A design method for a reinforcement system for classifying and zoning soft strata with coordinated tunnel-soil stiffness

Abstract

The present invention relates to a design method for a classification and zoning reinforcement system for soft strata with coordinated tunnel-soil stiffness, which is applicable to the reinforcement of soft strata around proposed and existing tunnels. This method combines the double-tube jet grouting pile and the ground sleeve valve pipe grouting technology, and divides the reinforcement area into a "resistance area" and a "stress isolation area". The resistance area is located on both sides of the tunnel, and provides horizontal resistance through inclined grid pile layout to reduce the stress release caused by excavation. Its scope is determined based on the beam-spring model constructed from shield construction parameters, and the reinforcement width and depth are optimized through the stiffness coordination between the tunnel and the resistance area; the stress isolation area is located outside the resistance area, aiming to block the transfer of additional dynamic and static stresses and optimize the mechanical response, and its scope is determined by the proportion of soft strata and the resistance coefficient. This method makes up for the theoretical deficiencies of the existing technology, provides a safe and efficient reinforcement system for proposed tunnels around existing tunnels, ensures the stability and normal operation of the tunnel structure, and has broad engineering application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of soft ground reinforcement, and particularly to a design method for a classification and zoning reinforcement system for soft ground with coordinated tunnel-soil stiffness Background Art

[0002] With the acceleration of the urban modernization process in China, the urban population density has increased, and the traffic pressure has intensified. To alleviate traffic congestion, more and more cities are expanding traffic resources by building subways. However, when a proposed subway tunnel is located in soft ground and needs to cross an existing tunnel, the construction will face severe technical challenges.

[0003] On the other hand, when constructing a tunnel in soft ground, the high water content, high compressibility, high sensitivity, low strength, low density, and low permeability of the soil may all lead to serious geological problems. Especially when a shield tunnel is constructed above an existing tunnel, it may cause a redistribution of formation stress, resulting in displacement, settlement, or even damage to the existing tunnel. In addition, construction disturbances may cause deformation of the surrounding strata, affecting the stability of the existing tunnel. If the settlement exceeds the safety range, the normal operation of the existing tunnel will be at risk. During long-term operation, the dynamic stress of the train is transmitted through the soft ground. Since the soft ground has poor absorption capacity for dynamic stress, the dynamic load may accumulate over a long period of time, posing a threat to the structural safety of the existing tunnel.

[0004] Existing soft ground reinforcement technologies have been applied to a certain extent in controlling ground settlement and deformation. The Chinese invention patent with the application number 201810721619.X discloses a reinforcement structure and method for a large cross-section tunnel group with soft soil and rich water passing under a structure, including an existing structure above the tunnel and a mined tunnel group structure below it; this invention is beneficial to the safe construction of the mined tunnel and is also very effective in controlling the settlement and deformation of the structure above the tunnel. However, when a proposed tunnel crosses an existing tunnel, the effectiveness of the above reinforcement scheme of this invention is insufficient, which may cause settlement or deformation of the existing tunnel. The Chinese invention patent with the application number 201811258850.6 discloses a ground reinforcement system and method for reinforcing an existing tunnel, including a tunnel and uplift piles. A plurality of uplift piles arranged in a row are provided on both sides of the tunnel operation, improving the reinforcement of the existing tunnel; however, the reinforcement technology of this invention focuses on the static control of the ground during construction and does not fully consider the long-term transmission effect of the train dynamic stress during tunnel operation, which may cause cumulative effects on the structural stability of the existing tunnel and increase potential safety hazards.

[0005] Therefore, the existing technology still has obvious limitations in dealing with the construction of a proposed tunnel crossing an existing tunnel and ensuring the safety during the operation period. There is an urgent need for an effective soft ground reinforcement technology to improve the bearing capacity of the foundation, reduce ground settlement and deformation during construction and operation, and ensure the safety and normal operation of the proposed and existing tunnels. Summary of the Invention

[0006] In view of the above problems, the present invention provides a design method for a classification and zoning reinforcement system for soft strata with tunnel-soil stiffness coordination.

[0007] The technical solution of the present invention is as follows:

[0008] A design method for a classification and zoning reinforcement system for soft strata with tunnel-soil stiffness coordination, comprising the following steps:

[0009] Step 1: Obtain the formation profile parameters of the location of the proposed tunnel and the existing tunnel according to geological exploration data; obtain the design parameters of the proposed tunnel according to the construction design data;

[0010] Step 2: Based on the design parameters of the proposed tunnel obtained in Step 1, determine the longitudinal reinforcement range of the reinforcement system along the proposed tunnel according to the design alignment of the proposed tunnel and the alignment of the existing tunnel; the reinforcement system divides the reinforcement area into a "resistance area" and a "stress isolation area", where:

[0011] The resistance area is located on both sides of the tunnel, providing horizontal resistance through inclined grid pile layout to reduce stress release caused by excavation. Its range is determined according to the beam-spring model constructed based on shield construction parameters, and the reinforcement width and depth are optimized through the stiffness coordination between the tunnel and the resistance area;

[0012] The stress isolation area is located outside the resistance area, aiming to block the transmission of additional dynamic and static stresses and optimize the mechanical response. Its range is determined by the proportion of soft strata and the resistance coefficient;

[0013] Step 3: Based on the formation profile parameters obtained in Step 1, determine the reinforcement depth of the resistance area in the reinforcement system according to the proportion of soft soil layers in the formation where the proposed tunnel is located H k and the reinforcement depth of the stress isolation area H y ;

[0014] Step 4: Construct a beam-spring model based on the tunnel design parameters obtained in Step 1 to simulate the cross-sectional deformation of the tunnel structure;

[0015] Step 5: On the basis of Step 4, change the surrounding loading and unloading conditions to obtain the change of the lateral convergence deformation of the tunnel structure with the change of the position of the proposed tunnel's arch waist on both sides within the reinforcement system range, and then determine the layout position and lateral range of the resistance area on both sides of the proposed tunnel's arch waist L k ;

[0016] Step 6: On the basis of Step 5, according to the tunnel stiffness of the proposed tunnel K 1 and the stiffness of the resistance area K kAdjust the lateral range of the resistance zone L k2 and the reinforcement depth H k2 ;

[0017] Step 7: Obtain the resistance utilization coefficient Δ( Q ), determine the relationship between the lateral reinforcement width of the strata on both sides of the planned tunnel and the resistance it can provide, and determine the lateral range of the stress isolation zone L y .

[0018] Furthermore, in the first step, the formation profile parameters of the locations of the planned tunnel and the existing tunnel obtained from the geological exploration data include the horizontal stratification of the formation and the unit weight of each soil layer γ , compression modulus E, Poisson's ratio μ , bedding coefficient m , cohesion c and internal friction angle φ .

[0019] Furthermore, in the first step, the design parameters of the planned tunnel obtained from the construction design data include the tunnel burial depth H , outer diameter of the lining , inner diameter of the lining , lining width and design alignment

[0020] Furthermore, in the second step, according to the design alignment of the planned tunnel and the alignment of the existing tunnel, the overlapping section of the planned tunnel and the existing tunnel and the 50 m sections before and after should be set as the ground grouting reinforcement range

[0021] Furthermore, in the third step, the definition of soft soil layers can include cohesive soil layers in the soft plastic and flowing plastic states, sandy soil layers in the loose state, as well as untreated fill and highly compressible soil layers. According to the proportion of soft soil layers in the formation where the planned tunnel is located, the longitudinal reinforcement sections of the overcrossing section are divided into two categories: semi-section reinforcement and full-section reinforcement

[0022] Furthermore, in the third step, double-fluid jet grouting piles are used for semi-section reinforcement, and the reinforcement depth is 2 m below the semi-section of the planned tunnel; for full-section reinforcement, double-fluid jet grouting piles are used in combination with ground sleeve valves. The reinforcement depth is 2 m below the soft soil layer. The reinforcement systems of the above two types of sections are both divided into a resistance zone and a stress isolation zone, that is, the reinforcement depth of the resistance zone H k and the reinforcement depth of the stress isolation zone H y are 2 m below the semi-section of the planned tunnel. The reinforcement depth of the resistance zone Hk And the reinforcement depth of the stress barrier zone H y Is 2m below the soft soil layer.

[0023] Furthermore, in the fourth step, the main cross-section model of the tunnel segment is simplified into beam elements, the interaction between the soil and the tunnel structure is simulated by springs, the internal forces and deformations of the tunnel structure are simulated by the spring model, the internal forces of the tunnel structure are analyzed by the elastic foundation beam method, and a beam-spring model is constructed by finite element software.

[0024] Furthermore, in the fourth step, determine the axial stiffness of the spring K s And the tunnel structure load, specifically:

[0025] The axial stiffness of the spring K s Is:

[0026]

[0027] Wherein, m Is the elastic foundation coefficient of the surrounding rock of the proposed tunnel. For the resistance area range on both sides of the arch waist of the proposed tunnel, it is taken as the foundation coefficient of the reinforced soil layer m k , and for the range around the tunnel except the arch waist, it is taken as the foundation coefficient of the soft soil layer; s Is 1 / 2 of the total length of adjacent lining units.

[0028] The tunnel structure load includes vertical soil pressure P 1 , horizontal soil pressure, self-weight of the lining G And foundation reaction force P v These four parts, where:

[0029] The vertical soil pressure is:

[0030]

[0031] The horizontal soil pressure includes the horizontal soil pressure at the top of the tunnel Q 1 And the horizontal soil pressure at the bottom of the tunnel Q 1 +Q 2 , where:

[0032]

[0033]

[0034] The self-weight of the lining is:

[0035]

[0036] The foundation reaction force is as follows:

[0037]

[0038] In the formula, P 0 is the ground load, K 0 is the coefficient of the earth pressure at rest of the surrounding soil layer, γ h is the unit weight of the tunnel lining.

[0039] Furthermore, in the fifth step, the horizontal layout position of the first row of jet grouting piles adjacent to the center line of the proposed tunnel in the resistance area is calculated by back-calculating through the central angle of the tunnel located on both sides of the arch waist in the resistance area. In the beam-spring model, by changing the coefficient of the earth pressure at rest K 0 of the soil layer around the proposed tunnel, the loading and unloading conditions around the tunnel are simulated, and the corresponding lateral convergence deformation amounts for different central angles of the tunnel are obtained, and then the horizontal layout position of the resistance area is determined when the lateral convergence amount meets the requirements of the reinforcement design.

[0040] The lateral range of the resistance area L k The calculation formula is:

[0041]

[0042] Furthermore, in the sixth step, according to the stiffness K 1 of the proposed tunnel and the equivalent stiffness K k of the resistance area, the adjusted lateral range L k2 of the resistance area and the reinforcement depth H k2 are respectively:

[0043]

[0044] Among them, K 1 is the stiffness of the proposed tunnel, which can be obtained from the construction design data in the first step, K k is the stiffness of the resistance area, that is, ; and are respectively the correction coefficients of the lateral range and the reinforcement depth, which are determined according to relevant engineering experience.

[0045] Further, in the seventh step, the resistance exertion coefficient Δ( Q ) is related to the horizontal reinforcement width of the stress barrier zone L y and the reinforcement degree, and is specifically expressed as:

[0046]

[0047] When the resistance exertion coefficient Δ( Q ) = 1, the minimum horizontal reinforcement width of the stress barrier zone can be obtained L y_min :

[0048]

[0049] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0050] 1. Through theoretical derivation combined with simplified numerical analysis, the present invention has developed a set of design methods for the classification and zoning reinforcement system applicable to soft strata. This method is based on solid theoretical support, is easy to operate, and has higher efficiency and accuracy compared with traditional engineering judgment and complex numerical simulation.

[0051] 2. The design method of the soft stratum classification and zoning reinforcement system for tunnel-soil stiffness coordination provided by the present invention can effectively ensure the structural safety and normal operation of the proposed and existing tunnels. The scheme design has strong engineering applicability, can not only meet the deformation control requirements of shield construction, but also significantly reduce the subsequent construction cost, and has broad potential for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a schematic diagram of a soft stratum classification and zoning reinforcement system for tunnel-soil stiffness coordination according to the present invention.

[0053] Figure 2 is a flowchart of the steps of a design method for a soft stratum classification and zoning reinforcement system for tunnel-soil stiffness coordination according to the present invention.

[0054] Figure 3 is a schematic diagram of the classification and zoning of the longitudinal reinforcement section of the proposed tunnel in the embodiment.

[0055] Figure 4 is a schematic diagram of the beam-spring model constructed according to the tunnel design parameters in the embodiment.

[0056] Figure 5 is a schematic diagram of the tunnel structure load calculation in the beam-spring model constructed in the embodiment.

[0057] Figure 6The relationship between the lateral convergence deformation of the tunnel structure and the central angle of the tunnel located in the reinforced soil mass in the embodiment.

[0058] Figure 7 Schematic diagram of the value range of the central angle of the tunnel where the tunnel structure is located in the reinforced soil mass in the embodiment.

[0059] Figure 8 Schematic diagram of the design of the classification and zoning reinforcement system for the tunnel-soil stiffness coordination in the soft stratum in the embodiment. Detailed implementation manners

[0060] The technical solutions provided by the present application will be further described below in conjunction with specific embodiments and their accompanying drawings. In combination with the following description, the advantages and features of the present application will become clearer.

[0061] Embodiment:

[0062] A proposed subway line crosses an existing operating line. The axial distance between the left and right lines of the proposed subway line is 15.3 - 17.2 m, the tunnel diameter is 6 m, and it crosses the existing operating line obliquely upward at an angle of 8° - 17°. The buried depth of the tunnel of the proposed subway line is 7 - 9 m, the buried depth of the tunnel of the existing line is 15 - 17 m, the minimum vertical net distance between the proposed tunnel and the existing tunnel is only 2.0 m, and the length of the overlapping section where the vertical net distance is less than 3.0 m is about 70 m. The strata where the tunnel is located mainly include miscellaneous fill, silt, silty clay, and sand, etc. To ensure the construction safety during the excavation of the proposed shield tunnel and the normal operation of the existing line, the classification and zoning reinforcement measures for the tunnel-soil stiffness coordination are adopted for the strata around the proposed and existing tunnels by using this method, as Figure 1 、 Figure 2 shown, and the specific steps are as follows:

[0063] Step 1: Obtain the stratum profile parameters of the locations of the proposed tunnel and the existing tunnel according to the geological exploration data; obtain the design parameters of the proposed tunnel according to the construction design data.

[0064] Step 2: Based on the design parameters of the proposed tunnel obtained in Step 1, determine the longitudinal reinforcement range of the reinforcement system along the proposed tunnel according to the design trend of the proposed tunnel and the trend of the existing tunnel; the reinforcement system divides the reinforcement area into a "resistance area" and a "stress isolation area", where:

[0065] The resistance area is located on both sides of the tunnel, providing horizontal resistance through inclined grid pile arrangement to reduce the stress release caused by excavation. Its range is determined according to the beam-spring model constructed by the shield construction parameters, and the reinforcement width and depth are optimized through the stiffness coordination between the tunnel and the resistance area;

[0066] The stress isolation area is located outside the resistance area, aiming to block the transmission of additional dynamic and static stresses and optimize the mechanical response. Its range is determined by the proportion of the soft stratum and the resistance coefficient.

[0067] Step 3: Based on the formation profile parameters obtained in Step 1, determine the reinforcement depth of the resistance zone in the reinforcement system according to the proportion of soft soil layers in the formation where the proposed tunnel is located. H k and the reinforcement depth of the stress isolation zone H y .

[0068] Step 4: Construct a beam-spring model based on the tunnel design parameters obtained in Step 1 to simulate the cross-sectional deformation of the tunnel structure.

[0069] Step 5: On the basis of Step 4, change the surrounding loading and unloading conditions to obtain the variation of the lateral convergence deformation of the tunnel structure with the change of the positions of both sides of the tunnel arch waist within the scope of the reinforcement system of the proposed tunnel, and then determine the layout position and lateral range of the resistance zone on both sides of the tunnel arch waist of the proposed tunnel. L k .

[0070] Step 6: On the basis of Step 5, adjust the lateral range K 1 and the reinforcement depth K k of the resistance zone according to the tunnel stiffness L k2 of the proposed tunnel H k2 .

[0071] Step 7: Obtain the resistance coefficient Δ( Q ) through theoretical calculation, determine the relationship between the reinforcement width of the strata on both sides of the proposed tunnel and the resistance it can provide, and determine the lateral range of the stress isolation zone L y .

[0072] Step 1 specifically includes the following sub-steps:

[0073] (1) Obtain the formation parameters of the locations of the proposed tunnel and the existing tunnel according to the geological exploration data: The proposed tunnel is located in a silt reclamation formation, and the underlying layer is silt and sandy clay layer; the existing operating line tunnel is located in sandy clay layer and completely weathered gneissic mixed granite, and the underlying layer is sandy clay layer and completely weathered gneissic mixed granite. The interlayer soil between the proposed tunnel and the existing tunnel mainly includes: organic sand, silt and plastic sandy clay. The unit weight γ , compression modulus E, Poisson's ratio μ , bedding coefficient m , cohesion c and internal friction angle φ are shown in Table 1 below.

[0074] Table 1 Physical and Mechanical Parameters of Each Formation

[0075]

[0076] (2)Obtain the design parameters of the proposed tunnel according to the construction design data: the buried depth H of the proposed tunnel is 7 - 9 m; the outer diameter of the lining = 6 m, the inner diameter of the lining = 5.4 m, and the lining width = 1.5 m. The proposed tunnel obliquely crosses the existing tunnel at an angle of 8° - 17°, and there is an overlapping section within the mileage range of DK17+77.87 ~ DK17+268.17.

[0077] Step 2 specifically includes the following content:

[0078] According to the alignment of the proposed tunnel and the existing tunnel above, the section within the mileage range of DK17+27 ~ DK17+318 of the proposed tunnel is set as the ground grouting reinforcement treatment range.

[0079] Step 3 specifically includes the following content:

[0080] (1)Reinforcement section classification: The silt, silty clay, organic matter - containing sand, medium sand, and coarse sand within the range of the proposed tunnel are all classified as soft soil layers. According to the proportion of soft soil layers in the stratum where the proposed tunnel is located, the ground grouting reinforcement treatment section DK17+27 ~ DK17+318 is divided into two categories: semi - section reinforcement and full - section reinforcement. As shown in the appendix Figure 3 , specifically: DK17+27 ~ DK17+114.3 is semi - section reinforcement, and DK17+114.3 ~ DK17+318 is full - section reinforcement.

[0081] (2)Partitioned stratum reinforcement measures: The above - mentioned semi - section reinforcement is carried out by double - pipe jet grouting piles, and the reinforcement depth is 2 m below the semi - section of the proposed tunnel. The full - section reinforcement adopts the reinforcement measures of double - pipe jet grouting piles combined with ground sleeve valves, and the reinforcement depth is 2 m below the soft soil layer. The reinforcement systems of the above two types of sections are both divided into a resistance area and a stress barrier area, that is, the reinforcement depth H k of the resistance area and the reinforcement depth H y of the stress barrier area in the semi - section reinforcement section are 2 m below the semi - section of the proposed tunnel, and the reinforcement depth H k of the resistance area and the reinforcement depth H y of the stress barrier area in the full - section reinforcement section are 2 m below the soft soil layer.

[0082] Step 4 specifically includes the following content:

[0083] (1) Establish a beam-spring model: According to the tunnel design parameters obtained in Step 1, construct a beam-spring model. As shown in Appendix Figure 4 , simplify the main cross-section model of the tunnel segment into beam elements, use springs to simulate the interaction force between the soil and the tunnel structure, adopt a local spring model to simulate the internal force and deformation of the tunnel structure, analyze the internal force of the tunnel structure using the elastic foundation beam method, and construct the above beam-spring model through finite element software. In the above tunnel structure load calculation, the soil resistance effect is not considered.

[0084] (2) Determine the axial stiffness of the spring K s :

[0085]

[0086] (3) The tunnel structure loads include vertical soil pressure P 1 , horizontal soil pressure, self-weight of the lining G and foundation reaction P v These four parts are shown in Appendix Figure 5 as shown in the figure.

[0087] Among them, since there is no surface load, that is P 0 = 0, the unit weight γ is taken as 18 (according to the geological exploration data, there are miscellaneous fill and silt above the tunnel, so the unit weight γ in the embodiment is taken as 18), the tunnel burial depth H is taken as 8, then the vertical soil pressure P 1 is:

[0088]

[0089] Among them, K 0 is taken as 0.6, then:

[0090]

[0091] The horizontal soil pressure at the top of the tunnel is: Q 1 = 86.4 kPa

[0092] The horizontal soil pressure at the bottom of the tunnel is: Q 1 +Q 2 = 86.4 + 64.8 = 151.2 kPa

[0093] Among them, γ h is taken as 25, and the self-weight of the liningG is:

[0094]

[0095] Among them, the foundation reaction force P v is:

[0096]

[0097] The specific content of Step Five is as follows:

[0098] (1) Analyze the lateral convergence deformation of the proposed tunnel: The lateral convergence deformation of the proposed tunnel is based on the beam-spring model in Step Four, and the in-situ lateral earth pressure coefficient of the soil layer around the proposed tunnel is changed K 0 to simulate the loading and unloading conditions around the tunnel. Attached Figure 6 shows the lateral convergence deformation of the tunnel structure of the proposed tunnel with the change of the central angle of the tunnel circle located in the resistance area on both sides of the arch waist when the subgrade coefficient of the reinforced soil m = 20 MPa / m and the in-situ lateral earth pressure coefficient K 0 = 0.6.

[0099] (2) Determine the horizontal layout position of the resistance area: According to the construction requirements, in order to control the lateral convergence deformation of the tunnel within 10 mm, the central angle of the tunnel circle located in the resistance area on both sides of the arch waist should not be less than 50°, as shown in the attachment Figure 7 . At this time, the horizontal layout position of the first row of jet grouting piles adjacent to the tunnel center line in the resistance area can be back-calculated through the central angle of the tunnel circle located in the resistance area on both sides of the arch waist , that is, 2.7 m away from the tunnel center line, as shown in the attachment Figure 8 .

[0100] (3) Determine the lateral range of the resistance area L k , for the convenience of guiding construction, only one decimal place is retained:

[0101]

[0102] The specific content of Step Six is as follows:

[0103] According to the design parameters of the proposed tunnel in Step One, it can be known that the stiffness of the tunnel K 1 is about 35 MN / m, and the stiffness of the resistance area can be obtained through , combined with the geological conditions of this project, the correction factors and ​They are taken as 0.3 and 0.35 respectively. According to the stiffness coordination between the tunnel and the resistance area, the adjusted lateral range of the resistance area L k2 and the reinforcement depth H k2 are respectively:

[0104]

[0105]

[0106] The specific content of Step Seven is as follows:

[0107] The minimum horizontal width of the stress isolation zone L y_min :

[0108]

[0109] For the convenience of guiding construction, the reinforcement depth of the stress isolation zone is the same as that of the resistance area, and the lateral range of the stress isolation zone L y is taken as 2.6 m.

[0110] In summary, in this case, a semi-section reinforcement scheme mainly using double-tube jet grouting piles is adopted in the range of DK17+27 to DK17+114.3, and the reinforcement depth is 2.6 m below the semi-section of the proposed tunnel; a full-section reinforcement scheme combining double-tube jet grouting piles and ground sleeve valves is adopted in the range of DK17+114.3 to DK17+318, and the reinforcement depth is 2.6 m below the coarse sand layer. The reinforcement width on the outside of the double lines of the proposed tunnel (the left side of the left-line tunnel and the right side of the right-line tunnel) is 7.3 m, of which the horizontal reinforcement width of the resistance area is 4.7 m, and the horizontal reinforcement width of the stress isolation zone is 2.6 m; the horizontal reinforcement width of the stress isolation zone in the middle area between the double lines of the proposed tunnel is obtained by subtracting the width of the resistance area from the actual interval between the left and right tunnels, specifically 1.6 m, as shown in the appendix Figure 8 as shown.

[0111] The above description is only a description of the preferred embodiment of the present application, and is not any limitation on the scope of the present application. Any change or modification made by any person skilled in the art according to the disclosed technical content shall be regarded as an equivalent effective embodiment, and all belong to the scope of protection of the technical solution of the present application.

Claims

1. A design method for a soft stratum classification and zoning reinforcement system with coordinated tunnel-soil stiffness, characterized in that: The following steps are involved: Step 1: Obtain the stratigraphic profile parameters of the proposed tunnel and the existing tunnel based on the geological survey data; obtain the design parameters of the proposed tunnel based on the construction design data; Step 2: Based on the design parameters of the proposed tunnel obtained in step 1, determine the reinforcement range of the reinforcement system along the longitudinal direction of the proposed tunnel according to the design direction of the proposed tunnel and the direction of the existing tunnel; the reinforcement system divides the reinforcement area into a "resistance zone" and a "stress isolation zone", where: The resistance zone is located on both sides of the tunnel. The horizontal resistance is provided by inclined grid piles to reduce the stress release caused by excavation. Its range is determined by the beam-spring model constructed based on the shield construction parameters. The reinforcement width and depth are optimized by coordinating the stiffness of the tunnel and the resistance zone. The stress isolation zone is located outside the resistance zone, aiming to isolate the transmission of additional dynamic and static stresses and optimize the mechanical response. Its range is determined by the proportion of weak formations and the resistance coefficient. Step 3: Based on the stratum profile parameters obtained in step 1, determine the reinforcement depth of the resistance zone in the reinforcement system according to the proportion of soft soil layers in the stratum where the proposed tunnel is located. H k and reinforcement depth of stress isolation area H y ; Step 4: Construct a beam-spring model based on the tunnel design parameters obtained in step 1 to simulate the cross-sectional deformation of the tunnel structure; Step 5: Based on step 4, change the surrounding loading and unloading conditions to obtain the changes in the lateral convergence deformation of the tunnel structure as the two sides of the proposed tunnel arch are located within the scope of the reinforcement system, and then determine the layout position and lateral range of the resistance zone on both sides of the proposed tunnel arch L k ; Step 6: Based on step 5, according to the tunnel stiffness of the proposed tunnel K 1 and resistance zone stiffness K k Adjust the lateral extent of the resistance zone L k2 and reinforcement depth H k2 ; Step 7: Obtain the resistance coefficient Δ( Q ), determine the relationship between the width of the stratum reinforcement on both sides of the proposed tunnel and the resistance it can provide, and determine the lateral range of the stress isolation zone L y .

2. A tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system design method as claimed in claim 1, characterized in that: In step one: The stratigraphic profile parameters of the proposed tunnel and the existing tunnel obtained from geological survey data include the horizontal stratification of the strata and the weight of each soil layer. γ , compression modulus E, Poisson's ratio μ , base bed coefficient m , Cohesion c and internal friction angle φ .

3. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 1, characterized in that: In step one: The design parameters of the proposed tunnel obtained from the construction design data include the tunnel burial depth H , Lining outer diameter , Lining inner diameter , Lining width and design trends.

4. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 1, characterized in that: In step 2: According to the design direction of the proposed tunnel and the direction of the existing tunnel, the overlapping section of the proposed tunnel and the existing tunnel and the section 50 m before and after should be set as the scope of ground grouting reinforcement.

5. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 1, characterized in that: In step three: The definition of soft soil layers includes clay layers in soft plastic and fluid plastic states, sand layers in loose states, and untreated fill and highly compressible soil layers. According to the proportion of soft soil layers in the stratum where the proposed tunnel is located, the longitudinal reinforcement section of the upper span is divided into two categories: half-section reinforcement and full-section reinforcement.

6. A tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system design method as claimed in claim 5, characterized in that: The half-section reinforcement adopts double-tube jet grouting piles, and the reinforcement depth is 2 m below the half-section of the proposed tunnel; the full-section reinforcement adopts double-tube jet grouting piles combined with ground sleeve valve pipe reinforcement measures, and the reinforcement depth is 2 m below the soft soil layer; The reinforcement systems of the above two types of sections are divided into resistance zone and stress isolation zone, that is, the reinforcement depth of the resistance zone of the half-section reinforcement section is H k and stress isolation area reinforcement depth H y The reinforcement depth of the resistance zone of the proposed tunnel is 2m below the half section and the full section reinforcement section. H k and stress isolation area reinforcement depth H y It is 2m below the soft soil layer.

7. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 1, characterized in that: In step 4: The main section model of the tunnel segment is simplified into a beam unit, the spring is used to simulate the force between the soil and the tunnel structure, the spring model is used to simulate the internal force and deformation of the tunnel structure, the elastic foundation beam method is used to analyze the internal force of the tunnel structure, and the beam-spring model is constructed through finite element software; Determine the axial stiffness of the spring K s and tunnel structure loads, specifically: The spring axial stiffness K s for: in, m is the elastic base coefficient of the surrounding rock around the proposed tunnel. For the resistance zone on both sides of the arch waist of the proposed tunnel, it is taken as the base coefficient of the reinforced soil layer. m k , the base bed coefficient of the soft soil layer is taken in the area around the tunnel except the arch waist; s 1 / 2 of the sum of the lengths of adjacent lining units; The tunnel structure load includes vertical earth pressure P 1. Horizontal soil pressure and lining deadweight G and foundation reaction P v Four parts, including: The vertical soil pressure is: The horizontal earth pressure includes the horizontal earth pressure at the top of the tunnel Q 1 and the horizontal earth pressure at the bottom of the tunnel Q 1 +Q 2, where: The deadweight of the lining is: The foundation reaction force is: In the formula, P 0 is the ground load, K 0 is the static lateral pressure coefficient of the surrounding soil layer, γ h The tunnel lining is heavy.

8. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 6, characterized in that: In step five: The horizontal layout position of the first row of jet grouting piles near the center line of the proposed tunnel in the resistance zone passes through the central angle of the tunnel located in the resistance zone on both sides of the arch waist. Reverse calculation to obtain; In the beam-spring model, the static lateral pressure coefficient of the soil layer around the proposed tunnel is changed K 0Simulate the loading and unloading conditions around the tunnel to obtain different tunnel center angles The corresponding lateral convergence deformation is used to determine the horizontal layout position of the resistance zone when the lateral convergence meets the reinforcement design requirements; Lateral extent of the resistance zone L k The calculation formula is: 。 9. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 1, characterized in that: In step six: According to the proposed tunnel stiffness K 1 and the equivalent stiffness of the resistance zone K k Adjusted lateral range of resistance zone L k2 and reinforcement depth H k2 They are: in, K 1 is the stiffness of the proposed tunnel, K k is the stiffness of the resistance zone, that is ; and are the correction factors for lateral range and reinforcement depth respectively.

10. The method for designing a tunnel-soil stiffness coordinated soft stratum classification and zoning reinforcement system according to claim 1, characterized in that: In step seven: Resistance exertion coefficient Δ( Q ) and the horizontal reinforcement width of the stress isolation area L y It is related to the degree of reinforcement, which can be expressed as: When the resistance coefficient Δ( Q ) = 1, the minimum horizontal reinforcement width of the stress isolation area is obtained L y_min : 。

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