Near-foundation-pit underground air-raid shelter construction influence analysis method based on spatial effect

Abstract

The invention discloses a near-foundation-pit underground air-raid shelter construction influence analysis method based on a spatial effect, which comprises the following steps that a finite element model is established by adopting a three-dimensional modeling method, a typical foundation pit section is selected for simulation, and the model comprises a foundation pit, an underground air-raid shelter and a support pile; selecting foundation pit material parameters corresponding to the finite element model, adopting a modified D-P constitutive model for a soil body, and adopting an elastic-plastic constitutive model for anchor cables and support piles; designing a calculation comparison work group; the calculation and comparison work groups comprise a comparison work group I under the condition of no air-raid shelter and a comparison work group II, a comparison work group II, a comparison work group III and a comparison work group V which are used for adjusting different anchor rod elevations, incident angles and anchoring section length parameters under the condition of air-raid shelter; comparing and verifying the correctness of the model according to a numerical simulation result of the calculation and comparison work group and actually measured data; and obtaining the influence analysis result of the underground air-raid shelter on displacement, soil pressure and structural internal force in the foundation pit construction process. The problem that the near-underground air-raid shelter space effect is not fully considered in foundation pit construction is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of civil engineering, in particular to a construction influence analysis method for near-foundation pit underground air-raid shelter based on spatial effect. BACKGROUND

[0002] At present, the construction safety and stability of foundation pit engineering are important links in engineering construction, especially under complex geological conditions or in the presence of existing underground structures, the construction difficulty and risk increase significantly. In recent years, with the continuous advancement of urban construction, near-foundation pit existing underground air-raid shelters have appeared in many areas, and their influence on foundation pit construction has gradually attracted attention. Due to the existence of underground air-raid shelters, the stress distribution of the surrounding soil will change, and lateral deformation will be induced, which will cause significant changes in the displacement of foundation pit supporting structures, post-pile soil pressure and structural bending moment, which puts higher requirements on the safety and stability of foundation pit construction.

[0003] At the same time, research on foundation pit construction is mostly focused on the design and optimization of supporting structures under ordinary geological conditions, while research on the spatial effect of near-foundation pit underground air-raid shelters and their influence on foundation pit construction is relatively less. The existing technology usually adopts the modified Mohr-Coulomb constitutive model to simulate the behavior of soil, and analyzes the mechanical response in the process of foundation pit excavation through numerical simulation software (such as Abaqus).

[0004] However, in the case of existing underground air-raid shelters, the existing research has not fully considered the specific influence of air-raid shelters on the whole process of foundation pit construction, especially the problems of insufficient anchor prestress, increased post-pile soil pressure and abnormal growth of enclosure structure bending moment, which may lead to excessive deformation of supporting structures, and even cause foundation pit instability and other serious consequences. In addition, there is a lack of systematic comparative analysis of the effects of different supporting schemes in the existing technology, which makes it difficult to provide scientific basis for actual construction. Therefore, it is urgent to carry out research on the spatial effect of near-foundation pit underground air-raid shelters to reveal the influence mechanism of displacement, soil pressure and structural internal force in the process of foundation pit construction. SUMMARY

[0005] Therefore, the present application provides a construction influence analysis method for near-foundation pit underground air-raid shelters based on spatial effect to solve the problem that the existing foundation pit construction technology fails to fully consider the spatial effect of near-foundation pit underground air-raid shelters.

[0006] In order to achieve the above purpose, the present application provides the following technical scheme:

[0007] A construction influence analysis method for near-foundation pit underground air-raid shelters based on spatial effect, comprising the following steps:

[0008] The finite element model is established by using a three-dimensional modeling method, and the finite element model comprises a foundation pit, an underground air-raid shelter and a supporting pile.

[0009] The material parameters of the foundation pit corresponding to the finite element model are selected, the soil body of the material parameters of the foundation pit adopts a modified D-P constitutive model, and the anchor cable and the supporting pile of the material parameters of the foundation pit adopt an elastic-plastic constitutive model.

[0010] The first to fifth comparison groups are designed and calculated.

[0011] The comparison groups comprise the first comparison group without the air-raid shelter and the second to fifth comparison groups with the air-raid shelter and different anchor rod elevations, incident angles and anchoring segment lengths.

[0012] The correctness of the model is verified according to the comparison between the numerical simulation results of the comparison groups and the measured data.

[0013] The influence analysis results of the underground air-raid shelter on the displacement, soil pressure and structural internal force in the foundation pit construction process are obtained.

[0014] On the basis of the above technical scheme, the present application is further described as follows:

[0015] As a further scheme of the present application,

[0016] The boundary condition setting of the finite element model in step S1 comprises:

[0017] The soil body is horizontally constrained, the bottom surface is vertically and horizontally constrained, and the upper surface is free.

[0018] The foundation pit has a depth of 12 m, the supporting pile has a length of 18 m, the underground air-raid shelter is located below the foundation pit, is 4 m away from the bottom of the foundation pit, has a radius of 2 m, has a center line with an angle of 30° with the side wall of the foundation pit, and has a length of 16 m.

[0019] As a further scheme of the present application,

[0020] The soil body parameters in step S2 comprise the density, elastic modulus, internal friction angle and cohesion of silty clay, sandy silt and pebble layer.

[0021] As a further scheme of the present application,

[0022] In step S4, the correctness of the model is verified by selecting the foundation pit profile closest to the underground air-raid shelter for modeling calculation and comparison with the measured data; the measured data comprise the horizontal displacement of the supporting structure, the horizontal displacement of the foundation pit and the ground surface behind the foundation pit, and the vertical displacement of the foundation pit and the ground surface behind the foundation pit.

[0023] As a further scheme of the present application,

[0024] The influence of the underground air-raid shelter on the displacement, soil pressure and structural internal force during the foundation pit construction process is obtained in step S5, and specifically includes:

[0025] The numerical values of the displacement, soil pressure and structural internal force during the foundation pit construction process are obtained under the conditions of having and not having the air-raid shelter, respectively, and the analysis results of the influence of the air-raid shelter on the foundation pit construction process are determined by comparison.

[0026] As a further scheme of the present application, it further includes:

[0027] An optimized support scheme is proposed, that is, the force distribution between the anchor rod and the support pile is improved by adjusting the incident angle of the anchor rod, so that the bending moment increase of the enclosure structure is reduced.

[0028] As a further scheme of the present application,

[0029] In step S3, the anchor rod elevation of one comparison group is set to 4m, the incident angle is set to 30°, the free section length is set to 7m, and the anchoring section length is set to 9m;

[0030] When the incident angle of the anchor rod and the anchoring section length are adjusted, the parameter configuration of one comparison group is adopted, that is, the anchor rod elevation is 4m, the incident angle is 30°, the free section length is 7m, and the anchoring section length is 9m;

[0031] By increasing the anchoring section length from 7m to 9m, the maximum value of the support pile horizontal displacement is reduced from -17.4mm to -14.8mm, with a reduction of 15%, and at the same time, the maximum value of the soil pressure behind the pile is reduced from -185.7kPa to -170.2kPa, with a reduction of 8%.

[0032] As a further scheme of the present application,

[0033] The modified D-P constitutive model is related to the nonlinear behavior and stress path-dependent characteristics of the soil body, and the mathematical expression is: σ = σ 0 + K (ε - ε 0 ), wherein σ is the current stress state, σ 0 is the initial stress state, K is the soil body stiffness matrix, ε is the strain value, and ε 0 is the initial strain value.

[0034] The present application has the following beneficial effects:

[0035] The method analyzes the influence of the underground air-raid shelter on the displacement, soil pressure and structural internal force during the foundation pit construction process by establishing a finite element model and combining with the field monitoring data, and reveals the significant effect of the spatial effect of the air-raid shelter on the foundation pit construction risk. Further, by adjusting the incident angle of the anchor rod and the anchoring section length, an optimized support scheme is proposed, which effectively reduces the construction risk. In particular, the technical scheme provides an important reference for similar projects, and has high practical value and promotional significance. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0037] Figure 1 This is an overall analysis flow chart of the construction impact analysis method of underground air-raid shelter near foundation pit based on spatial effect provided by the present invention.

[0038] Figure 2 This is one of the comparison graphs of the horizontal displacement change curves of support piles during the foundation pit construction process corresponding to the construction impact analysis method of underground air-raid shelter near the foundation pit based on spatial effect provided by the present invention.

[0039] Figure 3 This is the second comparison diagram of the horizontal displacement change curve of the support piles during the foundation pit construction process corresponding to the construction impact analysis method of underground air-raid shelter near the foundation pit based on spatial effect provided by the present invention.

[0040] Figure 4 This is a schematic diagram of the comparison and verification of the numerical calculation results corresponding to the construction impact analysis method of underground air-raid shelter near foundation pit based on spatial effect provided by the present invention and the field measured data.

[0041] Figure 5 This is a schematic diagram of the changes in soil pressure distribution behind piles with and without air-raid shelters during foundation pit construction, corresponding to the spatial effect-based construction impact analysis method for underground air-raid shelters near foundation pits provided by the present invention. DETAILED DESCRIPTION

[0042] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0043] The terms "upper", "lower", "left", "right", "middle", etc. used in this specification are only for the convenience of description and are not intended to limit the scope of the present invention. Changes or adjustments to their relative relationships should be regarded as within the scope of the present invention without substantially changing the technical content.

[0044] As Figures 1 to 5 shown, the embodiment of the present application provides a near-foundation pit underground air-raid shelter construction influence analysis method based on spatial effects, the core of which is to analyze the displacement, soil pressure and structural internal force in the construction process by establishing a finite element model, selecting material parameters, comparing and verifying the design of work groups, and proposing a feasible optimization support scheme. Not only does it help improve the safety and economy of foundation pit construction, but it also provides important theoretical support and technical guidance for foundation pit engineering under similar complex geological conditions. By establishing a finite element model and combining with field measurement data, the influence of underground air-raid shelters on foundation pit construction is systematically analyzed, and an optimization support scheme is proposed to reduce construction risks and improve foundation pit stability.

[0045] The following detailed description is made in conjunction with the specific drawings and part numbers in the accompanying drawings.

[0046] The near-foundation pit underground air-raid shelter construction influence analysis method based on spatial effects includes the following steps:

[0047] S1: Establish a finite element model; S2: Select material parameters; S3: Design and calculate comparison work groups; S4: Verify model correctness; S5: Analyze the influence of air-raid shelters on displacement, soil pressure and structural internal force during foundation pit construction; S6: Propose an optimization support scheme. The specific implementation of each step is as follows:

[0048] First, in step S1, when establishing a finite element model, a typical foundation pit profile is selected for three-dimensional modeling. The depth of foundation pit 1 is set to 12m, the length of support pile 3 is set to 18m, and underground air-raid shelter 2 is located below the foundation pit, with a distance of 4m from the bottom of the foundation pit, a radius of 2m, an angle of 30° between the center line and the side wall of the foundation pit, and a length of 16m. The model boundary conditions include:

[0049] The soil is subjected to horizontal constraint, the bottom is subjected to vertical and horizontal constraint, and the upper surface is free. The above geometric parameters and positions are based on actual engineering data to ensure that the model can accurately reflect the actual situation. In the modeling process, ANSYS or ABAQUS finite element software is used for simulation, the grid division precision is defined to improve the calculation efficiency and result accuracy, and the grid density is adjusted to avoid numerical divergence problems.

[0050] Second, in step S2, when selecting material parameters, the material parameters of the foundation pit soil, anchor cable and support pile are determined based on laboratory test results and field measurement data.

[0051] The modified D-P constitutive model is selected as the soil constitutive relationship of the foundation pit material parameters, which comprehensively considers the nonlinear behavior and stress path-dependent characteristics of the soil. The mathematical expression is: σ = σ0 + K(ε - ε0), where σ is the current stress state, σ0 is the initial stress state, K is the soil stiffness matrix, ε is the strain value, and ε0 is the initial strain value. Different densities, elastic moduli, internal friction angles, and cohesion parameters are assigned to different soil layers, i.e., silty clay, sandy silt, and gravel layer.

[0052] For example, the density of silty clay is 1800 kg / m 3 , the elastic modulus is 20 MPa, the internal friction angle is 20°, and the cohesion is 15 kPa; the density of sandy silt is 1900 kg / m 3 , the elastic modulus is 30 MPa, the internal friction angle is 30°, and the cohesion is 5 kPa; the density of gravel layer is 2100 kg / m 3 , the elastic modulus is 50 MPa, the internal friction angle is 35°, and the cohesion is 0 kPa.

[0053] The elastic-plastic constitutive model is used for the anchor cable and supporting pile of the foundation pit material parameters. The density of steel strand (Q345) is 7800 kg / m 3 , the elastic modulus is 210 GPa, and the Poisson's ratio is 0.3; the density of cast-in-place pile (C40 concrete) is 2600 kg / m 3 , the elastic modulus is 30 GPa, and the Poisson's ratio is 0.25. The selection of these material parameters ensures the reliability of the model and provides a scientific basis for subsequent analysis.

[0054] Next, in step S3, the design and calculation of the comparison group are designed, the influence of the underground air-raid shelter on the foundation pit construction is studied, and the effect of different supporting methods is explored. Figure 2 The comparison of the horizontal displacement change curve of the supporting pile during the foundation pit construction process is shown, and the horizontal displacement curve in it represents the displacement change under the conditions of with and without air-raid shelters. Through comparison, it can be found that the existence of air-raid shelters significantly increases the horizontal displacement during the excavation of the foundation pit. Five comparison groups are designed:

[0055] Comparison group one is used as the standard foundation pit construction condition without air-raid shelters; comparison groups two to five are set as control groups to adjust different anchor rod elevations, incident angles, and anchor segment lengths to evaluate their influence on the construction effect.

[0056] For example, comparison group four is used for construction on the construction site, with an anchor rod elevation of 4 m, an incident angle of 30°, a free segment length of 7 m, and an anchor segment length of 9 m. This comparison group design is based on the comparison and analysis of numerical simulation and field measurement data, ensuring its scientificity and feasibility.

[0057] In step S4, the model correctness is verified, the profile closest to the underground air-raid shelter is selected for modeling calculation, and compared with the field measured data. Figure 4 The comparison and verification diagram of numerical simulation results and field measured data is shown, and the main measured contents include the horizontal displacement of supporting structure, the horizontal displacement of foundation pit and ground surface behind the pit, and the vertical displacement of foundation pit and ground surface behind the pit. Among them, the maximum ground surface settlement behind the pit appears at 18m away from the foundation pit, the numerical simulation value is 12.3mm, the measured value is 11.8mm, and the deviation is 0.5mm; the horizontal displacement of supporting structure reaches the maximum value at the pile burial depth of 5m, the numerical simulation value is 14.2mm, and the measured value is 13.6mm. Further, the comparison results show that the numerical simulation model is in good agreement with the actual measured data, and the correctness of the model is verified. In addition, by comparing and analyzing the simulation results and the measured data under different comparison groups, the model parameter settings are further optimized, and the prediction accuracy is improved.

[0058] In step S5, the influence of air-raid shelter on displacement, soil pressure and internal force of structure during foundation pit construction process is analyzed, and the model calculation results are discussed in detail. Figure 5 The post-pile soil pressure distribution change diagram under the conditions of with and without air-raid shelter during foundation pit construction process is shown. By comparison, it can be found that the existence of air-raid shelter significantly increases the post-pile soil pressure. For example, under the condition of without air-raid shelter, the maximum horizontal displacement of supporting pile is-7.2mm when the foundation pit is excavated to 5m; after the prestressed anchor cable is applied, the maximum displacement is 13.8mm. Under the condition of with air-raid shelter, due to the insufficient prestressed anchor cable, the maximum horizontal displacement of supporting pile is-17.4mm after the foundation pit is excavated, which is about 50% higher than-11.6mm under the condition of without air-raid shelter. Further, under the condition of without air-raid shelter, the post-pile soil pressure reaches the maximum value of-162.3kPa when the foundation pit is excavated to the bottom; under the condition of with air-raid shelter, the maximum post-pile soil pressure is-185.7kPa, which is significantly larger than that under the condition of without air-raid shelter. In addition, under the condition of without air-raid shelter, the maximum bending moment of the retaining structure is-182kN·m after the foundation pit is excavated; under the condition of with air-raid shelter, due to the insufficient prestressed anchor cable, the maximum bending moment is-310kN·m, with an increase of 70%. The above comparison result data analysis obtains the spatial effect of air-raid shelter on foundation pit construction risk.

[0059] Finally, in step S6, the supporting scheme is optimized based on the above analysis results. The optimization scheme adopts the parameter configuration of comparison group four, i.e. anchor rod elevation of 4m, incident angle of 30°, free section length of 7m, and anchoring section length of 9m.

[0060] Further, the optimization scheme improves the stability and bearing capacity of the support structure by increasing the anchoring segment length and adjusting the incident angle, thereby reducing the horizontal displacement of the enclosure structure and the increase in the post-pile soil pressure. For example, by increasing the anchoring segment length from 7m to 9m, the maximum horizontal displacement of the support pile can be reduced from -17.4mm to -14.8mm, with a reduction of 15%; at the same time, the maximum post-pile soil pressure can be reduced from -185.7kPa to -170.2kPa, with a reduction of 8%. In addition, the optimization scheme also improves the stress distribution between the anchor rod and the support pile by adjusting the incident angle of the anchor rod, effectively reducing the bending moment increase of the enclosure structure.

[0061] In summary, the embodiments of the present application establish a finite element model and combine field measurement data to systematically analyze the influence of underground air-raid shelters on displacement, soil pressure and structural internal force during foundation pit construction, revealing the significant role of the spatial effect of air-raid shelters in foundation pit construction risk. Further, the optimization support scheme by adjusting the incident angle of the anchor rod and the anchoring segment length effectively reduces the construction risk, providing an important reference for similar projects, and has high practical value and promotional significance.

[0062] Although the present application has been described in detail above with general description and specific embodiments, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of protection required by the present application.

Claims

1. A method for analyzing the impact of underground air-raid shelter construction near foundation pit based on spatial effect, characterized in that: The method comprises the following steps: A finite element model was established using a three-dimensional modeling method. The finite element model included the foundation pit, underground air-raid shelter, and support piles. A typical foundation pit section near the foundation pit for underground air-raid shelter construction was selected for finite element simulation. The foundation pit material parameters corresponding to the finite element model are selected. The soil of the foundation pit material parameters adopts the modified DP constitutive model, and the anchor cables and supporting piles of the foundation pit material parameters adopt the elastic-plastic constitutive model. Design calculation and comparison work groups one to five; The calculation comparison work group includes comparison work group 1 under the condition of no air-raid shelter and comparison work groups 2 to 5 under the condition of air-raid shelter, which adjust the parameters of different anchor elevations, incident angles and anchor section lengths; The correctness of the model was verified by comparing the numerical simulation results of the calculation and comparison team with the measured data; Obtain analysis results on the impact of underground air-raid shelters on displacement, soil pressure, and structural internal forces during foundation pit construction.

2. The method for analyzing the construction impact of underground air-raid shelter near foundation pit based on spatial effect according to claim 1 is characterized in that: The finite element model boundary condition settings in step S1 include: Horizontal constraints are imposed on the soil, vertical and horizontal constraints are imposed on the bottom surface, and the upper surface is free; The foundation pit is 12m deep, the supporting piles are 18m long, and the underground air-raid shelter is located below the foundation pit, 4m from the bottom of the pit, with a radius of 2m, an angle of 30° between the center line and the side wall of the pit, and a length of 16m.

3. The construction impact analysis method of underground air-raid shelter near foundation pit based on spatial effect according to claim 2 is characterized in that: The soil parameters in step S2 include density, elastic modulus, internal friction angle and cohesion of silty clay, sandy silt and gravel layer.

4. The construction impact analysis method of underground air-raid shelter near foundation pit based on spatial effect according to claim 3 is characterized in that: When verifying the correctness of the model in step S4, the foundation pit section closest to the underground air-raid shelter is selected for modeling and calculation, and compared with the measured data; the measured data includes the horizontal displacement of the support structure, the horizontal displacement of the foundation pit and the surface behind the pit, and the vertical displacement of the foundation pit and the surface behind the pit.

5. The method for analyzing the construction impact of underground air-raid shelter near foundation pit based on spatial effect according to claim 4 is characterized in that: In step S5, the analysis results of the influence of the underground air-raid shelter on the displacement, soil pressure and structural internal force during the foundation pit construction are obtained, which specifically include: The displacement, soil pressure and structural internal force values ​​of the foundation pit construction process with and without air-raid shelters were obtained respectively, and the analysis results of the influence of the air-raid shelter on the foundation pit construction process were determined by comparison.

6. The method for analyzing the construction impact of underground air-raid shelter near foundation pit based on spatial effect according to claim 5 is characterized in that: Also includes: An optimized support scheme is proposed, which is to improve the force distribution between the anchor rod and the support pile by adjusting the incident angle of the anchor rod, thereby reducing the bending moment increase of the retaining structure.

7. The method for analyzing the construction impact of underground air-raid shelter near foundation pit based on spatial effect according to claim 6 is characterized in that: In step S3, the anchor elevation of one of the comparison groups is set to 4 m, the incident angle is set to 30°, the free section length is set to 7 m, and the anchor section length is set to 9 m; When adjusting the incident angle of the anchor rod and the length of the anchoring section, the parameter configuration of one of the comparison groups was adopted, that is, the anchor rod elevation was 4m, the incident angle was 30°, the free section length was 7m, and the anchoring section length was 9m; By increasing the anchoring section length from 7m to 9m, the maximum horizontal displacement of the support pile was reduced from -17.4mm to -14.8mm, a decrease of 15%. At the same time, the maximum soil pressure behind the pile was reduced from -185.7kPa to -170.2kPa, a decrease of 8%.

8. The method for analyzing the construction impact of underground air-raid shelter near foundation pit based on spatial effect according to claim 1 is characterized in that: The modified DP constitutive model associates the nonlinear behavior and stress path dependence characteristics of the soil, and its mathematical expression is: σ = σ0 + K(ε-ε0), where σ is the current stress state, σ0 is the initial stress state, K is the soil stiffness matrix, ε is the strain value, and ε0 is the initial strain value.

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