A tunnel assembly buffer structure crossing an active fault and a design method thereof

Abstract

The present invention relates to the field of tunnel and underground engineering technology, and specifically to an assembled buffer structure and design method for a tunnel crossing an active fault, wherein the assembled buffer structure is located in the active fault section and extends a certain length to both sides of the active fault section as a transition; the assembled buffer structure includes an initial support, a buffer layer and a secondary lining arranged in sequence from the outside to the inside; the buffer layer is assembled from a number of porous prefabricated parts. The buffer layer of the present invention can be compressed to a large extent without generating significant additional pressure on the secondary lining of the tunnel, can adapt to a large amount of fault dislocation, and is simpler to assemble using prefabricated parts, and has less impact on the tunnel construction environment; at the same time, the buffer structure design method of the present invention can calculate the required thickness of the buffer layer and design the filling material of the buffer layer according to different engineering needs, which is more accurate and reasonable than the traditional empirical design method.

Description

Technical Field

[0001] The invention relates to the technical field of tunnels and underground engineering, and in particular to an assembled buffer structure of a tunnel crossing an active fault and a design method thereof. Background Art

[0002] When a mining tunnel passes through an active fault, the existing technology uses a filling layer with a low elastic modulus between the secondary lining structure of the tunnel and the shotcrete within the fault zone, and sets a shock-absorbing joint along the longitudinal direction of the tunnel, wherein the material properties of the filling layer are crucial to the anti-fault effect. The material of the filling layer is generally asphalt concrete, rubber (such as patents CN103195447 A, CN 110159314 A) or foamed concrete (such as patents CN 101550831 A, CN 208456615U, CN 103485796 A). Among them, the elastic modulus of asphalt concrete is about 1000MPa, which is only about 1 / 30 of that of concrete, so as to reduce the squeezing force of the surrounding rock on the tunnel when the fault moves, and avoid structural damage.

[0003] This technology has the following problems: 1) Although the initial elastic modulus of rubber or asphalt concrete is low, the elastic modulus increases sharply with the increase of compression. Asphalt concrete is basically no longer compressible after being compressed to a certain amount, and this compressibility is often difficult to meet the requirements of the predetermined compression, and is not suitable for active fault dislocation with a large amount of dislocation; 2) The buffer layer is in the closed space between the secondary lining and the initial support of the tunnel. When the fault is dislocated, the buffer layer is not in a unidirectional compression state, but is also affected by the constraints in the other two directions in the closed space. In fact, it is in a three-way stress state, and the compressibility will be further reduced; 3) The mechanical properties of asphalt concrete or foam concrete are closely related to the construction process. It is difficult to meet its construction requirements by pouring on-site in the tunnel. The filling layer space between the secondary lining and the shotcrete is narrow, and the performance of the material formed on-site is difficult to meet expectations. The above problems cause the secondary lining of the tunnel to still be subjected to a large extrusion pressure under the action of fault dislocation, and the structure is easily damaged. Summary of the invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides an assembled buffer structure and a design method thereof which can significantly reduce the force exerted by the movement of an active fault on the secondary lining of a tunnel and meet the construction quality control requirements in a narrow space of a tunnel.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is a prefabricated buffer structure for a tunnel crossing an active fault, wherein the prefabricated buffer structure is located in the active fault section and extends a certain length to both sides of the active fault section as a transition; the prefabricated buffer structure includes initial support, a buffer layer and a secondary lining arranged in sequence from the outside to the inside; the buffer layer is assembled from a number of porous prefabricated parts.

[0006] Furthermore, a drainage prevention structure is provided between the buffer layer and the secondary lining; preferably, a drainage prevention structure is also provided between the initial support and the buffer layer.

[0007] Furthermore, the transition length of the assembled buffer structure is more than one time of the hole diameter.

[0008] Furthermore, the porous prefabricated part is cast by porous concrete or sandless concrete.

[0009] Furthermore, the porous preform is a honeycomb structure or a single-sided comb structure, and the buffer layer is assembled by one or more porous preforms.

[0010] Furthermore, the outer contour of the cross section of the honeycomb structure porous preform is hexagonal, quadrilateral or fan-shaped.

[0011] Furthermore, a plurality of porous preforms in the buffer layer are closely arranged or spaced apart.

[0012] The present invention also provides a design method for the tunnel assembly buffer structure crossing the active fault, wherein the buffer layer adopts one of the following two design methods according to the situation:

[0013] Method 1: Design the prefabricated parts according to the required compression amount of the buffer layer, make the porous prefabricated parts, and form the buffer layer by on-site positioning and assembly;

[0014] Method 2: Use a general porous preform to calculate the compression height ratio α of the buffer layer, and then calculate the thickness h0 of the buffer layer before compression based on the required compression △h of the buffer layer to determine the contours of the cross section of the buffer structure.

[0015] Furthermore, method one first determines the actual required compression amount △h of the buffer layer according to the dislocation amount of the active fault; then preliminarily proposes the thickness of the buffer layer before compression h0, and calculates the compression height ratio α of the buffer layer, α=1-△h / h0; when the loose volume coefficient of the buffer material after crushing is n, the actual required void ratio p of the buffer material is calculated according to the relationship between the void ratio of the buffer material and the compression height ratio p=1-α / n; the holes of the buffer material prefabricated block are designed according to the required void ratio p; the physical and mechanical properties of the designed buffer material prefabricated block are tested, and when the requirements are not met, the size and hole arrangement of the prefabricated block need to be adjusted.

[0016] Furthermore, method 2 first calculates the compression height ratio α=n(1-p) of a general porous preform based on the porosity p and loose volume coefficient n of a general porous preform; then determines the actual compression amount △h required for the buffer layer based on the dislocation amount of the active fault; and then calculates the required thickness h0 of the buffer layer before compression, h0=△h / (1-α).

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The buffer layer of the present invention is assembled from porous prefabricated parts, and the material has holes inside. When the active fault dislocation squeezes the tunnel and compresses and destroys the filling material in the compression area of ​​the buffer layer, the distance between the initial support and the secondary lining in the compression area is greatly reduced. Compared with traditional rubber or asphalt concrete filling materials, which begin to "become more compact with compression" after a small amount of compression, the porous prefabricated material of the buffer layer of the present invention can be compressed to a large extent without generating significant additional pressure on the secondary lining in the compression area of ​​the tunnel, and can thus adapt to a larger amount of fault dislocation;

[0019] (2) Compared with the traditional asphalt concrete pouring construction in the tunnel, the porous prefabricated parts of the present invention are prefabricated in the factory, which can ensure that the buffer layer filling material meets the required performance; they are transported to the tunnel for assembly, which meets the quality control requirements during construction in the narrow space of the tunnel. The assembly of prefabricated parts is simpler than the traditional on-site pouring construction, and has less impact on the tunnel construction environment;

[0020] (3) The buffer structure design method of the present invention can calculate the required thickness of the buffer layer and design the filling material of the buffer layer according to different engineering requirements, which is more accurate and reasonable than the traditional empirical design method. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A schematic diagram of the longitudinal section of a tunnel assembly buffer structure crossing an active fault;

[0023] Figure 2 A schematic cross-sectional view of a tunnel assembly buffer structure crossing an active fault;

[0024] Figure 3 A schematic cross-sectional view of a hexagonal honeycomb structure porous preform;

[0025] Figure 4 A schematic cross-sectional view of a quadrilateral honeycomb structure porous preform;

[0026] Figure 5 A schematic cross-sectional view of a fan-shaped honeycomb structure porous preform;

[0027] Figure 6 It is a schematic cross-sectional view of a single-sided comb-shaped porous preform;

[0028] Figure 7 Schematic diagram of the porous preform before and after compression;

[0029] Figure 8 It is a cross-sectional view of a single-sided comb-shaped porous prefabricated component;

[0030] Fig. 9 It is a cross-sectional view of a sector-shaped porous preform of a honeycomb structure. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0034] like Figure 1-Figure 2As shown, this embodiment provides a prefabricated buffer structure for a tunnel crossing an active fault. The prefabricated buffer structure is located in the active fault section and extends a certain length to both sides of the active fault section as a transition. The transition length is more than one time of the tunnel diameter. The prefabricated buffer structure includes an initial support, a buffer layer and a secondary lining arranged in sequence from the outside to the inside. The structure of this embodiment is similar to the conventional drill-and-blast tunnel composite lining, but a buffer layer is added between the initial support and the secondary lining. The tunnel drainage structure is generally arranged between the buffer layer and the secondary lining. If necessary, a drainage structure is added between the initial support and the buffer layer to further enhance the waterproof performance of the tunnel lining. The buffer layer is assembled from a number of porous prefabricated parts that can undergo a large amount of compression. The compression of the buffer layer can absorb the dislocation of the active fault, reduce the adverse effects of the fault dislocation on the tunnel lining structure, and thus ensure the stability and safety of the tunnel crossing the active fault.

[0035] The buffer layer of this embodiment is composed of several prefabricated parts assembled in the circumferential and longitudinal directions. The porous prefabricated parts are prefabricated in the factory according to the designed shape and performance, which can effectively improve the preparation quality of the buffer layer filling material, and then transported to the tunnel for assembly, which can effectively solve the problem of difficult to ensure material performance during on-site casting, and has less impact on the tunnel construction environment. When the porous prefabricated parts are prefabricated, positioning parts can be embedded on the porous prefabricated parts, and positioning parts can be embedded in the corresponding positions of the initial support. During assembly, it is only necessary to connect the positioning parts on the porous prefabricated parts with the corresponding positioning parts on the initial support. The positioning parts can be positioning steel bars, etc.

[0036] The porous prefabricated parts described in this embodiment can be cast by sandless concrete or porous concrete, and the strength, porosity and compressibility of the porous concrete can be adjusted as needed. There are a large number of large-diameter holes in the prefabricated parts, and the volume of the entity after compression and destruction of the prefabricated parts is relatively small compared to the overall volume of the original prefabricated parts, so that the buffer layer has high compressibility, and the stress of the buffer layer when it is compressed will not increase significantly with the compression and deformation of the material, that is, when the active fault is displaced, the buffer layer will not produce a significant force on the secondary lining.

[0037] To optimize the above embodiment, the plurality of porous preforms in the buffer layer can be closely arranged in both the circumferential and longitudinal directions of the tunnel; in order to further increase the porosity of the buffer layer and increase the compression of the buffer layer, the plurality of porous preforms in the buffer layer can be continuously arranged in one direction of the circumferential and longitudinal directions and spaced in the other direction, or the plurality of porous preforms in the buffer layer can be spaced in both the circumferential and longitudinal directions.

[0038] To optimize the above embodiment, in order to further increase the porosity of the porous preform, the porous preform may adopt a honeycomb structure, such as Figure 3-Figure 5As shown, by adjusting the size of the holes in a single porous preform or changing the number and distribution of the holes, the porosity of the porous preform can be adjusted, thereby meeting the different requirements of different projects for the compressibility of the buffer structure; the porous preform can also adopt a single-sided comb-shaped structure, such as Figure 6 As shown, the porosity of the porous prefabricated part can be adjusted by adjusting the width and spacing of the comb teeth. Usually, the comb teeth of the porous prefabricated part with a single-sided comb-shaped structure are close to the initial support, and the shape of the comb back can be adjusted to an arc shape according to the contour of the secondary lining, so that it fits tightly with the secondary lining, which is convenient for arranging the waterproof and drainage structure. The buffer layer can be assembled with a single honeycomb structure porous prefabricated part, or with a single unilateral comb-shaped structure porous prefabricated part, or with a combination of a honeycomb structure porous prefabricated part and a unilateral comb-shaped structure porous prefabricated part.

[0039] Specifically, the cross-sectional outer contour of the honeycomb structure porous preform may be a hexagon, such as Figure 3 As shown, it is convenient for the close arrangement of the porous preforms. According to different needs, the cross-sectional outer contour of the honeycomb structure porous preform can also be a quadrilateral, a fan-shaped, etc. Figure 4 and Figure 5 As shown, it can also be any other shape that is easy to assemble.

[0040] There are two methods for designing the above-mentioned tunnel prefabricated buffer structure that crosses the active fault. The porous prefabricated parts can be designed according to the required compression amount, or the buffer layer can be designed using universal prefabricated parts. The calculation method of the main parameters in the buffer structure design is now introduced.

[0041] The required compression amount △h of the buffer layer is determined according to the amount of fault dislocation. Let the thickness of the buffer layer before compression be h0, and the thickness of the buffer layer after the tunnel is compressed and deformed by fault dislocation be h2, as shown in Figure 7 As shown, h2=h0-△h.

[0042] The compression height ratio α is taken as the height of the buffer layer after compression / the height before compression, that is, α=h2 / h0=1-△h / h0.

[0043] Taking unit length for calculation, the volume of the buffer layer space before compression is recorded as V0, and the remaining space volume after compression is αV0.

[0044] The solid volume of the buffer layer is recorded as V1, and the void volume in the solid is recorded as V2 (i.e. V0 = V1 + V2), then:

[0045] The porosity of the buffer layer is p=V2 / V0=1-V1 / V0, or V1 / V0=1-p.

[0046] The loose volume of the buffer layer filling material after compression damage is larger than the solid volume V1. Assume that the loose volume coefficient is n (according to experience, the loose volume coefficient n of sandless concrete is about 1.1-1.2). Since the strength of the buffer layer filling material is lower than the strength of the tunnel lining structure, the buffer layer is destroyed first under the action of fault dislocation. Assuming that the loose volume after crushing is equal to the remaining space volume after compression, we have:

[0047] nV1=αV0, or V1 / V0=α / n.

[0048] It can be concluded that the relationship between the void ratio p of the buffer layer and the compression height ratio α and the loose volume coefficient n of the filling material is: p=1-α / n.

[0049] A. When the porous prefabricated component is designed according to the required compression amount of the buffer layer, the design method of the tunnel assembly buffer structure crossing the active fault includes the following steps:

[0050] 1) According to the dislocation of the active fault, determine the actual required compression amount △h of the buffer layer.

[0051] 2) Preliminarily determine the thickness of the buffer layer before compression as h0.

[0052] 3) According to the relationship between the compression height ratio α of the buffer layer, the actual required compression amount △h of the buffer layer and the thickness h0 of the buffer layer before compression: α=1-△h / h0, the compression height ratio α of the buffer layer is calculated;

[0053] 4) Measure the loose volume coefficient n of the porous preform;

[0054] 5) According to the relationship between the loose volume coefficient n and the compression height ratio α and the actual required porosity p of the buffer layer: p = 1-α / n, the required porosity p of the buffer material is calculated;

[0055] 6) According to the actual situation, select the appropriate outer contour of the porous preform and the arrangement of the porous preform; then, according to the actual porosity p required by the buffer material and the outer contour and arrangement of the porous preform, design the size and distribution of the holes or slots of the porous preform, and carry out detailed design of the porous preform in combination with the structural and strength requirements;

[0056] 7) Conduct physical and mechanical property tests on the porous prefabricated parts. If the requirements are not met, the structural shape and hole arrangement need to be adjusted. If the requirements are met, the prefabricated porous prefabricated parts are positioned and assembled on site to form an assembled buffer structure that can adapt to the movement of active faults.

[0057] B. When a general porous prefabricated component is used, the design method of the tunnel assembly buffer structure crossing the active fault comprises the following steps:

[0058] 1) When a porous preform with a certain porosity and hole arrangement is subjected to standardized manufacturing process and a large number of physical and mechanical property tests, and its material properties are standardized, it can become a universal preform for the buffer layer. At this time, the porosity p of the universal porous preform and the loose volume coefficient n of the preform after crushing are easy to obtain;

[0059] 2) According to the relationship between the porosity p and the loose volume coefficient n of the preform and the compression height ratio α: α = n (1-p), the compression height ratio α of the universal porous preform is calculated;

[0060] 3) According to the dislocation of the active fault, the actual required compression amount △h of the buffer layer is determined. Then, according to the relationship between the compression amount △h of the buffer layer and the compression height ratio α and the thickness h0 of the buffer layer before compression: h0 = △h / (1-α), the required thickness h0 of the buffer layer before compression is calculated. Based on this, the tunnel cross-section with a buffer layer can be designed.

[0061] 4) The general prefabricated parts are positioned and assembled on site to form an assembled buffer structure that can adapt to the movement of active faults.

[0062] The design method of this embodiment is further described below in conjunction with a specific engineering example.

[0063] (1) The maximum vertical displacement of a tunnel project crossing an active fault section is predicted to be 0.5 m, and the actual required compression △h of the buffer layer is taken as 0.5 m.

[0064] A. When designing a porous preform according to the required compression of the buffer layer:

[0065] The initial thickness of the buffer layer is 1.2m, so the compression height ratio α = 0.583;

[0066] The loose volume coefficient of a porous concrete material after crushing is n = 1.1, and the void ratio required for making porous prefabricated parts using this material is calculated to be p = 1-α / n = 0.47;

[0067] Hole design of porous prefabricated parts:

[0068] 1) If using Figure 6 The single-sided comb-shaped porous preform has a void ratio of

[0069] Wherein, m is the number of intervals between comb teeth, d is the spacing between adjacent comb teeth, h is the height of the comb teeth, H is the sum of the heights of the comb teeth and the comb back, and L is the width of a single porous preform;

[0070] Figure 6The number of intervals between the middle comb teeth is m=7; when h=50 cm, H=60 cm, and the width of a single porous preform is L=100 cm, d=8.0 cm can be obtained according to the void ratio calculation formula.

[0071] The cross section of the single-sided comb-shaped porous preform is as follows: Figure 8 As shown, it is laid in two layers, upper and lower, to meet the requirement of 0.5m compression of the 1.2m thick buffer layer (the units marked in the figure are centimeters).

[0072] 2) If adopted Figure 5 The porous preform of the fan-shaped honeycomb structure has a void ratio of Wherein, S is the cross-sectional area of ​​the fan-shaped porous preform, m is the number of regular hexagonal holes, and b is the side length of the regular hexagonal holes;

[0073] Figure 5 The number of regular hexagonal holes m = 18, S = 7926.39 cm 2 According to the void ratio calculation formula, b = 8.92 cm.

[0074] The cross section of the fan-shaped honeycomb structure porous preform is obtained as follows Fig. 9 As shown, it is laid in two layers, upper and lower, to meet the requirement of 0.5m compression of the 1.2m thick buffer layer (the units marked in the figure are centimeters).

[0075] B. When using general prefabricated parts:

[0076] If the void ratio of a general preform is p=61.5%, the loose volume coefficient n=1.3.

[0077] When the universal preform is used as the filling material of the buffer layer, the compression height ratio of the buffer layer is α=n(1-p)=0.5.

[0078] Thus, the thickness of the buffer layer before compression is obtained as h0 = △h / (1-α) = 1 m.

[0079] That is, when the universal prefabricated component is used, the buffer layer thickness of the tunnel passing through the active fault section only needs to be 1.0 m, and the contours of the tunnel cross section are further designed.

[0080] (2) After the initial support is completed, the porous prefabricated components are assembled and laid from the invert to the arch top using positioning steel bars, and a drainage structure is arranged inside the porous prefabricated components. The subsequent construction process is the same as the conventional drilling and blasting method.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A tunnel assembly buffer structure for crossing an active fault, characterized in that: The assembled buffer structure is located in the active fault section and extends a certain length to both sides of the active fault section as a transition; the assembled buffer structure includes initial support, buffer layer and secondary lining arranged in sequence from outside to inside; the buffer layer is assembled from a number of porous prefabricated parts; the buffer layer is compressed to absorb the dislocation of the active fault, thereby reducing the adverse effects of the fault movement on the tunnel lining structure, thereby ensuring the stability and safety of the tunnel crossing the active fault; the buffer layer is assembled from a number of assembled porous prefabricated parts along the circumferential and longitudinal directions; the porous prefabricated parts are prefabricated in the factory according to the designed shape and performance, and then transported to the tunnel for assembly; when the porous prefabricated parts are prefabricated, positioning parts are embedded in the porous prefabricated parts At the same time, positioning parts are embedded in the positions corresponding to the initial support. During assembly, it is only necessary to connect the positioning parts on the porous prefabricated parts with the corresponding positioning parts on the initial support. The positioning parts are positioning steel bars. The porous prefabricated parts are cast with porous concrete. The strength, porosity and compression indexes of the porous concrete are adjusted as needed. There are a large number of large-diameter holes in the porous prefabricated parts. The volume of the porous prefabricated parts after compression and destruction is relatively small compared to the overall volume of the original porous prefabricated parts, so that the buffer layer has a high compressibility. The stress of the buffer layer when it is compressed will not increase significantly with the compression and deformation of the material, that is, when the active fault is displaced, the buffer layer will not produce a significant force on the secondary lining. The porous preformed part is a honeycomb structure or a single-sided comb-shaped structure, and the buffer layer is assembled by one or more porous preformed parts; when the porous preformed part adopts a honeycomb structure, the porosity of the porous preformed part is adjusted by adjusting the size of the holes in a single porous preformed part or changing the number and distribution of the holes, thereby meeting the different requirements of different projects for the compressibility of the buffer structure; when the porous preformed part adopts a single-sided comb-shaped structure, the porosity of the porous preformed part can be adjusted by adjusting the width and spacing of the comb teeth; the comb teeth of the porous preformed part with a single-sided comb-shaped structure are close to the initial support, and the shape of the comb back is adjusted to an arc shape according to the contour of the secondary lining, so that it fits tightly with the secondary lining, which is convenient for arranging the drainage structure.

2. The tunnel assembly buffer structure for crossing an active fault as claimed in claim 1, characterized in that: An anti-drainage structure is arranged between the buffer layer and the secondary lining; an anti-drainage structure is also arranged between the initial support and the buffer layer to enhance the waterproof performance of the tunnel lining.

3. The tunnel assembly buffer structure for crossing an active fault as claimed in claim 1, characterized in that: The transition length of the assembled buffer structure is more than one time of the hole diameter.

4. The tunnel assembly buffer structure for crossing an active fault as claimed in claim 1, characterized in that: The outer contour of the cross section of the porous preform of the honeycomb structure is hexagonal, quadrilateral or fan-shaped.

5. The tunnel assembly buffer structure for crossing an active fault as claimed in claim 1, characterized in that: In the buffer layer, a plurality of porous preforms are closely arranged or spaced apart.

6. A design method for a tunnel assembly buffer structure crossing an active fault according to any one of claims 1 to 5, characterized in that: The buffer layer adopts any one of the following two design methods: Method 1: designing a porous prefabricated part according to the required compression amount of the buffer layer, manufacturing the porous prefabricated part, and forming the buffer layer through on-site positioning and assembly; Method 2: Using a common porous preform to calculate the buffer layer compression height ratio α , and then the actual compression required by the buffer layer △ h Calculate the thickness of the buffer layer before compression h 0, determine the contours of the buffer structure cross section.

7. The design method according to claim 6, characterized in that: Method 1: First, determine the actual required compression of the buffer layer based on the dislocation of the active fault. h ; Then preliminarily formulate the thickness of the buffer layer before compression h 0, calculate the compression height ratio of the buffer layer α , α =1-△ h / h 0; when the loose volume coefficient of the buffer material of the buffer layer is broken, n According to the relationship between the void ratio of the cushioning material and the compression height ratio p =1- α / n , calculate the actual void ratio required for the buffer material p ; According to the actual situation, select the appropriate porous prefabricated part outer contour and porous prefabricated part arrangement, and then according to the actual required void ratio of the buffer material p The size and distribution of the holes of the porous prefabricated parts are designed according to the outer contour and arrangement of the porous prefabricated parts, and the detailed design of the porous prefabricated parts is carried out in combination with the structural and strength requirements; the physical and mechanical properties of the porous prefabricated parts are tested, and when the requirements are not met, the structural shape and hole arrangement need to be adjusted; when the requirements are met, the prefabricated designed porous prefabricated parts are positioned and assembled on site to form an assembled buffer structure that can adapt to the movement of active faults.

8. The design method according to claim 6, characterized in that: In the second method, when a porous preform with a certain porosity and hole arrangement is subjected to standardized manufacturing process and a large number of physical and mechanical property tests, its material properties can be standardized to become a universal porous preform for the buffer layer. p and loose volume coefficient of general porous prefabricated parts after crushing n， Calculating the Compression Height Ratio of Generic Porous Preforms α = n (1- p );Then, according to the dislocation of the active fault, determine the actual compression required for the buffer layer△ h , and then according to the actual compression required by the buffer layer △ h and compression height ratio α Thickness of buffer layer before compression h 0 relationship: h 0=△ h / (1- α ), calculate the required buffer layer thickness before compression h 0, based on which the tunnel cross section with a buffer layer can be designed; the general porous prefabricated parts are assembled on site to form an assembled buffer structure that can adapt to the movement of active faults.

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