A construction method of small-bin jump-digging across an operating subway tunnel

Abstract

A kind of small bin jump-digging construction method crossing over operating subway tunnel, comprising the following steps: the soil layer between new tunnel and existing structure in construction area is reinforced by pile body and ring beam reinforcement scheme, and multiple stress release holes are drilled at intervals to replace the traditional direct excavation of foundation pit operation mode, the stress release holes are drilled sequentially and at intervals, and then the soil between the holes is excavated to form a foundation pit, the extrusion stress of the soil excavation is released into the interstice of the stress release holes, which can effectively reduce the ground rebound caused by large-area excavation unloading, effectively control the rebound and uplift deformation of the underlying tunnel caused by foundation pit excavation, and at the same time, the stress release function of the stress release holes is maintained by the continuous maintenance of the form of the stress release holes by the retaining wall slurry, and the foundation pit is excavated one by one in this state, so that the construction deformation is always small, and the safety construction environment of the new tunnel is ensured, which facilitates the tunnel construction and ensures the construction safety and operation safety of the tunnel passing through the area.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering construction technology, and in particular to a method for small-section skip excavation construction over an operating subway tunnel. Background Technology

[0002] Currently, with the commencement of a new round of urban rail transit construction projects across various regions, various types of construction crossing existing operational tunnels have gradually become commonplace, resulting in numerous deep foundation pit projects crossing or laterally penetrating operational tunnels. However, current technological levels are insufficient to fully guarantee the safety of existing operational tunnels and the effectiveness of tunnel construction during crossings. Therefore, close-proximity construction of existing lines, including crossings, has become a major technical challenge that urgently needs to be overcome.

[0003] Under normal circumstances, when constructing a new project that crosses an existing operational tunnel, the excavation and unloading of the foundation pit will inevitably cause the underlying tunnel to heave and deform. Various ground reinforcement measures have emerged as a result. However, regardless of the reinforcement scheme adopted, the impact on surrounding traffic and nearby structures (such as underground pipelines) is unavoidable, sometimes even causing serious environmental damage. For tunnels constructed on-site with limited space, complex geological conditions, and high engineering risks, especially those crossing existing tunnels, pipelines, and nearby structures, the construction is particularly challenging. Risks remain, including significant disturbance to the surrounding soil, excessive displacement or deformation of adjacent structures, and disruption to the normal operation of existing structures. A more systematic design and construction methodology is needed to guide this process. Otherwise, not only is the implementation effect difficult to guarantee, but the construction costs are also prohibitively high.

[0004] Chinese patent literature discloses the following: Existing Tunnel Crossing System and Construction Method Based on Pit Jump Excavation and Arch Conversion (CN111305219 A): The system includes retaining piles, a lattice steel frame, and an arch structure; the pit is divided into several small pits in a planar manner, located on both sides of the existing tunnel, arranged longitudinally in rows, and extending downwards below the arch bottom of the existing tunnel. This invention is based on a "divide and conquer" pit excavation method. However, although this method provides stable protection by adding a retaining structure, due to the large area of ​​the pit, the large-area excavation and unloading operations during the excavation of the new tunnel still cause a high amount of ground rebound, which will cause significant disturbance to adjacent existing structures and the existing tunnel. This will cause a certain degree of rebound and heave deformation in the tunnel below the pit excavation area, which is detrimental to the construction safety and operational safety of the tunnel area. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a method for constructing a small-section skip-excavation method for crossing an operating subway tunnel. This method aims to reduce the disturbance caused by the excavation of a new tunnel to adjacent existing structures and tunnels, reduce the ground rebound caused by large-area excavation and unloading, effectively control the rebound and heave deformation of the tunnel below caused by the excavation of the foundation pit, ensure smaller construction deformation, facilitate tunnel construction, and ensure the safety of the tunnel during construction and operation in the area.

[0006] This invention is implemented through the following technical solution: a method for small-section skip-excavation construction over an operating subway tunnel, comprising the following steps:

[0007] S1: Select the foundation above the vertical intersection area of ​​the new tunnel and the existing tunnel as the construction area, and select the foundation above the areas on both sides of the existing tunnel as the extension area. Ensure that the overhead trajectory of the extension area overlaps with the new tunnel. Carry out pile reinforcement at the junction of the extension area and the construction area to ensure that the pile array formed by the pile driving isolates the extension areas on both sides from the construction area.

[0008] S2: Divide the construction area into zones to ensure that the zone is divided into multiple parallel and connected sub-zones. The two ends of the parallel sub-zones are connected to the pile arrays of the extension zones on both sides. A ring beam is fixedly set at the ground surface at the boundary of each sub-zone, and the outline of the ring beam overlaps with the outline of the sub-zone boundary.

[0009] S3: Starting from one end of the parallel small section body, drill multiple stress relief holes in the end section. The multiple stress relief holes are distributed in parallel according to the extension trajectory of the parallel small section body. For each stress relief hole drilled, apply wall protection mud to the inside of the hole and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction.

[0010] Crossing an adjacent small section, continue drilling multiple stress relief holes at the intervals to form identical parallel hole bodies, and apply wall-protecting mud to each stress relief hole in the same way;

[0011] Perform continuous skip drilling operations in the same manner, drill multiple stress relief holes in parallel at multiple spaced small sections, and apply wall protection mud to each stress relief hole in the same manner.

[0012] S4: Drill multiple stress relief holes in a small section where no stress relief hole is drilled at one end. The multiple stress relief holes are distributed in parallel according to the extension trajectory of the parallel body of the small section. For each stress relief hole drilled, apply wall protection mud to the inside of the hole and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction.

[0013] Crossing an adjacent small section, continue drilling multiple stress relief holes in the small sections where no stress relief holes have been drilled, forming the same parallel distribution of holes. Apply wall protection mud to each stress relief hole in the same way, and add a suction device to ensure that the wall protection mud is in a state of continuous pumping out and sucking in.

[0014] Perform continuous skip drilling operations in the same manner, drill multiple stress relief holes in parallel in the remaining multiple small sections with multiple intervals, apply wall protection mud to each stress relief hole in the same manner, and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction.

[0015] S5: Starting from one end of the parallel small section, remove all the wall slurry from each stress relief hole in the end small section, and excavate the soil around the stress relief hole after the wall slurry has been removed, so that the end small section presents a hollow groove shape.

[0016] Crossing an adjacent small section, the mud suction and soil excavation of the spaced small sections are carried out in the same way. The suction and skip excavation operations are carried out continuously in the same interval, so that the small sections side by side present an intermittent foundation pit shape.

[0017] S6: Starting from a small section that has not been excavated at one end, remove all the wall slurry from each stress relief hole. Excavate the soil around the stress relief hole after the wall slurry has been removed. Perform suction and skip excavation operations on the remaining small sections that have not been excavated in the same way, so that the small sections are arranged in a continuous parallel foundation pit shape.

[0018] S7: Use the foundation pit of the small section as the construction site for the new tunnel and carry out the construction project of the new tunnel.

[0019] Furthermore, in step S3, multiple calculation examples containing stress relief holes are established using the finite element method. The deformation of the existing tunnel in the deformation cloud diagram of each calculation example is analyzed. The calculation example in which the maximum deformation of the existing tunnel is ≤ the preset value A is selected as the result example. The modeling data of the stress relief holes in the result example is used as the actual construction dimensions. The drilling of stress relief holes is carried out according to the actual construction dimensions.

[0020] Furthermore, the preset value A = 1.25 mm.

[0021] Furthermore, in step S5, during the excavation process, the reinforcement plane range is determined based on the geological conditions of the small compartment and the excavation depth to reinforce the strata. The reinforcement depth is from the bottom of the lock ring beam to the bottom of the pit. Only after the reinforcement strength reaches the preset requirements can the excavation of the foundation pit below continue.

[0022] Furthermore, in step S5, jet grouting is used to reinforce the bottom wall of the inner cavity of each foundation pit. During the stratum reinforcement, the depth of the pilot hole and the grouting pressure are controlled to avoid damage to the existing tunnel structure, and the existing tunnel is monitored simultaneously.

[0023] Furthermore, in step S7, when constructing a new tunnel, the inverted shaft wall construction method is used for the design and construction of the vertical shaft in the foundation pit of the small section. The initial support is a combination of one or more of shotcrete, anchor bolts, grid steel frame and temporary steel support. The bottom grid is installed at the design elevation of the pit bottom so that the bottom grid is connected to the steel pipe shed. The secondary lining should preferably be made of cast-in-place reinforced concrete.

[0024] Furthermore, in step S7, when constructing a new tunnel, the construction ground is pre-reinforced. Once the reinforcement strength reaches the preset requirements, the foundation pit is excavated, the rigidity of the retaining structure adjacent to the existing tunnel is strengthened, and dewatering work is carried out.

[0025] Furthermore, in step S7, when constructing the new tunnel, steel pipe sheds are installed longitudinally along the bottom of the pit using the working shaft of the new tunnel. The steel pipe sheds are constructed according to the design position, and the borehole deviation is measured using an inclinometer to control the direction of the pipe shed installation. The construction error of the steel pipes in both the plane and longitudinal direction is not greater than the preset value. After the foundation pit is excavated to the design elevation, it is connected by a bottom sealing grid.

[0026] The beneficial effects of this invention are as follows: In the construction area, the soil layer between the new tunnel and existing structures is reinforced using a pile and ring beam reinforcement scheme, reducing the impact on existing structures during the excavation of the new tunnel. Furthermore, the traditional direct excavation of the foundation pit is replaced by the intermittent drilling of multiple stress relief holes. By drilling these stress relief holes sequentially and intermittently, and then excavating the foundation pit using the soil between the holes, the compressive stress from the excavated soil is released into the gaps of the stress relief holes. This effectively reduces the amount of ground rebound caused by large-area excavation and unloading, effectively controlling the rebound and heave deformation of the tunnel below caused by the foundation pit excavation. Simultaneously, the wall-protecting mud continuously maintains the correct shape of the stress relief holes and their stress-relieving effect. Under these conditions, the working foundation pit is excavated one by one, thereby ensuring minimal construction deformation at all times and providing a safe construction environment for the new tunnel. This facilitates tunnel construction and ensures the safety of the tunnel during construction and operation in the area. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of a newly constructed tunnel crossing an existing tunnel in one embodiment of the present invention;

[0028] Figure 2 This is a plan view of the excavation of a newly built tunnel foundation pit in one embodiment of the present invention;

[0029] Figure 3This is a deformation cloud diagram of the initial drilling state of a stress relief hole in one embodiment of the present invention;

[0030] Figure 4 This is a deformation cloud diagram of a stress relief hole drilled at one interval in one embodiment of the present invention;

[0031] Figure 5 This is a deformation cloud diagram of the secondary initial drilling state of the stress relief hole in one embodiment of the present invention;

[0032] Figure 6 This is a deformation cloud diagram of the secondary interval drilling state of the stress relief hole in one embodiment of the present invention;

[0033] Figure 7 This is a deformation cloud diagram of the initial excavation state of the foundation pit in one embodiment of the present invention;

[0034] Figure 8 This is a deformation cloud diagram of a foundation pit under one-interval excavation state in one embodiment of the present invention;

[0035] Figure 9 This is a deformation cloud diagram of the secondary initial excavation state of the foundation pit in one embodiment of the present invention;

[0036] Figure 10 This is a deformation cloud diagram of the secondary intermittent excavation state of the foundation pit in one embodiment of the present invention;

[0037] Figure 11 This is a schematic diagram of the curve variation of the maximum deformation of an existing tunnel in one embodiment of the present invention;

[0038] Figure 12 This is a deformation cloud diagram of the initial excavation state of the foundation pit in a pair of proportions of the present invention;

[0039] Figure 13 This is a deformation cloud diagram of the excavation state of a foundation pit during one interval in a pair of proportions of the present invention.

[0040] Figure 14 This is a deformation cloud diagram of the secondary interval excavation state of the foundation pit in a pair of proportions of the present invention.

[0041] Figure 15 This is a deformation cloud diagram of the secondary interval excavation state of the foundation pit in a pair of proportions of the present invention.

[0042] Figure 16 This is a schematic diagram showing the curve variation of the maximum deformation of an existing tunnel in a pair of proportions of the present invention.

[0043] In the diagram: 1-existing tunnel, 2-newly built tunnel, 2a-pile body, 3-ring beam, 4-shaft. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0045] Example 1

[0046] like Figure 1-2 As shown, a method for constructing a small-section skip-excavation project over an operating subway tunnel includes the following steps:

[0047] S1: Select the foundation above the vertical intersection area of ​​the new tunnel 2 and the existing tunnel 1 as the construction area, and select the foundation above the areas on both sides of the existing tunnel 1 as the extension area. Ensure that the overhead trajectory of the extension area overlaps with the new tunnel 2. Reinforce the area by driving piles at the junction of the extension area and the construction area. Ensure that the pile array 2a formed by the pile driving isolates the extension areas on both sides outside the construction area, thereby reducing the impact of the new tunnel 2 on the existing structures on the side when it is excavated.

[0048] S2: Divide the construction area into zones to ensure that the zone is divided into multiple parallel and connected sub-zones. The two ends of the parallel sub-zones are connected to the pile array 2a of the extension zone on both sides. A ring beam 3 (fixed by embedded parts) is fixed at the ground surface at the boundary of each sub-zone. The outline of the ring beam 3 overlaps with the outline of the sub-zone boundary, thereby reducing the impact on adjacent existing structures when the new tunnel 2 is excavated and passing through, and is conducive to the soil stability of subsequent drilling and excavation work.

[0049] S3: Multiple calculation examples of stress relief holes were established using the finite element method in CAE software FLAC3D. The deformation of existing tunnel 1 caused by stress relief holes in each calculation example was analyzed. The calculation example with the maximum deformation of existing tunnel 1 ≤ 1.25mm was selected as the result example, and the results are as follows: Figures 3-6 The deformation cloud map shown depicts stress relief holes with a diameter of 1.5 meters arranged sequentially in a skip-zone manner across various sub-sections. Simultaneously, the deformation of the existing tunnel 1, as shown in the deformation cloud map, is detected at each drilling step. Then, according to... Figures 7-10 The soil between each stress relief hole was excavated to create a foundation pit, and the deformation of the existing tunnel 1, as shown in the deformation cloud diagram, was measured during each excavation step; the results were obtained. Figure 11 The diagram showing the curve of the maximum deformation of the existing tunnel 1 shows that the maximum bulge occurs at the right tunnel arch, which is nearly 1.36 mm high. The final bulge height is about 1.2 mm, and the deformation is relatively small. Based on this, it is calculated that the deformation bulge under the stress relief hole model size in this example meets the preset requirements.

[0050] pass Figures 3-11FLAC3D finite element testing can prove that replacing the traditional direct excavation of the foundation pit with the intermittent drilling of multiple stress relief holes can effectively reduce the amount of ground rebound caused by large-area excavation and unloading, and effectively control the rebound and heave deformation of the tunnel below caused by foundation pit excavation.

[0051] Using the modeling data of the stress relief holes in the FLAC3D result example as the actual construction dimensions, the stress relief holes were drilled according to the actual construction dimensions, and then... Figures 3-6 The following drilling operations were performed using the same arrangement sequence shown:

[0052] Starting from one end of the parallel small section body, multiple stress relief holes are drilled in the end section. The multiple stress relief holes are distributed in parallel according to the extension trajectory of the parallel small section body. For each stress relief hole drilled, wall protection mud is applied to the inside of the hole, and a suction device is added to ensure that the wall protection mud is continuously pumped out and sucked in, so that the wall protection mud can continuously maintain the upright shape of the stress relief hole and its stress relief effect.

[0053] By crossing an adjacent small section, multiple stress relief holes are drilled at the interval small sections to form the same parallel distribution of holes. The wall protection mud is applied to each stress relief hole in the same way to avoid the squeezing effect of adjacent soil in the interval construction method, and further reduce the deformation impact of related components.

[0054] Perform continuous skip drilling operations in the same manner, drill multiple stress relief holes in parallel at multiple spaced small sections, and apply wall protection mud to each stress relief hole in the same manner to ensure that the deformation stress of multiple small sections is released in advance by the stress relief holes.

[0055] S4: Drill multiple stress relief holes in a small section where no stress relief hole is drilled at one end. The multiple stress relief holes are distributed in parallel according to the extension trajectory of the parallel body of the small section. For each stress relief hole drilled, apply wall protection mud to the inside of the hole and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction.

[0056] Crossing an adjacent small section, continue drilling multiple stress relief holes in the small sections where no stress relief holes have been drilled, forming the same parallel distribution of holes. Apply wall protection mud to each stress relief hole in the same way, and add a suction device to ensure that the wall protection mud is in a state of continuous pumping out and sucking in.

[0057] Perform continuous skip drilling in the same manner, drill multiple stress relief holes in parallel in the remaining small sections with multiple intervals, and apply wall protection mud to each stress relief hole in the same manner, and add a suction device to ensure that the wall protection mud is continuously pumped out and sucked in; in this way, all small sections are successfully protected by stress relief holes, and the rebound deformation of the overall soil is effectively controlled.

[0058] S5: Press Figures 7-10 The following excavation operations will be carried out in the same arrangement sequence shown:

[0059] Starting from one end of the parallel section, all the protective mud from each stress relief hole in the end section is removed. The soil around the stress relief hole after the protective mud has been removed is excavated, making the end section appear as a hollow trench. Due to the buffering effect of the pre-arranged stress relief holes, the compressive stress of the excavated soil is released into the gaps of the stress relief holes, effectively reducing the stress compression on the sides and below of the foundation pit, thereby protecting the structure of the existing tunnel 1 below from being affected.

[0060] Crossing an adjacent small section, the mud suction and soil excavation are carried out in the same way for the interval small sections. The suction and skip excavation operations are carried out continuously in the same interval, so that the small sections side by side present an interval-type foundation pit shape, ensuring the formation of multiple foundation pits.

[0061] While excavating each foundation pit, jet grouting was used to reinforce the bottom wall of the inner cavity of each foundation pit. During the stratum reinforcement, the depth of the pilot hole and the grouting pressure were controlled to avoid damage to the existing tunnel 1 structure. Simultaneously, monitoring of the existing tunnel 1 was carried out to further ensure the stability of the soil layer between the new tunnel 2 and the existing structures.

[0062] S6: Starting from a small section that has not been excavated at one end, remove all the protective mud from each stress relief hole. Excavate the soil around the stress relief holes where the protective mud has been removed. Repeat the same suction and skip-excavation operation on the remaining small sections that have not been excavated, creating a continuous parallel foundation pit structure. This successfully establishes all the foundation pit structures. At this point, if... Figure 11 As shown, the final deformation of the existing tunnel 1 is only 1.2mm. The deformation of the existing tunnel 1 is effectively controlled by the offsetting effect of multiple sets of stress relief holes on the deformation of the construction soil, ensuring a safe construction environment for the new tunnel 2.

[0063] S7: The foundation pit of the small section is used as the construction site of the new tunnel 2. The construction of the new tunnel 2 is carried out. The final deformation of the existing tunnel 1 is controlled by the protection of the above-mentioned hole body. The rebound and heave deformation of the tunnel below caused by the excavation of the foundation pit are effectively controlled, and the construction deformation is kept small at all times. This facilitates the tunnel construction and ensures the construction safety and operation safety of the tunnel passing through the area.

[0064] Preferably, in this step, when constructing the new tunnel 2, the vertical shaft 4 is designed and constructed using the inverted shaft wall construction method within the foundation pit of the small section. The initial support is a combination of one or more of shotcrete, anchor bolts, grating steel frame and temporary steel support. The bottom grating is installed at the design elevation of the pit bottom so that the bottom grating is connected to the steel pipe shed. The secondary lining should preferably use cast-in-place reinforced concrete, which effectively improves the stability of the foundation pit.

[0065] Preferably, in this step, when constructing the new tunnel 2, the construction ground is pre-reinforced, and the foundation pit is excavated after the reinforcement strength reaches the preset requirements. The rigidity of the retaining structure on the side adjacent to the existing tunnel 1 is strengthened, and dewatering is carried out to ensure that the foundation pit construction is not affected by dewatering.

[0066] Preferably, in this step, when constructing the new tunnel 2, steel pipe sheds are installed longitudinally along the bottom of the tunnel using the working shaft of the new tunnel 2. The steel pipe sheds are constructed according to the design position, and the borehole deviation is measured using an inclinometer to control the direction of the pipe shed installation. The construction error of the steel pipes in both the plane and longitudinal direction is not greater than the preset value. After the foundation pit is excavated to the design elevation, it is connected by a bottom sealing grid to ensure the standardization of construction dimensions.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that the process of arranging stress relief holes is skipped, and the following steps are included:

[0069] S1: Select the foundation above the vertically intersecting area of ​​the new tunnel 2 and the existing tunnel 1 as the construction area, and select the foundation above the areas on both sides of the existing tunnel 1 as the extension area. Ensure that the overhead trajectory of the extension area overlaps with the new tunnel 2. Carry out pile reinforcement at the junction of the extension area and the construction area to ensure that the pile array 2a formed by the pile driving isolates the extension areas on both sides from the construction area.

[0070] S2: Divide the construction area into zones to ensure that the zone is divided into multiple parallel and connected sub-zones. The two ends of the parallel sub-zones are connected to the pile body 2a array of the extension zone on both sides. A ring beam 3 is fixedly set at the ground surface at the boundary of each sub-zone, and the outline of the ring beam 3 overlaps with the outline of the sub-zone boundary.

[0071] S3: Starting from one end of the parallel small sections, the soil in the end small section is excavated to make the end small section appear as a hollow trench.

[0072] By crossing an adjacent small section, the same method is used to perform skip excavation on the intermittent small sections, so that the parallel small sections present an intermittent foundation pit shape.

[0073] S4: Start excavating the soil from one end of the small section that has not been excavated. Repeat the same process for the remaining small sections that have not been excavated, so that the small sections are arranged in a continuous parallel foundation pit shape.

[0074] S5: Use the foundation pit of the small section as the construction site for the new tunnel 2, and carry out the construction project of the new tunnel 2.

[0075] A mathematical model was established based on the above operational steps. Calculation examples for each step, excluding stress relief holes, were created using the finite element method in the CAE software FLAC3D. The deformation of the existing tunnel 1 in each calculation example was analyzed, resulting in... Figures 12-15 Deformation cloud map ( Figures 12-15 (Following the steps in sequence S2-S5 of this comparative example), and deriving as follows: Figure 16 The diagram showing the curve of the maximum deformation of the existing tunnel 1 indicates that, due to the lack of stress relief holes and soil buffering effect, the comparative example directly carried out the foundation pit jump excavation work. The maximum bulge appeared at the right tunnel arch top, which was nearly 2 mm high, and the final bulge height was about 1.68 mm. The deformation of the existing tunnel 1 was significantly higher than the preset value of 1.25 mm, which proves that the traditional excavation method provided by this comparative example will cause a large amount of deformation.

[0076] Compared to Comparative Example 1, Example 1 can significantly control the deformation of the existing tunnel 1 to a smaller level (1.2 mm). The construction method of stress relief holes provided in Example 1 has obvious construction advantages, which is beneficial to tunnel construction and ensures the construction safety and operation safety of the tunnel when it passes through the area.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. It should be understood that, for those skilled in the art, other modifications, alterations, and equivalent substitutions can be made to the present invention without departing from the feature scope defined in the claims, and these should all fall within the protection scope of the present invention.

Claims

1. A method for constructing a small-section skip-excavation method for crossing an operating subway tunnel, characterized in that: Includes the following steps: S1: Select the foundation above the vertical intersection area of ​​the new tunnel and the existing tunnel as the construction area, and select the foundation above the areas on both sides of the existing tunnel as the extension area. Ensure that the overhead trajectory of the extension area overlaps with the new tunnel. Carry out pile reinforcement at the junction of the extension area and the construction area to ensure that the pile array formed by the pile driving isolates the extension areas on both sides from the construction area. S2: Divide the construction area into zones to ensure that the zone is divided into multiple parallel and connected sub-zones. The two ends of the parallel sub-zones are connected to the pile arrays of the extension zones on both sides. A ring beam is fixedly set at the ground surface at the boundary of each sub-zone, and the outline of the ring beam overlaps with the outline of the sub-zone boundary. S3: Starting from one end of the parallel small section body, drill multiple stress relief holes in the end section. The multiple stress relief holes are distributed in parallel according to the extension trajectory of the parallel small section body. For each stress relief hole drilled, apply wall protection mud to the inside of the hole and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction. Crossing an adjacent small section, continue drilling multiple stress relief holes at the intervals to form identical parallel hole bodies, and apply wall-protecting mud to each stress relief hole in the same way; Perform continuous skip drilling operations in the same manner, drill multiple stress relief holes in parallel at multiple spaced small sections, and apply wall protection mud to each stress relief hole in the same manner. S4: Drill multiple stress relief holes in a small section where no stress relief hole is drilled at one end. The multiple stress relief holes are distributed in parallel according to the extension trajectory of the parallel body of the small section. For each stress relief hole drilled, apply wall protection mud to the inside of the hole and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction. Crossing an adjacent small section, continue drilling multiple stress relief holes in the small sections where no stress relief holes have been drilled, forming the same parallel distribution of holes. Apply wall protection mud to each stress relief hole in the same way, and add a suction device to ensure that the wall protection mud is in a state of continuous pumping out and sucking in. Perform continuous skip drilling operations in the same manner, drill multiple stress relief holes in parallel in the remaining multiple small sections with multiple intervals, apply wall protection mud to each stress relief hole in the same manner, and add a suction device to ensure that the wall protection mud is in a state of continuous pumping and suction. S5: Starting from one end of the parallel small section, remove all the wall slurry from each stress relief hole in the end small section, and excavate the soil around the stress relief hole after the wall slurry has been removed, so that the end small section presents a hollow groove shape. Crossing an adjacent small section, the mud suction and soil excavation of the spaced small sections are carried out in the same way. The suction and skip excavation operations are carried out continuously in the same interval, so that the small sections side by side present an intermittent foundation pit shape. S6: Starting from a small section that has not been excavated at one end, remove all the wall slurry from each stress relief hole. Excavate the soil around the stress relief hole after the wall slurry has been removed. Perform suction and skip excavation operations on the remaining small sections that have not been excavated in the same way, so that the small sections are arranged in a continuous parallel foundation pit shape. S7: Use the foundation pit of the small section as the construction site for the new tunnel and carry out the construction project of the new tunnel.

2. The method for constructing a small-section skip-excavation method for crossing an operating subway tunnel as described in claim 1, characterized in that: In step S3, multiple calculation examples containing stress relief holes are established using the finite element method. The deformation of the existing tunnel in the deformation cloud diagram of each calculation example is analyzed. The calculation example in which the maximum deformation of the existing tunnel is ≤ the preset value A is selected as the result example. The modeling data of the stress relief holes in the result example is used as the actual construction dimensions. The drilling of stress relief holes is carried out according to the actual construction dimensions.

3. The method for small-section skip-excavation construction over an operating subway tunnel as described in claim 2, characterized in that: The preset value A = 1.25 mm.

4. The method for constructing a small-section skip-excavation method for crossing an operating subway tunnel as described in claim 1, characterized in that: In step S5, during the excavation process, the reinforcement plane range is determined based on the geological conditions of the small compartment and the excavation depth to reinforce the strata. The reinforcement depth is from the bottom of the lock ring beam to the bottom of the pit. Only after the reinforcement strength reaches the preset requirements can the excavation of the foundation pit below continue.

5. The method for constructing a small-section skip-excavation method for crossing an operating subway tunnel as described in claim 1, characterized in that: In step S5, jet grouting is used to reinforce the bottom wall of the inner cavity of each foundation pit. During the stratum reinforcement, the depth of the pilot hole and the grouting pressure are controlled to avoid damage to the existing tunnel structure. Simultaneously, the existing tunnel is monitored.

6. The method for constructing a small-section skip-excavation method for crossing an operating subway tunnel as described in claim 1, characterized in that: In step S7, when constructing a new tunnel, the vertical shaft is designed and constructed using the inverted shaft wall construction method in the foundation pit of the small section. The initial support is a combination of one or more of shotcrete, anchor bolts, grid steel frame and temporary steel support. The bottom grid is installed at the design elevation of the pit bottom so that the bottom grid is connected to the steel pipe shed. The secondary lining is made of cast-in-place reinforced concrete.

7. The method for constructing a small-section skip-excavation method for crossing an operating subway tunnel as described in claim 1, characterized in that: In step S7, when constructing a new tunnel, the construction ground is pre-reinforced. Once the reinforcement strength reaches the preset requirements, the foundation pit is excavated, the rigidity of the retaining structure adjacent to the existing tunnel is strengthened, and dewatering is carried out during construction.

8. The method for constructing a small-section skip-excavation method for crossing an operating subway tunnel as described in claim 1, characterized in that: In step S7, when constructing a new tunnel, steel pipe sheds are installed longitudinally along the bottom of the pit using the working shaft of the new tunnel. The steel pipe sheds are constructed according to the design position, and the borehole deviation is measured using an inclinometer to control the direction of pipe shed installation. The construction error of the steel pipes in both the plane and longitudinal direction is not greater than the preset value. After the foundation pit is excavated to the design elevation, it is connected by a bottom sealing grid.

Images