Main projects: site leveling → survey and lofting → foundation construction (excavation) → foundation formwork fabrication and installation → foundation concrete pouring (concrete pouring) → pier and abutment reinforcement fabrication and installation → concrete pier (abutment) cap → beam slab prefabrication and installation → abutment back backfilling → flaky cone slope → guardrail base concrete → bridge deck pavement and other ancillary works.
Precast hollow slab and T-beam: construction preparation → making bottom formwork, side formwork and core formwork → binding steel bar → installing side formwork → pouring bottom slab concrete → installing core formwork → pouring side wall concrete → binding top steel bar → pouring beam top concrete → curing concrete → hoisting.
Ⅰ. Bored cast-in-place pile
According to the geological conditions, CZ30 percussion drill pipe cone is used to drill bored piles in this contract section, and the construction method is as follows:
1. Measurement and positioning
The position of bored pile shall be set out by the coordinate method of total station, and the surrounding casing shall be buried and marked.
Ⅱ. Preparation before drilling
(1) Level the site and build an island by cofferdam.
The dry land island is higher than the ground 10 ~ 20 cm. The elevation of the island surface built in water should be higher than the construction water level 1.0 ~ 1.5 m, and the area of the island top surface should meet the walking needs of drilling rigs and cranes.
(2) Buried liner
The lining is made of 6 ~ 10 mm steel plate by rolling. The diameter of the casing is 20 ~ 25cm larger than the diameter of the borehole, and the length varies according to different geological conditions. Generally, the excavation method is adopted, and the excavation diameter should be 80 ~ 100 cm larger than the outer diameter of the casing. After hoisting in place, check the alignment. Plane center displacement is not more than 50cm, and keep vertical. Clay is used to fill and tamp the surrounding symmetry. The top surface of the casing should be 0.2~0.5m higher than the island surface and 0.5 ~ 2.0m higher than the construction water level or groundwater level/kloc-0. The bottom of underwater piers and liners shall be at least 0.5m into the river bed. ..
(3) Preparation of clay:
Before drilling, store enough clay to meet the needs of pulping. Clay has strong pulping ability and high viscosity.
(4) The drilling rig is in place
The positioning of drilling rig is very important for drilling quality and smooth drilling. When positioning, the center of the pipe cone should be aligned with the center of the pile position, and the drilling rig should be firmly supported.
ⅲ. Exercise
(1) mud preparation
Multi-stage pore-forming process has its own pulp-making function. You don't have to mix the slurry outside the hole first, you can add clay directly into the hole and mix the slurry by yourself through the punching action of the pipe cone. During the construction period, the mud performance shall be measured at least twice per shift.
(2) Opening up
In order to ensure the smooth drilling, it is necessary to treat the bottom hole wall of casing. When drilling, don't push the footage in a hurry. Fill more clay at the bottom of casing 1m, and reinforce the bottom hole wall of casing repeatedly with a solid drill with a diameter of 50cm. After the wall of casing bottom hole is reinforced, small tube cone drilling can be carried out.
(3) small tube and taper hole drilling
After the hole wall at the bottom of the casing is reinforced, drill with a small cone (cone diameter 0.46m), and drill with the cone and slag. When drilling, you can drill to the bottom of the hole at one time or drill in sections.
(4) reaming:
After drilling the small hole with a small tube cone, gradually replace the tube cone with a tube cone matching the drilling diameter, and carry out reaming until the designed aperture is reached. When reaming, small tube and cone drilling method should be adopted, drilling to the bottom at one time or drilling in sections.
(5) stroke selection
When the hole wall is stable and drilling is normal, it is generally 0.6 ~ 1.0m, and when the hole is prone to collapse or shows signs of collapse, it is 0.35~0.6m.
(6) Keep the head height.
Because every time the reaming hole is drilled in stages, the hole wall protected in the last reaming will be destroyed, so we should always pay attention to protecting the water head height. The head height should be higher than the construction water level or underground water level 1.5 ~ 1.8m, and not lower than the casing upper mouth 10 ~ 20cm. When cutting ballast, water should be replenished in time, and the head height can be increased when passing through the stratum with strong water permeability or showing signs of hole collapse.
(7) Clay input
In the stratum that needs mud to protect the wall, clay should be often put into the hole during drilling to ensure the mud quality. For holes with a diameter of 0.75 ~1.25m in sandy soil and pebble soil, put 0.5 ~ 1.0m3 clay per linear meter; For holes with a diameter of 1.5 ~ 2.0m, put clay 1.0 ~ 1.2m3 per linear meter.
Ⅳ. Hole cleaning
After the hole is formed, the drill bit is basically dug out with a pipe cone, and then the hole is cleaned by ion suspension method, that is, 24 hours before the hole cleaning, a paste mixture is prepared according to the ratio of 1 (sawdust): 0.3 (caustic soda): 1 (cement): 30 (clay), and the hole is cleaned. Dissolve the paste mixture evenly in the mud at the bottom of the hole, and remove the slag with a pipe cone. When the mud specific gravity is 1.03 ~ 1.06, hole cleaning is completed.
ⅴ. Hoisting the reinforcing cage
Reinforcing cages are made by reinforcing bars in sections and installed by drilling rig or crane. The reinforcing cage is extended and welded by two electric welding machines, connected in sections and lowered in sections. After positioning the reinforcing cage, concrete should be poured in time to prevent hole collapse.
ⅵ. Pouring underwater concrete
Underwater concrete is poured by conduit method. The diameter of the conduit is 250mm, the wall thickness is 8mm, and the general section length is 2.0 mm. In addition, the length of 1 section is 4m, and the length of two sections is 1m, so as to facilitate the adjustment of the length of the conduit. The conduit joint is sealed and waterproof with rubber ring, underwater concrete is mixed on site, and the rig is hoisted into the warehouse.
The pouring amount of the first batch of concrete must be calculated so that it has certain impact energy, mud can be discharged from the conduit, and the lower opening of the conduit can be buried in the concrete, and the depth is not less than1m. When the funnel is filled with concrete, the iron wire on the waterproof plug is cut, and the concrete goes down to the bottom of the hole with the waterproof plug to discharge mud. During the whole pouring process, the conduit is buried in the concrete for 2 ~ 6m, and the concrete pouring surface gradually rises due to the overpressure of the concrete in the conduit until it is higher than the design elevation1m.
ⅶ, pier construction
(1) steel bar: it is uniformly processed by the steel bar processing factory and transported to the site for binding and molding. After passing the inspection, proceed to the next working procedure.
(2) Concrete engineering
1) formwork: in order to ensure the engineering quality, the steel formwork made by the factory is used for the construction formwork. Sponge is clamped at the joint to prevent slurry leakage and ensure flatness.
2) Support: generally, steel scaffolding is used as the support of pier cap.
3) After the formwork is supported, use theodolite to adjust the horizontal and vertical directions, and use cable wind rope for reinforcement to ensure that the construction is not disturbed.
4) Concrete is mixed centrally in the mixing station, transported to the site by concrete truck, matched with bucket by crane, and fed into the mould through funnel and string tube.
(1) In the process of concrete mixing, we should pay attention to the coordination of mixing speed and concrete pouring speed, check and correct the slump of concrete at any time, and strictly control the water cement ratio and mixture ratio.
(2) When the concrete pouring height exceeds 2m, a string of rollers shall be set to make it fall.
(3) The interval between concrete pouring shall not exceed the specified requirements.
(4) Concrete shall be poured in layers according to a certain thickness, and the thickness of each layer shall be less than 30cm.
(5) Concrete vibrating shall be carried out by designated personnel in strict accordance with regulations:
When vibrating, collision with embedded parts such as formwork and steel bars should be avoided to avoid vibration leakage and resurgence. Every time vibrating, the vibrator should be inserted into the lower concrete by 5- 10 cm until the concrete stops sinking, no obvious bubbles emerge, the surface is smooth and filled with cement slurry. Ensure that the concrete is dense, smooth in appearance and free of honeycomb and pits.
5) After the formwork is dismantled, it shall be bound with plastic film for water conservation to keep the concrete surface moist, and the water conservation time shall be implemented according to the specification requirements.
Eight, precast hollow slab beam construction
(1) basic manufacturing
Steel plate base is adopted and effectively fixed with anchor bolts. The surface of steel plate is polished and demoulded with high efficiency release agent.
(2) Side formwork and mandrel: The side formwork is made of steel formwork made by the factory, with 5 sets of side formwork and 5 and a half sets of middle formwork; The mandrel adopts air bag or flat die.
(3) Tie the non-prestressed steel bars, install and fix the drawing pipe, and glue the drawing pipe joint with plastic tape to prevent the cement slurry in the concrete from infiltrating into the channel. The steel hinge wire passes through the traction tube to increase its rigidity.
(4) After the formwork, end formwork and steel formwork pass the supervision inspection, the concrete at the bottom of the slab shall be poured. After the bottom concrete is poured and vibrated, the core mould is installed and the concrete on both sides and the top of the slab is poured. The top concrete should be scraped clean.
(5) Withdraw the tube drawing and dismantle the mandrel in time after the final setting of curing, so as to avoid the difficulty of demoulding after tube drawing for a long time. After 24 hours of concrete pouring, the side formwork can be removed and the plate girder can be maintained in time. When necessary, film covering and steam curing can be used for installation and construction, and the strength of concrete reaches the design strength.
Nine, bridge deck pavement
Clean the top surface of the main girder, sprinkle water, bind the steel bar, place φ 25 small steel bar heads between the steel mesh and the top surface of the main girder, with the vertical and horizontal spacing of 1m, and assign special personnel to look after the steel bar during pouring to prevent dislocation. Concrete truck is used for concrete transportation, concrete pump is used for vertical transportation, imported vibrating beam is used for concrete vibrating, and the whole construction is carried out. Strictly control the thickness and smoothness of concrete during construction. Reserve expansion joint slot, spread colored cloth and sprinkle water for health preservation. In order to ensure that the thickness of bridge deck pavement is more than 8cm, the elevation should be lowered in advance according to the situation, and the pre-lowering value is δ-2 cm, δ-2 ≥ 0. During the bridge deck construction, put an inverted trapezoidal block with the same size and shape as the notch at the exit, and take it out after the asphalt pavement is completed.
D, backfilling
1. All materials used for backfilling shall meet the requirements of technical specifications, and the filler shall be fully compacted, with good water permeability and free of impurities such as grass roots, decaying plants or frozen soil blocks.
4. Backfill soil shall be filled in layers, and the thickness of each layer shall be generally controlled within 10- 15cm. The paving thickness shall be uniform and flat as far as possible. When backfilling in rainy season, the filling surface should be made into a slope of 3%-4% to facilitate drainage.
3. Backfilling of structures should follow the principle of symmetry on both sides. And do basically the same elevation to prevent uneven backfill from damaging the structure.
4. Backfilling of foundation pit shall be carried out under the condition of eliminating accumulated water, and the backfilling work shall be approved by the supervision engineer. Subgrade slope should be dug into steps to ensure backfill quality.
5. Before backfilling, divide the backfilling elevation by sections, determine the testing frequency, and fill in the testing records.
[6] When backfilling, a special person shall be appointed to be responsible, and it shall be clear who is responsible for backfilling each structure.
Once the backfill height shall be constructed as specified in the design drawings. Before the beam (slab) is hoisted, the allowable backfill height of light bridge (culvert) shall not be filled.
⒏ The height of backfill soil at the top of circular pipe culvert must be greater than 50 cm before vehicles can be released. When vehicles pass through the circular pipe culvert, they should slow down to avoid crushing the circular pipe.
5, gravel cushion construction
A. prepare the lower bearing layer and accept the subgrade or cushion. When the soil foundation is rolled by a 12- 15t three-wheel roller or equivalent roller (for 2-3 times), the spring should be handled in time if the surface is loose, and the inspection and acceptance should be carried out according to the specification requirements.
B. Select the qualified material yard that meets the requirements of aggregate grading range of subbase for material preparation.
C. Construction lofting: after the midline is restored, nail a pile every 10m, set up side piles 0.33-0.5m outside the edges of both sides for horizontal measurement, and mark the design elevation of the subbase edge with obvious signs on the side piles.
D. The loose paving coefficient determined by the test section in advance, and the required quantity of each section is calculated, transported to the construction site by dump truck, evenly unloaded on the lower bearing layer, and paved in time.
E. Use bulldozers and workers to evenly spread gravel on the lower bearing layer, with the surface as flat as possible, and with specified road arches or cross slopes. Check the water content in time, fill it when it is insufficient, and spread the paving shoulder material at the same time.
F. Use a roller to quickly roll on a flat road section to expose potential unevenness.
G. Stay wires to check the elevation. According to the design elevation, make a section of three elevation points every 10m, make obvious marks, and use dump trucks with manual or trolley to repair and reshape.
H. Leveling and shaping shall be done by manual machinery, and the elevation shall be checked at any time. (and set aside a certain settlement amount)
First, when rolling with a three-wheeled roller, a vibratory roller should be used. During the rolling process, the surface should be kept moist at any time, and the degree of compaction should be checked until it meets the specification requirements.
J. it is forbidden to open to traffic until the upper bearing layer is ready. Conduct self-inspection and acceptance first, and deal with the unqualified parts until they meet the requirements.
K. Main construction machinery:
Bulldozer, waterwheel, dump truck, loader, roller.
L, cushion construction technology (see table 5- 1 1)
6. Grass-roots construction
A, the construction process flow chart (see table 5- 12).
B, construction preparation
1. Submit the "Report on Construction of Grass-roots Unit" to the supervision unit stationed in the construction site, and the grass-roots construction can only be started after approval.