Protection method for shield underneath pass building structure in covering type karst area

Abstract

The invention belongs to the technical field of modern traffic, and particularly discloses a cover type karst area shield underneath pass building structure protection method which comprises the steps that a bedrock boundary and the soil body property of an upper covering layer are obtained through geological drill holes in the periphery of a building structure; the relative position relation of the building structure, the shield tunnel and the bedrock interface is obtained; selecting a suitable stratum model according to the soil body property of the upper covering layer; a range parameter calculation formula under the critical condition is determined, and the building structure protection range is obtained; grouting the boundary of the protection range to form an isolation curtain; fully paving and grouting within a certain depth range below the bed rock within the protection range; and in the protection range, isolation grouting is conducted on a soil body above a bedrock interface to form a stable reinforcing isolation layer, and inclined hole grouting is adopted in the range below the earth surface of the building structure to avoid the area without the ground grouting condition. The construction and operation safety maintenance cost of the shield underneath pass building structure in the covering type karst development area is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of modern transportation technology, specifically relating to a method for protecting shield tunnels passing under buildings in karst-covered areas. It is applicable to the protection of shield tunnels passing under existing buildings (such as historical buildings, residential areas, high-rise buildings or other structures) in karst-covered development areas, and is used for the safety protection of facilities around urban subway tunnels when the shield tunnel is located in the upper karst overburden layer. Background Technology

[0002] Overburdened karst areas possess a unique binary structure of rock and soil boundary, with severely developed underlying limestone karst, posing a significant risk of disturbance and collapse. In recent years, with the development of underground space, particularly the rapid growth of urban rail transit, increased human engineering activities have led to more frequent karst collapse problems. Subway construction inevitably involves tunneling under important existing buildings and structures, especially in areas with well-developed overburden karst. If construction disturbance triggers bedrock karst cave collapse, the risks to the tunnel boring machine (TBM) are enormous, and the damage to existing buildings and structures on the surface can result in incalculable socio-economic losses.

[0003] One of the main challenges in addressing the aforementioned engineering issues lies in determining the protection scope. Different overburden layers above bedrock karst caves have different collapse mechanisms, resulting in varying impact ranges. Furthermore, the protection scope must simultaneously meet the protection requirements of both the tunnel section and the superstructures. Another major challenge is the implementation of protection measures. Since important structures are typically not relocated when the tunnel boring machine passes under them, and ground conditions are limited, it is impossible to obtain the location of the karst cave below the bedrock through surface drilling. Moreover, it is difficult to take relevant measures from the surface area where the structures are located.

[0004] A review of existing patents and research reveals that some inventions have studied the control and protection scope of tunnels in karst-developed areas with overburden layers for external operations. However, these methods are not applicable to the protection of existing buildings and structures on the ground, cannot provide corresponding protection ranges and treatment measures, and are only suitable for single cohesive or sandy soil layers. Some inventions have also researched shaft excavation methods, involving open-cut shaft excavation in open areas adjacent to buildings and structures, followed by full-range horizontal grouting of the karst strata after reaching the working face of the shield tunnel, and then backfilling the shaft. However, this method is not suitable for overburdened karst-developed areas, and shaft excavation requires deep penetration into the bedrock; the greater the pit depth, the higher the cost, resulting in poor economic efficiency. Furthermore, open-cut construction causes significant disturbance, easily triggering secondary disasters such as karst collapse, leading to damage to surface buildings and structures. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for protecting structures under shield tunneling in karst-covered areas. This method effectively prevents the collapse of karst overburden, protects ground structures, and provides dual safety assurance for both the construction and operation of subway sections. It also significantly reduces the construction and operational safety maintenance costs of structures under shield tunneling in karst-covered areas.

[0006] To achieve the above objectives, the present invention employs the following technical measures: a method for protecting structures under a shield tunnel in a karst area, comprising the following steps: 1) Obtain the bedrock boundary and the properties of the overlying soil by drilling around the building or other effective methods; 2) Obtain the relative positional relationships of the building structure, shield tunnel, and bedrock interface; 3) Select the appropriate stratigraphic model based on the properties of the overlying soil layer; 4) By determining the relative positional relationship between the tunnel, buildings, and strata in the section to be constructed, the formula for calculating the range parameters under critical conditions is determined, and the protection range of the buildings is obtained. 5) Grouting is carried out at the boundary of the protected area to form an isolation curtain. The grouting holes penetrate the karst development zone of the bedrock layer to block the hydraulic connection between the inside and outside and fill the karst caves at the bottom of the wall. Grouting is also carried out at a certain depth below the bedrock within the protected area to fill the karst caves and block the hydraulic channels in the bedrock fissures. 6) Within the protection area, the soil above the bedrock interface is isolated by grouting to form a stable reinforced isolation layer. For the area below the ground surface of buildings and structures, inclined hole grouting is used to avoid areas without ground grouting conditions.

[0007] Optionally, the overburden layer is a pure sand layer, a pure clay layer, or an interlayer containing bedrock, and the protection range is calculated by selecting the corresponding geological model according to the geological conditions.

[0008] Optionally, obtaining the relative positional relationship between the building structure, the shield tunnel, and the bedrock interface includes: the outer diameter of the tunnel section to be constructed. D and building span B ; Control and protection zone distance of buildings and structures S 1; Distance from the center of the tunnel in the section to be constructed to the mid-span of the building or structure S 2. and the distance from the center of the tunnel to the bedrock surface in the section to be constructed H ; Approach range of the tunnel section to be constructed S 3.

[0009] Furthermore, the stratigraphic model is divided into two types based on the properties of the overburden soil: a sandy soil interbedded with cohesive soil interbedded with sandy soil.

[0010] Furthermore, when the overburden is a sandy soil layer, the collapse is a funnel-shaped collapse with a collapse angle, which is determined by model tests or engineering experience methods. When the overburden is cohesive soil, the collapse is a soil-cavity type collapse, which is considered a vertical collapse.

[0011] Furthermore, when the overburden is cohesive soil and there is a sandy soil interlayer above the bedrock surface, a cohesive soil interlayer model with sandy soil is selected for calculation, wherein: The thickness of the cohesive soil layer is H n The thickness of the sandy soil interlayer is H sj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: ; When there are no interlayers, it simplifies to a pure cohesive soil model. H sj =0, then: ; Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ; When there are no interlayers, it simplifies to a pure cohesive soil model. H sj =0, then: ; To simultaneously meet the safety protection requirements of both the tunnel section to be constructed and the superstructure, the larger of the two values ​​is taken on both the left and right sides outside the structural boundary of the building, denoted as [value missing]. L : .

[0012] Furthermore, when the overburden is sandy soil and there is a cohesive soil interlayer above the bedrock surface, a sandy soil interlayer model with cohesive soil is selected for calculation, wherein: The thickness of the sandy soil layer is H s The thickness of the cohesive soil interlayer is H nj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: ; When there are no interlayers, it is simplified to a pure sandy soil model.H s = H 1, then: ; Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ; When there are no interlayers, it is simplified to a pure sandy soil model. H nj =0, then: ; To simultaneously meet the safety protection requirements of both the tunnel section to be constructed and the superstructure, the larger of the two values ​​is taken on both the left and right sides outside the structural boundary of the building, denoted as [value missing]. L : .

[0013] Furthermore, the protection range is the sum of the larger values ​​on the left and right sides outside the structural boundary of the building plus the length of the building's span B.

[0014] Optionally, in step 5), the depth of the boundary vertical grouting curtain should be greater than the depth of the full-coverage grouting layer.

[0015] Optionally, in step 6), if the soil above the bedrock interface is sandy soil or there is a cohesive soil layer with a thickness less than the minimum safe thickness, isolation grouting is performed to form a stable reinforced isolation layer.

[0016] Optionally, in step 6), the area below the ground surface of the building or structure shall be grouted using inclined boreholes to avoid areas without ground grouting conditions, and the grouting reinforcement thickness shall not be less than the minimum safe thickness.

[0017] Preferably, the minimum safe thickness is not less than 5m.

[0018] Compared with existing technologies, the present invention has the following advantages and effects: 1) This invention is applicable to shield tunnels passing under important buildings and structures, and the shield tunnel is located in the bedrock overburden layer of a karst development zone. Pre-treatment of the strata before shield tunneling can simultaneously meet the safety protection requirements of the tunnel section and the overburden structure.

[0019] 2) This invention is applicable to a wide range of geological formations, including complex geological formations where the karst overburden is sandy soil, cohesive soil, or has interlayers.

[0020] 3) This invention proposes a method for determining the protection range of shield tunnels passing under buildings and structures in karst areas.

[0021] 4) The protection measures of this invention avoid the surface of buildings and structures, avoid the problem of demolition of buildings and structures, are easy to implement, reliable in quality, safe and economical, and can effectively prevent the collapse of karst overburden. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram of an example of a cohesive soil-sand interlayer model; Figure 2 This is a schematic diagram of an example of a model with interlayered sandy soil and cohesive soil. Detailed Implementation

[0023] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0024] A method for protecting structures tunneled under a shield tunnel in a karst area includes the following steps: 1) Obtain the properties of the overburden soil and the depth of the bedrock surface by geological drilling or other geological exploration methods around the building or structure. H 1; 2) Based on the design dimensions of existing buildings and the tunnel section to be constructed, the outer diameter of the tunnel section to be constructed is obtained. D and building span B ; 3) Obtain the control protection zone distance of the building or structure according to the requirements of the building or structure owner. S 1; 4) Based on the underpass relationship of the tunnel section to be constructed, obtain the distance from the center of the tunnel section to the mid-span of the building structure. S 2. and the distance from the center of the tunnel to the bedrock surface in the section to be constructed H ; 5) Determine the proximity range of the tunnel section to be constructed based on current standards, regulations, or the requirements of the property owner. S 3. Soil disturbance outside this area can be considered to have minimal impact on the tunnel structure of the section to be constructed. Current national standards generally require that soil disturbance outside this area be minimal. D The scope, local standards may be narrowed to 2 D The scope shall be determined based on the actual requirements of the project; 6) Based on the properties of the overburden soil, the stratigraphic models are mainly divided into two categories: sandy soil interbedded with cohesive soil interbedded with cohesive soil interbedded with sandy ... sandy soil interbedded with cohesive soil interbedded with sandy soil interbedded with sandy soil interbedded with cohesive soil inter ① If the overburden is mainly cohesive soil, and there is a sandy soil interlayer above the bedrock surface, the cohesive soil interlayer sandy soil interlayer model should be selected for calculation. Among these, Sandy soil collapse is a funnel-shaped collapse with a collapse angle, which is determined by model tests or engineering experience; cohesive soil collapse is a cave-shaped collapse and can be regarded as a vertical collapse. Based on geological survey data, the thickness of the cohesive soil layer is as follows: H n The thickness of the sandy soil interlayer is H sj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: ; When there are no interlayers, it simplifies to a pure cohesive soil model. H sj =0, then: ; Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ; When there are no interlayers, it simplifies to a pure cohesive soil model. H sj =0, then: ; Because it is necessary to simultaneously meet the safety protection requirements of both the tunnel section to be constructed and the superstructure, the protection zone outside the boundary of the superstructure on the side closer to the tunnel section to be constructed is taken as the larger of the two values, denoted as . L The protected area outside the boundary on the other side of the building structure is taken as value L 1; .

[0025] ② If the overburden is mainly sandy soil, and there is a cohesive soil interlayer above the bedrock surface, the sandy soil interlayer model with cohesive soil should be selected for calculation. Among these, Sandy soil collapse is a funnel-shaped collapse with a collapse angle, which is determined by model tests or engineering experience; cohesive soil collapse is a cave-shaped collapse and can be regarded as a vertical collapse. Based on geological survey data, the thickness of the sandy soil layer is as follows: H s The thickness of the cohesive soil interlayer is H nj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained.L 1: ; When there are no interlayers, it is simplified to a pure sandy soil model. H s = H 1, then: ; Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ; When there are no interlayers, it is simplified to a pure sandy soil model. H nj =0, then: ; Because it is necessary to simultaneously meet the safety protection requirements of both the tunnel section to be constructed and the superstructure, the protection zone outside the boundary of the superstructure on the side closer to the tunnel section to be constructed is taken as the larger of the two values, denoted as . L The protected area outside the boundary on the other side of the building structure is taken as value L 1; .

[0026] In summary, the overall ground protection range is the sum of the larger values ​​on the left and right sides outside the structural boundary of the building, plus the length of the building's span B.

[0027] 7) After determining the protection area, vertical grouting is performed at its boundary to form a vertical grouting curtain. The grouting holes are arranged in a quincunx pattern, with the arrangement parameters determined comprehensively based on the grouting area, geology, and karst development. The depth must penetrate the karst development zone of the bedrock layer to block the hydraulic connection between the inside and outside, fill the karst caves at the bottom of the wall, and also serve as a boundary constraint for subsequent grouting, enhancing the grouting effect. Furthermore, full-coverage grouting is performed at a certain depth below the bedrock within the protection area to fill karst caves and block hydraulic channels in bedrock fissures. This depth is determined based on the karst development. The depth of the boundary vertical grouting curtain should be greater than the depth of the full-coverage grouting layer.

[0028] 8) Within the protected area, if the soil above the bedrock interface is sandy soil or there is a layer of cohesive soil with a thickness less than the minimum safe thickness, isolation grouting is required to form a stable reinforced isolation layer. For the area below the ground surface of buildings and structures, surface inclined hole grouting should be used to avoid areas without surface grouting conditions. The grouting reinforcement thickness should not be less than the minimum safe thickness to reduce the impact of uneven bedrock deposition and collapse funnels below. If the soil layer above the bedrock interface is cohesive soil and the thickness meets the minimum safe thickness requirement, isolation grouting is not required.

[0029] The minimum safe thickness is determined by model tests or engineering experience, and is generally not less than 5m.

[0030] 9) After the above protective measures are implemented, the shield tunnel can be excavated normally.

[0031] Example 1: Figure 1 This is a schematic diagram of an embodiment of the present invention based on an interlayered model of cohesive soil and sandy soil, wherein: The shield tunnel 5 passes under the existing building 4. The shield tunnel 5 is located in the cohesive soil layer 2 of the overburden layer. There is a sandy soil interlayer 3 between the cohesive soil layer 2 and the bedrock karst development zone 1. Existing building 4 is a single high-rise building, which cannot be relocated and needs to be protected in situ. However, the ground conditions are limited, and it is impossible to obtain the location of the karst cave below the bedrock through ground drilling. It is also difficult to take relevant measures from the surface area where the building is located. It is necessary to determine the protection scope and take effective karst collapse prevention measures.

[0032] Specifically, the implementation steps for determining the scope of protection are as follows: First, based on the geological borehole data around the buildings, the properties of the overburden soil and the depth of the bedrock surface in the area to be tunneled under the shield are determined by fitting the data. H 1; Then, based on the design dimensions of the existing buildings and the tunnel section to be constructed, the outer diameter of the tunnel section to be constructed is obtained. D and building span B ; According to the requirements of the building property owner, the distance to the control protection zone outside the building boundary was obtained. S 1; Based on the underpass relationship of the tunnel section to be constructed, the distance from the center of the tunnel section to the mid-span of the building structure is obtained. S 2. and the distance from the center of the tunnel to the bedrock surface in the section to be constructed H ; Based on current standards, regulations, or the requirements of the property owner, the approximate range of the tunnel section to be constructed is obtained. S 3. The soil disturbance outside this range can be considered to have minimal impact on the tunnel structure of the section to be constructed. Specifically, in this embodiment, the disturbance of the soil outside the section structure is considered to be minimal. D Scope, i.e. S 3 = 3.5 D ; Based on geological survey data, the thickness of the cohesive soil layer is as follows: H n The thickness of the sandy soil interlayer is H sj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: Since the safety protection requirements of both the tunnel section to be constructed and the superstructure need to be met simultaneously, in this embodiment, the tunnel section to be constructed is located to the left of the structural boundary of the superstructure, and the larger value is taken for the overall protection range on the left side of the ground. L 2. The overall protection area on the right side of the ground is taken as follows: L 1, meaning the overall ground protection area is L 2+ B + L 1.

[0033] After determining the protection area, treatment plans need to be implemented for the strata and karst cave development areas within the area. The treatment plans mainly include a vertical grouting curtain 6, a full-coverage grouting layer 7, and an isolation grouting layer 8. The specific implementation steps are as follows: Step 1: Surface drilling and grouting are carried out at the boundary of the protected area to form a vertical grouting curtain 6. Its depth needs to penetrate the karst development zone of the bedrock to block the hydraulic connection between the inside and outside. The isolation curtain can also serve as a boundary constraint for subsequent grouting and enhance the grouting effect.

[0034] Step two: Based on the karst development revealed by surrounding geological boreholes, surface drilling grouting is used to grout a depth of 10m below the bedrock within the protected area, forming a full-coverage grouting zone 7 to fill karst caves and block hydraulic channels in bedrock fissures. Where surface grouting is not feasible for buildings and structures, inclined borehole grouting should be used in other surface areas.

[0035] Step 3: Since the layer above the bedrock interface in this embodiment is a sandy soil interlayer, surface drilling grouting is used to isolate the sandy soil layer within the protection area, forming a stable isolation grouting layer 8. The grouting reinforcement thickness should not be less than the minimum safe thickness to reduce the impact of uneven bedrock deposition and subsidence funnels below; in this embodiment, the minimum safe thickness is 5m. Where there are no surface grouting conditions for buildings and structures, inclined hole grouting should be used in other surface areas.

[0036] In step two, the grouting depth reaches the bottom of the known karst cave 9 discovered by the surrounding boreholes.

[0037] In step one, the grouting depth of the boundary isolation curtain should be greater than the depth of the internal full-coverage grouting strip in step two.

[0038] In steps one, two, and three, the vertical and inclined hole grouting on the ground are arranged in a quincunx pattern. The specific arrangement parameters are determined comprehensively based on the grouting range, geology, and karst development.

[0039] In steps one, two, and three, during grouting drilling, if karst caves are found while drilling in the bedrock, they must be filled densely to enhance the stability of the bedrock, block the hydraulic channels in the bedrock fissures, and reduce the risk of karst cave collapse.

[0040] After the above protective measures are implemented, the shield tunnel can be excavated normally.

[0041] Example 2: Figure 2 This is a schematic diagram of an embodiment of the present invention based on an interlayered model of sandy soil and cohesive soil; wherein, The shield tunnel 5 passes under the existing building 4. The shield tunnel 5 is located in the sandy soil layer 2 of the overburden. There is a cohesive soil interlayer 3 between the sandy soil layer 2 and the bedrock karst development zone 1. Four of the existing buildings are cultural relics and cannot be relocated in coordination, so they need to be protected in situ. However, the ground conditions are limited, and it is impossible to obtain the location of the karst caves below the bedrock through ground drilling. It is also difficult to take relevant measures from the surface area where the buildings are located. It is necessary to determine the protection scope and take effective karst collapse prevention measures.

[0042] Specifically, the implementation steps for determining the scope of protection are as follows: First, based on the geological borehole data around the buildings, the properties of the overburden soil and the depth of the bedrock surface in the area to be tunneled under the shield are determined by fitting the data. H 1; Then, based on the design dimensions of the existing buildings and the tunnel section to be constructed, the outer diameter of the tunnel section to be constructed is obtained. D and building span B ; According to the requirements of the building property owner, the distance to the control protection zone outside the building boundary was obtained. S 1; Based on the underpass relationship of the tunnel section to be constructed, the distance from the center of the tunnel section to the mid-span of the building structure is obtained. S 2. and the distance from the center of the tunnel to the bedrock surface in the section to be constructed H ; Based on current standards, regulations, or the requirements of the property owner, the approximate range of the tunnel section to be constructed is obtained. S 3. The soil disturbance outside this range can be considered to have minimal impact on the tunnel structure of the section to be constructed. Specifically, in this embodiment, the disturbance is considered to be minimal outside the tunnel structure. D Scope, i.e. S 3 = 2.5 D ; Based on geological survey data, the thickness of the sandy soil layer is as follows: H s The thickness of the cohesive soil interlayer is H nj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: ; Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ; Since the safety protection requirements of both the tunnel section to be constructed and the superstructure need to be met simultaneously, in this embodiment, the tunnel section to be constructed is located to the left of the structural boundary of the superstructure, and the larger value is taken for the overall protection range on the left side of the ground. L 2. The overall protection area on the right side of the ground is taken as follows: L 1, meaning the overall ground protection area is L 2+ B + L 1.

[0043] After determining the protection area, treatment plans need to be implemented for the strata and karst cave development areas within the area. The treatment plans mainly include a vertical grouting curtain 6 and a full-coverage grouting layer 7. The specific implementation steps are as follows: Step 1: Vertical grouting curtain 6 is formed by drilling vertical holes in the ground to form a vertical grouting curtain at the boundary of the protected area. Its depth needs to penetrate the karst development zone of the bedrock to block the hydraulic connection between the inside and outside. The isolation curtain can also serve as a boundary constraint for subsequent grouting and enhance the grouting effect.

[0044] Step two: Based on the karst development revealed by surrounding geological boreholes, surface drilling grouting is used to grout a depth of 12m below the bedrock within the protected area, forming a full-coverage grouting zone 7 to fill karst caves and block hydraulic channels in bedrock fissures. Where surface grouting is not feasible for buildings and structures, inclined borehole grouting should be used in other surface areas.

[0045] Step 3: Since the layer above the bedrock interface in this embodiment is a cohesive soil interlayer, it should be determined whether isolation grouting is required. In this case, the soil layer above the bedrock interface is cohesive soil and its thickness meets the minimum safe thickness requirement, so isolation grouting is not required; the cohesive soil interlayer itself can reduce the impact of uneven deposition and collapse funnel of the underlying bedrock.

[0046] In step two, the grouting depth reaches the bottom of the known karst cave 9 discovered by the surrounding boreholes.

[0047] In step one, the grouting depth of the boundary isolation curtain should be greater than the depth of the internal full-coverage grouting strip in step two.

[0048] In both steps one and two, the ground drilling grouting adopts a quincunx pattern, and the specific layout parameters are determined comprehensively based on the grouting range, geology, and karst development.

[0049] In steps one and two, during grouting drilling, if karst caves are found while drilling in the bedrock, they must be filled densely to enhance the stability of the bedrock, block the hydraulic channels in the bedrock fissures, and reduce the risk of karst cave collapse.

[0050] After the above protective measures are implemented, the shield tunnel can be excavated normally.

[0051] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for protecting structures under a shield tunnel in a karst area, characterized in that, Includes the following steps: 1) Obtain the bedrock boundary and the properties of the overlying soil by drilling around the building; 2) Obtain the relative positional relationships of the structures, shield tunnel, and bedrock interface; 3) Select the appropriate stratigraphic model based on the properties of the overlying soil layer; 4) By determining the relative positional relationship between the tunnel, buildings, and strata in the section to be constructed, the formula for calculating the range parameters under critical conditions is determined, and the protection range of the buildings is obtained. 5) Grouting is carried out at the boundary of the protected area to form an isolation curtain. The grouting holes penetrate the karst development zone of the bedrock layer to block the hydraulic connection between the inside and outside and fill the karst caves at the bottom of the wall. Grouting is also carried out at a certain depth below the bedrock within the protected area to fill the karst caves and block the hydraulic channels in the bedrock fissures. 6) Within the protected area, the soil above the bedrock interface is isolated by grouting to form a stable reinforced isolation layer. For the area below the ground surface of buildings and structures, inclined hole grouting is used to avoid areas without ground grouting conditions.

2. The method for protecting structures under a shield tunnel in a karst area according to claim 1, characterized in that, The overburden layer is a pure sand layer, a pure clay layer, or an interlayer containing bedrock. The protection range is calculated by selecting the corresponding geological model based on the geological conditions.

3. The method for protecting structures under shield tunneling in karst areas according to claim 1, characterized in that, The acquisition of the relative positional relationships of the building structure, the shield tunnel, and the bedrock interface includes: outer diameter of the tunnel section under construction D and building span B ; Control and protection zone distance of buildings and structures S 1; Distance from the center of the tunnel in the section to be constructed to the mid-span of the building or structure S 2. and the distance from the center of the tunnel to the bedrock surface in the section to be constructed H ; Approach range of the tunnel section to be constructed S 3.

4. The method for protecting structures under shield tunneling in karst areas according to claim 3, characterized in that, The stratigraphic models are divided into two types based on the properties of the overburden soil: sandy soil interbedded with cohesive soil interbedded with sandy soil.

5. The method for protecting structures under shield tunneling in karst areas according to claim 4, characterized in that, When the overburden is a sandy soil layer, the collapse is a funnel-shaped collapse with a collapse angle. The collapse angle α is determined by model tests or engineering experience methods. When the overburden is cohesive soil, the collapse is a soil-cavity type collapse, which is considered a vertical collapse.

6. The method for protecting structures tunneled under a shield tunnel in a karst area according to claim 5, characterized in that, When the overburden is cohesive soil and there is a sandy soil interlayer above the bedrock surface, the cohesive soil interlayer sandy soil interlayer model is selected for calculation, wherein: The thickness of the cohesive soil layer is H n The thickness of the sandy soil interlayer is H sj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: ； When there are no interlayers, it simplifies to a pure cohesive soil model. H sj =0, then: ； Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ； When there are no interlayers, it simplifies to a pure cohesive soil model. H sj =0, then: ； Because it is necessary to simultaneously meet the safety protection requirements of both the tunnel section to be constructed and the superstructure, the protection zone outside the boundary of the superstructure on the side closer to the tunnel section to be constructed is taken as the larger of the two values, denoted as . L The protected area outside the boundary on the other side of the building structure is taken as value L 1; 。 7. The method for protecting structures under a shield tunnel in a karst area according to claim 5, characterized in that, When the overburden is sandy soil and there is a cohesive soil interlayer above the bedrock surface, the sandy soil interlayer model with cohesive soil is selected for calculation, wherein: The thickness of the sandy soil layer is H s The thickness of the cohesive soil interlayer is H nj ; Based on the control protection distance of the buildings and structures, the protection zone range under critical conditions is obtained. L 1: ； When there are no interlayers, it is simplified to a pure sandy soil model. H s = H 1, then: ； Based on the control protection distance of the tunnel section to be constructed, the protection zone range under critical conditions is obtained. L 2: ； When there are no interlayers, it is simplified to a pure sandy soil model. H nj =0, then: ； Because it is necessary to simultaneously meet the safety protection requirements of both the tunnel section to be constructed and the superstructure, the protection zone outside the boundary of the superstructure on the side closer to the tunnel section to be constructed is taken as the larger of the two values, denoted as . L The protected area outside the boundary on the other side of the building structure is taken as value L 1; 。 8. The method for protecting structures under a shield tunnel in a karst area according to claim 6 or 7, characterized in that, The protection range is the sum of the larger values ​​on the left and right sides outside the structural boundary of the building, plus the length of the building's span B.

9. The method for protecting structures under a shield tunnel in a karst area according to claim 1, characterized in that, In step 5), the depth of the vertical grouting curtain at the boundary is greater than the depth of the full-coverage grouting layer.

10. The method for protecting structures under a shield tunnel in a karst area according to claim 1, characterized in that, In step 6), if the soil above the bedrock interface is sandy soil or there is a cohesive soil layer with a thickness less than the minimum safe thickness, isolation grouting is performed to form a stable reinforced isolation layer. For the area below the ground surface of buildings and structures, surface inclined hole grouting should be used to avoid areas where there is no ground grouting condition, and the grouting reinforcement thickness should not be less than the minimum safe thickness. The minimum safe thickness is not less than 5m.

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