Simplified calculation method for long-term operation settlement of underground box type structure

Abstract

The invention discloses a simplified calculation method for long-term operation settlement of an underground box type structure. The simplified calculation method comprises the steps that firstly, a calculation model is established according to geological and design data, and long-term cyclic load parameters are determined; then respectively calculating the settlement caused by the initial static load and the additional settlement obtained by equivalently calculating the cyclic load effect by introducing a cumulative plastic strain and cumulative pore water pressure model; and finally, synthesizing the total settlement amount to evaluate overall and differential settlement under long-term operation. According to the method, simplicity and convenience of a layered summation method and a clear physical mechanism of a cyclic accumulation model are fused, a unified analysis framework suitable for the presence or absence of a pile foundation is constructed, dynamic prediction of whole-life-cycle settlement of the structure is achieved, optimal design of a foundation scheme can be directly guided, and the method is suitable for large-scale popularization and application. And the reliability of long-term settlement prediction and the efficiency of engineering design are remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geotechnical engineering and underground structure design, and particularly relates to a simplified calculation method for long-term operation settlement of an underground box structure. BACKGROUND

[0002] With the acceleration of current urban renewal process, underground sewage treatment plants are widely used for the purpose of saving land space and improving ecological environment. During the long-term operation of the box structure of the underground sewage treatment plant, the periodic fluctuation of the internal water level and the vibration generated by the equipment operation continuously act on the foundation, resulting in significant cumulative plastic deformation and pore water pressure of the foundation soil, especially saturated soft clay. This long-term settlement caused by cyclic effect is often the main reason for the cracking of the structure connection, the failure of waterproofing and the operation obstacle of the equipment.

[0003] At present, the settlement calculation of such structures in engineering practice mostly follows the traditional layer-wise summation method or finite element static analysis. These methods have obvious limitations: first, the cumulative effect of long-term cyclic load is not fully considered, and the weakening of soil stiffness and the continuous development of plastic strain cannot be truly reflected; second, there is a lack of unified analysis framework for pile foundation and non-pile foundation, and existing methods often separate the two, making it difficult to effectively compare the technical and economic options at the design stage; in addition, although complex dynamic consolidation finite element analysis can partially simulate this process, it has problems such as complex modeling, high calculation cost and difficulty in obtaining parameters, which is not suitable for rapid iteration of multiple schemes in the design stage. Therefore, there is an urgent need for a settlement prediction method that can accurately reflect the long-term deformation mechanism of soil under cyclic load, while considering the efficiency of engineering design, and is suitable for different foundation forms. SUMMARY

[0004] To solve the above technical problems, the application provides a simplified calculation method for long-term operation settlement of an underground box structure to solve the problems existing in the prior art.

[0005] To achieve the above purpose, the application provides a simplified calculation method for long-term operation settlement of an underground box structure, comprising: constructing a calculation model according to geological survey data and structural design drawings, and dividing the foundation soil in the compression layer range below the base in the model into a plurality of horizontal soil layers; simplifying the operation period cyclic load into an equal amplitude load with a specific amplitude and total cycle number; calculating the initial static settlement based on the soil layer parameters and static load distribution in the calculation model; calculating the cumulative plastic strain and cumulative pore water pressure generated by the foundation soil based on the equal amplitude load; and calculating the cyclic additional settlement based on the cumulative plastic strain and cumulative pore water pressure; A total long-term settlement amount is obtained based on the cyclic additional settlement and the initial static settlement.

[0006] Optionally, a mode of settlement calculation is determined according to the planar size, buried depth and geological conditions of the box-type structure; the basis for dividing the foundation soil body into a plurality of horizontal soil layers is the soil layer distribution, physical and mechanical indexes and underground water level conditions in the geological survey report; wherein the mode of settlement calculation is to calculate the settlement of the entire box as a whole or to divide the box into a plurality of sections for separate calculation.

[0007] Optionally, based on the operation characteristics of the water storage system of the underground sewage treatment plant, the typical period and amplitude of water level fluctuation are determined, and the cyclic pressure amplitude generated by the water level fluctuation on the bottom plate of the box is calculated.

[0008] Optionally, when calculating the initial static settlement, if there is no pile foundation, the layered summation method is used for calculation; if there is a pile foundation, the Mindlin-Gerts method is used for calculation.

[0009] Optionally, the following model is used to calculate the cumulative plastic strain: ; wherein, , , is a soil cyclic cumulative strain parameter, which is determined through indoor dynamic triaxial test; is the initial effective overburden pressure of the soil layer, N is the number of cycles, is the amplitude of the equal-amplitude load.

[0010] Optionally, when calculating the cumulative pore water pressure based on the equal-amplitude load and the cumulative plastic strain, the following model is used: ; wherein, f is a pore pressure saturation value coefficient, 0

[0011] Optionally, the process of calculating the cyclic additional settlement based on the cumulative plastic strain and the cumulative pore water pressure comprises: calculating the direct plastic strain settlement according to the cumulative plastic strain; calculating the settlement caused by the dissipation of the cumulative pore water pressure according to the cumulative pore water pressure; if the box-type structure does not have a pile foundation, summing the direct plastic strain settlement and the settlement caused by the dissipation of the cumulative pore water pressure to obtain the cyclic additional settlement; if the box-type structure has a pile foundation, the pile shaft compression amount also needs to be calculated, summed with the direct plastic strain settlement and the settlement caused by the dissipation of the cumulative pore water pressure to obtain the cyclic additional settlement.

[0012] Optionally, the pile shaft compression amount is calculated based on the cyclic load at the top of the pile, the length of the pile, the cross-sectional area of the pile shaft and the elastic modulus of the pile shaft material, and the calculation formula is: ; wherein, is the cyclic load on the pile top, is the length of the pile, is the cross-sectional area of the pile body, is the elastic modulus of the pile body, the cyclic load on the pile top Based on the amplitude of the equal-amplitude load, the area of the box bottom plate, and the number and arrangement form of the pile foundation, the total long-term settlement is determined by the mechanical distribution principle.

[0013] Optionally, the difference settlement is evaluated based on the total long-term settlement, and the box structure design is optimized according to the settlement evaluation result.

[0014] Compared with the prior art, the present application has the following advantages and technical effects: (1) Mechanism and practicality: the present application innovatively combines the empirical model describing the cyclic weakening of soil with the classical soil mechanics theory, and grasps the nature of long-term settlement from the physical mechanism, while ensuring the engineering practicability of the method.

[0015] (2) Unified analysis framework: for the first time, a long-term settlement calculation process suitable for both pile foundation and non-pile foundation is provided, which provides a standardized tool for rapid comparison and selection in the initial selection stage of the scheme.

[0016] (3) Whole-process dynamic prediction: by introducing the number of cycles , the dynamic simulation of the settlement development process of the structure during the entire operation period is realized, which can provide key time nodes for the preventive maintenance of the structure.

[0017] (4) Strong guidance: the method finally closes the loop with design optimization, which can directly guide the selection of foundation type and reinforcement measures, and significantly improves the reliability and economy of the design scheme. DETAILED DESCRIPTION

[0018] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of this application and their description are used to explain the application and are not intended to limit the application. In the drawings: Figure 1 is the method flowchart of the embodiment of the present application; Figure 2 is a schematic diagram of a non-pile foundation box-type water storage system model of the embodiment of the present application; Figure 3 is a schematic diagram of the distribution of each soil layer of the embodiment of the present application; Figure 4 is a schematic diagram of the periodic fluctuation of the water level in the pool during the operation period of the embodiment of the present application; Figure 5 is a comparison diagram of the total long-term settlement development curves under the conditions of with and without pile foundation; The components include: 1. Overlying soil layer; 2. Upper layer of underground box; 3. Pretreatment area; 4. Biochemical treatment area; 5. Deep treatment area; 6. Auxiliary functional area; 7. Inlet pipe; 8. Grille unit; 9. Outlet unit; 10. Auxiliary unit; 11. Inspection and coordination unit; 12. Pile foundation. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a simplified calculation method for the long-term operational settlement of an underground box-type structure, including: Step 1: Determine the calculation model, foundation stratification, and long-term cyclic loads; Based on the geological survey report and structural design drawings, a calculation model is established that includes the box-type structure, foundation soil, and pile foundations (if any). The foundation soil within the compressible layer below the foundation is divided into several horizontal soil layers. The main cyclic loads during the operation period (such as periodic fluctuations in the pool water level) are analyzed and simplified to have specific amplitudes. Total number of loops Equal amplitude load. Figure 2 A typical model of a pile-foundation box-type water storage system is presented. The structural components of the computational model consist of the overlying soil layer 1, the upper underground box layer 2, and internal functional zones (such as the pretreatment zone 3, biochemical treatment zone 4, deep treatment zone 5, and auxiliary functional zone 6). The inlet pipe 7, grid unit 8, outlet unit 9, auxiliary unit 10, and drainage coordination unit 11 reflect the operational components of the box. The distribution and loads of these components affect the stress distribution of the foundation soil. When calculating the initial static settlement, the static loads (such as the structural self-weight and water weight) in these areas must be considered and transferred to the foundation soil layer through the box bottom plate to determine the additional stress. And, combined with soil layer parameters, perform layered summation calculation.

[0022] Step 2: Calculate the initial static settlement ; Case A (no pile foundation): Using the traditional layered summation method, calculate the initial settlement caused by static loads such as the structure's self-weight and the weight of the overlying soil: where, is the additional stress due to static load at the point of interest in the i-th soil layer (using Boussinesq or Mindlin solution), is the thickness of the i-th soil layer, is the compression modulus of the i-th soil layer. The distribution of each soil layer is provided for guidance of layering and parameter selection. Figure 3 Case B (with pile foundation): the initial settlement of pile foundation is calculated using the equivalent action layer summation method or the Mindlin-Gerts method

[0023] The pile-pile cap system is regarded as an equivalent deep foundation, and the compression deformation of the underlying soil layers is calculated, or a detailed calculation is performed based on the pile-soil interaction theory. For the case with pile foundation, the pile foundation 12 in the i-th soil layer represents the arrangement of the pile foundation, and its geometric size and arrangement form will affect the distribution of the load on the pile top and the settlement calculation. Figure 2

[0024] Step 3: cyclic cumulative effect analysis; For the foundation soil in the range of the main stress layer under the box foundation bottom plate, the cumulative plastic strain after the i-th cycle is calculated using the empirical model: where, , , is the cyclic cumulative strain parameter of the soil body, which is determined by indoor dynamic triaxial test; is the initial effective overburden pressure of the soil layer. For the case with pile foundation, the change of stress distribution in the soil caused by the pile foundation needs to be considered, and the cumulative strain of the soil below the pile tip and between the piles is calculated.

[0025] The cumulative pore water pressure caused by cyclic load is calculated: For each layer of soil, the cumulative pore water pressure after the i-th cycle is calculated using the empirical formula: or where, , is the cyclic pore pressure growth parameter of the soil body, which is determined by test; f is the pore pressure saturation value coefficient, which controls the limit value of pore pressure growth, and theoretically for normally consolidated soft clay or loose sand, f takes a value close to 1.0; for over-consolidated clay or dense sand, f takes a value less than 1.0. ​​​This is the pore pressure growth rate coefficient, which controls the rate at which pore pressure increases with plastic strain; its value typically ranges from 1 to 100. The more sensitive the soil is to cyclic loading, the... The larger the value, the better. β is the growth curve morphology index, which controls the shape of the pore pressure-strain curve. Its value range is usually 0.5~2.0, and most soils take a value around 1.0. Figure 4 This diagram illustrates the periodic fluctuations in the pool water level during the operational period. It is based on actual operational data (such as water level monitoring records) and is used to determine the amplitude of the cyclic load. The period and cycle drive the calculation of cumulative plastic strain and pore water pressure.

[0026] Step 4: Calculate the settlement caused by long-term cyclic loading effects ; The long-term cumulative settlement caused by cyclic loading is divided into two parts: a. Direct plastic strain settlement : Due to accumulated plastic strain It is generated directly.

[0027] b. Settlement due to the dissipation of accumulated pore pressure : Due to accumulated pore water pressure This leads to a reduction in the effective stress of the foundation, which is then generated by the dissipation of accumulated pore pressure.

[0028] For cases without pile foundations: Will Considered as acting in The additional stress increment on the soil layer is calculated using the layer summation method. .

[0029] For cases with pile foundations: The impact of the pile on the dissipation of excess pore pressure and the soil compression mode needs to be carefully considered. As a rigid component, the pile alters the stress distribution and drainage boundary within the foundation. In this case, a simplified engineering approach can be adopted: the vertical compression of the soil within the pile's radius should be consistent with the pile's compression; elastic compression of the pile material: under cyclic loading, the pile itself will undergo elastic compression. Its value can be determined according to the formulas of mechanics of materials. Calculation, where For pile top cyclic load, For the pile length, The cross-sectional area of ​​the pile body This is the elastic modulus of the pile material.

[0030] Reconsolidation deformation of the compressive soil layer below the pile tip. As the driving stress, calculate the additional compression it causes, and treat this part as... The simplification is based on the load transfer mechanism of pile foundation, which considers that the soil below the pile tip is the main area to bear additional load and produce compression, and the pore pressure dissipation and reconsolidation of this area contribute most to the overall settlement. The calculation can be completed by using one-dimensional reconsolidation theory considering stress history. The total cyclic additional settlement is: Step 5: Calculate the total long-term settlement and evaluate the differential settlement; The total settlement of the structure after experiencing cyclic load is the sum of the initial static settlement and the cyclic load settlement: By changing the number of cycles , draw the settlement development curve over time. Calculate the settlement of key points such as the corner points of the box, the middle, and the shaft (if present), and evaluate whether the differential settlement meets the allowable value specified in the specification.

[0031] Step 6: Design feedback and optimization based on the prediction results; If the predicted value of long-term settlement or differential settlement does not meet the design requirements, return to the design stage for optimization.

[0032] Pile-free foundation optimization: Consider increasing the thickness of the bottom plate, setting up a raft foundation, or performing foundation reinforcement (such as replacement or mixing piles).

[0033] Pile foundation optimization: Consider adjusting the pile length, pile diameter, pile spacing, or using different pile types.

[0034] Re-enter the optimized parameters into the model calculation until the requirements are met.

[0035] The step 1 is specifically: First, according to the planar size of the box structure, the buried depth, and the geological conditions, determine whether to consider the entire box as a large foundation for overall settlement calculation or to divide it into several sections for separate calculation. Then, according to the geological exploration report, reasonably divide the layers, and for the case of pile foundation, extend the layers to a sufficient depth below the pile tip. Finally, based on the operation characteristics of the underground sewage treatment plant storage system, determine the typical period and amplitude of water level fluctuation, and calculate the cyclic pressure amplitude .

[0036] The settlement calculation in step 2 for the case of pile foundation prefers the Mindlin-Gerts method. This method is based on Mindlin's solution to calculate the additional stress caused by pile tip and pile side resistance in the soil, and uses the layer summation method to calculate the total settlement. When calculating, the geometric size of the pile, arrangement, pile load, and soil engineering property parameters need to be input.

[0037] In the step 3 and step 4, for the case of pile foundation, the transfer path of cyclic load is changed. The cyclic load acting on the bottom plate of the box is mainly transferred to the deep soil through the pile foundation. Therefore, in the calculation of the soil settlement of the pile and the soil layer under the pile and , the adopted should be understood as the amplitude of the cyclic load acting on the top of the pile, or the amplitude of the cyclic dynamic stress in the soil around the pile obtained by the analysis of the pile-soil interaction.

[0038] The pore pressure reconsolidation settlement of the case of pile foundation in the step 4 , a simplified model can be used: considering that the compression deformation of the pile body itself is small, the excess static pore pressure generated by the cyclic load mainly affects the compressible soil layer below the pile end, and it is assumed that the reconsolidation settlement of the part of the soil layer constitutes the main part. Accordingly, only the of the soil layer below the pile end can be calculated.

[0039] In the step 6, the evaluation of the differential settlement should focus on the connection between the box and the auxiliary shaft / channel, the mutation of the plane shape of the box, and the change of the hardness of the foundation soil. For the box with pile foundation, attention should also be paid to the differential settlement that may be caused by the uneven arrangement of the pile foundation. A set of rapid comparison process including two schemes of no pile foundation and pile foundation is established. According to the preliminary geological conditions and the load, the long-term settlement and the differential settlement under the two schemes are calculated respectively. Combined with the engineering cost, the construction difficulty and the long-term performance, the optimal foundation scheme is selected, or the optimization direction of the combined foundation (such as long and short piles, variable stiffness leveling) is proposed.

[0040] The present application is described in detail below in combination with examples, but the protection scope of the present application is not limited thereto.

[0041] Example 1, large rainwater storage tank without pile foundation; Engineering overview: A reinforced concrete rectangular box of underground rainwater storage tank, 100 meters long, 40 meters wide, and 10 meters deep. The foundation soil is mainly silty clay, the layer thickness is more than 30 meters, and the natural raft foundation is adopted.

[0042] Implementation process: S1: analyze the operation data, determine the daily fluctuation amplitude of the water level as 2 meters, and calculate the amplitude of the cyclic load acting on the bottom plate as 20 kPa. The design period is 50 years, and the total number of cycles is 18250. The foundation compression layer is divided into 12 layers. S2: calculate the initial static settlement by using the Mindlin solution to calculate the additional stress of the base, and using the layer summation method, the initial static settlement is calculated as 85 mm.

[0043] S3: calculate the cyclic settlement of the box by using the method of cyclic stress path, and the cyclic settlement is calculated as 20 mm. ​​

[0044] S3 & S4: Calculate the cyclic cumulative model parameters (e.g. ) of the representative soil layers, and obtain the additional settlement caused by cyclic loading within a 50-year operating period as 55 mm.

[0045] S5 & S6: Total long-term settlement is 140 mm. It is calculated that the maximum differential settlement rate meets the specification requirements. Therefore, the pile-free foundation scheme is feasible in terms of settlement control, and the design is adopted.

[0046] Example 2, Pile Foundation Underground Sewage Treatment Plant Tank; Project Overview: The main tank of a certain underground sewage treatment plant has poor geological conditions, with deep soft clay on the surface. In order to control settlement, a prestressed high-strength concrete pipe pile foundation is used, with a pile diameter of 0.8 meters, a pile length of 40 meters, and the pile end entering the dense silt layer.

[0047] Implementation Process: S1: Load analysis and layering are similar to Example 1, but the geological model focuses on the distribution and properties of the soil layers below the pile end.

[0048] S2: Use the Mindlin-Gerts method to calculate the settlement of the pile foundation. The calculation considers the group pile effect, and the initial settlement is 30 mm.

[0049] S3 & S4: Focus on the cyclic cumulative effect of the pile end bearing layer and the underlying soil layer. The calculation shows that due to the pile foundation transferring most of the cyclic load to the deep low-compressibility soil layer, its cyclic additional settlement is relatively small, about 18 mm.

[0050] S5 & S6: Total long-term settlement is 48 mm. Compared with the pile-free foundation scheme in Example 1, the pile foundation scheme reduces the total settlement by about 66%, and the differential settlement is significantly reduced. Although the cost is higher, for sewage treatment structures with strict settlement control requirements, this pile foundation scheme is proven to be necessary and effective.

[0051] Figure 5 The figure shows the comparison of total long-term settlement development curves under the conditions of pile foundation and pile-free foundation, which is based on the total settlement calculated in Step 5 with the change of cycle number , where the curve data comes from the calculation results of Example 1 and Example 2, reflecting the development trend of settlement over time under different foundation forms.

[0052] Through the comparison of the above examples, it can be clearly seen that the application process of the method under different foundation forms and its supporting role in scheme decision-making.

[0053] Example Two A simplified calculation method for long-term operation settlement of underground box-type structures is provided in this embodiment, comprising: Step 1: Engineering generalization and load analysis; According to the structural design drawings and engineering survey report, the geometric size, buried depth and foundation form (whether there is a pile foundation) of the box-type structure are determined. The foundation soil within the compression depth range is divided into several calculation layers. Based on the operation characteristics of underground sewage treatment plants, the internal water level fluctuation law is statistically analyzed and simplified as an equal-amplitude cyclic load with a specific cyclic load stress amplitude and total cyclic action times.

[0054] Step 2: Initial static settlement calculation; For the case without pile foundation: the additional stress generated by the structure self-weight and overburden weight and other static loads at the midpoint of each soil layer is calculated using elastic theory, and then the initial settlement is calculated using the layer-wise summation method. Specifically: the product of the additional stress of each soil layer and the corresponding soil layer thickness is calculated, then divided by the compression modulus of the soil layer, and finally the settlement amounts of each soil layer are added up.

[0055] For the case with pile foundation: the equivalent action layer-wise summation method or the more accurate Mindlin-Drucker method is used. The latter calculates the stress field caused by the side friction and end resistance of a single pile in the soil, and superimposes them to consider the pile-soil interaction, so as to solve the initial settlement of the pile foundation.

[0056] Step 3: Analysis of cyclic cumulative effect; For the main stress soil layer below the base, its deformation response under long-term action of cyclic load is calculated: Cumulative plastic strain: an empirical model is used for prediction, which is expressed as: the cumulative plastic strain of the soil is the product of the model parameters A, the mth power of the ratio of the cyclic load stress amplitude to the effective overburden stress of the soil, and the bth power of the number of cycles N. The key model parameters A, m, and b need to be determined through indoor dynamic triaxial tests. For the case of pile foundation, the dynamic stress amplitude transmitted by the pile to the soil around the pile and at the pile end should be taken as the cyclic load stress amplitude.

[0057] Cumulative pore water pressure: two models can be used for estimation. One is the product of model parameter B and the natural logarithm of (1 plus the product of model parameter C and the number of cycles N). The second is the product of model parameter f, the effective overburden stress of the soil, and (1 minus the negative α times the βth power of the cumulative plastic strain of the natural constant e). The specific parameters in the model need to be obtained through experimental data fitting.

[0058] Step 4: Calculation of cyclic additional settlement; The cyclic additional settlement caused by long-term operation consists of two parts: Direct plastic strain settlement: the direct contribution from the accumulated plastic strain of the soil under cyclic loading, which is equal to the sum of the product of the calculated accumulated plastic strain of each soil layer and the corresponding soil layer thickness.

[0059] Pore pressure reconsolidation settlement: caused by the re-compression of the soil during the dissipation of the accumulated pore water pressure.

[0060] Without pile foundation, the accumulated pore water pressure in each soil layer can be regarded as additional stress, and the settlement caused by it can be calculated by the layer summation method.

[0061] With pile foundation, simplified calculation can be performed, mainly considering the reconsolidation settlement of the soil layer below the pile tip caused by pore pressure dissipation. Specifically, the settlement contribution of each soil layer can be calculated as follows: the product of the rebound index of the soil layer and the thickness of the soil layer, divided by 1 plus the initial void ratio of the soil layer, multiplied by the common logarithm value of the ratio of the sum of the effective overburden stress and the accumulated pore water pressure to the effective overburden stress of the soil layer. Finally, the calculation results of each soil layer are summed.

[0062] Total cyclic additional settlement is the sum of the direct plastic strain settlement and the pore pressure reconsolidation settlement.

[0063] Step 5: Total settlement synthesis and safety evaluation; The total settlement of the structure after N cycles of cyclic loading is the sum of the initial static settlement and the corresponding cyclic additional settlement. By calculating the final total settlement of the box at key positions (such as corner points, middle, and shaft connections) under the designed total number of cycles, it is evaluated whether the differential settlement produced meets the limit requirements of the building foundation design specification and other relevant standards.

[0064] Step 6: Design feedback and optimization decision; Design guidance based on prediction results: If the settlement of the no-pile foundation scheme exceeds the limit, the thickness of the foundation slab can be increased, a cushion layer can be set, or the foundation soil can be reinforced (such as cement soil mixing pile).

[0065] If the settlement of the pile foundation scheme exceeds the limit or is not economical, the pile length, pile diameter, pile spacing, or variable stiffness leveling design can be optimized.

[0066] Through iterative calculation, a safe, economical, and reasonable foundation scheme is finally determined.

[0067] The above is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A simplified calculation method for long-term settlement of underground box-type structures, characterized by, The method comprises the following steps: constructing a calculation model according to geological survey data and structural design drawings, and dividing the foundation soil in the compression layer range below the base in the model into several horizontal soil layers; simplifying the cyclic load in the operation period into an equal-amplitude load with a specific amplitude and total cycle number; calculating the initial static settlement based on the soil layer parameters and static load distribution in the calculation model; calculating the cumulative plastic strain and cumulative pore water pressure generated by the foundation soil based on the equal-amplitude load; calculating the cyclic additional settlement based on the cumulative plastic strain and cumulative pore water pressure; obtaining the total long-term settlement based on the cyclic additional settlement and the initial static settlement.

2. The simplified calculation method of long-term operation settlement of an underground box structure according to claim 1, characterized in that, According to the planar size, buried depth and geological conditions of the box structure, the mode of settlement calculation is determined; the basis for dividing the foundation soil into several horizontal soil layers is the soil layer distribution, physical and mechanical indexes and underground water level conditions in the geological survey report; wherein, the mode of settlement calculation is to calculate the settlement of the entire box as a whole or to divide the box into several sections for separate calculation.

3. The simplified calculation method of long-term operation settlement of an underground box structure according to claim 1, wherein, Based on the operation characteristics of the water storage system of the underground sewage treatment plant, the typical period and amplitude of water level fluctuation are determined, and the cyclic pressure amplitude generated by the water level fluctuation on the bottom plate of the box is calculated.

4. The simplified calculation method for long-term operation settlement of the underground box structure according to claim 1, characterized in that, when calculating the initial static settlement, if there is no pile foundation, the layered summation method is used for calculation; if there is a pile foundation, the Mindlin-Gerts method is used for calculation.

5. The simplified calculation method for long-term operation settlement of the underground box structure according to claim 1, characterized in that, the following model is used to calculate the cumulative plastic strain: ； wherein, , , is the cyclic accumulated strain parameter of soil, which is determined by indoor dynamic triaxial test; is the initial effective overburden pressure of soil layer, N is the number of cycles, is the amplitude of equal amplitude load.

6. The simplified calculation method for long-term operation settlement of the underground box structure according to claim 5, characterized in that, when calculating the cumulative pore water pressure based on the equal-amplitude load and the cumulative plastic strain, the following model is used: ； wherein, f is the pore pressure saturation value coefficient, 0 < f ≤ 1; α is the pore pressure growth rate coefficient; β is the growth curve shape index.

7. The simplified calculation method for long-term operation settlement of the underground box structure according to claim 1, characterized in that, the process of calculating the cyclic additional settlement based on the cumulative plastic strain and the cumulative pore water pressure includes: calculating the direct plastic strain settlement according to the cumulative plastic strain; calculating the settlement caused by the cumulative pore pressure dissipation according to the cumulative pore water pressure; if there is no pile foundation in the box structure, the direct plastic strain settlement and the settlement caused by the cumulative pore pressure dissipation are summed to obtain the cyclic additional settlement; if there is a pile foundation in the box structure, the pile body compression amount also needs to be calculated, and the direct plastic strain settlement and the settlement caused by the cumulative pore pressure dissipation are summed to obtain the cyclic additional settlement.

8. The simplified calculation method for long-term operation settlement of the underground box structure according to claim 1, characterized in that, the pile body compression amount is calculated based on the cyclic load at the top of the pile, the pile length, the cross-sectional area of the pile body and the elastic modulus of the pile body material, and the calculation formula is: ； wherein, is the cyclic load at the pile top, is the length of the pile, is the cross-sectional area of the pile body, is the elastic modulus of the pile body, the cyclic load at the pile top is determined by the mechanical distribution principle based on the amplitude of the equal-amplitude load, the area of the box bottom plate, and the number and arrangement form of the pile foundation.

9. The simplified calculation method for long-term operation settlement of the underground box structure according to claim 1, characterized in that, Further comprising, evaluating differential settlement based on the total long-term settlement; and optimizing the box-type structure design according to the settlement evaluation result. Further comprising, evaluating differential settlement based on the total long-term settlement; and optimizing the box-type structure design according to the settlement evaluation result.

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