What are the technical specifications for bored pile construction? The following Zhongda Consulting brings technical specifications for bored pile construction. The specific content is for reference only.
1 The preparation work for bored pile construction should comply with the following regulations:
1) When the drilling site is on dry land, debris should be removed and the soft soil should be leveled and compacted. The site is located on a steep slope. Sometimes, sleeper steel, etc. can also be used to set up a working platform
2) In shallow water, it is appropriate to use the island cofferdam method for construction. The area of ??the island should be determined according to the drilling method, equipment size, etc.
3) When the drilling site is in deep water or the silt is thick, a working platform can be set up for construction. The platform must be strong and stable and can withstand all static and live loads during construction operations. At the same time, the safety of construction equipment should be considered. Enter and exit. If the water flow is stable, the drilling rig can be set up on the ship or pontoon for drilling operations, but the anchor must be stable to ensure accurate pile positioning.
4) When drilling using the rotary method or impact method, a mud circulation purification system needs to be installed, which should be considered when planning the construction site or working platform.
5) A strong and watertight hole guard should be installed before drilling. The inner diameter of the casing should be larger than the diameter of the drill bit. When using a rotary drill, the hole diameter should be about 20cm larger than the drill bit. When using an impact drill, the hole diameter should be about 40cm larger than the drill bit. The top surface of the casing should be 2m higher than the construction water level or underground water level. It should also meet the height requirements of the mud surface in the hole. When building on dry land or island, it should be 0.5m higher than the construction ground.
The burial depth of the casing should comply with the following regulations:
(1) On the beach, the clay soil should not be less than 1m, and the sandy soil should not be less than 2m. When the surface soil is soft, the casing should be buried at least 0.5m into the harder and denser soil layer. When the casing is buried on the beach, clay should be backfilled around the casing and compacted in layers. The casing can be sunk by methods such as hammering, pressurization and vibration.
(2) When building an island in the water, the casing should be buried 1m below the river bed surface; on the underwater platform, the burial depth can be determined according to factors such as the maximum construction water level, flow rate, erosion and geological conditions, and if necessary, it should be driven into an impermeable layer. When sinking the casing on the underwater platform, there should be guiding equipment to control the position of the casing.
(3) The deviation between the center of the top surface of the casing and the designed pile position shall not be greater than 5cm, and the inclination shall not be greater than 1%.
2 When drilling in sandy soil, gravel soil or clay interlayer, bentonite mud should be used to protect the wall. When drilling holes in clayey soil, when the plasticity index is greater than 15 and the floating ballast capacity meets the construction requirements, the original soil in the hole can be used to make slurry to protect the wall. When drilling with an impact drill, the clay can be processed and put into the hole, and the drill bit can be used to impact and make slurry.
Mud performance indicators should be determined according to the drilling method and geological conditions, and should comply with the following regulations: Mud proportion: For a positive circulation rotary drilling rig, the entry mud proportion is 1.1 to 1.3; for impact drilling rigs, solid drill bits are used for drilling. The specific gravity of the mud at the bottom of the hole should not be greater than: 1.3 for sand and clay; 1.4 for large boulder and pebble layer; and 1.2 for rock. The specific gravity of the entry mud of a reverse circulation rotary drilling rig can be 1.05 to 1.15.
Viscosity: 16-22s for general formations, 19-28s for loose and slump-prone formations.
Sand content: Newly prepared mud shall not exceed 4%.
Colloid rate: not less than 95%.
PH value: should be greater than 6.5.
In order to increase the viscosity and colloid ratio of the mud, an appropriate amount of sodium carbonate, caustic soda, etc. can be added to the mud, and the amount should be determined through testing. All performance indicators should be tested after slurry making. The specific gravity and sand content of the mud should be checked at any time during the drilling process, and the mud test record form should be filled in.
3 Drilling construction
1) Drilling rig installation and drilling:
(1) Before installing the drilling rig, the bottom frame should be leveled and kept stable. Produce displacement and subsidence. The top of the drilling rig should be tightened symmetrically by the wind rope, and the deviation between the center of the drill bit or drill pipe and the center of the casing should not be greater than 5cm.
(2) No matter which method is used for drilling, the hole position must be accurate, and the initial hole wall should be vertical, round and solid.
(3) When drilling shore piles, the mud level in the hole should be more than 0.5m higher than the bottom of the casing or 1.5-2.0m above the groundwater level. When constructing beach piles, it must be higher than the ground outside the hole. 0.5m or more. When constructing piles in water, the mud surface elevation in the hole should be 0.5m or more higher than the highest tide level in any case. After removing slag and stopping drilling during impact drilling, water or mud should be replenished in the hole in time to maintain the height of the water head in the hole and the specific gravity and viscosity of the mud.
(4) When drilling, the speed of lifting and lowering the drill bit should be uniform, and the speed should not be too sharp or change suddenly. The soil excavated from the hole should not be accumulated around the drill hole.
(5) Drilling operations should be carried out continuously. When drilling is stopped for any reason, the drilling rig with drill pipe should lift the drill bit more than 5m from the bottom of the hole. Other drilling rigs should lift the drill bit out of the hole, and the hole opening should be Add protective cover. During the drilling process, soil layer changes should be frequently checked and recorded, and checked with the geological profile. After the drilling reaches the designed depth, the hole location, hole diameter, hole depth and hole shape should be inspected, and the drilling record form should be filled out. The hole position deviation shall not be greater than 10cm.
2) Impact drilling
(1) Cross-shaped drill bits are suitable for gravel soil and rock layers; tubular drill bits are suitable for sand, clay, sand and gravel layers. When drilling by impact method, the weight of the drill bit should take into account the adsorption effect of the mud and the weight of the wire rope and spreader, so that the total weight does not exceed the lifting capacity of the winch.
(2) When starting drilling, a small stroke should be used to open the hole. Normal impact drilling can only be carried out after the drilling depth exceeds the total height of the drill bit plus the normal stroke. During the drilling process, the rope should be loosened frequently and in an appropriate amount, and the hammer should not be hit empty; the ballast should be removed frequently so that the drill bit often hits the fresh formation. The amount of loose rope each time should be determined according to the geological conditions, drill bit form and drill bit weight.
(3) The steel wire rope used to hang the drill bit must be twisted in the same direction, soft and high-quality, without dead bends or broken wires, and the safety factor should not be less than 12. A steering device must be installed between the wire rope and the drill bit and the connection must be firm. During the drilling process, its status and rotation should be checked frequently to ensure normal and flexible rotation. When the main rope and the wire rope of the drill bit are overlapped, the diameters of the two ropes should be the same and the twisting directions must be consistent.
(4) There should be spare drill bits at the drilling site. If the diameter of the drilling bit is found to be worn by more than 15mm, it should be replaced and repaired in time. Before replacing a new drill bit, check the hole to the bottom and confirm that the drilling is normal before inserting a new drill bit.
(5) In order to prevent the wall of the adjacent hole from collapsing due to impact vibration or affecting the strength of the poured concrete in the adjacent hole, drilling should be started only after the compressive strength of the concrete in the adjacent hole reaches 2.5MPa.
3) Rotary drilling:
(1) The forward and reverse circulation rotary drilling rig is suitable for clay soil, sand soil, gravel soil, and the drilling diameter and depth can be selected according to the geological conditions. Drilling rigs and drill bits. The lifting pulley of the rotating drilling rig and the clamping machine that fixes the drill pipe should be on the same vertical line to keep the drilling vertical.
(2) An appropriate amount of mud should be put into the casing before drilling. When starting drilling, it is advisable to drill at a low speed and at a slow speed. After drilling to 1m below the casing, drill at a normal speed. The drilling speed should be compatible with the mud displacement. When drilling in soil layers such as sand and soft soil that are prone to collapse, low-speed and light-pressure drilling should be used. At the same time, the water head in the hole should be increased and the mud proportion should be increased.
(3) When using a reverse circulation drilling rig to drill holes, the drill bit should be lifted about 20cm away from the bottom of the hole, and drilling can only begin after the mud circulation is smooth. During the drilling process, the water head in the casing should be maintained, and different drilling speeds, mud weights, and mud volumes should be used for different soil layers.
4) Rotary drilling rig drilling:
(1) Rotary drilling rig is suitable for construction in various soil strata, sandy soil, sand, gravel, and bedrock below medium hardness. Before construction, different types of drill bits should be selected according to different geological conditions.
(2) When drilling, the hole casing should be 20 to 30cm above the ground, and slurry should be replenished into the hole in time to maintain sufficient mud pressure. When the casing is followed during drilling, the bottom opening of the casing should be adapted to the rotary digging depth of the drill bit to ensure that over-excavation is not carried out.
(3) During the drilling operation, changes in the ground where the main machine is located and the ground where the outriggers are supported should be observed. If sinking is found, the machine should be stopped in time. When the machine is shut down for a long time for any reason, the safety hook of the casing mouth should be hung firmly.
6) Handling of abnormal drilling conditions:
(1) After a hole collapse occurs in a drilling hole, the cause and location should be identified and analyzed and processed. When the hole collapse is not serious, measures such as increasing the mud weight and increasing the head depth of the casing can be used to continue drilling; when the hole collapse is serious, backfill and re-drill the hole. When drilling with the impact method, you can throw clay blocks and small stones into the hole, and use a low hammer to squeeze the clay blocks and small stones into the hole wall to prevent the hole from collapsing.
(2) When bent holes and shrinkage holes occur during drilling, the drill bit of the rotary drilling rig can generally be lifted to the deflection and scanned repeatedly until the hole is straight. If a severely curved plum blossom hole probe occurs, a mixture of small stones or pebbles and clay should be used to backfill the deflection. After the filler has settled, drill holes again to correct the deflection.
(3) When the drill is stuck, it is not advisable to force it.
The cause and the location of the drill bit should be identified, and measures such as shaking the rope and other measures should be taken to loosen the drill bit before lifting it up.
(4) When a diamond falls out, the situation should be identified and dealt with as soon as possible.
(5) When a drill gets stuck or falls off, personnel are strictly prohibited from entering a drill hole without a casing or other protective facilities. When it is necessary to enter a borehole with protective facilities, it is necessary to confirm that there are no harmful gases in the borehole and to ensure safety measures such as anti-toxic, anti-drown and anti-burial measures are in place before entering, and a dedicated person should be responsible for on-site command.
4 Clearing holes and installing steel cages should meet the following requirements:
1) Drill holes to the design elevation, and check the verticality of the hole diameter, depth, and position to confirm that the drilling is qualified. , the hole should be cleaned immediately. The allowable sediment thickness before pouring underwater concrete should meet the design requirements. If there are no design requirements: column piles should not be larger than 5cm; friction piles should not be larger than 20cm. The following methods can be used for hole cleaning:
(1) The slag extraction method is suitable for impact or punching drilling.
(2) The mud suction method is suitable for impact drilling where the soil is dense and difficult to collapse.
(3) The pulp changing method is suitable for forward and reverse circulation rotary drilling.
2) No matter which method is used to clean the hole, clean water or fresh mud should be added to the hole in time when pumping slag or mud to maintain the water level in the hole.
3) Hole cleaning should meet the following standards: the mud discharged or extracted from the hole should be free of 2-3mm particles by hand, the mud specific gravity should not be greater than 1.1, the sand content should be less than 2%, and the viscosity should be 17-20s; pouring The sediment thickness at the bottom of the front hole of underwater concrete shall not be greater than 5cm for column piles and not greater than 20cm for friction piles. It is strictly prohibited to use the method of deepening the drilling depth instead of clearing the hole.
4) After the hole clearing reaches the standard, steel cages should be installed and underwater concrete poured. The material processing, joints and installation of the steel cage should comply with the relevant regulations of the Ministry of Railways’ current concrete and masonry construction standards. If the steel cage is hoisted into the hole and does not affect the hole cleaning, it should be hoisted before the hole is cleaned. When hoisting, be careful to prevent the hole wall from collapsing. After the steel cage is inserted into the hole, it should be positioned accurately and firmly, with the plane position deviation not greater than 10cm, and the bottom elevation deviation not greater than ±10cm. Lifting rings should be evenly installed on the upper end of the steel cage, and pads for controlling the thickness of the protective layer of steel bars should be symmetrically placed on the outside of the steel cage. Before pouring underwater concrete for column piles, spray water or air to the bottom of the drilled hole for 3 to 5 minutes to stir up the sediment at the bottom of the hole. The pressure of the water or air jet should be 0.05MPa greater than the pressure at the bottom of the hole.
5 Underwater concrete conduits should comply with the following regulations:
1) The inner wall of the steel conduit should be smooth and round, the inner diameter should be consistent, and the interfaces should be tight. The diameter of the conduit should be adapted to the pile diameter and concrete pouring speed, and can be 20 to 30cm. The length of the conduit pipe sections, the middle section should be 2m long, the bottom section can be 4m, and 1m long conduit should be used under the funnel.
2) The catheter should be trial assembled and pressure tested before use, and should be numbered and marked in order from bottom to top. The axis deviation of the conduit after assembly should not exceed 0.5% of the drilling depth and should not be greater than 10cm. The nuts of the connecting bolts should be on top when connecting; the pressure test pressure should be 1.5 times the hydrostatic pressure at the bottom of the hole.
3) The length of the conduit should be determined according to the depth of the hole and the height of the working platform. The distance between the bottom of the funnel and the upper mouth of the drill hole should be greater than the length of one section of the intermediate pipe. The conduit joint flange should be equipped with a tapered loop, and there should be no flange at the lower end of the bottom section of the conduit. Spiral threaded joints can be used when conditions permit, but an anti-loosening device must be provided.
4) The conduit should be located in the center of the drill hole, and a lifting test should be conducted before pouring concrete. The capacity of the conduit hoisting and lifting equipment should be compatible with the total weight and frictional resistance of all conduits filled with concrete, and there should be a certain safety reserve.
6 Underwater concrete pouring, in addition to complying with the relevant provisions of the Ministry of Railways’ current concrete and masonry-related construction standards, should also comply with the following provisions:
1) Initial inventory of concrete It should be met that after the first batch of concrete is put into the hole, the depth of the conduit buried in the concrete should not be less than 1m and should not be greater than 3m; when the pile body is long, the depth of the conduit buried in the concrete can be appropriately increased. A tight and reliable water isolation device must be installed at the bottom of the funnel. The device must have good water isolation performance and be able to drain smoothly.
2) Underwater concrete should be poured continuously without stopping in the middle. And the interval time for removing the conduit should be shortened as much as possible. The pouring time of each pile should not be too long and should be completed within 8 hours. After the concrete is poured, the orifice casing located below the ground and below the top of the pile should be pulled out before the concrete is initially set.
3) During the process of pouring concrete, the 2.5m position of the top surface of the concrete in the hole should be measured. The bored pile should be measured symmetrically at two places on the circumference. When removing the conduit, the burial depth at the lower concrete surface should be used. To control, keep the buried depth of the pipe within the range of 1 to 3m. When the concrete pouring surface is close to the design elevation, containers such as sampling boxes should be used to directly take samples to determine the top position of the concrete to ensure that the top surface of the concrete is poured to about 1.0m above the design elevation of the pile top.
4) Before pouring underwater concrete, you should fill in the "Project Inspection Certificate" to check the condition of bored pile holes and steel cages. During the process of pouring underwater concrete, you should fill in the "Underwater Concrete Pouring" Record".
5) During the underwater concrete pouring process, if the pipe leaks or pulls out of the concrete surface, mechanical failure or other reasons cause a broken pile accident, the pile should be re-drilled or remedial measures should be studied with relevant units.
7 The quality testing of piles should comply with the following regulations:
1) The quality of concrete in the pile body of all bored piles should be tested by low-strain variation testing method.
2) Piles with poor geological conditions and pile lengths exceeding 50m should undergo ultrasonic testing according to design requirements.
3) No less than one set of concrete inspection specimens should be used for each pile.
4) For piles with quality problems, the concrete of the pile body should be drilled for identification and inspection.
5) For bridges, extra-large bridges or structures that need to control the sediment thickness at the bottom of piles, drill holes should be sampled and inspected based on 3% to 5% of the total number of piles.
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