Bored pile foundation construction.
1) Cofferdam. 1) Steel cofferdam.
After the construction of the bored pile, the steel sleeve box is assembled and launched with the help of the drilling platform. The steel casing of the high pile foundation is used as the load-bearing column of the steel sleeve box suspension system, the main beam of the suspension system (Bailey beam or section steel) is installed on the load-bearing column, the beam (mostly section steel) is installed on the main beam, and the guide chain or jack is installed on the beam. The drilling platform is used to assemble the first section of the steel casing, and the guide frame is welded between the casing and the steel casing to overcome the impact of water flow and ensure the accurate sinking position. Then lift the first section of the sleeve box with a guide chain or jack, remove the drilling platform at the lower part of the sleeve box, sink the steel sleeve box into the water to the self-floating state, continue to assemble the second section of the steel sleeve box, and then inject water to sink until the steel sleeve box is grounded. After the steel sleeve box is planted, use a long-arm excavator, grab bucket or air suction dredge to continue to sink to the design elevation, and then throw sandbags or flakes inside and outside the cutting edge after clearing the bottom, and then seal the steel sleeve box.
2) Steel sheet pile cofferdam.
The steel sheet pile is constructed by vibrating pile driver, and the pile frame is kept vertical when inserting and driving. The insertion sequence starts from the upstream and closes the dragon downstream, inserting from one corner to the other on each side. When inserting and driving steel sheet piles, the verticality of the pile should be strictly controlled, especially the first pile should be controlled from two mutually perpendicular directions at the same time to ensure verticality. For the foundation bored pile at the large water depth, the steel platform method is used to drill the hole, and the water is pumped to clear the bottom and pour the cushion cap and the underwater pier body.
3) Lock steel pipe pile cofferdam.
To meet the material force within the safe value, before inserting and driving the steel pipe pile, the pilot hole is carried out first, and then the steel pipe pile is inserted, and then the anchoring concrete is poured in the pipe until the cofferdam is closed, so as to solve the problem that the lock steel pipe pile can not be inserted into the rock or the steel pipe cannot be stabilized when the overburden is shallow, and the problem of water seepage at the bottom of the lock steel pipe and the insufficient anchoring force in the rock formation are solved, and in the excavation of deep-water rock formation, high-risk operations such as underwater blasting and underwater excavation are avoided.
Arrange the site and build the operating platform: erect the trestle bridge on both sides of the river to connect the main pier, and set up the working platform around the cofferdam to connect with the trestle as the water transportation channel and the operating platform for the cofferdam construction.
Installation of the guide frame: A rectangular guide frame with a width equal to the diameter of the steel casing is built along the center line of the cofferdam.
Installation of the steel casing: The lower end of the steel casing is driven into the riverbed soil layer by a vibratory hammer.
Construction pilot hole: the rotary drilling rig is vertically aligned, the core of the rock layer is drilled through the barrel bit, the slag drill bit is taken to clear the hole, and the core is taken to the calculated total depth of soil.
Move the steel casing along the center line of the cofferdam, make the steel casing align with the construction position of the next pilot hole, and continue to construct a plurality of pilot holes according to steps and steps.
Inserting and beating the lock steel pipe pile: the lock steel pipe pile is inserted into a plurality of pilot holes in turn, and is inserted into place by a vibrating hammer, and the two adjacent lock steel pipe piles are connected by a lock pipe at the same time.
Pouring anchor concrete: the high-pressure air duct is used to suction the sediment in the locked steel pipe pile, the concrete conduit is lowered, and the lock pipe is inserted through the vibratory hammer to make the underwater concrete fill to the riverbed surface in the locked steel pipe pile and the pilot hole.
Lock and stop water: Put a waterproof film at the connection position of the lock pipe, and then pour the waterproof mortar.
2) Bored pile construction process.
1) Construction preparation.
Before construction, the site at the bridge site should be leveled, and treated according to the surface and geological conditions to prevent the drilling rig from being unstable during the drilling process, resulting in safety accidents and affecting the quality of the project. Before drilling, carefully check the coordinates of each pile and confirm that they are correct before drilling.
2) Drill into holes.
Before drilling, the guide casing is embedded and poured into the wall protection mud.
The slurry is made of high-quality bentonite, and the appropriate pulping is selected.
The preparation and circulation separation system consists of a slurry mixer, a slurry pool, a slurry separator, a slurry sedimentation processor, etc.
The dosage of admixture in the bentonite pulping ratio should be tested first to check whether the performance indicators of the compound meet the requirements.
When the drilling rig drills, arrange two adjacent piles to construct the holes, and when it is indeed impossible to stagger them, it is necessary to wait until the concrete strength of the adjacent bored piles reaches 2Drilling can be carried out after more than 5MPa to avoid disturbing the adjacent pile foundation that has been constructed.
During the drilling process, the drilling slag is fished out at any time, the formation is judged and the mud index is checked, and according to the formation changes, different drilling speeds and drilling pressures are used to adjust the mud performance in a timely manner, strengthen the wall protection, and keep the hole wall stable.
Control the drilling and lifting speed of the drill bucket.
The drilling speed should be strictly controlled during the drilling process of the rotary drilling rig to avoid a large drilling scale.
Control measures for stuck buried drilling during drilling construction.
Stuck drilling is the most prone construction accident of rotary drilling rigs, therefore, proactive measures should be taken to prevent it during the construction process. When the drilling rig is stuck in the construction of the drilling rig, practical measures should be taken to deal with the construction accident in a timely manner.
The method of dealing with stuck buried drills is as follows:
a) Direct lifting method: the crane can be used to lift directly upward.
b) Dredging method around the drill bucket: that is, using underwater cutting or reverse circulation and other methods to clean the ballast around the drill barrel, and then lifting.
3) Hole cleaning. When the drilling depth meets the design requirements, immediately check the hole depth, hole diameter and the amount of sediment at the bottom of the hole, confirm that the design requirements are met, report to the supervision engineer for approval, and after approval, immediately clean the hole, and the quality of the hole meets the design and specification requirements.
4) Processing and installation of steel cages.
The reinforcement cage is processed in the reinforcement processing plant, and the reinforcement cage is made and numbered according to the whole section or section processing of the pile length to ensure that the adjacent segments can be matched and tied on the tire frame. The flatbed truck is transported to the site, and the verticality of the reinforcement cage is checked before lowering to ensure that the center line of the upper and lower reinforcement cages is consistent when docking. In addition to being welded to the reinforcement cage when the bottom section of the reinforcement cage is installed, the rest of the sections are pre-tied in the reinforcement cage. The top of the steel cage steel casing is welded and fixed to prevent the steel frame from floating during the concrete pouring process.
5) Underwater concrete pouring.
The conduit for pouring underwater concrete adopts a threaded conduit, and the depth of the conduit is controlled at the bottom of the conduit 35 40cm from the bottom of the hole.
Before pouring underwater concrete, the thickness of the sediment at the bottom of the hole is tested again, and the hole must be cleaned again if it does not meet the requirements to ensure that the thickness of the sediment at the bottom of the hole meets the specified requirements.
After the concrete pouring begins, it is carried out quickly and continuously, without interruption, and the concrete pouring elevation is more than 1m higher than the design elevation, and the excess part is chiseled off before the construction of the bearing cap to ensure that there is no loose layer at the pile head.
6) Pile bearing capacity testing: The concrete quality of all bored piles is tested according to the design requirements.
7) Precautions for construction.
Due to the heavy equipment of the drilling rig, the construction site must be flat and have a certain hardness to avoid the subsidence of the drilling rig.
During the construction of the drilling rig, the drill bucket was inspected and found that the side teeth were grinding and the drill bucket was not tightly closed, and it must be repaired in time.
When the mud is injected for the first time, the slurry is carried out vertically to the middle of the pile hole to avoid the mud from washing its bottom along the wall of the casing, resulting in loose soil at the bottom of the casing.
Because the clay layer is drilled too deep, it is easy to cause necking, and the drilling depth is strictly once drilled during the construction of the drilling rig.
When the reinforcement cage or hole finder is placed in the hole, it is lifted by the crane and put it vertically and stably into the hole to avoid damaging the hole wall, causing the hole wall to collapse, and the waste pile accident occurs when the concrete is poured.
According to different geological conditions, it is necessary to detect the performance index of the mud when pouring concrete after hole cleaning to ensure the supporting effect of the mud on the hole wall.
Other construction technology matters shall be constructed in strict accordance with the technical specifications and standards for bridge construction.