Model test device for simulating influence of foundation pit excavation unloading on existing subway segment

Abstract

The utility model discloses a model test device for simulating the influence of excavation and unloading of a foundation pit on existing subway segments, which belongs to the technical field of foundation pit excavation machines and comprises a model box and a 3D (three-dimensional) printing shield tunnel model arranged in the model box. The model box comprises detachable supports symmetrically arranged on the two sides and a continuous wall structure arranged between the detachable supports. Two laser displacement meters are arranged on the inner side wall of the 3D printing shield tunnel model, eight surrounding rock pressure meters are evenly arranged on the outer side wall of the 3D printing shield tunnel model, and the 3D printing shield tunnel model is composed of a plurality of shield rings. According to the model test device for simulating the influence of excavation and unloading of the foundation pit on the existing metro segment, the deformation characteristics and the soil pressure distribution rule of a metro shield tunnel under the excavation and unloading effects of the upper foundation pit and the side foundation pit can be tested.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of foundation pit excavation, especially to a model test device for simulating the influence of foundation pit excavation unloading on existing subway segments. BACKGROUND

[0002] With the development of urban rail transit and the exploitation and utilization of underground space, more and more projects of foundation pit excavation near the operating shield tunnel are carried out. The unloading mode caused by the construction of foundation pit excavation has an important influence on the shield tunnel of the subway.

[0003] The existing research results focus on the analysis of the deformation mechanism under the unloading action of the foundation pit, and provide a lot of useful experience for the protection of the subway tunnel during the construction of the foundation pit. However, the existing research results have less research on the distribution law of the earth pressure of the subway tunnel under the unloading action of the foundation pit.

[0004] Based on this, the method of similar material model test is applied to study the deformation characteristics and the distribution law of the earth pressure of the subway shield tunnel under the unloading action of the upper foundation pit and the lateral foundation pit excavation. SUMMARY

[0005] The utility model discloses a model test device for simulating the influence of foundation pit excavation unloading on existing subway segments to solve the problems in the above background.

[0006] To achieve the above object, the utility model provides a model test device for simulating the influence of foundation pit excavation unloading on existing subway segments, which comprises a model box and a 3D printed shield tunnel model arranged in the model box.

[0007] Preferably, the continuous wall structure is filled with soil, and the continuous wall structure is composed of organic plates with a thickness of 5mm which are spliced by glass glue, and the continuous wall structure is a long rectangular structure with an open top and bottom.

[0008] Preferably, the 3D printed shield tunnel model has a length of 420mm, a wall thickness of 7.5mm, an outer diameter of 150mm and an inner diameter of 135mm, and each shield ring has a length of 30mm.

[0009] Preferably, each shield ring comprises six segments, the adjacent segments are connected by bolts, and the bolts are tied by wire.

[0010] Preferably, the surrounding rock pressure gauge adopts a micro soil pressure gauge connected with a uT7116 high-speed static strain gauge for data reading and collection of the micro soil pressure gauge.

[0011] Therefore, the model test device for simulating the influence of foundation pit excavation unloading on existing subway segments can test the deformation characteristics and soil pressure distribution law of a subway shield tunnel under the excavation unloading action of an upper foundation pit and a side foundation pit.

[0012] The technical scheme of the utility model will be further described below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 FIG. 1 is a structural schematic view of a model box of an embodiment of the model test device for simulating the influence of foundation pit excavation unloading on existing subway segments;

[0014] Figure 2 FIG. 4 is a structural schematic view of a shield ring of an embodiment of the model test device for simulating the influence of foundation pit excavation unloading on existing subway segments;

[0015] Figure 3 FIG. 5 is a comparison chart of the collapsible coefficients of an embodiment of the utility model;

[0016] Reference signs: 1, model box; 2, detachable support; 3, continuous wall structure; 4, shield ring; 41, standard block; 42, adjacent block; 43, capping block; 5, bolt. DETAILED DESCRIPTION

[0017] The technical scheme of the utility model will be further described below with reference to the drawings and embodiments.

[0018] Unless otherwise defined, the technical terms or scientific terms used in the utility model should be understood as the usual meanings by those skilled in the art to which the utility model belongs. The terms "first", "second" and similar terms used in the utility model do not represent any order, number or importance, but are only used to distinguish different components. The terms "include" or "contain" and similar terms mean that the elements or objects before the terms cover the elements or objects listed after the terms and their equivalents, without excluding other elements or objects. The terms "connect" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "up", "down", "left", "right" and the like are only used to represent relative positional relationships, which can change accordingly when the absolute positions of the described objects change.

[0019] EMBODIMENT

[0020] The technical solutions in the embodiments of the utility model will be clearly and completely described below with reference to the drawings.

[0021] In the embodiment, a subway foundation pit construction project near a subway line No.9 in a certain city is taken as an engineering background, the line is mainly constructed by a shield method, a staggered joint connection mode is adopted, each ring is assembled by six segments including a capping block 43, an adjoining block 42, a standard block 41, etc., an inner diameter of the assembled shield tunnel is 5.4m, a diameter is 6.0m, a lining segment adopts a 300mm-thick C50 prefabricated concrete segment, a ring width is 1.2m, and M30 bolt connection is adopted at the segment joint.

[0022] According to the similar three theorem (similar positive theorem, π theorem and similar inverse theorem), the following influencing factors are mainly considered when determining the similar coefficient of the test device in the embodiment:

[0023] (1) Actual size of the foundation pit and the shield tunnel engineering prototype and working conditions of the test model box 1;

[0024] (2) Ensure that the soil in the neighborhood range of the shield tunnel and the foundation pit can provide sufficient force for the shield tunnel under the unloading action of the foundation pit excavation, and ensure that the shield tunnel can fully deform;

[0025] (3) Meet the measurement accuracy requirements of the displacement and earth pressure of the 3D printed shield tunnel model.

[0026] Under the above conditions, the related literature of similar model tests is referred to and the test economy and feasibility are considered, finally the geometric similarity ratio C L =40, the elastic modulus ratio C E =40 are selected as the basic similarity ratio, on this basis, the geometric similarity relationship of the remaining variables is derived, and the specific values are shown in Table 1.

[0027] Table 1 Similarity relationship of model test

[0028] Physical quantity Dimension Similarity relation Similarity ratio (prototype / model) Geometric dimension L [C L ]]> 40 Force F C F =C L 2 C γ ]]> 40 2 ]] Specific gravity FL -3 ]]> C γ ]]> 1 Elastic modulus FL -2 ]]> C E ]]> 40 Poisson's ratio 1 C μ ]]> 1 Water content 1 C ω ]]> 1 Stress FL -2 ]]> C σ =C E ]]> 40

[0029] As shown in Figures 1-2 , a model test device for simulating the influence of foundation pit excavation unloading on existing subway segments, comprising a model box 1 and a 3D printed shield tunnel model arranged in the model box 1; the size of the model box 1 is 1.2m*0.6m*0.8m (length* width*height), the material is transparent organic glass, the model box 1 comprises detachable supports 2 symmetrically arranged on both sides and a continuous wall structure arranged between the detachable supports 2; three detachable supports 2 are arranged on each side, and are steel structures to maintain the stability of the model box 1.

[0030] The inside of the continuous wall structure is filled with soil, the continuous wall structure is simulated by organic glass (PMMA) with a thickness of 5 mm, the organic glass is cut according to the size, and then spliced into a long rectangular structure with the top and bottom open by glass glue, the size is 500 mm x 300 mm x 250 mm (length x width x height), and the elastic modulus and geometric similarity ratio are both 40:1, the elastic modulus of the organic glass is 31 MPa, and the Poisson's ratio is 0.3.

[0031] The 3D printed shield tunnel model is modeled by using Catia software, and has a geometric similarity ratio of 1:40, a length of 420 mm, a wall thickness of 7.5 mm, an outer diameter of 150 mm, an inner diameter of 135 mm, and a length of each shield ring 4 of 30 mm. The 3D printed shield tunnel model is composed of a plurality of shield rings 4, each of which includes six segments, which are obtained by 3D printing using ABS plastic, and the elastic modulus of the ABS segments after binding is 0.88 GPa, and the Poisson's ratio is 0.39; adjacent segments are connected by bolts 5, and the bolt 5 connection is connected by lashing; the six segments include one capping block 43, two abutting blocks 42 and three standard blocks 41.

[0032] Two laser displacement meters are arranged on the inner side wall of the 3D printed shield tunnel model, the model of the displacement meter is GFL-Z100N-RS485, the appearance size is 45.9 mm x 30 mm x 21 mm, the measurement range of the displacement meter is 65 mm-135 mm, the measurement accuracy is 70 μm, the resolution accuracy is ±0.1% (F.S.), which can meet the requirements of test accuracy; eight surrounding rock pressure gauges are uniformly arranged on the outer side wall of the 3D printed shield tunnel model, a miniature soil pressure gauge is used, the model is TYC type, the diameter of the soil pressure gauge is 28 mm, the thickness is 10 mm, and the range is 20 kPa; the miniature soil pressure gauge is connected with a uT7116 type high-speed static strain meter, which is used for data reading and collection of the miniature soil pressure gauge.

[0033] The similar soil is prepared by using four materials of remolded soil, CaO powder, industrial salt and gypsum powder obtained from the project site, wherein the remolded soil and gypsum powder are used as aggregate and adhesive, the CaO powder simulates the structure of the retaining soil, and the industrial salt simulates the collapsibility of the retaining soil. Under the conditions of density of 1.5 g / cm 3 , and water content of 14%, three different samples with industrial salt percentage content of 0%, 4% and 10% (gypsum powder ratio is 2%, and CaO ratio is 6%) are prepared for compression test, and the test results are shown in Figure 3 . Finally, the test of gypsum powder 2%, CaO 6%, industrial salt 4% and remolded soil 88% is selected as the soil similar material of the model test.

[0034] The shield tunnel and the surrounding soil body jointly experience three stress field changes: ① After the tunnel construction is completed (the underground continuous wall is pre-embedded), the surrounding soil body gradually reaches stability with the consolidation settlement, and the process is realized by model standing. ② The foundation pit is excavated and unloaded, and the shovel is used for uniform excavation, and the scale of foundation pit maintenance is observed after each excavation to prevent over-excavation; the process is composed of three excavations, and the total excavation depth is 0.3 m, and the average specific gravity of the soil body is about 20.73 kN / m 3 , the unloading amount is 20.73 kN / m 3 * 0.3 m = 6.22 kPa. ③ After the construction is completed, the tunnel and the surrounding soil body reach the stable state again, and the process is still realized by model standing. The specific construction steps are shown in the following table 2:

[0035] Table 2 Model test flow table

[0036]

[0037] In order to explore the influence of the two working conditions of the side foundation pit and the upper foundation pit on the existing tunnel, a total of 33 tests are performed. The tunnel crown depth is fixed at 0.4 m, the foundation pit width above the tunnel is designed as B = 0.3 m, 0.5 m; the foundation pit width of the side foundation pit is designed as: B = 0.2 m, 0.3 m, 0.5 m; the horizontal net spacing between the foundation pit and the tunnel is designed as: S x = 0.5D, 1D, 1.5D (D is the tunnel diameter, 0.15 m); the foundation pit excavation depth is: h = 0.1 m, 0.2 m, 0.3 m. The model schematic diagram and the specific test scheme are shown in the following figure and table 3:

[0038] Table 3 Model test scheme table

[0039]

[0040]

[0041] Through the test setting of the embodiment, the rationality of the test device of the embodiment can be proved.

[0042] Therefore, the model test device for simulating the influence of foundation pit excavation unloading on existing subway segments adopts the above structure, and can test the deformation characteristics and soil pressure distribution law of the subway shield tunnel under the excavation unloading of the upper foundation pit and the side foundation pit.

[0043] It should be pointed out finally that: the above examples are only used to illustrate the technical solutions of the utility model and not to limit them, although the utility model has been explained in detail with reference to the preferred embodiments, ordinary skilled in the art should understand that: its still can modify or equivalent replace the technical solutions of the utility model, and these modifications or equivalent replacements also can not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the utility model.

Claims

1. A model test device for simulating the influence of foundation pit excavation unloading on existing subway segments, characterized in that: The model box comprises detachable supports symmetrically arranged on both sides and a continuous wall structure arranged between the detachable supports; two laser displacement meters are arranged on the inner side wall of the 3D printed shield tunnel model; eight surrounding rock pressure gauges are uniformly arranged on the outer side wall of the 3D printed shield tunnel model; and the 3D printed shield tunnel model is composed of a plurality of shield rings.

2. The model test device for simulating the influence of foundation pit excavation unloading on existing subway segments according to claim 1, characterized in that: The continuous wall structure is filled with soil, and is a long rectangular structure with the top and bottom being open, and is formed by splicing organic plates with a thickness of 5mm through glass glue.

3. The model test device for simulating the influence of foundation pit excavation unloading on existing subway segments according to claim 1, characterized in that: The 3D printed shield tunnel model has a length of 420mm, a wall thickness of 7.5mm, an outer diameter of 150mm and an inner diameter of 135mm, and each shield ring has a length of 30mm.

4. The model test device for simulating the influence of foundation pit excavation unloading on existing subway segments according to claim 1, characterized in that: Each shield ring comprises six segments, adjacent segments are connected through bolts, and the bolt connection adopts wire binding; the six segments comprise one top-sealing segment, two abutting segments and three standard segments.

5. The model test device for simulating the influence of foundation pit excavation unloading on existing subway segments according to claim 1, characterized in that: The surrounding rock pressure gauges adopt micro soil pressure gauges, and the micro soil pressure gauges are connected with uT7116 high-speed static strain gauges for data reading and collection of the micro soil pressure gauges.

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