When the pile must pass through sandy soil interlayer with a certain thickness, its applicability must be comprehensively considered according to pile pressing force and final pressure of pile machine, soil layer characteristics, pile section specification and pile layout form, high and low groundwater level, pressure stabilizing time and times before final pressure; The ability of static pressure pile driver to pass through the sand layer is limited, so it needs to be determined by pile test; In karst areas where karst caves and gullies are fully developed, static pressure piles should be used with caution, and in areas where there are many boulders and obstacles in the soil layer, static pressure piles should be used with caution; The connection of prestressed concrete piles can adopt end plate welding connection, flange connection, mechanical meshing connection and threaded connection, and the number of joints of each pile shall not exceed 3; The pile end is embedded into the prestressed concrete hollow pile of strongly weathered rock, completely weathered rock and unsaturated soil that are easy to soften with water.
According to the experience of Guangdong, the pressure value at the start of the pile body obtained by the re compaction after 24 hours after the completion of pile sinking of the pressure test pile is used as the reference value of the vertical compressive ultimate bearing capacity of a single pile; The characteristic value of twice the vertical compressive bearing capacity of a single pile can also be used for re compaction.
Schematic diagram of pile position identification for surveying and setting out.
It is strictly prohibited to hold the pile tip in the vertical state of pile body before welding; When lifting and feeding piles, the position of single lifting point shall be 0.3 times the pile length; When the crane on the machine is in the process of pile lifting and pile feeding, the pile pressing machine is strictly prohibited to walk and adjust; During pile feeding, the joint position on both sides of the pipe pile body shall be placed at the gap of adjacent fixtures.
Basic provisions static pressure method is generally applicable to high-pressure compressible clay layer or soft clay layer of sandy soil.
When the verticality deviation of the pile body is greater than 0.8%, the cause shall be found out and corrected; When the pile tip enters the hard soil layer, it is strictly prohibited to forcibly correct the deviation by moving the frame and other methods; In the process of pile pressing, attention shall be paid to the integrity of the concrete of the pile body.
After pile sinking, effective anti-seepage measures shall be taken within about 2m above the pile end.
2.
Pile driver is in place.
The pile driver is in place at the site to achieve “three supplies and one leveling”, and the site bearing capacity shall meet the pile driving requirements of pile driver, generally 140kpa / m2; When the site does not meet the pile driving conditions of pile driver: ⑴ when the site is soft plastic and flow plastic mucky soil, replace it or directly fill it with 1 ~ 1.5m brick slag; (2) when the site is a general miscellaneous soil layer, it can be directly filled with brick slag with a thickness of 0.3 ~ 0.5m; (3) if the pile driving requirements of the pile driver are still not met, the brick slag can be thickened according to the situation to ensure that the pile driver is not trapped; After the pile driver enters the site, adjust the frame vertically, align the center of the clamping jaw (the center line hammer can be hung) with the pile position, and level the pile driver.
Process flow practice 1 pile test diagram basic provisions of pile test: engineering pile should be selected for pressure test pile; The specification, length and geological conditions of pressure test pile shall be representative; The pressure test pile shall be selected near the technical hole of geological exploration; The pressure method and pressure conditions shall be consistent with the construction of engineering piles; The pressure test pile shall be recompressed after 24h rest; It is not applicable to foundation piles whose bearing stratum is easily softened weathered rock and sandy soil layer.
Data shall be provided: records of the whole process of pile pressing, including pile pressing force, final pressure value, final pressing times, final pile length, pile end bearing layer, etc.
Taking the static pressure pile project management of Longguang real estate as an example, this paper interprets the process and Practice for reference.
The welding shall be carried out in layers, evenly and continuously, and the number of welding layers shall not be less than 2.
at different soil depths; Visual inspection record of integrity of pile body concrete after holding pressure; Overall operation of pile driver; Pile joint type and joint construction records; Re compression data; Detailed records of abnormal conditions.
Center line: the center line of hoop shall coincide with the center line of pile body.
3.
If the lower pile body is slightly inclined, the upper pile body shall be straight with the lower pile body, and the surfaces at both ends shall be closely fitted, and there shall be no gap at the joint; Two workers should weld symmetrically.
The position of control pile and benchmark shall be based on the principle of not being affected by pressure pile; Position the pile with wooden pile or short reinforcement, and mark the outer contour of the pile with white ash.
Bearing capacity test: the vertical compressive capacity of a single pile can be tested by the pressure test pile combined with the re compaction method.
4.
The pile sinking process of pressing the precast pile into the soil through the pile pressing mechanism of the static pile pressing machine to provide reaction with the dead weight of the pile pressing machine and the counterweight on the frame, which has no damage to the pile, no noise, no vibration, no impact No pollution and other advantages.
It is a method of engineering pile foundation construction.
6 pile pressing drawing the soil depth of each pile pressing is generally 1.5 ~ 2.0m; The pressing speed during pile pressing shall not be greater than 1m / min; During pile pressing, the verticality of the pile body shall be observed frequently, and the verticality deviation shall not be greater than 0.5%.
The number of pressure test piles shall not be less than 1% of the total number of engineering piles and not less than 5.
Source: in case of infringement by Luban alliance of construction engineering, please contact to delete the static pressure pile (static pressure reinforced concrete precast pile).
It is strictly prohibited to cool with water or drive directly after welding..
7 pile connection drawing pile top is 50 ~ 100cm above the ground for pipe pile welding, carbon dioxide shielded welding should be adopted, and 2 layers and 3 passes of welds should be adopted; The surface of the pile connection shall be clean, the upper and lower pile bodies shall be aligned, and the dislocation shall not be greater than 2mm.
The hole leading operation and pile driving shall be completed in the same shift; When there is ponding in the pilot hole, the open pile tip should be used.
If the pile body does not sink during re compaction, it indicates that the bearing capacity of this pile can meet the design requirements.
Micro expansive concrete can be used to fill the core or flexible waterproof materials can be precoated on the inner wall; For projects without static load test piles in the design stage, pressure test piles must be carried out before formal pile pressing construction.
Lifting pile in place lifting pile in place concrete precast pile can only be lifted when the concrete strength reaches 70% of the strength design value, and can only be transported and pressed for pile construction when the strength reaches 100% of the strength design value; For static pressure pile with steel pile tip, the welding of pile tip shall be completed before pile feeding and hoisting.
Drawing of pre bored pile driving: ① hard interlayer is difficult to penetrate, ② thick sand layer is difficult to penetrate, ③ pile breaking caused by soft upper and hard lower, and ④ ground uplift; Diameter of pilot hole: 50 ~ 100mm smaller than pile diameter; Lead hole length: generally not more than 12m; Hole leading method: long auger dry drilling method should be adopted, and the deviation of drilling verticality should not be greater than 0.5%; The construction of hole leading operation and pile driving operation shall be closely coordinated and driven while drilling.
5 vertical alignment of pile alignment to middle straightening pile body: pile tip alignment pile position and pile pressure into the soil 0.5~1.0m, suspend down pressure, correct the vertical deviation of pile body is not more than 0.3% when the pressure can be formally lowered.
Four to six points should be spot welded evenly and symmetrically before formal welding.
The natural cooling time of manual arc welding shall not be less than 5min, and the natural cooling time of carbon dioxide shielded welding shall not be less than 3min.
Once cracks or corners are found in the pile body, the machine shall be shut down immediately, the causes shall be found out, and the pressure shall be applied after improvement measures are taken; Floating machine is strictly prohibited during pile pressing; Each pile shall be continuously pressed to the bottom at one time, and shall not stop without reason.
The welds in the welding effect drawing of pile extension shall be free of surface defects such as dents, undercuts, weld beading, slag inclusion and cracks; The welded joint shall be cooled naturally before it can be driven.
