A method and system for collaborative design of preloading above a lower tunnel and composite foundation

Abstract

The application provides a method and system for collaborative design of preloading above a lower tunnel and a composite foundation, and relates to the technical field of geotechnical engineering and structural engineering. The foundation of the region to be designed is divided into a core sensitive area, a transition area and a peripheral area. The core sensitive area and the transition area are both treated by a composite foundation, and the pile spacing and pile length of the transition area are designed to gradually change. The application can ensure the safety of the lower tunnel structure and also take into account the economy. Based on the geometric and spatial position data of the region to be designed, the region division result, the pile parameters of the transition area and the core sensitive area, a first three-dimensional numerical calculation model is established and a preloading load is applied to obtain the first structural mechanics response data of each first monitoring point of the lower tunnel. According to the first structural mechanics response data, the design scheme is output when the lower tunnel is safe based on the preset safety standard, which further ensures the safety of the lower tunnel structure.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and structural engineering, specifically to a method and system for the coordinated design of surcharge preloading and composite foundation above an underpass tunnel. Background Technology

[0002] In airport vertical development and flight area expansion projects, soft soil foundations and fill roadbeds are widely distributed within the flight area, often necessitating surcharge preloading on weak foundations to control post-construction settlement. When an existing underpass tunnel exists beneath the flight area, the significant additional stress and settlement generated by the large-area surcharge above may threaten the structural safety of the underpass tunnel.

[0003] To protect underpasses, existing technologies use composite foundations for reinforcement. However, the common approach is to use a uniform, one-size-fits-all method of laying piles evenly across the entire area. This not only results in excessive reinforcement in areas far from the underpass, leading to wasted costs, but more seriously, it creates a sudden change in stiffness at the boundary between the reinforced and unreinforced areas. Under load, this can easily cause differential settlement and stress concentration, which can have adverse effects on the underpass and the upper road structure.

[0004] Therefore, when carrying out surcharge preloading treatment above the airport flight area underpass, how to coordinate the foundation settlement to meet the standards and the structural safety of the underpass, while also taking into account economic efficiency, has become an urgent technical problem to be solved. Summary of the Invention

[0005] In view of this, in order to solve the above-mentioned technical problems, the present invention provides a method and system for the coordinated design of surcharge preloading above underpass tunnels and composite foundation.

[0006] The present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for the coordinated design of surcharge preloading above an underpass tunnel and composite foundation, comprising: When it is determined that a combined design scheme of surcharge preloading and composite foundation is required, the foundation of the area to be designed is divided into a core sensitive area, a transition area, and an outer area, resulting in a regional division. The core sensitive area is located directly above the underpass tunnel in the area to be designed, and the transition area is located between the core sensitive area and the outer area. Both the core sensitive area and the transition area are treated with composite foundation. Based on the geological type of the core sensitive area and the transition area, determine the pile type to be used in the core sensitive area and the transition area; Based on the preset pile shape and pile arrangement, with the aim of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements, the pile diameter, pile spacing and pile length of the core sensitive area are determined; Based on the preset slope ratio, the pile length distribution of the transition zone is determined according to the width of the transition zone and the pile length of the core sensitive zone. The pile length of the transition zone adopts a gradual design, and the other pile parameters are the same as those of the core sensitive zone. Based on the geometric and spatial location data of the area to be designed, the area division results, and the pile parameters of the transition zone and the core sensitive zone, a first three-dimensional numerical calculation model is established, and the ground stress balance is performed on the first three-dimensional numerical calculation model; multiple first monitoring points are set on the underpass tunnel in the first three-dimensional numerical calculation model; An overload preload is applied to the top of the transition zone and the outer zone of the first three-dimensional numerical calculation model, and the first structural mechanical response data at each of the first monitoring points are obtained. Based on the preset safety standards and according to the first structural mechanical response data, it is determined whether the underpass is safe, and a first judgment result is obtained; When the first judgment result is yes, the design scheme is output; the design scheme includes the region division result, as well as the pile parameters of the transition zone and the core sensitive zone.

[0008] Optional, also includes: When the first judgment result is negative, under the premise of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements, at least one pile parameter among the pile diameter, pile spacing and pile length of the core sensitive area and the transition area is adjusted in the first three-dimensional numerical calculation model. Reapply surcharge preload to the transition zone and the outer zone of the first three-dimensional numerical calculation model, and reacquire the first structural mechanical response data at each of the first monitoring points; Based on the preset safety standards and the current first structural mechanical response data, it is determined whether the underpass is safe, and the current first judgment result is obtained; If the first judgment result is yes, output the design scheme; If the current first judgment result is negative, the following step is performed: under the premise that the bearing capacity of the composite foundation of the core sensitive area and the transition area meets the preset bearing capacity requirements, in the first three-dimensional numerical calculation model, at least one of the pile parameters of the pile diameter, pile spacing and pile length of the core sensitive area and the transition area is adjusted to iteratively optimize the relevant pile parameters until the design scheme is output.

[0009] Optionally, before dividing the foundation of the area to be designed into a core sensitive zone, a transition zone, and a peripheral zone, and obtaining the zone division results, the following steps are also included: Based on the geometric and spatial location data of the area to be designed, a second three-dimensional numerical calculation model is established, and the ground stress balance is performed on the second three-dimensional numerical calculation model; each of the first monitoring points is set on the underpass in the second three-dimensional numerical calculation model; The surcharge preload is applied to a designated area at the top of the second three-dimensional numerical calculation model, and the second structural mechanical response data at each of the first monitoring points are obtained. Based on the aforementioned safety standards and according to the second structural mechanical response data, it is determined whether the underpass is safe, and a second determination result is obtained. Based on a preset finite element model, the first void ratio and the second void ratio of the roadbed soil requiring surcharge preloading treatment in the design area are determined at a set time. Based on the first void ratio, the second void ratio, and the initial void ratio of the roadbed soil, the degree of consolidation of the roadbed soil at the set time is calculated. The set time is the end time of surcharge preloading. Based on the additional stress increment generated by the surcharge preload at each layer of the subgrade soil, the thickness of each layer of the subgrade soil and the compression modulus, the total settlement of the subgrade soil is calculated. Based on the degree of consolidation and the total settlement, the post-construction settlement of the roadbed soil is calculated within a set time period; the set time period starts from the set time. Subtract the post-construction settlement from the total settlement to obtain the target difference. Determine whether the target difference meets the preset difference requirement to obtain a third judgment result. When both the second and third judgment results are yes, it is determined that the scheme of using only surcharge preloading is feasible; If the second judgment result is negative and the third judgment result is positive, it is determined that a combined design scheme of surcharge preloading and composite foundation is required.

[0010] Optionally, the security standards include: The peak values ​​of horizontal displacement, vertical displacement, and radial displacement of the underpass are all less than preset displacement thresholds; and the peak value of the additional stress increment on the outer wall of the underpass lining is less than or equal to the preset stress increment threshold.

[0011] Optionally, when the underpass tunnel is a shield tunnel, the safety standards also include: The peak value of the joint opening of the shield tunnel segments in the underpass is less than a preset opening threshold; and the peak value of the crack width of the shield tunnel segments in the underpass is less than a preset width threshold.

[0012] Optionally, the core sensitive area is enclosed by a first boundary obtained by extending the outer edge of the underpass tunnel to both sides of the underpass tunnel by a first preset multiple of the underpass tunnel span, and the distance extended to both sides of the underpass tunnel from the outer edge of the underpass tunnel is not less than the first preset distance. The transition zone is enclosed by the first boundary and a second boundary obtained by extending outward from the first boundary by a second preset multiple of the underpass span, or the transition zone is enclosed by the first boundary and a second boundary obtained by extending outward from the first boundary by a second preset distance.

[0013] Optionally, the value range of the first preset multiple is 1 to 1.5; The first preset distance ranges from 8m to 12m; The value range of the second preset multiple is 0.5 to 1; The second preset distance ranges from 6m to 10m.

[0014] Optionally, the underpass can be a single tunnel or a group of tunnels.

[0015] Optionally, the pile length in the core sensitive area meets the first pile length control principle, which includes that the pile bottom does not contact the arch of the underpass tunnel, and the distance between the pile bottom and the arch of the underpass tunnel is not less than a preset safety distance. The pile length in the transition zone meets the second pile length control principle, which includes that the difference in pile length between adjacent control sections does not exceed a preset difference threshold.

[0016] Secondly, the present invention also provides a collaborative design system for surcharge preloading and composite foundation above an underpass tunnel, comprising: The partitioning module is used to divide the foundation of the area to be designed into a core sensitive zone, a transition zone, and an outer zone when it is determined that a combined design scheme of surcharge preloading and composite foundation is required, thus obtaining the area partitioning result; the core sensitive zone is located directly above the underpass tunnel in the area to be designed, and the transition zone is located between the core sensitive zone and the outer zone; both the core sensitive zone and the transition zone are treated with composite foundation; The first determining module is used to determine the pile type to be used in the core sensitive area and the transition area based on the geological type of the core sensitive area and the transition area; The second determining module is used to determine the pile diameter, pile spacing, and pile length of the core sensitive area based on the preset pile shape and pile layout, with the aim of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements. The third determining module is used to determine the pile length distribution of the transition zone based on the preset slope ratio, the width of the transition zone, and the pile length of the core sensitive zone. The pile length of the transition zone adopts a gradual design, and the other pile parameters are the same as those of the core sensitive zone. A module is established to build a first three-dimensional numerical calculation model based on the geometric and spatial location data of the area to be designed, the area division results, and the pile parameters of the transition zone and the core sensitive zone, and to perform ground stress balance on the first three-dimensional numerical calculation model; multiple first monitoring points are set on the underpass tunnel in the first three-dimensional numerical calculation model; The monitoring module is used to apply a surcharge preload to the top of the transition zone and the outer zone of the first three-dimensional numerical calculation model, and to acquire the first structural mechanical response data at each of the first monitoring points. The judgment module is used to determine whether the underpass is safe based on a preset safety standard and the first structural mechanical response data, and to obtain a first judgment result; The output module is used to output a design scheme when the first judgment result is yes; the design scheme includes the region division result, and the pile parameters of the transition zone and the core sensitive zone.

[0017] This invention employs the above technical solution. When the foundation settlement meets the standards, but the underpass tunnel structure is unsafe, it determines that a combined design scheme of surcharge preloading and composite foundation is necessary. The foundation of the area to be designed is then divided into a core sensitive zone, a transition zone, and an outer zone. Both the core sensitive zone and the transition zone are treated with composite foundations. Furthermore, the pile spacing and pile length in the transition zone are designed with gradual changes, while the remaining pile parameters are the same as in the core sensitive zone. This allows the invention to reduce the number of piles required, and the transition zone provides a gradual change in stiffness and a smooth stress transition, avoiding the abrupt change in reinforcement from a densely piled arrangement in the core sensitive zone to a pileless arrangement in the outer zone. The invention, through its arrangement, ensures the structural safety of underpass tunnels while maintaining economic efficiency. Furthermore, based on the geometric and spatial location data of the area to be designed, the regional division results, and the pile parameters of the transition zone and core sensitive area, a first three-dimensional numerical calculation model is established. A surcharge preloading load is applied to the top of the transition zone and the outer perimeter of the first three-dimensional numerical calculation model, and the first structural mechanical response data at each first monitoring point of the underpass tunnel are obtained. Based on preset safety standards and the first structural mechanical response data, when the underpass tunnel is deemed safe, a design scheme is output, further ensuring the structural safety of the underpass tunnel. Therefore, the invention can simultaneously ensure that foundation settlement meets standards and the structural safety of the underpass tunnel while maintaining economic efficiency when performing surcharge preloading treatment above an airport flight area underpass tunnel. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a method for the coordinated design of overpass preloading and composite foundation for underpass tunnels, as provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the layout of a method for coordinating surcharge preloading and composite foundation design above an underpass tunnel, provided by an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the first three-dimensional numerical calculation model provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the second three-dimensional numerical calculation model provided in the embodiment of the present invention; Figure 5 This is a structural schematic diagram of a collaborative design system for surcharge preloading and composite foundation above an underpass tunnel, provided by an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Figure 1 This is a flowchart illustrating a method for the coordinated design of overpass preloading and composite foundation for underpass tunnels, as provided in an embodiment of the present invention. Figure 1 As shown, this process includes: Step 101: When it is determined that a combined design scheme of surcharge preloading and composite foundation is required, the foundation of the area to be designed is divided into a core sensitive area, a transition area and an outer area, and the area division results are obtained. The core sensitive area is located directly above the underpass tunnel in the area to be designed, and the transition area is located between the core sensitive area and the outer area. Both the core sensitive area and the transition area are treated with composite foundation.

[0022] Figure 2 This is a schematic diagram illustrating the layout of a method for coordinating surcharge preloading and composite foundation design above an underpass tunnel, as provided in an embodiment of the present invention. (Reference) Figure 2The core sensitive area is enclosed by a first boundary obtained by extending the outer edge of the underpass to both sides of the underpass by a first preset multiple of the underpass span, and the distance between the outer edge of the underpass to both sides of the underpass is not less than the first preset distance. Figure 2 In this design, the area between the outer edge of the underpass and the corresponding first boundary constitutes the tunnel edge extension zone. The width of this extension zone is not less than a first preset distance. There are two tunnel edge extension zones, located on either side of the underpass. The first preset multiple ranges from 1 to 1.5, and the first preset distance ranges from 8m to 12m. In practical applications, technicians typically set the first preset multiple to 1 under normal working conditions, and to 1.5 under important engineering projects or deep soft soil conditions, while simultaneously ensuring that "the distance between each extension zone on either side of the underpass, based on the outer edge of the underpass, is not less than the first preset distance."

[0023] The transition zone is enclosed by a first boundary and a second boundary obtained by extending the underpass span outward from the first boundary by a second preset multiple, or by the first boundary and a second boundary obtained by extending the underpass span outward from the first boundary by a second preset distance. The second preset multiple ranges from 0.5 to 1, and the second preset distance ranges from 6m to 10m. In practical applications, technicians typically set the second preset multiple to 0.5 or the second preset distance to 8m under normal operating conditions.

[0024] It should be noted that the area outside the transition zone is the outer perimeter zone. The impact of surcharge on the outer perimeter zone is no longer sensitive to the tunnel. Therefore, only conventional surcharge preloading treatment is used, and composite foundation piles are not installed.

[0025] Step 102: Determine the pile type to be used in the core sensitive area and the transition area based on the stratigraphic type of the core sensitive area and the transition area.

[0026] Specifically, this invention pre-defines the pile type to be used for different strata types. For example, when the strata are mainly composed of cohesive soil, silt, and silty clay, the pile type used is CFG (Cement Fly-ash Gravel Pile); when the strata are mainly composed of collapsible loess and silt, the pile type used is lime-soil compaction pile or soil compaction pile; and when the strata are mainly composed of saturated silt, saturated silt, and soft clay, the pile type used is cement-soil mixing pile.

[0027] It should be noted that the geological strata types in the core sensitive area and the transition area are often the same, and the same type of pile is used in both areas. This avoids the use of multiple pile type combinations and ensures the simplicity of the technology and the ease of quality control.

[0028] Step 103: Based on the preset pile shape and pile layout, with the aim of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements, determine the pile diameter, pile spacing and pile length of the core sensitive area.

[0029] Specifically, the pile shape can be circular, and the pile arrangement can be either an equilateral triangle or a rectangular arrangement. The pile diameter can be greater than or equal to 0.4m.

[0030] The preset bearing capacity requirement can be a composite foundation bearing capacity greater than 200 kPa. For example, when the pile type used is a lime-soil compaction pile or a soil compaction pile, the corresponding formula for calculating the composite foundation bearing capacity is as follows: ......(1) When CFG piles or cement-soil mixing piles are used, the calculation formula for the bearing capacity of the corresponding composite foundation is as follows: ......(2) In the formula, and The bearing capacity of the composite foundation is calculated using formula (1) and formula (2), respectively. The replacement rate; This is the single pile bearing capacity utilization factor; The characteristic value of the original roadbed bearing capacity, and the pile-soil stress ratio. for / , The characteristic value of pile bearing capacity. = / ; This is the bearing capacity utilization coefficient of the soil between piles; This is the cross-sectional area of ​​the pile; For the single pile bearing capacity, it should be noted that the single pile bearing capacity involved should be determined according to different situations, as shown in formulas (3) and (4).

[0031] When the pile type used is cement-soil mixing pile, Take the minimum value from the following two formulas: ......(3) When the pile type used is CFG pile, Take the minimum value from the following two formulas: ......(4) In the formula, The average cubic compressive strength of standard pile test blocks cured for 28 days; The reduction factor for the pile body is n; n is the number of subgrade soil layers. The circumference of the pile body; The end resistance utilization factor is typically taken as 0.4 to 0.6. This refers to the thickness of the i-th layer of foundation soil around the pile, which is also the length of the pile corresponding to the i-th layer of foundation soil around the pile. Let be the ultimate lateral resistance of the i-th layer of foundation soil around the pile; This represents the end resistance of the soil at the pile tip.

[0032] When the pile shape is circular and the pile layout is an equilateral triangle, the replacement rate is... The calculation formula is: ......(5) When the pile shape is circular and the pile layout is rectangular, the replacement rate is... The calculation formula is: ......(6) In the formula, Let be the side length of the equilateral triangle; The diameter of the pile; and These are the lengths of the two sides of the rectangle. If it's a square, then... = .

[0033] In this embodiment of the invention, the pile length in the core sensitive area satisfies a first pile length control principle. This first pile length control principle includes that the pile bottom does not contact the arch of the underpass tunnel, and the distance between the pile bottom and the arch of the underpass tunnel is not less than a preset safety distance. For example, ... Figure 2 As shown, the shortest distance between the bottom of the pile and the arch of the underpass tunnel is greater than or equal to the preset safety distance, which ranges from 3m to 5m.

[0034] Step 104: Based on the preset slope ratio, determine the pile length distribution of the transition zone according to the width of the transition zone and the pile length of the core sensitive zone. The pile length of the transition zone adopts a gradual design, and the other pile parameters are the same as those of the core sensitive zone.

[0035] In this embodiment of the invention, the pile length in the transition zone meets the second pile length control principle, which includes ensuring that the difference in pile length between adjacent control sections does not exceed a preset difference threshold to avoid differential settlement. For example, the preset difference threshold can be 3m.

[0036] For details, please refer to Figure 2While maintaining the same pile spacing, pile shape, pile layout, and pile diameter as the core sensitive area, the pile length gradually decreases from the outer edge of the core sensitive area. In a specific example, assuming the width of the transition zone is 6 meters, the preset slope ratio is 1:2, and the pile length in the core sensitive area is 20m, then when determining the pile length distribution in the transition zone, based on the slope ratio of 1:2, the pile length at the outer edge of the transition zone is reduced by 6 × 1 / 2 = 3m compared to the pile length in the core sensitive area, that is, gradually changing from 20m to 20m-3m. Therefore, the pile length distribution in the transition zone is 20m, 20m-0.5m, 20m-1m, 20m-1.5m, 20m-2m, 20m-2.5m, and 20m-3m; the pile length difference between adjacent control sections is 0.5m, which meets the requirement of the second pile length control principle that the pile length difference between adjacent control sections should not exceed 3m. It should be noted that if the pile length difference calculated in the aforementioned manner exceeds the preset difference threshold, the preset difference threshold will be used as the pile length gradient to determine the pile length distribution.

[0037] Step 105: Based on the geometric and spatial location data of the area to be designed, the regional division results, and the pile parameters of the transition zone and the core sensitive zone, establish a first three-dimensional numerical calculation model and perform ground stress balance on the first three-dimensional numerical calculation model; multiple first monitoring points are set on the underpass tunnel in the first three-dimensional numerical calculation model.

[0038] Specifically, Figure 3 This is a schematic diagram of the structure of the first three-dimensional numerical calculation model provided in an embodiment of the present invention. Figure 3 As shown, the underpass is a group of tunnels located in the tunnel area. The area above the tunnel area is divided into a core sensitive zone, a transition zone, and an outer zone. Figure 3 (The outer area is not marked in the text). The division principle is the same as above, except that the dividing line is changed to the boundary line of the tunnel area, and the span of the underpass is taken as the largest underpass span in the tunnel group. The top of the transition zone and the outer area will be subject to surcharge preloading; therefore, the top of the transition zone and the outer area is called the surcharge preloading zone.

[0039] Step 106: Apply surcharge preload to the top of the transition zone and outer zone of the first three-dimensional numerical calculation model, and obtain the first structural mechanical response data at each first monitoring point.

[0040] like Figure 2 As shown, the slope ratio of the surcharge preload in the transition zone is the aforementioned preset slope ratio, and the value range of the slope ratio is 1:1.5 to 1:2.0.

[0041] The first structural mechanical response data includes at least the additional stress increment of the tunnel lining outer wall, the tunnel's horizontal displacement, vertical displacement, and radial displacement. When the underpass tunnel is a shield tunnel, the first structural mechanical response data also includes the shield segment joint opening and the shield segment crack width. It is understood that the first structural mechanical response data is time-series data.

[0042] Secondly, the surcharge preloading load is a preset value, calculated back from theoretical calculations. Specifically, the determination of the surcharge preloading load aims at controlling post-construction settlement. First, the allowable post-construction settlement is determined according to specifications (e.g., 0.2 to 0.3m for runways, 0.3 to 0.4m for taxiways and aprons). Then, based on geological survey data (soil layer thickness and compression modulus), the total settlement of the foundation under a given load is estimated. And predict the degree of consolidation U(t) that can be achieved within the preloading time t; and then use the relationship = ×[1 Calculate the post-construction settlement using U(t)], and use it as... ≤[ Using [condition] as the criterion, the minimum surcharge preload that can meet the post-construction settlement requirements is determined through trial calculation and iteration. This load is the surcharge preload value required by the design.

[0043] Step 107: Based on the preset safety standards and the first structural mechanical response data, determine whether the underpass is safe and obtain the first judgment result.

[0044] Specifically, safety standards include: The peak values ​​of horizontal displacement, vertical displacement, and radial displacement of the underpass are all less than the preset displacement thresholds; and the peak value of the additional stress increment on the outer wall of the underpass lining is less than or equal to the preset stress increment threshold.

[0045] When the underpass tunnel is a shield tunnel, the safety standards also include: The peak value of the joint opening of the shield tunnel segments in the underpass is less than the preset opening threshold; and the peak value of the crack width of the shield tunnel segments in the underpass is less than the preset width threshold.

[0046] In a specific example, the preset safety standards include: the peak value of the additional stress increment on the outer wall of the tunnel lining is less than or equal to 20 kPa; the peak values ​​of the tunnel's horizontal displacement, vertical displacement, and radial displacement are all less than 15 mm; the peak value of the shield segment joint opening is less than 2 mm; and the peak value of the shield segment crack width is less than 0.2 mm.

[0047] If all parameters in the first structural mechanical response data meet the relevant requirements of the preset safety standards, the underpass is determined to be safe; otherwise, the underpass is determined to be unsafe.

[0048] Step 108: If the first judgment result is yes, output the design scheme; the design scheme includes the regional division result, as well as the pile parameters of the transition zone and the core sensitive zone.

[0049] This invention employs the above technical solution. When the foundation settlement meets the standards, but the underpass tunnel structure is unsafe, it determines that a combined design scheme of surcharge preloading and composite foundation is necessary. The foundation of the area to be designed is then divided into a core sensitive zone, a transition zone, and an outer zone. Both the core sensitive zone and the transition zone are treated with composite foundations. Furthermore, the pile spacing and pile length in the transition zone are designed with gradual changes, while the remaining pile parameters are the same as in the core sensitive zone. This allows the invention to reduce the number of piles required, and the transition zone provides a gradual change in stiffness and a smooth stress transition, avoiding the abrupt change in reinforcement from a densely piled arrangement in the core sensitive zone to a pileless arrangement in the outer zone. The invention, through its arrangement, ensures the structural safety of underpass tunnels while maintaining economic efficiency. Furthermore, based on the geometric and spatial location data of the area to be designed, the regional division results, and the pile parameters of the transition zone and core sensitive area, a first three-dimensional numerical calculation model is established. A surcharge preloading load is applied to the top of the transition zone and the outer perimeter of the first three-dimensional numerical calculation model, and the first structural mechanical response data at each first monitoring point of the underpass tunnel are obtained. Based on preset safety standards and the first structural mechanical response data, when the underpass tunnel is deemed safe, a design scheme is output, further ensuring the structural safety of the underpass tunnel. Therefore, the invention can simultaneously ensure that foundation settlement meets standards and the structural safety of the underpass tunnel while maintaining economic efficiency when performing surcharge preloading treatment above an airport flight area underpass tunnel.

[0050] In this embodiment of the invention, the method for coordinated design of surcharge preloading above the underpass tunnel and composite foundation may further include: (1) When the first judgment result is negative, under the premise of ensuring that the bearing capacity of the composite foundation of the core sensitive area and the transition area meets the preset bearing capacity requirements, in the first three-dimensional numerical calculation model, at least one of the pile parameters of the pile diameter, pile spacing and pile length of the core sensitive area and the transition area is adjusted.

[0051] (2) Reapply surcharge preload to the transition zone and outer zone of the first three-dimensional numerical calculation model, and reacquire the first structural mechanical response data at each first monitoring point.

[0052] (3) Based on the preset safety standards, determine whether the underpass is safe according to the current first structural mechanical response data, and obtain the current first judgment result.

[0053] If the first judgment result is yes, output the design scheme.

[0054] If the current first judgment result is negative, then, under the premise of ensuring that the bearing capacity of the composite foundation in the core sensitive area and the transition area meets the preset bearing capacity requirements, the step of adjusting at least one of the pile parameters in the core sensitive area and the transition area in the first three-dimensional numerical calculation model is performed to iteratively optimize the relevant pile parameters until the design scheme is output.

[0055] In this embodiment of the invention, before dividing the foundation of the area to be designed into a core sensitive area, a transition area, and a peripheral area, and obtaining the area division result, the method for coordinated design of surcharge preloading and composite foundation above the underpass tunnel of the present invention may further include: (1) Based on the geometric and spatial location data of the area to be designed, a second three-dimensional numerical calculation model is established, and the ground stress balance is performed on the second three-dimensional numerical calculation model; each first monitoring point is set on the underpass in the second three-dimensional numerical calculation model.

[0056] Specifically, the geometric and spatial location data includes the structural dimensions of the tunnel lining structure and the pavement structure, as well as the relationship between the tunnel structure and its spatial location. Figure 4 This is a schematic diagram of the structure of the second three-dimensional numerical calculation model provided in an embodiment of the present invention. Figure 4 As shown, the second three-dimensional numerical calculation model includes a group of tunnels located in the tunnel region and roadbeds of different geological types. The model's mesh can be a hexahedral structured mesh.

[0057] It should be noted that both the first and second three-dimensional numerical calculation models use the tunnel direction as the y-axis, the roadbed vertical direction as the z-axis, and the direction perpendicular to the plane containing the y-axis and z-axis as the x-axis (this invention only applies to...). Figure 4 The x-axis, y-axis, and z-axis are shown in the diagram. When establishing the first and second three-dimensional numerical calculation models, this invention considers the boundary effects of Saint-Venant's principle and can utilize software such as FLAC3D and PLAXIS. In the second three-dimensional numerical calculation model, the contact relationships between each structural layer are accurately set, such as between the roadbed and the roadbed, between the surrounding rock and the secondary lining, and between the secondary lining and the initial support, clearly defining their normal contact stiffness and tangential friction coefficient. Regarding boundary conditions, the top of the model is set as a free boundary, the bottom as a completely fixed constraint, and normal displacement constraints are applied to the remaining sides. After initially establishing the three-dimensional numerical calculation model, parameter attributes are set. Specifically, these attributes are set based on the obtained physical and mechanical parameters of the roadbed and surrounding rock, the physical and mechanical parameters of the surcharge preloaded soil, and the physical and mechanical parameters of the tunnel lining structure. The physical and mechanical parameters of the roadbed and surrounding rock include the elastic modulus, compression modulus, unit weight, cohesion, internal friction angle, and Poisson's ratio for each layer of roadbed and surrounding rock. The physical and mechanical parameters of the surcharge preloaded soil include the unit weight and elastic modulus of the surcharge preloaded soil. The physical and mechanical parameters of tunnel lining structures include elastic modulus, Poisson's ratio, and specific gravity.

[0058] After setting the parameter properties, perform geostress balancing. The purpose of geostress balancing is to eliminate the initial displacement and internal forces caused by self-weight. After geostress balancing, the maximum soil displacement is controlled within 1×10⁻⁶. -5 Within a range of m, the model exhibits no significant initial deformation, and the stress field conforms to the in-situ stress state, ensuring the accuracy and reliability of subsequent calculations for surcharge preloading, composite foundations, and tunnel structure response. Generally, a single stress balancing operation is insufficient; multiple stress balancing operations can be performed.

[0059] Underpass tunnels can be single tunnels or tunnel groups. Tunnel types can include shield tunnels for rail transit, horseshoe-shaped high-speed rail tunnels, or heavy-haul railway tunnels.

[0060] (2) Apply surcharge preload to the top designated area of ​​the second three-dimensional numerical calculation model and obtain the second structural mechanical response data at each first monitoring point.

[0061] Specifically, the designated area at the top is specified by the technical personnel. The second three-dimensional numerical calculation model is a three-dimensional refined finite element numerical calculation model. In the finite element analysis, the surcharge preload is simulated using a uniformly distributed load.

[0062] (3) Based on safety standards, the safety of the underpass tunnel is determined according to the second structural mechanical response data, and the second judgment result is obtained.

[0063] (4) Based on the preset finite element model, determine the first void ratio and the second void ratio of the roadbed soil that needs to be preloaded in the design area at the set time. Based on the first void ratio, the second void ratio and the initial void ratio of the roadbed soil, calculate the degree of consolidation of the roadbed soil at the set time. The set time is the end time of the preload.

[0064] Specifically, the preset finite element model is based on existing technology and can be a finite element model for surcharge preloading of soft soil foundations based on Biot's consolidation theory and using the MCC (Modified Cam-Clay model) as the soil constitutive model. For example, the preset finite element model can be Abaqus.

[0065] First porosity Second porosity and initial porosity The process of determining the value includes: taking in-situ samples of the roadbed soil, and determining the initial void ratio of the roadbed soil before consolidation based on laboratory tests. Then, based on the preset finite element model, the first void ratio of the roadbed soil requiring surcharge preloading treatment in the design area is determined at a set time. And the second porosity when the porosity is stable It should be noted that the method for determining that the porosity has reached a stable state is as follows: before the calculation, a clear stability criterion is set in the incremental options of the analysis step in the software (preset finite element model), and the function switch of "automatically detect steady state and end" is turned on; the specific steady state parameter is as follows: pore water pressure change rate ≤ 0.1 kPa / s, which means that when the change in pore water pressure per second at all nodes in the model is less than this value, the preset finite element model considers that the subgrade soil has reached a steady state and will automatically terminate the calculation of the current analysis step.

[0066] The formula for calculating the degree of consolidation U(t) of the subgrade soil at a given time is as follows: ......(7) (5) Calculate the total settlement of the roadbed soil based on the additional stress increment generated by the surcharge preload at each layer of the roadbed soil, the thickness of each layer of the roadbed soil and the compression modulus.

[0067] Specifically, the formula for calculating the total settlement s of the roadbed soil is as follows: ......(8) In the formula, For the surcharge preload in the first The additional stress increment generated at the foundation soil point of the layer; For the first The thickness of the foundation soil in the tiered channel; For the first The compression modulus of the foundation soil. It should be noted that... The relationship with the surcharge preload p is as follows: =f(p), that is, the surcharge preload p is generated The fundamental reason is that in the foundation, p changes with depth and location, and through the stress diffusion principle in soil mechanics (such as the Boussinesq solution), it is transformed into stress at different soil depths. .

[0068] (6) Calculate the post-construction settlement of the roadbed soil within a set time period based on the degree of consolidation and the total settlement. The set time period starts from a set time and the duration of the set time period is set by the technical personnel, such as a set time period of two years.

[0069] Specifically, post-construction settlement This refers to the settlement that continues to occur after the completion of the project. The calculation formula is as follows: ......(9) (7) Subtract post-construction settlement from total settlement to obtain target difference value. Determine whether target difference value meets preset difference value requirements and obtain third judgment result.

[0070] In a specific example, for a runway post-construction settlement scenario, the preset difference requirement can be a target difference within the range of 0.2m to 0.3m; for a taxiway and apron post-construction settlement scenario, the preset difference requirement can be a target difference within the range of 0.3m to 0.4m.

[0071] (8) When both the second and third judgment results are yes, it is determined that the scheme of using only surcharge preloading is feasible.

[0072] If the second judgment result is negative and the third judgment result is positive, it is determined that a combined design scheme of surcharge preloading and composite foundation is required.

[0073] This invention establishes a three-dimensional numerical calculation model, applies a surcharge preload to the model, and analyzes the displacement and additional stress of the tunnel structure. Building upon traditional displacement control, it innovatively uses "the peak value of the additional stress increment on the outer wall of the tunnel lining being less than or equal to 20 kPa" as the core control indicator. It constructs a dual-control judgment system of "safety control value (displacement + stress) + post-construction settlement," accurately identifying and solving the problem of "excessive additional stress in the tunnel," a problem most easily overlooked in conventional design. This fundamentally avoids the problem of "displacement safety but structural damage." Simultaneously, by maintaining a safe distance (≥3 to 5 m) between the core area pile bottom and the tunnel roof, it avoids the risk of pile tip puncture, ensuring the dual safety of the lower tunnel structure during both construction and operation.

[0074] In practical applications, if a combined design scheme of surcharge preloading and composite foundation is adopted, subsequent on-site testing of the composite foundation in the airport flight area should only be carried out after the pile construction is completed and the pile curing age meets the requirements. Specifically, the curing age for cement-soil mixing piles and CFG piles should not be less than 28 days; the curing age for lime-soil compaction piles and soil compaction piles should not be less than 14 days. See Table 1 for detailed composite foundation quality inspection standards.

[0075] Table 1 Quality Inspection Standards for Composite Foundations

[0076] It should be noted that the pile length, pile diameter, and mixing blade rotation diameter in Table 1 can be obtained through basic measurements; while the average compaction coefficient of the pile fill and the pile strength can also be obtained through basic indoor physical and mechanical tests.

[0077] During project acceptance, the bearing capacity of the composite foundation is verified by static load testing. The maximum load should not be less than twice the characteristic value of the design bearing capacity. The static load test is conducted at the design elevation of the pile top, with a 100mm–150mm coarse or medium sand cushion layer laid under the bearing plate. The test pit size should be no less than three times the width of the bearing plate, and the clear distance between the support point of the reference beam and the bearing plate should be no less than 2m. The number of test points should be no less than three. If the range is ≤30% of the average value, the average value is taken as the characteristic value of the bearing capacity; otherwise, the number of tests should be increased and determined comprehensively based on the actual project conditions.

[0078] The characteristic value of the bearing capacity of composite foundations is taken from the flat section of the pressure-settlement curve: for lime-soil compaction pile / soil compaction pile composite foundations, the load corresponding to s / b = 0.008 is taken; for CFG pile composite foundations, the load corresponding to s / b is 0.008 for coarse-grained soil foundations and s / b is 0.01 for cohesive soil / silt foundations; for cement-soil mixing pile composite foundations, the load corresponding to s / b is 0.006 to 0.008, and the higher value is taken when the pile strength is ≥1.0MPa and uniform. It should be noted that the characteristic value of bearing capacity determined by relative deformation should not be greater than 1 / 2 of the maximum loading pressure, and when the side length or diameter of the bearing plate is greater than 2m, it is calculated as 2m.

[0079] For the verification of the bearing capacity of the composite foundation, when the average compaction coefficient of the pile filling is obtained by construction monitoring, the bearing capacity of the designed composite foundation can also be verified by formula (10). When the composite foundation is a lime-soil compaction pile or a soil compaction pile, and the pile layout is an equilateral triangle pile (circular pile) or a square pile (circular pile), and the maximum dry density of the soil between the piles and the average dry density of the roadbed soil have been determined in the laboratory, the replacement rate after construction can be calculated in reverse, as shown in formula (10). By using formula (1) and formula (10), it can be verified whether the composite foundation of the lime-soil compaction pile or the soil compaction pile in Table 1 meets the design requirements.

[0080] ......(10) In the formula, This is the soil compaction coefficient between piles; This represents the maximum dry density of the soil between the piles. This represents the average dry density of the roadbed soil.

[0081] The vertical bearing capacity of a single pile is also tested using static load tests. Anchor piles or surcharge methods are used to provide the reaction force. The compressive stress at the surcharge support should not exceed the characteristic value of the foundation bearing capacity. When the surcharge requirements are met, engineering piles can be used as supports. The ultimate vertical bearing capacity of a single pile is determined according to the following principles: When the load-settlement curve shows a steep drop and the pile top settlement is >40mm, the load corresponding to the starting point of the steep drop is taken; when the settlement under the current load is ≥2 times the settlement of the previous level and has not stabilized within 24 hours, the previous level load is taken; when the pile length is >25m and the curve is gradually changing, and the settlement is >60mm~80mm, the load corresponding to a settlement of 40mm is taken.

[0082] The low-strain reflected wave method was used to detect the integrity of the pile body. Low-energy excitation was applied to the pile top using a hammer, force bar, or vibrator. Velocity time-domain waveforms were collected at the pile top, and the degree and location of pile defects were determined based on the waveform characteristics. The average wave velocity and defect location were calculated according to formulas (11) to (12). The pile quality was determined based on the pile integrity coefficient. Judgment (see Equation 13): Class I pile body intact ( Class II piles Although there are minor defects, they do not affect the normal performance of the pile structure's bearing capacity and can all meet the usage requirements; Class IV piles ( The piles of Class III have serious defects and are directly deemed unqualified and should be scrapped; The defects are obvious and affect the bearing capacity of the pile structure. Therefore, it is necessary to conduct on-site process verification and cause investigation, optimize the construction process, and then conduct on-site tests again.

[0083] ... (11) ......(12) , ......(13) In the formula, This represents the average wave velocity of the pile body; The length of the pile at the measuring point; The time difference (ms) is between the first peak of the velocity wave and the peak of the reflected wave at the bottom of the column. The distance from the pile defect to the sensor installation point; The time difference (ms) between the first peak of the velocity wave and the peak of the defect reflection wave. This is the pile integrity coefficient, also known as the wave impedance ratio at the defect point; The amplitude of the velocity signal of the incident wave; The amplitude of the velocity signal of the defect-reflected wave; The reflection coefficient; The wave impedance of the pile body above the defect; The wave impedance of the pile body below the defect is given.

[0084] This invention verifies the rationality and reliability of the aforementioned design scheme by analyzing and judging the results of on-site composite foundation tests.

[0085] Based on a general inventive concept, the present invention also provides a system for the coordinated design of surcharge preloading and composite foundation above an underpass tunnel, which is applied to the method for the coordinated design of surcharge preloading and composite foundation above an underpass tunnel as described above. Figure 5 This is a structural schematic diagram of a collaborative design system for surcharge preloading and composite foundation above an underpass tunnel, provided by an embodiment of the present invention. Figure 5 As shown, this system includes: The partitioning module 51 is used to divide the foundation of the area to be designed into a core sensitive area, a transition area, and an outer area when it is determined that a combined design scheme of surcharge preloading and composite foundation is required, and to obtain the area partitioning result. The core sensitive area is located directly above the underpass tunnel in the area to be designed, and the transition area is located between the core sensitive area and the outer area. Both the core sensitive area and the transition area are treated with composite foundation.

[0086] The first determining module 52 is used to determine the pile type to be used in the core sensitive area and the transition area based on the stratigraphic type of the core sensitive area and the transition area.

[0087] The second determining module 53 is used to determine the pile diameter, pile spacing and pile length of the core sensitive area based on the preset pile shape and pile layout, with the aim of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements.

[0088] The third determining module 54 is used to determine the pile length distribution of the transition zone based on the preset slope ratio, the width of the transition zone, and the pile length of the core sensitive zone. The pile length of the transition zone adopts a gradual design, and the other pile parameters are the same as those of the core sensitive zone.

[0089] Module 55 is established to build a first three-dimensional numerical calculation model based on the geometric and spatial location data of the area to be designed, the regional division results, and the pile parameters of the transition zone and the core sensitive zone, and to perform ground stress balance on the first three-dimensional numerical calculation model; multiple first monitoring points are set on the underpass tunnel in the first three-dimensional numerical calculation model.

[0090] The monitoring module 56 is used to apply a preload load to the top of the transition zone and the outer zone of the first three-dimensional numerical calculation model, and to acquire the first structural mechanical response data at each first monitoring point.

[0091] The judgment module 57 is used to determine whether the underpass is safe based on the preset safety standards and the first structural mechanical response data, and to obtain the first judgment result.

[0092] Output module 58 is used to output a design scheme when the first judgment result is yes; the design scheme includes the regional division result, as well as the pile parameters of the transition zone and the core sensitive zone.

[0093] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0094] It should be noted that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means at least two.

[0095] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0096] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0097] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0098] Furthermore, the functional units in the various embodiments of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0099] The storage media mentioned above can be read-only memory, disk, or optical disk, etc.

[0100] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0101] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for collaborative design of preloading above a tunnel and composite foundation, characterized in that, include: When it is determined that a combined design scheme of surcharge preloading and composite foundation is required, the foundation of the area to be designed is divided into a core sensitive area, a transition area, and an outer area, resulting in a regional division. The core sensitive area is located directly above the underpass tunnel in the area to be designed, and the transition area is located between the core sensitive area and the outer area. Both the core sensitive area and the transition area are treated with composite foundation. Based on the geological type of the core sensitive area and the transition area, determine the pile type to be used in the core sensitive area and the transition area; Based on the preset pile shape and pile arrangement, with the aim of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements, the pile diameter, pile spacing and pile length of the core sensitive area are determined; Based on the preset slope ratio, the pile length distribution of the transition zone is determined according to the width of the transition zone and the pile length of the core sensitive zone. The pile length of the transition zone adopts a gradual design, and the other pile parameters are the same as those of the core sensitive zone. Based on the geometric and spatial location data of the area to be designed, the area division results, and the pile parameters of the transition zone and the core sensitive zone, a first three-dimensional numerical calculation model is established, and the ground stress balance is performed on the first three-dimensional numerical calculation model; multiple first monitoring points are set on the underpass tunnel in the first three-dimensional numerical calculation model; An overload preload is applied to the top of the transition zone and the outer zone of the first three-dimensional numerical calculation model, and the first structural mechanical response data at each of the first monitoring points are obtained. Based on the preset safety standards and according to the first structural mechanical response data, it is determined whether the underpass is safe, and a first judgment result is obtained; When the first judgment result is yes, the design scheme is output; the design scheme includes the region division result, as well as the pile parameters of the transition zone and the core sensitive zone.

2. The method according to claim 1, wherein, Also includes: When the first judgment result is negative, under the premise of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements, at least one pile parameter among the pile diameter, pile spacing and pile length of the core sensitive area and the transition area is adjusted in the first three-dimensional numerical calculation model. Reapply surcharge preload to the transition zone and the outer zone of the first three-dimensional numerical calculation model, and reacquire the first structural mechanical response data at each of the first monitoring points; Based on the preset safety standards and the current first structural mechanical response data, it is determined whether the underpass is safe, and the current first judgment result is obtained; If the first judgment result is yes, output the design scheme; If the current first judgment result is negative, the following step is performed: under the premise that the bearing capacity of the composite foundation of the core sensitive area and the transition area meets the preset bearing capacity requirements, in the first three-dimensional numerical calculation model, at least one of the pile parameters of the pile diameter, pile spacing and pile length of the core sensitive area and the transition area is adjusted to iteratively optimize the relevant pile parameters until the design scheme is output.

3. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to claim 1, characterized in that, Before dividing the foundation of the area to be designed into a core sensitive zone, a transition zone, and a peripheral zone, and obtaining the zone division results, the following steps are also included: Based on the geometric and spatial location data of the area to be designed, a second three-dimensional numerical calculation model is established, and the ground stress balance is performed on the second three-dimensional numerical calculation model; each of the first monitoring points is set on the underpass in the second three-dimensional numerical calculation model; The surcharge preload is applied to a designated area at the top of the second three-dimensional numerical calculation model, and the second structural mechanical response data at each of the first monitoring points are obtained. Based on the aforementioned safety standards and according to the second structural mechanical response data, it is determined whether the underpass is safe, and a second determination result is obtained. Based on a preset finite element model, the first void ratio and the second void ratio of the roadbed soil requiring surcharge preloading treatment in the design area are determined at a set time. Based on the first void ratio, the second void ratio, and the initial void ratio of the roadbed soil, the degree of consolidation of the roadbed soil at the set time is calculated. The set time is the end time of surcharge preloading. Based on the additional stress increment generated by the surcharge preload at each layer of the subgrade soil, the thickness of each layer of the subgrade soil and the compression modulus, the total settlement of the subgrade soil is calculated. Based on the degree of consolidation and the total settlement, the post-construction settlement of the roadbed soil is calculated within a set time period; the set time period starts from the set time. Subtract the post-construction settlement from the total settlement to obtain the target difference. Determine whether the target difference meets the preset difference requirement to obtain a third judgment result. When both the second and third judgment results are yes, it is determined that the scheme of using only surcharge preloading is feasible; If the second judgment result is negative and the third judgment result is positive, it is determined that a combined design scheme of surcharge preloading and composite foundation is required.

4. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to any one of claims 1 to 3, characterized in that, The safety standards include: The peak values ​​of horizontal displacement, vertical displacement, and radial displacement of the underpass are all less than preset displacement thresholds; and the peak value of the additional stress increment on the outer wall of the underpass lining is less than or equal to the preset stress increment threshold.

5. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to claim 4, characterized in that, When the underpass tunnel is a shield tunnel, the safety standards also include: The peak value of the joint opening of the shield tunnel segments in the underpass is less than a preset opening threshold; and the peak value of the crack width of the shield tunnel segments in the underpass is less than a preset width threshold.

6. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to claim 1, characterized in that, The core sensitive area is enclosed by a first boundary obtained by extending the outer edge of the underpass tunnel to both sides of the underpass tunnel by a first preset multiple of the underpass tunnel span, and the distance extended to both sides of the underpass tunnel from the outer edge of the underpass tunnel is not less than the first preset distance. The transition zone is enclosed by the first boundary and a second boundary obtained by extending outward from the first boundary by a second preset multiple of the underpass span, or the transition zone is enclosed by the first boundary and a second boundary obtained by extending outward from the first boundary by a second preset distance.

7. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to claim 6, characterized in that, The value of the first preset multiple ranges from 1 to 1.5; The first preset distance ranges from 8m to 12m; The value range of the second preset multiple is 0.5 to 1; The second preset distance ranges from 6m to 10m.

8. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to claim 1, characterized in that, The underpass can be a single tunnel or a group of tunnels.

9. The method for coordinated design of surcharge preloading and composite foundation above an underpass tunnel according to claim 1, characterized in that, The pile length in the core sensitive area meets the first pile length control principle, which includes that the pile bottom does not contact the arch of the underpass tunnel, and the distance between the pile bottom and the arch of the underpass tunnel is not less than a preset safety distance. The pile length in the transition zone meets the second pile length control principle, which includes that the difference in pile length between adjacent control sections does not exceed a preset difference threshold.

10. A collaborative design system for surcharge preloading and composite foundation above an underpass tunnel, characterized in that, include: The partitioning module is used to divide the foundation of the area to be designed into a core sensitive zone, a transition zone, and an outer zone when it is determined that a combined design scheme of surcharge preloading and composite foundation is required, thus obtaining the area partitioning result; the core sensitive zone is located directly above the underpass tunnel in the area to be designed, and the transition zone is located between the core sensitive zone and the outer zone; both the core sensitive zone and the transition zone are treated with composite foundation; The first determining module is used to determine the pile type to be used in the core sensitive area and the transition area based on the geological type of the core sensitive area and the transition area; The second determining module is used to determine the pile diameter, pile spacing, and pile length of the core sensitive area based on the preset pile shape and pile layout, with the aim of ensuring that the composite foundation bearing capacity of the core sensitive area and the transition area meets the preset bearing capacity requirements. The third determining module is used to determine the pile length distribution of the transition zone based on the preset slope ratio, the width of the transition zone, and the pile length of the core sensitive zone. The pile length of the transition zone adopts a gradual design, and the other pile parameters are the same as those of the core sensitive zone. A module is established to build a first three-dimensional numerical calculation model based on the geometric and spatial location data of the area to be designed, the area division results, and the pile parameters of the transition zone and the core sensitive zone, and to perform ground stress balance on the first three-dimensional numerical calculation model; multiple first monitoring points are set on the underpass tunnel in the first three-dimensional numerical calculation model; The monitoring module is used to apply a surcharge preload to the top of the transition zone and the outer zone of the first three-dimensional numerical calculation model, and to acquire the first structural mechanical response data at each of the first monitoring points. The judgment module is used to determine whether the underpass is safe based on a preset safety standard and the first structural mechanical response data, and to obtain a first judgment result; The output module is used to output a design scheme when the first judgment result is yes; the design scheme includes the region division result, and the pile parameters of the transition zone and the core sensitive zone.

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