Construction method for perpetual and temporary combined formwork-erecting-free box culvert to penetrate through existing extra-large bridge in limited space

Abstract

The invention provides a construction method for a permanent and temporary combined formwork-erecting-free box culvert to penetrate through an existing extra-large bridge in a limited space. The method comprises the following steps: S1, leveling a site and drilling; s2, construction of cast-in-place piles; s3, high-pressure jet grouting pile construction; s4, constructing a concrete top beam and a continuous beam; s5, excavation of the foundation pit; s6, hanging a net and spraying concrete; s7, reinforcing steel bars are bound on the box culvert, and an inner formwork is reinforced; and S8, box culvert concrete pouring. According to the construction method, construction of penetrating through the extra-large piers in the limited space is achieved, safety and stability of a foundation pit slope are effectively maintained, earthwork collapse is prevented, the supporting piles replace formworks and wall concrete of pier walls in a permanent and temporary combination mode, the formwork manufacturing and installing engineering amount and the dismantling amount of temporary supporting pile engineering are effectively reduced, and the construction efficiency is improved. The construction period is shortened, the cost is saved, and the box culvert super-bridge penetrating construction is efficiently and safely completed.

Description

Technical Field

[0001] The invention belongs to the field of water conservancy engineering, and in particular relates to a construction method for a permanent and temporary combined formwork-free box culvert for confined space support piles to cross an existing super-large bridge. Background Art

[0002] Vertical fully adjustable axial flow pump, the water inlet culvert of the pump station has to pass through the piers of the super-large bridge on the G347 expressway. The overall terrain of the area is flat and open. There are villages and farmlands around the bridge site, and the space is small and limited. There is only 4.23m of clearance from the bottom of the beam to the ground. The special rock and soil in the bridge site area are mainly fill and soft soil. The fill is fill soil and plain fill, which has little impact on the bridge project; the soft soil is mainly silty silty clay, with poor engineering properties and large thickness. Under the condition of limited space, high water level and interlayered geology of loam and sand, the foundation pit is excavated to a depth of 7m to the foundation surface. The edge of the foundation pit is only 20cm away from the two piers. The earthwork collapses easily during the excavation process. The normal driving of synchronous vehicles on the bridge deck columns is prone to sliding and damage of the columns due to vibration caused by vehicle movement, thus affecting the safe operation of the super-large bridge. Summary of the invention

[0003] In view of this, the present invention aims to propose a construction method for a box culvert crossing an existing super-large bridge with a permanent and temporary combination of support piles in a confined space and without formwork. By effectively utilizing the narrow space, the support piles replace the wall concrete of the formwork and pier wall in a permanent and temporary combination manner, which effectively reduces the amount of formwork manufacturing and installation engineering. At the same time, the application of support piles in the pier wall reduces the amount of demolition of temporary projects and saves economic costs.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0005] A construction method for a permanent and temporary combination of a formwork-free box culvert for confined space support piles crossing an existing super-large bridge includes the following steps:

[0006] S1, leveling the site and drilling;

[0007] S2, cast-in-place pile construction;

[0008] S3, high pressure jet grouting pile construction;

[0009] S4, construction of concrete cap beam and continuous beam;

[0010] S5, foundation pit excavation;

[0011] S6, mesh shotcrete;

[0012] S7, box culvert reinforcement and inner formwork reinforcement;

[0013] S8. Pouring of box culvert concrete.

[0014] Furthermore, in step S1, after measuring and laying out the lines and cleaning the base surface, the slope is cut according to the excavation boundary line at a slope ratio of 1:1, and the original ground site is partially excavated in layers to an elevation of 13.00m, so that the clearance of the bridge is 5.23m to meet the requirements of mechanical construction of bored piles.

[0015] Further, in step S2, before construction, the pile machine is first placed in position according to the layout point, so that the base and the top are stable, and no displacement or settlement occurs during drilling and operation, so that the lifting pulley rim, the turntable center and the pile hole center should be on the same plumb line, and the verticality can be controlled during the construction process to ensure that it is less than 1%;

[0016] Bury the casing and use the cross-line to locate the center line of the pile; during the process, ensure that the mud circulates smoothly, and the mud surface in the casing is more than 1.0m higher than the groundwater level. When affected by water level fluctuations, the mud surface is more than 1.5m higher than the highest water level;

[0017] During the hole cleaning process, the slurry is continuously replaced until the underwater concrete is poured;

[0018] The mud is made of high-quality expansive soil for wall protection. Before pouring concrete, the mud density within 500mm of the hole bottom is less than 1.25; the sand content shall not be greater than 8%;

[0019] Viscosity: general formations> 28s, colloid rate> 95%;

[0020] After the hole reaches the designed elevation, the hole depth, hole diameter, hole wall verticality and sediment thickness are ≤100mm. After meeting the requirements, pour concrete.

[0021] Furthermore, in step S3, a double-tube method is used, the pressure of the high-pressure cement slurry should be no less than 25 MPa, the flow rate should be no less than 70 L / min, and the air flow pressure should be no less than 0.6 MPa. The lifting speed should be 0.1 m / min×0.2 m / min;

[0022] The rotary jet grouting uses ordinary Portland cement with a strength grade of 42.5, with admixtures and additives added, and the cement slurry mix ratio is configured at 20%.

[0023] Furthermore, when the jetting pipe is inserted, the distance between the jet hole and the high-pressure grouting pump shall not exceed 50m; the allowable deviation of the drilling position shall be ±50mm; the allowable deviation of the verticality shall be 1%; when the jetting grouting pipe is penetrated into the soil and the nozzle reaches the designed elevation of -2.20m, the jetting grouting can be carried out;

[0024] After the jet grouting parameters reach the specified value, the jet pipe is lifted according to the process requirements of the rotary jetting, and the jet grouting is performed from the bottom up by rotary jetting; the overlapping length of the jet pipe lifted in sections shall not be less than 100mm; after the rotary jetting grouting is completed, the jet pipe is quickly pulled out;

[0025] The use of grouting backfill or secondary grouting in the original hole position can prevent the slurry solidification and shrinkage from affecting the elevation of the pile top; when local expansion and reinforcement or increased strength are required, repeated spraying measures are adopted.

[0026] Further, in step S4, 11 DN800 cast-in-place piles with a length of 19.5 m and a pile spacing of 4 m are set in the middle pier, and a 0.6 m×0.8 m reinforced concrete beam is arranged vertically on the top of the pile as an internal support;

[0027] 82 DN800 cast-in-place piles with a length of 19.5m and a pile spacing of 1m are set at the edge of the water inlet culvert. A 1.0m×0.8m cap beam is set on the top of the pile to connect with the reinforced concrete beam to maintain the stability of the bridge foundation.

[0028] Furthermore, in step S5, after the crown beam and the inner support beam reach the designed strength value, a small excavator is used to excavate from the bottom of the beam in layers from both ends to the middle, and then transported to both ends of the bridge for loading and transportation; after excavation, the soil of the middle pier and the cast-in-place piles on both sides should be cleaned, roughened, and reinforced immediately.

[0029] Furthermore, in step S6, a 6.5@200×200mm steel mesh is hung inside the concrete support pile, and 10cm thick C20 fine stone concrete is sprayed for leveling, and the fine stone concrete surface inside the support pile replaces the outer formwork.

[0030] Furthermore, the foundation pit is dewatered by open drainage, and a sump is set up to pump water to nearby channels to control the water level in the foundation pit to no higher than 5.6m. A 20cm retaining wall is set on the top of the foundation pit to prevent rainwater from entering the foundation pit.

[0031] Furthermore, in step S7, a concrete cushion layer is poured on the foundation surface, and the box culvert reinforcement is tied, wherein the middle support pile is wrapped in the middle pier column reinforcement; the formwork is reinforced, and the outer side is replaced by sprayed fine stone concrete, and only the inner formwork of the box culvert is reinforced; the box culvert concrete is poured and maintained to complete the construction of the box culvert.

[0032] Compared with the prior art, the construction method for the confined space support pile permanent and temporary combined with formwork-free box culvert crossing the existing super-large bridge described in the present invention has the following advantages:

[0033] (1) The present invention is used for a construction method of a permanent and temporary combined formwork-free box culvert crossing an existing super-large bridge in a confined space. The cast-in-place piles of the foundation are used as support piles and side support piles. The cap beam and continuous beam are cast with concrete to form a support system and combined with high-pressure rotary jet piles to cut off the seepage channels of the foundation pit to protect the stability of the slope soil of the foundation pit. The invention solves the resonance generated by the bridge when vehicles are running, which causes the slip of the bridge piers, and meets the normal traffic needs of the super-large bridge during the construction process.

[0034] (2) The present invention is used for a construction method of a box culvert that crosses an existing extra-large bridge with a permanent and temporary combination of support piles in a confined space and without formwork. The thickness of the middle pier of the water inlet box culvert is increased to 100 cm, and its 11 supporting cast-in-place support piles are wrapped in the wall of the middle pier to achieve a permanent and temporary combination of temporary concrete cast-in-place support piles, reduce the removal of temporary concrete support piles, and eliminate material waste.

[0035] (3) The present invention is used for a construction method of a box culvert that crosses an existing extra-large bridge with permanent and temporary support piles in a confined space and is combined with formwork-free construction. A 6.5@200×200mm steel mesh is hung on the inner side of the concrete support pile, and 10cm thick C20 fine stone concrete is sprayed for leveling. The fine stone concrete surface on the inner side of the support pile replaces the outer formwork, thereby shortening the formwork time, saving a large amount of formwork material, and improving the construction efficiency of the box culvert. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0037] Figure 1 It is a cross-sectional schematic diagram of a construction method for a permanent and temporary combined formwork-free box culvert for crossing an existing extra-large bridge for supporting piles in a confined space according to an embodiment of the present invention.

[0038] Description of reference numerals:

[0039] 1. Bridge pier; 2. Bridge slab; 3. Cast-in-place piles; 4. Middle support piles; 5. Cast-in-place support piles; 6. High-pressure jet jet piles; 7. Crown beam; 8. Continuous beam; 9. Mesh concrete; 10. Box culvert. DETAILED DESCRIPTION

[0040] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0041] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" 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 a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0043] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0044] A construction method for confined space support piles, permanent and temporary, combined with formwork-free box culverts crossing existing super-large bridges, such as Figure 1 As shown, the following steps are included;

[0045] S1, leveling the site and drilling; preferably, after measuring and setting out the lines and cleaning the base surface, the slope is leveled according to the excavation boundary line at a slope ratio of 1:1, and the original ground site is partially excavated in layers to an elevation of 13.00m, so that the clearance of the bridge is 5.23m to meet the mechanical construction requirements of the bored pile 3.

[0046] S2, construction of cast-in-place pile 3; preferably, before construction, the cast-in-place pile 3 is mechanically placed in place according to the layout point, so that the base and the top are stable, and no displacement or settlement occurs during drilling and operation, so that the lifting pulley rim, the center of the turntable and the center of the pile hole should be on the same plumb line, and the verticality can be controlled during the construction process to ensure that it is less than 1%;

[0047] Bury the casing and use the cross-line to locate the center line of the pile; during the process, ensure that the mud circulates smoothly, and the mud surface in the casing is more than 1.0m higher than the groundwater level. When affected by water level fluctuations, the mud surface is more than 1.5m higher than the highest water level; during the hole cleaning process, continuously replace the mud until pouring underwater concrete;

[0048] The mud uses high-quality expansive soil to protect the wall. Before pouring concrete, the mud density within 500mm of the bottom of the hole is less than 1.25; the sand content shall not be greater than 8%; viscosity: general strata>28s, colloid rate>95%; after the hole reaches the designed elevation, the hole depth, hole diameter, hole wall verticality, sediment thickness ≤100mm, and concrete is poured after meeting the requirements.

[0049] S3, high pressure jet grouting pile 6 construction; preferably, the double-tube method is adopted, the pressure of high pressure cement slurry should be not less than 25MPa, the flow rate should be not less than 70L / min, the air flow pressure should be not less than 0.6MPa. The lifting speed should be 0.1m / min×0.2m / min;

[0050] The rotary jet grouting uses ordinary Portland cement with a strength grade of 42.5, with admixtures and additives added, and the cement slurry mix ratio is configured at 20%.

[0051] Preferably, when the jetting pipe is penetrated, the distance between the jet hole and the high-pressure grouting pump is not greater than 50m; the allowable deviation of the drilling position should be ±50mm; the allowable deviation of the verticality is 1%; when the jetting grouting pipe is penetrated into the soil and the nozzle reaches the designed elevation of -2.20m, the jetting grouting can be carried out;

[0052] After the jet grouting parameters reach the specified value, the jet pipe is lifted according to the process requirements of the rotary jetting, and the jet grouting is performed from the bottom up by rotary jetting; the overlapping length of the jet pipe lifted in sections shall not be less than 100mm; after the rotary jetting grouting is completed, the jet pipe is quickly pulled out;

[0053] The use of grouting backfill or secondary grouting in the original hole position can prevent the slurry solidification and shrinkage from affecting the elevation of the pile top; when local expansion and reinforcement or increased strength are required, repeated spraying measures are adopted.

[0054] S4, construction of concrete cap beam 7 and continuous beam 8; preferably, 11 DN800 cast-in-place piles 3 with a length of 19.5m and a pile spacing of 4m are arranged in the middle pier, and a 0.6m×0.8m reinforced concrete beam is arranged vertically on the top of the pile as an internal support;

[0055] 82 DN800 cast-in-place piles 3 with a length of 19.5m and a pile spacing of 1m are arranged at the edge of the water inlet box culvert 10, and a 1.0m×0.8m cap beam 7 is arranged on the top of the pile to connect with the reinforced concrete beam to keep the bridge foundation stable.

[0056] S5, excavation of foundation pit; preferably, after the crown beam 7 and the inner support beam reach the designed strength value, a small excavator is used to excavate from the bottom of the beam in layers from both ends to the middle, and then transported to both ends of the bridge for loading and transportation; after excavation, the soil of the middle pier and the cast-in-place piles 3 on both sides should be cleaned, roughened, and reinforced immediately.

[0057] S6, mesh spraying concrete; In step S6, a 6.5@200×200mm steel mesh is hung inside the concrete support pile, and 10cm thick C20 fine stone concrete is sprayed for leveling, and the fine stone concrete surface inside the support pile replaces the outer formwork.

[0058] Preferably, the foundation pit is dewatered by open drainage, a sump is set up, and the water is pumped to a nearby channel to control the water level in the foundation pit to be no higher than 5.6m; a 20cm retaining wall is set on the top of the foundation pit to prevent rainwater from entering the foundation pit.

[0059] S7, the box culvert 10 is reinforced with steel bars and the inner formwork is reinforced; preferably, a concrete cushion is poured on the foundation surface, and the box culvert 10 is reinforced with steel bars, wherein the middle support pile 4 is wrapped in the middle pier column steel bars; the formwork is reinforced, and the outer side is replaced with sprayed fine stone concrete, and only the inner formwork of the box culvert 10 is reinforced; the box culvert 10 is poured with concrete and maintained to complete the construction of the box culvert 10.

[0060] S8, box culvert 10 concrete pouring.

[0061] Yangwan Pump Station is located on the south side of the Yangwan River estuary, about 400m away from the Yangwan River estuary, at K66+200m of Tongma Dam, with a designed flow rate of 55m3 / s. It uses a vertical fully adjustable axial flow pump. The scale of the pump station is large (2) type and the grade is II. The main function of the pump station is drainage. The water intake culvert 10 (size 4.5m×3.5m×4) of the pump station has to pass between the 24# and 25# piers of the sixth joint of the super-large bridge on the G347 expressway section. The overall terrain of the area is flat and open. There are villages and farmlands around the bridge site, and the space is small and limited. There is only 4.23m of clearance from the bottom of the beam to the ground. The special rock and soil in the bridge area are mainly fill and soft soil. The fill is fill soil and plain fill, which has little impact on the bridge project; the soft soil is mainly silty silty clay, with poor engineering properties and large thickness. In the design process, the impact of the thick soft soil layer on the foundation to be adopted for the bridge should be fully considered. In order to improve the bearing capacity of the pressure water tank foundation, cast-in-place pile 3 treatment is adopted to reduce settlement. The geology is Quaternary system, the new lake deposits are silty loam, silty clay, clay, loam-sand interlayers, etc. The shallow hole groundwater is stored in the surface loose silty fine sand and fill layer. The groundwater in this layer is mainly affected by atmospheric precipitation and surface water. The groundwater depth is 0.5m~2.2m, and the water level is 8.7m~11.3m. Under the condition of limited space, high water level and interlayer of loam and sand, the foundation pit is excavated to the foundation surface to a depth of 7m. The edge of the foundation pit is only 20cm away from the two piers. The excavation process is easy to cause earthwork collapse. The synchronous vehicle is easy to cause the column to slide and damage due to the vibration caused by the movement of the vehicle, thus affecting the safe operation of the super-large bridge. The project department gathered ideas to fully utilize the cast-in-place piles 3 of the foundation as support piles and side support piles to cast the crown beam 7 and the continuous beam 8 with concrete to form a support system and combine it with the high-pressure rotary jet pile 6 to cut off the seepage of the foundation pit and protect the stability of the slope soil of the foundation pit. This support system solves the problem of large-span foundation pit excavation, effectively maintains the stability of the foundation pit slope, and meets the normal traffic needs of the super-large bridge during construction. Since the construction space in this area is limited and there are no extra manual operation channels, the cast-in-place support piles 5 on both sides will be replaced by hanging steel mesh and spraying fine stone concrete for leveling in a permanent and temporary manner, and the middle cast-in-place support piles 5 will be roughened and cleaned to replace the middle wall of the two box culverts 10. Through the effective use of narrow space, the support piles replace the wall concrete of the formwork and pier wall in a permanent and temporary manner, effectively reducing the amount of formwork manufacturing and installation engineering. At the same time, the support piles are applied to the pier wall to reduce the amount of demolition of temporary projects and save economic costs. The project summarizes the application effects of solving the above series of problems and develops a construction method for the permanent and temporary combination of support piles in confined spaces to cross the existing super-large bridge without formwork box culverts; Specific embodiment:

[0063] The water inlet culvert 10 of the pump station will pass between the 24# and 25# piers of the sixth bridge of the G347 high-speed section. Due to the narrow space and the normal operation of the super-large bridge, in order to prevent the bridge pier column 1 from sliding and damaging due to vibration, cast-in-place support piles 5, crown beams 7, and continuous beams 8 are used for support. At the same time, high-pressure rotary jet cement mixing piles are used on both sides to cut off the high head of water from penetrating into the foundation pit, ensuring the safety and stability of the foundation pit. First, the site is leveled to an elevation of 13.0m, and the rotary drilling rig is used to drill the cast-in-place piles 3. The designed pile length is 19.5m, and the pile bottom elevation is -7.70m, until the middle pier and the cast-in-place piles 3 on both sides are all completed; then the high-pressure rotary jet pile 6 machine is put in place, and high-pressure rotary jet cement mixing piles are constructed along the cast-in-place piles 3 on both sides to form a water cut-off barrier. After the cast-in-place piles 3 and cement mixing piles meet the strength requirements, the earthwork is excavated to the bottom elevation of 12.2m of the crown beam 7 and the continuous beam 8, and the pile heads are chiseled off to construct the crown beam 7 and the inner support continuous beam 8. In order to ensure the safety of the surrounding environment of the foundation pit, safety monitoring points are arranged. After the crown beam 7 and the inner support beam reach the designed strength value, a small excavator is used to excavate from the bottom of the beam in layers from both ends to the middle, and then transported to both ends of the bridge for loading and transportation. After excavation, the soil of the middle pier and the cast-in-place piles 3 on both sides should be cleaned, roughened, and rebar planted immediately, and steel mesh should be hung on the inner wall of the supporting piles on both sides, and fine stone concrete should be sprayed until the spraying of concrete is completed. The foundation pit is dewatered by open drainage, and a sump is set up. The water is pumped into the nearby ditch by a water pump to ensure that the foundation surface is dry and water-free. The construction of the box culvert 10 is completed by pouring a concrete cushion layer on the foundation surface, tying the steel bars of the box culvert 10 (where the middle support pile 4 is wrapped in the steel bars of the middle pier column), reinforcing the formwork (the outer side is replaced by sprayed fine stone concrete, and only the inner formwork of the box culvert 10 is reinforced), pouring concrete for the box culvert 10, and maintaining the box culvert 10.

[0064] The construction method of the confined space support piles combined with the permanent and temporary formwork-free box culvert crossing the existing super-large bridge solves the problem of construction between the piers of the super-large bridge in the confined space. It not only effectively maintains the safety and stability of the foundation pit slope to prevent earth collapse, but also replaces the formwork and pier wall concrete with the support piles in a permanent and temporary combination manner, effectively reducing the formwork manufacturing and installation work and the demolition of temporary support piles, shortening the construction period and saving costs, and completing the construction of the box culvert 10 crossing the super-large bridge efficiently and safely.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method for a permanent and temporary combination of a formwork-free box culvert for confined space support piles crossing an existing super-large bridge, characterized in that: The steps include: S1, leveling the site and drilling; S2, cast-in-place pile construction; S3, high pressure jet grouting pile construction; S4, construction of concrete cap beam and continuous beam; S5, foundation pit excavation; S6, mesh shotcrete; S7, box culvert reinforcement and inner formwork reinforcement; S8. Pouring of box culvert concrete.

2. The construction method for the permanent and temporary combined formwork-free box culvert for confined space support piles crossing an existing super-large bridge according to claim 1 is characterized in that: In step S1, after surveying and laying out the lines and cleaning the base surface, the slope is cut according to the excavation boundary line at a slope ratio of 1:1, and the original ground site is partially excavated in layers to an elevation of 13.00m, so that the clearance of the bridge is 5.23m to meet the requirements of mechanical construction of bored piles.

3. The construction method for a permanent and temporary combination of a confined space support pile and a formwork-free box culvert crossing an existing super-large bridge according to claim 1 is characterized in that: In step S2, before construction, the pile machine is first placed in position according to the layout point, so that the base and the top are stable, and no displacement or settlement occurs during drilling and operation, so that the lifting pulley rim, the center of the turntable and the center of the pile hole should be on the same plumb line, and the verticality can be controlled during the construction process to ensure that it is less than 1%; Bury the casing and use the cross-line to locate the center line of the pile; during the process, ensure that the mud circulates smoothly, and the mud surface in the casing is more than 1.0m higher than the groundwater level. When affected by water level fluctuations, the mud surface is more than 1.5m higher than the highest water level; During the hole cleaning process, the slurry is continuously replaced until the underwater concrete is poured; The mud is made of high-quality expansive soil for wall protection. Before pouring concrete, the mud density within 500mm of the hole bottom is less than 1.25; the sand content shall not be greater than 8%; Viscosity: general formations> 28s, colloid rate> 95%; After the hole reaches the designed elevation, the hole depth, hole diameter, hole wall verticality and sediment thickness are ≤100mm. After meeting the requirements, pour concrete.

4. The construction method for a permanent and temporary combination of a formwork-free box culvert for confined space support piles crossing an existing super-large bridge according to claim 1 is characterized in that: In step S3, a double-tube method is used, the pressure of the high-pressure cement slurry should be no less than 25 MPa, the flow rate should be no less than 70 L / min, and the air flow pressure should be no less than 0.6 MPa. The lifting speed should be 0.1 m / min×0.2 m / min; The rotary jet grouting uses ordinary Portland cement with a strength grade of 42.5, with admixtures and additives added, and the cement slurry mix ratio is configured at 20%.

5. The construction method for the permanent and temporary combined formwork-free box culvert for confined space support piles crossing an existing super-large bridge according to claim 4 is characterized in that: When the jetting pipe is inserted, the distance between the jet hole and the high-pressure grouting pump shall not exceed 50m; the allowable deviation of the drilling position shall be ±50mm; the allowable deviation of verticality shall be 1%; when the jetting grouting pipe is penetrated into the soil and the nozzle reaches the designed elevation of -2.20m, grouting can be sprayed; After the jet grouting parameters reach the specified value, the jet pipe is lifted according to the process requirements of the rotary jetting, and the jet grouting is performed from the bottom up by rotary jetting; the overlapping length of the jet pipe lifted in sections shall not be less than 100mm; after the rotary jetting grouting is completed, the jet pipe is quickly pulled out; The use of grouting backfill or secondary grouting in the original hole position can prevent the slurry solidification and shrinkage from affecting the elevation of the pile top; when local expansion and reinforcement or increased strength are required, repeated spraying measures are adopted.

6. The construction method for a permanent and temporary combination of a formwork-free box culvert for confined space support piles crossing an existing super-large bridge according to claim 1 is characterized in that: In step S4, 11 DN800 cast-in-place piles with a length of 19.5 m and a pile spacing of 4 m are set in the middle pier, and a 0.6 m×0.8 m reinforced concrete beam is arranged vertically on the top of the pile as an internal support; 82 DN800 cast-in-place piles with a length of 19.5m and a pile spacing of 1m are set at the edge of the water inlet culvert. A 1.0m×0.8m cap beam is set on the top of the pile to connect with the reinforced concrete beam to maintain the stability of the bridge foundation.

7. The construction method for a permanent and temporary combination of a confined space support pile and a formwork-free box culvert crossing an existing super-large bridge according to claim 1 is characterized in that: In step S5, after the crown beam and the inner support beam reach the designed strength value, a small excavator is used to excavate from the bottom of the beam in layers from both ends to the middle, and then transported to both ends of the bridge for loading and transportation; after excavation, the soil of the middle pier and the cast-in-place piles on both sides should be cleaned, roughened, and reinforced immediately.

8. The construction method for a permanent and temporary combination of a confined space support pile and a formwork-free box culvert crossing an existing super-large bridge according to claim 1 is characterized in that: In step S6, a 6.5@200×200mm steel mesh is hung inside the concrete support pile, and 10cm thick C20 fine stone concrete is sprayed for leveling, and the fine stone concrete surface inside the support pile replaces the outer formwork.

9. The construction method for a permanent and temporary combination of a confined space support pile and a formwork-free box culvert crossing an existing super-large bridge according to claim 8 is characterized in that: The foundation pit is dewatered by open drainage, and a sump is set up to pump water to nearby channels to control the water level in the foundation pit to no higher than 5.6m. A 20cm retaining wall is set on the top of the foundation pit to prevent rainwater from entering the foundation pit.

10. The construction method for a permanent and temporary combination of a formwork-free box culvert for confined space support piles crossing an existing super-large bridge according to claim 1 is characterized in that: In step S7, a concrete cushion layer is poured on the foundation surface, and the box culvert reinforcement is tied, wherein the middle support pile is wrapped in the middle pier column reinforcement; the formwork is reinforced, and the outer side is replaced by sprayed fine stone concrete, and only the inner formwork of the box culvert is reinforced; the box culvert concrete is poured and maintained to complete the construction of the box culvert.

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