Construction method for supporting old foundation pit

Abstract

The invention provides an old foundation pit supporting construction method. The old foundation pit supporting construction method comprises the steps that earthwork is excavated to a preset distance below a floor slab of the negative first floor of a basement; construction of a vertical reinforced concrete transfer beam and a first horizontal transfer beam of a newly-built building foundation pit is conducted within the height range of a top plate and a bottom plate of the negative first layer of an original building basement; earth is excavated for the second time to the position with the preset distance below a basement second floor slab; and construction of the remaining vertical reinforced concrete transfer beams and the second horizontal transfer beam of the newly-built building foundation pit is conducted within the height range of the top plate and the bottom plate of the negative second layer of the original building basement. When the deep foundation pit support construction of the newly-built building is carried out, the vertical reinforced concrete transfer beam is used for transferring force, and the vertical reinforced concrete transfer beam and an original building basement form a complete support system; the purposes of combining a new foundation pit supporting system and an old foundation pit supporting system and fully utilizing an old foundation pit supporting wall or an old building outer wall are achieved through the technical means of newly arranging a force transmission support, a vertical reinforced concrete transfer beam, a horizontal section steel transfer beam and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of new foundation pit support, and more particularly to a construction method for reusing an existing foundation pit support. Background Art

[0002] With the rapid development of cities and the increasing deep development and utilization of urban underground space, there are more and more cases of constructing new underground spaces adjacent to existing underground spaces and implementing a new underground space in phases. In both cases, the problems of connection and utilization of new and old deep foundation pit support structures are faced.

[0003] Currently, the conventional foundation pit support method is to adopt an independent row of piles (continuous wall) anchor or row of piles (continuous wall) strut support method. However, in the construction of connecting a new foundation pit with an existing building basement, the workload of demolishing the support system is large and the cost is high. Summary of the Invention

[0004] In view of this, the present invention provides a construction method for reusing an existing foundation pit support, aiming to solve the problems of large workload and high cost in demolishing the support system in the construction of connecting a new foundation pit with an existing building basement.

[0005] The present invention provides a construction method for reusing an existing foundation pit support, which includes the following steps: a primary excavation step of excavating the soil to a preset distance below the floor slab of the first basement floor; an upper beam construction step of constructing a vertical reinforced concrete transfer beam and the first horizontal transfer beam of the new building foundation pit within the height range between the top slab and the bottom slab of the first basement floor of the original building, so that the axial force of the foundation pit support system is transmitted through the first horizontal transfer beam of the foundation pit to the vertical reinforced concrete transfer beam, the original building support wall and the basement wall, and then transmitted to the bottom slab and the top slab of the first basement floor of the original building to form an upper support structure; a secondary excavation step of excavating the soil again until reaching a preset distance below the floor slab of the second basement floor; a middle beam construction step of constructing the remaining vertical reinforced concrete transfer beams and the second horizontal transfer beam of the new building foundation pit within the height range between the top slab and the bottom slab of the second basement floor of the original building, so that the axial force of the foundation pit support system is transmitted through the second horizontal transfer beam to the vertical reinforced concrete transfer beam and the original building support wall, and then transmitted to the bottom slab and the top slab of the second basement floor of the original building to form a lower support structure; a third excavation step of excavating the soil again until reaching the bottom of the foundation pit; a primary structure construction step of constructing a replacement support plate between the bottom of the foundation pit and the second basement floor slab and the support piles and backfilling the soil, and demolishing the second horizontal transfer beam; a secondary structure construction step of constructing a replacement support plate between the second basement floor slab and the first basement floor slab and the support piles and backfilling the soil, demolishing the first horizontal transfer beam, and constructing the basement structure to the ground elevation; a beam demolition step of demolishing the support system between the first stage and the second stage of construction and connecting the structures of the first stage and the second stage of construction, so that the basements of the new and old buildings are integrated.

[0006] Further, for the above-mentioned construction method of reusing the foundation pit support, the initial excavation step includes the following sub-steps: the earth excavation sub-step, excavating the earth in the second-phase newly-built foundation pit with a slope to a preset distance below the elevation of the first-floor slab of the original building in the first phase; the positioning and setting-out sub-step, conducting surveying and setting-out and marking the vertical reinforced concrete transfer beam on the inner side of the second-phase newly-built foundation pit and the inner side of the basement of the original building in the first phase; the scaffolding erection sub-step, erecting a scaffolding working platform on the cushion layer of the excavation area in the second-phase newly-built foundation pit; the demolition sub-step, demolishing the wall structure of the basement of the original old building.

[0007] Further, for the above-mentioned construction method of reusing the foundation pit support, after the demolition sub-step, the following sub-steps are also included: the waste transportation sub-step, transporting the demolished construction waste out and conducting dust reduction and cleaning.

[0008] Further, for the above-mentioned construction method of reusing the foundation pit support, the wall structure of the basement of the original old building is demolished from top to bottom, section by section, and layer by layer.

[0009] Further, for the above-mentioned construction method of reusing the foundation pit support, the construction of the vertical reinforced concrete transfer beam includes the following sub-steps: the chiseling and bar planting sub-step, chiseling off part of the wall and the capping beam of the basement of the original building in the first phase, chiseling the concrete surface at the connection with the new building in the second phase, and bar planting on the retaining wall of the original building in the first phase; the steel bar binding sub-step, binding the bar planted on the retaining wall of the original building in the first phase with the first horizontal transfer beam; the stirrup binding sub-step, binding the stirrups at the pre-construction position of the vertical reinforced concrete transfer beam; the formwork installation sub-step, installing the construction formwork at the pre-construction position of the vertical reinforced concrete transfer beam; the concrete pouring sub-step, pouring the concrete in the construction formwork to obtain the vertical reinforced concrete transfer beam.

[0010] Further, for the above-mentioned construction method of reusing the foundation pit support, the beam demolition step specifically includes the following sub-steps: the first-floor demolition sub-step, demolishing the original structure above the first basement floor and the diaphragm wall, constructing the first-floor floor surface, supporting with a scaffold in the first basement floor, and demolishing it only after the concrete has completely reached the design strength; the second-floor demolition sub-step, demolishing the original structure above the second basement floor and the diaphragm wall, and constructing the new structure above the second basement floor; the re-demolition sub-step, demolishing the structure of the third basement floor, the floor slab and the diaphragm wall in the connection area, and completing the construction of the new structure at the connection.

[0011] Further, for the above-mentioned construction method of reusing the foundation pit support, the support system between the first phase and the second phase includes: the vertical reinforced concrete transfer beam, the basement wall of the first-phase building, and part of the structure of the retaining wall of the first-phase building.

[0012] Further, in the above-mentioned construction method for reusing the foundation pit support, the demolition of the support system between the first and second construction phases is carried out using the inverse construction method.

[0013] Further, in the above-mentioned construction method for reusing the foundation pit support, two layers of backtop scaffolds are erected between the bottom slab of the second basement floor and the bottom of the top beam of the first basement floor to backtop the bottom slab and top slab between the first and second basement floors of the original building.

[0014] Further, in the above-mentioned construction method for reusing the foundation pit support, the vertical reinforced concrete transfer beam forms a reinforced concrete structure with the original basement wall and the original support wall by means of implanting steel bars.

[0015] The construction method for reusing the foundation pit support provided by the present invention uses a vertical reinforced concrete transfer beam to transfer force during the construction of the deep foundation pit support of a new building, forming a complete support system with the basement of the original building; through technical means such as newly installed force transfer braces, vertical reinforced concrete transfer beams, and horizontal steel-concrete transfer beams, the purpose of combining the new and old foundation pit support systems and making full use of the old foundation pit support wall or the external wall of the old building is achieved, thereby reducing the cost of the new foundation pit support and at the same time reducing the workload of demolishing the support system; solving the connection problem between the new foundation pit and the basement of the old building, giving full play to the effect of reusing, realizing green energy conservation and environmental protection, and solving the problems of large workload and high cost of demolishing the support system in the connection construction between the existing new foundation pit and the basement of the old building. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0017] Figure 1 is a flow chart of the construction method for reusing the foundation pit support provided by the embodiment of the present invention;

[0018] Figure 2 is a schematic structural diagram after the initial excavation provided by the embodiment of the present invention;

[0019] Figure 3 is a schematic structural diagram after the construction of the upper beam provided by the embodiment of the present invention;

[0020] Figure 4 is a schematic structural diagram after the secondary excavation provided by the embodiment of the present invention;

[0021] Figure 5 is a schematic structural diagram after the construction of the middle beam provided by the embodiment of the present invention;

[0022] Figure 6Schematic diagram of the structure after re-excavation provided by an embodiment of the present invention;

[0023] Figure 7 Schematic diagram of the structure after the first-stage structure construction provided by an embodiment of the present invention;

[0024] Figure 8 Schematic diagram of the structure after the secondary structure construction provided by an embodiment of the present invention;

[0025] Figure 9 Schematic diagram of the structure after the beam is demolished provided by an embodiment of the present invention;

[0026] Figure 10 Schematic diagram of the structure after the beam is demolished provided by an embodiment of the present invention;

[0027] Figure 11 Flow chart of the initial excavation step provided by an embodiment of the present invention;

[0028] Figure 12 Flow chart of the construction of the vertical reinforced concrete transfer beam provided by an embodiment of the present invention;

[0029] Figure 13 Flow chart of the beam demolition step provided by an embodiment of the present invention;

[0030] Figure 14 Schematic diagram of the structure after the first floor at the connection is demolished and constructed provided by an embodiment of the present invention;

[0031] Figure 15 Schematic diagram of the structure after demolishing the original structure above the second basement floor and the diaphragm wall provided by an embodiment of the present invention;

[0032] Figure 16 Schematic diagram of the structure after constructing the structure above the second basement floor provided by an embodiment of the present invention. Detailed implementation manners

[0033] Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. Hereinafter, the present invention will be described in detail with reference to the drawings and in combination with the embodiments.

[0034] See Figure 1 , which is a flow chart of the method for constructing a recycled foundation pit support provided by an embodiment of the present invention.

[0035] As shown in the figure, the method includes the following steps:

[0036] The initial excavation step S1 is to excavate earth to a preset distance below the basement negative one floor slab.

[0037] Specifically, Figure 2 As shown, four original support plates 2 of the first phase are arranged on the right side of the outer wall 1 of the basement, which serve as the negative third floor, the negative second floor, the negative first floor and the ground floor respectively; a vertically arranged underground continuous wall 3 is arranged at the right end of the original support plate 2 at the negative first floor and below it, and three-axis mixing piles 4 of the original building of the first phase are arranged on the left and right sides of the underground continuous wall 3. The underground continuous wall 3 and the three-axis mixing piles 4 serve as the original supporting walls, and a constructed concrete plate 5 is arranged above the underground continuous wall 3 between the negative first floor and the ground floor, which serves as the original basement wall. A mounting railing 6 is arranged above the constructed concrete plate 5. Among them, a constructed cap beam 51 is arranged at the top of the constructed concrete plate 5. The earthwork can be excavated on a large scale to the first support bottom elevation first, and the earthwork adjacent to the original building side is excavated to a preset distance below the basement first floor bottom slab, wherein the preset distance can be 1m, that is, the earthwork adjacent to the original building side is excavated to 1m below the basement first floor bottom slab, that is, Figure 2 The AA position is shown. In the later stage, the slope of the newly built foundation pit is excavated to 1m below the level of the floor slab of the first underground floor of the original old building, and a 1:1 slope is adopted.

[0038] The upper beam construction step S2 is to construct vertical reinforced concrete transfer beams and the first horizontal transfer beam of the new building foundation pit within the height range of the top and bottom plates of the basement negative first floor of the original building, so that the axial force of the foundation pit support system is transmitted to the vertical reinforced concrete transfer beams, the original building support walls and the basement walls through the first horizontal transfer beam of the foundation pit, and then transmitted to the bottom and top plates of the basement negative first floor of the original building to form an upper support structure.

[0039] Specifically, the vertical reinforced concrete transfer beam 7 within the height range of the top and bottom plates of the basement of the original building and the first horizontal transfer beam 8 of the foundation pit of the new building are constructed. Figure 3 As shown, the vertical reinforced concrete transfer beam 7 is connected to the original basement wall and the original supporting wall, i.e., the original supporting wall, by means of embedded reinforcement to form a reinforced concrete structure. The axial force of the foundation pit support system is transmitted to the vertical reinforced concrete transfer beam 7, the original building supporting wall and the basement wall through the first horizontal transfer beam 8 of the normal foundation pit, and then to the first floor slab and top slab of the basement of the original building, forming a safe and stable support structure. Of course, the vertical reinforced concrete transfer beam, the crown beam, the first waist beam, the first supporting beam can also be constructed, and the lower lap joint of the vertical reinforced concrete transfer beam can be reserved.

[0040] Secondary excavation step S3, secondary excavation of earthwork until a preset distance below the basement negative second floor slab.

[0041] Specifically, after the vertical reinforced concrete transfer beam 7, the capping beam, the first waist beam, and the first support beam, i.e., the first horizontal transfer beam 8 reach the design strength, the soil is excavated to the elevation of the bottom of the second support. The soil of the original building is excavated to a preset distance below the basement two-layer floor slab. The preset distance can be 1 m, that is, the soil adjacent to the original building side is excavated to 1 m below the basement one-layer floor slab, that is, at B-B as Figure 4 shown.

[0042] Construction step S4 of the middle beam: The remaining vertical reinforced concrete transfer beams and the second horizontal transfer beam of the new building foundation pit are constructed within the height range of the basement negative two-layer top slab and the bottom slab of the original building, so that the axial force of the foundation pit support system is transmitted to the vertical reinforced concrete transfer beam and the original building support wall through the second horizontal transfer beam, and then transmitted to the basement negative two-layer floor slab and the top slab of the original building, forming a lower support structure.

[0043] Specifically, the remaining vertical reinforced concrete transfer beams, the second waist beam, and the support beam are constructed. As Figure 5 shown, the vertical reinforced concrete transfer beam 7 within the height range of the basement two-layer top slab and the bottom slab of the original building and the second horizontal transfer beam 9 of the new building foundation pit are constructed. The axial force of the foundation pit support system is transmitted to the vertical reinforced concrete transfer beam 7 and the original building support wall, i.e., the original support wall, through the second horizontal transfer beam 9, and then transmitted to the basement two-layer floor slab and the top slab of the original building, forming a safe and stable support structure. That is to say, the vertical reinforced concrete transfer beam is used to transmit the force, forming a complete support system with the basement of the original building. Through the force transmission of the vertical reinforced concrete transfer beam, the foundation pit support of the new building and the floor slab of the basement of the original building form a whole, ensuring the axial force transmission of the foundation pit support project and the construction safety of the foundation pit support project.

[0044] Re-excavation step S5: The soil is excavated again until the bottom of the foundation pit.

[0045] Specifically, after the second waist beam and the second horizontal transfer beam 9 reach 80% of the design strength, the soil is excavated in layers and sections to the bottom of the foundation pit. As Figure 6As shown in the figure. Among them, a drainage ditch 10 is provided at the bottom of the foundation pit. During the later stage, the slope excavation in the newly built foundation pit is carried out to 1 m below the elevation of the first basement floor of the original old building, and the slope form of 1:1 is adopted. After the excavation is completed, a 100-mm-thick C20 cushion is constructed for each vertical reinforced concrete transfer beam, and a sewage pump is installed inside to pump water outwards. During the period of removing the basement wall of the previous building and constructing the vertical reinforced concrete transfer beam, the construction team shall arrange a special person to track the water surface elevation in the pit to prevent the water in the sump from overflowing into the basement of the old building through the groove of the vertical reinforced concrete transfer beam. If the drainage of the water pump in the sump cannot meet the requirements during sufficient rainfall, the subcontracting team shall promptly take drainage measures. Water pumps shall be stored in the basement of the old building to promptly drain the rainwater overflowing into the drainage ditch of the basement of the old building.

[0046] For the construction step S6 of the primary structure, a replacement support plate is constructed between the bottom of the foundation pit and the second basement floor slab of the basement and the retaining piles, and the soil is backfilled, and the second horizontal transfer beam is removed.

[0047] Specifically, construct the foundation, the third basement floor, and the second basement floor structures, and construct a replacement support plate between the foundation slab and the second basement floor slab of the basement and the retaining piles and backfill the soil to this elevation. After the replacement support plate reaches the strength, remove the second horizontal transfer beam 9. Among them, cohesive soil or stone powder and other backfill materials are used for the backfill soil, and the compactness of the backfill material can be guaranteed, as Figure 7 shown.

[0048] For the construction step S7 of the secondary structure, a replacement support plate is constructed between the second basement floor slab and the first basement floor slab of the basement and the retaining piles, and the soil is backfilled, and the first horizontal transfer beam is removed, and the basement structure is constructed to the ground elevation.

[0049] Specifically, continue to construct the basement to the first basement floor slab, and backfill the soil to this elevation, construct the replacement support plate. After the strength of the replacement support plate reaches 80% of the designed strength, remove the first horizontal transfer beam 8, and continue to construct the basement structure to the ground ±0.000, as Figure 8 shown.

[0050] For the beam removal step S8, remove the retaining system between the first-phase and second-phase construction, and connect the structures of the first-phase and second-phase construction so that the basements of the new and old buildings are integrated.

[0051] Specifically, remove the retaining system between the original building and the newly built building and connect the underground structures. That is, after the basement of the new building is completed, the vertical reinforced concrete transfer beam, the foundation pit retaining structure of the original building, and the basement side wall and other structures can be removed, and the basements of the new and old buildings are connected together, as Figure 9 shown. Among them, the removal of the retaining system between the first-phase and second-phase construction is carried out by the inverse construction method, with the first floor as the boundary, and the construction periods of the above-ground and underground parts do not interfere with each other. Among them, the retaining system between the first-phase and second-phase construction includes: vertical reinforced concrete transfer beam, the basement wall of the first-phase building, and some structures of the retaining wall of the first-phase building.

[0052] In this embodiment, construction preparation may be performed first, followed by technical preparation, site preparation, and material and equipment preparation.

[0053] In this embodiment, the vertical reinforced concrete transfer beam construction adopts flow operation, and the vertical reinforced concrete transfer beam formwork and reinforcement materials are transported to the basement of the original building through the gap of the vertical reinforced concrete transfer beam position, and all relevant materials are used in rotation. After the vertical reinforced concrete transfer beam is fully constructed, a vertical reinforced concrete transfer beam groove is reserved, and the excess materials and garbage are transported to the foundation pit of the new building through this groove for unified treatment. After the construction of the last vertical reinforced concrete transfer beam is completed, the remaining materials and garbage are transported to the outside through the passage of the basement of the original building. During the construction process, safe and civilized construction should be carried out to keep the site clean and tidy. It is forbidden to pile materials and garbage in the basement. If materials or garbage are accidentally dropped in the basement during the construction process, personnel should be arranged to clean it up and restore it in time.

[0054] In this embodiment, the early stage building is connected with the later expansion building, and the foundation pit support of the early stage building needs to adopt underground continuous wall plus internal support. The replacement support adopts the replacement support plate construction, and it is strictly forbidden to directly backfill the earth between the outer wall of the basement and the underground continuous wall. After the construction is completed, the early stage building can be put into use and function normally.

[0055] Because the earthwork was not backfilled between the outer wall and underground continuous wall of the previous building's basement, when the vertical reinforced concrete transfer beam was chiseled out, a support of the main beam of the previous building structure would be chiseled out, leaving the top plate of the previous building in a cantilevered state, posing a major safety hazard. A top-returning method is adopted to avoid cantilevering of one end of the plate, that is, a two-layer top-returning scaffolding 11 can be set up between the bottom plate of the second negative floor of the basement and the bottom of the top plate of the first negative floor, so as to top-return the bottom plate and top plate between the first negative floor and the second negative floor of the original building's basement, specifically including:

[0056] 1) Use steel pipe scaffolding to return to the top in the basement. The range of the scaffolding is from the bottom plate of the second negative floor to the bottom of the top plate beam of the first negative floor, and two layers are built. The scaffolding uses ф48*3.5 steel pipes, the vertical pole spacing is 600*600mm, the step distance is 1500mm, and the vertical and horizontal sweeping poles are no more than 200mm from the ground. In the early stage of the basement, 4 rows of scaffolding are built along the main beam direction, and 3 rows of scaffolding are built along the secondary beam direction. The specific erection method is as follows Figure 10 As shown, in the original building basement wall, that is, the guard arm column area 52 where the concrete slab 5 has been constructed, that is, the area that has been chiseled out, there are cross-arranged main beams 53 and secondary beams 54, and a return scaffolding 11 is set up at the intersection of the main beam 53 and the secondary beam 54. The second-floor scaffolding of the basement in the early stage of the construction can be fully erected within 8m of the basement wall.

[0057] 2) The top support is in the middle of the bottom of the beam, on the small cross bar. The free end of the top support should not be larger than 300mm and should be not less than 150mm into the bar.

[0058] 3) Before the vertical reinforced concrete transfer beam area is chiseled out, a 120mm thick 200mm high retaining wall is built on the first floor of the basement of the previous building. Ordinary cement bricks are used for double-sided plastering, or colored strips are used to cover the vertical reinforced concrete transfer beam area to prevent rainwater or garbage from falling into the basement of the previous building from the vertical reinforced concrete transfer beam groove.

[0059] If there are heavy equipment such as transformer boxes on the top plate of the basement of the previous building, there are vertical reinforced concrete transfer beams within the force range of the equipment, and there are no frame beams in the top plate area of ​​the basement of the previous building where the equipment is located. Before the vertical reinforced concrete transfer beams are removed, take measures to return to the top at the equipment location, reinforce the top plate of the basement of the previous building, and set up scaffolding from the second negative floor to the bottom of the first negative floor, and return to the top two layers. Use ф48*3.5 scaffolding pipes for returning to the top, and set up full-floor support scaffolding on the first and second floors of the basement within the equipment range, with a vertical and horizontal spacing of 750mm, a step distance of 1500mm, and a sweeping rod no more than 200mm from the ground. Add a scissors brace every four meters. First top and then dismantle, and after the erection of the top reinforcement scaffolding is completed and multiple parties pass the acceptance, proceed to the next process.

[0060] See also Figure 11 , which is a flowchart of the initial excavation step provided by an embodiment of the present invention. As shown in the figure, the initial excavation step S1 includes the following sub-steps:

[0061] In the earth excavation sub-step S11, earth is excavated in the newly built foundation pit of the second phase by slope setting to a preset distance below the floor slab elevation of the first-basement floor of the original building of the first phase.

[0062] Specifically, the slope of the newly built foundation pit in the later stage is excavated to 1m below the elevation of the floor slab of the first underground floor of the original old building, and a 1:1 slope is adopted. After the excavation is completed, a 100mm thick C20 cushion layer is constructed in each vertical reinforced concrete transfer beam, and a sewage pump is installed inside to pump water out. During the period of chiseling the basement wall of the previous building and the construction of the vertical reinforced concrete transfer beam, the construction team needs to arrange a special person to track the water surface elevation in the pit to prevent the water in the sump from overflowing into the basement of the old building through the vertical reinforced concrete transfer beam groove. If there is enough rainwater and the water pump in the sump cannot meet the requirements, the subcontracting team should take drainage measures in time. The basement of the old building should reserve a water pump to discharge the rainwater overflowing into the drainage ditch of the basement of the old building in time.

[0063] The positioning and laying out sub-step S12 is to measure and lay out and mark the vertical reinforced concrete transfer beams on the inner side of the newly built foundation pit of the second phase and the inner side of the basement of the original building of the first phase.

[0064] Specifically, according to the foundation pit support design drawings, measurements are carried out to mark the specific positions of the vertical reinforced concrete transfer beams on the inner side of the foundation pit and the inner side of the basement of the original building.

[0065] Scaffolding erection sub-step S13: Erect a scaffolding working platform on the cushion layer in the excavation area of the newly built foundation pit in the second phase.

[0066] Specifically, the demolition mainly adopts manual chiseling with mechanical assistance. The construction workers use the erected scaffolding working platform. A scaffolding working platform is erected on the cushion layer in the excavation area of the new building foundation pit. According to the top elevation of the vertical reinforced concrete transfer beam and the floor elevation of the first basement floor of the original building, the scaffolding pipes for the demolition platform are made of ф48*3.5 steel pipes. Two rows are erected with a spacing of 700*700m, four rows transversely, a step distance of 1500mm, and the longitudinal and transverse bottom bars are not more than 200mm from the ground. The bottom of the throw rod is fixed on the cushion layer in the excavation area of the new building foundation pit. The side of the demolition platform close to the original retaining wall is fixed to the 300mm thick concrete wall panel. The distance between the scaffolding and the wall is not more than 300mm. The operating surface of the scaffolding is paved with wire mesh and covered with fixed formwork.

[0067] Demolition sub-step S14: Demolish the wall structure of the basement of the original old building.

[0068] Specifically, (1) The demolition must be carried out from top to bottom, section by section, and layer by layer. Cross-operation between upper and lower levels is strictly prohibited. (2) The workers with chiseling tools use air compressors for chiseling, and the chiseled concrete blocks are stacked and centrally processed into the newly built foundation pit through the trough of the vertical reinforced concrete transfer beam. All personnel within the warning line wear protective earphones and masks during demolition, and special personnel are assigned to water. When the excavator is operating, noise and dust pollution should be avoided as much as possible. (3) During the demolition construction process, special personnel are assigned to monitor the structural state of the original building. When unstable states are found, the operation should be stopped immediately and effective measures should be taken in a timely manner to eliminate potential hazards.

[0069] Waste transportation out sub-step S15: Transport the demolished construction waste out and carry out dust reduction and cleaning.

[0070] Specifically, (1) The demolished construction waste is transported to the location designated by the owner by self-unloading trucks. (2) The incoming vehicles need to be led by special personnel to drive on the designated route, and the speed is controlled at 10 km / h. (3) Loading is carried out by excavators and transported by self-unloading trucks, covered with tarpaulins, the surrounding roads are cleaned in a timely manner, and a sprinkler truck is regularly used for dust reduction.

[0071] In the initial excavation step S1, the following points need to be noted: (1) Before the demolition construction, necessary reinforcement measures must be taken for the retained part as required. (2) Measures should be taken to ensure the stability of the operation platform, and the demolished components should have a safe placement area. (3) During the construction, a special person must be responsible for monitoring the structural state of the building to be demolished, and records should be kept. When a trend of unstable state is found, the operation must be stopped and effective measures should be taken to eliminate the hidden dangers. (4) The removed materials and construction waste should be cleaned up in a timely manner, and it is strictly prohibited to throw them from a height. The removed materials and construction waste should be transported out in a timely manner by a tower crane. (5) The demolition construction should be carried out in sections, and vertical cross-operation is not allowed. The holes on the working surface should be closed. (6) During the demolition, a sprinkler truck should be used to sprinkle water on the demolition part to reduce dust and prevent dust, ensuring that there is no dust pollution in the construction site. (7) To reduce noise, construction machinery with excessive noise should be avoided during the construction period, and the construction time is determined from 7:30 in the morning to 10:00 in the evening.

[0072] See Figure 12 , which is a flow chart of the construction of a vertical reinforced concrete transfer beam. As shown in the figure, the construction of the vertical reinforced concrete transfer beam, that is, in the upper beam construction step and the middle beam construction step, the construction of the vertical reinforced concrete transfer beam can include the following sub-steps:

[0073] The sub-step S21 of chiseling and implanting steel bars: Chisel off part of the wall and the capping beam of the basement of the original building in the first phase, chisel the concrete surface at the connection with the new building in the second phase, and implant steel bars on the retaining wall of the original building in the first phase.

[0074] Specifically, the site is leveled and excavated to 1 m below the floor slab. Manually chisel off part of the wall and the capping beam of the basement of the previous building, chisel the concrete surface at the connection with the new building, and clean up the garbage and dust. Wait for professional steel bar implanting personnel to implant steel bars on the retaining wall of the previous building according to the specification requirements. Another three groups of steel bars of the same specification are implanted at points outside the vertical reinforced concrete transfer beam for pull-out test. After the chiseling is completed and passes the acceptance, and the signature of the supervision engineer is confirmed, the subsequent construction procedures can be carried out. The steel bars are implanted according to the position of the vertical reinforced concrete transfer beam, and manual drilling, hole cleaning, hole inspection, glue injection, and steel bar implantation are carried out. The length of the implanted steel bars must meet the specification requirements. After each process passes the acceptance, the next process can be carried out.

[0075] The sub-step S22 of steel bar binding: Bind the implanted steel bars on the retaining wall of the original building in the first phase with the first horizontal transfer beam.

[0076] Specifically, after the post-inserted bars reach the required strength and pass the acceptance inspection, the steel bar workers enter the site to start tying. The tying is carried out simultaneously with the first support beam. The reserved steel bar lapping length is provided at the lower end of the vertical reinforced concrete transfer beam. When mechanical connection is adopted, the joints are staggered. When tying and installing the steel bars, a wire should be pulled for positioning; the installation should be carried out in sequence, and welding or tying should be carried out in accordance with the specifications. (1) Sleeve the column stirrups: According to the spacing required by the drawing, calculate the number of stirrups for each column. First, sleeve the stirrups on the lapped bars extended from the lower layer, and then erect the column steel bars. Tie at least 3 knots within the lapping length, and the ties should be towards the center of the column. If the main bars of the column adopt plain round steel bars for lapping, the corner hooks should form a 45-degree angle with the formwork, and the hooks of the middle steel bars should form a 90-degree angle with the formwork. (2) Lap and tie the vertical load-bearing steel bars; after the main bars of the column are erected, the lap length of the joints should meet the design requirements. If there is no design requirement, when the main bars are < ф16, lap joint tying can be adopted; when ф16 ≤ main bars ≤ ф22, welding connection is adopted; when the main bars ≥ 22, mechanical connection is adopted. (3) When the vertical bars of the column adopt mechanical or welding connection, no more than 50% of the joint positions are allowed in the same cross-section according to the specifications. (4) Draw the stirrup spacing line: On the erected vertical steel bars of the column, draw the stirrup spacing line with chalk according to the requirements of the drawing.

[0077] For the sub-step S23 of stirrup tying, tie the stirrups at the pre-construction position of the vertical reinforced concrete transfer beam.

[0078] Specifically, (1) Move the sleeved stirrups upward according to the drawn stirrup position line, and tie them from top to bottom. It is advisable to adopt the overlapping tying method. (2) The stirrups should be perpendicular to the main bars. All intersections of the stirrup corners and the main bars should be tied, and the intersections of the main bars and the non-corner parts of the stirrups should be tied in a staggered pattern like a plum blossom. (3) The overlapping parts of the stirrup hooks should be arranged staggered along the vertical bars of the column and tied firmly. (4) In areas with seismic requirements, the ends of the column stirrups should be bent into a 135-degree angle, and the length of the straight part should not be less than 10d (d is the diameter of the stirrup). (5) The stirrups at the upper and lower ends of the column should be encrypted. The length of the encrypted area and the stirrup spacing within the encrypted area should meet the requirements of the design drawing and the construction specifications, not greater than 100mm and not greater than 5D (D is the diameter of the main bar). If the design requires stirrups to be provided with tie bars, the tie bars should hook the stirrups. (6) The thickness of the column steel bar protection layer should meet the specification requirements. If the outer skin of the main bar is 25mm, the spacer blocks should be tied to the outer skin of the vertical bars of the column, with a spacing of generally 1000mm (or use plastic clips to clip on the outer vertical bars) to ensure the accuracy of the thickness of the main bar protection layer. At the same time, a steel bar spacing frame can be adopted to ensure the correctness of the steel bar position. When the cross-sectional size of the column changes, the column should be bent within the slab, and the bent size should meet the design requirements.

[0079] For the sub-step S24 of formwork installation, install the construction formwork at the pre-construction position of the vertical reinforced concrete transfer beam.

[0080] Specifically, after the steel bars pass the acceptance inspection, formwork is erected for the vertical reinforced concrete transfer beam. The formwork uses composite aluminum formwork. Steel pipes are used as ribs, processed in the factory and assembled and reinforced on-site. Since the size of the vertical reinforced concrete transfer beam is large, certain requirements are imposed on the stiffness of the formwork and supports during the later concrete pouring process. The formwork support of the vertical reinforced concrete transfer beam must be fabricated and reinforced strictly in accordance with the specification requirements to prevent phenomena such as the damage of the support system caused by insufficient reinforcement measures during pouring. (1) Construction process flow of column formwork: After the steel bars are concealed and inspected, formwork is assembled, release agent is brushed, the control line of formwork position is snapped, sundries in the formwork are cleared, column lines are redrawn, leveling is done, steel bars are concealed and inspected, steel pipe inclined supports are erected, the formwork is adjusted and reinforced, pre-inspection is carried out, concrete is poured, cured, the concrete strength is inspected, formwork removal application is made, formwork is removed, the formwork is trimmed, release agent is brushed, inspection and acceptance are carried out, pre-inspection is done, and the next cycle is carried out. (2) Construction technology of column formwork installation: After the steel bars of the vertical reinforced concrete transfer beam are tied, 300 mm of dry sand is laid at the bottom position of the vertical reinforced concrete transfer beam according to the position of the vertical steel bars of the vertical reinforced concrete transfer beam. The vertical steel bars pass through the sand layer and enter the lower soil body, and the penetration depth is the lap length of the main steel bars of the vertical reinforced concrete transfer beam, so as to facilitate the construction of the lower vertical reinforced concrete transfer beam. According to the column cross-sectional size, ordinary scaffolding pipes and φ14 tie bolts are used for horizontal reinforcement of the column. A 50*100 mm square wood backing strip is set every 1 m for the formwork of the vertical reinforced concrete transfer beam. The first horizontal reinforcement is at the bottom of the column, and the second formwork lock is 200 mm from the bottom of the column. The column hoop spacing above is 500 mm. The formwork of the vertical reinforced concrete transfer beam uses a 915 mm*1830 mm*19 mm model formwork. When installing, the columns on the same axis must be aligned with a string line. The maximum deviation should be less than 2 mm. After the column formwork is installed, the plumbness of the four corners is checked by hanging a line, and the error requirement is less than 3 mm. After formwork removal, the formwork is cleaned in time, release agent is brushed, and it is stored at the designated place according to the specifications for future use.

[0081] In the concrete pouring sub-step S25, concrete is poured in the construction formwork to obtain the vertical reinforced concrete transfer beam.

[0082] Specifically, after the steel bars and formwork are installed and passed the acceptance inspection, the concrete pouring can be carried out. Before pouring the concrete, contact the mixing plant to make it ready to continuously supply a sufficient amount of concrete. After the concrete transport truck arrives at the site, check the concrete production time, slump and segregation conditions. After determining that the concrete is qualified, it can be put into use. The concrete should be poured in layers, and the thickness of each layer of pouring should not exceed 40 cm. When pouring the concrete, use an insertion vibrator for vibration, and complete it continuously at one time. If it is necessary to pause due to reasons, the pause time should not exceed the allowable pause time, and the new concrete should be poured before the previous layer of concrete starts to set. When pouring the concrete, regularly check and measure the erection of the formwork. If there are deformations, displacements, etc., take timely measures to correct them. (1) The concrete used is commercial concrete, which is transported to the pouring point by a concrete mixer truck and conveyed by a truck-mounted pump. (2) Concrete transportation: The concrete is directly conveyed into the warehouse by a concrete pump. At the beginning of the transportation, use cement mortar with the same concrete grade to moisten the conveying pipe. During the concrete transportation process, keep the uniformity of the concrete, without stratification, segregation, or slurry leakage. Adding water in the middle is strictly prohibited. (3) Concrete vibration: Use an insertion vibrator for vibration. The vibrator is inserted vertically or at a 45° angle. When inserting, it should be "inserted quickly and pulled out slowly". The vibration time is generally 20 - 30 s. It should be based on the concrete surface being horizontal, no longer significantly sinking, no longer showing bubbles, and the surface showing ash slurry. When inserting the vibrator, it should be uniform to prevent missing vibration. (4) Concrete curing: After the concrete is poured, curing can start about 12 hours later. It can be covered with a plastic film. The curing time is generally not less than 7 days. (5) During the concrete construction process, there should be special personnel to check the steel bars and formwork to prevent them from deforming. (6) When the concrete reaches 80% of the design strength, continue with the next process construction.

[0083] After the construction of the basement of the new building is completed, it is necessary to demolish some structures of the vertical reinforced concrete transfer beam, the basement wall of the previous building, and the retaining wall of the previous building to ensure the connection between the previous building and the basement of the new building. After the demolition, promptly carry out the construction of the floor slabs of the previous building and the new building in the area of the vertical reinforced concrete transfer beam to ensure the stability of the building structure. This demolition project is a partial demolition, and attention should be paid to the protection of the structures that are not demolished. Among them, the demolition at the connection between the previous and later stages is constructed using the top-down method. Taking the first floor as the boundary, the construction periods of the above-ground and underground parts do not interfere with each other.

[0084] See Figure 13 , which is a flow chart of the beam demolition steps provided by the embodiment of the present invention. As shown in the figure, the beam demolition step S8 specifically includes the following sub-steps:

[0085] The first-floor demolition sub-step S81: Demolish the original structure above the first basement floor and the diaphragm wall, construct the first-floor floor, support it with a scaffold in the first basement floor, and it can be demolished after the concrete completely reaches the design strength.

[0086] Specifically, first carry out the demolition and construction at the connection on the first floor, specifically: such as Figure 14As shown, demolish the original structure above the first basement floor and the diaphragm wall, construct the first-floor slab, support it with scaffolding in the first basement floor, and only demolish it after the concrete has fully reached the designed strength. As Figure 14 shown, demolish the structure between the lower part of the newly built structure 12 at the junction of the first and second phases and the first basement floor and located on the left side of the second-phase structure 14, i.e., the newly built structure. Among them, Figure 14 the column bars in the wave frame in the first basement floor slab pass through in advance.

[0087] For the demolition sub-step S82 of the second floor, demolish the original structure above the second basement floor and the diaphragm wall, and construct the newly built structure above the second basement floor.

[0088] Specifically, for the demolition and construction of the second basement floor at the connection, first, as Figure 15 shown, demolish the original structure above the second basement floor and the diaphragm wall, such as Figure 15 the first-phase structure 13 and the first-phase diaphragm wall 15 in the dotted line part shown; then, as Figure 16 shown, construct the structure above the second basement floor. Among them, Figure 16 the part in the wave frame is completed before the construction of the third basement floor, and the column bars in the third basement floor slab pass through in advance.

[0089] For the re-demolition sub-step S83, demolish the structure of the third basement floor, the floor slab, and the diaphragm wall in the connection area, and complete the construction of the newly built structure at the connection.

[0090] In summary, for the construction method of reusing the foundation pit support provided in this embodiment, when constructing the deep foundation pit support of a new building, a vertical reinforced concrete transfer beam is used to transfer force, forming a complete support system with the basement of the original building; through technical means such as newly installed force transfer struts, vertical reinforced concrete transfer beams, and horizontal steel conversion beams, the purpose of combining the new and old foundation pit support systems and making full use of the old foundation pit support wall or the external wall of the old building is achieved, thereby reducing the cost of the new foundation pit support and at the same time reducing the workload of demolishing the support system; solving the connection problem between the new foundation pit and the basement of the old building, giving full play to the effect of reusing, realizing green energy conservation and environmental protection, and solving the problems of large workload and high cost of demolishing the support system in the connection construction between the existing new foundation pit and the basement of the old building.

[0091] It should be noted that in the description of the present invention, the terms indicating the direction or positional relationship such as "upper", "lower", "left", "right", "inner", "outer", etc. are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0092] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and defined, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0093] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A construction method for reusing old foundation pit support, characterized in that: include: The initial excavation step is to excavate the earth to a preset distance below the basement floor slab; The upper beam construction step is to construct the vertical reinforced concrete transfer beam and the first horizontal transfer beam of the new building foundation pit within the height range of the top and bottom plates of the basement of the original building, so that the axial force of the foundation pit support system is transmitted to the vertical reinforced concrete transfer beam, the original building support wall and the basement wall through the first horizontal transfer beam of the foundation pit, and then to the bottom and top plates of the basement of the original building, forming an upper support structure; Secondary excavation step: secondary excavation of earthwork until the preset distance below the basement negative second floor slab; The middle beam construction step is to construct the remaining vertical reinforced concrete transfer beams and the second horizontal transfer beam of the new building foundation pit within the height range of the top and bottom plates of the original building's basement negative second floor, so that the axial force of the foundation pit support system is transmitted to the vertical reinforced concrete transfer beams and the original building support wall through the second horizontal transfer beam, and then to the bottom and top plates of the original building's basement negative second floor, forming a lower support structure; The second excavation step is to excavate the earth again until the bottom of the foundation pit; The first structural construction step is to replace the support plate and backfill the soil between the bottom of the foundation pit and the second floor of the basement and the supporting piles, and remove the second horizontal transfer beam; Secondary structure construction steps: replace the support plate and backfill soil between the basement negative second floor slab and the negative first floor slab and the supporting piles, remove the first horizontal transfer beam, and construct the basement structure to the ground level; The beam removal step is to remove the support system between the first and second phases of construction, and connect the first and second phase structures to connect the basements of the new and old buildings into one.

2. The construction method for reusing old foundation pit support according to claim 1 is characterized in that: The initial excavation step includes the following sub-steps: The earthwork excavation sub-step is to excavate the earthwork in the newly built foundation pit of the second phase to a preset distance below the floor slab elevation of the first underground floor of the original building of the first phase; The positioning and setting out sub-step is to measure and set out and mark the vertical reinforced concrete transfer beams on the inside of the newly built foundation pit of the second phase and the inside of the basement of the original building of the first phase; The scaffolding erection sub-step is to erect a scaffolding work platform on the cushion layer of the excavation area in the newly built foundation pit of the second phase; In the demolition sub-step, the basement wall structure of the original old building is demolished.

3. The construction method for reusing old foundation pit support according to claim 2 is characterized in that: After the removal sub-step, the method further includes the following sub-steps: In the garbage transportation sub-step, the demolished construction waste will be transported out and dust will be removed and cleaned.

4. The construction method for reusing old foundation pit support according to claim 2 is characterized in that: The original basement wall structure of the old building was demolished from top to bottom, section by section, and floor by floor.

5. The construction method for reusing old foundation pit support according to any one of claims 1 to 4, characterized in that: The construction of the vertical reinforced concrete transfer beam includes the following sub-steps: In the step of roughening and reinforcing bar planting, part of the walls and crown beams of the basement of the original building of the first phase are removed, the concrete surface of the connection with the new building of the second phase is roughened, and reinforcing bars are planted on the supporting walls of the original building of the first phase; The reinforcement tying sub-step is to tie the embedded reinforcement of the original building support wall of the first phase to the first horizontal transfer beam; The stirrup tying sub-step is to tie the stirrups at the pre-construction position of the vertical reinforced concrete transfer beam; The template installation sub-step is to install the construction template at the pre-construction position of the vertical reinforced concrete transfer beam; The concrete pouring sub-step is to pour concrete in the construction formwork to obtain a vertical reinforced concrete transfer beam.

6. The construction method for reusing old foundation pit support according to any one of claims 1 to 4, characterized in that: The beam removal step specifically includes the following sub-steps: The first floor demolition sub-step is to demolish the original structure and ground-connected walls above the first basement level, construct the first floor, and support the first basement level with scaffolding. The demolition can only be carried out after the concrete reaches the designed strength. The second floor demolition sub-step is to demolish the original structure and ground-connected walls above the second basement floor, and to construct the new structure above the second underground floor; In the demolition sub-step again, the third underground floor, the base plate structure and the underground continuous wall in the connection area are demolished to complete the construction of the new structure at the connection.

7. The construction method for reusing old foundation pit support according to any one of claims 1 to 4, characterized in that: The support system between the first and second construction phases includes: vertical reinforced concrete transfer beams, the basement walls of the first phase building, and a partial structure of the support walls of the first phase building.

8. The construction method for reusing old foundation pit support according to any one of claims 1 to 4, characterized in that: The dismantling of the support system between the first and second construction phases is carried out using a reverse construction method.

9. The construction method for reusing old foundation pit support according to any one of claims 1 to 4, characterized in that: Two layers of scaffolding are set up between the bottom slab of the second basement floor and the bottom of the top slab beam of the first basement floor to restore the bottom slab and top slab between the first and second basement floors of the original building.

10. The construction method for reusing old foundation pit support according to any one of claims 1 to 4, characterized in that: The vertical reinforced concrete transfer beam forms a reinforced concrete structure with the original basement wall and the original supporting wall by means of embedded reinforcement.

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