Large deep foundation pit rotating trestle and construction method

Abstract

The invention relates to a large deep foundation pit rotating trestle and a construction method, the large deep foundation pit rotating trestle comprises a trestle body and a supporting body, the supporting body and the trestle body are integrated, the supporting body is arranged below the trestle body, and the trestle body is divided into a straight section, a rotating slope section and a soil slope ramp; the straight sections are arranged on the edge of the top of the foundation pit, between the two rotating slope sections and at the tail ends of the rotating slope sections respectively, the rotating slope sections are arranged between the two straight sections, the tail end of the last straight section is provided with a soil slope ramp, and the soil slope ramp is directly communicated with the bottom of the large deep foundation pit. The trestle has the beneficial effects that the trestle occupies a small area of the deep foundation pit, bottom construction of the deep foundation pit is not affected, the construction difficulty of the deep foundation pit is reduced, the construction efficiency is high, the bearing capacity is high, the construction transportation capacity of the deep foundation pit is improved, the transportation efficiency is improved, and the construction progress of the deep foundation pit is accelerated.

Description

Technical Field

[0001] The invention relates to the technical field of deep foundation pit rotating trestle construction, in particular to a large deep foundation pit rotating trestle and a construction method. Background Art

[0002] With the current high-quality and high-speed development of the country, there are more and more large-scale and complex deep foundation pit engineering projects. Most of the construction sites are located in densely populated urban areas with complex surrounding construction environments. The construction sites are relatively small. In order to ensure the transportation of earth and stone and materials, the vertical transportation of earth and stone generally adopts reserved soil ramps and hardened them for vehicle traffic. However, due to the large overall construction depth of some projects, the maximum arm length of the excavator is 12M, the construction site is too tight, and the traditional straight ramp cannot meet the transportation needs.

[0003] In the past, the commonly used trestles in China include: reserved earth trestles, earth-rock combined trestles, straight section + slope section trestles, pure steel structure trestles and prefabricated steel trestles. These methods have large excavation surfaces and are difficult to construct. They are not suitable for the transportation of earth and stone in large and complex deep foundation pits and have low transportation efficiency. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a large-scale deep foundation pit rotating trestle and a construction method, which adopts the method of integrating the trestle and the support, and reinforcing the strength of the trestle with a steel structure and a mixed concrete structure. The trestle adopts the internationally leading rotating trestle design concept of a rotating type + straight section + earth slope ramp structure for the construction and transportation of deep foundation pits, which increases the load capacity of construction and transportation, occupies a small area for construction, and reduces the construction difficulty. During transportation, the combination of a rotating slope + a straight section reduces the transportation difficulty of deep foundation pit construction, improves transportation efficiency, and improves the adaptability of the construction speed of high-speed, large and complex deep foundation pits, thereby ensuring the construction progress of large deep foundation pits.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A large deep foundation pit rotating trestle comprises a trestle and a support body, wherein the support body and the trestle are integrally formed, the support body being arranged below the trestle, the trestle being divided into a straight section, a rotating slope section and an earth slope ramp, the straight sections being arranged at the top edge of the foundation pit, between two rotating slope sections and at the tail end of the rotating slope section, a rotating slope section being arranged between the two straight sections, an earth slope ramp being arranged at the tail end of the last straight section, and the earth slope ramp leading directly to the bottom of the large deep foundation pit.

[0007] Furthermore, the pier is divided into a pier deck and an internal support structure, the internal support structure is arranged on the lower surface of the pier deck, the internal support structure is fixedly connected to the support body, and the internal support structure is supported by a steel structure frame.

[0008] Furthermore, the support body includes a lattice column and a steel cage, the lattice column is supported on the lower surface of the trestle, the steel cage is arranged inside the lattice column space, the four sides of the lattice column are fixedly connected to the steel cage, and the main reinforcement of the steel cage is connected to the side of the lattice column with oblique steel bars.

[0009] Furthermore, the lattice columns use angle steel joints, the angle steel joints of the same cross section do not exceed 50% of the cross section, the adjacent angle steels are staggered by no less than 60cm, and the angle steel joints are reinforced with short angle steels of the same material on the inner side of the angle steel at the connection position.

[0010] Furthermore, a positioning bar is arranged every 2m on the main reinforcement of the steel cage, and the positioning bars are equally divided at 360°, with a total of 4 bars.

[0011] A construction method for a large deep foundation pit rotating trestle, the construction method is implemented based on the deep foundation pit rotating trestle, and the steps of the large deep foundation pit rotating trestle construction method are as follows:

[0012] S1. Drilling: The drilling speed for soil layer construction is 5 min / m, for strongly weathered siltstone layer is 15 min / m, for moderately weathered siltstone is 90 min / m, and the thickness of sediment in the hole should not exceed 10 cm;

[0013] S2. Hole cleaning: Use a grab bucket to grab the soil repeatedly until the sediment in the hole is removed. Pour concrete within half an hour after the hole is cleaned;

[0014] S3. Fabrication and hanging of steel cage: The steel cage is fabricated on site at the steel yard;

[0015] S4. Lattice column processing: Lattice columns are processed and manufactured off-site;

[0016] S5. Welding of lattice column and steel cage: weld one horizontal steel bar to the main reinforcement of the steel cage on each side of the lattice column, with a 20-30mm clearance from each side of the lattice column. The steel cage is located in the middle of the lattice column, and the distance between each side of the lattice column and the steel cage is uniform;

[0017] S6. Lower the lattice column to the designed elevation: Use a crane to install it, with the lifting point located at the top of the lattice column. Calculate the four coordinate points of the extended lines of the midpoints of the four sides of the lattice column, and then lay out the lines. The positioning deviation should be less than 50mm.

[0018] S7. Check verticality: Use two theodolites to control the position in the vertical direction, mark the position, and check it according to the survey record. After the steel cage is put into the hole, install a positioning guide frame at the falling position of the lattice column. The positioning hole in the middle of the guide frame is 50mm larger than the lattice column on each side to facilitate screw connection and column position adjustment. A guide column of the same specification as the lattice column is set on the top of the guide frame. The guide column is connected to the four sides of the installed lattice column at the bottom by bolts. The lattice column to be installed is checked with a ruler during the falling process.

[0019] S8. Lowering the conduit: Before installing the conduit, pre-assemble it, do a watertight pressure test, and check its verticality; after all the conduits are assembled, inject water for a water pressure test to check for water leakage; after the conduit passes the assembly inspection, dismantle it in sections according to its strength and the capacity of the lifting equipment; during the conduit lowering process, make the conduit in the center of the hole, and it is strictly forbidden to collide with the steel cage. It is installed in sections from bottom to top in the order of pre-assembly; after the lowering is completed, the height of the lower end of the conduit from the bottom of the hole is 30 to 50 cm;

[0020] S9. Concrete pouring: The underwater concrete mix ratio is designed, which has greater fluidity during the pouring process, and the initial setting time of the poured concrete is extended to more than 6 hours;

[0021] S10. Hole backfilling: After pouring concrete, backfill the pile hole evenly around the lattice column to avoid squeezing the lattice column due to uneven backfilling. Backfill densely;

[0022] S11, trestle measurement;

[0023] S12, excavation to the bottom elevation of the trestle platform cushion: the trestle platform is a connecting platform connecting the first straight section, and excavation is carried out to the designed bottom elevation;

[0024] S13, trestle platform construction work: after excavating to the designed elevation, leveling and re-measurement of elevation are carried out to ensure the flatness and elevation of the bottom; at the same time, the base is compacted, and then a 100mm thick concrete cushion is applied as the concrete support bottom formwork;

[0025] S14. Excavation to the bottom elevation of the cushion layer of the first straight section of the trestle platform: the height difference of the excavation shall not be greater than 1m, and the slope shall be no greater than 1:2. It is strictly forbidden to excavate the foundation pit too deep. A gap of no less than 250mm shall be left between the mechanical excavation and the retaining wall piles. The bucket shall not collide with the retaining wall piles, internal supports, lattice columns, and waist beams. The soil on the pile surface shall be removed manually. Prevent over-excavation and disturbance of the soil at the bottom of the pit. When the mechanical excavation is 140-160mm from the bottom of the pit, the remaining soil shall be removed manually.

[0026] S15. Trestle construction: Formwork support: The trestle formwork adopts wooden formwork, and the formwork reinforcement adopts wooden beams and scaffolding steel pipes. The formwork should be cleaned and coated with isolation agent before erection. Before each concrete pouring, ensure that the formwork is clean and smooth;

[0027] Concrete pouring for trestle bridge: When pouring concrete for trestle bridge, a vibrating rod is used. The vibrating rod is inserted into the surface of the lower concrete layer by no less than 5 cm. The vibration point spacing is 50 to 80 cm. The vibration time is 20 to 30 seconds. The concrete is poured to the designed elevation and leveled with tools. No one is allowed to go up before the concrete begins to set, and no construction load is allowed.

[0028] Scissor brace setting: lattice columns are laid in layers and connected with connecting beams. Scissor braces are set between the lattice columns and the connecting beams. The scissor braces are set crosswise, with one end of the scissor brace located at the bottom of the upper connecting beam and the other end located at the top of the connecting beam. The scissor braces improve the supporting force of the lattice columns;

[0029] S15, repeat steps S13 to S14 until the construction of the trestle is completed;

[0030] S16, Pier monitoring: Horizontal displacement monitoring: Monitoring points are pre-buried and arranged along both sides of the pier. The monitoring points are spaced 10m apart, with no less than one monitoring point on each side. Horizontal displacement monitoring points are forced to be monitored by centering, and the signs are buried in the reinforced ground at the top of the pier and well marked.

[0031] Vertical displacement: monitoring points are arranged along both sides of the trestle, with a spacing of 10m between monitoring points. There are no less than 2 monitoring points on each side. They can be located in the same section as the horizontal displacement, and the monitoring points can be co-located with the displacement monitoring points.

[0032] Furthermore, in the step S9, the surface position of the cast-in-hole concrete is detected by using a detection hammer, which includes a measuring rope and a hammer. The hammer is hung in the hole with the tested measuring rope. The hammer passes through the mud sedimentation layer and stays 10 to 20 cm below the concrete surface. The sinking depth of the measuring rope and the hammer is used as the concrete pouring depth.

[0033] Furthermore, the horizontal displacement monitoring in step S16 adopts the polar coordinate method.

[0034] Furthermore, in the step S16, the vertical displacement is measured using a geometric leveling method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The combination of lattice columns and steel cages is fixedly connected to the supporting structure inside the trestle, with strong bearing capacity, which improves the transportation capacity of deep foundation pit construction, improves transportation efficiency, and speeds up the progress of deep foundation pit construction.

[0037] 2. The trestle adopts a rotating + straight section + earth slope ramp structure, with a small excavation working surface and a small construction workload. The trestle occupies a small area of ​​the deep foundation pit and does not affect the bottom construction of the deep foundation pit, thereby reducing the difficulty of deep foundation pit construction and improving construction efficiency. It improves the adaptability of the construction speed of large and complex deep foundation pits and ensures the construction progress of large deep foundation pits. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a schematic diagram of a large deep foundation pit rotating trestle structure.

[0039] Figure 2 The present invention is a schematic diagram of the development of a large deep foundation pit rotating trestle structure.

[0040] Figure 3 It is a flow chart of the rotary trestle construction method of the present invention.

[0041] Figure 4 It is a schematic diagram of the welding structure of the lattice column and the steel cage described in the present invention.

[0042] Figure 5 It is a cross-sectional schematic diagram of the guide frame described in the present invention.

[0043] Figure 6 It is a schematic diagram of the scissors support of the trestle described in the present invention.

[0044] In the figure: 1. trestle platform; 2. first straight section; 3. first rotating slope section; 4. middle straight section; 5. last rotating slope section; 6. last straight section; 7. earth slope ramp; 8. lattice column; 9. steel cage; 10. scissor brace; 11. connecting beam; 12. deep foundation pit; 13. guide frame. DETAILED DESCRIPTION

[0045] The specific embodiments of the present invention are further described below:

[0046] like Figure 1-Figure 6 As shown, a large deep foundation pit rotating trestle comprises a trestle and a supporting body, wherein the supporting body and the trestle are of the same body, the supporting body is arranged below the trestle, the trestle is divided into a straight section, a rotating slope section and an earth slope ramp, a trestle platform 1 is arranged on the upper plane of the foundation pit, the trestle platform 1 is connected to a first straight section 2, the first straight section 2 is connected to a first rotating slope section 3, the first rotating slope section 3 is connected to a middle straight section 4, the middle straight section 4 is connected to a tail rotating slope section 5, the tail rotating slope section 5 is connected to a tail straight section 6, the tail end of the tail straight section 6 is connected to an earth slope ramp 7, and the other end of the earth slope ramp 7 leads directly to the bottom of a large deep foundation pit 12.

[0047] Furthermore, the pier is divided into a pier deck and an internal support structure, the internal support structure is arranged on the lower surface of the pier deck, the internal support structure is fixedly connected to the support body, and the internal support structure is supported by a steel structure frame.

[0048] Furthermore, the support body includes a lattice column 8 and a steel cage 9. The lattice column 8 is supported on the lower surface of the pier, and the steel cage 9 is arranged inside the space of the lattice column 8. The four sides of the lattice column 8 are fixedly connected to the steel cage 9. The main reinforcement of the steel cage 9 is connected to the side of the lattice column 8 by oblique steel bars.

[0049] Furthermore, the lattice column 8 adopts angle steel joints, the angle steel joints of the same cross section do not exceed 50% of the cross section, the adjacent angle steels are staggered by no less than 60cm, and the angle steel joints are reinforced with short angle steels of the same material on the inner side of the angle steel at the connection position.

[0050] Furthermore, a positioning rib is provided on the main reinforcement of the steel cage 9 every 2 m, and the positioning ribs are equally divided at 360°, with a total of 4 ribs.

[0051] The structural features of the large deep foundation pit rotating trestle described are as follows: the circular trestle spirals downhill from the top of the first straight section 1 to 9m above the bottom of the foundation pit, and the subsequent height difference is excavated using a soil slope ramp 7. The circular trestle ramp adopts a reinforced concrete structure with a slope of 1:8. The lower part is provided with a soil slope ramp 7 to the bottom of the deep foundation pit 12 for vehicles to travel. The completion of the rotating trestle construction relieves the pressure of the progress control in the later stage of earthwork excavation. The bottom of the trestle adopts steel columns to support lattice columns 8. The lattice columns 8 include steel columns and concrete column piles. The upper steel columns are steel components, and the lower column piles are reinforced concrete bored cast-in-place pile foundations.

[0052] A construction method for a large deep foundation pit rotating trestle, the construction method is implemented based on the deep foundation pit rotating trestle, and the steps of the large deep foundation pit rotating trestle construction method are as follows:

[0053] S1: Drilling: Preparations should be made before drilling, and original records of drilling should be kept during the drilling project. The pile boring machine must be installed firmly, squarely, horizontally, safely and reliably to ensure that it does not tilt or move during construction. Ensure that the verticality of the drilled hole and the pile position deviation meet the design and specification requirements. When the hole depth has reached the design requirements, the hole should be inspected and the hole depth should be measured on site. The hole depth should not be less than the designed hole depth, and the sediment thickness should not be greater than 10cm.

[0054] S2: Hole cleaning: The purpose of hole cleaning is to remove drilling cuttings and sediment. Use a grab bucket to grab the soil repeatedly until the sediment in the hole is removed. When the hole cleaning is completed, check the hole depth, sediment at the bottom of the hole, etc., and fill in the hole completion report in time. Concrete should be poured within half an hour after hole cleaning.

[0055] S3: Fabrication and hanging of steel cage 9: While the drilling rig is drilling into the hole, the steel cage 9 is processed and manufactured in the steel bar yard. The specifications, quantity and quality requirements of welding used in the manufacture of steel cage 9 are strictly in accordance with the design drawings and relevant specifications. The manufacturing deviation of steel cage 9 should be strictly controlled within the allowable deviation range. To ensure the thickness of the steel bar protective layer, steel cage 9 can only be welded and installed after acceptance.

[0056] S4: Processing of steel lattice 8: The lattice column 8 is processed and manufactured off-site. The appearance of the material is inspected and accepted. Only qualified ones can be manufactured. The joints of the lattice columns 8 should be staggered when they are butt-welded to ensure that the angle steel joints of the same section do not exceed 50%, and the staggered position of adjacent angle steels is not less than 60cm. The angle steel joints are reinforced with short angle steels of the same material on the inner side of the angle steel at the weld position.

[0057] Permissible deviation of structural column processing:

[0058] project Specified value and allowable deviation (mm) Inspection method Cutting length ±5 Steel ruler measurement Local allowable deformation ±2 Level measurement Weld thickness ≥10 Vernier scale Column bending h / 250 and not more than 5mm Level ruler Diagonal length of angle steel in the same plane ±5 Measure diagonal points with a ruler Angle steel joint ≤50%, the staggered position of adjacent angle steels shall not be less than 60cm Steel ruler measurement Weld surface flatness ±2 Level ruler Section size ±1% side length Steel ruler measurement Yadaka 0.1％L Steel ruler measurement End plane inclination value 2mm Steel ruler measurement

[0059] S5: Welding of lattice column 8 and steel cage 9: weld one Φ16 horizontal steel bar to the main reinforcement of steel cage 9 on each side of lattice column 8, with a movable range of 20-30mm from each side of lattice column 8, so that steel cage 9 is located in the middle of lattice column 8, and ensure that the spacing between each surface of lattice column 8 and steel cage 9 is uniform, so that the position of lattice column 8 can be slightly adjusted after hoisting, so that its position is accurate and the column body is vertical; two 1.0m Φ16 steel bars are used to be obliquely welded to the main reinforcement of steel cage 9 on four surfaces of lattice column 8, with a welding length of 100mm. The steel bars have a certain length to form a flexible connection, so that the lattice column 8 can be relatively slightly adjusted.

[0060] S6: The lattice column 8 is lowered to the designed elevation: The lattice column 8 is installed by a 25T crane, and the lifting point is located at the upper part of the lattice column. After the drilling of the column pile is completed, the mud and soil around the drilling hole are cleaned up, and the surveyor calculates the four coordinate points of the extended line of the midpoints of the four sides of the lattice column, and then lays out the line, and the positioning deviation is less than 50mm.

[0061] S7: Check verticality: measure the four positioning points to the profiled beam, use two theodolites to control the position in the vertical direction, mark the position, and report to the supervisor for re-checking according to the measurement record. After the steel cage 9 is put into the hole, the positioning guide frame 13 is installed at the falling position of the lattice column 8. The frame height is 1500mm, and the frame body is 14# channel steel butt welded. The positioning hole in the middle of the guide frame 13 is 50mm larger than the lattice column on each side, which is convenient for screw inspection connection and column position adjustment. A guide column of the same specification as the lattice column 8 is set on the top of the guide frame 13. The guide column is connected to the four sides of the installed lattice column 8 at the bottom by Φ28 bolts. The lattice column 8 to be installed is detected with a ruler during the falling process, and finally it is ensured that the center and orientation of the lattice column 8 meet the design requirements, and the screws are tightened to prevent displacement, and then a lower guide tube is set in the lattice column 8 for pouring concrete.

[0062] S8: Lowering the conduit: Before installing the conduit, it should be pre-assembled and subjected to a watertight pressure test.

[0063] Pre-assembly: Select a flat site, lay out the pads, nail a straight line on the pads to make them reach the horizontal requirement, then assemble on the pads according to the use length and check its verticality.

[0064] Pressure test: After all the conduits are assembled, water is injected for water pressure test to check for any leakage. If there is leakage, the test will be continued after renovation until there is no leakage. After the conduit passes the assembly inspection, it can be dismantled in sections according to its strength and the capacity of the lifting equipment.

[0065] During the lowering process of the conduit, the conduit should be placed in the center of the hole as much as possible, and it is strictly forbidden to collide with the steel cage 9. The conduit should be installed in sections from bottom to top in the order of assembly. After the lowering is completed, the height of the lower end of the conduit from the bottom of the hole is 30 to 50 cm.

[0066] S9: Concrete pouring: The design of underwater concrete mix ratio not only ensures sufficient strength, greater fluidity during pouring, high cohesion and water retention, but also requires that its initial setting time be extended to more than 6 hours to ensure that the concrete poured first during the pouring process has a certain plasticity. The position of the concrete surface in the hole is detected by a detection hammer. A hammer is suspended into the hole with a tested measuring rope, so that it passes through the mud sedimentation layer and stays on the concrete surface or 10 to 20 cm below the surface. The sinking depth of the hammer shown by the measuring rope is used as the concrete pouring depth.

[0067] S10: Hole backfilling: After the lattice column 8 is poured, the hole needs to be backfilled in time. Before backfilling, safety measures should be taken around the pile hole. Yellow sand is used as the backfilling material. When backfilling, the lattice column 8 is backfilled evenly around to avoid the lattice column 8 being squeezed due to unbalanced backfilling. The backfilling must be dense.

[0068] S11, trestle measurement;

[0069] Because the rotating trestle needs to be cast in sections following the progress of earthwork excavation, during the construction period, the elevation difference between the first trestle platform 1 and the first straight section 2 of the trestle is 7m, and the elevation difference between the last tail straight section 6 and the trestle platform 1 is 14m.

[0070] S12, excavation to the bottom elevation of the trestle platform cushion layer: the trestle platform 1 is a connecting platform connecting the first straight section 2, and is excavated to the designed bottom elevation;

[0071] S13, trestle platform 1 construction work: after excavation to the designed elevation, leveling and re-measurement of elevation are carried out to ensure the flatness and elevation of the bottom; at the same time, the base is compacted to prevent the bottom formwork from settling after concrete pouring and affecting the quality of concrete support, and a 100mm thick concrete cushion layer is applied as the concrete support bottom formwork.

[0072] S14. Excavation to the bottom elevation of the cushion layer of the first straight section 2 trestle platform: the height difference of each layer shall not be greater than 1m, and the slope shall be no greater than 1:2. It is strictly forbidden to excavate the foundation pit too deep. A gap of no less than 250mm shall be left between the mechanical excavation and the retaining wall piles. The bucket shall not collide with the retaining wall piles, internal supports, lattice columns 8, waist beams, etc. The soil on the pile surface shall be removed manually; in order to prevent over-excavation and disturbance of the soil at the bottom of the pit, when the mechanical excavation is about 150mm from the bottom of the pit, the remaining soil shall be removed manually.

[0073] The length of a single-sided welded joint of a steel bar shall not be less than 10d; the length of a double-sided welded joint shall not be less than 5d; the overlap area percentage of a welded joint shall not exceed 50%. The overlap length of a tied joint shall not be less than 35d, and the center and both ends of the overlap shall be tied with steel wires respectively. The tied joints should be staggered, and the overlap area percentage shall not exceed 50%; the anchorage length of all node steel bars is 35d unless otherwise specified in the drawings.

[0074] After the threading of the mechanical connection thread of the steel bar is completed, it needs to be manually polished. If there is a broken wire, it should be reprocessed. And ensure that the edge of the polished surface is free of burrs. The polished section should be perpendicular to the vertical surface of the steel bar axis to ensure that the steel bar can be tightly connected when it is butt-jointed. The number of threads of the Φ22 thread head is 12, the total length of the threading is 30mm, and the pitch is 2.5mm. The number of threads of the Φ25 thread head is 11, the total length of the threading is 33mm, and the pitch is 3.0mm.

[0075] S15. Pier construction: Formwork support: The pier formwork adopts wooden formwork, and the formwork reinforcement adopts 80*100 wooden beams and Φ48mm scaffolding steel pipes. The formwork should be cleaned and coated with isolation agent before erecting. Ensure that the formwork is clean and smooth before each concrete pouring.

[0076] Concrete pouring of trestle bridge: the vibrating rod should be inserted into the surface of the lower concrete for no less than 5cm, the vibration point spacing is 50cm, and the vibration time is 20 to 30 seconds to ensure that the concrete is vibrated densely, without missing vibrations and without over-vibration. When the concrete is poured to the designed elevation, it should be scraped and leveled in time with tools such as push plates and rulers. It should be compacted and smoothed before the initial setting of the concrete. After finishing, attention should be paid to the protection of the finished product. No one is allowed to go up before the final setting, and no construction load should be added. Since whether the concrete reaches the strength will directly affect whether the lower earthwork can be excavated, therefore, ensure that the supporting concrete reaches the strength before the lower earthwork is excavated. The formwork can be removed one day after the concrete pouring is completed, and the curing period is not less than 7 days and nights.

[0077] Scissor brace setting: lattice columns 8 are laid in layers and connected with connecting beams 11. Scissor braces 10 are set between lattice columns 8 and connecting beams 11. Scissor braces 10 are set crosswise, with one end of scissor braces 10 located at the bottom of upper connecting beam 11 and the other end located at the top of connecting beam 11. Scissor braces 10 improve the supporting force of lattice columns 8. Now, a method of installing a manual hoist on lattice columns 8 is adopted, and the hoist is fixed on the lattice column 8 plate under connecting beam 11; the scissor brace 10 is hoisted to the installation position by a hoist; the manual arc welding construction method is adopted to splice two shorter channel steels; the channel steel is butt-welded by full welding. The weld height is 8mm. After the butt welding is completed, the steel plate is attached to the weld for welding reinforcement; the steel plate is also welded to the channel steel by full welding, and the weld is 8mm.

[0078] S15, repeat steps S13 to S14 until the construction of the trestle is completed;

[0079] S16: Horizontal displacement of monitoring points: The monitoring points are arranged along both sides of the trestle, with a spacing of 10m between monitoring points, and no less than one monitoring point on each side; the horizontal displacement monitoring points are buried in the reinforced ground surface at the top of the trestle with forced centering monitoring signs, and marked with paint. The monitoring points are monitored in a pre-buried manner.

[0080] Vertical displacement: monitoring points are arranged along both sides of the trestle, with a spacing of 10m between monitoring points. No less than 2 monitoring points on each side can be located in the same section as the horizontal displacement; the monitoring points can be co-located with the displacement monitoring points.

[0081] The vertical displacement is measured by geometric leveling method, using Leica level to observe and record field observation data files. It is implemented in accordance with the "Urban Rail Transit Engineering Survey Specification" (GB50308-2017). The main technical indicators and requirements are shown in Table S20-1. Each monitoring period forms a closed leveling route and measures at least two working base points in parallel as a check.

[0082] S20-1 Main technical indicators and requirements for vertical displacement monitoring point observation

[0083] Serial number project tolerance 1 Error in deformation point elevation ±0.3mm 2 Mean error of height difference between adjacent deformation points ±0.1mm

[0084] Horizontal displacement monitoring mainly uses total station and supporting prism set for observation, and polar coordinate method is proposed for horizontal displacement monitoring:

[0085] Polar coordinate method: Place the instrument at a known point A, and the backsight point is another known point B. By measuring the angle AB-AP and the distance from point A to point P, the coordinates of point P are calculated. Assume that the coordinates of point A are A(XA, YA), and the azimuth angle of A-B is αA-B, then the calculation formula for the coordinates of point P (XP, YP) ​​is:

[0086] Xp=X A +S·cos(a A-B +β)

[0087] Yp=Y A +S·sin(a A-B +β)

[0088] From the differential formula we can get:

[0089] ΔXp=cos(a A-B +β)·ΔS-sin(a A-B +β)·S·Δβ / ρ

[0090] ΔYp=sin(a A-B +β)·ΔS+cos(a A-B +β)·S·Δβ / ρ

[0091] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A large deep foundation pit rotating trestle, comprising a trestle and a support body, characterized in that: The support body and the trestle are of the same body, and the support body is arranged under the trestle. The trestle is divided into a straight section, a rotating slope section and an earth slope ramp. The straight sections are respectively arranged at the top edge of the foundation pit, between the two rotating slope sections and at the tail end of the rotating slope section. The rotating slope section is arranged between the two straight sections, and the earth slope ramp is arranged at the tail end of the last straight section, and the earth slope ramp leads directly to the bottom of the large deep foundation pit.

2. A large deep foundation pit rotating trestle according to claim 1, characterized in that: The trestle is divided into a trestle deck and an internal support structure. The internal support structure is arranged on the lower surface of the trestle deck, the internal support structure is fixedly connected to the support body, and the internal support structure is supported by a steel structure frame.

3. A large deep foundation pit rotating trestle according to claim 1, characterized in that: The support body includes a lattice column and a steel cage. The lattice column is supported on the lower surface of the trestle. The steel cage is arranged inside the lattice column space. The four sides of the lattice column are fixedly connected to the steel cage. The main bars of the steel cage are connected to the sides of the lattice column by oblique steel bars.

4. A large deep foundation pit rotating trestle according to claim 2, characterized in that: The lattice columns use angle steel joints, the angle steel joints of the same section do not exceed 50% of the section, the adjacent angle steels are staggered by no less than 60cm, and the angle steel joints are reinforced with short angle steels of the same material on the inner side of the angle steel at the connection position.

5. A large deep foundation pit rotating trestle according to claim 2, characterized in that: A positioning bar is arranged every 2m on the main reinforcement of the steel cage, and the positioning reinforcement is equally arranged at 360°, with a total of 4 bars.

6. A construction method for a large deep foundation pit rotating trestle, the construction method is implemented based on a deep foundation pit rotating trestle, characterized in that: The steps of the large deep foundation pit rotating trestle construction method are as follows: S1. Drilling: The drilling speed for soil layer construction is 5 min / m, for strongly weathered siltstone layer is 15 min / m, for moderately weathered siltstone is 90 min / m, and the thickness of sediment in the hole should not exceed 10 cm; S2. Hole cleaning: Use a grab bucket to grab the soil repeatedly until the sediment in the hole is removed. Pour concrete within half an hour after the hole is cleaned; S3. Fabrication and hanging of steel cage: The steel cage is fabricated on site at the steel yard; S4. Lattice column processing: Lattice columns are processed and manufactured off-site; S5. Welding of lattice column and steel cage: weld one horizontal steel bar to the main reinforcement of the steel cage on each side of the lattice column, with a 20-30mm clearance from each side of the lattice column. The steel cage is located in the middle of the lattice column, and the distance between each side of the lattice column and the steel cage is uniform; S6. Lower the lattice column to the designed elevation: Use a crane to install it, with the lifting point located at the top of the lattice column. Calculate the four coordinate points of the extended lines of the midpoints of the four sides of the lattice column, and then lay out the lines. The positioning deviation should be less than 50mm. S7. Check verticality: Use two theodolites to control the position in the vertical direction, mark the position, and check it according to the survey record. After the steel cage is put into the hole, install a positioning guide frame at the falling position of the lattice column. The positioning hole in the middle of the guide frame is 50mm larger than the lattice column on each side to facilitate screw connection and column position adjustment. A guide column of the same specification as the lattice column is set on the top of the guide frame. The guide column is connected to the four sides of the installed lattice column at the bottom by bolts. The lattice column to be installed is checked with a ruler during the falling process. S8. Lowering the conduit: Before installing the conduit, pre-assemble it, do a watertight pressure test, and check its verticality; After all the ducts are assembled, water is injected for a hydraulic test to check for water leakage. After the ducts are assembled and tested, they are disassembled in sections according to their strength and the capacity of the lifting equipment. During the lowering process of the conduit, the conduit should be placed in the center of the hole, and it is strictly forbidden to collide with the steel cage. It should be installed in sections from bottom to top in the pre-assembled order; after the lowering is completed, the height of the lower end of the conduit from the bottom of the hole should be 30 to 50 cm; S9. Concrete pouring: The underwater concrete mix ratio is designed, which has greater fluidity during the pouring process, and the initial setting time of the poured concrete is extended to more than 6 hours; S10. Hole backfilling: After pouring concrete, backfill the pile hole evenly around the lattice column to avoid squeezing the lattice column due to uneven backfilling. Backfill densely; S11, trestle measurement; S12, excavation to the bottom elevation of the trestle platform cushion: the trestle platform is a connecting platform connecting the first straight section, and excavation is carried out to the designed bottom elevation; S13, trestle platform construction work: after excavating to the designed elevation, leveling and re-measurement of elevation are carried out to ensure the flatness and elevation of the bottom; at the same time, the base is compacted, and then a 100mm thick concrete cushion is applied as the concrete support bottom formwork; S14. Excavation to the bottom elevation of the cushion layer of the first straight section of the trestle platform: the height difference of the excavation shall not be greater than 1m, and the slope shall be no greater than 1:

2. It is strictly forbidden to excavate the foundation pit too deep. A gap of no less than 250mm shall be left between the mechanical excavation and the retaining wall piles. The bucket shall not collide with the retaining wall piles, internal supports, lattice columns, and waist beams. The soil on the pile surface shall be removed manually. Prevent over-excavation and disturbance of the soil at the bottom of the pit. When the mechanical excavation is 140-160mm from the bottom of the pit, the remaining soil shall be removed manually. S15. Trestle construction: Formwork support: The trestle formwork adopts wooden formwork, and the formwork reinforcement adopts wooden beams and scaffolding steel pipes. The formwork should be cleaned and coated with isolation agent before erection. Before each concrete pouring, ensure that the formwork is clean and smooth; Concrete pouring for trestle bridge: When pouring concrete for trestle bridge, a vibrating rod is used. The vibrating rod is inserted into the surface of the lower concrete layer by no less than 5 cm. The vibration point spacing is 50 to 80 cm. The vibration time is 20 to 30 seconds. The concrete is poured to the designed elevation and leveled with tools. No one is allowed to go up before the concrete begins to set, and no construction load is allowed. Scissor brace setting: lattice columns are laid in layers and connected with connecting beams. Scissor braces are set between the lattice columns and the connecting beams. The scissor braces are set crosswise, with one end of the scissor brace located at the bottom of the upper connecting beam and the other end located at the top of the connecting beam. The scissor braces improve the supporting force of the lattice columns; S15, repeat steps S13 to S14 until the construction of the trestle is completed; S16, Pier monitoring: Horizontal displacement monitoring: Monitoring points are pre-buried and arranged along both sides of the pier. The monitoring points are spaced 10m apart, with no less than one monitoring point on each side. Horizontal displacement monitoring points are forced to be monitored by centering, and the signs are buried in the reinforced ground at the top of the pier and well marked. Vertical displacement: monitoring points are arranged along both sides of the trestle, with a spacing of 10m between monitoring points. There are no less than 2 monitoring points on each side. They can be located in the same section as the horizontal displacement, and the monitoring points can be co-located with the displacement monitoring points.

7. The construction method of a large deep foundation pit rotating trestle according to claim 5, characterized in that: In the step S9, the surface position of the cast-in-hole concrete is detected by using a detection hammer, which includes a measuring rope and a hammer. The hammer is hung in the hole with the tested measuring rope. The hammer passes through the mud sedimentation layer and stays 10 to 20 cm below the concrete surface. The sinking depth of the measuring rope and the hammer is used as the concrete pouring depth.

8. The construction method of a large deep foundation pit rotating trestle according to claim 5, characterized in that: In the step S13, the horizontal displacement monitoring adopts the polar coordinate method.

9. The construction method of a large deep foundation pit rotating trestle according to claim 5, characterized in that: In the step S13, the vertical displacement is measured using a geometric leveling method.

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