A construction method for extending a negative three-layer space of a subway station by open excavation first and then by underground excavation

Abstract

The application relates to a construction method for expanding a negative three-layer space by open excavation of a subway station and then by underground excavation, which comprises the following steps: step 1, construction of a demolishable part of a surrounding pile of an open excavation station and a dewatering well; step 2, construction of a demolishable part of a negative three-layer conventional structure, a temporary steel pipe column and a temporary end wall structure of an open excavation station; step 3, construction of a demolishable part of a negative two-layer and a negative one-layer structure; and step 4, expansion of a ground space under a non-demolishable part by underground excavation from two ends of the demolishable part, and the like steps. The superior technical effect of the application is that the construction method for expanding a negative three-layer space by open excavation of a subway station and then by underground excavation completely solves the problem that the large area of a subway open excavation structure to be demolished, the high cost and long period of local land expropriation and demolition restrict the construction progress of a station, and compared with a conventional open excavation method, the method is less affected by land expropriation and demolition, and provides a new efficient construction method for many stations which are difficult to start construction on schedule due to the progress of land expropriation and demolition.

Description

Technical Field

[0001] This invention belongs to the field of subway construction technology, specifically involving a construction method of first excavating a subway station with open excavation and then tunneling to expand the third basement level. Background Technology

[0002] The construction of subway stations is significantly affected by land acquisition and demolition, especially for two- or three-line interchange stations, which have high requirements for the space of the third basement level. When the above-ground buildings are important or the land acquisition and demolition costs are high, it is difficult for some open-cut subway stations to be constructed on schedule and within the prescribed space, making it difficult to meet the requirements for construction progress and structural functionality.

[0003] In response to this situation, the usual methods currently used are to coordinate multiple times to extend the construction period, increase land acquisition and demolition costs to meet compensation requirements, change structural and functional requirements, and modify the plan to allow transfers at other stations. There is no other way. Summary of the Invention

[0004] This invention provides a construction method for first excavating a subway station using the open-cut method and then using the tunnel method to expand the space to the third basement level.

[0005] The construction method of first excavating the subway station using the open-cut method and then expanding the third basement level using the tunnel method includes the following steps:

[0006] Step 1: Construction of some open-cut station retaining piles and dewatering wells can be carried out.

[0007] Step 2 involves the demolition and requisition of the conventional structure of the third basement level of the open-cut station, temporary steel pipe columns, and temporary end wall structure.

[0008] Step 3: Construction of the secondary and primary basement levels can be carried out.

[0009] Step 4: From both ends of the demolishable portion, excavate the underground space of the undemolished portion using a tunneling method.

[0010] Step 5: Construction of the large pipe shed perpendicular to the excavation direction;

[0011] Step 6: Grouting construction from the temporary end cap wall to the full-section of the extended section;

[0012] Step 7: Construction of the horse-head gate, three-level platform, and vertical transportation within the tunnel;

[0013] Step 8, Special measures for the construction of the upper pilot tunnel;

[0014] Step 9: Special measures for the construction of the intermediate and lower pilot tunnels;

[0015] Step 10: Construct the secondary lining of the extended structure layer by layer from bottom to top;

[0016] Step 11: Destroy the initial support and temporary end wall on one side layer by layer.

[0017] Furthermore, in step 1, the construction of the expropriated portion of the open-cut station retaining piles and dewatering wells includes:

[0018] Step 1.1: Use an excavator to dig retaining pile foundation pits around the open-cut section of the station that can be acquired and demolished. The diameter of the retaining pile foundation pits is 1.2m@1.5m.

[0019] Step 1.2: Construct dewatering wells on the outside of the main structure of the demolishable section. The dewatering wells of the underground excavation extension section are located inside the station structure. The drainage pipes of the dewatering wells pass through the bottom slab of the structure. Install waterproof steel sleeves and weld double-layer water-stop steel plates. Construct a reinforced concrete wall protective structure around the dewatering wells. After the protective structure around the dewatering wells is completed, stop dewatering and backfill with micro-expansion waterproof concrete to seal it.

[0020] Furthermore, in step 2, conventional structures, temporary steel pipe columns, and temporary end walls are constructed on the third basement level of the excavated section of the station where land can be acquired and demolished.

[0021] Step 2.1: Construct the structural base slab and bottom beams in sequence; briefly describe the construction of the structural base slab and bottom beams;

[0022] Step 2.2, Construction of conventional side walls: Tie the side wall reinforcement. After the side wall reinforcement is tied, set up the large formwork for the side wall, and then pour the side wall concrete.

[0023] Step 2.3: Construct temporary steel pipe columns and temporary end walls:

[0024] First, steel pipe columns are fabricated in sections, each section being 1.5 to 2 meters long. A steel plate 400 mm wide, 500 mm long, and 10 mm thick is welded to the middle of each section. One end of the steel plate is welded to the middle of the steel pipe column section, and the other end is welded to the longitudinal reinforcement of the temporary wall. The steel pipe column and the temporary wall are then anchored together to form an integral construction beam. The steel pipe column is then installed at the bottom of the beam, and concrete is poured into the steel pipe column.

[0025] Then, the temporary wall reinforcement bars are tied and welded to the steel pipe column. Next, the formwork is installed and the temporary wall concrete is poured. Finally, the top beam support, the bottom formwork of the top beam, the reinforcement bars, the side formwork, and the concrete are installed in sequence.

[0026] Furthermore, in step 3, the construction may involve the demolition and requisition of parts of the basement level 2 and basement level 1 structures:

[0027] Step 3.1 Construct the intermediate slab structure between the third basement level and the second basement level;

[0028] Step 3.2 Construct the side walls of the second basement level;

[0029] Step 3.3 Construct the intermediate slab between the second basement level and the first basement level;

[0030] Step 3.4 Construct the structural side walls of the first basement level;

[0031] Step 3.5 Top slab construction.

[0032] Furthermore, in step 4, the construction space beneath the ground in the un-demolished portion is expanded by tunneling from both ends of the demolishable portion:

[0033] The excavation section is 50m long, 3.7m wide and 11.2m high, divided into three layers, with two temporary inverted arches, and excavation is carried out from both ends toward the middle.

[0034] Furthermore, in step 5, the large pipe shed is constructed perpendicular to the excavation direction:

[0035] Perpendicular to the excavation direction, a large pipe shed is constructed in the structure of the second basement level above the third basement level of the tunnel expansion. The pipe shed is erected 800mm away from the top of the middle plate of the initial support. The pipe shed uses steel pipes with a diameter of 108mm, a wall thickness of 6mm (H), a length of 8m (L), a longitudinal spacing of 0.5m (F), and an external insertion angle of 0°.

[0036] Furthermore, in step 6, grouting is performed across the entire cross-section from the temporary end cap wall to the extended section:

[0037] Before excavation, an opening was made at the temporary end wall. Grouting was carried out from the inside of the third basement level of the station. The grouting holes were designed to be spaced 0.75m apart in a quincunx pattern. The reinforcement range was: 3m outside the east side of the excavation outline and the arch, and 1m outside the low excavation outline of the tunnel. Full-section grouting reinforcement and water-stopping measures were adopted.

[0038] The formation reinforcement grouting adopts the WSS retreat grouting process, with a horizontal and vertical grouting spacing of 0.75m, a diffusion radius of 1m, and grouting pressure controlled between 0.5 and 1 MPa.

[0039] The grout mix ratio is as follows: For the lower pilot tunnel, which has a sand layer at the bottom, a cement and water glass grout is used for filling; for the upper and middle pilot tunnels, which consist of clay and fine sand layers, the grouting material is selected with a cement grout to water glass volume ratio of 1:1, a cement grout water-cement ratio of 1:0.5–0.75, and a water glass concentration of 40 Baume degrees; for the tunnel bottom, a water glass to phosphoric acid mixture of 1:1 is used, with a phosphoric acid concentration of 75%–85% and a dilution of 20%–30%.

[0040] Furthermore, in step 7, the construction of the three-tiered platform, the gable gate, and the vertical transportation within the tunnel is carried out:

[0041] Step 7.1: Using I-25b steel, construct slag removal platforms at the locations of the middle and lower guide tunnels;

[0042] Step 7.2: During the construction of the open-cut structure of the station, φ32 round steel bars are pre-embedded at 1m and 2m from the center line of the tunnel entrance in the direction of the major and minor mileage, and at 1m from the entrance of the tunnel. A 5t electric hoist is installed to hoist and transport the steel grating.

[0043] Step 7.3, Construction of the horse-head gate:

[0044] Step 7.3.1 Install a row of guide pipes at the entrance of the tunnel. The guide pipes have an outer diameter of [missing information]. Steel welded pipe, L=5m, external insertion angle 25°, circumferential spacing 300mm, after entering the tunnel, the guide pipe adopts the outer diameter Steel welded pipes, L=3m, circumferential spacing 300mm, longitudinal spacing 1.5m, external insertion angle 15°, are injected with cement grout;

[0045] Step 7.3.2 The steel grating at the horse-head gate position is arranged in three close rows. The second and third steel grating frames are immediately welded to the first frame to make them a whole.

[0046] Step 7.3.3 Install reinforcing bars for the vertical grille of the horse-head gate and the retaining piles, and weld "L" shaped steel bars for fixation.

[0047] Furthermore, in step 8, the upper pilot tunnel is constructed:

[0048] Step 8.1, Pre-excavation borehole: Use a Luoyang shovel to lay a geological exploratory borehole in the pilot tunnel on the working face. The initial excavation depth shall not be less than 5m, and the pre-excavation borehole shall be no less than 3m before each excavation.

[0049] Step 8.2, Piling Breaking: The pilot tunnel longitudinally penetrates the original 1200mm retaining piles of the structure, which are broken using a pneumatic pick. Each breaking length does not exceed 0.6m. During each excavation, the retaining piles are broken from top to bottom first, and vertical I-beams 25b steel are erected near the temporary end wall. The top grid is erected while the top soil is being excavated. Then the vertical steel grid on the other side is excavated, and anchor bolts are installed.

[0050] Step 8.3, Vertical steel welding: When constructing the temporary end wall, a -200×10mm temporary steel plate needs to be pre-embedded longitudinally along the side wall. After the guide tunnel is excavated and the retaining piles are removed, the shotcrete at the original retaining pile location is cleaned up, and the reserved longitudinal -200×10mm temporary steel plate is chiseled out. The upper and lower parts of the vertical I-25b steel are welded and fixed to the reserved longitudinal steel plate respectively.

[0051] Step 8.4, Supplementary grouting at the structure after the completion of the upper guide tunnel: After the upper guide tunnel is excavated to 5 meters, backfill grouting is carried out at the intersection of the top of the initial support and the second basement level of the station to ensure that the soil, concrete structure, and the remaining area of ​​the removed retaining piles are tightly sealed.

[0052] Step 8.5, Relative Excavation Reservation Distance: Break through the portals at both ends of the upper guide tunnel and excavate in opposite directions, leaving a distance of not less than twice the width of the guide tunnel, i.e., 7.4 meters, in the middle for one-way passage.

[0053] Furthermore, in step 9, the lower pilot tunnel is constructed:

[0054] Step 9.1: Excavate the lower guide tunnel 3-5 meters after the upper guide tunnel. The excavation length of the lower guide tunnel is 1.2m. The middle guide tunnel and the lower guide tunnel are connected by wire sawing to break the 1.2m retaining piles in one go.

[0055] Step 9.2, Breaking the stake:

[0056] The 4m section of the pilot tunnel entrance was demolished using pneumatic picks. The subsequent excavation steps first involved mechanical and manual excavation of the soil outside the main support piles within the tunnel body, followed by the installation of vertical steel gratings and shotcrete.

[0057] Then, using an electric hammer, a construction saw was installed at the location of the support pile and the temporary concrete wall. The support pile was cut into 3 sections, each 1.2m long, and temporary vertical and horizontal supports were installed and shotcreted.

[0058] Two pilot tunnel sections were excavated and closed. Two temporary vertical supports of 25A steel were erected at one time. The top and side wall grids were also constructed simultaneously for both sections.

[0059] Step 9.3, Welding of vertical steel sections:

[0060] The vertical temporary vertical supports of the middle and lower pilot tunnels and the longitudinal -200×10mm temporary steel plates reserved for the temporary end walls are welded and bolted to the column nodes reserved for the upper initial support.

[0061] In the construction of vertical steel welding, the treatment of the gap between the reserved steel plate position and the bolt connection of the column node reserved in the initial support above:

[0062] When the gap is 5mm, a steel plate with t=5mm, a length of not less than 100mm, and a width less than 20mm of the flange plate of type I25a steel is used to fill it. The filling steel plate is arranged in the center, and each side is 10mm smaller than the flange plate. It is welded to the flange plate and the reserved steel plate respectively.

[0063] When the gap is 5-20mm, a steel plate with a t=10mm diameter, a length of not less than 100mm, and a width less than 20mm of the flange of the I-25a type steel plate is used for filling and welding.

[0064] When the gap is greater than 20mm, a 100mm square tube is used for filling and welding, based on the actual measured length of the gap.

[0065] Furthermore, in step 10, the secondary lining of the extended structure is constructed layer by layer from bottom to top:

[0066] Step 10.1: Excavate a temporary central partition wall at the location of the lower guide tunnel, connect it to the existing structural base slab, and construct the extended structural base slab;

[0067] Step 10.2: Construct the sidewall inside the lower guide tunnel, up to 300mm from the bottom of the first-layer middle partition wall;

[0068] Step 10.3: The remaining space in the lower guide tunnel is filled with 600×600 cup-lock brackets.

[0069] Step 10.4: Remove the temporary inverted arch on the upper part of the side wall of the lower guide tunnel, and construct the side wall of the guide tunnel during construction;

[0070] Step 10.5: The remaining space in the central guide tunnel is equipped with a 600×600 cup-lock bracket, which is installed throughout the entire space;

[0071] Step 10.6: Remove the temporary invert arch on the upper part of the side wall of the middle guide tunnel and construct the side wall at the upper guide tunnel;

[0072] Step 10.7: The remaining space in the upper guide tunnel is filled with 600×600 cup-lock brackets.

[0073] Step 10.8: Remove the temporary partition wall at the upper guide tunnel and connect it with the existing structural top slab to construct the extended structural top slab.

[0074] Further, in step 11, the initial support and temporary end cap wall on one side are broken down layer by layer:

[0075] Step 11.1: Remove the full-span scaffolding of the upper guide tunnel, break the remaining temporary intermediate partition wall, and break the temporary end cap wall;

[0076] Step 11.2: Remove the temporary invert arch at the bottom of the upper pilot tunnel and break the temporary central partition wall and temporary end wall of the middle pilot tunnel.

[0077] Step 11.3: Remove the temporary invert arch at the bottom of the central pilot tunnel and break the temporary central partition wall and temporary end wall of the lower pilot tunnel section;

[0078] Step 11.4: Convert the stress on the original open-cut structure's steel pipe columns and temporary end walls into the stress on the steel pipe columns and extended structure.

[0079] The superior advantages of the construction method of first excavating the subway station and then excavating the third basement level using the cut-and-cover method described in this invention are as follows:

[0080] 1. The construction method of first excavating the subway station and then excavating the third basement level using the cut-and-cover method described in this invention completely solves the problem of the large area of ​​land acquisition and demolition, high local land acquisition and demolition costs, and long cycle that restrict the construction progress of the subway station.

[0081] 2. The construction method of first excavating the subway station and then tunneling to expand the third basement level, as described in this invention, is less affected by land acquisition and demolition compared with the conventional open-cut method. It provides a new and efficient construction solution for many stations that are difficult to start on schedule due to the progress of land acquisition and demolition.

[0082] 3. The construction method of first excavating the subway station and then tunneling to extend the third basement level, as described in this invention, only requires the construction of the functional area of ​​the third basement level structure. This reduces the construction of the second basement level and the first basement level above the extension section, reduces the waste of structural space, and lowers the project cost by about 15%.

[0083] 4. The construction method of first excavating the subway station and then excavating the third basement level as described in this invention has small construction settlement due to welding the excavation structure with the reserved steel plate. It is safe, reliable, and technically mature. Its widespread use can shorten the construction period by 25-30%. Attached Figure Description

[0084] Figure 1 This is a schematic diagram of the construction method of the present invention, which involves first excavating the subway station in the open-cut style and then excavating the third basement level through the tunnel. Detailed Implementation

[0085] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0086] like Figure 1 As shown, the construction method of first excavating the subway station and then tunneling to expand the third basement level includes the following steps:

[0087] The construction method of first excavating the subway station using the open-cut method and then expanding the third basement level using the tunnel method includes the following steps:

[0088] Step 1, the construction of the excavated station retaining piles and dewatering wells that can be acquired and demolished includes:

[0089] Step 1.1: Use an excavator to dig retaining pile foundation pits around the open-cut section of the station that can be acquired and demolished. The diameter of the retaining pile foundation pits is 1.2m@1.5m.

[0090] Step 1.2: Construct dewatering wells on the outside of the main structure of the demolishable section. The dewatering wells of the extended section of the tunnel are located inside the station structure. The drainage pipes of the dewatering wells pass through the bottom slab of the structure. Install waterproof steel sleeves and weld double-layer water-stop steel plates. Construct a reinforced concrete wall protective structure around the dewatering wells. After the extended protective structure around the dewatering wells is completed, stop dewatering and backfill with micro-expansion waterproof concrete to seal it.

[0091] Step 2: Construct the conventional structure, temporary steel pipe columns, and temporary end wall structure on the third basement level of the open-cut station in the area eligible for land acquisition and demolition.

[0092] Step 2.1: Construct the structural base slab and bottom beams in sequence; briefly describe the construction of the structural base slab and bottom beams;

[0093] Step 2.2, Construction of conventional side walls: Tie the side wall reinforcement. After the side wall reinforcement is tied, set up the large formwork for the side wall, and then pour the side wall concrete.

[0094] Step 2.3: Construct temporary steel pipe columns and temporary end walls:

[0095] First, steel pipe columns are fabricated in sections, each section being 1.5 to 2 meters long. A steel plate 400 mm wide, 500 mm long, and 10 mm thick is welded to the middle of each section. One end of the steel plate is welded to the middle of the steel pipe column section, and the other end is welded to the longitudinal reinforcement of the temporary wall. The steel pipe column and the temporary wall are then anchored together to form an integral construction beam. The steel pipe column is then installed at the bottom of the beam, and concrete is poured into the steel pipe column.

[0096] Then, the temporary wall reinforcement is tied and welded to the steel pipe column. Next, the formwork is installed and the temporary wall concrete is poured. Finally, the top beam support, the bottom formwork of the top beam, the reinforcement, the side formwork, and the concrete are installed in sequence.

[0097] Step 3: Construction can proceed by demolishing or acquiring parts of the basement level 2 and basement level 1 structures.

[0098] Step 3.1 Construct the intermediate slab structure between the third basement level and the second basement level;

[0099] Step 3.2 Construct the side walls of the second basement level;

[0100] Step 3.3 Construct the intermediate slab between the second basement level and the first basement level;

[0101] Step 3.4 Construct the structural side walls of the first basement level;

[0102] Step 3.5 Top slab construction;

[0103] Step 4: From both ends of the demolishable portion, proceed with the underground excavation of the undemolished portion to expand the construction space below ground.

[0104] The excavation section is 50m long, 3.7m wide and 11.2m high, divided into three layers, with two temporary invert arches, and excavation is carried out from both ends toward the middle.

[0105] Step 5, Construction of the large pipe shed perpendicular to the excavation direction:

[0106] Perpendicular to the excavation direction, a large pipe shed is constructed in the structure of the second basement level above the third basement level of the tunnel expansion. The pipe shed is erected 800mm away from the top of the middle plate of the initial support. The pipe shed uses steel pipes with a diameter of 108mm, a wall thickness of 6mm (H), a length of 8m (L), a longitudinal spacing of 0.5m (F), and an external insertion angle of 0°.

[0107] Step 6: Grouting construction from the temporary end cap wall to the full-section of the extended section:

[0108] Before excavation, an opening was made at the temporary end wall. Grouting was carried out from the inside of the third basement level of the station. The grouting holes were designed to be spaced 0.75m apart in a quincunx pattern. The reinforcement range was: 3m outside the east side of the excavation outline and the arch, and 1m outside the low excavation outline of the tunnel. Full-section grouting reinforcement and water-stopping measures were adopted.

[0109] The formation reinforcement grouting adopts the WSS retreat grouting process, with a horizontal and vertical grouting spacing of 0.75m, a diffusion radius of 1m, and grouting pressure controlled between 0.5 and 1 MPa.

[0110] The grout mix ratio is as follows: For the lower pilot tunnel, which has a sand layer at the bottom, a cement and water glass grout is used for filling; for the upper and middle pilot tunnels, which consist of clay and fine sand layers, the grouting material is selected with a cement grout to water glass volume ratio of 1:1, a cement grout water-cement ratio of 1:0.5–0.75, and a water glass concentration of 40 Baume degrees; for the tunnel bottom, a water glass to phosphoric acid mixture of 1:1 is used, with a phosphoric acid concentration of 75%–85%, diluted by 20%–30%.

[0111] Step 7: Construction of the three-level platform, the gable gate, and vertical transportation within the tunnel:

[0112] Step 7.1: Using I-25b steel, construct slag removal platforms at the locations of the middle and lower guide tunnels;

[0113] Step 7.2: During the construction of the open-cut structure of the station, φ32 round steel bars are pre-embedded at 1m and 2m from the center line of the tunnel entrance in the direction of the major and minor mileage, and at 1m from the entrance of the tunnel. A 5t electric hoist is installed to hoist and transport the steel grating.

[0114] Step 7.3, Construction of the horse-head gate:

[0115] Step 7.3.1 Install a row of guide pipes at the entrance of the tunnel. The guide pipes have an outer diameter of [missing information]. t = 3.5mm steel welded pipe, L = 5m, external insertion angle 25°, circumferential spacing 300mm, after entering the tunnel, the guide pipe adopts the outer diameter 3.5mm steel welded pipe, L=3m, circumferential spacing 300mm, longitudinal spacing 1.5m, external insertion angle 15°, cement grouting is performed;

[0116] Step 7.3.2 The steel grating at the horse-head gate position is arranged in three close rows. The second and third steel grating frames are immediately welded to the first frame to make them a whole.

[0117] Step 7.3.3 Install reinforcing bars for the vertical grille of the horse-head gate and the retaining piles, and weld "L" shaped steel bars for fixation;

[0118] Step 8, Construction of the upper pilot tunnel:

[0119] Step 8.1, Pre-excavation borehole: Use a Luoyang shovel to lay a geological exploratory borehole in the pilot tunnel on the working face. The initial excavation depth shall not be less than 5m, and the pre-excavation borehole shall be no less than 3m before each excavation.

[0120] Step 8.2, Piling Breaking: The pilot tunnel longitudinally penetrates the original 1200mm retaining piles of the structure, which are broken using a pneumatic pick. Each breaking length does not exceed 0.6m. During each excavation, the retaining piles are broken from top to bottom first, and vertical I-beams 25b steel are erected near the temporary end wall. The top grid is erected while the top soil is being excavated. Then the vertical steel grid on the other side is excavated, and anchor bolts are installed.

[0121] Step 8.3, Vertical steel welding: When constructing the temporary end wall, a -200×10mm temporary steel plate needs to be pre-embedded longitudinally along the side wall. After the guide tunnel is excavated and the retaining piles are removed, the shotcrete at the original retaining pile location is cleaned up, and the reserved longitudinal -200×10mm temporary steel plate is chiseled out. The upper and lower parts of the vertical I-25b steel are welded and fixed to the reserved longitudinal steel plate respectively.

[0122] Step 8.4, Supplementary grouting at the structure after the completion of the upper guide tunnel: After the upper guide tunnel is excavated to 5 meters, backfill grouting is carried out at the intersection of the top of the initial support and the second basement level of the station to ensure that the soil, concrete structure, and the remaining area of ​​the removed retaining piles are tightly sealed.

[0123] Step 8.5, Relative Excavation Reservation Distance: Break through the portals at both ends of the upper pilot tunnel and excavate in opposite directions, leaving a distance of not less than twice the width of the pilot tunnel, i.e., 7.4 meters, in the middle for one-way passage;

[0124] Step 9, construct the lower pilot tunnel:

[0125] Step 9.1: Excavate the lower guide tunnel 3-5 meters after the upper guide tunnel. The excavation length of the lower guide tunnel is 1.2m. The middle guide tunnel and the lower guide tunnel are connected by wire sawing to break the 1.2m retaining piles in one go.

[0126] Step 9.2, breaking the pile:

[0127] The 4m section of the pilot tunnel entrance was demolished using pneumatic picks. The subsequent excavation steps first involved mechanical and manual excavation of the soil outside the main support piles within the tunnel body, followed by the installation of vertical steel gratings and shotcrete.

[0128] Then, using an electric hammer, a construction saw was installed at the location of the support pile and the temporary concrete wall. The support pile was cut into 3 sections, each 1.2m long, and temporary vertical and horizontal supports were installed and shotcreted.

[0129] Two pilot tunnel sections were excavated and closed. Two temporary vertical supports of 25A steel were erected at one time. The top and side wall grids were also constructed simultaneously for both sections.

[0130] Step 9.3, Welding of vertical steel sections:

[0131] The vertical temporary vertical supports of the middle and lower pilot tunnels and the longitudinal -200×10mm temporary steel plates reserved for the temporary end walls are welded and bolted to the column nodes reserved for the upper initial support.

[0132] In the construction of vertical steel welding, the treatment of the gap between the reserved steel plate position and the bolt connection of the column node reserved in the initial support above:

[0133] When the gap is 5mm, a steel plate with t=5mm, a length of not less than 100mm, and a width less than 20mm of the flange plate of type I25a steel is used to fill it. The filling steel plate is arranged in the center, and each side is 10mm smaller than the flange plate. It is welded to the flange plate and the reserved steel plate respectively.

[0134] When the gap is 5-20mm, a steel plate with t=10mm, a length of not less than 100mm, and a width less than 20mm of the flange plate of type I25a steel is used for filling and welding.

[0135] When the gap is greater than 20mm, a 100mm square tube is used for filling and welding according to the actual measured length of the gap.

[0136] In step 10, the secondary lining of the extended structure is constructed layer by layer from bottom to top:

[0137] Step 10.1: Excavate a temporary central partition wall at the location of the lower guide tunnel, connect it to the existing structural base slab, and construct the extended structural base slab;

[0138] Step 10.2: Construct the sidewall inside the lower guide tunnel, up to 300mm from the bottom of the first-layer middle partition wall;

[0139] Step 10.3: The remaining space in the lower guide tunnel is filled with 600×600 cup-lock brackets.

[0140] Step 10.4: Remove the temporary inverted arch on the upper part of the side wall of the lower guide tunnel, and construct the side wall of the guide tunnel during construction;

[0141] Step 10.5: The remaining space in the central guide tunnel is equipped with a 600×600 cup-lock bracket, which is installed throughout the entire space;

[0142] Step 10.6: Remove the temporary invert arch on the upper part of the side wall of the middle guide tunnel and construct the side wall at the upper guide tunnel;

[0143] Step 10.7: The remaining space in the upper guide tunnel is filled with 600×600 cup-lock brackets.

[0144] Step 10.8: Remove the temporary partition wall at the upper guide tunnel and connect it with the existing structural top slab to construct the extended structural top slab;

[0145] Step 11: Demolish the initial support and temporary end wall on one side layer by layer:

[0146] Step 11.1: Remove the full-span scaffolding of the upper guide tunnel, break the remaining temporary intermediate partition wall, and break the temporary end cap wall;

[0147] Step 11.2: Remove the temporary invert arch at the bottom of the upper pilot tunnel and break the temporary central partition wall and temporary end wall of the middle pilot tunnel.

[0148] Step 11.3: Remove the temporary invert arch at the bottom of the central pilot tunnel and break the temporary central partition wall and temporary end wall of the lower pilot tunnel section;

[0149] Step 11.4: Convert the stress on the original open-cut structure's steel pipe columns and temporary end walls into the stress on the steel pipe columns and extended structure.

[0150] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the protection scope of this invention.

Claims

1. A construction method for first excavating a subway station using the open-cut method and then expanding the third basement level through the tunnel method, characterized in that, Includes the following steps: Step 1: Construction of some open-cut station retaining piles and dewatering wells can be carried out. Step 2 involves the demolition and requisition of the conventional structure of the third basement level of the open-cut station, temporary steel pipe columns, and temporary end wall structure. Step 3: Construction of the secondary and primary basement levels can be carried out. Step 4: From both ends of the demolishable portion, excavate the underground space of the undemolished portion using a tunneling method. Step 5: Construction of the large pipe shed perpendicular to the excavation direction; Step 6: Grouting construction from the temporary end cap wall to the full-section of the extended section; Step 7: Construction of the horse-head gate, three-level platform, and vertical transportation within the tunnel: Step 7.1: Using I-25b steel, construct slag removal platforms at the locations of the middle and lower guide tunnels; Step 7.2: During the construction of the open-cut structure's central slab at the station, pre-embed at positions 1m and 2m from the centerline of the tunnel's head gate towards the major and minor mileage directions, and at 1m from the entrance of the tunnel. 32mm round steel bars, equipped with a 5t electric hoist, are used to lift and transport the steel grating; Step 7.3, Construction of the horse-head gate: Step 7.3.1 Install a row of guide pipes at the entrance of the tunnel. The guide pipes have an outer diameter of [missing information]. 42mm, t=3.5mm steel welded pipe, L=5m, external insertion angle 25°, circumferential spacing 300mm, after entering the tunnel, the guide pipe adopts the outer diameter 42mm, t=3.5mm steel welded pipe, L=3m, circumferential spacing 300mm, longitudinal spacing 1.5m, external insertion angle 15°, for cement grouting; Step 7.3.2 The steel grating at the horse-head gate position is arranged in three close rows. The second and third steel grating frames are immediately welded to the first frame to make them a whole. Step 7.3.3 Install reinforcing bars for the vertical grille of the horse-head gate and the retaining piles, and weld "L"-shaped steel bars for fixation; Step 8, Special measures for the construction of the upper pilot tunnel: Step 8.1, Pre-excavation borehole: Use a Luoyang shovel to lay a geological exploratory borehole in the pilot tunnel on the working face. The initial excavation depth shall not be less than 5m, and the pre-excavation borehole shall be no less than 3m before each excavation. Step 8.2, Piling Breaking: The pilot tunnel longitudinally penetrates the original 1200mm retaining piles of the structure, which are broken using a pneumatic pick. Each breaking length does not exceed 0.6m. During each excavation, the retaining piles are broken from top to bottom first, and vertical I-beams 25b steel are erected near the temporary end wall. The top grid is erected while the top soil is being excavated. Then the vertical steel grid on the other side is excavated, and anchor bolts are installed. Step 8.3, Vertical steel welding: When constructing the temporary end wall, a 200×10mm temporary steel plate needs to be pre-embedded longitudinally along the side wall. After the guide hole is excavated and the retaining piles are broken, the shotcrete at the original retaining pile location is cleaned up, and the reserved longitudinal 200×10mm temporary steel plate is chiseled out. The upper and lower parts of the vertical I-25b steel are welded and fixed to the reserved longitudinal steel plate respectively. Step 8.4, Supplementary grouting at the structure after the completion of the upper guide tunnel: After the upper guide tunnel is excavated to 5 meters, backfill grouting is carried out at the intersection of the top of the initial support and the second basement level of the station to ensure that the soil, concrete structure, and the remaining area of ​​the removed retaining piles are tightly sealed. Step 8.5, Relative Excavation Reservation Distance: Break through the portals at both ends of the upper pilot tunnel and excavate in opposite directions, leaving a distance of not less than twice the width of the pilot tunnel, i.e., 7.4 meters, in the middle for one-way passage; Step 9, Special measures for the construction of the middle and lower pilot tunnels: Step 9.1: Excavate the lower guide tunnel 3-5 meters after the upper guide tunnel. The excavation length of the lower guide tunnel is 1.2m. The middle guide tunnel and the lower guide tunnel are connected by wire sawing to break the 1.2m retaining piles in one go. Step 9.2, breaking the pile: The 4m section of the pilot tunnel entrance was demolished using pneumatic picks. The subsequent excavation steps first involved mechanical and manual excavation of the soil outside the main support piles within the tunnel body, followed by the installation of vertical steel gratings and shotcrete. Then, using an electric hammer, a construction saw was installed at the location of the support pile and the temporary concrete wall. The support pile was cut into 3 sections, each 1.2m long, and temporary vertical and horizontal supports were installed and shotcreted. Two pilot tunnel sections were excavated and closed. Two temporary vertical supports of 25A steel were erected at one time. The top and side wall grids were also constructed simultaneously for both sections. Step 9.3, Welding of vertical steel sections: The 25a type steel temporary vertical supports and the 200×10mm longitudinal temporary steel plates reserved for the temporary end walls of the middle and lower pilot tunnels are welded and bolted to the column nodes reserved for the upper initial support. In the construction of vertical steel welding, the treatment of the gap between the reserved steel plate position and the bolt connection of the column node reserved in the initial support above: When the gap is 5mm, a steel plate with t=5mm, a length of not less than 100mm, and a width less than 20mm of the flange plate of type I25a steel is used to fill it. The filling steel plate is arranged in the center, and each side is 10mm smaller than the flange plate. It is welded to the flange plate and the reserved steel plate respectively. When the gap is 5-20mm, a steel plate with t=10mm, a length of not less than 100mm, and a width less than 20mm of the flange of the I-25a type steel plate is used for filling and welding. When the gap is greater than 20mm, a 100mm square tube is used for filling and welding according to the actual measured length of the gap. Step 10: Construct the secondary lining of the extended structure layer by layer from bottom to top. Step 10.1: Excavate a temporary central partition wall at the location of the lower guide tunnel, connect it to the existing structural base slab, and construct the extended structural base slab; Step 10.2: Construct the sidewall inside the lower guide tunnel, up to 300mm from the bottom of the first-layer middle partition wall; Step 10.3: The remaining space in the lower guide tunnel is filled with 600×600 cup-lock brackets. Step 10.4: Remove the temporary inverted arch on the upper part of the side wall of the lower guide tunnel, and construct the side wall of the guide tunnel during construction; Step 10.5: The remaining space in the central guide tunnel is equipped with a 600×600 cup-lock bracket, which is installed throughout the entire space; Step 10.6: Remove the temporary invert arch on the upper part of the side wall of the middle guide tunnel and construct the side wall at the upper guide tunnel; Step 10.7: The remaining space in the upper guide tunnel is filled with 600×600 cup-lock brackets. Step 10.8: Remove the temporary partition wall at the upper guide tunnel and connect it with the existing structural top slab to construct the extended structural top slab; Step 11: Destroy the initial support and temporary end wall on one side layer by layer: Step 11.1: Remove the full-span scaffolding of the upper guide tunnel, break the remaining temporary intermediate partition wall, and break the temporary end cap wall; Step 11.2: Remove the temporary invert arch at the bottom of the upper pilot tunnel and break the temporary central partition wall and temporary end wall of the middle pilot tunnel. Step 11.3: Remove the temporary invert arch at the bottom of the central pilot tunnel and break the temporary central partition wall and temporary end wall of the lower pilot tunnel section; Step 11.4: Convert the stress on the original open-cut structure's steel pipe columns and temporary end walls into the stress on the steel pipe columns and extended structure.

2. The construction method according to claim 1, characterized in that, In step 1, the construction of expropriated sections of the open-cut station retaining piles and dewatering wells can be carried out, including: Step 1.1: Use an excavator to dig retaining pile foundation pits around the open-cut section of the station that can be acquired and demolished. The diameter of the retaining pile foundation pits is 1.2m × 1.5m. Step 1.2: Construct dewatering wells on the outside of the main structure of the demolishable section. The dewatering wells of the underground excavation extension section are located inside the station structure. The drainage pipes of the dewatering wells pass through the bottom slab of the structure. Install waterproof steel sleeves and weld double-layer water-stop steel plates. Construct a reinforced concrete wall protective structure around the dewatering wells. After the protective structure around the dewatering wells is completed, stop dewatering and backfill with micro-expansion waterproof concrete to seal it.

3. The construction method according to claim 1, characterized in that, In step 2, the construction of the conventional structure of the third basement level of the open-cut station, temporary steel pipe columns, and temporary end wall structure can be carried out: Step 2.1: Construct the structural base slab and bottom beam in sequence; Step 2.2, Construction of conventional side walls: Tie the side wall reinforcement. After the side wall reinforcement is tied, set up the large formwork for the side wall, and then pour the side wall concrete. Step 2.3: Construct temporary steel pipe columns and temporary end walls: First, steel pipe columns are fabricated in sections, each section being 1.5 to 2 meters long. A steel plate 400 mm wide, 500 mm long, and 10 mm thick is welded to the middle of each section. One end of the steel plate is welded to the middle of the steel pipe column section, and the other end is welded to the longitudinal reinforcement of the temporary wall. The steel pipe column and the temporary wall are then anchored together to form an integral construction beam. The steel pipe column is then installed at the bottom of the beam, and concrete is poured into the steel pipe column. Then, the temporary wall reinforcement bars are tied and welded to the steel pipe column. Next, the formwork is installed and the temporary wall concrete is poured. Finally, the top beam support, the bottom formwork of the top beam, the reinforcement bars, the side formwork, and the concrete are installed in sequence.

4. The construction method according to claim 1, characterized in that, In step 3, the construction can involve the demolition and requisition of parts of the basement level 2 and basement level 1 structures: Step 3.1 Construct the intermediate slab structure between the third basement level and the second basement level; Step 3.2 Construct the side walls of the second basement level; Step 3.3 Construct the intermediate slab between the second basement level and the first basement level; Step 3.4 Construct the structural side walls of the first basement level; Step 3.5 Roof slab construction.

5. The construction method according to claim 1, characterized in that, In step 4, the excavation of the underground space of the un-expropriated part is carried out from both ends of the requisitionable part: the excavation section is 50m long, 3.7m wide and 11.2m high, divided into three layers, with two temporary invert arches, and the excavation is carried out from both ends towards the middle.

6. The construction method according to claim 1, characterized in that, In step 5, the construction of the large pipe shed perpendicular to the excavation direction: Perpendicular to the excavation direction, a large pipe shed is constructed in the structure of the second basement level above the third basement level of the tunnel expansion. The pipe shed is erected 800mm away from the top of the middle plate of the initial support. The pipe shed uses steel pipes with a diameter of 108mm, a wall thickness of 6mm (H), a length of 8m (L), a longitudinal spacing of 0.5m (F), and an external insertion angle of 0°.

7. The construction method according to claim 1, characterized in that, In step 6, before excavation, an opening is made at the temporary end wall, and grouting is injected from the inside of the third basement level of the station. The grouting holes are designed to be spaced 0.75m apart in a quincunx pattern. The reinforcement range is: 3m outside the east side of the excavation outline and the arch, and 1m outside the low excavation outline of the tunnel. Full-section grouting reinforcement and water-stopping measures are adopted. The formation reinforcement grouting adopts the WSS retreat grouting process, with a horizontal and vertical grouting spacing of 0.75m, a diffusion radius of 1m, and grouting pressure controlled between 0.5 and 1 MPa. The grout mix ratio is as follows: the bottom of the lower pilot tunnel contains a sand layer, which is filled with cement and water glass grout; the upper and middle pilot tunnels are clay and fine sand layers, and the grouting material is selected with a cement grout and water glass volume ratio of 1:1, a cement grout water-cement ratio of 1:0.5 to 0.75, and a water glass concentration of 40 Baume degrees; the bottom of the tunnel uses water glass and phosphoric acid in a 1:1 ratio, with a phosphoric acid concentration of 75% to 85% and a dilution of 20% to 30%.

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