CFG (cement fly ash gravel) pile is a high bond strength pile formed by mixing cement, fly ash, gravel, stone chips or sand and water according to a certain mix proportion, which forms a composite foundation together with the soil and cushion between piles
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It can not only give full play to the potential of pile materials, but also make full use of the bearing capacity of natural foundation, and can make use of local materials according to local conditions
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It has the advantages of high efficiency, low cost, small deformation after construction and fast settlement stability
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CFG pile foundation treatment includes CFG pile body, pile cap (plate) and cushion
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Structure type: pile + plate, pile + cap + cushion (this form is adopted in this bid section) 2
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CFG pile construction technology 1
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Equipment selection and allocation ﹣ CFG pile can be constructed by vibrating pipe sinking drill or long screw drill
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The specific type and model of pile forming machinery to be selected depends on the specific situation of the project
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For clayey soil, silt soil and muddy soil, vibration sinking pipe pile forming technology is adopted
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For the area with hard soil layer, the vibration pipe sinking machine will cause great vibration to the existing pile, which will cause the pile to be cracked or broken
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For the soil with high sensitivity, the vibration will damage the structural strength and reduce the bearing capacity of the soil
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For the area where the quality of hole forming is required to be high, the pile forming technology of pump pressure in long spiral drilling pipe is used
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The design of this bid section adopts long screw drilling machine for construction
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There are also two types of construction machinery for pumping concrete in long auger pipe: walking type and crawler type, as shown in the following figure: crawler type long auger rig walking type long auger rig according to the schedule and process test, the equipment configuration is well implemented and maintained in time, so that all machinery are in normal condition, meet the needs of construction, and do not affect the progress and quality of construction
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2
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The raw materials such as cement, fly ash, crushed stone and admixtures selected for the selected materials and mix proportion shall meet the requirements and relevant standards for the quality acceptance of raw materials, and shall be sampled and inspected according to the regulations
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According to the design requirements of indoor mix proportion test, select the appropriate mix proportion
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3
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Process flow 3-1 level the site, check, remove and protect the upper and underground pipelines in the construction site
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Clear the surface vegetation, level the drilling site according to the measured original ground elevation and the design pile top elevation, the ground elevation should be 50cm higher than the design pile top elevation, reserve the drainage slope, make drainage ditch and other measures, and use the roller to roll the original ground to K30 ≥ 30MPa / M, so as to meet the self weight and anti overturning requirements of the long screw drill
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3-2 for construction lofting, a steel drill with a diameter of 8mm is used to drive a 20cm deep hole vertically at the pile position, lime water or lime powder is poured into the hole, and markers are inserted into the hole
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Disposable wood and bamboo chopsticks can be used to facilitate the search after the pile position is buried
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Construction site 3-3 drill pipe verticality control: after the drill is in place, the pile machine hangs two-way plumb ball, and the side station personnel determine whether the verticality deviation of the machine body meets the specification or design requirements by measuring the relative distance between the plumb ball and the upper and lower ends of the drill pipe, so as to ensure that the allowable verticality deviation of CFG pile is not more than 1.0%
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Pile position control: before the construction of each pile, determine whether the pile machine is aligned with the pile center by measuring the adjacent longitudinal and transverse pile positions with ruler
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Before the construction of each pile, the on-site personnel shall check the pile alignment and the verticality of the drill pipe of the pile machine, and the drilling can be started only after the requirements are met
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At the beginning of 3-4 drilling, close the drill bit valve, move the drill pipe downward until the drill bit touches the ground, and start the motor to drill
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Generally, it should be slow first and then fast
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This can not only reduce the drill pipe shaking, but also check the deviation of drilling, so as to correct it in time
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In the process of drilling, if it is found that the drill pipe is shaking or difficult to drill, the footage should be slowed down, and the perpendicularity and pile position of the drill pipe should be checked in time, otherwise, it is easy to cause the deviation and displacement of the pile hole, and even damage the drill pipe and drilling tool
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Pile length control: make a clear length mark on the body of the pile driver
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In order to facilitate the construction control at night, it needs reflective materials for marking
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The minimum scale of the mark is generally 50cm or 25cm
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According to the footage mark on the rig tower, stop drilling when the hole reaches the design elevation
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The drilling spoil shall be transported to the designated site in time
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3-5 pouring concrete long auger drill to the design elevation, stop drilling, pump concrete to the drill pipe core pipe, when the drill pipe core pipe is full of mixture, start to lift the drill pipe, press the mixture, pull out the pipe and pump at the same time, it is strictly forbidden to lift the pipe before pumping
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The concrete slump and mixing time shall be controlled according to the parameters determined by the technological test, and the mixing time shall not be less than 1min
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When pumping concrete, it is strictly forbidden to pump concrete (especially end bearing pile) after pulling pipe
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When pulling pipe, the drill pipe must stop rotating
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The speed of pulling pipe should be controlled according to the parameters determined by the test pile
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The speed of pulling pipe should be uniform and penetrate the hard geological section
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Low grade slow drilling, soft stratum and fast drilling should be adopted to reduce the reaming coefficient
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Concrete pumping must also be continuous
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If the concrete is not supplied in time, the drilling rig and other materials will be damaged
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If the time is long, the pile may be broken or the drill may be held, especially in saturated sand and silt
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The concrete shall be poured to 50cm above the designed CFG pile top elevation, and the pumping of concrete shall be stopped
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The volume of cast-in-place concrete shall not be less than the design pile length plus the volume of over cast pile head
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According to the specific situation of 3-6 drilling rig, generally drill 4 or 5 holes to move the drilling rig once
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No matter the pile spacing, it is not suitable to push the construction from the surrounding to the inside of the circle, because this limits the lateral deformation of the soil between the piles, and it is easy to cause large-area uplift of the soil, so it is more likely to break the pile
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The scheme of pushing from the center to the outside or from one side to the other can be adopted
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When there is a weak layer in the ground and there is a hole channeling phenomenon, the drilling rig should adopt the hole skipping operation, and then drill the adjacent pile position after the mixture at the adjacent position solidifies
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3-7 remove drilling mud the drilling mud must be removed at any time during drilling, and the remaining drilling mud shall be removed after the rig is displaced
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It should be noted that: (1) except for 50 small excavators, no mechanical equipment is allowed to enter the CFG pile drilling and grouting site
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(2) the original soil between piles below the designed pile top elevation shall not be disturbed during excavation
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(3) it is not allowed to dig the cast-in-place CFG pile to damage the pile head
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3-8 naturally cured CFG piles are buried under the ground, and the top of the pile is capped with wet clay, so there is no need for special maintenance
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After the completion of pile grouting, the soil between piles can be excavated and cleaned after the age of mixture reaches 14 days
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During the natural maintenance period, the drilling and grouting site must be protected, and no machinery is allowed to enter the drilling and grouting area
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3-9 when cutting pile head and excavating soil between piles, the excavator is easy to collide with the pile head and cause shallow broken pile
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In the construction, the pile head is cut twice to avoid man-made damage to the pile head: first, before the concrete solidifies after the completion of CFG pile pouring, the wet cut pile is cleaned out with the drilling mud by a small excavator, leaving 30 ~ 50cm uncut
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After the strength reaches 80%, the small excavator is used (bucket width 0.6m) to excavate the soil between piles, and use the modified cutter to cut, so as to reduce the damage to the pile body
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After cutting, the section is smooth
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3-10 pile inspection 3.10.1 pile integrity inspection CFG pile integrity is tested by low strain dynamic test
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The integrity of pile body is determined according to the test results
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Low strain test of pile body 3.10.2 strength of CFG pile mixture 1 group of standard Cube Specimens of mixture is made for each shift
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After 28 days of standard curing, the compressive strength of specimens is tested
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According to the test results to determine the quality.
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