(1) Preparatory work
1. Before construction, engineering geological data and hydrogeological data should be mastered, and the quality inspection report of various raw materials and products used should be available.
2. During construction, measures such as safe production and environmental protection shall be formulated in accordance with relevant regulations.
3. The construction of the pouring pile should have a complete and effective construction record.
(2) Hole forming method and equipment selection
According to the piling method, it can be divided into mud wall holes, dry work holes, cylinder (immersed pipe) pouring piles and blasting holes, and the types of construction tools and soil conditions can refer to the following table:
(3) The mud wall is formed into holes
1. Mud preparation and cylinder burial
(1) The mud preparation is designed according to the construction machinery, technology and the mix ratio of the cross-soil layer, and the high plastic clay or bentonite should be selected.
(2) The depth of burial of the protective cylinder shall comply with the relevant regulations. The top surface of the guard cylinder should be 2m higher than the construction water level or groundwater level and 0.3m higher than the construction ground. Its height should still meet the requirements of the height of the mud surface in the hole.
(3) Before pouring concrete, the relative density of mud after clearing the hole should be less than 1.10; the sand content should not be greater than 2%; the viscosity should not be greater than 20pa. S。
(4) Mud ponds and mud collection facilities should be set up on the site, and waste mud and slag should be treated and must not pollute the environment.
Slurry preparation
Mud viscosity testing
The protective cylinder is buried
2. Positive and reverse cycle drilling
(1) When the mud wall is formed, the drilling speed is controlled according to the mud replenishment situation; the drilling rig is kept stable.
(2) In the process of drilling, if there is a phenomenon of oblique hole, collapse hole and slurry around the guard cylinder, instability, etc., the drilling should be stopped first, and then drilled after corresponding measures are taken.
(3) The drilling hole reaches the design depth, and before pouring concrete, the thickness of the sediment at the bottom of the hole should meet the design requirements. The design does not require that the sediment thickness of the end-bearing pile should not be greater than 100mm, and the slag thickness of the friction pile should not be greater than 300mm.
Positive and negative loop schematic
Basic principles of underwater pouring concrete:
3. Impact drilling into holes
(1) When the impact drilling is opened, it should be struck with a low hammer, repeatedly impacting the wall to keep the mud surface in the hole stable.
(2) Effective technical measures should be taken to prevent disturbance of hole walls, collapse holes, reaming holes, card drilling and drop drilling and mud loss and other accidents.
(3) Every 4 to 5m hole drilled into the test hole once, before changing the drill bit or at the easy to shrink hole, the hole is tested and should be recorded.
(4) The mud should be replenished in time during the slag discharge process.
(5) When encountering beveled holes, plum blossom holes, collapsed holes, etc. in the punching hole, measures should be taken before the construction can continue.
(6) The hole wall with poor stability should be recycled by mud or discharged by slag pumping cylinder, and the mud index before pouring concrete after hole clearance meets the requirements.
Impact into holes
[The basic principle of impact drilling] is to use a heavy hammer to continuously improve and then free fall down, smash the rock or soil layer at the bottom of the hole, and then pour mud into it to float out the fine stone slag, and the impact drill is mainly used in the rock layer to form holes.
4. Spin to dig a hole
【Rotary drilling rig construction steps】Rotary drilling rig in place→ buried guard barrel→ drill bit lightly landed on the ground after rotating drilling → when the drill bit is filled with soil sand to lift out the hole outside the → rotary drilling rig, dump the soil sand in the earth or the ground→ close the drill bit trap, spin drilling rig back to the original position, lock the drilling machine rotating body → put down the drill bit → drilling to complete, clear the hole and determine the depth→ put into the steel cage and conduit → for concrete pouring→ pull out the guard cylinder and clean the pile head sedimentation backfill, into a pile.
Spin to dig a hole
(1) Rotary drilling into the hole filling pile should be based on different formation conditions and groundwater level burial depth, using different hole forming processes.
(2) The capacity of mud preparation should be greater than the amount of mud required at the time of drilling, and the amount of mud reserve of each set of drilling rigs should not be less than the volume of a single pile.
(3) Before the hole is formed and every time the drill bucket is proposed, the condition of the drill bucket and the drill pipe connection pin, the drill bucket door connection pin and the wire rope should be checked, and the slag on the drill bucket should be removed.
(4) The rotary drilling rig should adopt the jump digging method and synchronously replenish the mud according to the drilling speed to keep the required mud surface height unchanged.
(5) The control index of sediment thickness at the bottom of the hole meets the requirements.
(4) Dry operation into holes
1. Long auger drilling
(1) After the drilling rig is positioned, it should be re-inspected, the deviation between the drill bit and the pile site should not be greater than 20mm, and the drilling speed should be slow when opening the hole; during the drilling process, it is not appropriate to reverse or lift the drill pipe.
(2) When the drilling process encounters a stuck drill, the drilling rig shakes, deflects or an abnormal sound occurs, the drilling should be stopped immediately, the cause should be ascertained, and the corresponding measures should be taken before the operation can continue.
(3) After drilling to the design level, the concrete should be pumped into the concrete and paused for 10 to 20 seconds, and then the drill pipe should be slowly lifted. The drilling speed should be determined according to the soil layer and ensure that there is a certain height of concrete in the pipe.
(4) After the concrete pressure irrigation is completed, the steel cage should be inserted to the design depth immediately, and the residual concrete in the drill pipe and the pump (soft) pipe should be removed in time.
2. Drill hole to expand the bottom
(1) The drill pipe should be kept vertically stable and the position accurate to prevent the expansion of the hole diameter caused by the shaking of the drill pipe.
(2) The thickness of the virtual soil part of the bottom hole of the bottom hole construction of the drilled bottom pile should meet the design requirements.
(3) When pouring concrete, the first time should be poured into the top surface of the expanded bottom position, and then vibrate and compact; when the concrete is within 5m below the top of the pile, it should vibrate with the pouring, and the height of each pouring should not be more than 1.5m.
(Note) Generally used in the construction of the bottom expansion pile type, the upper part does not require expansion, and the drilling pressure is increased when drilling to the bottom of the pile, so that the bottom expansion drill bit can be opened radially to form an expansion.
3. Manual digging
1) Artificially dug piles must be selected under the premise of ensuring construction safety.
(2) The cross-section of the dug pile is generally round, and there are also square piles; the hole diameter is 1200~2000mm, and the maximum can reach 3500mm; the digging depth should not exceed 25m.
(3) Using concrete or reinforced concrete support hole wall technology, the thickness of the retaining wall, the tensile reinforcement, reinforcement, and concrete strength grade should meet the design requirements; the deviation between the centerline of the well circle and the design axis shall not be greater than 20mm; the lap length of the upper and lower section of the protective wall concrete shall not be less than 50mm; each section of the retaining wall must be guaranteed to vibrate and compact, and the construction should be completed on a daily basis; the rapid coagulant should be used according to the water infiltration of the soil layer; and the formwork demolition should be carried out after the concrete strength is greater than 2.5MPa.
(4) After the hole is dug to the design depth, the bottom of the hole should be treated. It must be done that the surface of the hole is free of slag, mud and sediment.
(5) Key points in the construction of steel cages and poured concrete
1. The processing of the reinforcement cage should meet the design requirements. Appropriate reinforcement measures should be taken during the production, transportation and hoisting of steel cages to prevent deformation.
2. When the rebar cage is suspended into the hole, it shall not collide with the hole wall, and reinforcement measures should be taken to fix the position of the rebar cage after it is in place.
3. The inner diameter of the reinforced cage of the immersed pipe infusion pile should be 60 to 80 mm smaller than the inner diameter of the casing, and the pile of underwater concrete infused with the catheter should be more than 100 mm larger than the outer diameter of the conduit connection.
4. The underwater pouring concrete used in the perfusion pile should be ready-mixed concrete, and the aggregate particle size should not be 40mm larger.
5. The process of pouring pile should be continuously constructed, and the concrete must be poured within 4 hours after the steel cage is put into the mud.
6. After the concrete pouring of the pile top is completed, it should be 0.5 to 1m higher than the design elevation to ensure that the pile base surface concrete reaches the design strength after the pile head floating slurry layer is chiseled.
7. When the temperature is below 0 °C, the poured concrete should take thermal insulation measures, and the temperature of the concrete at the time of pouring shall not be lower than 5 °C. When the temperature is higher than 30 °C, the concrete should be slowed down according to the specific situation.
8. The actual amount of poured concrete of the pouring pile shall not be less than the calculated volume; the ratio of the average diameter of any section of the casing perfusion pile to the design diameter shall not be less than 1.0.
(6) Underwater concrete infusion
1. The pile hole inspection is qualified, and after the hoisting of the steel cage is completed, the conduit is placed to pour the concrete.
2. The concrete mix ratio should be determined by test, must have good and easyness, and the slump degree should be 180~220mm.
3. The catheter should meet the following requirements:
(1) The inner wall of the catheter should be smooth and round, the diameter should be 20 to 30cm, and the section length should be 2m.
(2) The catheter must not leak water, and the test should be tested and pressed before use.
(3) The deviation of the catheter axis should not exceed 0.5% of the hole depth, and should not be greater than 10cm.
(4) The conical trap should be added to the flange joint of the conduit; the spiral wire buckle joint must have a device to prevent loosening.
4. The water trap ball used should have good water insulation performance and should ensure smooth discharge.
5. When starting to pour concrete, the distance from the bottom of the catheter to the bottom of the hole should be 300~500mm; the first time the conduit is buried below the concrete pouring surface should not be less than 1m; the depth of the conduit buried in the concrete should be 2~6m.
6. The pouring underwater concrete must be continuously constructed, and the speed of the lifting pipe should be controlled, and it is strictly forbidden to lift the catheter out of the concrete pouring surface. Failures during the perfusion process should be recorded for the record.