Huaigou Bridge is located on Huaigou near Yuanzhou District of Guyuan City, with the center pile number K 1+9 10, and the included angle between the axis and Huaigou is 105 degrees. The starting pile number of the bridge is K 1+825.5 and the ending pile number is K 1+944.5. Huaigou Bridge is a 4-40m assembled prestressed concrete T-beam bridge, with column piers and hollow thin-walled piers. The maximum pier height is 47.9m, and the foundation is bored piles. The abutment is a ribbed abutment for bored pile foundation, with a total length of 169 m and a width of 20 m. Pier adopts cylindrical pier and hollow thin-walled pier.
The diameter of bored pile foundation of this bridge is φ 1.5 and φ 1.8, both of which are designed as supporting piles. * * *φ 1.5 bored pile is 544m, φ 1.8 bored pile is 2840m. It is planned to use rotary drilling rig to form holes and pipe method to pour underwater concrete.
The construction process of bored pile is as follows: leveling the site → setting up the workbench → releasing the pile position → burying the pile casing → positioning the drilling rig → drilling → hole formation → hole cleaning → lifting the drill → lowering the reinforcing cage → lowering the conduit → pouring underwater concrete → pulling out the pile casing → chiseling off the pile head → acceptance.
1 construction preparation
Leveling the construction site of pier and abutment, releasing the pile position and cross pile with total station, so as to check the pile position at any time. Make steel liners, process steel cages for bored piles, store clay, check the tightness of underwater concrete conduits, prepare mud pools and sedimentation tanks, and take measures to discharge mud to prevent environmental pollution.
(1) Buried liner. All steel liners are adopted, the inner diameter is 20 ~ 30cm larger than the pile diameter, and the section length is 2.0 ~ 2.5m The buried depth of the lining is 2.0~3.0m, and the top of the lining is at least 0.3m above the ground, which is more than 1.5m higher than the groundwater level. Excavate and bury the dry land liner, and compact the periphery of the liner with clay. The joint of the gasket should be welded tightly to avoid water leakage.
(2) The gasket shall be buried vertically accurately. The deviation between the center of the top surface and the center of the bottom surface of the liner and the design is less than 2cm, and the vertical inclination of the liner is not more than 65438 0%.
(3) Preparation of slurry. The performance index of clay for wall protection should meet the specification requirements. In order to ensure the quality of slurry supply, a slurry tank, a slurry storage tank and a sedimentation tank are set up during construction. Mud tank and mud pump are used for mud transportation. Check mud specific gravity, viscosity, sand content, colloid rate, etc. Adjust at any time during drilling, and adjust in time to ensure good wall protection and smooth drilling. Generally, mud index shall be kept at relative density 1.20 ~ 1.40, viscosity at 22-23 Pa.s, sand content ≤4 and gum content ≥95, which shall be filled in in time. Mud should be recycled, and waste mud should be properly treated after precipitation.
(4) The drilling rig is in place. Rotary drilling rig is adopted. After the drilling rig is in place, level the base, measure and check whether the center of the drill bit and the center of the casing are on a vertical line, and whether the deviation from the center of the hole is within the allowable range of the specification. Check whether the verticality of drill pipe meets the requirements, whether the connection between drill pipe and drill bit is firm, and whether the operation is good.
2 drilling operations
Before spudding, level the drilling rig vertically and horizontally, install the guide sleeve, slowly lower the drilling rig and align the drill bit with the hole position. When the power indicator deviates to the no-load state, start tripping in. During drilling, observe the ammeter at any time. If it exceeds the rated current, slow down the tripping speed. In the process of operation, when it is necessary to change the rotation direction of the drill pipe, it is necessary to wait until the drill pipe completely stops rotating before restarting.
When drilling or crossing the junction of soft and hard soil, in order to keep the drill pipe vertical, it is advisable to drill slowly. When drilling in the soil layer containing pumice and breccia or in the soft plastic cohesive soil layer with high water content, the sloshing of drill pipe should be reduced as much as possible to avoid enlarging the aperture.
During drilling, the accumulated soil at the orifice and the scattered soil on the ground shall be removed at any time. In case of abnormal conditions such as water seepage, hole collapse and necking in the hole, the drilling tool should be lifted out of the hole and properly handled.
When drilling in hard interlayer, the following methods can be adopted: for stones with diameter less than 10cm, ordinary auger bit can be used for drilling; For stones with a diameter larger than 1/4, it is advisable to drill slowly with a rake bit inlaid with cemented carbide. Some stones can be squeezed into the hole wall, and some can be drilled along the spiral drill pipe.
Prevention and treatment of several common drilling accidents;
Well collapse: Well collapse mostly occurs in loose sand layer, mostly due to insufficient mud viscosity, insufficient head pressure, poor wall protection and operational reasons. Treatment method: If there are few hole collapses, the mud index can be increased, the mud proportion can be increased, and drilling can be continued; If it is serious, clay can be backfilled in the hole and compacted before drilling.
Inclined hole: when drilling, inclined holes are produced due to the deviation of drilling direction, which seriously affects the installation and pile-forming quality of reinforcing cage. The main causes of inclined holes are incorrect and unstable installation of drilling rig, bent drill pipe and poor operation. , and the hole bending phenomenon when encountering large rocks during drilling. When the inclined hole is not serious, the drilling rig can be readjusted to continue drilling; Severe cases can be treated by repeatedly drilling up and down to make the drilling straight; In severe cases, clay should be backfilled in the hole and re-drilled after compaction.
3 hole cleaning and hole forming inspection
After the hole is finally formed, it will be inspected with the supervision engineer and submitted for inspection and approval. After passing the test, clean the holes quickly. Slag cleaning method and slurry changing method are used for hole cleaning. It is forbidden to use the method of deepening drilling instead of hole cleaning. Measure the hole diameter, hole depth, hole position and sedimentation thickness, and ensure that it meets the design and construction requirements before pouring concrete. After cleaning the hole, take out the mud sample from the bottom of the hole and test the performance index. Mud should meet the standard: the relative density is1.03—1.1; Viscosity17—20pa.s; The sand content is 98%. Measure the thickness of sediment at the bottom of the hole, and the thickness should be less than 5cm. After hole cleaning, the quality inspector will measure the aperture and inclination, and fill in the record carefully. After passing the inspection, it shall be reported to the supervision engineer for inspection, and the next working procedure can be carried out only after passing the inspection.
4 steel skeleton production, transportation and hoisting in place
4. 1 output
The varieties, specifications and technical performance of steel bars, machinery and covered electrode shall meet the current national standards and design requirements. The mechanical properties of cold-drawn steel bars must meet the specification requirements, and the steel bars should be straight without cracks and oil stains on the surface. The steel skeleton is made by stiffening rib forming method. The reinforcing cage is fabricated in sections and welded with holes, and the length of each section is 8- 10m. At the same time, according to the requirements of the protective layer, steel bars "ears" are welded on the outer side of the main reinforcement of the skeleton, which are arranged at intervals of about 2.0m along the vertical direction of the gap, and 4-6 bars are symmetrically arranged around each lane.
4.2 Transportation of skeleton
Skeleton transportation adopts the way of adding brackets on flat cars to ensure that the steel skeleton is not deformed during transportation.
4.3 Lifting and Positioning of Skeleton
The steel skeleton is hoisted and positioned by crane. In order to ensure that the skeleton is not deformed during hoisting, two Chinese fir poles are tied between the middle point and the third point. When hoisting, first raise the first hoisting point, slightly hoist the skeleton, and then hoist the skeleton with the second hoisting point at the same time until the design elevation is reached. The skeleton is fixed on the tic-tac-toe frame temporarily set at the orifice through channel steel or steel pipe, and the lifting point can be relaxed. The upper and lower parts of the skeleton are connected to ensure that the axes of the main reinforcement are concentric. At the same time, measure whether the elevation of steel skeleton meets the design, and the deviation shall not be greater than 5 cm. The quality inspector shall make detailed marks and require the supervision engineer to carry out tests. Only after passing the inspection can we enter the inspection items of steel bar installation in the next working procedure.
5 pouring underwater concrete
Pouring concrete is supplied by commercial concrete and mixing station. Concrete is transported to the construction site by tanker. The slump and temperature of the commercial concrete entering the site are detected by the quality inspector and the operator one by one, and the slump is controlled by the supervision engineer. After the test results meet the specifications and construction requirements, concrete pouring can be carried out.
Underwater concrete is poured by conduit method. The conduit is made of seamless steel pipe with a wall thickness of 3mm, an inner diameter of 300 mm, a middle section of 2m and a bottom section of 4 m.. The catheter is connected by thread. Before use, the conduit should be straightened, and the tensile force and water tightness tests should be carried out through trial assembly to ensure that the conduit does not leak water or slurry when pouring underwater concrete and prevent the conduit from breaking. The calculation formula of watertight pressure is as follows: P=rChC-rWHW.
P Maximum internal pressure that the guide tube may bear (KPa).
RC-weight of concrete mixture (24kN/m3)
HC —— the maximum height (m) of the concrete column in the conduit, based on the total length of the conduit or the estimated maximum height;
Rw refers to the severity of water or mud in the borehole (kN/m3)
HW —— Depth in borehole or mud (m).
2) Pay attention to the following items when installing the catheter.
(1) The length of the catheter must be accurately measured and recorded as the basis for installation and removal of the catheter;
(2) Before the catheter is hoisted into the hole, measure the depth of the hole with a measuring rope, and the bottom of the catheter should be kept about 0.4m away from the bottom of the hole, so as to avoid sediment blocking the lower opening of the catheter and causing pipe sticking accidents;
(3) When hoisting the conduit, keep the conduit vertical to prevent the inclined steel skeleton from getting stuck;
(4) If the catheter lowering is blocked, find out the reasons and take measures such as crawling, crawling, forward and backward rotation to alleviate it, and the method of lifting high and descending sharply shall not be adopted;
(5) When the catheter is lowered, check whether the thread is loose section by section.
6 chisel away the pile head
After 24 hours of concrete pouring, the pile head shall be excavated without affecting the construction of other piles. At this time, 10 ~ 20 cm should be reserved to chisel out the pile head, and then chisel out the pile head concrete after it reaches the design strength, so as to ensure the quality of the pile head concrete meets the specifications.
7 conclusion
Through the strict technical control of the above key processes, the qualified rate of bored pile construction of Huaigou Bridge is 100%, which fully meets the design requirements.
The detailed information of "Talking about the Construction of Bored Piles in Huaigou Bridge" can be found in Zhong Da Consulting and Construction Network, and all the relevant construction information you want is available.
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