Originated from丨PowerChina Municipal Group
The construction process is made by the long auger drilling rig into a hole, the concrete is pumped into the pile into a pile, and then the reinforcement cage is sunk into the concrete of the pile body by using a vibrator. This construction method has been widely used because of the advantages of no mud pollution, fast construction speed, high construction efficiency and low cost. Let's come to the project site of Daxing 2-002A plot of China Hydropower Company to take a look at how to construct the reinforcement cage after the long spiral bored pressure filling pile of foundation pit support?
Long spiral bored pressure grouting pile construction technology
The long auger drilling pile technology is to use the long auger drilling rig to drill to the design elevation, use the concrete pump to press out the superfluidic fine stone concrete from the bottom of the drill bit, lift the drill bit while pressing and pouring the concrete until the pile, after the concrete is poured to the design elevation, and then insert the reinforcement cage into the concrete pile to the design elevation at one time with the help of the steel cage self-weight or the use of a special vibration device to form a reinforced concrete cast-in-place pile.
01
Measure pay-off positioning
The construction site should be leveled, with a flat width of 12m to meet the requirements of safe walking of pile drivers and tank trucks. To the owner to provide the level point and measurement control network for the introduction, on the extension of the axis to do points to establish the control network, each control point with no less than 0.2 m³ concrete pouring, in the middle of the embedded parts placed in the embedded, carved cross as the axis of the guide point, in the pile foundation construction process, should be checked every day on the site measurement control points, and do a good job of effective protection. Elevation measurement and positioning pile position: Before the construction of the slope protection pile, the elevation of the construction operation face is measured, and the drilling depth calculated from the construction operation face is calculated.
Pile position measurement and acceptance
02
Steel cage processing
After the steel bar is transported to the site, collect the product quality certificate and certificate, check the appearance of the sign and steel bar on each bundle (plate) of steel bar, do a good job of acceptance, and timely extract the raw material test pieces of the steel bar and send them to the laboratory for inspection, and can only be used after passing the test. The main reinforcement of steel bar welding is concentric welding, and the thickness of the weld and the width of the weld should not be less than the requirements of the specification.
Acceptance of reinforcement cage
According to the design, calculate the length of stirrup material and the length of the main reinforcement distribution section, straighten the required steel bar and cut it in batches with a cutting machine for later use. Make stirrups on the rebar ring making table and weld them as required. Place the support frame on the same horizontal plane at a distance of 2~3m to align with the center line, and then place the main reinforcement with a fixed length on the welded support frame. The stirrups are inserted into the main reinforcement according to the design requirements and kept perpendicular to the main reinforcement for spot welding or binding. The reinforcement cage is positioned with protective ribs, and 4 are symmetrically welded along the main reinforcement around the reinforcement cage every 4m.
03
The drilling rig is in place and the hole is formed
Calculate the hole depth according to the design pile length and the elevation of the working face, and mark the hole depth at the corresponding position of the drilling rig fuselage or drill pipe. The drilling rig moves to the pile position to align the pile position and puts the drill bit, the drilling rig tower body should be kept vertical, and the verticality of the drill pipe should be measured with a theodolite or line hammer, and the verticality deviation control specification is within the allowable range.
The pile driver is in place
Schematic diagram of the borehole
The spacing of the slope protection piles of this project is small, in order to prevent the slope protection pile from being extruded on the adjacent pile body and pile head after casting, the project adopts the "every other dozen one" jumping construction, jumping construction from one end to the other end, and the drilling rig is then moved from the beginning to the end of the beating is completed. In order to ensure the impact of the piling process on the stratum and adjacent piles, the Lintie section adopts the "interval two to one" jumping method.
Schematic diagram of the drilling construction route
04
Pressurized concrete
After the drill bit reaches the design elevation, the drill pipe stops drilling and starts pumping concrete, and the concrete can only be lifted after pumping the concrete to the bottom of the hole and pressurized, and it is strictly forbidden to pump the concrete after the drill is lifted. Lifting the drill while pumping concrete, the rate of lifting must match the pumping volume, so that the drill bit is always buried below the concrete surface. The piling process should be carried out continuously.
Concrete pouring
When concrete pressure filling, the overfilling height of the pile top should not be less than 0.5m, and the filling coefficient of concrete pressure filling should be greater than 1.0. After the concrete pouring of the pile hole is completed, the drilling rig is rapidly shifted to create conditions for the placement of the reinforcement cage.
05
The reinforcement cage is hoisted
After the concrete pouring of the pile body is completed, the reinforcement cage should be inserted immediately to prevent the time delay from too long and the concrete solidification should affect the lower cage. The vibrating rod is penetrated into the reinforcement cage at the ground level, and the top of the reinforcement cage should be connected with the vibration device. The reinforcement cage is lifted upright at the orifice, and measures should be taken to prevent deformation when the reinforcement cage is hoisted, and the hole position should be aligned when it is placed, and ensure that it is vertical and centered, and there should be a special person to command the cage. The reinforcement cage should be continuously lowered and not easy to stop.
After the vibrator is inserted into the reinforcement cage, the crane is used to move to the vicinity of the orifice. The crane driver is required to operate accurately and smoothly to prevent the destruction of the reinforcement cage when rotating.
Hang the reinforcement cage
The lifting reinforcement cage adopts the flat lifting method, and the lifting point is located at the connection between the stirrups of the reinforcement cage and the main reinforcement, and the lifting point is symmetrical and lifts at one time. The reinforcement cage is provided with 2-4 lifting points to ensure that the reinforcement cage is not deformed during lifting. Lifting the steel cage into the hole to adapt to the alignment of the hole, keep vertical, lightly, slowly put into the hole, if there is an obstacle should stop the drop, find out the cause for treatment, it is strictly forbidden to lift and fall and force down. When the reinforcement cage is lowered, it is required that technical personnel are present to measure the elevation of the top of the casing on the spot, and accurately calculate the length of the suspension bar, so as to control the pile top elevation of the reinforcement cage and the floating of the reinforcement cage.
The reinforcement cage starts to be inserted
Precautions: When the reinforcement cage is sunk by vibration, the crane driver should always give the vibrator an upward force, maintain the vertical restraint of the vibrator, and keep the reinforcement cage sinking along the direction of the plumb weight. Reasonably control the insertion speed of the reinforcement cage. In the process of cage unloading, the vibrating hammer and the self-weight of the reinforcement cage must be pressed in first, and then the vibrating hammer must be started when it cannot be pressed in order to prevent the deviation of the reinforcement cage caused by the vibration of the vibrating hammer.
After the reinforcement cage is inserted into the design position, the power supply of the vibrating hammer is turned off, and finally the wire rope is removed, and the steel pipe and the vibrating hammer are lifted out of the hole with a long auger drilling rig, and the vibratory hammer is opened once every 3m in the process of lifting to ensure the compactness of the concrete.
The reinforcement cage is inserted into place for elevation review
06
Chisel the pile head
In order to ensure the quality of the pile head of the slope protection pile, the over-filling height of the supporting pile is not less than 50cm, and the earthwork between the piles is excavated after the pile is completed, and the pile head is chiseled to the design elevation.
Chisel off the pile head
07
Pile detection
According to the drawings and specifications, after the construction of the slope protection pile is completed, the integrity of the pile should be tested by low strain detection test, and the number of tests shall not be less than 20% of the total number of piles, and shall not be less than 5. The concrete should be tested on the strength of on-site test blocks, and the number of tests per 50m³ should not be less than 2 groups (respectively, 7d and 28d strength should be determined), and each group of test blocks should not be less than 3.
Integrity inspection of support piles
Daxing 2-002A plot project is located in the DX04-0101 block of Xihongmen Town, the northern area of Daxing District, Beijing, west of the Fifth Ring Road, adjacent to the South Fifth Ring Road, Beijing-Kaifeng Expressway, planned Guangyang Street, and the current Huaifang West Road, with a planned total land area of 82,500 square meters and a new total construction area of 257,900 square meters, of which the above-ground construction area is 165,000 square meters and the underground construction area is 94,100 square meters. The main functions of the project include: the office building of the northern regional company and the new energy company, the office building of the Beijing Survey and Design Research Institute, 10 apartment buildings, above-ground supporting facilities and public service facilities; underground parking garages for motor vehicles and non-motor vehicles; Underground supporting rooms, property rooms, apartment storage rooms and related equipment rooms, etc.
Project image map