Deformation control method for newly-built structure above rail transit operation tunnel

Abstract

A deformation control method for newly-built structure above rail transit operating tunnel, which is combined with adjustable axial force anchor cable and pipe roof core control system, has mature technology and can be completely implemented on site with little operation difficulty. The method realizes active and fine adjustment of anchor cable axial force, provides data feedback combined with monitoring points on the operating tunnel floor, track and side wall, and can adjust the vertical deformation of existing line in real time, so that the rail transit structure is always in the optimal state, which cannot be achieved by the existing overpass scheme. The method makes it possible to overpass the operating tunnel in small distance and long distance, and realizes the effective combination of active control system, foundation pit support and permanent protection system of anchor cable. The shaft provides space for pipe roof construction and anchor cable installation, and also serves as the retaining structure of the new structure foundation pit. After the construction is completed, the shaft top is sealed to realize the permanent protection of the anchor cable device, and the entire system is effectively connected, reducing the project investment.

Description

Deformation control method for newly constructed structures above operating tunnels of rail transit Technical Field

[0001] This invention relates to the field of technology, and in particular to a method for controlling the deformation of newly constructed structures above railway operation tunnels. Background Technology

[0002] Urban rail transit, due to its advantages of saving land, speed, punctuality, and environmental friendliness, has been planned and constructed on a large scale in major Chinese cities. Currently, my country has 6,000 kilometers of operational rail transit, exceeding the total operational mileage of rail transit in all other countries combined. As a major municipal public works project, the operational safety of rail transit is crucial to the lives and work of millions of people in each city, necessitating strict control over operational safety risks. To effectively ensure the operational safety of rail transit, my country has promulgated numerous operational safety management regulations, such as the "Urban Rail Transit Operation Management Measures" (Ministry of Construction Order No. 140) and the "Technical Specification for Structural Safety Protection of Urban Rail Transit" (CJJ / T202-2013). Cities that have opened rail transit systems have also successively promulgated local rail transit operational safety management measures. The operational safety assurance measures in these regulations mainly focus on the strict deformation control of the civil engineering structure and track structure of rail transit.

[0003] On the other hand, as a crucial urban infrastructure, rail transit is often located in the heart of cities, such as commercial hubs, integrated transportation centers, and beneath main urban roads, where the land above it has high development and utilization value. With the increasing development of urban underground space and the increasingly networked layout of rail transit, the conflict between the demand for underground land use around operating tunnels and the prohibition of development based on operational safety considerations is becoming increasingly prominent. Currently, most new construction projects are located on both sides of rail transit tunnels, while construction directly above them (such as integrated utility tunnels, underground passages, or underground commercial streets) is rare. This is because excavation and unloading directly above would cause severe uplift of the operating tunnel, exceeding the allowable adjustment range of the track fasteners, posing a significant risk of operational safety accidents.

[0004] New construction projects that cross operational rail transit systems will inevitably cause vertical displacement (settlement or bulging) of the track and structure. This displacement can generally be adjusted using track fasteners to restore the original track surface elevation. However, compared to new construction projects that cross beneath rail transit systems causing settlement, track fasteners have a much smaller capacity to handle bulging deformation. The permissible bulging deformation for operational safety is only 3mm, while fasteners can adjust for settlement up to 20mm. Therefore, implementing overhead crossing projects is extremely difficult. For operational tunnels with expansion joints, these are inherently weak points in track-structure connections and prone to water leakage. The differential deformation on both sides of the expansion joint caused by overhead construction further increases the difficulty of the project. If track bulging defects already exist before the crossing construction, the rail transit operator will directly prohibit such overhead crossing projects. How to solve the problem of crossing above operational tunnels, especially long-distance (greater than twice the width of the operational tunnel) and short-distance (vertical distance less than 2m) overhead crossings directly above operational tunnels, is a pressing technical challenge that my country needs to address.

[0005] For projects involving partial or vertical crossings above the tunnel, the current main solution is to use a post-construction cover structure to somewhat suppress the vertical heave of the operating tunnel (e.g., patent: A method for excavating a foundation pit above an operating rail transit tunnel (authorization announcement number: CN104532849B)). However, this solution does not fundamentally address the issue of reducing the overhead load. Therefore, the operating tunnel will continue to rise during excavation, especially in areas with poor soil properties, where this solution is unsuitable. Furthermore, this solution lacks active control measures and cannot proactively control the heave deformation of the operating tunnel during excavation. Therefore, it cannot solve the problem of unloading during excavation directly above the tunnel. Because the above measures are ineffective in controlling heave, they are even less effective in handling situations where new structures are constructed directly above an operating tunnel over long distances with small intervals.

[0006] Therefore, in view of the above-mentioned defects, the designers of this invention, through dedicated research and design, and by integrating years of experience and achievements in related industries, have developed a deformation control method for newly constructed structures above railway operation tunnels to overcome the aforementioned defects. Summary of the Invention

[0007] The purpose of this invention is to provide a deformation control method for newly constructed structures above operating tunnels of rail transit, which can completely solve the problems of engineering construction above operating tunnels, realize active and dynamic control of vertical deformation during the excavation process, and make it possible to construct new structures directly above operating tunnels over long distances with small intervals. This ensures the safety of rail transit operation while releasing usable urban underground space, improving urban functions, and enhancing the quality of urban living.

[0008] To achieve the above objectives, this invention discloses a deformation control method for newly constructed structures above operational rail transit tunnels, characterized by comprising the following steps:

[0009] Step 1: Collect as-built data of the operating tunnel and conduct on-site surveys to detect the planar and vertical positions of the underground structure of the existing operating rail transit, the geomechanical parameters of the strata, the geometric dimensions of the existing rail transit structure, and the track structure information;

[0010] Step 2: Conduct deformation monitoring on existing rail transit tunnels. The monitoring range extends 50m beyond each end of the crossing section along the tunnel length. Track vertical displacement monitoring points are set up on the operating tunnel tracks to control the absolute value of vertical deformation, and sidewall vertical displacement monitoring points are set up on both sides of the tunnel section to monitor the lateral tilt of the structure.

[0011] Step 3: Install anchor cables from the ground on both sides of the operating tunnel, with three anchor cables as a group. The starting point of the soil layer where no uplift deformation occurs is used as the boundary line between the free section and the anchoring section of the prestressed anchor cable.

[0012] Step 4: After constructing the lock ring beam on the ground, the vertical shaft is manually excavated using the inverted shaft wall construction method. The side walls of the vertical shaft are constructed using steel grating and shotcrete.

[0013] Step 5: Install a horizontal pipe curtain inside the shaft, then construct the pipe curtain cap beam, install steel pipe columns, and construct the anchor cable cap beam in sequence. After the anchor cables pass through the above components from bottom to top, install an adjustable axial force device. Perform the first stage of tensioning according to the current heave situation to achieve the first adjustment of the vertical displacement of the track.

[0014] Step Six: Excavate the foundation pit above the pipe jacking, and install steel walers and steel supports as the excavation progresses. During the excavation process, the anchor cables are tensioned for the second time to adjust the axial force of the anchor cables, thereby changing the vertical pressure applied by the pipe jacking to the operating tunnel and achieving dynamic adjustment of the tunnel's vertical displacement.

[0015] Step 7: After the foundation pit is excavated to the designed bottom elevation, the foundation slab and waterproofing are constructed, the foundation slab of the new structure is constructed, the steel supports are removed, the main structure construction is completed, and cohesive soil is backfilled on the new structure to the ground level.

[0016] Step 8: Continuously monitor the vertical displacement of the operating tunnel. After the deformation stabilizes, permanently fix the adjustable axial force device, backfill the top of the shaft to the ground, remove the shaft structure 2.5m below the ground, seal the top, and fill with plain concrete to form protection.

[0017] Step five specifically includes: installing a horizontal pipe curtain inside the shaft; backfilling plain concrete from the bottom of the shaft to below the pipe curtain capping beam; constructing the pipe curtain capping beam within the clear space of the shaft structure; reserving a PVC sleeve above the pipe curtain capping beam for anchor cables to pass through; after completing the pipe curtain capping beam construction, installing steel pipe columns on the upper part of the pipe curtain capping beam; passing anchor cables from bottom to top; continuing to backfill cement soil upwards to 1m below the support axis of the new structure foundation pit; continuing to backfill limiting plain concrete to a height of 2m; then backfilling cement soil to 0.5m below the support axis of the foundation pit; constructing the anchor cable capping beam; again reserving a PVC sleeve for anchor cables to pass through from bottom to top; installing an adjustable axial force device; and performing the first stage of tensioning based on the current heave situation to achieve the first adjustment of the vertical displacement of the track.

[0018] In determining the free section of the prestressed anchor cable, numerical calculations are performed on the excavation conditions to obtain the heave deformation of each soil layer below the existing structure. The soil layer corresponding to ΔSn≤0.025∑ΔSi is found. In the above formula, ΔSn is the calculated deformation value of the soil layer with a thickness of 0.5m above the calculation depth, and ΔSi is the calculated deformation value of the i-th soil layer within the calculation depth range. The soil layer that satisfies the above formula is basically no longer heaves, that is, the soil layer that does not heave upwards. This position is set as the end point of the free section and the starting point of the anchorage section, thereby determining the length of the free section.

[0019] The adjustable axial force device includes a base steel plate, rolling elements, a rotatable internal threaded sleeve, a vertically movable external threaded sleeve, a limiting bolt, and an anchor head. The base steel plate is pre-embedded in the reinforced concrete anchor cable crown beam using multiple anchor bars. The upper surface of the base steel plate is provided with two ball track grooves for the rolling elements to roll. Edge limiting protrusions are provided on the outer side of the ball track grooves. The rolling elements contain two rings of high-carbon chromium steel balls. The upper part of the rolling elements is a rotatable internal threaded sleeve. A limiting bolt is provided between the base steel plate and the rotatable internal threaded sleeve to limit their horizontal misalignment. The anchor head of the anchor cable is connected to the vertically movable external threaded sleeve to fix the end of the anchor cable. The vertically movable external threaded sleeve is threadedly connected to the rotatable internal threaded sleeve.

[0020] Wherein: the vertically movable external threaded sleeve has a vertical travel stroke of not less than 150mm.

[0021] Wherein: the vertically movable external threaded sleeve includes a sleeve top seat at the upper end and an external threaded part with external threads at the lower end, and the vertically movable external threaded sleeve has a grouting hole in the middle and multiple upper anchor cable holes around the grouting hole.

[0022] Wherein: the rotatable internal threaded sleeve includes a sleeve base at the lower end and an internal threaded part with internal threads at the upper end, and the rotatable internal threaded sleeve has multiple anchor cable holes around the periphery of the limiting bolt.

[0023] The anchor head is made of a 65mm thick steel plate and has grouting holes and anchor cable holes.

[0024] Wherein: the pipe curtain includes multiple steel pipes arranged at intervals, and the steel pipes are equipped with steel cages and cast-in-place concrete. The steel pipes are connected by interlocking angle steel and reinforcing ribs.

[0025] Wherein: the steel cage inside the tube curtain extends into the tube curtain crown beam, and the ends of the steel pipes of the tube curtain are connected to the connecting pads that are pre-embedded in the tube curtain crown beam with anchor bars by full welding.

[0026] As can be seen from the above, the deformation control method for newly constructed structures above rail transit operating tunnels of the present invention has the following effects:

[0027] 1. Through an active and dynamic control system, construction above long-distance, parallel-track tunnels becomes possible. This method can free up urban space for development while ensuring the operational safety of existing rail transit lines. This method has the following characteristics:

[0028] 2. Through the core control system of adjustable axial force anchor cable + pipe jacking, the technology is mature, can be fully implemented, and is very easy to operate. It can achieve active and precise adjustment of the anchor cable axial force. Combined with the data feedback provided by the monitoring points on the floor, track and side walls of the operating tunnel, it can adjust the vertical deformation of the existing line in real time, so that the rail transit structure is always in the optimal state. This is something that existing overpass schemes cannot do, making it possible to pass over operating tunnels with small clearance, long distance and smooth flow.

[0029] 3. To compensate for the vertical displacement defects caused by the rail transit overpass project, the adjustment values ​​are uniformly incorporated into the displacement adjustment control target of this overpass project. Therefore, this plan will not only not worsen the operating conditions of the tunnel, but will also adjust the final track condition to the optimal level.

[0030] 4. It effectively integrates the active control system, foundation pit support, and permanent anchor cable protection system. The shaft provides space for pipe jacking and anchor cable installation, while also serving as a retaining structure for the new structural foundation pit. After construction, the top of the shaft is sealed, achieving permanent protection for the anchor cable devices. The entire system is effectively interconnected, reducing project investment.

[0031] 5. By setting up steel pipe columns, the axial force adjustment device can be adjusted at the ground level, eliminating the need for construction personnel to enter the bottom of the shaft, thus reducing the difficulty of implementation and ensuring the safety of the workers.

[0032] 6. Pipe curtains are installed at the expansion joints of the operating tunnel. The steel pipes in each pipe curtain are interlocked with angle steel to form a whole. The ends are anchored into the same capping beam, so that each pipe curtain forms a whole structure. This effectively controls the differential deformation on both sides of the expansion joint and provides an effective solution to the difficulties of tunneling.

[0033] The details of this invention will become apparent from the following description and the accompanying drawings. Attached Figure Description

[0034] Figure 1 shows a schematic diagram of steps one and two of the deformation control method for newly constructed structures above rail transit operation tunnels according to the present invention.

[0035] Figure 2 shows a schematic diagram of step three of the present invention.

[0036] Figure 3 shows a schematic diagram of step four of the present invention.

[0037] Figure 4 shows a schematic diagram of step five of the present invention.

[0038] Figure 5 shows a schematic diagram of step six of the present invention.

[0039] Figure 6 shows a schematic diagram of step seven of the present invention.

[0040] Figure 7 shows a schematic diagram of step eight of the present invention.

[0041] Figure 8 shows a schematic diagram of the construction location of the pipe curtain in this invention.

[0042] Figure 9 shows a schematic diagram of the tube curtain structure in this invention.

[0043] Figure 10 shows a schematic diagram of the connection between the tube curtain and the tube curtain cap beam in this invention.

[0044] Figure 11 shows a schematic diagram of the adjustable axial force device in this invention.

[0045] Figure 12 shows a schematic diagram of the vertically movable external threaded sleeve in this invention.

[0046] Figure 13 shows a schematic diagram of the rotatable internal threaded sleeve in this invention.

[0047] Figure 14 shows a schematic diagram of the anchor head structure in this invention.

[0048] Figure label:

[0049] 101. Operating tunnel; 102. Sidewall vertical displacement monitoring point; 103. Track vertical displacement monitoring point; 104. Prestressed anchor cable free section; 105. Prestressed anchor cable anchorage section; 106. Shaft; 107. Locking beam ring; 108. Pipe jacking; 109. Pipe jacking capping beam; 110. PVC sleeve; 111. Plain concrete; 112. Lower cement-soil layer; 113. Confined plain concrete layer; 114. Upper cement-soil layer; 15. Steel pipe column; 116. Anchor cable cap beam; 117. Adjustable axial force device; 118. Foundation; 119. Steel support; 120. Steel waler; 121. New structure; 122. Cohesive soil; 123. Plain concrete filling; 124. Expansion joint; 1081. Steel pipe; 1082. Reinforcing cage; 1083. Cast-in-place concrete; 1084. Grouting pipe; 1085. Interlocking angle steel; 1086. Reinforcing rib; Detailed Implementation

[0050] Referring to Figures 1 to 7, the deformation control method for newly constructed structures above rail transit operation tunnels of the present invention is shown.

[0051] The deformation control method for newly constructed structures above rail transit operating tunnels includes parameter determination, which may include determination of the free section (non-grouting section) of prestressed anchor cables, determination of the anchoring section (grouting section), determination of the horizontal spacing of anchor cables, and determination of an adjustable axial force device, so as to achieve active and dynamic control of the vertical deformation of existing rail transit structures by dynamically adjusting the axial force of anchor cables.

[0052] In determining the free section of the prestressed anchor cable, the anchor cable is installed on the ground to facilitate anchor cable construction and subsequent axial force adjustment. Without adopting existing line uplift deformation control measures, numerical calculations are performed on the excavation conditions to obtain the uplift deformation of each soil layer below the existing structure. The soil layer corresponding to ΔSn≤0.025∑ΔSi is found, where ΔSn is the calculated deformation value of a soil layer with a thickness of 0.5m above the calculation depth, and ΔSi is the calculated deformation value of the i-th soil layer within the calculation depth range. The soil layer satisfying the above formula can be considered as a soil layer that has essentially stopped uplifting, i.e., a soil layer that does not experience upward uplift. This position is set as the end of the free section and the starting point of the anchorage section, thus determining the length of the free section.

[0053] The determination of the anchorage section includes determining its diameter and length. Traditional grouting anchor cables are preferred, with a common diameter of 150mm to 200mm. When the calculated anchorage section length exceeds 35m, jet grouting anchor cables are used instead, with a diameter of 300mm to 600mm selected based on the geological conditions. Regarding the load on the anchorage section, it is determined by 1.2 times the weight of the excavated soil required for the new construction project. Therefore, the anchorage section length should ideally be controlled within 35m, with traditional grouting anchor cables being the preferred choice. When it exceeds 35m, jet grouting anchor cables are used, and in this case, the anchorage section length limit is no longer required.

[0054] In determining the horizontal spacing of the anchor cables, the anchor cables are grouped into groups of three, and the horizontal spacing of a single anchor cable within a group is preferably 1.5m, with the spacing of each group preferably being 12m.

[0055] As shown in Figure 11, the adjustable axial force device 117 may include a base steel plate 1171, rolling elements 1178, a rotatable internal threaded sleeve 1173, a vertically movable external threaded sleeve 1174, a limiting bolt 1176, and an anchor head 1175. The base steel plate 1171 is pre-embedded in the reinforced concrete anchor cable crown beam 116 using multiple anchor bars 1172. The upper surface of the base steel plate 1171 is flush with the anchor cable crown beam 116. (See also Figure 14.) The upper surface of the base steel plate 1171 may be provided with two ball track grooves 1177 for the rolling element 1178 to roll. Edge limiting protrusions 1179 are provided on the outer side of the ball track grooves 1177. The rolling element 1178 may contain two rings of high-carbon chromium steel balls. The upper part of the rolling element 1178 is a rotatable internal threaded sleeve 1173. A limiting bolt 1176 is provided between the base steel plate 1171 and the rotatable internal threaded sleeve 1173 to limit their horizontal misalignment. The anchor head 1175 of the anchor cable 125 is connected to a vertically movable external threaded sleeve 1174 to fix the anchor cable end. The vertically movable external threaded sleeve 1174 is threaded to the rotatable internal threaded sleeve 1173, so that when the axial force of the anchor cable needs to be adjusted, rotating the rotatable internal threaded sleeve 1173 realizes the vertical displacement of the upper vertically movable external threaded sleeve 1174. Preferably, the vertical travel of the vertically movable external threaded sleeve is not less than 150 mm.

[0056] As shown in Figure 12, the vertically movable external threaded sleeve 1174 includes a sleeve top seat 11741 at the upper end and an external threaded part 11742 with external threads at the lower end. The vertically movable external threaded sleeve 1174 has a grouting hole with a diameter of 40mm located in the middle and a plurality of upper anchor cable holes 11743 located around the grouting hole.

[0057] As shown in Figure 13, the rotatable internal threaded sleeve 1173 includes a sleeve base 11731 at the lower end and an internal threaded part 11732 with an internal thread at the upper end. The internal thread of the internal threaded part 11732 engages with the external thread of the external threaded part 11742 to achieve vertical movement. The rotatable internal threaded sleeve 1173 also has multiple corresponding lower anchor cable holes 11733 around the periphery of the limiting bolt 1176.

[0058] The anchor head 1175 can be made of a 65mm thick steel plate, which can also be provided with corresponding grouting holes and anchor cable holes.

[0059] It also includes the determination of the vertical shaft, which will be constructed using a manual excavation and inverted shaft wall method with steel grating and shotcrete, and will be located outside the plane area of ​​the operating tunnel. The vertical shaft will be used to install anti-heave pipe jacking and will also serve as a support structure during the excavation of the foundation pit for new structures. The determination of the vertical shaft includes four aspects: plane dimensions, depth, thickness and reinforcement, and backfill determination.

[0060] The vertical shaft's plan dimensions should be as small as possible to minimize the impact of vertical excavation on the existing rail transit structure. The shaft width should consider the cap beam's load-bearing capacity and the space required for pipe jacking construction. A net shaft width of 2m and a net length of 3.5m are recommended to ensure sufficient space for installing three anchor cables per group within the shaft. This also eliminates the need for additional intermediate supports, reducing costs and improving construction efficiency. Regarding the shaft depth, the shaft structure also serves as the foundation pit support structure. The embedment depth of the support structure at the bottom of the pit should be determined based on calculations. When the calculated depth is lower than the top slab of the existing rail transit structure, the bottom should extend 2m below the tunnel top slab. The thickness of the shaft support structure should consider both the shaft's load-bearing capacity during excavation and the support structure's capacity during the excavation of the new structure's foundation pit. A thickness of 250mm is recommended. The horizontal reinforcement of the steel grating should be determined based on the circumferential stress under the shaft excavation conditions. The vertical reinforcement should be determined based on the vertical stress during the foundation pit excavation stage. The cross-sectional reinforcement should be calculated based on a box girder with a web height equal to the 2m net width of the shaft. Regarding the backfilling of the vertical shaft, the backfilling material is determined according to different vertical positions. From bottom to top, the backfilling materials are plain concrete, reinforced concrete (pipe jacking cap beam), cement soil, plain concrete (corresponding position of the foundation pit support), cement soil, and reinforced concrete (anchor cable cap beam).

[0061] It also includes the determination of the pipe jacking, as shown in Figures 8 and 9. Multiple sets of pipe jacks 108 are deployed above the rail transit tunnel within the crossing area. The ends of the pipe jacks 108 are anchored to the reinforced concrete pipe jacking capping beam 106 via steel cages. The vertical deformation of the operating tunnel is controlled through the axial force transmission path of anchor cable—anchor cable capping beam—steel pipe column—pipe jacking capping beam—pipe jacking—operating tunnel. The determination of the pipe jacking includes three parts: cross-sectional dimensions, length, and planar spacing.

[0062] The cross-section of the pipe curtain is calculated based on a simply supported beam, and the load is calculated as 1.2 times the unloaded weight of the soil above replaced by a single pipe curtain. As shown in Figure 9, the pipe curtain consists of multiple spaced steel pipes 1081, each containing a reinforcing cage 1082 and cast-in-place concrete 1083. The preferred wall thickness of the steel pipe is 20mm, with an outer diameter of 400mm and an inner diameter of 360mm. The length of the pipe curtain is equal to the distance between the inner surfaces of the initial support structures of the shafts on both sides of the tunnel, i.e., pipe curtain length = tunnel width + 500mm on each side + twice the initial support thickness of the shafts. Preferably, the pipe curtain consists of groups of five steel pipes, with a spacing of 12 meters between each group. The horizontal spacing between each steel pipe 1081 within a group is 550mm, and the steel pipes 1081 are connected by interlocking angle steel 1085 and reinforcing ribs 1086 to form a whole. Grouting pipes 1084 are installed around the steel pipes. As shown in Figure 10, the steel cage 1082 inside the tube curtain 108 extends into the tube curtain crown beam 106. The end of the steel pipe 1081 of the tube curtain 108 is connected to the connecting pad 1086, which is pre-embedded in the tube curtain crown beam 106 by anchor bars 1087, by full welding 1088. The tube curtain crown beam 106 is provided with crown beam steel bars 1061.

[0063] It should be noted that the above values ​​are only recommended values ​​for initial calculations. Specific projects should be calculated based on actual conditions, and the recommended values ​​should be verified and modified according to the calculations.

[0064] After determining the three main components—adjustable axial force prestressed anchor cables, shafts, and pipe jacking—the deformation control method for the newly constructed structure above the rail transit operating tunnel was determined. The specific steps of the method are as follows:

[0065] Step 1: As shown in Figure 1, collect the as-built data of the operating tunnel 101 and conduct on-site investigation. This includes detecting the planar and vertical positions of the existing underground structure of the operating rail transit, the geomechanical parameters of the strata, the geometric dimensions of the existing rail transit structure, and relevant information such as the track structure. The focus is on understanding the type of track fasteners and the vertical deformation during previous operations to determine the maximum allowable uplift limit during the crossing. If vertical deformation already existed during previous operations, this project can be used for correction and adjustment, and the uplift control limit can be modified accordingly. The location of expansion joint 124 (as shown in Figure 8) should be investigated in detail. Shafts and pipe curtains should be installed at the location of the expansion joint to effectively control differential deformation on both sides of the joint.

[0066] Step Two: Referring to Figure 1, deformation monitoring is conducted on the existing rail transit tunnel. The monitoring range extends 50m beyond each end of the tunnel section along its length. Track vertical displacement monitoring points 103, installed on the operating tunnel tracks, are used to control the absolute value of vertical deformation. Sidewall vertical displacement monitoring points 102, installed on both sides of the tunnel section, are used to monitor the lateral tilt of the structure. Monitoring data is fed back in real time during construction to ensure dynamic construction.

[0067] Step 3: As shown in Figure 2, anchor cables are installed from the ground on both sides of the operating tunnel. The recommended horizontal distance between the anchor cables and the operating tunnel is 1.7m. Three anchor cables are grouped together, with a spacing of 12m between each group in the plane. Along the length of the line, the installation range extends outwards from the beginning and end points of the overlapping sections between the new structure and the operating tunnel by one times the structural height of the operating tunnel. The boundary between the heaved and deformed soil layer and the prestressed anchor cable free section 104 and the prestressed anchor cable anchored section 105 is used as the dividing line.

[0068] Step 4: As shown in Figure 3, after constructing the locking ring beam 107 on the ground, the vertical shaft 106 is manually excavated using the inverted shaft wall construction method. The sidewalls of the vertical shaft 106 can be constructed using 250mm thick steel grating and shotcrete. The planar dimensions of the vertical shaft 106 are 4m x 2.5m. While ensuring sufficient construction space for the internal pipe jacking and meeting the bearing capacity requirements of the shaft as a foundation pit support structure sidewall, the planar dimensions of the shaft should be minimized as much as possible. The vertical shafts on both sides of the operating tunnel should be excavated symmetrically and synchronously. During the excavation process, the lateral tilt of the existing line should be monitored, and the monitoring data should guide the dynamic construction of the shaft excavation. To facilitate later adjustment of the anchor cable axial force, the bottom of the shaft will not be sealed. When the bottom of the shaft is 2m lower than the top slab of the operating tunnel, the soil layer in the middle of the shaft and the operating tunnel should be grouted for reinforcement to ensure the tunnel's resistance to horizontal deformation.

[0069] Step 5: As shown in Figure 4, a horizontal pipe curtain 108 is installed inside the shaft, and cast-in-place concrete is pumped in. Plain concrete 111 is backfilled from the bottom of the shaft to below the pipe curtain cap beam 109, serving as the foundation for the pipe curtain cap beam 109. The pipe curtain cap beam 109 is constructed within the clear space of the shaft structure, i.e., a planar width of 2m, a planar length of 3.5m, and a section height of 1.5m (see also Figure 8). The reinforcing cage 1082 of the pipe curtain 108 is anchored into the pipe curtain cap beam for secure connection. A 150mm diameter PVC sleeve 110 is reserved above the pipe curtain cap beam for the anchor cable 125 to pass through from bottom to top. After the pipe curtain cap beam construction is completed, a 400mm inner diameter steel pipe column 115 is installed on the upper part of the pipe curtain cap beam, with the anchor cable 125 passing through from bottom to top (see Figure 10 for reference). Backfilling continues upwards with lower cement soil 112 to 1m below the support axis of the new structure foundation pit. Then, backfilling continues with limiting plain concrete 113 to a height of 2m. Next, backfilling with upper cement soil 114 to 0.5m below the support axis of the foundation pit, and constructing the anchor cable cap beam 116. Again, a 150mm diameter PVC sleeve is reserved for the anchor cable to pass through from bottom to top. An adjustable axial force device 117 is installed, and the first stage of tensioning is performed according to the current uplift situation to achieve the first adjustment of the vertical displacement of the track. During the backfilling of each layer, special attention should be paid to compaction and densification around the steel pipe column to provide peripheral restraint and ensure its compressive and bending stability. This step describes the use of two vertical supports for a newly constructed foundation pit. Specific engineering projects may require adjustments based on actual conditions.

[0070] Step Six: As shown in Figure 5, after driving retaining piles between the shafts, the foundation pit for the new structure is excavated vertically layer by layer and in planar blocks. The foundation pit is excavated above the pipe curtain 108 to form the base 118. The single vertical excavation height is 1m, and the planar block length is 8m. Steel walers 120 and steel supports 119 are installed simultaneously with the excavation. Based on monitoring data, the anchor cable 125 is tensioned for the second time. This is achieved by rotating the rotatable internal threaded sleeve to adjust the length of the anchor cable, thereby adjusting the axial force of the anchor cable 125. This changes the vertical pressure applied by the pipe curtain to the operating tunnel, thus achieving dynamic adjustment of the tunnel's vertical displacement and always keeping the track's vertical displacement in an optimal state.

[0071] Step 7: As shown in Figure 6, after the foundation pit is excavated to the designed bottom elevation, the foundation slab and waterproofing are constructed, the foundation slab of the new structure 121 is constructed, the steel supports are removed, and the main structure construction is completed. Cohesive soil 122 is backfilled onto the new structure up to ground level. During this stage, the construction of the main structure and the backfilling of the soil above are both under loading conditions. Anchor cables are mainly released to achieve load balance and stability above the tunnel.

[0072] Step 8: As shown in Figure 7, continuously monitor the vertical displacement of the operating tunnel. After the deformation stabilizes, fill the internal space of the vertically movable threaded sleeve and the rotatable internal threaded sleeve with grout through the reserved grouting holes to permanently fix the axial force of the anchor cable. Backfill the top of the shaft to the ground surface, and remove the shaft structure 2.5m below the ground surface. Construct a top sealing layer and fill with plain concrete to form permanent anchor head protection. This completes the construction of the new structure above the rail transit tunnel.

[0073] It is obvious that the above description and account are merely illustrative and not intended to limit the disclosure, application, or use of this invention. Although embodiments have been described and illustrated in the accompanying drawings, the invention is not limited to the specific examples exemplified by the drawings and described in the embodiments as currently considered the best mode for carrying out the teachings of the invention. The scope of the invention will include any embodiments falling within the foregoing description and the appended claims.

Claims

1. A method for deformation control of newly constructed structures above operating tunnels for rail transit, characterized in that... The process includes the following steps: Step 1: Collect as-built data of the operating tunnel and conduct on-site surveys to detect the planar and vertical positions of the existing underground structure of the operating rail transit, the geomechanical parameters of the strata, the geometric dimensions of the existing rail transit structure, and the track structure information; Step 2: Conduct deformation monitoring of the existing rail transit tunnel. The monitoring range extends 50m beyond each end of the crossing section along the tunnel length. Vertical displacement monitoring points are set up on the track of the operating tunnel to control the absolute value of vertical deformation, and vertical displacement monitoring points are set up on the sidewalls on both sides of the tunnel section for... For monitoring the lateral tilt of the structure; Step 3: Install anchor cables from the ground on both sides of the operating tunnel, with three anchor cables as a group. The starting point of the soil layer where no uplift deformation occurs is used as the boundary line between the free section and the anchoring section of the prestressed anchor cable. In determining the free section of the prestressed anchor cable, numerical calculations are performed on the excavation conditions to obtain the uplift deformation of each soil layer below the existing structure. The soil layer corresponding to ΔSn≤0.025∑ΔSi is found. In the above formula, ΔSn is the calculated deformation value of the soil layer with a thickness of 0.5m above the calculation depth, and ΔSi is the calculated deformation of the i-th soil layer within the calculation depth range. The soil layer that satisfies the above formula is a layer where the soil no longer heaves, i.e., a soil layer that will not heave upwards. This position is set as the end point of the free section and the starting point of the anchorage section, thus determining the length of the free section; Step 4: After constructing the lock ring beam on the ground, the vertical shaft is manually excavated using the inverted shaft wall construction method. The side walls of the vertical shaft are constructed with steel grating and shotcrete; Step 5: A horizontal pipe curtain is installed inside the vertical shaft. The pipe curtain cap beam is constructed in sequence, followed by the installation of steel pipe columns and the construction of the anchor cable cap beam. After the anchor cables pass through the above components from bottom to top, an adjustable axial force device is installed. The first stage is carried out according to the current heave situation. Tensioning is used to achieve the initial adjustment of the vertical displacement of the track. Specifically, this includes: installing a horizontal pipe curtain inside the shaft; backfilling plain concrete from the bottom of the shaft to below the pipe curtain capping beam; constructing the pipe curtain capping beam within the clear space of the shaft structure; reserving PVC sleeves above the pipe curtain capping beam for anchor cables to pass through; after completing the pipe curtain capping beam construction, installing steel pipe columns on the upper part of the pipe curtain capping beam; passing anchor cables from bottom to top; continuing to backfill with lower cement soil up to 1m below the support axis of the new structure foundation pit; continuing to backfill with limiting plain concrete to a height of 2m; and then backfilling with upper cement soil to 0m below the support axis of the foundation pit.At 5m, the anchor cable capping beam is constructed. A PVC sleeve is pre-installed for the anchor cable to pass through from bottom to top. An adjustable axial force device is then installed. Based on the current uplift situation, the first stage of tensioning is performed to achieve the initial adjustment of the track's vertical displacement. Step Six: The foundation pit is excavated above the pipe curtain. Steel walers and steel supports are installed simultaneously with the excavation. During the excavation process, the anchor cables undergo a second tensioning, thereby adjusting the anchor cable axial force and causing changes in the vertical pressure applied to the operating tunnel by the pipe curtain, thus achieving dynamic adjustment of the tunnel's vertical displacement. Step Seven: After the foundation pit is excavated to the designed bottom elevation, the base slab and waterproofing are constructed. The base slab of the new structure is constructed, the steel supports are removed, and the main structure construction is completed. Cohesive soil is backfilled onto the new structure to ground level. Step Eight: The vertical displacement of the operating tunnel is continuously monitored. After the deformation stabilizes, the adjustable axial force device is permanently fixed. The top soil of the shaft is backfilled to ground level, and the shaft structure 2.5m below ground level is removed. The top end is sealed, and plain concrete is poured to form protection.

2. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 1, characterized in that: The adjustable axial force device includes a base steel plate, rolling elements, a rotatable internal threaded sleeve, a vertically movable external threaded sleeve, a limiting bolt, and an anchor head. The base steel plate is pre-embedded in the reinforced concrete anchor cable crown beam using multiple anchor bars. The upper surface of the base steel plate is provided with two ball track grooves for the rolling elements to roll. Edge limiting protrusions are provided on the outer side of the ball track grooves. The rolling elements contain two rings of high-carbon chromium steel balls. The upper part of the rolling elements is a rotatable internal threaded sleeve. A limiting bolt is provided between the base steel plate and the rotatable internal threaded sleeve to limit their horizontal misalignment. The anchor head of the anchor cable is connected to the vertically movable external threaded sleeve to fix the end of the anchor cable. The vertically movable external threaded sleeve is threadedly connected to the rotatable internal threaded sleeve.

3. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 2, characterized in that: The vertically movable external threaded sleeve has a vertical travel stroke of not less than 150 mm.

4. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 2, characterized in that: The vertically movable external threaded sleeve includes an upper sleeve top seat and a lower external threaded part with external threads. The vertically movable external threaded sleeve has a grouting hole in the middle and multiple upper anchor cable holes around the grouting hole.

5. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 2, characterized in that: The rotatable internal threaded sleeve includes a sleeve base at the lower end and an internal threaded part with internal threads at the upper end. The rotatable internal threaded sleeve has multiple anchor cable holes around the periphery of the limiting bolt.

6. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 2, characterized in that: The anchor head is made of a 65mm thick steel plate, which has grouting holes and anchor cable holes.

7. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 1, characterized in that: The pipe curtain comprises multiple spaced steel pipes, each containing a reinforcing cage and cast-in-place concrete. The steel pipes are connected by interlocking angle steel and reinforcing ribs.

8. The deformation control method for newly constructed structures above rail transit operating tunnels as described in claim 7, characterized in that: The steel cage inside the tube curtain extends into the tube curtain crown beam, and the ends of the steel pipes of the tube curtain are fully welded to the connecting pads that are pre-embedded in the tube curtain crown beam with anchor bars.

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