Steel pipe column and construction method of subway station in upper-soft and lower-hard stratum

Abstract

The present application relates to a steel pipe column and a construction method of a subway station in a soft upper and hard lower stratum, by safely connecting a foundation reinforcement cage with the bottom of the steel pipe column, and simultaneously lowering the steel pipe column and the foundation reinforcement cage as a whole into a hole, the stability of the steel pipe column after the construction of the bottom foundation can be effectively ensured, the construction space of the bottom foundation of the steel pipe column is saved, and then the size of the bottom foundation of the steel pipe column can be reduced, so that when the hole is formed, the hole can be divided into an upper large-diameter hole and a lower small-diameter hole, the volume of the hard rock hole is reduced, the construction difficulty of the hard rock hole is further reduced, the hole forming efficiency is improved, and the engineering investment is saved. At the same time, the steel pipe column and the foundation reinforcement cage are simultaneously lowered into the hole as a whole, the process of installing the mechanical positioning head of the steel pipe column is omitted, the construction process is simpler, and the construction efficiency of the steel pipe column can be further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel pipe column construction, in particular to a construction method of a steel pipe column and a subway station in a soft-over-hard stratum subway station. BACKGROUND

[0002] At present, some cities in China represented by Qingdao, Shenzhen and Chongqing have the stratum characteristics that the upper part is Quaternary soil and the lower part is bedrock. The bedrock protrudes early and has high strength, and the uniaxial compressive strength of individual bedrock is greater than 100 MPa. When building a subway open-cut station, more and more stations (tunnel sections) using cover-excavation method construction are adopted due to the limitation of site and traffic conditions, in order to achieve the purpose of quickly restoring the road. Steel pipe columns are the first choice in the design of cover-excavation method construction due to their high axial pressure ratio and stiffness. Steel pipe columns are fast and safe in construction, and can be used as support piles for restoring the road together with the station roof in cover-excavation reverse construction, and can also be used as structural frame columns of the later permanent structure.

[0003] When constructing a steel pipe column in a general cover-excavation method subway station, a rotary drill is first used to form a hole. Considering the space required for the installation of the steel pipe column foundation, the space required for the installation of the upper steel pipe column is (mm): 1400mm (outer diameter of the station roof beam ring plate) + 50x2 (flange of the steel casing) + 16x2 (wall thickness of the steel casing) + 150x2 (steel pipe column hoisting space) = 1832mm. The general hole forming diameter is about 2.0m. Then, the foundation reinforcement cage and the upper wall protection steel pipe are lowered, and the bottom foundation is poured with concrete. The cement slurry in the hole is pumped out, and the hole is entered by a person. The pile head is chiseled to install the positioner. The steel pipe column is hoisted and poured with internal and external concrete of the steel pipe column. The bottom plate (beam) of the station structure, pile cap and the connection between the pile cap and the steel pipe column are completed, and finally the entire steel pipe column construction is completed. At present, the use of HPE hydraulic vertical positioner can cancel the step of manually installing the positioner in the hole, greatly improving the safety. The diameter and length of the column, which are the most important design parameters of the steel pipe column, cannot be adjusted at will because the pile length is limited by the track surface depth of the station structure. The buried depth of the subway station in reality is getting deeper and deeper. In cities where the bedrock protrudes early, it is difficult to form a hole in the lower part of the steel pipe column. Therefore, optimizing the pile diameter of the steel pipe column has become a breakthrough to solve this problem.

[0004] The difficulties of the steel pipe column in the hole forming of the upper soft and lower hard stratum mainly include the following aspects: 1) when the station is deeply buried, the uniaxial compressive strength of the bedrock is high, basically reaching the level of hard rock, and the rock stratum is complete, so that the drill bit is severely worn during drilling, the drill rod and the machine body are severely damaged, the cutting teeth need to be frequently replaced, the drill rod needs to be frequently repaired, and the repair cycle of the drill rod is long, which seriously affects the construction efficiency; 2) during the hole forming process, the strength of the slightly weathered granite is high, and the rock mass is complete, so that the reserved pile core cannot be broken after the ring cutting construction, and the core taking is difficult, and the core taking needs to frequently replace the drill bit or equip the drill machine to extract the slag sample, which consumes a long time, and the construction of the steel pipe column is a key link of the cover excavation method construction station on the key line, which also affects the construction efficiency; 3) high-pressure air is injected during the mechanical process, which causes the mud to flow out, the level of civilized construction is low, and the construction requirements of the new era subway construction are not met.

[0005] With the development of more and more urban rail transit, urban land resources are more precious, and the frequency of using steel pipe columns is gradually increased. Due to the large construction space, the upper soft and lower hard stratum construction is a key problem in construction. The existing application number CN201610791163.5 Chinese invention patent does not solve the problems faced by the large-diameter hole forming, and the application number CN202122722202.5 utility model also makes some beneficial attempts, that is, the bottom of the steel pipe column is provided with an extension pipe, and the bottom of the anti-pulling pile concrete can be continuously poured, but the bottom foundation of the steel pipe column needs to be placed outside, which causes the hole forming to be still large, and the hole forming problem still exists. SUMMARY

[0006] The purpose of the present application is to solve the problem that the bottom foundation of the steel pipe column needs to be placed outside, which causes the hole forming to be still large, and the hole forming problem still exists.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A construction method of a steel pipe column in an upper soft and lower hard stratum subway station, comprising the following construction steps:

[0009] S1, a first steel casing is buried and a hole is formed in the first steel casing, then a second steel casing is buried downward at the bottom of the first steel casing and a hole is formed in the second steel casing, and the bottom of the second steel casing after being buried is lower than the bottom elevation of the bottom foundation of the steel pipe column;

[0010] S2, the foundation steel cage connected to the bottom of the steel pipe column and the steel pipe column are lowered as a whole to the bottom of the second steel casing, and then the bottom foundation is formed by pouring the foundation steel cage;

[0011] S3, pouring concrete into the steel pipe column, such as pouring C50 micro-expanding concrete into the steel pipe column, to complete the construction of the steel pipe column.

[0012] Wherein, the foundation steel cage refers to the steel cage of the bottom foundation of the steel pipe column, which forms the bottom foundation of the steel pipe column after pouring concrete, and the diameter of the first steel casing is larger than that of the second steel casing.

[0013] The construction method of the steel pipe column in the soft upper and hard lower stratum subway station described in the present application can effectively ensure the stability of the bottom foundation of the steel pipe column after construction by safely connecting the foundation steel cage with the bottom of the steel pipe column and lowering the steel pipe column and the foundation steel cage as a whole into the hole, saving the construction space of the separately constructed bottom foundation of the steel pipe column, thereby reducing the size of the bottom foundation of the steel pipe column, so that the hole can be divided into an upper large-diameter hole and a lower small-diameter hole when the hole is formed, reducing the volume of the hard rock hole, thereby reducing the construction difficulty of the hard rock hole, improving the hole forming efficiency, and saving engineering investment. At the same time, lowering the steel pipe column and the foundation steel cage as a whole into the hole eliminates the process of installing the mechanical positioning head of the steel pipe column, making the construction process simpler and further improving the construction efficiency of the steel pipe column. The large-diameter hole is shortened, which can reduce the injection of high-pressure air and improve the level of civilized construction.

[0014] Preferably, the connecting step of the steel pipe column and the foundation steel cage is:

[0015] Welding a connecting steel plate at the bottom of the steel pipe column, and welding the top of the main reinforcement of the foundation steel cage with the connecting steel plate can ensure the safe connection of the foundation steel cage with the bottom of the steel pipe column.

[0016] Preferably, the length of the top of the main reinforcement of the foundation steel cage extending into the bottom of the round steel pipe of the steel pipe column is LaE, which satisfies the anti-seismic anchoring capacity of the bottom foundation of the steel pipe column and the bottom of the steel pipe column.

[0017] Preferably, when the steel pipe column and the foundation steel cage are connected, the round steel pipe of the steel pipe column is sealed by the connecting steel plate, and the top of the main reinforcement is welded with the connecting steel plate after passing through the connecting steel plate, which can ensure the durability and strength of the steel pipe column as a permanent structure.

[0018] Preferably, the bottom of the first steel casing after being buried is located at or below the soil-rock boundary.

[0019] The bottom of the first steel casing after being buried is located at the soil-rock boundary line, so that the large-diameter first steel casing is not extended into the rock layer, and the difficulty of hole forming is lower; and the large-diameter first steel casing covers the entire height of the soft soil layer, so that the internal space of the hole is large, and the construction is more convenient. The bottom of the first steel casing after being buried is located below the soil-rock boundary line, which can improve the stability of the first steel casing after being buried, and reduce the possibility of deformation and displacement of the first steel casing. The deeper the depth of the bottom of the first steel casing after being buried into the rock layer, the greater the difficulty of hole forming.

[0020] Preferably, in step S1, the outer diameter of the first steel casing is 1900mm-2100mm, and the outer diameter of the second steel casing is 1400mm-1600mm.

[0021] The outer diameter of the second steel casing is larger than the size of the lower part of the steel pipe column, which ensures that it can be normally lowered.

[0022] Preferably, in step S3, a layer of cement mortar with the same grade as the concrete in the steel pipe column and with a thickness of 10cm-20cm is first poured, and then the concrete is quickly poured into the steel pipe column, so as to avoid the bouncing of the coarse aggregate of the concrete and the shrinkage and creep of the concrete caused by long-time construction.

[0023] A construction method of a subway station in an upper-soft-and-lower-hard stratum, comprising the following steps:

[0024] S01, using the construction method of the steel pipe column in the subway station in the upper-soft-and-lower-hard stratum to construct the bottom foundation of the steel pipe column and pour concrete into the steel pipe column;

[0025] S02, embedding a sounding pipe outside the steel pipe column, and backfilling fine sand outside the steel pipe column to the top of the steel pipe column;

[0026] S03, after the initial setting of the concrete in the steel pipe column is completed, the construction of the roof and roof beam of the subway station in the range of the steel pipe column is completed, then the top of the steel pipe column is backfilled with gravel, and then the first steel casing is removed;

[0027] S04, excavating downward to the top structure elevation position of the subway station, constructing the top structure at the top of the steel pipe column, and then backfilling the part above the top structure to restore traffic;

[0028] S05, excavating a foundation pit under the protection of the top structure of the subway station, and constructing the middle structure and the bottom structure connecting the subway station and the steel pipe column from top to bottom, to complete the construction of the structures related to the subway station and the steel pipe column.

[0029] Meanwhile, the mud in the hole is discharged.

[0030] The construction method of the subway station in the upper-soft lower-hard stratum can greatly improve construction efficiency and save engineering investment.

[0031] Preferably, between steps S03 and S04, the method further comprises the steps of backfilling from the top of the steel pipe column to 20-30 cm below the original ground by backfilling soil, then installing a steel mesh, and then pouring concrete to the original ground to prevent deformation of the steel pipe column caused by extrusion of large machinery walking. The top structure at the top of the steel pipe column, such as the roof, roof beam, and the upper ring plate, lower ring plate and pressing plate of the roof and roof, is installed, and the pouring of the roof of the station is completed according to the design. After the installation of the steel pipe column is completed, the road traffic can be quickly restored.

[0032] Preferably, when the second steel casing is exposed during the excavation of the foundation pit under the protection of the top structure of the subway station, the exposed part of the second steel casing is temporarily cut.

[0033] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present application are:

[0034] 1. The construction method of the steel pipe column in the subway station in the upper-soft lower-hard stratum, by safely connecting the foundation reinforcement cage with the bottom of the steel pipe column, and simultaneously lowering the steel pipe column and the foundation reinforcement cage as a whole into the hole, can effectively ensure the stability of the steel pipe column after the bottom foundation construction, saving the construction space of the bottom foundation of the steel pipe column, thereby reducing the size of the bottom foundation of the steel pipe column, so that the hole can be divided into an upper large-diameter hole and a lower small-diameter hole when the hole is formed, reducing the volume of the hard rock hole, thereby reducing the construction difficulty of the hard rock hole, improving the hole forming efficiency, and saving engineering investment. At the same time, by simultaneously lowering the steel pipe column and the foundation reinforcement cage as a whole into the hole, the process of installing the mechanical positioning head of the steel pipe column is omitted, making the construction process simpler and further improving the construction efficiency of the steel pipe column.

[0035] 2. The construction method of the steel pipe column in the subway station in the upper-soft lower-hard stratum, by connecting the steel plate to the round steel pipe of the steel pipe column to seal the bottom, and safely connecting the foundation reinforcement cage with the bottom of the steel pipe column, can ensure the durability and strength of the steel pipe column as a permanent structure, and can improve the supporting capacity of the steel pipe column after construction, making the subway station structure more secure.

[0036] 3. The construction method of the subway station in the upper-soft lower-hard stratum can greatly improve construction efficiency and save engineering investment. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic view of the first steel casing and the second steel casing buried and the hole formed in step S1.

[0038] Figure 2 is a schematic diagram of the whole lowering of the steel pipe column and the foundation reinforcement cage into place by step S2;

[0039] Figure 3 is Figure 2 is a schematic diagram of the first steel casing, the second steel casing and the steel pipe column in the upper soft and lower hard stratum;

[0040] Figure 4 is a schematic diagram of the pouring of concrete into the steel pipe column and the backfilling outside the steel pipe column;

[0041] Figure 5 is a schematic diagram of the removal of the first steel casing in step S03;

[0042] Figure 6 is a schematic diagram of the excavation of the foundation pit in step S05;

[0043] Figure 7 is Figure 2 is a schematic diagram of the first steel casing, the second steel casing and the steel pipe column in the upper soft and lower hard stratum;

[0044] Figure 8 is a schematic diagram of the first steel casing, the second steel casing and the steel pipe column after the pouring of concrete into the steel pipe column;

[0045] Figure 9 is a schematic diagram of the construction of the structure related to the steel pipe column in the subway station in the upper soft and lower hard stratum after the completion of the construction.

[0046] Figure legend: 11-first steel casing; 12-mud wall; 13-second steel casing; 21-steel pipe column; 22-foundation reinforcement cage; 221-main reinforcement; 222-circular reinforcement; 23-upper ring plate; 24-pressing plate; 25-lower ring plate; 26-bolts; 27-acoustic pipe; 28-circular steel pipe; 29-connection steel plate; 33-fine sand; 34-C50 micro-expansion concrete; 35-bottom foundation; 41-reinforcement mesh; 42-backfilling soil; 43-top structure; 51-middle structure; 52-bottom structure. DETAILED DESCRIPTION

[0047] The present application will be described in detail below with reference to the drawings.

[0048] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0049] Example 1

[0050] The present example provides a construction method of a steel pipe column in a subway station in an upper soft and lower hard stratum, comprising the following construction steps:

[0051] S1, such as Figure 1 As shown, a first steel casing 11 is buried and a hole is formed in the first steel casing 11, and then a second steel casing 13 is buried downward from the bottom of the first steel casing 11 and a hole is formed in the second steel casing 13. The bottom of the buried second steel casing 13 is lower than the bottom elevation of the bottom foundation 35 of the steel pipe column 21;

[0052] S2, such as Figure 2 As shown, the foundation steel cage 22 connected to the bottom of the steel pipe column 21 and the steel pipe column 21 are lowered as a whole to the bottom of the second steel casing 13, and then the foundation steel cage 22 is poured to form the bottom foundation 35;

[0053] S3, such as Figure 3 and Figure 8 As shown, concrete is poured into the steel pipe column 21 to complete the construction of the steel pipe column 21.

[0054] The base steel cage 22 refers to the steel cage of the bottom foundation 35 of the steel pipe column 21. After pouring concrete, the bottom foundation 35 of the steel pipe column 21 is formed. Figure 4 As shown, the diameter of the first steel casing 11 is larger than the diameter of the second steel casing 13. Figure 2 As shown, the diameter selection standard of the steel pipe column 21 is the same as that of the prior art. The top of the steel pipe column 21 has an upper ring plate 23, a tie plate 24 and a lower ring plate 25. The positions of the upper ring plate 23, the tie plate 24 and the lower ring plate 25 correspond to the construction of the top structure 43 in the subway station, as shown in FIG. Figure 5 As shown. Figure 2 and Figure 7 As shown, the steel pipe column 21 includes a round steel pipe 28 and a bolt 26 located outside the bottom of the round steel pipe 28 .

[0055] like Figure 1 As shown, the bottom of the buried first steel casing 11 is suitably located at the soil-rock boundary or below the soil-rock boundary. The bottom of the buried first steel casing 11 is located at the soil-rock boundary, so that the hole formed in the large-diameter first steel casing 11 will not extend into the rock layer, and the hole forming difficulty is lower; and the hole formed in the large-diameter first steel casing 11 covers the entire height of the soft soil bottom layer, and the internal space of the hole is large, making construction more convenient. The bottom of the buried first steel casing 11 is located below the soil-rock boundary, which can improve the stability of the first steel casing 11 after burial and reduce the possibility of deformation and displacement of the first steel casing 11. The bottom of the buried first steel casing 11 is not suitable for entering the rock layer very deep to avoid excessive difficulty in hole forming.

[0056] In the embodiment, the outer diameter of the first steel casing 11 is 1900mm-2100mm, which is larger than the outer diameter of the upper part of the steel pipe column 21, so that the steel pipe column 21 can be lowered into the first steel casing 11 and the second steel casing 13 as a whole; the outer diameter of the second steel casing 13 is 1400mm-1600mm, which is larger than the outer dimension of the steel pipe column 21, so as to ensure that the second steel casing 13 can be normally lowered, and the gap between the outer sides of the second steel casing 13 and the steel pipe column 21 can be used for pouring concrete of the foundation reinforcement cage 22.

[0057] In the embodiment, the connection between the steel pipe column 21 and the foundation reinforcement cage 22 can be performed before step S2, and the connection steps of the steel pipe column 21 and the foundation reinforcement cage 22 are as follows:

[0058] The connecting steel plate 29 is welded at the bottom of the steel pipe column 21, and the top of the main reinforcement 221 of the foundation reinforcement cage 22 is welded with the connecting steel plate 29, so as to ensure that the foundation reinforcement cage 22 is safely connected with the bottom of the steel pipe column 21.

[0059] As shown in Figure 2 and Figure 3 The foundation reinforcement cage 22 includes vertical main reinforcement 221 and annular reinforcement 222 connecting the main reinforcement 221 into one body, the length of the top of the main reinforcement 221 of the foundation reinforcement cage 22 extending into the bottom of the round steel pipe 28 of the steel pipe column 21 is LaE, which meets the anti-seismic anchoring capacity of the bottom foundation 35 of the steel pipe column 21 and the bottom of the steel pipe column 21. When the steel pipe column 21 and the foundation reinforcement cage 22 are connected, the round steel pipe 28 of the steel pipe column 21 is sealed by the connecting steel plate 29, and as shown in Figure 3 the top of the main reinforcement 221 is welded with the connecting steel plate 29 after penetrating through the connecting steel plate 29, so as to ensure the durability and strength of the steel pipe column 21 as a permanent structure.

[0060] In the embodiment, when the concrete is poured into the steel pipe column 21 in step S3, a layer of cement mortar with the same grade as the concrete in the steel pipe column 21 and with a thickness of 10cm-20cm is first poured, and then C50 micro-expansion concrete is quickly and continuously poured, so as to avoid the concrete shrinkage and creep caused by long construction time, and to avoid the bouncing of the coarse aggregate of the concrete.

[0061] The method for constructing steel pipe columns in subway stations with soft upper and hard lower strata described in this embodiment effectively ensures the stability of the bottom foundation 35 of the steel pipe column 21 after construction by securely connecting the foundation reinforcement cage 22 to the bottom of the steel pipe column 21 and simultaneously lowering the steel pipe column 21 and the foundation reinforcement cage 22 as a whole into the borehole. This eliminates the need for separate construction space for the bottom foundation 35 of the steel pipe column 21, thereby reducing the size of the bottom foundation 35 of the steel pipe column 21. This allows the borehole to be divided into a large-diameter upper borehole and a small-diameter lower borehole during borehole construction, thereby reducing the volume of boreholes in hard rock and thus reducing the construction difficulty of hard rock borehole construction, improving borehole efficiency, and saving project investment. Furthermore, by simultaneously lowering the steel pipe column 21 and the foundation reinforcement cage 22 as a whole into the borehole, the process of installing a mechanical positioning head for the steel pipe column 21 is eliminated, making the construction process simpler and further improving the construction efficiency of the steel pipe column 21.

[0062] Example 2

[0063] This embodiment provides a method for constructing a subway station in soft upper and hard lower strata, comprising the following steps:

[0064] S01, using the construction method of the steel pipe column in the subway station with soft upper and hard lower strata described in Example 1 to construct the bottom foundation 35 of the steel pipe column 21 and pour concrete into the steel pipe column 21; specifically including steps S1-S3 in Example 1;

[0065] S02, such as Figure 4 As shown, an acoustic detection pipe 27 is pre-buried outside the steel pipe column 21, and fine sand 33 is backfilled outside the steel pipe column 21 to the top of the steel pipe column 21. The backfilling of fine sand 33 can limit the steel pipe column 21 before excavating the foundation pit and reduce the influence of the steel pipe column 21 on the outside, thereby reducing the possibility of damage or deformation of the steel pipe column 21; at the same time, the mud in the hole is discharged;

[0066] S03, such as Figure 5 As shown, after the initial setting of the concrete in the steel pipe column 21 is completed, the construction of the subway station roof and roof beam within the range of the steel pipe column 21 is completed. This part of the construction does not completely construct the subway station roof and roof beam. It mainly constructs a part above the steel pipe column 21, and reserves joints such as connectors to facilitate the complete construction of the remaining roof and roof beam and connect them with the roof and roof beam above the steel pipe column 21; then backfill the top of the steel pipe column 21 with crushed stone, and then remove the first steel casing 11. After the first steel casing 11 is removed, Figure 6 The dotted line in the upper middle part is shown;

[0067] S04, such as Figure 5As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic;

[0068] S05、as Figure 6 As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic; Figure 9 As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic;

[0069] As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic; Figure 5 As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic.

[0070] As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic; Figure 6 As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic. Figure 6 As shown, the top structure 43 of the subway station is excavated to the top level position, the top structure 43 is constructed, and the top structure 43 refers to the remaining roof and roof beam, etc., and then the upper part of the top structure 43 is backfilled to restore traffic.

[0071] The subway station construction method for the upper-soft lower-hard stratum described in the present application can greatly improve the construction efficiency and save engineering investment.

[0072] Embodiment 3

[0073] The embodiment provides a subway station construction method for an upper-soft lower-hard stratum, which is the specific construction steps S01-S05 in embodiment 2, as follows:

[0074] Step S01 includes steps S1-S3;

[0075] S1, determine the size of the first steel casing 11 according to the size of the roof beam, bury the first steel casing 11 so that the bottom of the first steel casing 11 is located at the soil-rock boundary, i.e. the boundary between soil and rock layers, to avoid large-diameter hole forming in the rock layer, use the rotary drill to first excavate the upper part to form a large-diameter hole of about 2.0 m, if the station has a large burial depth, the hole diameter can be appropriately increased to ensure the construction space of the roof and roof beam, the hole diameter of the steel pipe column 21 in the remaining design elevation is about 1.5 m, which is the diameter of the second steel casing 13 inside, mud wall 12 is used in the drill hole, complete the hole forming process in the entire upper soft and lower hard stratum, the entire process is complete 2 times hole forming, and the hole diameter in the upper soft soil layer is greater than that in the lower rock layer, as shown in Figure 1 ;

[0076] After hole forming is completed, the connection of the foundation steel cage 22 and the steel pipe column 21 is first performed. As shown in Figure 3 , when the foundation steel cage 22 is made, the length LaE (steel anti-seismic anchoring length) should be reserved on the upper part of the foundation steel cage 22, and the upper steel is the main reinforcement 221, as shown in Figure 3 , a connecting steel plate 29 with a thickness t = 20 mm is welded at the bottom of the round steel pipe 28 of the steel pipe column 21, the connecting steel plate 29 seals the bottom of the round steel pipe 28, the main reinforcement 221 extends into the bottom of the steel pipe column 21 after passing through the connecting steel plate 29, and the position of the main reinforcement 221 passing through the connecting steel plate 29 is point-welded to make the foundation steel cage 22 and the steel pipe column 21 safely connected, and the fixing of the foundation steel cage 22 and the steel pipe column 21 is completed.

[0077] Then enter step S2: as shown in Figure 2 and Figure 7As shown, the prefabricated steel pipe column 22 and foundation reinforcement cage 21 are lowered together. Specifically, the HPE hydraulic pipe insertion machine is installed to complete the positioning and centering. The horizontality of the HPE hydraulic vertical insertion machine is adjusted to recheck the center position. The steel pipe column 22 is slowly lifted by a crawler crane and a truck crane, aligned with the HPE hydraulic vertical insertion machine, and slowly placed vertically into the HPE hydraulic vertical insertion machine to complete the lowering of the steel pipe column 22 and reinforcement cage. The steel pipe column 22 is hoisted into the HPE hydraulic vertical insertion machine, lowered into the hole through the second flange, and then the HPE hydraulic vertical insertion machine firmly grasps the steel pipe column 22 and re-measures the verticality of the steel pipe column 22. Once the verticality meets the requirements, the sensor installation continues. After the steel pipe column 22 is lowered and inserted to the designed bottom surface, the horizontality is adjusted and the verticality of the steel pipe column is re-measured before the steel pipe column is fixed, and the fixing of the steel pipe column is finally completed. The positioning and lowering of the steel pipe column and the foundation reinforcement cage as a whole by the HPE hydraulic pipe insertion machine is an existing technology, which can ensure that the steel pipe column is lowered to the specified position and can ensure accuracy. After the steel pipe column is lowered to the specified position, the steel pipe column and the foundation reinforcement cage are hoisted as a whole by the upper lifting mechanism to prevent the weight of the steel pipe column from squeezing the foundation reinforcement cage, thereby preventing the foundation reinforcement cage from being deformed or damaged. Then, super-slow-setting concrete (slow-setting time 12h to 16h) is used to cast the foundation reinforcement cage under the steel pipe column pile to form the bottom foundation 35. When casting the foundation reinforcement cage, it can be cast from the gap between the second steel casing and the steel pipe column, or it can be cast in the casting conduit reserved on the bottom cover of the steel pipe column.

[0078] S3, such as Figure 8 As shown, pouring concrete into the steel pipe column 21, the pouring of C50 slightly expansive concrete in the steel pipe column should be carried out continuously. Before pouring, a layer of cement mortar with a thickness of 10cm-20cm and the same grade as the expansive concrete should be poured first to avoid bouncing of the coarse aggregate of the concrete.

[0079] After pouring concrete into the steel pipe column 21, step S02 is entered: after pre-burying the acoustic detection pipe 27, fine sand 33 is backfilled on the outside of the steel pipe column 22 to the top of the column, and the mud in the hole is discharged at the same time.

[0080] S03: If Figure 5 As shown, after the concrete in the steel pipe column 22 reaches initial setting, the construction of the subway station roof (beam) structure is completed. After backfilling the top of the column with gravel, the first steel casing 11 is removed and immediately backfilled with stone chips or sand to 25 cm below the original ground. At the same time, a φ16@250mm*250mm steel mesh 41 is used to pour a 25 cm thick layer of C30 reinforced concrete to prevent deformation caused by squeezing of the steel pipe column 22 by the movement of large machinery.

[0081] S04: Excavate to the top structure 43 level of the subway station, construct the top structure 43, specifically, install the top plate and the upper ring plate, lower ring plate and tie plate of the top plate beam, and complete the pouring of the top plate of the subway station according to the design, complete the installation of the steel pipe column, and finally restore the road traffic.

[0082] S05: Excavate the foundation pit under the protection of the top plate and top plate beam of the subway station, cut off the second steel casing 13 while excavating, simultaneously construct the middle plate (beam) and bottom plate (beam) of the subway station, pile cap and connecting members thereof and the steel pipe column, and complete the entire construction of the steel pipe column of the subway station, as shown in Figure 6 and Figure 9 .

[0083] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for constructing a subway station in a soft upper and hard lower stratum, characterized by, The method comprises the following steps: S01, using the construction method of the steel pipe column in the upper-soft and lower-hard stratum subway station to construct the bottom foundation (35) of the steel pipe column (21) and pour concrete into the steel pipe column (21); The construction method of the steel pipe column in the upper-soft and lower-hard stratum subway station comprises the following construction steps: S1, burying the first steel casing (11) and forming a hole in the first steel casing (11), then burying the second steel casing (13) at the bottom of the first steel casing (11) and forming a hole in the second steel casing (13), the bottom of the buried second steel casing (13) being lower than the bottom elevation of the bottom foundation (35) of the steel pipe column (21); in step S1, the bottom of the buried first steel casing (11) is located at or below the soil-rock boundary; S2, integrally lowering the foundation reinforcement cage (22) connected to the bottom of the steel pipe column (21) and the steel pipe column (21) to the bottom of the second steel casing (13), then pouring the foundation reinforcement cage (22) to form the bottom foundation (35); S3, pouring concrete into the steel pipe column (21) to complete the construction of the steel pipe column (21); S02, pre-burying a sounding pipe (27) outside the steel pipe column (21), and backfilling fine sand (33) outside the steel pipe column (21) to the top of the steel pipe column (21); S03, after the initial setting of the concrete in the steel pipe column (21) is completed, the construction of the subway station roof and roof beam in the range of the steel pipe column (21) is completed, then the top of the steel pipe column (21) is backfilled with gravel, and then the first steel casing (11) is removed; S04, excavating downward to the top structure (43) elevation position of the subway station, constructing the top structure (43), and then backfilling the above part of the top structure (43) to restore traffic; S05, under the protection of the top structure (43) of the subway station, excavating the foundation pit downward, and constructing the middle structure (51) and the bottom structure (52) of the subway station connected with the steel pipe column (21) from top to bottom, to complete the construction of the structures related to the steel pipe column (21) of the subway station.

2. The method according to claim 1, wherein The connection steps of the steel pipe column (21) and the foundation reinforcement cage (22) are: Welding a connecting steel plate (29) at the bottom of the steel pipe column (21), and welding the top of the main reinforcement (221) of the foundation reinforcement cage (22) to the connecting steel plate (29).

3. The method according to claim 2, wherein The length of the top of the main reinforcement (221) of the foundation reinforcement cage (22) extending into the bottom of the round steel pipe (28) of the steel pipe column (21) is LaE.

4. The method according to claim 3, wherein When the steel pipe column (21) and the foundation reinforcement cage (22) are connected, the round steel pipe (28) of the steel pipe column (21) is sealed by the connecting steel plate (29), and the top of the main reinforcement (221) is welded to the connecting steel plate (29) after passing through the connecting steel plate (29).

5. The method according to any one of claims 1 to 4, wherein the method is characterized by, In step S1, the outer diameter of the first steel casing (11) is 1900mm-2100mm, and the outer diameter of the second steel casing (13) is 1400mm-1600mm.

6. The construction method of a subway station in soft over hard ground strata as claimed in any one of claims 1 to 4, wherein In step S3, a layer of cement mortar with the same grade as the concrete in the steel pipe column (21) and a thickness of 10cm-20cm is poured first, and then concrete is poured into the steel pipe column (21).

7. The method according to claim 1, wherein Between steps S03 and S04, there is also a step of backfilling from the top of the steel pipe column (21) to 20-30 cm below the original ground by backfilling soil (42), then installing a steel mesh (41), and then pouring concrete to the steel mesh (41).

8. The method according to claim 7, wherein When excavating the foundation pit under the protection of the top structure (43) of the subway station, when the second steel casing (13) is exposed, the exposed part of the second steel casing (13) is temporarily cut.

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