1 Project overview:
The radish bay operation area in Guigang City is located in the east of Guigang City, Guangxi Zhuang Autonomous Region. The hydraulic structure of the working area 1#, 2# and 3# berths is a double cantilever box girder pier structure, and the hydraulic structure of 4#, 5# and 6# berths is a gravity pier+high pile beam-slab structure. Designed annual cargo throughput: 654.38+600,000 tons of groceries and 30,000 TEU containers. Finally, the annual throughput of groceries is 65438+800,000 tons, and the annual throughput of containers is 50,000 TEU.
The riverbed of this section is open U-shaped, with exposed bedrock in some sections and floodplain in some areas. There are I, II and III alluvial terraces on both banks of Yujiang River. The wharf area has been eroded and cut for a long time, with ground elevation of 20.40 m ~ 49.04 m and natural slope angle of 15 ~ 20. The surface vegetation is generally developed, and the stratum structure is from top to bottom. The bedrock is thick layered limestone with shallow caves.
2 construction process flow
Punching cast-in-place pile is to lift the impact hammer to a certain height, use the impact energy of the free fall of the impact hammer to impact and break the soil layer or rock, and discharge the mud residue through mud circulation to achieve the purpose of hole formation.
The technological process of punching cast-in-place pile is as follows: leveling machine position → positioning and unreeling → sinking steel casing → installing punching machine in place → punching → hole cleaning → making and hoisting steel cage in place → secondary hole cleaning → pouring concrete → pulling out steel casing after concrete is finally set.
(1) Flat punching position:
Because the punching pile is located on the bank slope, it is uneven. In order to avoid the inclination and hole position deviation of the punching machine, it is necessary to level the punching position and place sleepers.
(2) Positioning and unreeling:
According to the pile site plan, the positioning data provided by the owner and the elevation datum point, the survey control network is made on site. Control points must be firm, and the position and elevation should be checked and corrected regularly. Make original records of pile location measurement and setting out, and timely sort out and submit the measurement results.
(3) Embedded gasket:
3. 1 The casing is made of 6 ~ 8 mm steel plate, with 400×400mm slurry inlet and outlet at the upper part, and the inner diameter of the casing is larger than the designed pile diameter100 ~150 mm. ..
3.2 Excavate the casing according to the pile diameter, the diameter should be 300mm larger than that of the casing, the buried depth of the casing should be greater than 1m, and it should enter the undisturbed soil layer not less than 0.5m, the casing mouth should be 200mm higher than the surface, the mud inlet and outlet should be aligned with the circulating tank, and the surrounding area should be tamped with clay to prevent the casing from loosening, skewing or sinking during drilling.
3.3 When burying the liners, the surveyors should monitor to ensure that the center of the liners coincides with the center of the pile location with a deviation of ≤50mm or less, and the verticality deviation of the buried liners is ≤ 1%.
3.4 After the pile casing is buried, measure the elevation of the pile casing mouth as the elevation of the pile orifice; It is also the basis for hoisting reinforcing cage and pouring concrete top elevation.
(4) Mud preparation and mud pool setting:
Set a mud pool at a suitable position and use a mud mixer to make pulp. During hole cleaning, the ballast in the mud pit and mud ditch shall be cleaned, and high-quality mud shall be continuously replaced until underwater concrete is poured. Mud index values are as follows:
Specific gravity: 1. 10 ~ 1.30
Viscosity: 20 ~ 28g
Sand content: < 8%
(5) Punching machine installed in place:
When installing the punching machine, it should be carefully adjusted to make the center of pulley, hammer rope and hole position reach three points and one line, and the punching machine workbench must be horizontal and stable. After the installation is completed, accurately measure the height difference between the casing mouth and the table top, and the punching construction can only be carried out after the supervision of Party A issues the report of pile hole opening and the design book of pile hole.
(6) punch holes with a punch:
Punching process is an important process in punching cast-in-place pile construction, and mastering its key points plays a decisive role in punching quality. The main points of drilling work are as follows:
6. 1 When rushing in, carefully observe the footage and the drainage and slag discharge of sand pump; When the discharge is reduced or the amount of pressure in the effluent is large, the feeding speed should be controlled to prevent the reverse circulation from being interrupted due to the high specific gravity of the circulating liquid.
6.2 Punching parameters should be selected and adjusted according to stratum, pile diameter, reasonable displacement of sand pump and economic punching speed of punching machine.
6.3 In case of abnormal conditions such as hole collapse and sand gushing in the hole, immediately lift the hammer away from the bottom of the hole, control the pump quantity, keep the circulation of flushing liquid, suck out the hole collapse and sand gushing, and at the same time convey mud with satisfactory performance into the hole, and keep the head pressure to resist sand gushing and hole collapse. After re-drilling, the pump displacement should not be too large to prevent the hole wall from being sucked down.
6.4 After rushing into the designed hole depth and stopping punching, lift the punch away from the bottom of the hole 100 ~ 150 mm, and continue to maintain mud circulation. When necessary, rotate the mud pump at a low speed, and at the same time, send clean mud or clean water to the hole, and clean the hole by reverse circulation for about 15 ~ 20min, so that the sand content of the returned mud meets the specified requirements. 6.5 In the process of punching, the hole position should be detected frequently to prevent the punching machine from shifting. If there is displacement, adjust the punching machine as soon as possible.
6.6 In the process of punching, the wire rope should be replaced frequently according to the footage of the punching hammer to ensure the safety of punching. Install flexible safety wire rope on the upper part of the impact hammer before use, so that it can be salvaged in time and quickly when the impact hammer falls.
(7) Borehole inspection
When the hole depth meets the design requirements, the hole depth, aperture and inclination shall be finally checked. If abnormal deviation is found, it should be handled, such as hole sweeping and reaming.
(8) hole cleaning
After the pile hole inspection is qualified, the hole can be cleaned. In addition to the standard of hole cleaning, the thickness of sediment shall not exceed the specification requirements of ≤50cm, and the indexes of mud after hole cleaning shall also meet the requirements, with the relative density of1.03 ~1.10; The viscosity is 17Pa? s~20Pa？ s； Manufacture of Sand-containing Reinforcing Cage (9)
9. 1 The reinforcing cage shall be made in strict accordance with the drawing requirements, and the performance indexes of raw materials shall meet the specifications and design requirements, and sampling tests shall be conducted.
9.2 In order to ensure the thickness of the protective layer, a layer of guide noses is set at the bottom of the reinforcing cage every 3m, with three on each layer, arranged according to the central angle of 120, and staggered up and down by 60. The top of the reinforcing cage is provided with lifting rings.
9.3 Install ultrasonic testing tube. When laying, the position should be strictly controlled to ensure the straightness of the whole butt joint, and at the same time, it should be convenient for butt joint.
(10) Reinforcement cage hoisting
After the reinforcing cage is in place, align the center of the casing and lower it slowly to avoid disturbing the hole wall. When hanging, deformation and distortion should be prevented. After lowering to the design elevation, its axis position should coincide with the pile position, and then it should be fixed on the drilling platform with string rods through rings.
(1 1) conduit installation
The diameter of the conduit is φ3002m~5m, and each section is 2 ~ 5m long. In addition, there are 1m and 1.5m long conduits, and the joints are connected with threads and sealed with rubber rings. Before use, the conduit shall be subjected to watertight pressure test and joint tensile test not less than 1.25MPa, and the capacity of the hopper shall be determined by calculation.
(12) Check mud index and sediment thickness.
Before pouring underwater concrete, the performance index and sedimentation thickness of mud in the hole should be checked again. If it exceeds the requirements, the hole should be cleaned for the second time, and underwater concrete can be poured only after it meets the requirements.
(13) pouring underwater concrete
13. 1 Underwater concrete is pumped by concrete to the site for pouring, and the slump of concrete is controlled at 18cm ~ 22cm, and the water cement ratio is controlled at 0.54.
13.2 the first batch of concrete shall ensure that the buried depth of the conduit is not less than1m. Cement mortar should be used in the initial part or 1 ~ 2 hopper, and it should be poured into the hole as soon as possible.
13.3 the first batch of concrete falls, and the concrete shall be poured continuously. During the whole perfusion process, the buried depth of the catheter should be controlled between 2m and 6m. Use measuring rope to measure the height of concrete surface in pile hole frequently, and adjust the buried depth of conduit in time. The vibrating concrete of the conduit should be lifted continuously to make the concrete surface roughly balanced. In the process of pouring underwater concrete, the depth of concrete surface shall be measured by special personnel, and the underwater concrete pouring record shall be filled in. Analyze the cause of the abnormal situation.
13.4 when pouring concrete, the concrete delivery pump pipe should be aligned with the side of the hopper, and not directly aligned with the conduit mouth, so as to avoid a large concrete drop, forming a high-pressure air bag or segregation in the conduit and causing a pipe sticking accident.
13.5 the elevation of the concrete pouring top surface of the cast-in-place pile should be 50 cm ~ 100 cm higher than the design elevation to ensure the concrete strength of the pile top. The excess part shall be removed to the top of pile 20cm before the initial setting of concrete, and the remaining 20cm shall be removed before the pile extension, and there shall be no loose layer on the residual pile head.
13.6 at the end of concrete pouring, the pouring quantity of concrete should be checked to determine whether the measured pouring height of concrete is correct.
(14) Removing and pulling out the steel sleeve
After concrete pouring, the steel casing can be removed after the concrete to be poured reaches the final setting time, and the specific time depends on the construction temperature and cement performance.
(15) Precautionary measures for broken piles and interlayer
In the construction of cast-in-place pile, due to the influence of operation errors, poor equipment and hydrogeological conditions, pile breakage and interlayer are easy to occur, resulting in major engineering quality accidents. To this end, the following preventive measures were formulated before construction:
15. 1 After the hole is formed, the hole should be carefully cleaned to ensure that the performance index of mud in the pile hole is within the required range, and the thickness of sediment should be reduced as much as possible, so as to reduce the sediment carried by the first batch of concrete, and the hole wall will remain during boiling, forming a cavity.
15.2 before the first batch of concrete pouring, the height from the bottom of the conduit to the bottom of the hole and the quantity of the first batch of concrete should be strictly controlled. During the pouring process, water supply and power failure should be avoided to prevent the first batch of concrete from being stuck or buried too deeply or too little, resulting in broken piles.
15.3 Carefully measure the concrete pouring surface, strictly control the buried depth of the conduit, and avoid the measurement error. If the conduit is buried too deeply, it may be impossible to pull out the conduit due to the initial setting of concrete, resulting in engineering accidents; If it is too shallow, it will cause mud inclusion due to the constant disturbance of the hole wall during the boiling of concrete, and the phenomenon of pipe detachment will occur, resulting in mud inclusion or broken piles.
15.5 strictly control the mix proportion of concrete construction, and it is forbidden that the slump of concrete is too large or too small, which will cause pipe blockage, increase the risk of broken piles, or cause concrete segregation or hollowing of foundation piles, which will affect the quality of finished piles. Adding pumping retarding water reducer into concrete can prolong the initial setting time of concrete and increase the workability of construction.
(16) Pile quality
The original design of Radish Bay Wharf in Guigang City has 25 punching piles and 58 manual digging piles. Due to geological reasons, manual digging piles were changed to punching piles, and 4- 1-5# and 3-3-2# gravity piers were also changed to punching piles, and each pier was composed of four piles. All 9 1 piles have been tested by guangxi traffic Quality Inspection Center, and the pile body integrity is excellent, including 67 first-class piles and 24 second-class piles.
summary
Punching cast-in-place pile is a concealed project, especially the two processes of punching and pouring underwater concrete are the most prone to problems, so management should be paid attention to in construction. Once there is a problem, we must carefully analyze the actual situation, find out the cause of the accident, and put forward a technically simple and feasible treatment method.
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