Loose and soft stratum film bag pile advance support device and support parameter calculation method

Abstract

The invention discloses a loose and soft stratum film bag pile advance support device and a support parameter calculation method. The device comprises a flexible film bag, a pipe shed steel pipe and a grouting pipe. Wherein the multiple flexible film bags are sequentially arranged on the outer side wall of the pipe shed steel pipe in a sleeving mode in the length direction of the pipe shed steel pipe, and the two ends of each flexible film bag are fixedly connected with the pipe shed steel pipe in a sealed mode through binding pieces. An inner cavity of each flexible film bag communicates with one end of the corresponding grouting pipe, and the other end of each grouting pipe is located outside the corresponding flexible film bag. Oriented filling of grout is achieved by grouting the flexible film bags bound on the steel pipes, so that the stratum is compacted and reinforced after expansion of the flexible film bags, a continuous arch shell structure is formed, and the reinforcing effect is obviously superior to that of a traditional advanced small guide pipe; the problems of uncontrollable grouting diffusion, poor reinforcement continuity and the like existing in a traditional advanced support technology are solved, and the problem of grout leakage in a traditional pipe roof method is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and particularly to a membrane bag pile advanced support device and a support parameter calculation method for loose and soft strata. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily to be regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] In tunnel construction, loose and soft strata (such as sandy soil, soft clay, silty soil, etc.) widely exist. Especially in shallow tunnels of urban subway construction, the stability of the strata is crucial for engineering safety. Loose and soft strata usually show loose particles, unstable structure, low shear strength, and are often accompanied by characteristics such as high water content and rich groundwater, resulting in engineering accidents such as collapse, settlement, and water inrush extremely easily during the tunnel excavation process, posing a serious threat to construction safety.

[0004] The existing pipe shed support and advanced small duct grouting technologies recommended by the current "Tunnel Design Code" have the following limitations in loose and soft strata: In pipe shed support, the grouting body between the steel pipe and the strata has poor grouting adhesion due to insufficient interface roughness, and serious slurry leakage occurs, making it difficult to form a continuous reinforced body. Although the advanced small duct can reinforce the soil in the short term through grouting, its grouting range is significantly restricted by the permeability of the strata. The slurry diffuses disorderly in the loose strata, resulting in insufficient reinforcement uniformity. The lack of synergy between the ducts makes the overall shear strength of the reinforced area low, and inaccurate control of the grouting pressure is likely to cause formation splitting or material waste. Especially when reinforcing soft and loose strata, engineering risks such as excessive settlement of the arch crown and failure of the support structure are likely to occur. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a membrane bag pile advanced support device and a support parameter calculation method for loose and soft strata. By grouting into the flexible membrane bag tied to the steel pipe, the slurry is filled directionally, and then the strata is compacted and reinforced by the expansion of the flexible membrane bag, forming a continuous arch shell structure, which is significantly superior to the reinforcement effect of the traditional advanced small duct. It not only overcomes the problems of uncontrollable grouting diffusion and poor reinforcement continuity existing in the traditional advanced support technology, but also avoids the slurry leakage problem in the traditional pipe shed method. Specifically, the technical solutions of the present invention are as follows.

[0006] First, the present invention discloses an advanced support device for membrane bag piles in loose and soft strata, including: a flexible membrane bag, a pipe-roof steel pipe, and a grouting pipe. Among them: a plurality of the flexible membrane bags are sequentially sleeved on the outer sidewall of the pipe-roof steel pipe along the length direction of the pipe-roof steel pipe, and both ends of each flexible membrane bag are hermetically and fixedly connected to the pipe-roof steel pipe through lashing members. The inner cavity of each flexible membrane bag is communicated with one end of a grouting pipe, and the grouting pipe is distributed along the length direction of the pipe-roof steel pipe and fixed on its outer sidewall, and the other end of the grouting pipe is located outside the flexible membrane bag.

[0007] Further, the length of the grouting pipe corresponding to the flexible membrane bag closer to the tail end of the pipe-roof steel pipe is longer, and the grouting pipe sequentially passes through each flexible membrane bag before the tail-end flexible membrane bag, but is not communicated with the inner cavities of these flexible membrane bags.

[0008] Further, the outer diameter d of the pipe-roof steel pipe is 80 - 150 mm, and the wall thickness δ ≥ 6 mm. Optionally, the outer diameter of the grouting pipe is 30 - 40 mm, and the wall thickness is 3 - 5 mm.

[0009] Further, the distance between adjacent flexible membrane bags is not greater than 20 cm. Optionally, the diameter of the flexible membrane bag does not exceed 400 mm.

[0010] Further, the sidewall of the part of the grouting pipe located in the flexible membrane bag has grouting holes. Optionally, the diameter of the grouting holes is 10 - 20 mm.

[0011] Secondly, the present invention discloses a calculation method for the support parameters of the advanced support device for membrane bag piles in loose and soft strata, including the following steps:

[0012] (1) Obtain the initial formation parameter information of the loose and soft strata, and then preliminarily determine the drilling radius R0, the expansion radius R u of the membrane bag pile, and the membrane bag pile spacing D for later use.

[0013] (2) Obtain the functional relationship e = f(σ) of the change of the void ratio e under different compressive stresses σ n of the loose and soft strata. Then measure the quantitative mapping relationship between the void ratio e and the elastic modulus E, cohesion C, and internal friction angle of the loose and soft strata, and establish the void ratio control equations E = f(e), C = f(e), for later use.

[0014] (3) According to the parameter information in step (1) and the drilling radius R0, the expansion radius R u of the membrane bag pile, calculate the formation compaction stress distribution equation σ u corresponding to the expansion radius R r (r) of the membrane bag pile.

[0015] (4) According to the σ r (r) in step (3), and combined with the e = f(σ) in step (2), calculate the spatial distribution equation e r (r) = f(σ r (r)) of the void ratio of the compacted formation, and then substitute this spatial distribution equation into the E = f(e), C = f(e), one by one to obtain the spatial distribution equations E(r), c(r), of the elastic modulus E, cohesion C, and internal friction angle for backup.

[0016] (5) Since the composite reinforcement formed by the membrane bag pile advanced support device in the loose and soft formation consists of three parts: the pipe shed steel pipe, the slurry in the flexible membrane bag, and the compacted soil around it. Therefore, the mechanical parameters of the composite reinforcement are calculated by the area weighted average method of the reinforcement area.

[0017] (6) Then, according to the mechanical parameters of the composite reinforcement in step (5), calculate the stability of the object to be reinforced under the composite reinforcement, check whether there is a plastic zone, and whether the indexes such as crown settlement and horizontal convergence meet the specifications. Once there is a situation where one or several indexes exceed the limit, adjust the expansion radius R u of the membrane bag pile and the membrane bag pile spacing D, and then repeat steps (2) to (6) until all the calculated indexes meet the specification requirements. At this time, the expansion radius R u of the membrane bag pile and the membrane bag pile spacing D are used as the reference basis for the support parameters during actual construction in the project.

[0018] Furthermore, in step (1), the initial formation parameter information includes: initial void ratio e0, initial elastic modulus E, shear modulus G, initial cohesion C, initial internal friction angle initial in-situ stress σ0. Optionally, this parameter information can be obtained through geological exploration and laboratory tests.

[0019] Furthermore, in step (1), the methods for the borehole radius R0, the expansion radius R u of the membrane bag pile, and the membrane bag pile spacing D are as follows: The borehole radius R0 is not less than 1.2 times the total outer diameter of the pipe shed steel pipe and the grouting pipe to ensure smooth installation. The expansion radius R u of the membrane bag pile and the membrane bag pile spacing D are initially determined according to the Technical Specification for Compaction Grouting Piles (T / CWEA 5 - 2018).

[0020] Furthermore, in step (2), the E = f(e), C = f(e), equation curves are obtained through fitting analysis of the data from indoor oedometer compression tests.

[0021] Further, in step (3), the formation compaction stress distribution equation σ r (r) is calculated according to formulas (1) and (2):

[0022]

[0023] In formulas (1) and (2), r is the radial distance from the center of the pipe shed steel pipe, e0 is the initial void ratio, E is the initial elastic modulus, G is the initial shear modulus, C is the initial cohesion, is the initial internal friction angle, σ0 is the initial in-situ stress, and P u is the maximum reaming pressure.

[0024] Further, in step (5), the calculation method for the mechanical parameters of the composite reinforced body includes:

[0025] (i) Calculate the elastic modulus E1, cohesion C1, and internal friction angle of the compacted soil which are respectively calculated using the following formulas (3), (4), (5), and combined with the spatial distribution equations E(r), c(r) in step (4), for calculation:

[0026]

[0027]

[0028] In the above formulas (3), (4), (5), D is the membrane bag pile spacing, R u is the expansion radius of the membrane bag pile, d is the outer diameter of the pipe shed steel pipe, and similarly, r is the radial distance from the center of the pipe shed steel pipe.

[0029] (ii) Calculate the area S1 of the pipe shed steel pipe, the area S2 of the hardened slurry inside the flexible membrane bag, and the area S3 of the compacted soil within the range of the spacing D of a single membrane bag pile, which are respectively calculated using the following formulas (6), (7), (8):

[0030]

[0031] S2 = πRu 2 - S1 (7);

[0032] S3 = D 2 - S2 (8).

[0033] In the above formulas (6), (7), (8), d is the outer diameter of the pipe shed steel pipe; δ is the wall thickness of the pipe shed steel pipe; D is the membrane bag pile spacing, and R u is the expansion radius of the membrane bag pile.

[0034] (iii) Measure the elastic modulus E2, cohesion C2, and internal friction angle of the pipe-roof steel pipe Measure the elastic modulus E3, cohesion C3, and internal friction angle of the hardened slurry in the flexible membrane bag Then, calculate the mechanical parameters of the composite reinforced body according to the following formulas (9), (10), and (11), including: the elastic modulus E of the composite reinforced body n , the cohesion C of the composite reinforced body n , and the internal friction angle of the composite reinforced body

[0035]

[0036] Furthermore, in step (5), the evaluation of whether the stability meets the requirements includes: whether there is a plastic zone obtained according to the "Code for Design of Highway Tunnels" (JTG 3370.1-2018), whether the crown settlement meets the requirements obtained according to the "Code for Construction Technology of Highway Tunnels" (JTG / T 3660-2020), and whether the horizontal convergence meets the requirements obtained according to the "Code for Design of Highway Tunnels" (JTG 3370.1-2018).

[0037] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0038] (1) Aiming at the deficiencies of the existing pipe-roof support and advanced small pipe grouting technologies in loose and soft strata, the present invention first uses the proposed new membrane bag pile advanced support device to reinforce the loose and soft strata. Thus, the expansion body formed by the slurry injected into the flexible membrane bag squeezes the surrounding loose and soft strata, enabling the weak and loose strata to reconstruct the particle skeleton under the extrusion, forming a high-density circumferential compaction zone, and enhancing the shear strength through the interlocking action of soil particles. Coupled with the reinforced body formed by the hardened slurry in the flexible membrane bag and the reinforced body formed by the pipe-roof steel pipe and the grouting pipe fixed on its outer wall, a multi-layer nested composite reinforcement system with continuous spatial stress connection is constructed in the loose and soft strata. By utilizing the synergy of soil transformation and structural support, the elastic modulus and shear strength of the strata are significantly improved. In addition, the constraint of the flexible membrane bag on the slurry effectively inhibits the slurry seepage, enhances the interface bonding strength, and overcomes the defect of easy structural debonding in traditional pipe-roof support.

[0039] (2) Based on the above new membrane bag pile advanced support device as a means of strengthening loose and soft strata, the present invention proposes a calculation method for the matching support parameters, realizing the quantitative calculation of the technological parameters of the membrane bag pile advanced support for tunnel loose and soft strata. Thus, during the grouting process, the diffusion range of the grout can be effectively controlled, avoiding problems such as waste caused by the disorderly diffusion of the grout in the strata and uneven support effects, and ensuring the support effect. The experimental results show that after adopting the support parameters calculated by the method of the present invention, the grout retention rate in the target reinforcement area reaches 100%, greatly improving the utilization rate of the grout. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The attached drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0041] Figure 1 It is a schematic structural diagram of the support device before the membrane bag expands in the following embodiments.

[0042] Figure 2 It is a schematic structural diagram of the support device after the membrane bag expands in the following embodiments.

[0043] Figure 3 It is a schematic diagram of the membrane bag pile advanced support device in the working state in the following embodiments.

[0044] Figure 4 It is a simplified diagram of the soil extrusion stress based on the cavity expansion theory in the following embodiments.

[0045] Figure 5 It is a schematic diagram of the equivalent calculation principle of the composite reinforcement area in the following embodiments.

[0046] Figure 6 It is a curve of the change in the void ratio of the strata under different compressive stresses in the following embodiments.

[0047] Figure 7 It is a curve of the change in the elastic modulus under different void ratios in the following embodiments.

[0048] Figure 8 It is a curve of the change in cohesion and internal friction angle under different void ratios in the following embodiments.

[0049] Figure 9 It is a curve of the compaction stress distribution of the membrane bag pile in the following embodiments.

[0050] The above-mentioned Figures 1 to 5 The numerical marks in the figures respectively represent: 1 - flexible membrane bag, 2 - pipe roof steel pipe, 3 - grouting pipe, 4 - binding piece, 5 - grouting hole, 6 - tunnel, 7 - loose and soft strata, 8 - compaction reinforcement area, 9 - membrane bag pile advanced support device. DETAILED DESCRIPTION OF THE INVENTION

[0051] It should be noted that the following detailed description is illustrative and aims to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0052] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0053] For the convenience of description, if the words "upper", "lower", "left", and "right" appear in the present invention, they only indicate the same directions as the upper, lower, left, and right of the accompanying drawings themselves, and do not limit the structure. They are only for facilitating the description of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to needs to have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0054] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments for a pre-support device for film bag piles in loose and soft strata and a calculation method for support parameters.

[0055] Refer to Figure 1 and Figure 2, An example of an advanced support device for membrane bag piles in loose and soft strata includes: a flexible membrane bag 1, a pipe-roof steel pipe 2, and a grouting pipe 3. Specifically: The flexible membrane bag 1 can be a reel-type nylon fiber bag with open ends at both ends. It is sleeved on the pipe-roof steel pipe 2, and both ends of the flexible membrane bag 1 are hermetically and fixedly connected to the pipe-roof steel pipe 2 and the grouting pipe 3 through binding members 4 (such as steel wires, etc.). A number of flexible membrane bags 1 are sequentially sleeved along the length direction of the pipe-roof steel pipe 2, and the distance between adjacent flexible membrane bags 1 is not greater than 20 cm, such as 5 cm, 10 cm, 15 cm, 20 cm, etc. The inner cavity of each flexible membrane bag 1 is communicated with one end of a grouting pipe 3, and the grouting pipe 3 is distributed along the length direction of the pipe-roof steel pipe 2 and fixed on its outer side wall. The length of the grouting pipe corresponding to the flexible membrane bag 1 closer to the tail end of the pipe-roof steel pipe 2 is longer, and the grouting pipe 3 sequentially passes through each flexible membrane bag 1 before the flexible membrane bag 1 at the tail end, but is not communicated with the inner cavities of these flexible membrane bags 1. The other end of the grouting pipe 3 is located outside the flexible membrane bag 1 so as to be connected to a grouting pump for grouting. After the slurry enters the flexible membrane bag 1 from the port of the grouting pipe 3, it causes the flexible membrane bag 1 to expand. The outer diameter d of the pipe-roof steel pipe 2 can be arbitrarily selected between 80 and 150 mm, and the wall thickness δ ≥ 6 mm. The outer diameter of the grouting pipe 3 can be arbitrarily selected between 30 and 40 mm, and the wall thickness can be arbitrarily selected between 3 and 5 mm. Flexible membrane bags 1, pipe-roof steel pipes 2, and grouting pipes 3 with other size specifications can also be selected according to actual needs.

[0056] In another embodiment, referring to Figure 1 and Figure 2 , the side wall of the part of the grouting pipe 3 of the advanced support device for membrane bag piles in the above embodiment located in the flexible membrane bag 1 has grouting holes 5 to increase the grouting efficiency. The diameter of the grouting holes 5 can be arbitrarily selected between 10 and 20 mm, such as 10 cm, 15 cm, 20 cm, etc.

[0057] Referring to Figure 3, when using the above-mentioned membrane bag pile advanced support device 9 of this embodiment to reinforce the loose and soft stratum 7 of the tunnel 6, first, the expansive body formed by the slurry injected into the flexible membrane bag 1 is used to extrude the surrounding loose and soft stratum to form a compaction reinforcement zone 8, so that the soft and loose stratum reconstructs the particle skeleton under the extrusion, forms a circumferential compaction zone with high density, and enhances the shear strength through the interlocking action of soil particles, and the transformation of the soil body is realized by the above actions. Coupled with the solidified body formed by the slurry in the flexible membrane bag 1 and the solidified body formed by the pipe-roof steel pipe 2 and the grouting pipe 3 fixed on its outer wall, a multi-layer nested composite reinforcement system with continuous spatial stress connection is constructed in the loose and soft stratum 7, and the elastic modulus and shear strength of the stratum are significantly improved by the coordination of soil body transformation and structural support. In addition, the leakage of the slurry is effectively inhibited by the restraint of the flexible membrane bag 1 on the slurry, the interfacial bonding strength is improved, and the defect of easy structural debonding in the traditional pipe-roof support is overcome.

[0058] Based on the above-mentioned membrane bag pile advanced support device 9 specifically for reinforcing the loose and soft stratum in the example of this embodiment, this embodiment exemplifies a quantitative calculation method for the advanced support process parameters matching it, so as to provide a scientific basis for the actual grouting construction of the project, accurately control the slurry diffusion range, avoid the waste and uneven support effect caused by the disordered diffusion of the slurry in the stratum, and ensure the support effect. Specifically, in this embodiment: the diameter of the flexible membrane bag 1 is 400 mm, the length is 1200 mm, the outer diameter of the pipe-roof steel pipe 2 is 108 mm, the wall thickness is 6 mm, the outer diameter of the grouting pipe 3 is 32 mm, and the wall thickness is 4 mm. The last flexible membrane bag 1 is sleeved at a position 0.5 m from the bottom end of the pipe-roof steel pipe 2, and the distance between adjacent membrane bags is 0.1 m. The grouting material uses cement-sodium silicate double-fluid slurry, the double-fluid volume ratio of the cement slurry to the sodium silicate slurry is 3:1, the sodium silicate modulus is 2.4, and the on-site slurry parameters are optimized and adjusted according to the effect. The buried depth of the tunnel 6 arch is 14 m, the upper boundary of the loose and soft clay stratum 7 is 3 m away from the tunnel 6 arch, and the lower boundary is below the tunnel 6 arch and 1 m away from the tunnel 6 arch. The calculation method includes the following steps:

[0059] (1) Through geological exploration and laboratory tests, the stratum characteristics of the loose and soft stratum section 7 are obtained, and the initial stratum parameter information is obtained, including: the initial void ratio e0 = 0.876, the initial elastic modulus E = 7.2 MPa, the shear modulus G = 2.7 MPa, the initial cohesion C = 34.2 KPa, the initial internal friction angle The initial in-situ stress σ0 = 129.1 Kpa. Then, based on this parameter information, it is preliminarily determined that: the drilling radius R0 is 100 mm, which is convenient for the membrane bag pile advanced support device to smoothly enter the drilling, and the expansion radius R of the membrane bag pileu The spacing D between the membrane bag piles is initially determined as R according to Sections 3.2.3 and 3.2.4 of the Technical Specification for Compaction Grouting Piles (T / CWEA 5-2018). u R = 0.2 m, D = 0.8 m, for backup use.

[0060] (2) Measure the variation curve of the void ratio e of the loose and soft formation under different compressive stresses σ n through an indoor confined compression test. Use data analysis software to perform non-linear fitting on the curve, ensuring that the fitting determination coefficient is above 0.95, and obtain the functional relationship e = f(σ) = -0.035σ n + 0.892 for the variation of the void ratio e of the loose and soft formation under different compressive stresses σ 0.344 At the same time, measure the quantitative mapping relationship between the void ratio e and the mechanical parameters of the loose and soft formation (including the elastic modulus E, cohesion C, and internal friction angle ) of the loose and soft formation, and establish a void ratio control equation: elastic modulus E = f(e) = 0.578e -5.075 + 5.717, cohesion C = f(e) = 7.555e -2.477 + 25.229, internal friction angle are respectively as shown in Figure 6 , Figure 7 and Figure 8 .

[0061] (3) According to the initial formation parameter information, borehole radius R0, and membrane bag pile expansion radius R u in step (1), calculate the formation compaction stress distribution equation σ u (r) corresponding to the membrane bag pile expansion radius R according to the following equations (1) and (2). The compaction stress sketch is shown in r , and the result is: σ Figure 4 (r) = 238.25r r - 12.692, as shown in -0.548 . Figure 9 .

[0062]

[0063] In equations (1) and (2), r is the radial distance from the center of the pipe roof steel pipe, e0 is the initial void ratio, E is the initial elastic modulus, G is the shear modulus, C is the initial cohesion, is the initial internal friction angle, σ0 is the initial ground stress, and the P u is the maximum hole expansion pressure.

[0064] (4) Substitute the σ rSubstitute (r) as a variable into the equation e = f(σ) in step (2) to calculate the spatial distribution equation e of the void ratio of the compacted formation r (r) = f(σ r (r)), and the result is: e r (r) = f(σ r (r)) = 0.356r 0.242 + 0.367. Then, take this e r (r) as a variable and substitute it into the E = f(e) and C = f(e) in step (2) respectively, to obtain the spatial distribution equations of the elastic modulus E, the cohesion C, and the internal friction angle E(r) = 3.507r -0.495 + 5.175, c(r) = 18.667r -0.222 + 23.415, reserved.

[0065] (5) Since the composite reinforced body formed by the membrane bag pile advanced support device in the loose and soft formation consists of three parts: the pipe shed steel pipe 2, the slurry in the flexible membrane bag 1, and the compacted soil around it. Therefore, the mechanical parameters of the composite reinforced body are calculated by the area weighted average method of the reinforcement area. The schematic diagram of the calculation principle is shown in Figure 5 . Specifically, it includes the following steps. The calculation methods of the mechanical parameters of the composite reinforced body include:

[0066] (i) Calculate the elastic modulus E1, cohesion C1, and internal friction angle of the compacted soil, which are respectively calculated by the following formulas (3), (4), (5) and combined with the spatial distribution equations E(r), c(r), in step (4):

[0067]

[0068]

[0069] In the above formulas (3), (4), and (5), D is the spacing of the membrane bag piles, R u is the expansion radius of the membrane bag piles, d is the outer diameter of the pipe shed steel pipe 2, and r is the radial distance from the center of the pipe shed steel pipe. The results are: the elastic modulus E1 = 15.4 MPa, the internal friction angle and the cohesion C1 = 44.7 MPa.

[0070] (ii) Calculate the area S1 of the pipe shed area formed by the pipe shed steel pipe 2 within the spacing D of a single membrane bag pile, the area S2 of the hardened slurry in the flexible membrane bag 1, and the area S3 of the compacted soil, which are calculated by the following formulas (6), (7), and (8) respectively:

[0071]

[0072] S2 = πRu 2 - S1 (7);

[0073] S3 = D 2 - S2 (8).

[0074] In the above formulas (6), (7), and (8), d is the outer diameter of the pipe-roof steel pipe; δ is the wall thickness of the pipe-roof steel pipe; D is the spacing of the membrane bag piles, and R u is the expansion radius of the membrane bag pile. The results are: S1 = 0.0019 m 2 , S2 = 0.1237 m 2 , S3 = 0.5136 m 2 .

[0075] (iii) The elastic modulus E of the pipe-roof steel pipe 2 is measured by the indoor tensile test of metal materials at room temperature and the improved triaxial compression test to be E = 2.1×10 5 MPa, and the internal friction angle cohesion C = 5 MPa. The elastic modulus E of the hardened slurry in the flexible membrane bag 1 is measured by the uniaxial compression deformation test of a cylinder and the improved triaxial compression test to be E = 3.5×10 4 MPa, the internal friction angle is 30°, and the cohesion c is 0.15 MPa.

[0076] (iv) Combining the calculation results in step (iii), calculate the mechanical parameters of the composite reinforcement body according to the following formulas (9), (10), and (11), including: the elastic modulus E n of the composite reinforcement body, the cohesion C n of the composite reinforcement body, and the internal friction angle

[0077]

[0078] The calculation results are: the elastic modulus E n of the composite reinforcement body = 6820.8 MPa, the cohesion C n of the composite reinforcement body = 35.92 MPa, and the internal friction angle

[0079] (6) Then, calculate whether the stability of the tunnel under the composite reinforcement body meets the requirements according to the mechanical parameters of the composite reinforcement body in step (5), including: whether there is a plastic zone obtained according to the "Highway Tunnel Design Code" (JTG 3370.1-2018), whether the crown settlement meets the requirements obtained according to the "Highway Tunnel Construction Technology Code" (JTG / T 3660-2020), and whether the horizontal convergence meets the requirements obtained according to the "Highway Tunnel Design Code" (JTG 3370.1-2018).

[0080] The results show that: there is no plastic zone, and both the crown settlement and the horizontal convergence meet the code requirements, and the expansion radius of the membrane bag and the pile spacing are reasonably designed. In addition, the experimental results show that: after adopting the support parameters calculated by the above method, the slurry retention rate in the target reinforcement area reaches 100%, greatly improving the slurry utilization rate.

[0081] It should be noted that if the verification results in step (6) show that there are one or more indicators exceeding the limit, then adjust the expansion radius R of the membrane bag pile u , the membrane bag pile spacing D, and then repeat steps (2) to (6) until all the calculated indicators meet the code requirements. At this time, the expansion radius R of the membrane bag pile u , the membrane bag pile spacing D are used as the reference basis for the support parameters during actual construction in the project.

[0082] Finally, it should be noted that any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention. Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A film bag pile advanced support device for loose and soft strata, characterized in that, Comprising: Pipe-roof steel pipes; Flexible membrane bags, a plurality of which are sequentially sleeved on the outer side wall along the length direction of the pipe-roof steel pipes, and both ends of each flexible membrane bag are hermetically and fixedly connected to the pipe-roof steel pipes through tying members; Grouting pipes, the inner cavity of each flexible membrane bag is communicated with one end of a grouting pipe, and the grouting pipes are distributed along the length direction of the pipe-roof steel pipes and fixed on the outer side wall thereof, and the other ends of the grouting pipes are located outside the flexible membrane bags.

2. The pre-support device for film bag piles in loose and soft strata according to claim 1, wherein, The length of the grouting pipe corresponding to the flexible membrane bag closer to the tail end of the pipe-roof steel pipe is longer, and the grouting pipe sequentially passes through each flexible membrane bag before the tail-end flexible membrane bag, but is not communicated with the inner cavities of these flexible membrane bags.

3. The pre-support device for film bag piles in loose and soft strata according to claim 1 or 2, characterized in that, The outer diameter d of the pipe-roof steel pipe is 80 - 150 mm, and the wall thickness δ ≥ 6 mm; Optionally, the outer diameter of the grouting pipe is 30 - 40 mm, and the wall thickness is 3 - 5 mm; Optionally, the distance between adjacent flexible membrane bags is not greater than 20 cm; Optionally, the diameter of the flexible membrane bag does not exceed 400 mm; Optionally, the side wall of the part of the grouting pipe located in the flexible membrane bag has grouting holes; Optionally, the diameter of the grouting holes is 10 - 20 mm.

4. The support parameter calculation method of the loose and soft stratum membrane bag pile advanced support device according to any one of claims 1-3, characterized in that Comprising the following steps: (1) Obtain the initial formation parameter information of the loose and soft formation, and then preliminarily determine the borehole radius R0, the expansion radius R of the membrane bag pile, u and the spacing D of the membrane bag piles for backup; (2) Obtain the functional relationship e = f(σ) of the change in void ratio e of the loose and soft formation under different compressive stresses σ; then measure the quantitative mapping relationship between the void ratio e and the elastic modulus E, cohesion C, and internal friction angle n of the loose and soft formation; and establish void ratio control equations E = f(e), C = f(e), for backup. Reserve; (3) According to the parameter information in step (1), the drilling radius R0, and the expansion radius R of the membrane bag pile u Calculate the expansion radius R of the membrane bag pile u The corresponding formation compaction stress distribution equation σ r (r); (4) According to the σ described in step (3) r (r), and combining with the e = f(σ) described in step (2), calculate the spatial distribution equation of the void ratio of the compacted formation e r (r) = f(σ r (r)), and then substitute this spatial distribution equation one by one into the E = f(e), C = f(e), to obtain the spatial distribution equations of the elastic modulus E, cohesion C, and internal friction angle E(r), c(r), for backup; (5) Since the composite reinforcement body formed by the membrane bag pile advanced support device in the loose and soft stratum is composed of three parts: the pipe-roof steel pipe, the slurry in the flexible membrane bag, and the compacted soil around it; Therefore, the mechanical parameters of the composite reinforcement body are calculated by the area weighted average method of the reinforcement area. (6) Then, calculate the stability of the object to be reinforced under the composite solidified body according to the mechanical parameters of the composite solidified body in step (5), check whether there is a plastic zone, and whether the indexes such as vault settlement and horizontal convergence meet the specifications. Once there is a situation where one or several indexes exceed the limit, then adjust the expansion radius R of the membrane bag pile u and the spacing D of the membrane bag piles, and repeat steps (2) to (6) until all the calculated indexes meet the specification requirements. At this time, the expansion radius R of the membrane bag pile u and the spacing D of the membrane bag piles are used as the reference basis for the support parameters during actual construction in the project.

5. The support parameter calculation method according to claim 4, characterized in that In step (1), the initial formation parameter information includes: initial void ratio e0, initial elastic modulus E, shear modulus G, initial cohesion C, and initial internal friction angle initial in-situ stress σ0; optionally, this parameter information can be obtained through geological exploration and laboratory tests.

6. The support parameter calculation method according to claim 5, characterized in that, In step (1), the methods for the drilling radius R0, the expansion radius R of the membrane bag pile u , and the spacing D of the membrane bag piles are as follows: The drilling radius R0 is not less than 1.2 times the total outer diameter of the pipe shed steel pipe and the grouting pipe to ensure smooth installation. The expansion radius R of the membrane bag pile u and the spacing D of the membrane bag piles are preliminarily determined according to the Technical Specification for Compaction Grouting Piles (T / CWEA 5-2018).

7. The support parameter calculation method according to claim 4, characterized in that, In step (2), the E = f(e), C = f(e), The equation curve is obtained by fitting and analyzing the data of the indoor confined compression test.

8. The support parameter calculation method according to claim 5, characterized in that, In step (3), the formation compaction stress distribution equation σ r (r) is calculated according to Equations (1) and (2): In formulas (1) and (2), r is the radial distance from the center of the pipe-roof steel pipe, e0 is the initial void ratio, E is the initial elastic modulus, G is the initial shear modulus, C is the initial cohesion, is the initial internal friction angle, σ0 is the initial in-situ stress, and P u is the maximum reaming pressure.

9. The support parameter calculation method according to claim 4, characterized in that In step (5), the calculation methods of the mechanical parameters of the composite reinforcement body include: (i) Calculate the elastic modulus E1, cohesion C1, and internal friction angle of the compacted soil They respectively adopt the following formulas (3), (4), (5), and combine with the spatial distribution equations E(r), c(r) in step (4), Calculate as follows: In the above formulas (3), (4), and (5), D is the spacing between the membrane bag piles, and R u is the expansion radius of the membrane bag pile, d is the outer diameter of the pipe shed steel pipe 2, and r is the radial distance from the center of the pipe shed steel pipe; (ii) Calculate the area S1 of the pipe-roof area, the area S2 of the hardened slurry in the flexible membrane bag, and the area S3 of the compacted soil within the spacing D of a single membrane bag pile, which are calculated by the following formulas (6), (7), and (8) respectively: S2 = πRu 2 - S1 (7); S3 = D 2 - S2 (8); In the above formulas (6), (7), and (8), d is the outer diameter of the pipe-roof steel pipe; δ is the wall thickness of the pipe-roof steel pipe; D is the spacing of the membrane bag piles, and R u is the expansion radius of the membrane bag pile; (iii) The elastic modulus E2, cohesion C2, and internal friction angle of the pipe-roof steel pipe are measured The elastic modulus E3, cohesion C3, and internal friction angle of the hardened paste in the flexible membrane bag are measured Then, according to the following formulas (9), (10), and (11), the mechanical parameters of the composite reinforcement body are calculated respectively, including: the elastic modulus E of the composite reinforcement body n , the cohesion C of the composite reinforcement body n , and the internal friction angle of the composite reinforcement body 10. The support parameter calculation method according to any one of claims 4-9, characterized in that, In step (5), the evaluation of whether the stability meets the requirements includes: whether there is a plastic zone obtained according to the "Highway Tunnel Design Code" (JTG 3370.1 - 2018), whether the crown settlement meets the requirements obtained according to the "Highway Tunnel Construction Technology Code" (JTG / T 3660 - 2020), and whether the horizontal convergence meets the requirements obtained according to the "Highway Tunnel Design Code" (JTG 3370.1 - 2018).

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