The punching and grabbing cone is lifted to the ground as a whole to unload the soil slag, and the hole is formed in turn
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Application: same as positive circulation
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What are its construction techniques? What kind of accident is it easy to encounter? Construction flow chart: 1
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③ Generally, the buried depth is 2-4m, which should not be less than 1.0m in cohesive soil; 1.5m in sandy soil; the height should be deepened to prevent the casing from sinking under special circumstances; at the same time, the requirements of slurry surface height in the hole should be met, and the top surface of the casing should be 0.2-0.5m higher than the island surface
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After sedimentation and purification in the sedimentation tank, it will be recycled
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5、 Drilling frame and drilling rig in place drilling frame is required to be able to bear the weight of drilling tools and other auxiliary equipment, have a certain stiffness, and have enough height
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Application: clay, loam, muddy soil layer, silt, gravel layer and bedrock are used to form holes through positive and negative circulation
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Then start the winch to lift the cone head, and the grabbing piece closes to grab the soil
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The maximum hole diameter can reach 1.5-4m, and the maximum hole depth is 60-90m, which can meet the requirements of all kinds of large foundation construction
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Production requirements of casing: ① the casing is usually made of reinforced concrete and steel, depending on the specific situation
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In the construction process, the construction quality has a great impact on the bearing capacity of the pile, so bored pile is a very important step in bridge engineering
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There is a heavy iron block and a movable grabbing piece on the head of the punching and grabbing cone
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The function of the casing: fix the position of the pile hole, protect the hole, prevent the surface water from flowing in, increase the water pressure in the hole, prevent the hole from collapsing, and guide the direction of the drill when forming the hole
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④ The top elevation of the casing shall meet the requirements of the water level setting height in the hole
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(6) drilling: (1) drilling with percussion drill: cross drill: construction points of percussion drilling: drilling after adjacent hole concrete reaches 2.5MPa; drilling with small stroke The depth of the hole is the normal impact after the stroke of the bit
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Mud consistency: when measuring, use your fingers to block the outlet under the funnel, pour 500ml and 200ml mud into the funnel through the filter, open the outlet, let the mud flow out from the funnel pipe, and use a stopwatch to measure the time (s) required to flow out 500ml mud, which is the mud consistency
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After burying, the clay should be used to fill and tamp symmetrically in layers around the casing
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Casing penetration depth: when hammering the pressurized steel casing, make sure that the steel casing is vertical and avoid inclination; avoid soaking around the orifice and causing hole collapse; bury the casing; 4
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② In the process of drilling, the hole center must be aligned with the pile center, and the drilling frame must be stable without displacement, inclination and subsidence
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to promote particle dispersion and prevent agglomeration and subsidence; organic: tannin, rubber, etc
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1-2 slurry overflow holes are set on the upper part of the casing
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to reduce viscosity ∧ slurry pit slurry wall protection bored pile : mud pit mud three indicators testing: mud three sets (hydrometer, viscometer, sand content tester) mud specific gravity: fill the mud cup with mud, cover and wipe the overflow mud
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Avoid the hole collapse caused by soaking around the orifice
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Features: the reverse circulation drilling rig has strong slag removal capacity, but the process is complex, improper operation is easy to cause hole collapse and buried drilling, and the price of reverse circulation drilling rig is relatively high
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③ When the drilling frame is installed in place, it shall be measured in detail
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② the inner diameter of the casing is slightly larger than the designed diameter of the bored pile
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It is suitable for punching in soft soil layer (sand and clay), but it is suitable to use percussion drill when encountering hard soil layer
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It has the advantages of high pile quality, standard hole diameter, small filling coefficient, thorough hole cleaning, fast speed, self-propelled and easy to move on site
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Medium and low stroke of cohesive soil, weathered layer and gravel: 1-2m sand pebble medium stroke: 2-3m bedrock, boulder and dense pebble layer high stroke: 3-5M cross bit drilling 1.5m above the hole diameter is divided into 2 stages, tubular bit drilling 0.7m above the hole is divided into 2-4 stages: grading and expanding drilling; ② full casing punching and grabbing drilling: features: no noise, no vibration; no mud; intuitive judgment during excavation According to the characteristics of soil and lithology, for end bearing pile, it is easy to determine the pile length on site; the excavation speed is fast and the excavation depth is large; the hole verticality is easy to master; the hole wall will not collapse, and the hole quality is high
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3
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Burying requirements of pile casing: (1) before drilling, set out and position on site, excavate the surface soil of pile hole according to pile position, and bury the pile casing
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Put the back on the support, move the traveling bar to make the lever level, and read out the scale on the left side of the traveling bar, which is the specific gravity of the mud
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Composition and requirements: ① water: pH value of water is between 7 and 8, without impurities; ② clay (or bentonite): plasticity index is greater than 25, particle size is less than 0.005mm, particle content is more than 50% of the total amount, and relative density is 1.1-1.5; ③ additive: inorganic: soda, etc
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The mud circulation mode of reverse circulation drilling is just the opposite, and the mud flows from the hole into the hole Inside, the drilling slag is sucked out from the top of the drill pipe through the center of the drill pipe by vacuum pump or other methods (such as air suction mud machine), or the slurry pump is drilled together with the drill cone to suck the drilling slag out of the hole from the bottom of the hole
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With the continuous development of science, bored pile is widely used in high-rise, super high-rise and bridge structures
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When the drill is aligned, water is discharged into the casing, and drilling is carried out with mud wall protection
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(3) positive circulation drilling: the positive circulation is to use the mud pump to pump the mud through the top of the hollow drill pipe at a certain pressure and eject it from the bottom of the drill pipe
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The thickness of steel casing is 4 ~ 8mm, and that of reinforced concrete casing is 8 ~ 10cm
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The base shall be padded and plugged with sleepers, and the top shall be fixed stably with cable wind rope, and it shall be checked frequently during drilling
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Features: the slag removal capacity is relatively weak, the drilling speed is slow, and the wear of drilling tools is relatively large, but the process is relatively simple, easy to operate, and the price of positive circulation drilling rig is relatively cheap
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② The method of digging or hammering, vibration and pressurization can be used for burying the casing, but attention should be paid to avoid cracking and inclination of the orifice
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For drilling with rotary drilling rig, it should be increased by 20-30 cm; for drilling with impact drill and grab drill, it should be increased by 30-40 cm
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Now, cross line is drawn on the casing to align the drill bit with the center line of the pile
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Pile position setting out, pile position setting out The station coordinate method is used to set out the position of bored pile, and mark around the casing after burying the casing
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Site preparation dry land: leveling and tamping the site shallow water: island building method} sand blowing island construction} sand blowing island construction is completed, steel bridge and sand blowing Island Road are smoothly connected} sand blowing island construction is completed, water construction road working face is fully spread deep water: cofferdam method} double wall steel cofferdam} caisson island construction} steel sheet pile cofferdam 2
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When the drill cone at the bottom rotates, it will loosen the soil into drilling slag, which will be suspended by the mud and overflow to the mud tank outside the hole with the mud rising
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The punching and grabbing cone is lifted to a certain height through the frame and the winch
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2
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④ reverse circulation drilling is used in reverse circulation drilling
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Mud preparation: mud skin is formed on the hole wall to stabilize the hole wall, suspend drilling slag, lubricate drilling tools and discharge slag in positive circulation
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7、 The purpose of finishing the hole and cleaning the hole for the first time: during the drilling process, a part of mud and drilling slag will sink at the bottom of the hole, and these sediments must be removed, so that the poured concrete can be closely combined with the stratum or rock, and the bearing capacity of the pile can be ensured.
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The construction process, installation requirements of casing and circulation of slurry wall protection are the same as those of impact drilling
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When it falls, release the drum brake, the grabbing piece opens, and the cone head falls freely into the soil
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