 to 1.00; for high-strength bolted flange connections, the value is 0.92 to 0.98; for temporary plug-in, pin-connected or other temporary connections, the value is 0.85 to 0.92. <![CDATA[μ e,j ]]> Installation deviation reduction factor For installation deviations not exceeding 25% of the allowable deviation, take 1.00; for 25% to 50%, take 0.95; for 50% to 75%, take 0.90; for 75% to 100%, take 0.85. <![CDATA[μ b,j ]]> End bearing pressure or boundary condition reduction factor For end bearing surfaces that are intact, pads that are sufficient, and force transmission that is clear, take 0.95 to 1.00; for local bearing or temporary supports, take 0.85 to 0.95. <![CDATA[μ q,j ]]> Construction quality and inspection status reduction factor For qualified tests with monitoring feedback, use 0.95 to 1.00; for routine acceptance tests only, use 0.90 to 0.95; for tests lacking data, use 0.85 to 0.90.

[0154] Table 1

[0155] in The value range is 0.75 to 1.00. For prefabricated stiffened supports that are factory-prefabricated, reliably connected, have small installation deviations, and have clearly defined end bearing conditions, μ j The preferred value is 0.90 to 1.00; for prefabricated stiffeners with temporary connections, large installation deviations, or unfavorable end bearing conditions, μ j The preferred value is 0.75 to 0.90.

[0156] It should be noted that the above The range of values ​​applies to prefabricated stiffened supports that have met the basic acceptance conditions. When there are situations such as unaccepted key connections, unclear end bearing conditions, or unqualified construction quality, it is not advisable to simply reduce μj for calculation. Instead, the corresponding support or candidate scheme should be excluded and a new candidate scheme should be generated.

[0157] in: α is used to characterize the contribution of the i-th replaced ordinary support to the support area of ​​the deep temporary tunnel entrance in the original support system. i The value of α ranges from 0 to 1. i The larger the value, the greater the impact on the stress and deformation of the opening's affected area after the ordinary support is removed, relocated, or replaced. α i The model sensitivity method can be used as a preferred method for determination. Specifically:

[0158] In the original support system model, the maximum horizontal deformation increment Δu in the affected area of ​​the opening is calculated by simulating the removal of the i-th ordinary support individually. i Or support reaction force loss ΔR i And determine by normalization as follows:

[0159] (3.2)

[0160] (3.3)

[0161] Where, ΣΔu i or ΣΔR iThis is the sum of the impact quantities after all ordinary supports to be replaced within the affected area of ​​the opening are removed one by one. This method allows us to correlate the actual contribution of ordinary supports to the opening area with the load distribution and deformation response in the structural model.

[0162] When a detailed model is lacking or for initial screening, α i Alternatively, the geometric influence zone method can be used, which determines the influence zone based on the overlap length or control range ratio between the i-th ordinary support and the deep temporary opening.

[0163] (3.4)

[0164] In the formula, L i,ov Let L be the effective influence length of the i-th ordinary support within the influence zone of the opening. i,inf Let α be the total influence length of the ordinary support. If the ordinary support completely passes through the influence zone of the opening, then α can be taken as α. i =1.0; if only partially affected, the value can be taken according to the overlap ratio; if not within the influence zone of the opening, α can be taken. i =0.

[0165] Step S52: Calculate the stiffness substitution factor:

[0166] (4);

[0167] In Equation 4:

[0168] For the first The candidate solution is in the... Stiffness substitution factor for each stage;

[0169] For the first The horizontal equivalent stiffness of the prefabricated stiffening brace;

[0170] For the first The horizontal equivalent stiffness of the root is replaced by that of the ordinary support.

[0171] when If the stiffness is not less than the preset stiffness safety control requirement, the candidate solution is deemed to meet the stiffness substitution requirement.

[0172] Step S53: Calculate the deformation control coefficient at the opening:

[0173] (5);

[0174] In Equation 5:

[0175] For the first The candidate solution is in the... The deformation control coefficient of the opening at each stage;

[0176] This refers to the maximum allowable deformation value for the enclosure structure, opening boundary, or basement structure.

[0177] For the first The candidate solution is in the... The maximum deformation value obtained from stage calculations or monitoring.

[0178] when If the deformation is not less than the preset deformation control requirement, the candidate scheme is deemed to meet the deformation control requirement of the opening.

[0179] Step S54: Calculate the boundary bearing capacity safety factor:

[0180] (6);

[0181] In Equation 6:

[0182] For the first The candidate solution is in the... The boundary bearing capacity safety factor of the stage;

[0183] The bearing capacity of the opening boundary components, walers, hidden beams, hidden columns, enclosure structures, or other pressure-bearing parts;

[0184] The design reaction force is transmitted from the prefabricated stiffening support to the boundary structure.

[0185] when If the pressure is not less than the preset boundary pressure control requirement, the candidate scheme is deemed to meet the boundary pressure requirement.

[0186] Step S55, calculate the stage transition safety factor:

[0187] (7);

[0188] In Equation 7:

[0189] For the first The candidate solution is in the... Safety factor for phase transition;

[0190] To bear the safety control coefficient;

[0191] This is the stiffness safety control factor;

[0192] This is the deformation safety control coefficient;

[0193] This is the boundary pressure safety control coefficient.

[0194] Determine whether the candidate scheme meets the transition conditions for the corresponding construction stage based on the stage transition safety factor:

[0195] when When the candidate solution is determined to satisfy the first condition, it is determined that the first condition is met. The transition conditions during the construction phase mean that the four control requirements of load-bearing capacity, stiffness, deformation, and boundary bearing pressure all meet the corresponding safety requirements, allowing for the removal of ordinary supports, the retention of prefabricated stiffened supports, the formation of deep and large temporary openings, the backfilling of basements, or subsequent support removal operations.

[0196] when When the candidate solution does not meet the first requirement, it is determined that the candidate solution does not satisfy the requirement. The transition conditions during the construction phase indicate that at least one of the four control indicators does not meet the safety requirements, and the quantity, location, spacing, cross-sectional dimensions, elevation, or opening formation sequence of the prefabricated stiffeners need to be adjusted and recalculated.

[0197] This discrimination method reflects the principle of controlling the weak links in the process of temporary tunnel support conversion at Shenzhen University.

[0198] The control items in the stage transition safety factor can be increased or decreased according to the needs of the project. For example, the support stability factor, node bearing capacity factor, floor constraint recovery factor, or monitoring feedback correction factor can be added.

[0199] Wherein: load-bearing safety control coefficient γ N Stiffness safety control factor γ K Deformation safety control coefficient γ D and boundary pressure safety control factor γ Q These parameters are used to set safety margins for four types of control indicators: bearing capacity, stiffness, deformation, and boundary bearing pressure. The indicators from different dimensions are normalized into a unified stage transition criterion. The coefficients can be determined according to Table 2 below:

[0200] coefficient Physical meaning Preferred value range Recommended values ​​for deep and large temporary opening scenarios in pipe jacking starting shafts <![CDATA[γ N ]]> Bearing safety control coefficient 1.10～1.30 1.20 <![CDATA[γ K ]]> Stiffness safety control factor 1.00～1.20 1.10 <![CDATA[γ D ]]> Deformation safety control coefficient 1.00～1.15 1.05 <![CDATA[γ Q ]]> Boundary bearing pressure safety control factor 1.10～1.30 1.20

[0201] Table 2

[0202] The principle for determining the values ​​of the above coefficients is as follows: when the engineering risk level is high, the duration of the tunnel is long, the surrounding environment is sensitive, or the monitoring feedback conditions are weak, the larger value within the corresponding range should be taken; when the engineering risk level is low, the temporary phase is short, and the monitoring feedback conditions are sufficient, the smaller value within the corresponding range can be taken.

[0203] For example: take γ N=1.20、γ K =1.10、γ D =1.05, γ Q =1.20, calculate the stage transition safety factor for each candidate scheme according to formula (7). The calculation results are as follows:

[0204] Candidate solutions <![CDATA[η N ]]> <![CDATA[η K ]]> <![CDATA[η D ]]> <![CDATA[η Q ]]> ST(k,t) Judgment Result Option A: 2 sticks per section, 6 sticks in total 1.42 1.27 1.18 1.34 1.12 Satisfy conversion conditions Option B: 3 sticks per section, 9 sticks in total 1.75 1.45 1.22 1.27 1.06 Satisfy conversion conditions Option C: 4 sticks per row, 12 sticks in total 2.10 1.80 1.30 1.24 1.03 Satisfy conversion conditions Option D: Two beams per section, moved outwards. 1.30 1.10 0.98 1.40 0.93 The conversion conditions are not met.

[0205] Table 2.1

[0206] The calculation process for scheme A is as follows:

[0207] ,

[0208] ,

[0209]

[0210] Therefore, Scheme A satisfies the transition conditions for this stage.

[0211] Although Option D has fewer supports, η D / γ D =0.98 / 1.05=0.93, which is less than 1.0, indicating that the deformation control of the opening does not meet the requirements. Therefore, it will not proceed to the subsequent minimum alternative support set optimization step. Schemes A, B, and C satisfy ST(k,t)≥1.0 and will proceed to the comprehensive evaluation function comparison.

[0212] Step S6, optimize candidate solutions for prefabricated stiffening supports:

[0213] Based on meeting the safety factor requirements for phase transition, a minimum alternative support set optimization algorithm is used to determine the optimal solution among multiple feasible candidate solutions, which minimizes the number of prefabricated stiffeners, maximizes the opening clearance, achieves a more balanced support arrangement, and reduces construction interference. Specifically, this includes:

[0214] Step S61, calculate the air release coefficient:

[0215] (8);

[0216] In Equation 8:

[0217] For the first The candidate solution is in the... The net air release coefficient for the stage;

[0218] This refers to the usable net clearance area of ​​the tunnel entrance area under this scheme;

[0219] The target is a large temporary tunnel opening area.

[0220] The larger the value, the greater the degree to which the candidate scheme releases construction space at the tunnel entrance.

[0221] Step S62, calculate the support offset influence coefficient:

[0222] (9);

[0223] In Equation 9:

[0224] For the first The candidate solution is in the... The support bias influence coefficient of the stage;

[0225] The eccentricity of the line of action of the resultant force of the prefabricated stiffening support in this scheme relative to the center line of the opening;

[0226] This refers to the width of the opening or the dimension controlling the direction.

[0227] The smaller the value, the more balanced the support arrangement, and the smaller the uneven effect on the opening boundary.

[0228] Step S63: Determine the degree of operational conflict based on the construction interference coefficient.

[0229] Construction interference coefficient Judge the first The candidate solution is in the... The degree of conflict between the stage and floor slab construction, hoisting path, equipment access, and underground connecting work space. The construction interference coefficient can be determined comprehensively based on factors such as the conflict between the support and the floor slab elevation, the range of the hoisting opening occupied by the support, the impact of the support on the equipment access width, and the impact of the support on subsequent slab repair construction.

[0230] Step S64, calculate the comprehensive evaluation function:

[0231] (10);

[0232] In Equation 10:

[0233] For the first The candidate solution is in the... The overall evaluation value of the stage;

[0234] =n r / n max , where n is the normalized value of the number of prefabricated stiffeners in the candidate scheme.r Let n be the number of prefabricated stiffeners in the r-th candidate scheme. max The maximum number of supports allowed among all candidate schemes;

[0235] The net air release coefficient is 1- This indicates the penalty for loss of net airspace;

[0236] in Calculate using the following formula:

[0237] (10.1)

[0238] In Equation 10.1:

[0239] (10.2);

[0240] The target is a large temporary tunnel opening area;

[0241] The effective clear area that can still be used for hoisting, equipment passage or underground connection operations after deducting the rigid support projection, support safety envelope area and temporary operation restricted area;

[0242] The area occupied by the rigid support projected onto the plane of the opening;

[0243] The area occupied to support the safe operating distance on both sides;

[0244] For temporary construction platforms, temporary supports, etc., which occupy space in stages;

[0245] The larger the value, the better the clearance and release effect of the opening;

[0246] To support the bias effect coefficient, it can be calculated using the following formula:

[0247] (10.3)

[0248] (10.4)

[0249] In the formula:

[0250] To control the directional width of the opening;

[0251] The eccentricity of the line of action of the resultant force of the prefabricated stiffening support in the candidate scheme relative to the center line of the opening;

[0252] The design axial bearing capacity or stage design reaction force of the j-th prefabricated stiffening support;

[0253] Let J be the plane coordinates of the j-th prefabricated stiffener;

[0254] The coordinates of the center line of the tunnel entrance; The smaller the value, the more balanced the support arrangement.

[0255] The construction interference coefficient is used to quantify the comprehensive impact of candidate support schemes on floor slab construction, hoisting path, equipment access, underground connection operations, and subsequent opening completion construction. It is determined by the following formula:

[0256] (10.5)

[0257] (10.6)

[0258] In the formula:

[0259] , , , All are dimensionless sub-items within the range of 0 to 1, and λ1, λ2, λ3, and λ4 are the weights of the corresponding sub-items; each sub-item is determined as shown in Table 3 below:

[0260] Sub-item meaning Quantitative calculation method Range of values <![CDATA[I h ]]> Sub-item of interference with floor slab or beam construction The conflict area between the support envelope zone and the construction area of ​​the floor slab, beam, or patch slab / the floor slab construction control area at this stage 0～1 <![CDATA[I p ]]> Lifting path interference sub-item The overlapping area between the support envelope and the hoisting channel or hoisting projection path / the hoisting path control area 0～1 <![CDATA[I e ]]> Equipment access or special construction interference sub-item min{1, max{0, Wreq-Wrem} / Wreq}, where Wreq is the required passage width and Wrem is the actual remaining width. 0～1 <![CDATA[I b ]]> Subsequent hole opening completion interference sub-items The conflict area between the support envelope area and the subsequent patching, beam reinforcement, or edge sealing construction area / the control area of ​​subsequent completion construction. 0～1

[0261] Table 3

[0262] For the scenario of the starting shaft hoisting opening in pipe jacking, the hoisting path and equipment access usually have a significant impact on the construction organization, so the following can be selected as the preferred option:

[0263] λ1=0.25, λ2=0.35, λ3=0.25, λ4=0.15.

[0264] Among them, the sub-item of interference with equipment passage or special construction can be further calculated using the following formula:

[0265] (10.7)

[0266] In the formula:

[0267] The required control width for equipment, components, or personnel access during this phase;

[0268] The actual remaining width after deducting the support envelope area and the safe operating distance;

[0269] Here are the weighting coefficients, where:

[0270]

[0271] Among them, w1 corresponds to the number of supports, w2 corresponds to the clearance release, w3 corresponds to the support stress balance, and w4 corresponds to construction interference. Typical values ​​under different engineering objectives are shown in Table 4 below:

[0272] Project target type <![CDATA[Number of w1 supports]]> <![CDATA[w2 clearance release]]> <![CDATA[The force on w3 is balanced]]> <![CDATA[Construction interference of w4]]> Balanced 0.25 0.25 0.25 0.25 Clearance priority 0.20 0.40 0.20 0.20 Recommended type of hoisting port for pipe jacking starting well 0.25 0.35 0.20 0.20 Force equilibrium priority type 0.20 0.25 0.35 0.20

[0273] Table 4

[0274] When the project focuses on reducing the number of supports, increase w1; when the project focuses on increasing the clearance of the opening, increase w2; when the project focuses on balanced support arrangement and uniform boundary stress, increase w3; when the project focuses on reducing interference with floor slab construction, hoisting paths, equipment access, and subsequent opening completion, increase w4. For the scenario of a deep and large temporary opening in the pipe jacking starting shaft in the embodiments of this application, w1=0.25, w2=0.35, w3=0.20, and w4=0.20 are preferred.

[0275] All of the above are dimensionless parameters, and The smaller the value, the better the overall effect of the candidate solution.

[0276] Comprehensive evaluation function It is used to comprehensively compare the number of supports, the clearance release at the opening, the balance of the support layout, and the degree of construction interference among feasible candidate schemes that meet the safety factor requirements of the phase transition.

[0277] Among them, the comprehensive evaluation function The calculation example is as follows:

[0278] To satisfy For schemes A, B, and C with a value ≥1.0, the comprehensive evaluation function is further calculated according to formula (10). Where w1=0.25, w2=0.35, w3=0.20, w4=0.20, and n... max =12, the calculation results are shown in Table 4.1 below:

[0279] Candidate solutions <![CDATA[N n ]]> <![CDATA[η C ]]> <![CDATA[1-η C ]]> <![CDATA[η E ]]> I J(k,t) in conclusion Option A: 2 sticks per section, 6 sticks in total 0.50 0.86 0.14 0.07 0.18 0.224 optimal Option B: 3 sticks per section, 9 sticks in total 0.75 0.74 0.26 0.04 0.32 0.351 Non-optimal Option C: 4 sticks per row, 12 sticks in total 1.00 0.62 0.38 0.03 0.48 0.485 Non-optimal

[0280] Table 4.1

[0281] The calculation process of the comprehensive evaluation function of Scheme A is as follows:

[0282]

[0283] The comprehensive evaluation functions for Scheme B and Scheme C are 0.351 and 0.485, respectively.

[0284] Since schemes A, B, and C all meet the stage transition safety factor requirements, but the comprehensive evaluation function of scheme A... The minimum requirement is met, therefore Option A is selected, which is to set 2 prefabricated stiffeners for each of the three height ranges, for a total of 6, as the optimal alternative support set for this embodiment.

[0285] The comprehensive evaluation function in the minimum alternative support set optimization algorithm can adjust its weight coefficients according to the engineering objectives. When the project prioritizes construction space, the weight of the clearance release coefficient can be increased; when the project prioritizes reducing the number of supports, the weight of the number of supports can be increased; when the project prioritizes stress balance, the weight of the support offset influence coefficient can be increased.

[0286] In all satisfied Among the candidate solutions, the solution with the smallest comprehensive evaluation function is selected as the optimal alternative support set:

[0287]

[0288] And it satisfies:

[0289]

[0290] Therefore, the first The optimal number, planar location, elevation, retention range, and removal sequence of prefabricated stiffeners in each construction stage.

[0291] Step S64, Output stage conversion construction sequence:

[0292] According to the optimal alternative support set Output the corresponding construction sequence for each construction stage, including:

[0293] Sequence of removal of ordinary supports;

[0294] The order of prefabricated stiffening supports should be retained.

[0295] The sequence of reconstructing the basement area (excluding openings);

[0296] The sequence of formation of the temporary tunnel entrance at Shenzhen University;

[0297] Sequence of underground connections or specialized construction projects;

[0298] Sequence of removal for prefabricated rigid supports in later stages;

[0299] The order of completing the basement structure in the opening area.

[0300] The following is combined with Figures 2 to 5 This document describes the conversion control method for the prefabricated stiffened support conversion and reinforcement system at the deep temporary opening of the pipe jacking starting shaft:

[0301] Example 1: Construction of temporary opening support conversion for deep and large pipe jacking starting shaft in basement

[0302] The foundation pit for a certain underground structural project is a long, narrow structure running east-west, with a plan dimension of approximately 64m long and 21m wide. The retaining structure of the pit adopts a combination of diaphragm walls and multiple internal supports. The internal supports are axially oriented north-south, with both ends supported by the retaining structures on the north and south sides of the pit, and arranged at approximately 5m intervals along the east-west direction. A total of seven internal supports are installed along the depth of the pit, with the first being a reinforced concrete support and the rest being steel supports.

[0303] The starting shaft for the underground connection construction is located in the western part of the middle of the foundation pit. A large vertical hoisting opening is required in the starting shaft area, with a planar dimension of approximately 14.7m × 14.7m. Ordinary internal supports are arranged at approximately 5m intervals along the east-west direction. The top elevation of the pipe jacking opening is approximately -3.9m, and the bottom elevation is approximately -18.7m. Three prefabricated rigid supports are installed within this height range. Based on the available space on the east and west sides of the hoisting opening, support elevations, floor slab elevation avoidance requirements, hoisting clearance requirements, and the bearing capacity of the opening boundary, the candidate schemes are generated as shown in Table 5 below:

[0304] Candidate solutions Arrangement Number of prefabricated stiffening supports Purpose of the solution Option A Two supports are installed near the east and west sides of the hoisting opening, for a total of six supports in three rows. 6 The number of support levels is relatively small, resulting in a large net short position. Option B Three sticks are set in each row, for a total of nine sticks across the three rows. 9 Increase load-bearing capacity and stiffness reserve Option C Four bars are set in each row, for a total of 12 bars across the three rows. 12 Further increase safety reserves, but take up more space. Option D Each row has 2 supports, but the supports are moved outwards, for a total of 6 supports across the three rows. 6 Compare the effects of shifting the support position outward on deformation control and offset.

[0305] Table 5

[0306] Because the hoisting opening is quite large, using ordinary steel supports would severely affect the lowering of the pipe jacking machine and the working space of the launching shaft; if large-section cast-in-place concrete supports are used, there will be problems such as large cross-section, long construction period, difficult demolition and a lot of construction waste.

[0307] Therefore, in this embodiment, prefabricated stiffening supports are installed near the east and west sides of the hoisting opening, with two supports on each side. Vertically, the top elevation of the pipe jacking entrance is approximately -3.9m, and the bottom elevation is approximately -18.7m. Three prefabricated stiffening supports are installed within this height range. The elevation of the prefabricated stiffening supports is consistent with or corresponds to the elevation of the corresponding steel supports, allowing them to participate in the retaining structure support together with ordinary steel supports during the excavation stage of the foundation pit.

[0308] During the excavation phase of the foundation pit, excavation was carried out in layers according to the conventional sequence, and ordinary internal supports were installed. At the same time, prefabricated stiffened supports were installed in the areas where hoisting openings and launching shafts were to be formed. Since the prefabricated stiffened supports are composite components of steel sections covered with concrete, their load-bearing capacity and stiffness are higher than those of ordinary steel supports. They can replace multiple ordinary steel supports in the opening area to undertake the horizontal support function in subsequent construction phases.

[0309] As the basement structure is rebuilt from bottom to top, the ordinary steel supports in non-jacking areas are gradually removed as the basement floor slabs are constructed, and the basement floor slabs and beams are formed layer by layer. In the area of ​​the pipe jacking starting shaft, the basement floor slab is not rebuilt temporarily, but the prefabricated stiffening supports are retained. Because the elevation of the prefabricated stiffening supports avoids the floor slab elevation, the floor slabs in non-opening areas can be constructed with the supports retained. Once the floor slab is completed and reaches its design strength, the ordinary supports for the corresponding stage are removed.

[0310] In the pipe jacking starting shaft area, as the basement structure in the non-opening area gradually takes shape, ordinary steel supports are removed, while prefabricated stiffened supports remain and assume the role of horizontal support in the opening area. This creates a support configuration where a small number of high-bearing-capacity prefabricated stiffened supports replace multiple ordinary steel supports, allowing the formation of a large 14.7m × 14.7m hoisting opening and a relatively deep starting shaft space.

[0311] After the backfilling of the non-jacking area of ​​the basement structure is completed, the construction of the jacking launching platform and related temporary structures is finished. The prefabricated stiffened supports continuously bear the force within three height ranges, ensuring the stability of the launching shaft area under the action of water and soil pressure outside the pit. Then, the jacking construction is carried out.

[0312] After the pipe jacking is completed, based on the safety factor determination results of the stage transformation, the temporary structures and prefabricated stiffening supports within the range of the pipe jacking starting shaft are removed layer by layer, and the basement floor slabs and beams in the starting shaft area are completed layer by layer, so that the opening area is finally transformed into a complete basement structure.

[0313] Example 2: Application of the stage transition safety factor in Example 1

[0314] In Example 1, the construction process is divided into the foundation pit excavation and support stage, the basement backfilling stage, the starting well opening formation stage, the pipe jacking starting construction stage, and the basement completion stage.

[0315] Taking the formation stage of the starting wellhead as an example, the first step is to identify the ordinary steel support sets within the lifting opening area that need to be removed or replaced. Based on the available space and support elevation on the east and west sides of the hoisting opening, several candidate layout schemes for prefabricated rigid supports are generated. .

[0316] Calculate the bearing capacity substitution factor for each candidate scheme. Stiffness substitution factor Deformation control coefficient at the tunnel entrance and boundary bearing pressure safety factor The minimum value after normalization is taken as the stage transition safety factor. .

[0317] when When it is determined that the ordinary steel supports within the corresponding range can be removed while the prefabricated stiffening supports are retained, then... In such cases, it is necessary to increase the number of prefabricated stiffeners, adjust their arrangement, increase the cross-sectional bearing capacity, or change the sequence of support conversion.

[0318] Example 3: Application of the Minimum Substitute Support Set Optimization Algorithm in Example 1

[0319] In Example 1, various prefabricated stiffening support alternatives can be generated for the hoisting port area. For example, two, three, or four stiffening supports can be set for each section, or the supports can be arranged near the edge of the hoisting port, at the outward position on both sides of the opening, or at the local reinforcement position.

[0320] For each candidate solution, the phase transition safety factor must be satisfied. Based on this, the net air release coefficient is further calculated. Support offset influence coefficient Construction interference coefficient And substitute it into the comprehensive evaluation function of formula (10):

[0321] Final selection The minimum solution is considered the optimal solution. In this embodiment, two prefabricated rigid supports are installed in each of the three height ranges, for a total of six prefabricated rigid supports. This can maximize the release of space inside the hoisting port and launching shaft while meeting the support safety requirements, and is therefore the preferred alternative support set.

[0322] The prefabricated stiffened bracing conversion reinforcement system provided in this invention provides a stage conversion control method for prefabricated stiffened bracing conversion reinforcement systems for deep and large temporary openings in underground structures. This method does not simply replace ordinary supports with high-bearing-capacity support components, but rather uses prefabricated stiffened bracing as a "conversion support unit" during the underground structure construction stage. During the foundation pit excavation stage, it works in conjunction with ordinary internal supports to bear force. During the basement backfilling and deep and large temporary opening formation stages, it replaces the ordinary supports that need to be removed within the opening area. After the underground connection or special construction is completed, it is gradually removed during the basement structure completion process, thereby achieving a safe conversion between the ordinary foundation pit support system, the deep and large temporary opening support system, and the permanent basement structure system. Building upon this foundation, a method for determining the safety factor during phase transitions is further proposed. This method integrates load-bearing capacity, stiffness replacement capacity, opening deformation control capacity, and boundary bearing capacity into the transition criteria. This is used to determine whether it is permissible to remove ordinary supports, retain stiffened supports, form deep and large temporary openings, or complete the basement structure at a given construction stage. Simultaneously, a minimum replacement support set optimization algorithm is proposed. Under the premise of meeting phase transition safety requirements, this algorithm comprehensively considers factors such as the number of supports, opening clearance release, support offset, and construction interference to determine the optimal number, location, elevation, and retention order of prefabricated stiffened supports. Therefore, this invention is not merely about the high load-bearing capacity of the stiffened supports themselves, but rather about the combined technical solution of "prefabricated stiffened support system + phase transition safety determination + minimum replacement support set optimization algorithm." Through a small number of high-load-bearing, prefabricated, and reusable stiffened supports, large-size, deep vertical temporary opening spaces are formed without sacrificing the safety of the underground structure support. This solves the problems of insufficient load-bearing capacity of traditional ordinary steel supports, large concrete support cross-sections and difficulty in removal, lack of quantitative criteria for deep and large opening transitions, and the impact of support arrangement on construction clearance.

[0323] The prefabricated stiffened brace conversion reinforcement system stage transition control method provided in this invention achieves force conversion between the ordinary support system, the stiffened brace system, and the permanent basement structure system by setting prefabricated stiffened braces in the area of ​​deep and large temporary openings in the underground structure and enabling them to undertake different support functions at different construction stages. Simultaneously, a stage transition safety factor determination method is used to determine whether it is permissible to remove ordinary supports, retain stiffened braces, form deep and large openings, or complete the basement structure at different stages. A minimum alternative support set optimization algorithm is used to determine the optimal number, location, and retention stage of stiffened braces under the premise of meeting safety requirements, thereby maximizing the release of construction space at the openings.

[0324] The prefabricated stiffened bracing conversion reinforcement system provided in this invention provides a phased conversion control method. This method replaces multiple ordinary supports that need to be removed within the area of ​​a deep, large temporary opening with prefabricated stiffened bracing. This reduces the number of supports while meeting higher bearing capacity and stiffness requirements, freeing up construction space inside the opening. By replacing the ordinary supports that need to be removed within the opening area with prefabricated stiffened bracing, the underground structure is converted from a conventional support state to a deep, large opening construction state. The prefabricated stiffened bracing works collaboratively with ordinary supports during the foundation pit excavation stage, gradually replacing ordinary supports during the basement backfilling and opening formation stages, and then gradually removing and completing the basement structure after the opening construction is finished.

[0325] The prefabricated stiffened bracing conversion reinforcement system provided in this invention provides a stage conversion control method. The prefabricated stiffened bracing can be prefabricated in the factory and assembled on site, which can reduce the amount of cast-in-place concrete support construction, reduce demolition difficulty, reduce construction waste, and has good green construction and reuse value.

[0326] The stage transition control method of the prefabricated stiffened brace conversion reinforcement system provided in this embodiment of the invention coordinates the elevation of the prefabricated stiffened brace with the elevation of the ordinary brace and avoids the elevation of the basement floor slab, so that the basement floor slab can be constructed with the support retained, avoiding the temporary support risk caused by removing the support first and then constructing the floor slab.

[0327] The prefabricated stiffened brace conversion reinforcement system provided in this invention provides a stage conversion safety factor, which integrates bearing capacity, stiffness replacement capacity, opening deformation control capacity and boundary bearing capacity into the judgment system, so that the stage conversions such as ordinary brace removal, stiffened brace retention, opening formation and basement completion have clear quantitative basis.

[0328] The prefabricated stiffened support conversion reinforcement system provided in this invention provides a stage transition control method that proposes a minimum replacement support set optimization algorithm. Under the premise of meeting stage transition safety conditions, it comprehensively considers the number of supports, the release of clearance at openings, support offset, and construction interference to determine the optimal stiffened support layout scheme, balancing support safety and construction efficiency. By replacing multiple ordinary supports that need to be removed within the opening area with a small number of high-bearing-capacity, high-rigidity, and prefabricable stiffened supports, and combining the stage transition safety factor determination method and the minimum replacement support set optimization algorithm, the method achieves a safe transition of the underground structure from a conventional foundation pit support state to a deep and large opening construction state, and then to a complete basement structure state. This solves the problems of insufficient bearing capacity of ordinary steel supports, large space occupation and difficult removal of large-section concrete supports, lack of quantitative criteria for support conversion in deep and large opening areas, and difficulty in balancing construction space and support safety in existing underground structure connection construction.

[0329] The stage transition control method of the prefabricated stiffened support conversion reinforcement system provided in this invention has a wide range of applications. It is not only applicable to the construction of pipe jacking starting shafts, but also to engineering scenarios in urban renewal that require the formation of deep and large temporary openings, such as connecting existing basements, adding new underground passages, equipment hoisting shafts, tunneling, pipe sheds, and freezing method construction.

[0330] This invention is not limited to the specific embodiments described above. Obviously, the embodiments described above are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of this invention are within the scope of protection of this invention. Those skilled in the art can make other modifications and variations to this invention. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for controlling the stage transition of a prefabricated stiffener conversion and reinforcement system, characterized in that, include: Step S1: Establish the original support system model: Determine the initial force relationship between the ordinary internal support, the enclosure structure and the basement structure based on the original support system model; Step S2: Divide the construction process into several stages: Divide the construction process of the deep and large temporary openings in the underground structure into several construction stages: Step S3: Identify the impact zone of the opening: Based on the planar and vertical extent of the proposed deep temporary opening and the location of the ordinary internal supports, identify the area affected by the opening. A collection of ordinary supports that need to be dismantled, relocated, or replaced by prefabricated stiffened supports during each construction phase due to the influence of openings; Step S4: Generate candidate prefabricated stiffener layout schemes: Based on the boundaries of the temporary opening at Shenzhen University, floor slab elevation avoidance requirements, construction clearance requirements, support force direction, and on-site installation conditions, generate several candidate prefabricated stiffener layout schemes: （2）； In Equation 2, For the first The first construction phase Individual support candidate solutions For the first Root prefabricated rigid support, The number of stiffening supports in this candidate scheme; Step S5: Calculate the stage transition safety factor: For each candidate scheme, calculate the bearing capacity substitution factor, stiffness substitution factor, opening deformation control factor, and boundary bearing pressure safety factor, and formulate the stage transition safety factor accordingly. ; when When the candidate solution is determined to satisfy the first condition, it is determined that the first condition is met. The conditions for conversion during the construction phase allow for the removal of ordinary supports, the retention of prefabricated rigid supports, the formation of deep and large temporary openings, the backfilling of basements, or subsequent support removal operations. when When the candidate solution does not meet the first requirement, it is determined that the candidate solution does not satisfy the requirement. The transition conditions during the construction phase require adjustments to the quantity, location, spacing, cross-sectional dimensions, or opening sequence of prefabricated rigid supports; Step S6, optimize candidate solutions for prefabricated stiffening supports: Based on meeting the safety factor requirements for phase transition, the optimal solution is determined from multiple feasible candidate solutions by using the minimum alternative support set optimization algorithm, which minimizes the number of prefabricated stiffeners, maximizes the clearance release at the opening, achieves a more balanced support layout, and minimizes construction interference.

2. The stage transition control method for the prefabricated stiffening bracing conversion reinforcement system according to claim 1, characterized in that, In step S5, the method for forming the stage transition safety factor includes: Step S51: Calculate the load-bearing substitution factor: （3）； In Equation 3: For the first The candidate solution is in the... The carrying capacity substitution coefficient of the stage; For the first The design axial bearing capacity of the prefabricated stiffening brace; For the first The design axial force of the root is replaced by that of ordinary support; For the first The load reduction factor of prefabricated stiffened supports during the construction phase; For the first Contribution coefficient of ordinary support to the influence zone of the tunnel entrance; For the first Additional horizontal load requirements arising from the formation of openings, missing floor slabs, or boundary transitions at each stage; Step S52: Calculate the stiffness substitution factor: （4）； In Equation 4: For the first The candidate solution is in the... Stiffness substitution factor for each stage; For the first The horizontal equivalent stiffness of the prefabricated stiffening brace; For the first The horizontal equivalent stiffness of the root replacing the ordinary support; Step S53: Calculate the deformation control coefficient at the opening: （5）； In Equation 5: For the first The candidate solution is in the... The deformation control coefficient of the opening at each stage; This refers to the maximum allowable deformation value for the enclosure structure, opening boundary, or basement structure. For the first The candidate solution is in the... The maximum deformation value obtained from stage calculations or monitoring; Step S54: Calculate the boundary bearing capacity safety factor: （6）； In Equation 6: For the first The candidate solution is in the... The boundary bearing capacity safety factor of the stage; The bearing capacity of the opening boundary components, walers, hidden beams, hidden columns, enclosure structures, or other pressure-bearing parts; The design reaction force transmitted from the prefabricated stiffening support to the boundary structure; Step S55, calculate the stage transition safety factor: （7）； In Equation 7: For the first The candidate solution is in the... Safety factor for phase transition; To bear the safety control coefficient; This is the stiffness safety control factor; This is the deformation safety control coefficient; This is the boundary pressure safety control coefficient.

3. The stage transition control method for the prefabricated stiffening bracing conversion reinforcement system according to claim 1, characterized in that, Methods for optimizing candidate solutions for prefabricated stiffeners include: Step S61, calculate the net air release coefficient: （8）； In Equation 8: For the first The candidate solution is in the... The net air release coefficient for the stage; This refers to the usable net clearance area of ​​the tunnel entrance area under this scheme; The target is a large temporary tunnel opening area; Step S62, calculate the support offset influence coefficient: （9）； In Equation 9: For the first The candidate solution is in the... The support bias influence coefficient of the stage; The eccentricity of the line of action of the resultant force of the prefabricated stiffening support in this scheme relative to the center line of the opening; This refers to the width of the opening or the dimension controlling the direction. Step S63: Determine the degree of operational conflict based on the construction interference coefficient. Construction interference coefficient Judge the first The candidate solution is in the... The degree of conflict between the stage and floor slab construction, hoisting path, equipment access, and underground connecting work space; Step S64, calculate the comprehensive evaluation function: （10）； In Equation 10: For the first The candidate solution is in the... The overall evaluation value of the stage; This is the normalized value for the number of prefabricated stiffeners in the candidate scheme; This is the net air release coefficient; To support the bias influence coefficient; This is the construction interference coefficient; These are the weighting coefficients; In all satisfied Among the candidate solutions, the solution with the smallest comprehensive evaluation function is selected as the optimal alternative support set: And it satisfies: Therefore, the first The optimal number, planar location, elevation, retention range, and removal sequence of prefabricated stiffeners in each construction stage.

4. The stage transition control method for the prefabricated stiffening brace conversion reinforcement system according to claim 3, characterized in that, Also includes: Step S64, Output stage conversion construction sequence: According to the optimal alternative support set Output the corresponding construction sequence for each construction stage, including: Sequence of removal of ordinary supports; The order of prefabricated stiffening supports should be retained. The sequence of reconstructing the basement area (excluding openings); The sequence of formation of the temporary tunnel entrance at Shenzhen University; Sequence of underground connections or specialized construction projects; Sequence of removal for prefabricated rigid supports in later stages; The order of completing the basement structure in the opening area.

5. The stage transition control method for the prefabricated stiffening bracing conversion reinforcement system according to claim 1, characterized in that, Obtain the basic parameters of the underground structure project, including the plan dimensions of the foundation pit, the form of the retaining structure, the location of the ordinary internal supports, the spacing of the ordinary internal supports, the elevation of the ordinary internal supports, the design axial force of the ordinary internal supports, the elevation of the basement floor slab, the layout of the basement beams and slabs, and the plan dimensions and vertical range of the proposed deep and large temporary openings. Establish the original support system model based on the basic parameters of the underground structure project.

6. The stage transition control method for the prefabricated stiffening brace conversion reinforcement system according to claim 1, characterized in that, The prefabricated rigid support is a prefabricated steel-concrete composite support component formed by internal steel sections, steel pipes, steel boxes or other steel components and external concrete under joint stress.

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