Construction technology of post-grouting technology of cast-in-place pile
OneProcess flow
Grouting pipe, grouting valve (cavity) production -- placing the grouting device with the sinking of the reinforcement cage -- secondary hole cleaning -- pile concrete pouring -- valve opening -- cement slurry preparation -- pressure grouting -- pressure grouting and hole plugging.
1. Make grouting pipes and grouting valves.
1.1. At the same time as making the steel cage, make the grouting pipe and grouting valve. The grouting pipe is made of seamless steel pipe with a diameter of 25mm, the joint is connected by threads, and the two ends are sealed with plugs. The upper part of the grouting pipe is 30 50cm higher than the piling operation face of the cast-in-place pile, and it is advisable not to be damaged by the collision when pouring concrete, and the reinforcement cage grows 5cm at the bottom of the pile.
1.2. The design adopts open grouting when the grouting pipe is made into a grouting nozzle valve (commonly known as a flower pipe or grouting valve) in the lowest 20cm, and the grouting hole with a drill bit is used to evenly drill out 4 rows (4 in each row), the spacing of 3cm, and the diameter of 3mm are used as the grouting nozzle, after the drilling is completed, the iron filings in the pipe should be cleaned up, and the grouting hole is blocked tightly with a pushpin, and the bicycle inner tube of the same diameter is covered on the outside and sealed with tape at both ends. In this way, the grouting nozzle forms a simple one-way device: when the pressure in the grouting pipe bursts the tire and the pushpin pops out during grouting, the cement slurry is pressed into the gravel layer through the pores of the grouting hole and the pushpin, and the device ensures that the concrete slurry will not block the grouting pipe when the concrete is poured.
1.3 design adopts closed grouting, use grouting cavity (also called grouting capsule), grouting cavity is laid flat at the lowest end of the reinforcement cage, the contact between the grouting cavity and the reinforcement cage adopts a diameter 6cm larger than the diameter of the reinforcement cage, and the thickness is 3 5mm round steel plate isolation, so as to avoid the reinforcement cage from penetrating the grouting capsule, and 2 arc-shaped grouting spray valves are symmetrically arranged in the grouting capsule, and the grouting chamber is filled with an appropriate amount of 15～3.0cm graded gravel filling to protect the grouting nozzle, the arc grouting nozzle valve is vertically connected to the grouting pipe by a "tee". When the grouting chamber sinks with the reinforcement cage, the grouting capsule should be fixed with iron wire.
2. Place the grouting device with the sinking of the reinforcement cage.
2.1. When the drilling depth of the cast-in-place pile reaches the design requirements, the drill bit of the drilling rig is left at the bottom of the hole for idling and slag cleaning. Repeat several times to clean the hole, the hole is cleared and the drill bit is raised, and the hole diameter, hole depth and verticality are tested by the full-time quality officer and the project supervisor, and after the acceptance is qualified, the drilling rig is removed, the cover plate is covered, the lifting of the reinforcement cage in the next process is carried out, and the grouting device is installed.
2.2. Since the installation of the reinforcement cage is carried out at the same time as the installation of the grouting device, it is necessary to pay attention to the protection of the grouting device during the installation of the reinforcement cage.
2.3. The hoisting of the reinforcement cage should be aligned with the hole position, hold it steady, and slow to avoid colliding with the hole position, and fix it immediately after it is in place. When decentralization is difficult, the cause should be ascertained, and the grouting device should not be forcibly decentralized.
2.4. When the multi-section reinforcement cage is hoisted, the reinforcement cage should be put into the hole after the orifice is lengthened, the cage body is fixed on the casing by using the upper part of the reinforcement cage erection rib inserted into the hole, and then the upper section of the reinforcement cage is temporarily hoisted by using the hoisting machinery to carry out the docking and binding of the two sections of the reinforcement cage. The grouting pipe is also installed in sections with the segmented sinking of the reinforcement cage, and the joint is wrapped with a sealing tape, and the pipe hoop is tightly connected up and down to avoid air leakage.
2.5. When welded connection steel cage or grouting pipe is adopted. After the reinforcement cage is docked or the grouting pipe is welded, the quality officer and the project supervisor should be asked to inspect and accept the weld, and then sink into the hole after cooling.
2.6. The elevation positioning of the reinforcement cage can be used to lock the boom. The boom ring is tied together with the casing to fix the reinforcement cage and prevent the reinforcement cage from floating when pouring concrete.
2.7. The grouting pipe is fixed with the position of the reinforcement cage, and the grouting pipe should be exposed to the surface, so as not to affect the pouring of underwater concrete at the orifice and ensure that the grouting pipe does not collide, and the general exposed surface height is 60 100cm.
2.8. The setting and installation method of grouting pipe, grouting valve and grouting chamber.
There are three ways to grouting after cast-in-place piles: grouting at the bottom of piles; pile pressure measurement slurry; Pile bottom, pile side compound grouting A post-grouting conduit adopts standard size steel pipes, generally 3 are vertically arranged along the reinforcement cage, of which 2 are set up for the length of the grouting pipe at the bottom of the pile, and should be tied and fixed or welded with the reinforcement cage stiffener. Another vertical grouting pipe is connected to the grouting pipe valve on the pile side. The grouting pipe valve on the pile side adopts an annular pipe valve, which is set every 6 12m at a distance of more than 5 15m from the bottom of the pile and less than 8m from the top of the pile. B grouting pipe is connected with the reinforcement cage in sections, the grouting pipe on the lower section of the reinforcement cage can be pre-tied firmly with iron wire before the lower cage, the grouting pipe of the upper section of the reinforcement cage can be temporarily fixed first, after the reinforcement cage is connected, the upper and lower sections of the grouting pipe are connected with a thread buckle, and reinforced on the reinforcement cage again. When the grouting pipe is connected, it is necessary to ensure its airtightness, and the nozzle is tightened with plugging wire and tape to prevent the mud from entering the pipe and causing blockage. After the reinforcement cage is lowered and the first pump water is carried out to clean the pipeline, the grouting pipe should be closed with different color plugs in time to see the difference. When the reinforcement cage is lowered and installed with the grouting cavity (valve) and grouting pipe, the reinforcement cage shall not be bent when hoisted, and confirm that the grouting cavity and grouting valve are intact, and the reinforcement cage shall not be pierced, forcibly twisted and collided after the bottom of the hole is lowered. The grouting valve should be able to withstand the hydrostatic pressure of more than 1MPa. d. In the construction process of placing conduits and pouring concrete, measures should be taken to strengthen the protection of the grouting cavity and grouting pipe to prevent damage caused by the collision of construction equipment.
3. Open the valve. When the steel cage is processed, a single grouting valve is made and installed at the bottom of the grouting pipe, and before the concrete is poured and solidified, the grouting pump must be used to open the grouting valve at the bottom of the grouting pipe, otherwise after the concrete is solidified, the grouting valve that is wrapped cannot be opened, and the grouting can not be successfully realized.
4. Preparation of cement slurry.
4.1. The water-cement ratio of cement slurry shall be prepared according to the design requirements, and the on-site construction can be appropriately adjusted according to the geological and hydrological conditions and the post-grouting process. The water-cement ratio of the slurry should be determined according to the saturation and permeability of the soil, and the general water-cement ratio should be 045～0.9。The slurry with low water-cement ratio should be mixed with a superplasticizer.
4.2. When pulping, it is advisable to use appropriate measurement methods for preparation, and the allowable error of batching is 5%.
4.3. Mixing time of cement slurry: when using ordinary mixer, the mixing time is not less than 3min; When using a high-speed mixer, the mixing time is not less than 30s. The slurry is sieved before use.
4.4. Seasonal stage pulping: in the cold season, the temperature of cement slurry should not be less than 5, and the mixture should be free of snow, ice and frost; In the cold season, if hot water is used to make pulp, the water temperature should not exceed 40. When pulping in the hot season, heat and sun protection measures should be taken, and the slurry temperature should not exceed 40.
4.5. For the prepared slurry, the test personnel should be arranged to make cement specimens, and the consistency test should be carried out, and the grouting can only be carried out after passing the test; The maximum retention time of cement slurry from mixing to use is determined by the test, and generally shall not exceed 4h.
4.6. When the grouting amount is large and relatively concentrated, a pulping station can be established to centralize pulping and transportation.
5. Pressure grouting.
5.1. The grouting operation should be completed within 2 30d after the pile is formed, and the concrete strength reaches 75% of the design value before the grouting operation can be implemented. In pile foundation engineering, post-grouting construction can only be carried out after the pile integrity test (often using small strain or acoustic wave detection method) is qualified.
5.2. Before grouting, the operation of the mixer and grouting pump should be inspected, and the pressure test of the grouting pipeline should be carried out.
5.3. The grouting sequence should be implemented in accordance with the design regulations, if the design documents are not clear, it can be determined by experienced post-grouting construction technicians according to geological and hydrological conditions. The grouting sequence should generally follow the principle of pile side first and then pile end, upper part first and then lower part, and peripheral and then center.
5.4. A certain amount of clean water should be injected before the formal injection of cement slurry.
5.5. The grouting adopts the principle of dual control of grouting volume and pressure, mainly based on grouting volume control, supplemented by pressure control, and the working pressure is generally 1 3MPa; The termination pressure should be implemented in accordance with the design provisions, if the design documents are not clear, according to the hydrological, geological conditions by the experienced post-grouting construction technicians to determine, the grouting termination pressure is generally 15～8.0MPa, unsaturated soil, fine particles, dense soil layer take the high value, on the contrary, take the low value.
5.6. The amount of grouting shall be implemented according to the design, if the design documents are not clear, it can be implemented according to the relevant requirements of the relevant specifications such as the "Technical Code for Building Pile Foundation" JGJ94 and the "Technical Code for the Construction of Highway Bridges and Culverts" JTG TF50.
5.7. The slurry flow rate should be controlled within 75L min during the grouting process, and the slurry flow rate should not be greater than 30L min when the grouting is terminated.
5.8. When the total amount of grouting reaches 75% of the design value, the grouting pressure exceeds the design grouting termination pressure value, and the grouting pressure has been large, the grouting can be terminated. The pressure holding time of grouting termination is 5min.
5.9. When there is an abnormal situation in the grouting process, the cause should be found out and treated accordingly before the grouting can be continued.
6. Pressure stabilization, slurry filling and hole plugging.
After the grouting is completed, the high-pressure hose should not be removed immediately, and the pressure should be stabilized about 5, so that the grout can fully penetrate into the pile side or the pile low soil, and then re-press a few times, so that the grouting pipe is filled with cement slurry, and finally the grouting pipe is blocked tightly with a wooden stopper, and the grouting is finished at this time.
IIQuality standards
1 Master project.
The raw material test meets the requirements of relevant specifications. The grouting termination pressure is not less than the design pressure and not more than 10MPa. The amount of grouting shall not be less than the minimum limit of the design amount of grouting volume.
2 General Items.
The grouting work is carried out within 2 30d of the pile. The temperature of the cement slurry is not less than 5 and not more than 40. The water-cement ratio of cement slurry meets the design requirements. Exceptions are handled properly and reliably. The construction records are complete and standardized.
IIIFinished product protection
1. The grouting pipe exposed to the ground is sealed with a plug, and different colors are used to mark the grouting pipe at the bottom of the pile and the grouting pipe on the pile side, and a small red flag warning is inserted near the grouting pipe to prevent collision or squeezing of the grouting pipe.
2. In the construction deployment, it should be considered that no temporary roads should be left at the place where there is a grouting pipe, and it is strictly forbidden for machinery and equipment to roll the grouting pipe.
3. During winter construction, it is necessary to grasp the temperature change in time, and the temperature is lower than 5 to wrap the grouting pipe exposed on the ground for anti-freezing, so as to avoid freezing or freezing cracking in the grouting pipe, resulting in the failure of grouting to be implemented.
4. Before the initial setting of the grouting, the collision of mechanical equipment should be avoided and the grouting pipe should be disturbed, so as not to affect the growth of the strength of the grout.
5. After the grouting is completed, the grouting nozzle should be blocked tightly with a wooden plug in time to prevent the grout from spewing out or backflowing.
Fourth, the projectQuality
1. If the grouting valve cannot be opened normally, the pressure of the grouting pump can be appropriately increased, and the grouting valve can be opened by pulse method, but the maximum pressure cannot exceed 10MPa.
2. If there is slurry on the ground, it should be treated by blocking the slurry channel, adjusting the water-cement ratio, reducing the grouting pressure, and gap grouting according to the specific situation.
3. If the grouting amount reaches 75% of the design grouting amount, the grouting pressure is less than 70% of the grouting termination pressure, and the grouting pressure has been very small, it should be treated by adjusting the water-cement ratio, interstitial grouting, and adding additives.
4. If special strata are encountered, such as fault zones, quicksands, weak layers, karst caves, etc., a technical special meeting should be held to study and deal with them.
5. The grouting work must be carried out continuously, if it is interrupted for any reason, it should be dealt with according to the following principles: a shorten the grouting interruption time as much as possible and resume the grouting work as soon as possible. When the interruption time exceeds 30min, try to flush the equipment and pipelines immediately to prevent the cement slurry from curing. c. When resuming grouting, the cement slurry with a large water-cement ratio should be injected first, and then the cement slurry with a normal water-cement ratio should be restored after the pipeline and grouting valve are unblocked.
6. When the grouting valve is all blocked and the grouting cannot be implemented, the pilot hole can be drilled in the center of the pile and around the pile, and the grouting system can be reinstalled to implement grouting. However, attention must be paid not to damage the reinforcement of the pile foundation, and the pilot hole should be treated according to the relevant specifications.
7. The distance between the grouting operation and the hole forming operation point should not be less than 8 10m. The grouting interval at the pile end on the pile side should not be less than 2h.
FiveSafetyConstruction
1. Strengthen mechanical maintenance, overhaul and maintenance, and operate mechanical and electrical equipment by special personnel.
2. Strict electricity management, the installation and removal of all power supplies and circuits at the construction site must be operated by licensed electricians, and electrical appliances must be strictly grounded, zeroed and leakage protected. The on-site cable should be overhead, and it is strictly forbidden to mop the floor and bury it in the compacted soil.
3. During high-pressure grouting, the operator should not stand in the throwing direction of the high-pressure hose joint.
4. Before grouting, drain the mud of the empty pile part in time, backfill the plain soil and tamp it or set up a safety cover (mesh) to cover it tightly to prevent the falling hole, and the wellhead position should be set up with obvious warning signs.
5. During the operation of the grouting pump, do not put your hand into or prevent other objects from falling into the plunger motion chamber. The high-pressure hose and grouting pipe of the grouting pump should be pre-installed with easy-to-operate safety double valves to ensure the safety of the fitting when installing and removing the joint.
SixGreenEnvironmentally friendly
1. Construction wastewater, waste slurry and slag shall be treated, and shall not be directly discharged to pollute the environment and poured into the specified location.
2. The cement slurry storage pool is set up at the position without piles. The capacity of the pool is not less than the number of slurry discharged twice by the mixer, which prevents the large number of slurry from overflowing, and can ensure the continuous demand for slurry. The cement slurry storage pool should be built with bricks, and the walls and bottom of the pool should be plastered with cement mortar.
3. The storage of volatile products such as oil should be sealed and the opening time should be shortened as much as possible.
4. It is strictly forbidden to burn plastic packaging, linoleum, rubber, plastic, leather packaging and other substances that produce toxic and harmful gases at the construction site.
5. When transporting cement and other fine-grained bulk materials that are easy to fly, cover them tightly with tarpaulin, and the amount of them should be moderate, and they should not be transported beyond the limit to reduce dust.
6. During the cement slurry mixing operation, the operator should be equipped with dust cover and other labor protection supplies. Vehicles entering and leaving the construction site should be cleaned.
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