A membrane bag pile advanced support device for loose and weak strata and a method for calculating support parameters.

Abstract

This invention discloses a membrane bag pile pre-support device and a method for calculating support parameters in loose and weak strata. The device includes: flexible membrane bags, pipe roof steel pipes, and grouting pipes. Several flexible membrane bags are sequentially fitted onto the outer wall of the pipe roof steel pipe along its length, and both ends of each flexible membrane bag are sealed and fixed to the pipe roof steel pipe by binding components. The inner cavity of each flexible membrane bag is connected to one end of a grouting pipe, and the other end of the grouting pipe is located outside the flexible membrane bag. This invention achieves directional filling of grout by injecting grout into the flexible membrane bags bound to the steel pipe, thereby utilizing the expansion of the flexible membrane bags to compact and reinforce the strata, forming a continuous arched shell structure. This significantly outperforms the reinforcement effect of traditional pre-support small pipes, overcoming not only the problems of uncontrollable grout diffusion and poor reinforcement continuity in traditional pre-support techniques, but also avoiding the grout seepage problem in the traditional pipe roof method.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to an advanced support device for membrane bag piles in loose and weak strata and a method for calculating support parameters. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In tunnel construction, loose and weak strata (such as sandy soil, soft clay, silty soil, etc.) are widely present, especially in shallow-buried tunnels in urban subway construction, where stratum stability is crucial to project safety. Loose and weak strata are typically characterized by loose particles, unstable structure, low shear strength, and are often accompanied by high water content and abundant groundwater. This makes them highly susceptible to engineering accidents such as collapse, settlement, and water inrush during tunnel excavation, posing a serious threat to construction safety.

[0004] The pipe roof support and advanced small-diameter pipe grouting technology recommended in the current "Tunnel Design Code" have the following limitations in loose and weak strata: In pipe roof support, the insufficient interface roughness between the steel pipe and the stratum leads to poor grout adhesion, severe grout leakage, and difficulty in forming a continuous reinforced body. While advanced small-diameter pipes can reinforce the soil in the short term through grouting, their grouting range is significantly limited by the permeability of the stratum. The disordered diffusion of grout in loose strata results in insufficient reinforcement uniformity. The lack of synergy between pipes leads to low overall shear strength in the reinforced area. Furthermore, inaccurate control of grouting pressure can easily cause stratum splitting or material waste. In particular, when reinforcing weak and loose strata, it can easily lead to engineering risks such as excessive crown settlement and support structure failure. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a membrane bag pile pre-support device and a method for calculating support parameters in loose and weak strata. It achieves directional filling of grout by injecting grout into a flexible membrane bag tied to a steel pipe, thereby utilizing the expansion of the flexible membrane bag to compact and reinforce the strata, forming a continuous arched shell structure. This significantly outperforms the reinforcement effect of traditional pre-support small-diameter pipes, overcoming not only the problems of uncontrollable grout diffusion and poor reinforcement continuity inherent in traditional pre-support techniques, but also avoiding the grout seepage problem in traditional pipe roof methods. Specifically, the technical solution of this invention is as follows.

[0006] First, this invention discloses a pre-support device for membrane bag piles in loose and weak strata, comprising: flexible membrane bags, pipe roof steel pipes, and grouting pipes. Specifically: several flexible membrane bags are sequentially fitted onto the outer wall of the pipe roof steel pipe along its length, and both ends of each flexible membrane bag are sealed and fixedly connected to the pipe roof steel pipe by binding components. The inner cavity of each flexible membrane bag communicates with one end of a grouting pipe, and the grouting pipe is distributed along the length of the pipe roof steel pipe and fixed to its outer wall, with the other end of the grouting pipe located outside the flexible membrane bag.

[0007] Furthermore, 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 passes through each flexible membrane bag before the flexible membrane bag at the tail end in sequence, but does not communicate with the inner cavity of these flexible membrane bags.

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

[0009] Furthermore, the spacing between adjacent flexible film bags is no greater than 20 cm. Optionally, the diameter of the flexible film bag does not exceed 400 mm.

[0010] Furthermore, the portion of the grouting pipe located within the flexible membrane bag has grouting holes on its sidewall. Optionally, the diameter of the grouting holes is 10-20 mm.

[0011] Secondly, this invention discloses a method for calculating the support parameters of the membrane bag pile advanced support device for loose and weak strata, comprising the following steps:

[0012] (1) Obtain initial formation parameter information of loose and weak strata, and then preliminarily determine the borehole radius based on these parameter information. R 0 Expansion radius of membrane bag pile R u Spacing between membrane bag piles D ,spare.

[0013] (2) Obtaining loose and weak strata under different compressive stresses σ n Lower porosity e The changing functional relationship e = f ( σ Then the porosity was measured. e elastic modulus of the loose and weak strata E Cohesion C internal friction angle Quantitative mapping relationship, establishing the void ratio control equationE = f ( e ), C = f ( e ), ,spare.

[0014] (3) Based on the parameter information described in step (1) and the borehole radius R 0 Expansion radius of membrane bag pile R u Calculate the expansion radius of the membrane bag pile R u Corresponding formation compaction stress distribution equation σ r ( r ).

[0015] (4) According to the σ described in step (3) r ( r ), and in conjunction with the steps described in step (2) e = f ( σ )Calculate the spatial distribution equation of the porosity of the compacted formation. e r ( r ) =f ( σ r ( r Then in step (2) E = f ( e ), C = f ( e ), Substituting each value into the spatial distribution equation, we obtain the elastic modulus respectively. E Cohesion C internal friction angle Spatial distribution equation E ( r ), c ( r ), ,spare.

[0016] (5) Since the composite reinforced body formed by the membrane bag pile advanced support device in the loose and weak strata consists of three parts: the steel pipe of the pipe roof, the slurry inside the flexible membrane bag, and the surrounding compacted soil, the mechanical parameters of the composite reinforced body are calculated using the area weighted average method of the reinforced area.

[0017] (6) Then, based on the mechanical parameters of the composite reinforcement body described in step (5), calculate the stability of the reinforced object under the composite reinforcement body, verify whether there is a plastic zone, and whether the indicators such as arch settlement and horizontal convergence meet the specifications. If one or more indicators exceed the limit, then the expansion radius of the membrane bag pile is adjusted. R u Spacing between membrane bag piles D After making adjustments, repeat steps (2) to (6) until all calculated indicators meet the specifications. At this point, the expansion radius of the membrane bag pile is... R u Spacing between membrane bag piles D This serves as a reference for support parameters during actual construction in the project.

[0018] Further, in step (1), the initial formation parameter information includes: initial porosity ratio. e 0 Initial elastic modulus E shear modulus G Initial cohesion C Initial internal friction angle Initial geostress σ 0 Alternatively, this parameter information can be obtained through geological exploration and laboratory testing.

[0019] Further, in step (1), the borehole radius R 0 Expansion radius of membrane bag pile R u Spacing between membrane bag piles D The method is: drilling radius R 0 The expansion radius of the membrane bag pile should be no less than 1.2 times the total outer diameter of the steel pipe and grouting pipe to ensure smooth installation. R u Spacing between membrane bag piles D Preliminary determination based on the Technical Specification for Compacted Grouting Piles (T / CWEA 5-2018).

[0020] Further, in step (2), the E = f ( e ), C = f ( e ), The equation curve was obtained through fitting analysis of indoor lateral compression test data.

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

[0022] (1);

[0023] (2).

[0024] In equations (1) and (2), the... r This is the radial distance from the center of the steel pipe in the pipe shed. e 0 The initial porosity, E For the initial elastic modulus, G For the initial shear modulus, C For the initial cohesion, The initial internal friction angle, σ 0 For the initial ground stress, the P u This is the maximum pore-expanding pressure.

[0025] Furthermore, in step (5), the calculation methods for the various mechanical parameters of the composite reinforcement body include:

[0026] (i) Calculate the elastic modulus of the compacted soil. E 1 Cohesion C 1 internal friction angle They respectively adopt the following equations (3), (4), and (5), and combine them with the spatial distribution equation described in step (4). E ( r ), c ( r ), calculate:

[0027] (3);

[0028] (4);

[0029] (5).

[0030] In the above equations (3), (4), and (5), D The spacing between the membrane bag posts is... R u The expansion radius of the membrane bag pile is [missing information]. d The outer diameter of the steel pipe in the pipe shed is the same as above. r This is the radial distance from the center of the steel pipe in the pipe shed.

[0031] (ii) Calculate the spacing between individual membrane bag posts D steel pipe area of ​​pipe shed within the scope S 1 The area of ​​the hardened slurry inside the flexible membrane bag S 2 The area of ​​the compacted soil S 3 The following formulas (6), (7), and (8) are used for calculation:

[0032] (6);

[0033] (7);

[0034] (8).

[0035] In the above equations (6), (7), and (8), d The outer diameter of the steel pipe in the pipe shed; δ The wall thickness of the steel pipe in the pipe shed; D The spacing between the membrane bag posts is... R u The expansion radius of the membrane bag pile is given.

[0036] (iii) Measure the elastic modulus of the steel pipe of the pipe roof. E 2 Cohesion C 2 internal friction angle The elastic modulus of the hardened slurry inside the flexible membrane bag was measured. E 3 Cohesion C 3 internal friction angle Then, the mechanical parameters of the composite solidified body are calculated according to the following formulas (9), (10), and (11), including the elastic modulus of the composite solidified body. E n Cohesiveness of composite solids C n Internal friction angle of composite reinforced bodies .

[0037] (9);

[0038] (10);

[0039] (11).

[0040] Further, in step (5), the assessment of whether the stability meets the requirements includes: whether there is a plastic zone according to the "Highway Tunnel Design Specification" (JTG 3370.1-2018), whether the crown settlement meets the requirements according to the "Highway Tunnel Construction Technical Specification" (JTG / T 3660-2020), and whether the horizontal convergence meets the requirements according to the "Highway Tunnel Design Specification" (JTG 3370.1-2018).

[0041] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0042] (1) To address the shortcomings of existing pipe roof support and advanced small-diameter pipe grouting technologies in loose and weak strata, this invention first employs a novel membrane bag pile advanced support device to reinforce loose and weak strata. The grout injected into the flexible membrane bag forms an expanding body that compresses the surrounding loose and weak strata, causing the strata to reconstruct a particle skeleton under this compression, forming a high-density circumferential compaction zone. Furthermore, the shear strength is enhanced through soil particle interlocking. In addition, the hardened grout in the flexible membrane bag forms a solidified body, and the pipe roof steel pipe and the grouting pipe fixed to its outer wall also form a solidified body. This creates a multi-layered, nested composite reinforcement system in the loose and weak strata, where stress is spatially continuous. The synergy between soil modification and structural support significantly improves the elastic modulus and shear strength of the strata. Furthermore, the flexible membrane bag effectively restrains grout leakage, improving interfacial bonding strength and overcoming the structural debonding defects common in traditional pipe roof support.

[0043] (2) Based on the above-mentioned novel membrane bag pile advanced support device as a means of reinforcing loose and weak strata, this invention proposes a matching support parameter calculation method, realizing the quantitative calculation of the process parameters of membrane bag pile advanced support in loose and weak strata of tunnels. This effectively controls the grout diffusion range during grouting, avoids waste and uneven support effect caused by disordered diffusion of grout in the strata, and ensures the support effect. Experimental results show that after using the support parameters calculated by the method of this invention, the grout retention rate in the target reinforcement area reaches 100%, which greatly improves the grout utilization rate. Attached Figure Description

[0044] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0045] Figure 1 The following is a schematic diagram of the structure of the support device before the expansion of the membrane bag in the following implementation.

[0046] Figure 2The following is a schematic diagram of the support device structure after the membrane bag expands in the following implementation.

[0047] Figure 3 The following is a schematic diagram of the Lizhong membrane bag pile advanced support device in use.

[0048] Figure 4 The following is a simplified diagram of soil displacement stress based on the circular hole expansion theory in the implementation of the patent.

[0049] Figure 5 The following is a schematic diagram illustrating the equivalent calculation principle of the composite reinforcement zone in the implementation.

[0050] Figure 6 The following are curves showing the variation of formation porosity under different compressive stresses in the following implementation.

[0051] Figure 7 The following are curves showing the change in elastic modulus under different void ratios in the embodiments.

[0052] Figure 8 The following are curves showing the changes in cohesion and internal friction angle under different porosity ratios in the following embodiments.

[0053] Figure 9 The following is a stress distribution curve for the compaction of membrane bag piles.

[0054] The above appendix Figures 1-5 The numbers in the middle represent: 1-flexible membrane bag, 2-steel pipe for pipe roof, 3-grouting pipe, 4-binding component, 5-grouting hole, 6-tunnel, 7-loose and weak stratum, 8-compacting reinforcement zone, and 9-membrane bag pile advanced support device. Detailed Implementation

[0055] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0056] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0057] For ease of description, the words "up," "down," "left," and "right" appearing in this invention only indicate that they are consistent with the up, down, left, and right directions of the accompanying drawings themselves. They do not limit the structure and are merely for the purpose of facilitating the description of this invention and simplifying the description. They do not indicate or imply that the device or component referred to needs to have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0058] The present invention provides a pre-support device for membrane bag piles in loose and weak strata and a method for calculating support parameters, in conjunction with the accompanying drawings and specific embodiments.

[0059] refer to Figure 1 and Figure 2 An example of a pre-support device for membrane bag piles in loose and weak strata is provided, comprising: 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 roll-type nylon fiber bag with open ends, which is fitted onto the pipe roof steel pipe 2, and both ends of the flexible membrane bag 1 are sealed and fixedly connected to the pipe roof steel pipe 2 and the grouting pipe 3 by binding components 4 (such as steel wire). A number of flexible membrane bags 1 are sequentially fitted along the length of the pipe roof steel pipe 2, and the distance between adjacent flexible membrane bags 1 is no more than 20cm, such as 5cm, 10cm, 15cm, 20cm, etc. The inner cavity of each flexible membrane bag 1 is connected to one end of a grouting pipe 3. The grouting pipes 3 are distributed along the length of the pipe roof steel pipe 2 and fixed to its outer wall. The grouting pipes corresponding to the flexible membrane bags 1 closer to the tail end of the pipe roof steel pipe 2 are longer. The grouting pipe 3 passes sequentially through each flexible membrane bag 1 before the tail end, but does not communicate with the inner cavity 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 connect with a grouting pump for grouting. The grout enters the flexible membrane bag 1 from the port of the grouting pipe 3 and expands. The outer diameter of the pipe roof steel pipe 2... d Any thickness between 80 and 150 mm is acceptable. δ ≥6mm. The outer diameter of the grouting pipe 3 can be selected arbitrarily between 30 and 40mm, and the wall thickness can be selected arbitrarily between 3 and 5mm. Other sizes and specifications of flexible membrane bags 1, pipe roof steel pipes 2 and grouting pipes 3 can also be selected according to actual needs.

[0060] In another implementation, refer to Figure 1 and Figure 2 In the above embodiment, the grouting pipe 3 located in the flexible membrane bag 1 has grouting holes 5 on its side wall to increase 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.

[0061] refer to Figure 3When using the membrane bag pile advanced support device 9 described in this embodiment to reinforce the loose and weak stratum 7 of tunnel 6, the grout injected into the flexible membrane bag 1 forms an expanding body that compresses the surrounding loose and weak stratum to form a compaction reinforcement zone 8. This allows the loose and weak stratum to reconstruct its particle skeleton under this compression, forming a high-density circumferential compaction zone. Furthermore, the soil particle interlocking enhances shear strength, thus achieving soil modification. In addition, the hardened grout in the flexible membrane bag 1 forms a reinforced body, and the pipe roof steel pipe 2 and the grouting pipe 3 fixed to its outer wall also form a reinforced body. This creates a multi-layered, nested composite reinforcement system in the loose and weak stratum 7, where stress is spatially continuous. The synergy between soil modification and structural support significantly improves the stratum's elastic modulus and shear strength. Furthermore, the flexible membrane bag 1 effectively restrains grout leakage, improves interfacial bonding strength, and overcomes the structural debonding defects common in traditional pipe roof support systems.

[0062] Based on the membrane bag pile advanced support device 9 specifically designed for reinforcing loose and weak strata as described in the above embodiments, this embodiment illustrates a quantitative calculation method for the advanced support process parameters matched with it. This method provides a scientific basis for the actual grouting construction of the project, enables precise control of the grout diffusion range, avoids waste and uneven support effects caused by disordered grout diffusion in the strata, and ensures the support effect. Specifically, this embodiment uses: the flexible membrane bag 1 has a diameter of 400mm and a length of 1200mm; the outer diameter of the pipe roof steel pipe 2 is 108mm and the wall thickness is 6mm; and the outer diameter of the grouting pipe 3 is 32mm and the wall thickness is 4mm. The last flexible membrane bag 1 is fitted 0.5m from the bottom end of the pipe roof steel pipe 2, and the spacing between adjacent membrane bags is 0.1m. The grouting material is a cement-water glass two-liquid grout, with a cement grout to water glass grout volume ratio of 3:1 and a water glass modulus of 2.4. The on-site grout parameters are optimized and adjusted according to the results. The arch of tunnel 6 is buried at a depth of 14m. The upper boundary of the loose, weak clay layer 7 is 3m from the arch of tunnel 6, and the lower boundary is below the arch of tunnel 6 and 1m from the arch. The calculation method includes the following steps:

[0063] (1) Through geological exploration and laboratory testing, the stratigraphic characteristics of the loose and weak strata section 7 were tested to obtain initial stratigraphic parameter information, including: initial porosity. e 0 =0.876, initial elastic modulus E =7.2MPa, shear modulus G=2.7MPa, initial cohesion C =34.2 kPa, initial internal friction angle =15.5°, initial geostress =129.1 kPa. Based on these parameters, the borehole radius was initially determined. R 0 The diameter is 100mm, which facilitates the smooth entry of the membrane bag pile pre-support device into the borehole. The expansion radius of the membrane bag pile is 100mm. R u The spacing D between the membrane bag piles and the piles is preliminarily determined according to 3.2.3 and 3.2.4 of the "Technical Specification for Compacted Grouting Piles" (T / CWEA 5-2018). R u =0.2m, D=0.8m, for backup.

[0064] (2) The loose and weak strata under different compressive stresses were determined by indoor confined compression test. Lower porosity e The variation curves were analyzed using data analysis software to perform nonlinear fitting, ensuring a coefficient of determination above 0.95, to obtain the results of loose and weak strata under different compressive stresses. Functional relationship of the change in lower porosity e Simultaneously, the porosity was measured. e The mechanical parameters of the loose and weak strata (including the elastic modulus E, cohesion C, and internal friction angle of the loose and weak strata) The quantitative mapping relationship of porosity is established, and the governing equation for porosity is: elastic modulus Cohesion internal friction angle , respectively Figure 6 , Figure 7 and Figure 8 .

[0065] (3) Based on the initial formation parameter information and borehole radius obtained in step (1), R 0 Expansion radius of membrane bag pile R u The expansion radius of the membrane bag pile is calculated according to the following formulas (1) and (2). R u Corresponding formation compaction stress distribution equation σ r ( r (See the simplified diagram of compaction stress.) Figure 4 The result is: ,See Figure 9 .

[0066] (1);

[0067] (2).

[0068] In equations (1) and (2), rThis is the radial distance from the center of the steel pipe in the pipe shed. e 0 The initial porosity, E For the initial elastic modulus, G For the shear modulus, C For the initial cohesion, The initial internal friction angle, σ 0 For the initial ground stress, the P u This is the maximum pore-expanding pressure.

[0069] (4) Take the σ from step (3) r ( r ) is substituted as a variable into step (2). e = f ( σ The spatial distribution equation for calculating the porosity of the compacted formation is used in this study. The result is: Then the e r ( r ) are used as variables and substituted into the values ​​described in step (2). , , In the process, the elastic modulus is obtained. E Cohesion C internal friction angle Spatial distribution equation , , ,spare.

[0070] (5) Since the composite reinforced body formed by the membrane bag pile advanced support device in the loose and weak strata consists of three parts: the steel pipe 2 of the pipe roof, the slurry inside the flexible membrane bag 1, and the surrounding compacted soil, the mechanical parameters of the composite reinforced body are calculated using the area-weighted average method of the reinforced area. A simplified diagram of the calculation principle is shown below. Figure 5 Specifically, the calculation methods for the various mechanical parameters of the composite reinforced body include the following steps:

[0071] (i) Calculate the elastic modulus of the compacted soil. E 1 Cohesion C 1 internal friction angle They respectively adopt the following equations (3), (4), and (5), and combine them with the spatial distribution equation described in step (4). E ( r ), c ( r ), calculate:

[0072] (3);

[0073] (4);

[0074] (5).

[0075] In the above equations (3), (4), and (5), D The spacing between the membrane bag posts is... R u The expansion radius of the membrane bag pile is [missing information]. d The outer diameter of the steel pipe 2 in the pipe shed is... r This represents the radial distance from the center of the steel pipe in the pipe roof. The result is: elastic modulus. E 1 =15.4MPa, internal friction angle = 20.6°, cohesion C 1 =44.7MPa.

[0076] (ii) Calculate the spacing between individual membrane bag posts D The area of ​​the pipe shed formed by the steel pipes 2 within the specified range. S 1 The area of ​​the hardened slurry inside the flexible membrane bag 1 S 2 The area of ​​the compacted soil S 3 The following formulas (6), (7), and (8) are used for calculation:

[0077] (6);

[0078] (7);

[0079] (8).

[0080] In the above equations (6), (7), and (8), d The outer diameter of the steel pipe in the pipe shed; δ The wall thickness of the steel pipe in the pipe shed; D The spacing between the membrane bag posts is... R u Let be the expansion radius of the membrane bag pile. The result is: S 1 =0.0019m 2 , S 2 =0.1237m 2 , S 3=0.5136m 2 .

[0081] (iii) The elastic modulus of the steel pipe 2 of the pipe roof was determined by indoor room temperature tensile test and modified triaxial compression test of metallic materials. E =2.1×10 5 MPa, internal friction angle =60°, cohesion C =5MPa. The elastic modulus of the hardened slurry in the flexible membrane bag 1 was determined by uniaxial compression deformation test of a cylinder and modified triaxial compression test. E =3.5×10 4 MPa, internal friction angle At 30°, cohesion c It is 0.15 MPa.

[0082] (iv) Based on 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 of the composite reinforcement body. E n Cohesiveness of composite solids C n Internal friction angle of composite reinforced bodies .

[0083] (9);

[0084] (10);

[0085] (11).

[0086] The calculation result is: the elastic modulus of the composite solidified body. E n =6820.8MPa, the cohesive strength of the composite solidified body C n =35.92MPa, the internal friction angle of the composite reinforced body =22.51°.

[0087] (6) Then, calculate whether the stability of the tunnel under the composite reinforcement meets the requirements based on the mechanical parameters of the composite reinforcement body described in step (5), including: whether there is a plastic zone according to the "Highway Tunnel Design Specification" (JTG 3370.1-2018), whether the crown settlement meets the requirements according to the "Highway Tunnel Construction Technical Specification" (JTG / T 3660-2020), and whether the horizontal convergence meets the requirements according to the "Highway Tunnel Design Specification" (JTG 3370.1-2018).

[0088] The results showed that there was no plastic zone, and the crown settlement and horizontal convergence met the specifications. The design of the membrane bag expansion radius and pile spacing was reasonable. Furthermore, the experimental results showed that after using the support parameters calculated using the above method, the grout retention rate in the target reinforcement area reached 100%, greatly improving the grout utilization rate.

[0089] It should be noted that if the verification results of step (6) show that one or more indicators exceed the limit, then the expansion radius of the membrane bag pile will be adjusted. R u Spacing between membrane bag piles D After making adjustments, repeat steps (2) to (6) until all calculated indicators meet the specifications. At this point, the expansion radius of the membrane bag pile is... R u Spacing between membrane bag piles D This serves as a reference for support parameters during actual construction in the project.

[0090] Finally, it should be noted that any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Although specific embodiments of this invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for calculating support parameters of a membrane bag pile advanced support device for loose and weak strata, characterized in that, The advanced support device includes: Pipe shed steel pipes; A number of flexible membrane bags are sequentially fitted onto the outer wall of the steel pipe of the pipe shed along its length, and both ends of each flexible membrane bag are sealed and fixed to the steel pipe of the pipe shed by binding components. Each of the flexible membrane bags has its inner cavity connected to one end of a grouting pipe, and the grouting pipe is distributed along the length of the pipe roof steel pipe and fixed on its outer side wall. The other end of the grouting pipe is located outside the flexible membrane bag. The calculation method includes the following steps: (1) Obtain initial formation parameter information of loose and weak strata, and then preliminarily determine the borehole radius based on these parameter information. R 0 Expansion radius of membrane bag pile R u Spacing between membrane bag piles D For backup; the initial formation parameter information includes: initial porosity ratio e 0 Initial elastic modulus E shear modulus G Initial cohesion C Initial internal friction angle Initial geostress σ 0 ; (2) Obtaining loose and weak strata under different compressive stresses σ n Lower porosity e The changing functional relationship e = f ( σ Then the void ratio was measured. e elastic modulus of the loose and weak strata E Cohesion C internal friction angle Quantitative mapping relationship, establishing the void ratio control equation , , ,spare; (3) Based on the parameter information described in step (1) and the borehole radius R 0 Expansion radius of membrane bag pile R u Calculate the expansion radius of the membrane bag pile R u Corresponding formation compaction stress distribution equation σ r ( r ): （1）； （2）； In equations (1) and (2), r This is the radial distance from the center of the steel pipe in the pipe shed. e 0 The initial porosity, E For the initial elastic modulus, G For the initial shear modulus, C For the initial cohesion, The initial internal friction angle, σ 0 The initial ground stress, P u Maximum pore-expanding pressure; (4) According to the σ described in step (3) r ( r ), and in conjunction with the steps described in step (2) e = f ( σ )Calculate the spatial distribution equation of the porosity of the compacted formation. e r ( r ) =f ( σ r ( r Then in step (2) , , Substituting each value into the spatial distribution equation, we obtain the elastic modulus respectively. E Cohesion C internal friction angle Spatial distribution equation E ( r ), c ( r ), ,spare; (5) Since the composite reinforced body formed by the membrane bag pile advanced support device in the loose and weak stratum consists of three parts: the pipe roof steel pipe, the slurry in the flexible membrane bag and the surrounding compacted soil, the mechanical parameters of the composite reinforced body are calculated by the area weighted average method of the reinforced area. (6) Then, based on the mechanical parameters of the composite reinforcement body described in step (5), calculate the stability of the reinforced object under the composite reinforcement body, verify whether there is a plastic zone, and whether the indicators such as arch settlement and horizontal convergence meet the specifications. If one or more indicators exceed the limit, then the expansion radius of the membrane bag pile is adjusted. R u Spacing between membrane bag piles D After making adjustments, repeat steps (2) to (6) until all calculated indicators meet the specifications. At this point, the expansion radius of the membrane bag pile is... R u Spacing between membrane bag piles D This serves as a reference for support parameters during actual construction in the project.

2. The method for calculating support parameters according to claim 1, characterized in that, 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 passes through each flexible membrane bag before the flexible membrane bag at the tail end in sequence, but does not communicate with the inner cavity of these flexible membrane bags.

3. The method for calculating support parameters according to claim 1, characterized in that, The outer diameter of the steel pipe of the pipe shed d= 80~150mm, wall thickness δ ≥6mm.

4. The method for calculating support parameters according to claim 1, characterized in that, The outer diameter of the grouting pipe is 30~40mm, and the wall thickness is 3~5mm.

5. The method for calculating support parameters according to claim 1, characterized in that, The distance between adjacent flexible film bags is no more than 20cm.

6. The method for calculating support parameters according to claim 1, characterized in that, The diameter of the flexible film bag does not exceed 400 mm.

7. The method for calculating support parameters according to claim 1, characterized in that, The grouting pipe has grouting holes on the side wall of the portion located in the flexible membrane bag.

8. The method for calculating support parameters according to claim 1, characterized in that, The diameter of the grouting hole is 10~20mm.

9. The method for calculating support parameters according to claim 1, characterized in that, In step (1), the initial stratigraphic parameter information can be obtained through geological exploration and indoor experimental testing.

10. The method for calculating support parameters according to claim 1, characterized in that, In step (2), the , , The equation curve was obtained through fitting analysis of indoor lateral compression test data.

11. The method for calculating support parameters according to claim 1, characterized in that, In step (5), the calculation methods for the various mechanical parameters of the composite reinforced body include: (i) Calculate the elastic modulus of the compacted soil. E 1 Cohesion C 1 internal friction angle They respectively adopt the following equations (3), (4), and (5), and combine them with the spatial distribution equation described in step (4). E ( r ), c ( r ), calculate: （3）； （4）； （5）； In the above equations (3), (4), and (5), D The spacing between the membrane bag posts is... R u The expansion radius of the membrane bag pile is [missing information]. d The outer diameter of the steel pipe 2 in the pipe shed is... r This is the radial distance from the center of the steel pipe in the pipe shed; (ii) Calculate the spacing between individual membrane bag posts D The area of ​​the pipe shed within the scope S 1 The area of ​​the hardened slurry inside the flexible membrane bag S 2 The area of ​​the compacted soil S 3 The following formulas (6), (7), and (8) are used for calculation: （6）； （7）； （8）； In the above equations (6), (7), and (8), d The outer diameter of the steel pipe in the pipe shed; δ The wall thickness of the steel pipe in the pipe shed; D The spacing between the membrane bag posts is... R u The expansion radius of the membrane bag pile; (iii) Measure the elastic modulus of the steel pipe of the pipe roof. E 2 Cohesion C 2 internal friction angle The elastic modulus of the hardened slurry inside the flexible membrane bag was measured. E 3 Cohesion C 3 internal friction angle Then, the mechanical parameters of the composite reinforcement are calculated according to the following formulas (9), (10), and (11), including the elastic modulus of the composite reinforcement. E n Cohesiveness of composite solids C n Internal friction angle of composite reinforced bodies ; （9）； （10）； （11）。

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