First, the classification of pile foundations and construction principles
1. Classified according to bearing piles
(1) Friction pile:
Friction pile: In the state of bearing capacity limit, the vertical load of the pile top is borne by the pile side resistance, and the pile end resistance is negligible.
End-bearing friction pile: Under the limit of the bearing capacity, the vertical load on the top of the pile is mainly borne by the resistance of the pile side.
(2) End bearing pile:
End-bearing pile: Under the limit of the bearing capacity, the vertical load at the top of the pile is borne by the resistance of the pile end, and the resistance on the side of the pile is negligible.
Friction end pile: Under the limit of the bearing capacity, the vertical load of the pile top is mainly borne by the pile end resistance.
2. Classification according to pile forming method
(1) Non-extruded piles: dry operation method drilling (digging) hole infusion pile, mud wall protection method drilling (digging) hole infusion pile, casing wall protection method drilling (digging) hole infusion pile;
(2) Partially extruded piles: punched piles, drilled extruded and infused piles, punched (hydrostatic) open steel pipe piles, open prestressed concrete hollow piles and H-shaped steel piles.
(3) Extruded piles: punched into (hydrostatic) prefabricated piles, closed prestressed concrete hollow piles and closed steel pipe piles.
3. Classification according to the use function
Anti-pulling piles, support piles, pressure piles, etc.
4. Construction principles
The pile forming process should be selected according to the principles of safe use and economic rationality according to the type of building structure, the nature of the load, the use function of the pile, the crossing of the soil layer, the holding layer of the pile end, the groundwater level, the construction equipment conditions, the construction environment, the construction experience, and the supply conditions of pile materials.
Second, drilling and pouring piles are commonly used mechanical equipment
The commonly used construction machinery and equipment for drilling and pouring piles are rotary drilling rig, impact drilling rig, cyclotron drilling rig, automobile crane, mud pump, excavator, electric welding machine, butt welding machine, etc.
1. Rotary drilling rig
Rotary drilling rig is a kind of construction machinery suitable for hole forming operations in construction foundation engineering. Widely used in municipal construction, highway bridges, high-rise buildings and other places of foundation construction engineering, with different drilling tools, suitable for dry (short spiral), or wet (rotary bucket) and rock formation (core drilling) hole forming operations, rotary drilling rig has a large installed power, large output torque, large axial pressure, flexible mobility, high construction efficiency and multi-functional characteristics. The rotary drilling rig adapts to the soil geological conditions in most parts of the mainland, has a wide range of use, and can basically meet the use of bridge construction, high-rise building foundation and other projects. At present, rotary drilling rigs have been widely promoted in various drilling pile projects.
At present, most rotary drilling rigs in the continental engineering community are German and Italian products and have become dominant.
The main domestic manufacturers are XCMG Machinery, Shanhe Intelligence, Sany Heavy Industry, Zoomlion and so on.
Rotary drilling rigs
2. Commonly used impact drilling rig
Rely on the vertical reciprocating movement of the drilling tool to cause the drill bit to hit the bottom of the well to break the rock formation. Its simple structure, there is no circulating well washing system, and the removal of rock chips cannot be carried out at the same time as the drilling rig, so the effect is low. There are two main types:
(1) Punching and grasping cone. The weight of the drill tool itself is used to impact the formation. The lower end of the drill tool is several sharp angled grab lobes that can be opened and closed, when the drill tool moves downward under the action of its own weight, the grab flap opens, cuts into the rock layer, and then the hoist lifts the drill tool through the wire rope, and the grab flap grabs the rock chips into the cone during the closing process, and the wellhead is lifted to unload the chips. The drilling depth is usually 40 to 50 meters, and the maximum depth is 100 to 150 meters.
(2) Wire rope impact drilling rig. It consists of a mast and a lifting pulley mounted at the top, a wire rope, an impact mechanism, a drilling tool, and an electric motor. During operation, the motor drives the impact mechanism through the transmission device, drives the wire rope to make the drill tool make a reciprocating movement up and down, and when it moves downward, it cuts into and breaks the rock layer by the weight of the drill itself, and the upward movement is pulled by the wire rope. The impact frequency is 30 to 60 times/min.
Impact drills
3. Commonly used cyclotron drilling rig
(1) Circulating mud washing turntable drilling rig. It consists of towers, hoists, turntables, drilling tools, mud pumps, faucets and electric motors. During operation, the power machine drives the turntable through the transmission device, and the active drill pipe drives the drill bit to rotate the crushing rock formation. There are two kinds of cycles: positive and negative. When the positive circulation drilling rig is working, the bottom rock chips are taken out of the wellhead through the circular channel outside the drill pipe, and after sedimentation in the sedimentation tank, the mud flows back to the mud pool for recycling. When the reverse circulation drilling rig is working, the mud flows into the bottom of the well from the wellhead after sedimentation in the sedimentation tank, and the mud carrying the rock chips is sucked out of the well by the sand and gravel pump through the drill bit inlet through the drill pipe cavity and sinks back to the sedimentation tank. The drilling rig forms a high upflow rate in the drill pipe, the ability to discharge rock chips and pebbles is strong, the drilling speed is fast, and it is suitable for loose formations with soil layers, sand layers and pebble diameters smaller than the inner diameter of the drill pipe.
(2) Pressure gas washing well turntable drilling rig. On the rotary rotary rig, the mud pump is replaced by an air compressor and the mud well is washed with compressed air. It is usually used in a reverse cycle, also known as a gas lift counter-cycle. It is suitable for arid areas with large well depths and water shortages and cold permafrost layers.
Boomerang rig
The working principle of the positive circulation drill rig (as shown in the figure below). The drilling rig is driven by the motor to drive the drill pipe, the drill bit rotates the drill hole, and at the same time starts the mud pump to apply pressure to the mud in the mud pool to pass through the hose, lift the faucet, the hollow drill pipe, and finally sprays out from the lower sides of the drill bit, washes the bottom of the hole, and the slag mixed with the mud rises along the hole wall and discharges through the orifice and flows into the circulation pool. After the slag is deposited, the cleaner mud flows back to the mud pool, thus forming a working cycle.
The duty cycle of the reverse circulation drilling rig (as shown in the figure below). The working mud circulation of this type of drilling rig is opposite to the direction of positive circulation, and the mud with debris enters the mud pump through the drill bit, hollow drill pipe, the water lifting head and hose, and then discharges from the gate valve of the pump into the mud pool, and then the mud flows into the hole well after precipitation.
4. Car crane
Automobile crane is mainly used for rebar cage hoisting, drilling rig displacement, concrete conduit lowering and other material hoisting; mainly according to the weight of the reinforcement cage and the actual lifting conditions on site.
5. Mud pump
6. Other equipment
Excavators, welding machines, butt welding machines, etc.
Third, the drilling and pouring pile construction process
1. Construction preparation
Drilling and pouring pile is an underground hidden project with high quality requirements, many construction processes, and continuous completion in a short period of time. To ensure that the construction is carried out in an orderly and fast-paced manner, it is necessary to make technical preparations, on-site preparations, labor preparations, mechanical equipment preparations, and material preparations before the start of construction.
1) Technical preparation
Drawing triage, survey intersection, construction organization design preparation review, technical submission;
Selection of construction methods and mechanical equipment according to geological data;
2) On-site work preparation
Site leveling, construction road planning and formation, steel processing site and transport road formation, mud pond, mud ditch layout and implementation, slag disposal site layout and setting, water and electricity layout and formation.
2. Measurement and positioning
The measurement control network is arranged according to the floor plan provided by the owner and the axis layout of each unit project.
The measurement control points, elevation reference points and other key parts handed over by the owner are key protection and identification, and the detailed text information is listed for the record.
The instruments used for pile position measurement and elevation measurement are total stations, levels and tower rulers.
According to the measurement control network provided by the owner, the total station measurement and discharge is adopted. Before the pile position is measured and released, the coordinates of each control point and pile position should be calculated according to the construction drawing and the coordinate system of the site area, and after review, fill in the "Construction Pile Position Coordinate List" for use when measuring and releasing the pile position.
Construction of piles that have not been experienced is strictly prohibited.
3. The protective cylinder is buried
(1) The sheath cylinder is generally made of steel plate, the thickness of the steel plate depending on the size of the hole diameter is 4 to 8mm, the inner diameter of the sheath should be larger than the pile diameter (rotary drilling rig is greater than 200mm, impact drilling rig is greater than 400mm), and the upper part should open 1 to 2 overflow holes.
(2) Under normal circumstances, the burial depth of the protective cylinder should not be less than lm in the clay soil; it should not be less than 1.5m in the sand soil; its height should still meet the requirements of the height of the mud surface in the hole. The soft soil layer such as silt should increase the depth of the protective cylinder; the top surface of the protective cylinder should be 500mm higher than the ground, and the construction water level and groundwater level should be 2000mmm higher.
(3) The protective cylinder in dryland and island construction can be excavated and buried, and the bottom and surrounding of the protective cylinder can be backfilled with clay soil and layered compaction; the water protection cylinder setting should strictly pay attention to the plane position, vertical tilt, and the protective cylinder sinking can be used to take the soil in the protective cylinder.
(4) After the cylinder is buried, the vertical line in the center of the cylinder should coincide with the center of the pile, unless otherwise specified in the design, the allowable error of the plane is 50mm, and the vertical line tilt is not more than 1%.
(5) The connection of the protective cylinder requires that there is no protrusion in the cylinder, and it should be tensile, compressive and non-leaking. The height and depth of the protective cylinder should be appropriately adjusted according to the impact of the rise and fall of the groundwater level, and if necessary, it should be penetrated into the impermeable layer.
4. Modulation of wall mud
(1) The wall mud is generally made of water, clay (or bentonite) and additives in a certain proportion, and can be mixed evenly through machinery in the mud pool and drilling.
(2) The configuration of the mud should be determined according to the engineering geology of the drilling hole, the hole position, the performance of the drilling rig, the circulation mode, etc.
5. Drilling construction
(1) General requirements
1) Before drilling, according to the engineering geological data and design data, the appropriate type and model of drilling rig should be used, and equipped with suitable drill bits to mix suitable mud.
2) Before the drilling rig is in place, the construction machinery should be adjusted and the preparation of the drilling should be inspected.
3) When the drilling rig is in place, measures should be taken to ensure that the center of the drill tool and the center of the guard cylinder coincide, and the deviation should not be greater than 20mm. After the drilling rig is in place, it should be flat and stable, and measures should be taken to fix it to ensure that there is no displacement and shaking during the drilling process, otherwise it should be dealt with in time.
4) The drilling operation should be carried out continuously in shifts, carefully fill in the drilling construction records, and the drilling situation and the next shift precautions should be explained when the shift is handed over. Drilling mud should be inspected and tested frequently, and should be corrected at any time when it does not meet the requirements. Changes in soil layers should be paid constant attention to, and slag samples should be taken at changes in soil layers, recorded in the record table after identification, and checked with geological profiles.
5) When drilling, it should be drilled slowly within a certain range under the protective cylinder, and the drilling can be accelerated after the guiding part or drill bit has all entered the soil layer.
6) When drilling, slag discharge or stopping drilling due to failure, the hole should always maintain the specified water level and the required relative density and viscosity of the mud.
(2) Rotary drilling rig into a hole
1) Rotary drilling rig is suitable for drilling piles of various diameters and various soil layers, and attention should be paid to controlling the drilling speed when forming holes, using decompression drilling to ensure the verticality of the holes, and adjust the relative density and viscosity of the mud according to the changes in the soil layer.
2) In clay, sandy soil into the hole should be used to use the tooth drill, the angle of the wing plate according to the soft and hard soil layer between 30 ° and 60 °, the number of knife bits according to the soft and hard arrangement of the soil layer, pay attention to stagger each other, to protect the knife holder. When making holes in pebble and gravel layers, flat-bottom wedge hob drills should be used, and flat-bottomed ball tooth hob drills should be used when making holes in harder rocks.
3) Piles with a depth of less than 30m can be used to form holes in positive circulation, piles with a depth of 30 to 50 meters should be recirculated by sand and gravel pumps, and piles with a depth of more than 50m should be used to reverse cycle into holes.
4) For piles with a large inclination angle of the soil layer and a hole depth greater than 50m, a guide device should be added to the drill bit and drill pipe to ensure the verticality of the hole.
5) The relative density of mud should be appropriately increased when drilling in silt and sandy soil; the relative density of mud should be increased when drilling in pebbles and gravel to improve the ability to carry slag; and water drilling can be used when drilling in dense clay.
6) When making holes in pebbles, gravel and rock formations, the weight of the drill tool should be increased, that is, the counterweight should be increased.
(3) Impact drilling machine into holes
1) When opening the hole, the low hammer should be struck, and when the topsoil is a weak soil layer such as silt and fine sand, it can be added to the clay block and small stone pieces to repeatedly impact the wall;
2) When forming a hole within 2m below the blade of the protective cylinder, a small stroke lm is used to improve the relative density of the mud, and the soft layer can add clay blocks to clip small stones;
3) When forming holes in sandy soil and sand layer, the medium stroke is 2~3m, and the relative density of mud is 1.2~1.4, and clay can be put into the hole;
4) When forming holes in the dense clay layer, a small stroke of 1 to 2m is used, and clear water and thin mud are pumped, and anti-stick drilling can be put into gravel and bricks;
5) When forming holes in the sand pebble layer, the medium and high stroke is 2~4m, and the relative density of mud is 1.2~1.3, and clay can be put into the hole;
6) When the weak soil layer or collapsed hole is backfilled and re-drilled, the small stroke lm is used, and the clay block is sandwiched with small stone pieces to repeatedly impact, and the relative density of mud is 1.3 to 1.5;
7) When encountering a lone stone, you can use pre-explosion or alternating high and low stroke impact to crush the lone stone and squeeze it into the hole wall.
(4) Precautions during drilling
1) When drilling, you should always pay attention to the firmness of the connection between the drill tool and the drill bit, the wear of the wire rope, etc. If there is any abnormality, it should be dealt with in time.
2) Large diameter pile holes can be graded into holes, and in general, the diameter of the first stage of holes is 0.6 to 0.8 times the diameter of the design pile.
3) In the process of drilling, there is a drill pipe beating, frame shaking, drilling does not enter the ruler and other abnormal situations, should be stopped immediately to check, troubleshooting; such as drill pipe or drill bit does not meet the requirements, should be replaced in time, after the test drill reaches normal, can be drilled.
4) After the drilling is completed, the concrete should be poured in time, or the orifice should be covered in time, and the traffic and pedestrians on the cover board should be prevented; the virtual soil should be cleaned up in time during the drilling process, and the soil at the mouth of the hole should be cleaned up in advance.
5) In the process of drilling into the hole, we should always pay attention to the changes in the soil layer, adjust the mud performance, and adopt a reasonable approach to ensure that the hole does not collapse and does not shrink the neck.
6. Clear the holes
(1) The hole clearance is carried out in two stages, the drilling depth meets the design requirements, the hole depth, hole diameter, perpendicularity of the hole, etc. are checked, and the first hole clearance is carried out after meeting the requirements; the steel skeleton and catheter are placed, and the second clearance should be carried out before the concrete pouring.
(2) According to the design requirements, the construction machinery adopts the methods of slurry exchange, pulp extraction, suction sludge, slag extraction, etc., and the second clearing of the hole is carried out according to the pore diameter, hole depth, design requirements of positive circulation, pump suction reverse cycle, gas lift reverse cycle and other methods.
(3) The sediment thickness and mud performance indicators after the second clearance should meet the design requirements, and generally should meet the following requirements; the sediment thickness friction pile ≤ 300mm, the end bearing pile ≤ 50mm, the friction end bearing or end bearing friction pile ≤ 100mm; the mud performance index before pouring concrete, the relative density within 500mm of the hole bottom ≤ 1.25, the viscosity ≤ 28s, and the sand content ≤8%.
(4) No matter what kind of hole clearing method is used, when clearing the hole and discharging slag, attention must be paid to maintaining the water head in the hole to prevent the hole from collapsing.
7. Production and installation of steel skeleton
(1) The production of the steel skeleton should meet the design and specification requirements.
(2) The long pile skeleton should be made in sections, and the length of the section should be determined according to the lifting conditions and the total length calculation, and it should be ensured that the steel skeleton is not deformed when moving and lifting, and the joints of the adjacent two sections of the steel skeleton need to be staggered according to the requirements of the relevant specifications.
(3) The outer side of the steel skeleton should be set up to control the thickness of the protective layer of the pad block, can be used with the same strength as the pile body concrete concrete concrete or welded with steel bar on the vertical main rib, the spacing is 2m vertically, the transverse circumference shall not be less than 4 places, and evenly arranged. A lifting ring should be provided at the top of the skeleton.
(4) After the production of large-diameter steel skeleton is completed, a cross brace or triangle brace should be set on the internal reinforcement hoop to ensure that the reinforced skeleton is not deformed during storage, movement and hoisting.
(5) The skeleton into the hole is generally used with a crane, and for small diameter piles without a crane, a drill rig drill frame, a pouring tower, etc. can be used. The lifting should be numbered according to the length of the skeleton into the hole, and measures should be taken to ensure that the skeleton is not deformed during the lifting process.
(6) When handling and hoisting, deformation should be prevented, and the placement should be aligned with the hole position to avoid collision with the hole wall, and it should be fixed immediately after being in place. When the steel skeleton crane is placed in the hole, it should be centered to prevent collision with the hole wall, and the steel skeleton crane should be placed in the hole so that its position meets the design and specification requirements, and to ensure that no displacement occurs during the placement of catheters, hole clearance and concrete pouring.
8. Concrete infusion
(1) The supply capacity of the concrete mixture when pouring underwater concrete should meet the filling of the pile hole within the specified time; The concrete pouring time shall not be longer than the initial setting time of the first batch of concrete.
(2) Concrete transportation should be selected concrete pump or concrete mixer transporter; when the transportation distance is less than 200m, it can be transported by motorized dump truck or other tight and solid, non-leakage, non-absorbent, easy to load and unload tools, and it is necessary to ensure that the concrete is not separated, has good ease and fluidity.
(3) The pouring underwater concrete is generally constructed by the steel conduit re-top method, the inner diameter of the conduit is 200 ~ 250mm, depending on the size of the pile diameter, the wall thickness is not less than 3mm; the diameter production deviation should not exceed 2mm; the wire buckle or flange connection is used between the conduit interfaces, and the gasket or rubber pad must be added when connecting, and the wire buckle or bolt is tightened. Before the use of the catheter, the watertight pressure and the joint tensile test (the test water pressure is generally 0.6 ~ 1.0 MPa) should be carried out to ensure the sealing of the catheter mouth. Before the catheter is placed, the hole depth and the total length of the catheter should be calculated, the length of the first catheter is generally 4 to 6m, the standard section is generally 2 to 3m, and 2 to 3 short sections of 0.5-1.0 m can be placed in the upper part to adjust the total length of the catheter. When the catheter is placed, it should be ensured that the position of the catheter in the hole should be centered to prevent collision with the steel skeleton.
(4) Technical requirements for pouring underwater concrete
1) When the concrete begins to be poured, the sealing plug under the funnel can be prefabricated concrete stopper, wooden stopper or inflatable bladder.
2) When the concrete is transported to the pouring site, its uniformity and slump degree should be checked, and if it does not meet the requirements, it should be mixed for a second time, and it should not be used when it still does not meet the requirements after the second mixing.
3) After the second clearance is completed, the underwater concrete should be poured immediately after passing the inspection, and the time interval should not be greater than 30min.
4) After the first batch of concrete infusion, the concrete should be continuously poured, and it is strictly forbidden to stop halfway.
5) In the process of perfusion, the position of the concrete surface in the well hole should be measured frequently, and the depth of the catheter burial should be adjusted in time, and the burial depth of the catheter should be controlled at 2 to 6m. It is strictly forbidden for the conduit to propose the concrete surface, and it is necessary to have a special person to measure the depth of the conduit and the height difference between the concrete surface inside and outside the pipe, and fill in the underwater concrete pouring record.
6) In the process of perfusion, you should always pay attention to observing the return of mud in the hole, listen to the sound of concrete falling in the catheter, and take corresponding treatment measures if there is any abnormality.
7) In the perfusion process, the catheter should be channeled up and down within a certain range to prevent the concrete from solidifying and increase the perfusion speed.
8) In order to prevent the steel skeleton from floating, when the top surface of the infused concrete is about lm from the bottom of the steel skeleton, the infusion speed of the concrete should be reduced, and when the concrete mixture rises to more than 4m of the bottom of the skeleton, the catheter is lifted so that the bottom mouth is higher than the bottom of the skeleton by more than 2m, and the normal perfusion speed can be restored.
9) The height of the pile top of the pouring pile should be higher than the design, generally 0.5 to 1.0m, to ensure the strength of the pile head concrete, the excess part must be chiseled before the pile is connected, and the pile head should have no loose layer.
10) Near the end of the infusion, the amount of concrete poured should be checked to ensure that the measured concrete infusion height is correct.
Fourth, the construction layout
The construction site should be leveled before the equipment enters the site; water, electricity, and construction vehicles should be laid in and out of the road; planned and arranged according to the needs of holes, filling, making steel cages, stacking concrete materials, temporary storage of waste water residue, storage of materials and tools, and construction of temporary facilities on the construction site.
Due to the large amount of waste slurry sewage and slurry-containing drilling slag generated during the construction process, a little careless management will flow around, making the work site muddy, affecting the passage of personnel and vehicles and the removal of equipment and equipment, polluting construction materials, and polluting the surrounding environment. Therefore, the preparation of the work site should consider the possibility of mud on the site, in addition to appropriately increasing the size and volume of the circulation system, it is also necessary to arrange a number of waste slurry drilling slag removal channels, if necessary, the passage can be laid with crushed stone slag and fully compacted or spare steel plates, on both sides of the channel and other low-lying water-prone places in the site to dig drainage ditches and pools, and often dredging to prevent sewage overflow.
After the site is delivered according to the requirements of "three links and one level", the site is considered according to the overall layout of the construction plan, the mud circulation system is reasonably arranged, and the material stacking is reasonable and convenient, neat and orderly, that is, it is necessary to take into account the convenience of material access and take care of the convenience of construction operation.
Fifth, quality standards and control points
(PS: Please consult the new version of the specification by yourself, mainly the new specification)
(1) Reinforcement cage quality inspection standard (mm)
(2) Concrete pouring pile construction quality inspection standard (mm)
Concrete Pouring Quality Inspection Standard (mm)
(3) Allowable deviation of concrete pouring pile pile position (mm)
1, the quality of construction machinery plays a vital role in ensuring the quality of construction, and choosing a good and suitable construction tool is the premise of quality control.
2, the pile machine in place first of all to ensure the accuracy of the engineering pile, for this reason, in addition to the comprehensive measurement of the engineering pile, but also in the pile machine in place when the retest engineering pile, and take different stations for review, in the case of possible, the application of steel rulers to the front and rear of the adjacent pile position for mutual verification. Pile position control in the construction of perfusion piles must be paid great attention to, and it will be difficult to make up for errors once they occur.
3, the basic requirements of the pile machine in place is accurate plane position, the pile machine is horizontal and stable, after installation in place to use the level ruler and measuring hammer calibration, due to the large vibration in the punching process, often because the pile machine is not solid and tilted, biased, therefore, in the punching process should still be timed or irregular review of whether the wire rope coincides with the center of the pile position, so that the perpendicularity of the pile and the pile position are guaranteed.
4, punching pile is by mud wall, to prevent collapse holes, the use of mud circulation to clear the hole slag, mud specific gravity and viscosity is the two most intuitive, the proportion of mud is too small to protect the wall, easy to collapse holes; the proportion of mud is too large will affect the progress of punching and the wall film is too thick, therefore, the correct control of the proportion of mud is an important part of the smooth construction of the hole and the quality assurance. In the construction process of punching and pouring piles, the specific gravity of mud is used to prevent the occurrence of reaming and collapsing holes according to different soil layers, so as to ensure the quality of the project.
5, the punching process, the amount of mud circulation should be adjusted according to the formation and the speed of the ruler, if the speed of the ruler is fast and the circulation amount is small, the mud must be viscous and the mud mass sediment is more, affecting the quality of the hole; if the circulation amount is large in the soft formation, it will cause the expansion of the diameter or even collapse of the hole. At the end of the hole, the hole depth, hole diameter and whether the pile hole reached the holding layer need to be checked to meet the design and specification requirements before the final hole.
6, punching pile is part of the squeezed soil into the hole method, should implement the principle of jumping, to prevent the pile load and punching caused by the stress release and affect the quality of the concrete just poured concrete, when it is impossible to adjust the avoidance, should be at least until the concrete pouring is completed for 72 hours before the adjacent pile construction.
7, the punching process, the amount of mud circulation should be adjusted according to the formation and the speed of the ruler, if the speed of the ruler is fast and the circulation amount is small, the mud must be viscous and the mud block sediment is more, affecting the quality of the hole; if the circulation amount is large in the soft formation, it will cause the expansion of the diameter or even collapse holes. At the end of the hole, the hole depth, hole diameter and whether the pile hole reached the holding layer need to be checked to meet the design and specification requirements before the final hole.
8. The technical performance requirements of the mud before concrete pouring are usually used to achieve the secondary clearing hole.
The first clearance is performed when punching the hole to the holding layer and entering the holding layer to reach the design depth requirements. The first clear hole is the basis of whether the technical requirements can be met, can not because there is a second clear hole and ignore the importance of the first clear hole, because the first clear hole suction is large, the ability to clear the hole is strong, can suck most of the sediment out of the hole; and the second clear hole is after the completion of the steel cage and the catheter, the use of the catheter for the hole clearance, the suction force is much smaller, the purpose is to remove the sediment that precipitates to the bottom of the hole or is hit by the steel cage in the process of the lower steel cage and the catheter. During the hole clearing process, the water head in the hole must be maintained to prevent the hole from collapsing.
9. The technical requirements for the production of steel cages are mainly:
(1) The diameter of the reinforcement cage should conform to the design size;
(2) The length of each section should not exceed 9 meters, nor should it be shorter than 5 meters, because if it is too long, it is easy to bend and deform when lifting, and if it is too short, it will increase the welding time, which is not good for the quality of the pile;
(3) When using a flange joint conduit, the stiffening hoop should be set on the outside of the main rib, the main rib generally does not have a bending hook, and the bending hook set according to the process requirements shall not be exposed inward, so as to prevent the catheter hook from causing the steel cage to float;
(4) The made steel cage should be stacked flat on a flat and clean site, and the height should not exceed two layers.
(5) The reinforcement cage should be hoisted section by section, orifice welding, and the main reinforcement welding method of the reinforcement cage is vertical welding, and the welding personnel are required to have a fairly high level of welding technology to ensure the welding quality.
(6) The steel cage should be speeded during the next cage, and the general pile hole should be completed within 2-4 hours.
10. Requirements for underwater concrete pouring
First of all, the strength grade of the concrete must meet the design requirements, in addition, according to the characteristics of the pouring pile, the underwater concrete also needs to be controlled: (1) initial condensation time: This indicator is very important for the pouring pile, and the initial condensation time provided by the general requirement is twice that of the actual pouring time, otherwise it is easy to have accidents such as catheter coagulation during the pouring process. (2) Good and easyness: the sand containing rate should be 40-45, and should be selected in the coarse sand, the maximum particle size of the coarse aggregate should be less than 40MM, when conditions can be used secondary, the slump degree is required between 180-220MM, when the slump is small, it is easy to block the catheter, and the slump is easy to occur when the slump is large.
The above technical requirements should be specified in the concrete supply contract.
(1) Before underwater concrete pouring, the sediment thickness and mud technical performance indicators of the pile bottom should be checked, and if it does not meet the requirements, the hole should be cleared again.
(2) When starting to pour concrete, in order to make the water insulation plug can be discharged smoothly, the distance from the bottom of the catheter to the bottom of the hole should be 300-500MM, and there should be enough concrete reserves, so that the conduit is buried in the concrete surface at a time below the standard of 0.8M or more, when the concrete is poured into the orifice and no longer returns the mud, indicating that the concrete pressure has been equal to or less than the resistance of its jacking in the pile, at this time the catheter should be lifted If it is necessary to increase 0.5-1.0M or more to pour concrete, some catheters should be removed at this time to reduce the depth of the conduit in the concrete, so that the power is greater than the resistance.
(3) The depth of the catheter burial should be 2-6M, the burial depth of the catheter is too large or too small is unfavorable, the burial depth is too large and easy to occur the pile breaking accident of the concrete condensing the conduit, the burial depth is too shallow and easy to flush the top surface of the concrete in the hole and the sediment mud is involved, resulting in mud to break the pile, and it is also easy to cause the accident of pulling the catheter out of concrete. Therefore, it should be done diligently and diligently, and there can be no situation of dismantling more than ten meters at a time.
(4) Control the amount of the last pouring, the pile top must not be low, and the pile top concrete must be ensured to reach the strength design value after the slurry height is removed.
(5) Underwater concrete must be continuously constructed each pile pouring time according to the initial condensation time of the initial concrete, do a good job of construction records, and record all faults in the pouring process.
Sixth, quality common diseases and prevention and control measures
7. Post management responsibilities during the construction of pile foundation projects
1. Technician management responsibilities
(1) Inspect the implementation of the construction plan during the construction process;
(2) Communicate with the foreman and quality inspector in time during the construction process, and communicate with the design institute in time to solve the design problems found.
2. Foreman management responsibilities
(1) The on-site foreman organizes the construction personnel to inspect the burial of the drilled pile guard cylinder, and the burial of the guard cylinder must meet the relevant technical requirements;
(2) After the pile is drilled, the on-site foreman is responsible for truthfully filling in the drilling record.
(3) After the pile is drilled, the foreman first organizes the construction team to conduct self-inspection and fill in the relevant acceptance forms, and after the self-inspection is qualified, the quality inspector will re-inspect, and after passing, the acceptance form will be submitted to the supervision for acceptance;
(4) Self-inspection content and requirements: (1) the drilling depth should meet the design requirements, (2) the mud index mud index is all qualified before the drilling rig can be lifted, and then check the sediment thickness, drilling diameter and verticality, the sediment thickness should be less than 20cm, the drilling diameter should not be less than the design pile diameter, the verticality is less than 1%;
(5) After passing the inspection of the pile hole, the steel cage should be installed in time, and the suspension time shall not be too long, and when the suspension time is too long, the sediment thickness should be re-inspected;
(6) The production of the reinforcement cage should meet the design and specification requirements, the variety, specification, model and quantity of the steel bar must meet the design requirements, and the thickness of the main rib protective layer is 50mm;
(7) The pile reinforcement cage should be hoisted into the hole immediately before the concrete pouring, and the reinforcement cage should be hoisted to ensure that it is not deformed, and the joints should be staggered according to regulations;
(8) After the completion of the construction of the reinforcement cage, the foreman first organizes the construction team to conduct self-inspection and fill in the relevant acceptance forms, and the quality inspector will re-inspect after passing the self-inspection, and submit the acceptance form to the supervision for acceptance after passing, and the allowable deviation of the steel cage production is: the spacing between the main ribs ± 10mm; The spacing of the stirrups ± 20mm, the outer diameter of the skeleton ± 10mm, and the verticality of the skeleton ±1%;
(9) After the reinforcement cage is lowered, check the central position and elevation of the reinforcement cage, the center deviation is less than 2cm, and the cage top elevation deviation is less than +2cm;
(10) After the steel cage is put down, the catheter should be installed in time for secondary clearance, the mud index of the secondary clearance hole should meet the requirements of the specification, the mud discharged from the hole is not 2-3mm particles by hand, the specific gravity of the mud is not more than 1.1, the sand content is <2%, the viscosity is 17-20s, the PH value > 6.5, and the concrete pouring can be carried out when the sediment thickness at the bottom of the hole should be less than 20cm;
(11) When pouring concrete, the first irrigation must ensure that the depth of the catheter is not less than 1m, and not more than 3m, and the depth of the pipe burial during the pouring process is not less than 1m, not more than 3m, and the pile is broken during the construction process;
(12) The height of the pile top shall not be less than 0.5m to ensure the strength of the concrete.
3. The management responsibilities of the tester in the construction process
(1) The reinforcement welded joint must be witnessed and sampled according to the requirements of the specification, and the quality of the reinforcement joint must meet the specifications;
(2) The steel bar raw materials must all be inspected and qualified to meet the requirements of the specification;
(3) The raw materials used in concrete must all be inspected and qualified, and the quality meets the requirements of the specification;
(4) During the process of concrete pouring, the quality of concrete should be checked, and the slump degree of concrete and the mold temperature of concrete (slump degree is 18-22cm, the mold temperature of concrete is 5-35 °C) and a record is formed;
(5) Each pile should be randomly sampled at the pouring site, and the concrete test block should not be less than 1 group, and the supervision unit should witness the sampling or parallel sampling;
(6) Provide material inspection information to the foreman and quality inspector in time, including copies of inspection reports such as steel bar raw materials, welded joints, concrete raw materials and concrete test blocks, to ensure that the materials used on the site are qualified and the information is filled in correctly.
4. Management responsibilities of quality inspectors in the construction process of pile foundation
(1) In strict accordance with the specifications and design requirements, the quality inspector supervises the whole process management of the pile foundation, and reviews and signs various quality record forms such as inspection batches, inspection certificates and quality tables, and submits them to the supervision company in a timely manner;
(2) The quality inspector supervises the construction of the pile foundation in strict accordance with the construction to ensure that the construction is carried out normally and orderly;
(3) Timely reflect the problems raised by the supervision to the relevant departments, and supervise the implementation of rectification, and do a good job of communication with the supervision unit;
(4) After passing the self-inspection of each inspection batch, report to the supervision unit for inspection in time, and organize the foreman and construction personnel to participate in the acceptance;
(5) During the construction of the pile foundation, the quality inspector shall send the problem in writing (rectification notice) to the foreman, and the foreman shall complete the rectification within the time specified in the notice and reply in writing after receiving the written notice.
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