Drilling machinery is installed on the drilling platform, and the mud circulation system is installed to carry out the drilling operation; the PHP high-performance mud is used in the drilling, the specific gravity of the mud is strictly controlled, the quality of the hole is ensured, and the hole is cleaned by the changing method after the hole is formed.
After clearing the hole, the crane will hoist the steel cage; the whole section of the steel cage is less than 15m prefabricated, and the section is more than 15m prefabricated, and the field welding is integrated into the whole. After the second clearing, the concrete pumping pipe is poured into the pile.
During construction, the thickness of the sediment in the hole, the time of the hole, the perfusion speed of the underwater concrete and the continuity of the perfusion must be strictly controlled to ensure the quality of the pile.
First, the drilling machine selection
According to the comprehensive analysis of the main span geology, hydrology and other natural conditions, combined with the existing construction machinery equipment and construction experience, the main span of the bridge deep water group pile foundation is planned to adopt GPS-22 full hydraulic rotary positive and negative circulation rotary drilling rig Drilling construction. The drilling machine adopts hydraulic transmission, centralized liquid-electric composite operation, safe and reliable; it can adopt two kinds of drilling techniques: positive and negative circulation. The drilling speed is fast and adapts to various formations. The maximum drilling diameter is 2.0m and the maximum drilling depth is 100m. Meet the needs of the construction of the deep water foundation of the Shaying River Bridge.
Second, the construction process
1, PHP high performance mud preparation
The role of PHP high-performance mud is mainly to balance the underlying pressure, suspend, carry drilling slag, lubricate and cool the drill bit, form mud and increase the stability of the hole wall. The geological conditions at the main pier of Shaying River Bridge are mostly silt and fine sand, which are easy to collapse. In order to protect the stability of the retaining wall during drilling construction, non-dispersive, low solid phase and high viscosity PHP must be used in pile foundation construction. High performance mud.
The selected PHP high performance mud index must meet the following requirements: 1) mud specific gravity: 1.15 to 1.35 for drilling, 1.05 to 1.1 for clearing; 2) viscosity 19 to 28s; 3) sand content ≤ 4%; The colloid rate is ≥96%; 5) the water loss rate is ≤20ml/30min; 6) the static shear force is 1~2.5Pa; 7) the pH value is 8~10.
When preparing PH high-performance mud, the order of clay and chemical compounding is clay→dispersant→flocculant→tackifier, such as clay→caustic soda (NaOH)→PHP→CMC. When adding chemicals, first make a water agent, then mix well in a mud mixer and add slowly.
Discharge treatment of mud: When drilling, the mud treated by the mud separator can be recycled and recycled. The hole is transported to the local environmental protection department by the car and disposed of properly to avoid polluting the environment. After the drilling is completed, the waste mud is transported to the designated location of the local environmental protection department by sealed vehicles. It is strictly forbidden to directly discharge drilling slag and waste mud into the beach and water bodies in the river.
2, drilling operations
Check whether the rig is running normally before drilling, whether there is any deformation at the bottom of the rig, whether the cable tying rope of the fixed rig is loose, and whether the position of the casing meets the design requirements.
When drilling, the speed of the footage is controlled according to the geological conditions, and the slow speed is started. After the normal drilling, the drilling speed is adjusted appropriately. The drilling bottom adopts the 80% relief drill that does not exceed the gravity of the drill (deducting the buoyancy). Into ensure that the hole is stable.
When the gimbal moves to the lower end of the rig chute, the drill pipe needs to be replaced. Before each replacement of the drill pipe, the drilling is stopped and the drilling machine is idle; the mud continues to circulate for about 1 to 3 minutes, and the drill pipe can be stopped after the drill pipe is exhausted. After stopping the pump and stopping the pump, the balance frame is lifted, the joint on the drill pipe is stuck in the hole, the connecting bolt of the balance frame and the drill pipe is removed, the balance frame is raised to the upper part of the drill frame, and the drill pipe to be exchanged is lifted by the auxiliary winch. The lower end is connected to the original drill pipe, and the upper end is connected to the balance frame. The drill must be raised outside the hole when drilling the slag, extracting the bit, removing the soil, repairing the rig, or stopping the drill for other reasons.
3, the first clear hole
After the completion of the inspection of the final hole, it is necessary to clear the hole in time. The main purpose of the hole clearing work is to ensure that the amount of mud in the mud, the relative density, and the deposited slag at the bottom of the bored pile can meet the corresponding technical indicators. The specification requires that it can better inject concrete. Sampling and clearing is a method commonly used for clearing pores. When the initial clearing is used, the changing method is usually used.
After the depth of the drilling hole meets the requirements of the design, the hole depth, the hole diameter, and the inclination of the hole are inspected. After all the indicators meet the requirements, the drilling slag and the mud are extracted by using a centrifugal suction pump to avoid cockroaches. The bad phenomenon of the hole, in the process of slag discharge, must ensure that the water head in the hole is higher than the construction water level 2.0m. After clearing the hole, after inspection, the emptying work is completed.
4, steel cage processing, lifting and sound tube installation
The steel cage is processed in the steel processing field. When the length of the steel cage is less than 15m, the whole section is prefabricated. When it exceeds 15m, it is prefabricated. Rebar removes oil and rust from the surface before use. The steel bars should be straight and free of local twists and turns. For the main rib length of the force less than 25mm, lap welding is used, the joint adopts double-sided weld, and the weld length is guaranteed to be within the allowable value range of 5d. For the main ribs with a diameter greater than 25 mm, an in-line threaded sleeve connection is used. The stirrups are spot-welded by spacer method, and welded one by one, and the welding is firm to ensure the displacement of the stirrups when the steel cage is lowered.
The steel cages are produced in strict accordance with the design drawings, and the indicators meet the design and specification requirements. Arrange the person to check the binding and geometric dimensions of the steel skeleton. Use a cross bracing to properly reinforce the cage so that deformation does not occur during the lifting process. Use a crane to lift the steel cage into the hole and use lap welding to connect at the air gap, while keeping the upper and lower sections on one axis.
The acoustic tube is connected by a threaded sleeve, which ensures the cleaning of the sleeve during construction and transportation. When connecting, the lubricant is applied to the sleeve to ensure smooth connection and water tightness.
The steel frame is slowly lowered when it is lowered. Pay attention to prevent collision of the hole wall. If it is difficult to decentralize, check the geological conditions of the stratum, analyze the cause, and then remove the resistance. After the depth of the steel cage is lowered to meet the design requirements, in order to prevent the occurrence of the cage failure during the lowering process, the hanger is used to firmly connect the steel cage to the platform or the casing. In the process of installing the steel cage, it is necessary to do the centering work, and strictly control the thickness of the concrete protection layer to ensure that it meets the design requirements.
5, catheter installation
The pipe is made of φ300mm seamless steel pipe, each section is 2.0m~5.0m long, and is equipped with 1~2 section length 0.5m~1.5m short pipe and threaded connection. Watertight, pressure-bearing and joint tensile tests are applied to the pipe before use to ensure that the pipe does not leak. After the catheter is installed, the bottom of the tube leaves a space of 250 mm to 400 mm from the bottom of the hole.
6, the second clear hole
Although the first clearing work was completed, the sediment was also produced at the bottom of the hole during the placement of the conduit and the steel cage. Therefore, after the conduit and the steel cage were in place, it was necessary to use the conduit to complete the second time. Empty the work. The second method of emptying is to install an elbow and a skin cage on the top of the pipe, pump the mud into the pipe, and then replace the sinking along the pipe from the bottom of the hole. The criterion for the second clearing hole is to ensure that the depth of the hole meets the design requirements, the mud density at the bottom of the hole is controlled to be within a range of not more than 1.15, and then the pouring of the underwater concrete is started.
7. Perfusion of underwater concrete
When installing the catheter, place it in the hole, straighten the axis, and place it smoothly to prevent the cage from colliding and colliding with the wall. A funnel and a storage hopper are arranged at the upper end of the duct, and the lower mouth is about 0.4 m from the bottom of the hole.
Underwater concrete is used. A rubber ball water-repellent facility is installed at the bottom of the funnel, and the first batch of concrete is poured by the chopping method. After the start of the pouring, it must be continuously poured to prevent the phenomenon of stoppage in the middle.
When the catheter is lifted, keep the position of the catheter centered and strictly control the depth of the catheter to ensure that the depth of the catheter is always greater than 1m. When the catheter is removed, the action must be followed, and the entire process time should be controlled within 15 minutes. The pile top perfusion elevation should be 0.5m higher than the design elevation. The steel casing for construction is pulled out after the end of the filling and before the concrete is initially set.
Precautions for construction: During the process of pouring concrete, if a certain amount of air concrete is not satisfied in the pipeline, it must be poured slowly when pouring concrete to prevent the formation of high-pressure airbag due to the presence of air, and a pipe blocking accident occurs. The rig operator must wear insulated rubber shoes with a safety helmet. The length of the dismantling pipe during the pile-plowing process shall be determined by the position of the concrete surface in the hole. Before the disassembly, the distance between the concrete face and the casing shall be measured. The number of pipe sections to be removed shall be calculated under the condition of ensuring that the buried pipe is not less than 2 m. When the pipeline is insufficiently buried in the underwater concrete, the hidden danger of the pile foundation concrete construction is reduced.
Third, summary
In summary, there are many factors affecting the construction of the bored pile foundation. During the construction process, the construction personnel must take effective measures against the frequently occurring problems to minimize the occurrence of similar adverse conditions. At the same time, the construction process is strictly controlled to ensure the quality of the project.