A test method and device for simulating excavation under pipe curtain support in sandy soil

Abstract

This invention relates to a test method for simulating excavation in sandy soil layers under pipe-roof support, and involves the technical field of underground engineering. The method involves deriving a similarity ratio suitable for the pipe-roof support system; selecting model materials that meet the similarity ratio to prepare a subway station model structure and model soil; conducting preliminary tests to explore the extent of soil disturbance caused by excavation and designing a model box that meets boundary effects; filling the model soil, and installing the model structure and monitoring and acquisition system at a predetermined location to collect test data during soil excavation. This method explores the deformation patterns of the strata and structures during excavation, reducing test costs, simplifying the test process, and lowering technical difficulty while meeting precision control requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of underground engineering, and in particular to a test method and device for simulating excavation under pipe curtain support in sandy soil layers. Background Art

[0002] Large-section excavation for subway stations supported by pipe-roof support is a novel construction method for subway stations. Compared to traditional pipe-roof methods, this method employs multiple cross supports beneath the pipe-roof structure, forming a combined support system of small-diameter pipe-roof and cross supports. This significantly improves bearing capacity, impacting construction safety and the surrounding environment. Compared with existing new pipe-roof support structures such as NTR, STS, and TSM, this support system reduces the complex connections between steel pipes and eliminates the need for post-jacking cutting. This simplifies on-site construction and significantly reduces the construction time. However, the underlying deformation patterns of the ground and structures caused by excavation under pipe-roof and cross-support systems remain unclear, lacking a systematic theoretical basis. Consequently, the current design of large-section subway station excavation methods supported by pipe-roof support relies primarily on construction experience and engineering analogies, introducing unpredictable risks to the design and construction of pipe-roof structures. Summary of the Invention

[0003] In response to the shortcomings and disadvantages of the existing technology, the present invention designs a test method for simulating excavation under pipe-roof support in sandy soil strata. Based on the derived similarity ratio suitable for the pipe-roof support system, similar materials that meet the similarity ratio are selected to prepare a subway station model structure and model soil; preliminary tests are carried out to explore the range of soil disturbance caused by soil excavation, and a model box that meets the boundary effect is designed; finally, the model soil is filled, and the model structure and data monitoring and acquisition equipment are arranged at the set position to collect test data.

[0004] To achieve the above object, the present invention adopts the following technical solution, a test method for simulating excavation under pipe curtain support in sandy soil strata, comprising the following steps:

[0005] (1) Derive the similarity ratio applicable to the pipe curtain support system. According to the main research content, list the physical quantities involved, then establish the relationship between the physical quantities, and establish the exponential equation. Finally, the similarity ratio of the main physical quantities is derived based on the similarity theory.

[0006] (2) Select similar materials that meet the similarity ratio to prepare the subway station model structure and model soil. The selection of the model pipe curtain is mainly controlled by the bending stiffness. The equivalent stiffness method is used to simulate the pipe curtain, and then the model material is selected and the relevant dimensions are determined.

[0007] When simulating beams, in order to facilitate the preparation of similar materials for beams, the elastic modulus of reinforced concrete is approximated to the elastic modulus of concrete; first select the simulation material, and then determine the size of the model beam based on the similarity relationship.

[0008] When simulating the side piles, firstly, the side piles are equivalent to underground continuous walls according to the equivalent formula of bending stiffness. Then, the thickness of the equivalent underground continuous wall is calculated according to the equivalent formula of bending stiffness. Based on the similarity relationship, the thickness of the model side wall is obtained.

[0009] When preparing similar materials of soil, some physical quantities are selected as main parameters according to the research content of the experiment. The main parameters of the prototype and model strictly abide by the similarity relationship, and the remaining parameters are kept within a certain range.

[0010] (3) Conduct preliminary tests to explore the scope of soil disturbance caused by soil excavation and design a model box that satisfies the boundary effect. Before designing the model box, conduct preliminary tests through numerical simulation to explore the model box boundary suitable for model testing. Combined with the results of numerical simulation, the size of the model box is determined.

[0011] (4) Fill the model soil, arrange the model structure and data monitoring and acquisition equipment at the set position, and collect test data.

[0012] Compared with the existing technology, the beneficial effects of the present invention are: the present invention can simulate the excavation process of a large-section subway station under pipe curtain support, thereby exploring the deformation laws of the strata and structures during the excavation process, reducing the test cost, simplifying the test process and reducing the technical difficulty while meeting the precision control. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0014] Figure 1 It is a schematic diagram of the process structure of the present invention;

[0015] Figure 2 This is a layout diagram of a pipe curtain model according to an embodiment of the present invention;

[0016] Figure 3 This is a front view of the crossbeam and side wall of the embodiment model of the present invention;

[0017] Figure 4 This is a top view of the crossbeam and side walls of the embodiment model of the present invention;

[0018] Figure 5 This is a schematic diagram of a model box according to an embodiment of the present invention;

[0019] Figure 6 It is a schematic diagram of an earth retaining plate according to an embodiment of the present invention.

[0020] 1. Welding rod, 2. Tin foil, 3. 502 glue, 4. Model beam, 5. Model side wall, 6. Groove, 7. Glass plate, 8. Model pipe curtain, 9. Fixing bracket, 10. Bolt, 11. Steel plate. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Currently, the deformation patterns of the strata and structures caused by excavation under the pipe-roof and cross-bracing support system are still unclear and lack a systematic theoretical basis. As a result, the design of the excavation method for large-section subway stations under pipe-roof support is currently mainly based on construction experience and engineering analogies, which brings unpredictable risks to the design and construction of the pipe-roof structure and cannot avoid the risks existing in construction.

[0023] Example 1

[0024] See Figure 1 A test method for simulating excavation under pipe curtain support in sandy soil strata comprises the following steps:

[0025] The physical parameter data of the physical pipe-roof support system are collected, force and length are selected as the basic dimensions, and the exponential equation between the physical parameter data is established using the dimensional matrix method, thereby obtaining the similarity relationship matrix of the physical parameter data;

[0026] Confirm the similarity ratio between physical parameter data based on the similarity relationship matrix, select similar materials that meet the similarity ratio, and build a similarity model for the tube curtain;

[0027] Based on the pipe-roof similarity model, multiple sets of numerical simulation pre-experiments are set up to obtain the range of soil disturbance caused by soil excavation, and a numerical set in which the soil is not affected by excavation is selected as the boundary condition of the similarity model;

[0028] The strata of the similar model are prepared in layers by a compaction method and filled into the similar model. At the same time, a data monitoring and acquisition device is set at a set position. After a set static time, the bottom layer is excavated, and the data monitoring and acquisition device detects and collects similar simulation data.

[0029] Example 1

[0030] The following combination Figure 1 The present invention is described in detail in a specific embodiment. A test method for simulating excavation under pipe curtain support in a sandy soil layer includes the following steps:

[0031] (1) Derive the similarity ratio applicable to the pipe curtain support system. According to the main research content, list the physical quantities involved, then establish the relationship between the physical quantities, and establish the exponential equation. Finally, the similarity ratio of the main physical quantities is derived based on the similarity theory.

[0032] (2) Select similar materials that meet the similarity ratio to prepare the subway station model structure and model soil. The selection of the model pipe curtain is mainly controlled by the bending stiffness. The equivalent stiffness method is used to simulate the pipe curtain, and then the model material is selected and the relevant dimensions are determined.

[0033] When simulating the beam, in order to facilitate the preparation of similar materials for the beam, the elastic modulus of reinforced concrete is approximately taken as the elastic modulus of concrete; the simulation material is first selected, and then the size of the model beam 4 is determined based on the similarity relationship.

[0034] When simulating the side piles, firstly, the side piles are equivalent to underground continuous walls according to the equivalent formula of bending stiffness. Then, the equivalent underground continuous wall thickness is calculated according to the equivalent formula of bending stiffness. Based on the similarity relationship, the thickness of the model side wall 5 is obtained.

[0035] When preparing similar materials of soil, some physical quantities are selected as main parameters according to the research content of the experiment. The main parameters of the prototype and model strictly abide by the similarity relationship, and the remaining parameters are kept within a certain range.

[0036] (3) Conduct preliminary tests to explore the scope of soil disturbance caused by soil excavation and design a model box that satisfies the boundary effect. Before designing the model box, conduct preliminary tests through numerical simulation to explore the model box boundary suitable for model testing. Combined with the results of numerical simulation, the size of the model box is determined.

[0037] (4) Fill the model soil, arrange the model structure and data monitoring and acquisition equipment at the set position, and collect test data.

[0038] Example 2

[0039] The following combination Figure 1 Specific embodiments of the present invention are described in detail.

[0040] (1) Derive the similarity ratio applicable to the tube-roof system:

[0041] The experiments in this embodiment of the present invention mainly study the surface settlement, pipe curtain deformation, and beam strain caused by excavation under pipe curtain support. According to the research content, the physical quantities involved are: elastic modulus E, cohesion c, soil internal friction angle φ, Poisson's ratio μ, bulk density γ, stress σ, strain ε, vertical displacement δ, geometric dimension L, load P, and section inertia moment I. Let X1, X2, X3, X4...X 11 Represented as physical quantities E, c, The exponent of μ…I, force F and length L are selected as the basic dimensions, the relationship between the physical quantities is established using the dimensional matrix, and the exponential equation is established based on the dimensional matrix:

[0042]

[0043] Then, a similarity relationship matrix can be listed. Combined with previous soil similarity model tests, it is known that the bulk density similarity ratio is generally taken as 1. Considering the limitations of actual engineering and indoor test sites, the geometric similarity ratio of the model test is 50. The similarity ratios of the main physical quantities in the test are as follows:

[0044] The geometric similarity ratio is 50. The similarity ratios of the main physical quantities in the experiment are as follows:

[0045] C E =C c =C δ =C L =50, C I =50 4 , C P =50 3

[0046]

[0047] Elastic modulus similarity ratio C E , cohesion similarity ratio C c , similarity ratio of soil internal friction angle Poisson's ratio similarity ratio C μ , strain similarity ratio C ε , vertical displacement similarity ratio C δ , geometric similarity ratio C L , load similarity ratio C P , similarity ratio of section moment of inertia C I .

[0048] (2) Select similar materials that meet the similarity ratio to prepare the subway station model structure and model soil:

[0049] The deformation of the pipe curtain is one of the main research contents of this experiment. Therefore, the selection of the model pipe curtain is mainly controlled by the bending stiffness. The bending stiffness equivalent method is used to simulate the pipe curtain structure and the cross support structure. The bending stiffness of the equivalent pipe curtain is calculated according to the following formula:

[0050] E eq I eq =E s I s +αE c I c

[0051] E eq I eq =50 5 E m I m

[0052] Among them, E s 、E c are the elastic moduli of steel pipe and concrete respectively; Is , I c are the section inertia moments of steel pipe and concrete respectively; E eq , I eq are the elastic modulus and section inertia moment of the equivalent rear pipe curtain respectively; E m , I m are the elastic modulus and section inertia moment of the model pipe curtain respectively; α is the ratio of the elastic modulus of concrete grouting to the elastic modulus of the steel pipe,

[0053] The above formula is used to calculate the equivalent bending stiffness of the pipe curtain. Select appropriate materials to simulate the pipe curtain, and conduct a tensile test on the material according to the requirements of the material tensile test specification to test its elastic modulus. Based on the elastic modulus, determine the material diameter of the simulated pipe curtain. In order to obtain the stratum and structural deformation caused by excavation under adverse working conditions, the lock buckle is not simulated in the model test design, and the bending performance of the lock buckle is not considered. The gap is filled by applying 502 glue 3 between the model pipe curtains, and a layer of tin foil 2 is laid on the top of the pipe curtain to simulate the retaining effect of the lock buckle. For the grouting reinforcement between pipes, the cement slurry reinforcement and the selected material are made to meet the similarity relationship, such as Figure 2 As shown, the material welding rod 1 is used to simulate the grouting reinforcement body, and is welded to the pipe roof using a welding gun.

[0054] For the beam, to facilitate the preparation of similar materials for the beam, the elastic modulus of reinforced concrete was approximated to that of concrete. First, the simulation material was selected, and then the dimensions of the model beam 4 were determined based on the similarity relationship.

[0055] According to the equivalent formula for flexural stiffness, the side piles are firstly equivalent to underground continuous walls, and the thickness of the underground continuous wall is calculated as follows:

[0056]

[0057] Where: D is the pile diameter, t is the pile diameter distance, and h is the equivalent ground-anchored wall thickness, unit: m.

[0058] The equivalent ground connection wall thickness is calculated by the above formula, and based on the similarity relationship, the thickness hm of the model side wall 5 is obtained.

[0059] Model beam 4 and side wall as Figure 3 and Figure 4 shown.

[0060] When preparing the soil analog material, since this test primarily studies pipe curtain deformation, beam strain, and surface settlement during excavation, and the soil's elastic modulus is the primary factor affecting surface settlement, the elastic modulus and compression modulus have the same similarity constant, so the compression modulus can be used as a primary parameter in the model test. When the compression modulus satisfies the similarity relationship, the elastic modulus is approximately assumed to also meet the similarity relationship. Pipe curtain deformation and beam strain are primarily caused by the deadweight of the overlying load during excavation, so the specific gravity of the prototype soil is used as another key parameter in the test. The prototype soil is primarily composed of medium-coarse sand in a medium-density stratum, with a cohesion of approximately 1.5 kPa. Engineering experience shows that variations in cohesion within the range of 0 to 1.5 kPa have limited impact on surface settlement, so cohesion is not considered a primary parameter. Therefore, when the compression modulus and specific gravity of the model soil meet similarity relationships with the prototype soil, and the cohesion and internal friction angle are within a certain range, the prepared model soil is considered to meet the test requirements. Fine sand, 325 mesh barite powder and 325 mesh bentonite were selected as raw materials for the preparation of model soil, and multiple groups of preparation schemes were designed: then, according to the requirements of similarity ratio, the matching ratio scheme was selected to prepare the model soil.

[0061] (3) Conduct preliminary tests to explore the scope of soil disturbance caused by soil excavation and design a model box that satisfies the boundary effect:

[0062] Preliminary tests were conducted through numerical simulations, and multiple groups of working conditions were set up to simulate the deformation of the pipe curtain, surface settlement and beam strain caused by excavation under different cover-span ratios and different beam spacings. The horizontal boundary condition of the numerical model was set to 2 times the excavation span, and the distance from the excavation hole to the bottom was 1 times the excavation height. The soil body adopted the modified Mohr Coulomb constitutive model, and the pipe curtain, beam and side piles adopted the elastic constitutive model. According to the numerical simulation results, the surface settlement is 0 after the distance from the excavation hole c, which means that the soil body after the distance from the excavation hole c is almost unaffected by the excavation. Based on this, the size of the model box that meets the boundary effect can be determined. The basic structure of the model box is as follows Figure 5 As shown. The model box is made of acrylic organic glass plates on all sides. The thickness of the organic glass plate is m1. The bottom is a steel plate with a thickness of m2. An iron plate is welded on the bottom plate to fix the model side piles. In order to reduce the deformation of the model box during the test, a steel frame is used to fix the outside of the model box. An excavation hole is reserved on the front side of the model box. The size of the excavation hole meets the similarity ratio. The excavation hole is 1 times the excavation height away from the bottom of the model box and c away from both sides of the model box. A rectangular hole is reserved on the back side of the model box. The size meets the requirements for the pipe curtain structure to be placed into the model box through this rectangular hole. The self-stabilizing ability of sand is weak. In order to avoid sudden collapse during excavation, two organic glass plates are connected with bolts for retaining soil. The retaining plate structure is as shown in the figure. Figure 6 As shown in the figure, the plexiglass is rigid enough and will not deform during the excavation process.

[0063] (4) Fill the model soil, place the model structure and data monitoring and acquisition equipment at the set location, and collect test data:

[0064] The model strata are prepared layer by layer using the compaction method. The fill mass for a single filling is calculated based on the theoretical density and the predetermined fill volume of the model box. The calculated soil is then compacted layer by layer with a certain force until it fills the predetermined fill height. Uniform compaction is performed after each filling height, and each layer of model soil is sampled and tested to ensure consistent soil density. During the model soil filling process, side piles, retaining walls, cross supports, a pipe curtain structure, and data monitoring and collection devices are installed. The retaining wall is designed to prevent the sandy soil with weak self-stabilization ability from suddenly collapsing during excavation. It consists of two plexiglass panels connected by bolts. The plexiglass is rigid enough to prevent deformation during excavation. After installation, it is left to stand for at least 24 hours to ensure the stability of similar materials. Finally, the soil is excavated and the test data is collected.

[0065] It should be noted that, in the present invention, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises", or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or includes elements that are inherent to such process, method, article, or apparatus.

[0066] The above embodiments are merely examples of the present invention and do not limit the scope of protection of the present invention. Any designs that are identical or similar to the present invention fall within the scope of protection of the present invention.

Claims

1. A test method for simulating excavation under pipe curtain support in sandy soil strata, characterized in that: The following steps are involved: The physical parameter data of the physical pipe-roof support system are collected, force and length are selected as the basic dimensions, and the exponential equation between the physical parameter data is established using the dimensional matrix method, thereby obtaining the similarity relationship matrix of the physical parameter data; Confirm the similarity ratio between physical parameter data based on the similarity relationship matrix, select similar materials that meet the similarity ratio, and build a similarity model for the tube curtain; Based on the pipe-roof similarity model, multiple sets of numerical simulation pre-experiments are set up to obtain the range of soil disturbance caused by soil excavation, and a numerical set in which the soil is not affected by excavation is selected as the boundary condition of the similarity model; The similar model is prepared in layers by a compaction method and filled into the similar model. At the same time, a data monitoring and acquisition device is set at a set position. After a set rest time, the bottom layer is excavated, and the data monitoring and acquisition device detects and collects similar simulation data; The experimental results of the simulation model of the pipe curtain deformation influence test in the pipe curtain support system are obtained, and the bending stiffness is used as the control condition for the selection of the model pipe curtain material in the simulation model; In the construction of the similar model, the pipe roof structure and the cross support structure are simulated equivalently by bending stiffness; The similarity model construction includes the following steps: Obtain the bending stiffness of the equivalent pipe-roof structure and cross-support structure, select the corresponding material to simulate the pipe-roof, and determine the dimensions of the simulated pipe-roof and cross-support based on the elastic modulus of the material; Preliminary tests were conducted through numerical simulations, with multiple working conditions set up to simulate excavation-induced pipe curtain deformation, ground settlement, and beam strain under different cover-span ratios and beam spacings. The horizontal boundary condition of the similar model is set to be twice the excavation span, and the distance between the excavation hole and the bottom is 1 times the excavation height; the soil of the stratum adopts the modified Mohr-Coulomb constitutive model, and the pipe curtain, beam and side pile adopt the elastic constitutive model.

2. A test method for simulating excavation under pipe-roof support in sandy soil as claimed in claim 1, characterized in that: The physical parameter data include: elastic modulus E, cohesion c, soil internal friction angle Poisson's ratio μ, bulk density γ, stress σ, strain ε, vertical displacement δ, geometric dimension L, load P, and section moment of inertia I.

3. A test method for simulating excavation under pipe-roof support in sandy soil as claimed in claim 2, characterized in that: The method of selecting force and length as basic dimensions and establishing an exponential equation between physical parameter data using a dimensional matrix includes the following steps: Let X1, X2, X3, X4…X11 represent the physical quantities E, c, The exponent of μ…I, force F and length L are selected as basic dimensions; The relationship between physical quantities is established using the dimensional matrix method; An exponential equation is established based on the dimensional matrix to obtain the similarity relationship matrix.

4. A test method for simulating excavation under pipe-roof support in sandy soil as claimed in claim 3, characterized in that: The similarity relationship matrix includes: bulk density similarity ratio, geometric similarity ratio, and then the similarity ratio of physical quantities in the simulation experiment is obtained as follows: C E =C c =C δ =C L =50,C I =504,C P =50 3 Among them, the elastic modulus similarity ratio C E , cohesion similarity ratio C c , similarity ratio of soil internal friction angle Poisson's ratio similarity ratio Cμ, strain similarity ratio Cε, vertical displacement similarity ratio C δ , geometric similarity ratio C L , load similarity ratio C P , similarity ratio of section moment of inertia C I .

5. The test method for simulating excavation under pipe-roof support in sandy soil as claimed in claim 1, characterized in that: The method of preparing the similar model stratum by layer by compaction method comprises the following steps: Based on the similarity ratio, the compression modulus and elastic modulus of the formation soil are determined; The weight of the underlying soil is determined based on the deformation of the pipe roof and the strain of the beam.

6. The test method for simulating excavation in sandy soil under pipe-roof support according to claim 1, characterized in that: The model stratum is prepared in layers by the tamping method, and the fill mass of the filling is calculated according to the theoretical density and the predetermined fill volume of the model box, and then the fill mass is tamped layer by layer until the calculated soil mass just fills the predetermined fill height; Each layer of model soil is sampled and tested to ensure uniform soil density. During the model soil filling process, side piles, retaining boards, cross supports, pipe curtain structures and data monitoring and collection devices are installed; among them, the retaining board is two plexiglass plates that are detachably connected.

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