1. After the official drawings of subgrade are issued, the engineering department will organize technicians from all construction work areas to review the drawings, which mainly includes the following contents: comparison between the width of subgrade construction land (including ancillary works) and the designed land acquisition width, structural size, reinforcement scope, engineering quantity, and recheck of basement reinforcement treatment scheme.

2. Investigate and remove obstacles and underground pipelines in the line.

3. Layout and joint measurement of traverse piles and leveling piles in subgrade lofting.

4. Material preparation: The mixture for CFG pile is mixed by mixing station, transported to the site by concrete tanker and pumped into piles. The mixture of CFG pile is composed of cement, fly ash, sand, gravel and water. Before construction, the mixing station should prepare all the materials used for CFG piles, and carry out tests and entry inspection.

Second, the test pile

1, the laboratory carries out mixture ratio test according to the design and construction requirements to determine the construction mixture ratio.

2. Check whether the equipment works normally and whether the construction technology is mature through pile test, so as to determine the speed of pipe drawing, reasonable feeding amount and mixture ratio. Before the formal construction, the pile-forming test was carried out according to the indoor mixture ratio and the designed pile length in the laboratory, and the number of test piles was 2.

3. Test pile detection

After 28 days of pile test, the bearing capacity of single pile and composite foundation is tested. After meeting the design requirements, CFG pile construction will be carried out in a large area according to the parameters determined by the test pile.

Third, mechanical equipment

Each working face is equipped with a long auger, a concrete delivery pump, one or two tankers and other equipment, including loaders, dump trucks and concrete mixing equipment.

Four. Construction technology of CFG pile

The construction adopts the construction technology of long spiral drilling and pumping the mixture into piles in the pipe.

1, process

Site leveling → measuring and lofting → drilling rig in place → drilling and hole forming → grouting and tube drawing → moving machine.

2. Level the site.

Before CFG pile construction, the site within the scope of reinforcement shall be leveled and rolled, and the original ground shall be treated (replaced with gravel soil) according to the design requirements.

3, measuring lofting

According to the design drawings, using the known traverse points and leveling points, the reinforcement scope of CFG piles and the pile position of each CFG pile are released on site, and the double inspection and re-inspection system is implemented for measurement.

CFG pile points are inserted with bamboo piles and marked with lime circles. Measure the elevation of the leveled ground (especially the elevation of the pile position), make records, and make disclosure (clean up the plane elevation, the design elevation of the pile bottom, and the depth of the pile bottom relative to the field plane), and distribute it to the site construction personnel to determine the depth of the pile bottom relative to the field plane.

4, construction technology

① The drilling rig is in place.

According to the released CFG pile position, put the drilling rig in place on site, and adjust it after the drilling rig is in place. Adjust the level of the drilling rig and the verticality of the drill pipe through the vertical ball hanging on the side of the drill pipe guide frame and the position of the control line marked on the guide frame. The allowable deviation of verticality is not more than 65438 0%. At the same time, in the process of drilling, pay attention to observe the vertical ball at any time to ensure that the rig is not deviated.

(2) mixing the mixture

The mixture is mixed by the mixing station according to the mixture ratio determined by the pile-forming test, and the mixing time of each plate is controlled according to the mixing time of ordinary concrete, which is generally controlled at 60~ 120s. The concrete tanker is transported to the construction site, pumped into the hole, and the slump of the mixture is controlled at 160mm ~ 180mm. When mixing materials, the dosage of water, cement, fly ash, gravel and sand shall be accurately measured in strict accordance with the construction mixture ratio, and the mixture shall be evenly mixed and the color shall be consistent, and there shall be no segregation or bleeding.

③ Drilling holes.

At the beginning of drilling, close the drill bit valve, move the drill pipe downward until the drill bit touches the ground and aligns with the pile position, and start the motor drilling. Drilling should be slow first and then fast. At the same time, check the deviation of drilling and correct it in time. Construction workers clean up the soil spun out of the drill pipe while drilling. In the process of hole formation, when the drill pipe shakes or drilling is difficult, the footage should be slowed down to prevent the deviation and displacement of the pile hole from damaging the drill pipe and drilling tool. According to the footage mark marked on the drill frame, drill the drill pipe to the designed pile bottom elevation, turn off the motor, stop drilling, and clean up the soil around the drilling hole.

④ perfusion and extubation

After drilling CFG pile to the design elevation, stop drilling and start pumping the mixture. Concrete pump is used to pump concrete. When the drill pipe core is filled with mixture, it is forbidden to pump and pull out the pipe at the same time. The pipe drawing speed of the pile is determined according to the conveying speed of the conveying pump, and is generally controlled at 2m/min ~ 3m/min. The piling process should be carried out continuously, so as to avoid stopping feeding due to problems in feeding. Finally, according to the design requirements, the pile mixture should be overfilled by 50cm. After the completion of the cast-in-place pile, the top of the pile is covered with soil and covered with protection. The control of mixture perfusion is calculated by recording the pumping times of concrete pump.

⑤ Move the machine.

After completing one pile, move the machine to the next pile, and the drilling rig moves through its own mobile chassis. Repeat the above construction sequence and method for the construction of the next pile. At the same time, before drilling, check the pile position (confirm that the drilling rig is in place) and the working performance of the drilling rig, and clean the drill pipe and drill bit after moving the drilling rig if necessary.

4, pile foundation detection

After the completion of CFG pile construction, after 10 days, the bearing capacity of low-strain composite foundation shall be tested according to the design requirements, and the low-strain detection shall be carried out according to 10% of the total number of piles, and the supervision unit shall witness the detection according to 20% of the number of tested piles; The bearing capacity of composite foundation shall be tested according to 2% of the total number of piles, and there shall be no less than 3 piles, which shall be witnessed by the supervision unit and confirmed by the design unit on site.

5, quality control in the process of construction

① Mix the mixture in strict accordance with the design mixture ratio, and control the slump between 160mm ~ 180mm. In the process of construction, the loss rate of slump is obtained according to the field test, and the slump is adjusted according to the test results to avoid the pipe blockage caused by the rapid loss of slump;

(2) When drilling, adjust the tube drawing speed strictly according to the test pile. When lifting the drill pipe, it is necessary to use static lifting, and under special circumstances, it is necessary to use lateral lifting. At the same time, the actual feed rate is determined by the pumping times of the concrete pump. The concrete surface must always be higher than the bit surface, and the bit is lower than the mixture surface 15~25cm. Ensure that the mixture in the drill pipe and soft and hard pipes is continuous;

(3) In order to ensure that CFG piles will not affect the quality of adjacent piles in the construction process, according to the geological conditions, interval piles and interval rows are adopted when necessary;

(4) Check the working state of the exhaust valve frequently during the construction, and clear it in time if it is found to be blocked, so as to avoid accumulation;

⑤ During the construction, the drilling and mixture supply must be closely coordinated to ensure the consistency of drilling and pumping materials, and to prevent the bearing capacity of CFG piles from being affected by insufficient pile ends;

⑥ According to the design requirements, ⑥ The top of ⑥CFG pile must be 50cm higher than the design elevation to ensure the strength of effective pile length.

6, pile head treatment

Manually excavate the foundation pit, cut off the protective pile head (50cm), and avoid disturbing the quality of the pile below the pile head when chiseling. The correct way to chisel the pile head is: first, hit the designed pile top elevation on the pile body with a level meter, and then two workers chisel away the redundant piles from opposite directions with two steel needles at the cutting position. After the pile head is removed, the top surface of the pile should be leveled and the residual soil in the site should be cleaned to facilitate the construction of gravel cushion.

7. Construction of gravel cushion on pile top

After the CFG pile passes the inspection, clean up the site and construct a gravel cushion with a thickness of 60cm and two layers. First, construct the lower cushion with a thickness of 30cm. Push the structure from one end to the other. Immediately after unloading, bulldozers shall be used for leveling and rollers shall be used for rolling. Slow static pressure will be used when rolling. Ensure that trucks and construction machinery always run on the gravel cushion. The truck should reverse into the site and leave the construction site after unloading. U-turn or emergency stop on the seat cushion is not allowed. When the bulldozer turns and turns around, it should be done on the cushion. It is not allowed to open the cushion and touch the pile head of CFG pile to avoid damaging the pile head.

After the cushion construction is completed, geogrids shall be laid. Before laying geogrids, a 5cm thick medium-coarse sand cushion should be laid on the cushion. The stress direction of geogrid should be consistent with the design. When laying, pay attention to the lap width of not less than 20cm, and the laying should be straight without bulging, folds and creases. Geogrids are fixed with U-shaped nails, with a spacing of 2m and a plum blossom arrangement, and the U-shaped nails are made of φ6 steel bars. Geogrid shall be laid and constructed at the same time with 5 cm medium coarse sand cushion. The medium-coarse sand cushion is paved manually by handcart, and finally the upper cushion is constructed. The construction method and requirements of the upper cushion are the same as those of the lower cushion.

Five, the construction quality assurance measures

1, strictly control the materials entering the site, ensure the use of materials such as cement, sand, crushed stone and additives that meet the requirements of the specification, and do the entry inspection test according to the standard inspection regulations, and issue inspection reports;

2, the mixture strength must meet the design requirements. Each machine-team makes a set of standard test blocks for 28d standard curing and tests the compressive strength of the test pieces;

3. When pouring the mixture on site, be sure to ensure the compactness of the mixture. Ensure the pile section size, and the bit lifting should be kept at a constant speed. The lifting speed shall not be greater than the concrete pouring speed to prevent shrinkage and pile breakage;

4. Monitor the quality of the mixture at any time during pouring to ensure the workability and slump of the mixture, and check the slump of each vehicle.

5, to prevent broken pile:

(1) The slump of the mixture shall be strictly controlled according to the design requirements;

(2) Ensure the supply of mixture;

(3) The pipe lifting speed is increased at a constant speed according to the determined parameters.

6, quality acceptance criteria:

(1) The varieties, specifications and quality of cement and coarse and fine aggregates used meet the design requirements;

(2) The number and arrangement of CFG piles meet the design requirements;

(3) The allowable vertical and horizontal deviation of pile position is 50mm, the verticality of pile body is 65438 0%, and the effective diameter of pile body is not less than the design value;

(4) The feeding amount of each pile shall not be less than the designed pouring amount;

(5) Effective pile length should meet the design requirements;

(6) The quality integrity of the pile body meets the design requirements;

(7) The bearing capacity and deformation modulus of the treated composite foundation meet the design requirements;

(8) For quality acceptance, the Interim Standard for Construction Quality Acceptance of Railway Subgrade Engineering of Passenger Dedicated Line shall be implemented.

Six, safety assurance measures

1, all on-site electrical equipment is used as leakage protection device, and the distribution line adopts three-phase five-wire system;

2, in strict accordance with the provisions of the relevant operating procedures, the use of construction machinery, the implementation of special plane, it is strictly prohibited to irrelevant personnel to enter;

3. The drilling rig should be placed stably, and the deviation of drill pipe centerline after installation should be less than 65438 0% of the total length;

4. In case of sticking during drilling, immediately cut off the power supply, stop tripping, and do not start it forcibly before finding out the problem;

5, in the process of drilling in case of frame shaking, moving, deflection should immediately stop drilling;

6, pump pipe elbow laying as far as possible, the bracket should be strong, the joint should be connected reliably;

7. It is forbidden to set the riser directly on the outlet of the concrete pump, and the outlet should be a horizontal pipe with a length not less than 10m;

8, when pumping hopper should keep a certain amount of mixture, shall not be empty;

9. When cleaning the pump pipe, no one is allowed in the range of 10m before export;

10, hoses, mixed liquid pump pipes and drill pipe joints must be firmly and tightly connected;

1 1. When drilling, the construction personnel must wear safety helmets;

12. When drilling, it is forbidden to remove the soil on the spiral piece by hand, but use a shovel to remove it. When removing soil, it should be removed horizontally, not with the rotation of the spiral blade, so as to avoid accidents.

Seven, environmental protection measures

1. The spoil produced by drilling shall be transported to the designated spoil ground in time and shall not be discarded at will. The site selection and protection of waste dumps shall comply with the provisions of environmental protection.

2. Mud generated by drilling and sewage generated when cleaning the pump shall be discharged to the sedimentation tank within the land requisition boundary, and discharged after sedimentation, and shall not be discharged at will.

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