1. What should I do if the drilling hole is offset?
1. Quality problems and phenomena
1) The hole is not vertical after being formed, and the deviation value is greater than the specified L/100.
2) The steel cage cannot enter the hole smoothly.
2. Cause analysis
1) The drilling rig is not in a horizontal position, or the construction site is not leveled and compacted, causing uneven settlement during the drilling process.
2) The foundation of the water drilling platform is unstable and not horizontal. During the drilling process, the drilling rig frame undergoes uneven deformation.
3) The drill pipe is bent and the joints are loose, causing the drill bit to shake in a large range.
4) When drilling near an old building, you encounter an obstacle and squeeze the drill bit to one side.
5) The soil layer is uneven in softness and hardness, causing uneven stress on the drill bit, or encountering boulders, probe stones, etc.
3. Preventive measures
1) Before the drilling rig is in place, the construction site should be leveled and compacted, and the drilling rig should be adjusted to a horizontal state. During the drilling process, frequent inspections should be made to ensure that the drilling rig is always working in a horizontal state. The water drilling rig platform must be installed and accepted before the drilling rig is put in place. The platform must be solid and level, and the drilling rig frame must be stable.
2) The lifting pulley groove on the top of the drilling rig, the drill pipe chuck, and the center of the casing pile position should be on the same vertical line, and the drilling rig should be prevented from shifting or excessive swing during drilling.
3) When constructing near old buildings, detection should be done in advance. If obstacles are found during the detection process, impact drills should be used for construction.
4) The drill pipe should be inspected frequently, and bent drill pipes should be adjusted or discarded in time.
5) When using an impact drill, the stroke should not be too large, and try to use secondary drilling to ensure the verticality of the hole.
4. Treatment measures
1) When encountering obstacles such as boulders, impact drills can be used to drill holes.
2) When the deflection of the borehole exceeds the limit, the clay should be backfilled and the borehole should be re-drilled after the sedimentation is dense.
2. What should I do if shrinkage holes occur during drilling?
1. Quality problems and phenomena
When using a hole probe to inspect the hole, the hole probe is blocked when it is lowered to a certain location, and the bottom of the hole cannot be inspected smoothly. The diameter of a certain part of the drilled hole is smaller than the design requirement, or the hole diameter gradually shrinks from a certain part.
2. Cause analysis
1) The geological structure contains a weak layer. When the borehole passes through this layer, the weak layer squeezes into the hole under the action of earth pressure to form shrinkage cavities.
2) The plastic soil layer in the geological structure expands when exposed to water, forming shrinkage cavities.
3) The drill bit wears too fast and is not repaired in time, resulting in shrinkage holes.
3. Preventive measures
1) According to geological drilling data and changes in soil quality during drilling, if weak layers or plastic soil are found, pay attention to scanning holes frequently.
2) Check the drill bit frequently. When wear occurs, repair welding in time. After repairing the drill bit with more wear, expand the hole to the designed pile diameter.
4. Treatment measures
When shrinkage holes occur, a drill bit can be used to scan the holes repeatedly until the designed pile diameter is met.
3. How to deal with hole collapse during drilling?
1. Quality problems and phenomena
Collapse of the well wall during the drilling process or after the hole is formed.
2. Cause analysis
1) Due to the low consistency of the mud and poor wall protection effect, water leakage occurs, or the casing is buried shallowly, or the surrounding sealing is not dense, causing water leakage; or the thickness of the clay layer at the bottom of the casing is insufficient, causing water leakage at the bottom of the casing. The mud head is not high enough and the pressure on the hole wall is reduced.
2) The relative density of the mud is too small, causing the pressure of the water head on the hole wall to be small.
3) When drilling in a soft sand layer, the drilling footage is too fast, the mud wall is formed slowly, and the well wall seeps.
4) The drilling operation was not continuous and the drilling stopped for a long time. The water head in the hole failed to remain 2m above the water level outside the hole or the groundwater level, which reduced the pressure of the water head on the hole wall.
5) Improper operation, collision with the hole wall when lifting the drill bit or lifting the steel cage.
6) There are large-scale equipment operations or temporary access roads near the drilling, which will cause vibration when vehicles pass by.
7) Concrete was not poured in time after cleaning the hole and left for too long.
3. Preventive measures
1) Do not set up temporary access roads near the borehole, and prohibit the operation of large equipment.
2) When burying the casing on land, 50cm thick clay should be filled at the bottom and around the casing. Pay attention to the compaction. The casing should be evenly backfilled to ensure its stability of the casing and prevent groundwater. Penetrate.
3) When vibrating the casing into the water, the casing should be sunk into the mud and permeable layer according to geological data. The joints between the casings should be sealed to prevent water leakage.
4) According to the geological exploration data provided by the design department, appropriate mud-specific gravity, mud viscosity, and different drilling speeds should be selected according to different geological conditions. For example, when drilling in a sand layer, the mud consistency should be increased, better slurry-making materials should be selected, the viscosity of the mud should be increased to strengthen the wall protection, and the footage speed should be appropriately reduced.
5) When the water level changes greatly during the flood season or in tidal areas, measures such as raising the casing, increasing the water head, or using a siphon should be taken to ensure that the water head pressure is relatively stable.
6) Drilling should be done continuously, and drilling should not be stopped midway unless there are special circumstances.
7) When lifting the drill bit and lowering the steel cage, it should be kept vertical, and try not to hit the hole wall.
8) If the preparation work for pouring is insufficient, do not clear the hole temporarily. Concrete must be poured in time after the hole clearing is qualified.
9) When supplying water, the water pipe must not be directly flushed into the hole wall, and surface water must not accumulate near the hole opening.
4. What should I do if the drill bit gets stuck during drilling?
1. Quality problems and phenomena
The drill bit is in the drill hole and cannot continue to operate.
2. Cause analysis
1) Plum blossom holes, probe stones, or shrinkage holes appear in the holes.
2) The drill bit is driven too hard, or the loose wire rope is too long, causing the drill bit to tip over and get stuck on the well wall.
3) The drill bit will be stuck by falling rocks or larger tools when the hole collapses.
4) After the shrinkage cavity occurs, the size of the drill bit after repair welding is increased, the impact is too strong, and the punch cone is sucked.
5) When using a percussion drill to drill in clay formations, the stroke is too large or the mud is too thick, and the punch cone is sucked.
3. Preventive measures
1) For stuck drills that can move up and down, you can slightly lift the drill bit up and down, and use a rotating wire rope to rotate the drill bit for easy lifting.
2) Don’t drill too hard.
3) When repairing the drill bit, ensure that the size matches the hole diameter.
4) When using an impact drill for construction, the stroke should not be too large to prevent the cone tip from tipping over and causing the drill to get stuck.
4. Treatment measures
1) When the soil quality is good or the drill is stuck in a stone hole, a small blasting vibration can be used to loosen the drill bit so that the drill bit can be lifted.
2) When the drill bit is stuck, try lifting it, down, left, and right to lift the drill cone.
3) Lift it with a jack or pulley, but pay attention to the firmness of the opening to prevent it from collapsing.
5. How to prevent the hole wall at the bottom of the bored pile casing from collapsing?
1. Quality problems and phenomena
The hole wall collapses; the drill tilts.
2. Cause analysis
1) The bottom and surroundings of the casing are not backfilled with clay or are not compacted enough, and the bottom of the casing is hollowed out during drilling or pouring.
2) Due to the unknown geological drilling data provided, the bottom of the casing is in a silt or sand layer.
3) The diameter of the casing is smaller.
4) Surface water seeps into the filling soil outside the casing, causing the filling soil to become soft.
3. Preventive measures
1) The bottom of the casing should be backfilled with at least 50cm thick clay. When the soil is sandy, the 0.5-1.0m range around the casing should also be backfilled and compacted with clay.
2) According to the geological data provided by the design department, the bottom of the casing should pass through the silt and sand layers.
3) The diameter of the casing should be 20-30cm larger than the design hole diameter (forward and reverse circulation drill with drill pipe), 30-40cm (submersible electric drill or impact drill without drill pipe).
4) The slurry outlet hole of the casing should be tamped with clay. At the same time, the slurry should be kept smooth and there should be no accumulation of water around it to avoid soil loss around the casing and cause collapse holes.
4. Treatment measures
1) When the bottom of the casing collapses during drilling in water, the casing should be sunk through the silt layer or sand layer.
2) When the bottom of the casing collapses, the drilling rig should be moved first, then the casing should be pulled out, backfilled with clay as required, and tamped, then the casing again and backfill the clay around the casing and compact it. If necessary, the casing should be lengthened, and then the casing can be re-drilled to the hole.
6. How to prevent the steel cage from deforming during the lifting and placing process?
1. Quality problems and phenomena
After lifting, the steel cage undergoes excessive torsion or bending deformation.
2. Cause analysis
1) When the steel cage is long, no temporary fixing rods are added.
2) The hanging point position is incorrect.
3) The spacing between stiffening stirrups is large, or the diameter is small and the stiffness is insufficient.
4) There are no reinforcing ribs at the lifting points.
3. Preventive measures
1) Add a stiffening stirrup every 2-2.5m on the steel cage, and stiffeners should be installed at the lifting points. Cross steel bars are added to the reinforcing bars to increase the stiffness of the reinforcing bars to enhance the deformation resistance. When the steel bars are caged into the well, the cross bars are cut off.
2) The steel cage should be drilled into the hole as a whole as much as possible. If the steel cage is too long and cannot be drilled into the hole as a whole, it should be divided into as few segments as possible to reduce the hole drilling time. The segmented steel cage should also be equipped with temporary fixing rods and sufficient supplies. Welding equipment should be used to shorten the welding time as much as possible; when the two steel cages are docked, the center lines of the upper and lower sections should be consistent. If it is possible to enter the hole as a whole, the temporary fixing rod should be set up as an integral hole on the inside of the steel cage. After entering the hole, the temporary fixing rod should be removed.
3) The position of the lifting point should be selected well. When the steel cage is short, one lifting point can be used, and when the steel cage is long, two lifting points can be used.
4. Treatment measures
If the steel cage is severely twisted and deformed, the cage must be disassembled and remade.
7. After the steel frame is in place, how to fix the steel frame so that it does not sink or deviate?
1. Quality problems and phenomena
The steel cage suddenly sank after being put in place; the center of the steel cage was offset.
2. Cause analysis
1) The steel cage is not firmly fixed or the fixing measures are improper.
2) There is an error in the measurement positioning or the conduit collides with the steel cage during the concrete pouring process.
3) During the construction process, no protective measures were taken at the pile position control points, and human movement occurred.
3. Preventive measures
1) After the steel cage is positioned, securely fasten the steel cage to the skid above the casing. Skidding should use 20cm×20cm×300~400cm rectangular wooden roots.
2) The backfill soil around the casing must be compacted to prevent the casing from shifting.
3) The measurement and positioning must be accurate, and control piles must be used for re-measurement and verification. Only after the re-verification is correct can underwater concrete pouring be carried out.
4. Treatment measures
For sunken or eccentric steel cages, before pouring concrete or before pouring into the steel cage, a crane can be used to lift it and reset it.
8. How to ensure that the steel cage floats up?
1. Quality problems and phenomena
1) The steel cage floats on the poured concrete floor.
2) When lifting the duct, the steel cage floats up.
2. Cause analysis
1) When the poured concrete is close to the bottom of the steel cage, the pouring speed is too fast, and the concrete holds up the steel cage; or the lifting pipe speed is too fast, driving the concrete to rise, causing the steel cage to float.
2) When lifting the conduit, the conduit is hung on the steel cage, and the steel cage rises together with the conduit.
3. Preventive measures
1) When the poured concrete is close to the steel cage, the pouring speed of the concrete should be appropriately slowed down. The normal pouring speed can only be resumed when the bottom of the conduit is raised to at least 2m inside the steel cage.
2) When placing the conduit, the center of the conduit should coincide with the center of the drilling hole as much as possible. Anti-hanging measures should be taken at the conduit joints to prevent the steel cage from being caught when the conduit is lifted, causing the steel cage to float.
4. Treatment measures
1) After the steel cage blocks the conduit, you can try to rotate the conduit to separate it from the steel cage.
2) When the steel cage is found to have signs of floating, it can be appropriately pressurized to prevent it from continuing to float.
9. How to prevent pile breakage when pouring underwater concrete?
1. Quality problems and phenomena
1) During the process of pouring concrete, due to the pipe being pulled out, the mud entered the pipe, causing the mud in the hole to suddenly drop rapidly.
2) Due to poor sealing at the conduit joints, mud enters the conduit. If the pouring continues, a mud interlayer will appear in the concrete.
3) The conduit cannot be lifted because the conduit is buried too deep, the processing time is too long when the concrete blocks the conduit, or the long pouring time causes the previously poured concrete to solidify.
4) In the non-damage detection, there is a mud layer in a certain part of the pile.
2. Cause analysis
1) The concrete slump is small, the segregation or the stone particle size is small, the pipe is blocked during the concrete pouring process, and the pipe is not cleared before the initial setting of the concrete, and the pipe has to be lifted, thus forming a broken pile.
2) Due to a calculation error, the distance between the bottom of the conduit and the bottom of the hole is large, so the first batch of poured concrete cannot bury the conduit, resulting in broken piles.
3) When the conduit is lifted, due to measurement or calculation errors, or blind lifting of the conduit, the conduit is lifted excessively, so that the bottom port of the conduit is pulled out of the concrete surface, or the conduit port is placed in the mud layer or the mixed layer of mud and concrete, causing a fracture. pile.
4) When lifting the conduit, the steel cage blocks the conduit and cannot be lifted before the concrete has initially set, causing the concrete pouring to be interrupted and the pile to be broken.
5) Leakage at the conduit interface causes mud to enter the conduit, forming an interlayer in the concrete, and causing the pile to break.
6) The conduit is buried too deep and the conduit cannot be lifted or pulled out, causing the pile to break.
7) Due to other unexpected reasons, the concrete cannot be continuously poured, and the interruption time exceeds the initial setting time of the concrete, resulting in the failure of the pipe to be lifted, resulting in broken piles.
3. Preventive measures
1) Before using the catheter, conduct a leak detection and tensile test on the catheter to prevent leakage of the catheter. Each section of conduit is assembled and numbered, and a review and inspection system must be established after the conduit is installed. The diameter of the conduit should be determined based on the pile diameter and the maximum particle size of the stone, and large-diameter conduits should be used as much as possible.
2) When lowering the conduit, the distance between its bottom opening and the bottom of the hole should be no more than 40-50cm. At the same time, it must be ensured that the conduit can be buried for at least 1m after the first batch of concrete is poured. In the subsequent filling process, the buried depth of the conduit is generally controlled within the range of 2-4m.
3) The slump of concrete should be controlled at 18-22cm, and good workability is required. If the pouring time is long, a retarder can be added to the concrete to prevent the concrete poured in advance from initially setting and blocking the conduit.
4) When making steel cages, butt welding is generally used to ensure a smooth weld. When lap welding is used, ensure that the weld does not form a staggered position within the steel bar to prevent the steel cage from blocking the conduit.
5) When lifting the conduit, carefully calculate the length of the conduit by measuring the depth of concrete filling and the length of the removed conduit. It is strictly forbidden to blindly lift the conduit without measurement and calculation. Generally, only one conduit can be removed at a time.
6) Key equipment must be on standby and sufficient materials must be prepared to ensure continuous pouring of concrete.
7) When concrete blocks the conduit, the conduit can be unplugged and shaken. When the length of the blocked conduit is short, steel can also be inserted into the conduit for impact to clear the conduit or an attached vibrator can be fixed on the conduit for vibration. Clear the concrete in the duct.
8) When the steel cage blocks the conduit, try to rotate the conduit to separate it from the steel cage.
10. How to ensure the quality of pile joints? What issues should be paid attention to when chiseling pile heads?
1. Quality problems and phenomena
1) If the pile head is broken too early, the concrete will be disturbed and affect the strength formation or cause cracks in the pile head concrete.
2) Chisel out the basin shape of the pile head. It is difficult to remove contaminants before connecting the columns, which affects the quality of the column connection.
3) The blasting method was used to break the pile head without authorization, and the dosage was not controlled accurately, resulting in excessive blasting of the pile head, resulting in the upper part of the pile body being broken.
2. Cause analysis
1) When the concrete strength is not formed or does not reach a certain strength (70%) before being chiseled out, it will disturb the concrete, destroy the strength of the concrete, or cause small cracks inside the concrete.
2) The calculation or measurement of the designed elevation of the pile top is inaccurate, causing the concrete pouring to end prematurely, and causing the pile head elevation to be lower than the design elevation.
3) When pouring underwater concrete, over-grouting was not carried out by the requirements of the “Specifications”, the height of over-grouting was insufficient, or over-grouting was impossible.
4) The consistency of the mud is large and the thickness of the siltation is large, resulting in a thick mixed layer of concrete and mud.
5) The hole cleaning is not complete or the siltation measurement is incorrect.
6) After pouring concrete, immediately dig grout to the designed elevation of the top of the pile, which may mix the mud into the concrete and reduce the pressure on the concrete at the pile head, resulting in a decrease in the strength of the concrete.
3. Preventive measures
1) When the concrete is poured close to the pile head, the funnel mouth should be raised at least 4m higher than the top of the pile. You can also build a 3m high platform and pour concrete on the platform so that the concrete can push the mud under the action of pressure. Push up.
2) When pouring concrete, it should be at least 80cm higher than the designed elevation of the pile top to ensure that the concrete at the top of the pile is dense under the weight of the overfilled portion, and to ensure that the concrete at the pile head does not contain mud.
3) After the concrete is poured, it must reach a certain strength (required to be above 70%, when the average temperature is above 15°C, the general age is enough to reach 7 days, and the age must be extended when the temperature is low) before the pile head can be broken. It is strictly prohibited to carry out grouting immediately after the concrete pouring is completed.
4) When chiseling the pile head to about 10cm from the designed position, attention should be paid to chiseling out the surroundings of the designed pile head elevation first and then chiseling out the middle part. After the pile head is broken, the shape should be flat or slightly in the middle of the pile. Raised to facilitate column connection or flushing of pile heads before pouring concrete for tie beams.
5) It is strictly prohibited to use blasting to break pile heads.
4. Treatment measures
If due to unexpected reasons, the concrete still contains mud after the pile head is removed, the removal should continue until the concrete contains mud and the strength meets the design requirements. At this time, the formwork can be supported to pour concrete. If the depth is large, the columns need to be connected first. If the depth is shallow, the concrete for the cap can be poured at the same time.
11. How to deal with the center deviation of bored piles?
1. Quality problems and phenomena
After removing the pile head, the center of the bored pile was measured and set out to check if there was any deviation from the design requirements.
2. Cause analysis
1) There is an error in pile positioning.
2) The shape of the casing does not meet the requirements or there is deviation during burial.
3) The positioning of the steel cage is inaccurate.
3. Preventive measures
1) Carefully review the pile position when positioning, prepare a riding control pile, and take certain protective measures so that the center of the drill bit can be accurately determined and the steel cage can be positioned accurately.
2) The shape of the casing must meet the requirements, and the backfill around it must be dense when buried to prevent movement during drilling.
3) The steel cage must be accurately positioned and firmly fixed. Concrete can only be poured after verification.
12. How to ensure the pouring quality of bored pile concrete?
1. Quality problems and phenomena
Concrete segregates; concrete strength is insufficient.
2. Cause analysis
1) There is a problem with the concrete raw materials and mix ratio, or the mixing time is insufficient.
2) The stringer is not used when pouring concrete, or the distance between the mouth of the stringer and the concrete surface is too large. Sometimes the concrete is poured directly into the hole at the hole, causing the mortar and aggregate to segregate.
3) When there is water in the hole, pour concrete before draining the water. Underwater pouring of concrete should have been used, but the dry pouring method was used instead, causing serious segregation of concrete on the pile body.
4) When pouring concrete, the leakage of the protective wall was not blocked, resulting in a large amount of water on the surface of the concrete. If the water was not removed, the concrete continued to be poured, or a bucket was used for drainage. As a result, the cement slurry was discharged together, resulting in poor concrete cementation.
5) Bureau
When it is necessary to dig holes for drainage, while the concrete is being poured into a certain pile body or before the concrete has initially set, the digging work of nearby pile holes is not stopped, and the digging of holes is continued to pump water, and the amount of water pumped is large. As a result, the groundwater flow will cover the hole. The cement slurry in the concrete of the pile body was taken away, and the concrete was in a granular state, with only the stones but no cement slurry visible.
3. Preventive measures
1) Qualified raw materials must be used, and the concrete mix ratio must be prepared by a laboratory with corresponding qualifications or subjected to a compression test to ensure that the strength of the concrete meets the design requirements.
2) When the dry pouring method is used for construction, string tubes must be used, and the distance between the mouth of the string tube and the concrete surface is less than 2m.
3) When the rising speed of the water level in the hole exceeds 1.5m/min, the underwater concrete pouring method can be used to pour concrete for the pile body.
4) When using precipitation to dig holes, the nearby drilling construction should be stopped while the concrete is being poured or before the concrete has initially been set.
5) If the concrete strength of the pile body does not meet the design requirements, pile replacement can be carried out.
Substructure (enlarged foundation)
13. Is the soil foundation pit soaked by water after being excavated to the base?
1. Quality problems and phenomena
After the foundation pit is excavated, the base soil is soaked by water, the soil layer becomes soft, and the bearing capacity is reduced.
2. Cause analysis
1) Due to continuous rainfall, water accumulates in the foundation pit.
2) The groundwater level is high and the precipitation effect is poor.
3) When using pit drainage, the drainage volume is less than the water output.
4) Due to various reasons, foundation construction was not carried out in time after the foundation pit was excavated. The foundation pit was exposed for too long, and surface water flowed into the foundation pit, or spring water seeped into the foundation pit.
3. Preventive measures
1) When the foundation pit is excavated to 30-50cm from the base, the next step can be arranged according to weather conditions. When the weather is fine, the reserved part will be dug out, and then the foundation pit will be inspected. Once the inspection is passed, the foundation construction will begin immediately.
2) During construction in the rainy season, to prevent water from flowing into the foundation pit, drainage ditches or soil ridges should be dug 0.5 to 1.0m away around the foundation pit.
3) When the groundwater level is high, well point dewatering should be used or drainage ditches and water collection wells should be dug around the foundation pit, and drainage should be done at any time to lower the groundwater level. The depth of the drainage ditch and water collection well should be 0.5m deeper than the foundation pit, and there should be According to the slope, the water collection well should be 1-1.5m deeper than the lowest point of the drainage ditch. The specific size depends on the precipitation range.
4) Sufficient drainage equipment should be prepared, and drainage should be carried out as the pit is excavated, as long as there is no accumulation of water in the pit.
5) When excavating a foundation pit near rivers and ditches, a water-carrying ditch should be dug outside the foundation pit to cut off the water source flowing into the foundation pit. The distance between the outside of the water-carrying ditch and the foundation pit should be greater than 3m.
6) Stop excavation when it approaches 20cm above the base elevation. Only when the groundwater level drops below 50cm above the base elevation can the bottom cleaning work be carried out.
4. Treatment measures
Excavate the water-soaked soft soil and backfill it with gravel, graded gravel, or lime soil to the design elevation.
14. When the foundation is of uneven geology, how to prevent the foundation from slipping or tilting?
1. Quality problems and phenomena
The foundation slips or tilts.
2. Cause analysis
1) The bearing capacity of the foundation is uneven, causing the foundation to tilt toward the side with a smaller bearing capacity.
2) The foundation is located on a sloping surface. The foundation is filled and half-excavated. The filled part is not firm, causing the foundation to slip or tilt toward the half-filled part.
3) During construction in mountainous areas, the foundation-bearing layer is located on the syncline level.
3. Preventive measures
1) If the foundation-bearing layer is located on an inclined rock, inwardly inclined steps can be made on the rock to improve the ability to resist tilting and sliding.
2) Choose feasible methods to reinforce the foundation according to the actual situation to improve the bearing capacity of the foundation.
3) Change the design so that the foundation is entirely on the excavation surface.
4) Try to keep the bearing layer away from the syncline rock surface. If it cannot be avoided, effective measures should be taken to anchor the bearing layer.
4. Treatment measures
When the foundation shows signs of tilting, the original loose soil can be consolidated into a whole body with a certain strength and anti-seepage performance by drilling holes in the foundation and grouting (cement slurry, chemicals and other reinforcements), or the rock gaps can be blocked. This can achieve the purpose of improving the bearing capacity of the foundation and preventing continued tilt.
15. How to ensure the pouring quality of large-volume concrete during the construction of the cap platform?
1. Quality issues
1) Cracks appear on the concrete surface.
2) Penetrating cracks appear in the concrete.
2. Cause analysis
1) Cracks caused by foundation deformation. Due to uneven settlement or horizontal displacement of the foundation, additional stress is generated on the structure, exceeding the tensile capacity of the concrete structure, resulting in structural cracking.
2) Cracks caused by temperature difference changes. During the construction process, after the concrete is poured, a large amount of heat is generated when the cement hydrates, causing the internal temperature to rise and the temperature difference between the inside and outside to be too large. Under the action of temperature stress, cracks appear on the concrete surface.
3) Cracks caused by concrete shrinkage. After the concrete is poured, plastic shrinkage and shrinkage are the main causes of cracks on the concrete surface.
3. Preventive measures
1) When the soil quality of the base changes greatly or the bearing capacity is uneven, it should be treated according to relevant regulations to ensure that the base has a uniform bearing capacity.
2) According to the actual situation, cement with low hydration heat should be selected, the cement dosage should be limited, the temperature of the aggregate entering the mold should be reduced, and the temperature should be cooled slowly.
3) To reduce the plastic shrinkage of concrete, the water-cement ratio of the concrete should be strictly controlled, vibrated densely, and excessive vibration should be avoided. To avoid shrinkage cracks, the curing should be strengthened after the concrete is poured to keep the concrete surface moist and avoid dryness and wetness.
4) For cement that has just left the factory, it must be matured for at least 2 weeks before use.
5) When the flat load-bearing surface of the cap is too large and the second layer of concrete cannot be poured before the first layer of concrete is initially set or reshaped, pouring can be done in blocks. The following regulations should be met during pouring:
a. The blocks should be arranged reasonably, and the average area of each block should not be less than 50m2.
b. The height of the blocks shall not exceed 2m.
c. The vertical joint surface between blocks should be parallel to the short side of the foundation plane section and perpendicular to the long side of the plane section.
d. The vertical joints between the upper and lower adjacent layers of concrete should be staggered and made into tongues and grooves, and treated as construction joints.
6) Add an appropriate amount of expansion agent to the concrete to compensate for the shrinkage of the concrete.
7) After the concrete is poured, to control the temperature difference between the inside and outside of the concrete, water can be stored on the top surface of the concrete and covered with plastic sheeting for curing, so that the surface temperature of the concrete can be controlled within a certain range and the temperature difference between the inside and outside of the concrete can be reduced.
8) Admixtures, flakes, and other methods can be added to the concrete to reduce the amount of cement.
9) When constructing during high-temperature seasons, construction during high-temperature periods should be avoided, and concrete pouring should be arranged when the temperature is low. At the same time, the raw materials are cooled down and mixed with cooling water to reduce the internal temperature after the concrete is poured.
10) When the temperature difference between the inside and outside of the concrete cannot be reduced after taking the above measures, iron pipes must be embedded inside the concrete to use a circulating cooling system for internal heat dissipation, or thin layers of continuous pouring must be used to speed up heat dissipation.
4. Treatment measures
1) When the cracks are small, they can be treated with methods such as carbon fiber reinforcement and epoxy resin infusion.
2) When cracks appear in the concrete foundation, nails can be used to seal the cracks or steel hoops can be used to reinforce and seal the cracks.
16. How to ensure the pouring quality of bridge pier concrete?
1. Quality problems and phenomena
1) Honeycomb and pitted surfaces appear on the concrete surface.
2) The protective layer of steel bars is thin.
3) The layered imprint is obvious.
4) Water lines appear on the concrete surface.
2. Cause analysis
1) The type of cement used is inappropriate.
2) The material gradation has changed, resulting in a large change in slump.
3) When the height of the bridge pier exceeds 2m, the concrete will segregate due to no string tubes, resulting in leakage or excessive vibration during vibration.
4) The steel protective layer pads are improperly set.
5) The time interval between the two layers of pouring is too long, or the vibrator rod does not penetrate deeply into the lower layer of concrete during vibration, resulting in the two layers of concrete not being well combined.
3. Preventive measures
1) Do not use slag cement, because after using slag cement, water marks will easily appear on the concrete surface.
2) Strictly control the slump of concrete to ensure the workability of concrete.
3) When the height of the bridge pier exceeds 2m, a casing should be installed when pouring concrete, or the concrete should be pumped to connect the casing to the layered pouring position.
4) The thickness of layered pouring and vibrating is generally every 30cm. When vibrating, the vibrating rod should penetrate the lower layer about 5cm. It should not be too thick, otherwise the vibrating effect will not be good. Concrete should be poured continuously, and the interval between pouring two layers should not be too long.
5) The pads for the protective layer of steel bars should be evenly placed around the steel cage.
6) Use the overall template to minimize joints. Use sponge strips or rubber strips to seal the joints.
4. Treatment measures
When the honeycomb area is small, it can be processed with high-grade mortar in time after the formwork is removed.
17. How to prevent horizontal cracks on the top of piers?
1. Quality problems and phenomena
After the formwork is removed, there are small cracks within about 40cm from the top surface, and sometimes annular horizontal cracks are formed along the stirrups.
2. Cause analysis
1) The concrete pressure on the top of the pier is small.
2) Over-vibration causes large stones to sink, and the aggregate at the top of the column is reduced, which easily forms annular horizontal cracks at the top stirrups.
3. Preventive measures
1) Perform secondary vibration before the initial setting of concrete. The use of secondary vibration can eliminate internal layers caused by plastic settlement, improve the aggregate interface structure, and increase concrete strength and high permeability.
2) Remove the uppermost stirrup.
3) After the secondary vibration is completed, press a sandbag on the top of the pier column to increase the pressure on the upper concrete.
4. Treatment measures
1) When the crack does not form an annular shape, epoxy resin can be used to pour the crack without sealing it.
2) When the crack forms an annular crack and the depth reaches or exceeds the stirrups, the part above the crack should be cut out and re-poured. When the depth of the crack does not reach the stirrup position, epoxy resin can be used to seal the crack.
18. How to accurately install the embedded steel plates under the supports during cap beam construction?
1. Quality problems and phenomena
1) The position of the embedded steel plate does not match the designed position, resulting in plane or elevation errors.
2) The concrete under the embedded steel plate is not dense.
2. Cause analysis
1) Due to measurement errors, the position of the embedded steel plate is inaccurate.
2) After the embedded steel plate is positioned, it shifts during the concrete pouring because it is not connected and fixed with the steel bars.
3) Because the steel bars under the steel plate are dense, it is difficult to vibrate concrete.
3. Preventive measures
1) After the steel bars of the cap beam are tied, the position of the embedded steel plate must be carefully measured and the position of the embedded steel plate must be determined. After the steel plate is positioned, careful retesting should be carried out to ensure that its top surface elevation is consistent with the design elevation.
2) After the embedded steel plate is positioned, it is welded together with the steel frame to ensure that there will be no displacement during concrete pouring.
3) Dig a small hole in the center of the embedded steel plate, and when pouring concrete, vibrate until the mortar flows out of the hole.
4) When pouring concrete first and then inserting embedded steel plates, a level should be used to monitor the entire process to ensure that the top surface elevation is within the allowable error range.
4. Treatment measures
When the bottom plate (no holes are drilled on the steel plate) is hollow or there is an error in the plane position or elevation, the embedded steel plate should be removed. You can drill holes in the steel plate first, and then reinstall the embedded steel plate and pour it under the control of a level and theodolite. Concrete.
19. What should I do if the bridge pier partially collapses or falls off during slip-form construction?
1. Quality problems and phenomena
The bridge piers partially collapsed or fell off.
2. Cause analysis
1) Improper segmentation.
2) The sliding mold is lifted too fast.
3) The height difference of the jack is too large.
4) The corners are not vibrated well and the concrete strength is low.
3. Preventive measures
1) The segmentation must be appropriate.
2) The lifting speed of the sliding mold must be appropriate and not too fast.
3) Always observe and pay attention to the height difference of the jack not to be too large.
4) When vibrating concrete, do not leak vibration to ensure the quality of vibration.
5) Control the slump of concrete and add admixtures to improve the early strength of concrete.
4. Treatment measures
1) Partial collapse or falling corners can be repaired with fine stone concrete of the same grade.
2) If the collapsed area is too large to be repaired, it will need to be cut out and re-poured.
20. What should you do if the formwork twists and shifts during the slip-form construction of the bridge pier?
1. Quality problems and phenomena
The template is twisted and shifted.
2. Cause analysis
1) The jack climbing speed is inconsistent.
2) The load on the operating platform is uneven.
3) The concrete pouring procedure is unreasonable.
4) Wind and external impact, etc.
3. Preventive measures
1) The climbing speed of the jack must be consistent.
2) Keep the loads on the platform evenly stacked and check frequently. If the load is found to be uneven, it must be corrected in time.
3) Concrete must be poured in layers. When the drop is large (such as more than 2m), a stringer tube must be installed to slow down the impact of the concrete. It is best to use pumped concrete connected to a stringer tube for layered pouring.
4. Treatment measures
1) When the formwork is tilted or offset, the climbing speed of the jack on the lower side of the formwork can be accelerated.
2) If the template is deflected and twisted at the same time, the deflection should be corrected first, and then the twist. The method is to increase the climbing speed of the diagonal jacks to create a favorable height difference in the formwork and adjust it to the correct position.
Thank You!
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