A, the construction preparation work
1. Site preparation
Before construction, the site should be leveled to facilitate the installation of drilling rigs. The pier 1-4# of this bridge is in water, and the annual water depth is about 1-2m. The island adopts earth bag cofferdam, and uses sand to build an E-shaped island with a length of 70m and a top width of 8m, and tamps it. The platform is higher than the normal water level 1.0m, and it is filled with 1: 1. There is a 5-meter-wide spillway between platform 0# and pier 1#.
2. Selection of machines and tools
At present, there are three commonly used drilling rigs: rotary drilling rig, impact drilling rig and impact drilling rig. Rotary drilling rig is mainly used for cohesive soil, sandy soil, gravel and pebbles with particle size less than 2/3 of drill pipe inner diameter and content less than 20%. The pore-forming diameter is 80-250cm, and the pore-forming depth is generally not more than 50m.
Impact drills are mainly used for geotechnical piles, and also for pile foundation construction of other soils. The pore-forming diameter is 80-200cm, and the pore-forming depth is generally not more than 50m.
Impact drills are mainly used for silt, clay, sand, gravel and pebbles. The pore-forming diameter is 60- 150cm, and the pore-forming depth is 20-40m.
According to the engineering soil conditions, pile diameter and pile length, choose the appropriate machinery. The bridge is a 5-span prestressed hollow slab continuous deck structure with a total length of 92 meters. The substructure is continuous beam pile foundation, with the designed pile diameter of1.2m and the pile length of 45m.. The engineering geology is that the riverbed 1-5m is clay and loam, the following 5- 15m is muddy soil, sandwiched with 3-5m medium coarse sand, 16-20m is medium sand layer, and 2 1-48m is loam, containing about10. According to the geological conditions of the bridge site, rotary drilling rig is used for construction.
3. Measuring lofting
(1) Set up a triangular closed traverse control network that meets the requirements of construction specifications, and retest the leveling base point.
(2) Determine the center line and pile position of the pier by coordinate method.
(3) Set control piles and add protective piles (all protective piles should be set in a stable and visibility place).
(4) The measured data shall be checked with the direct measurement (steel rule), and the measured data can be used only after it is confirmed to be correct and meets the requirements.
Step 4 embed the gasket
The axle housing is made of steel plate, which meets the requirements of durability, no deformation, no water leakage, convenient loading and unloading and reusability. The diameter of casing is 1.4m, and the length of each section is 2m.
The function of the gasket:
(1) Fix the pile position and conduct drilling guidance;
(2) Protect the orifice to prevent the orifice soil layer from collapsing;
(3) Isolate the surface water in the inner hole and keep the water level in the hole higher than the construction water level to stabilize the hole wall.
Precautions for embedding gasket:
(1) The plane position of the casing is buried accurately, with a deviation of not more than 50 mm, and the elevation at the top of the casing should be higher than the underground water level and the construction water level1.5-2.0m.. The overflow port of casing should be 0.2-0.3m higher than the ground, and the bottom of casing should be lower than the lowest water level in construction, generally lower than 0.1-0.3m. The buried depth of casing of this bridge is 3m.
(2) preparing slurry. According to the actual situation of this bridge, it is planned to build two mud pools between pier 0# 1#, pier 3# and pier 4#. It is best to use high-quality pure clay or bentonite as mud; If there is no good pure clay or bentonite, or it is difficult to transport it to a long distance, a small amount of additives can be added to improve the performance of the mud. The role of mud in drilling: to generate large hydrostatic pressure in the hole to prevent hole collapse; Mud leaked into the soil outside the hole. When drilling, a layer of cement is formed on the surface of the hole wall due to the action of the drill bit, which plays the role of wall protection, and at the same time, the water flow outside the hole is cut off, which can stabilize the water level in the hole. The large mud ratio has the effect of entraining drilling slag, which is beneficial to the discharge of drilling slag. The mud specific gravity is between 1.05- 1. 10. Because this pile is based on the soil layer with alternating clay and sand layers, clay is used as mud, and the specific gravity of mud is about 1. 10. Viscosity 16-25Pa/S, sand content ≤4%.
(3) Install the drilling rig. The drilling rig is a support for drilling holes, hanging steel cages and pouring concrete. During drilling, the hole-forming center must be aligned with the center of the pile position, and the drilling rig must be stable without displacement, inclination and sinking. After the rig is installed in place, it should be measured in detail, the base should be plugged with sleepers, and it should be checked frequently during drilling.
Second, drill holes.
When drilling, the mud pump and rotary table should be started first, so that a certain amount of mud can be stored in the hole before drilling. At the beginning of drilling, it should be done slowly at low speed. When drilling reaches a certain depth, drilling can be carried out at medium speed. However, when encountering sand layer, the drilling speed should be slowed down and the mud consistency should be appropriately improved. The drill bit repeatedly impacts the bottom of the hole and the surrounding soil layer by continuously lifting and lowering the cone, so that the clay mud and sand in the soil layer are squeezed to the hole wall or broken into slag, and the drilling slag is suspended in the mud and overflowed by the mud pump. During drilling, accidents such as hole collapse, well deviation, buried drilling or lost drilling should be prevented, and the following points should be noted:
(1) During drilling, the water level difference and mud concentration inside and outside the hole should be kept at all times to protect and fix the shaft wall and prevent hole collapse.
(2) During drilling, the drilling speed should be controlled and the mud consistency should be adjusted according to the geological exploration to prevent hole collapse, hole deviation and sticking. Drill slowly. In order to ensure the verticality of the pile, we will strengthen the correction in the construction. If there is well deviation, measures should be taken immediately to correct it. If it can't be corrected, we should seal the hole and drill again.
(3) Drilling should be done in one go. It is not advisable to stop drilling in the middle to avoid hole collapse. If the hole collapse is serious, it should be backfilled and re-drilled.
(4) When lifting the drill cone, it must be smooth to prevent collision with the casing bottom, hole wall and hook casing, and the drill pipe should be folded quickly and accurately.
(5) During drilling, the inspection of pile location and hole formation should be strengthened. After the hole is formed, the pile position, aperture, shape, depth, inclination and hole bottom should be checked according to the quality standard. After passing the test, immediately clean the hole, place the reinforcing cage and pour concrete.
Three, hole cleaning and hoisting reinforcing cage
The purpose of hole cleaning is to remove drilling slag and mud deposited at the bottom of the hole, so as to ensure the quality and bearing capacity of pouring concrete. Hole cleaning method: change slurry to clean holes. After drilling is completed, stop the footage, and continue to circulate slurry change and slag removal until the requirement of cleaning sediment is met (the specific gravity of mud is not more than 1.05). In addition, there are methods of slurry pumping and slag cleaning, and appropriate methods can be adopted according to actual conditions.
Matters needing attention when cleaning holes:
(1) The head height in the hole must be maintained;
(2) Before pouring concrete, the thickness of sediment at the bottom of the hole shall not be greater than the design requirements;
(3) The method of deepening the hole bottom shall not be used instead of hole cleaning.
The reinforcing cage shall be welded in sections in advance according to the design requirements, hoisted into the borehole by a large-tonnage crane or hoist on the drill frame, and the position of the reinforcing cage shall be corrected and fixed to prevent the reinforcing cage from floating after pouring concrete.
Fourthly, pouring underwater concrete.
After the final hole, the reinforcing cage is installed in place, and then the conduit is installed. The inner diameter of the conduit is 30cm, the wall thickness is 4mm, and each section is 2m. There are other adjusting sections with a length of 0.5-1.0m. The length of the conduit with a bottom section of 4.9m is determined according to the hole depth. Both ends of the conduit are connected with flanges and bolts, and rubber bands are padded to ensure water leakage. Before pouring concrete, the tightness of the conduit must be checked to ensure that the conduit seal is watertight. Insert the central catheter at a distance of 0.2-0.3m from the bottom of the hole (it is not allowed to be inserted into the mud deposited at the bottom of the hole), connect the funnel at the upper opening of the catheter, and set a waterproof plug. When there is enough concrete in the funnel, loosen the waterproof bolt, and the concrete will fall rapidly from the bottom of the funnel, and the water level in the hole will surge and overflow, indicating that the concrete is poured into the hole. A sufficient amount of concrete will press out all the water in the conduit, and the lower opening of the conduit will be buried in the concrete in the hole for more than1.0m. As the concrete is continuously poured into the hole through the conduit, the concrete initially poured into the hole and the water and mud on it will be continuously jacked up, and the conduit will be continuously lifted and removed until the concrete is poured into the hole.
Pouring underwater concrete is the last key process of bored pile construction, and its construction quality seriously affects the quality of pile. The following points must be noted:
(1) Concrete material requirements: Carefully design the underwater concrete mixture ratio, and the concrete must have good fluidity and workability. In order to prevent sticking, the gravel particle size is 1 ~ 3 cm, and the maximum particle size is not more than 4cm. Mix proportion of C25 underwater concrete: E032.5 cement: river sand: crushed stone: water: water reducer =1:1.82: 2.51.44: 0.03. The slump is 200mm, the cement dosage per cubic meter of concrete is 420kg, the water cement ratio is 0.44 (the actual water cement ratio is 0.5), and the sand ratio is 42%. The slump is 20 mm.
(2) The first batch of concrete must be guaranteed. In order to ensure that the first batch of concrete can squeeze out all the water in the conduit and meet the requirements of the initial buried depth of the conduit, it is necessary to calculate and determine the minimum volume of the funnel.
(3) The concrete must be mixed evenly, so as to shorten the transportation distance as much as possible, reduce bumps, and prevent the concrete from separating and sticking.
(4) The pouring of concrete must be carried out continuously to avoid interruption of pouring for any reason. The mixing and transportation of concrete must meet the requirements of continuous operation.
(5) During the pouring process, the concrete height in the hole and the missing manhole of the conduit shall be measured and recorded at any time, so as to control and ensure the proper depth of the conduit buried in the concrete, and prevent the conduit from being lifted too hard, and the bottom of the conduit being lifted off the concrete surface or buried too shallow, which will cause mud inclusion and pile breakage in the conduit, and prevent the conduit from being buried too deep, which will cause the concrete in the tube not to be pressed out or the conduit buried in the concrete, resulting in the interruption of pouring and pile breakage. Buried depth should be controlled at 2-4m. If the reinforcing cage is suspended and the concrete is close to the bottom of the reinforcing cage, in order to prevent the reinforcing cage from floating, the pouring speed should be slowed down first; Secondly, when the concrete enters the reinforcing cage at 1-2m, the conduit should be properly heightened to reduce the buried depth of the conduit and increase the buried depth of the lower part of the reinforcing cage.
(6) The elevation of the poured pile top should be higher than the design value, and the laitance and concrete within this range should be chiseled to ensure the quality of the pile top concrete. The preload value is 0.5-1.0m. After concrete pouring, pull out the steel casing and remove the excess concrete in time. However, the cleaned concrete must be 20cm higher than the design, and it will be chiseled to the design elevation after the concrete reaches the strength. (3-5cm can be left in actual construction).
(7) After pouring, check the concrete pouring quantity to determine whether the measured concrete pouring height is correct.
(8) preserve one's health and test piles.
Verb (abbreviation of verb) conclusion
With the rapid development of China's transportation infrastructure construction, bored pile, as a basic form, will still be widely used in highway bridges and other engineering fields because of its strong adaptability, moderate cost and simple construction. Cast-in-place pile is a hidden project. There are many factors that affect the construction quality of bored piles, so there are strict requirements for every link of the construction process.
The detailed information of "Construction Technology of Bored Piles for Bridge Piles" is available in Zhong Da Consulting & Construction Link, and all the relevant building construction information you want is available.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd