CN114703831A - Construction method of reinforced concrete cast-in-place pile under complex geological condition - Google Patents

Abstract

The invention relates to the technical field of building construction, in particular to a construction method of a reinforced concrete cast-in-place pile under a complex geological condition, which comprises the following steps: s1, leveling the field and setting out the pile position; s2, forming holes, taking soil, and installing a steel protective cylinder to a position X meters away from the natural terrace; s3, performing slurry wall protection construction; s4, entering rock, pulling out pipes and cleaning holes; s5, placing a reinforcement cage; s6, pouring concrete; and S7, post grouting, and checking and accepting. The invention adopts the construction process of the cast-in-place pile with the steel casing and the mud casing and the bored hole, solves the problems of easy hole collapse and buried drilling of the cast-in-place pile under the complicated geological conditions of the ultra-thick fly ash layer, vibration hole collapse during rock entering, water source shortage, serious water leakage, poor wall protection forming and the like, greatly reduces the cost and the working strength, and improves the construction efficiency.

Description

A construction method of reinforced concrete cast-in-place piles under complex geological conditions

technical field

The invention relates to the technical field of building construction, and more particularly, to a construction method of reinforced concrete cast-in-place piles under complex geological conditions.

Background technique

In view of the geological conditions of the deep mountain valleys and the fly ash backfill layer of the power plant, there are unfavorable conditions such as uneven geology and landforms of the original project, different elevations of the valley bottom, different rock mass strength, uneven thickness of the fly ash layer, and thick backfill thickness. At the same time, the fly ash layer has the disadvantages of uneven particle dispersion, loose structure, easy water permeability, easy collapse, and large filling coefficient. Through data comparison and analysis, the fly ash layer plays a negative wear resistance role in the stress of the pile body, while the fly ash layer plays a negative role in the stress of the pile body. The material contained in the ash has a corrosive effect on the steel reinforcement in the pile.

After many tests of piles using a single construction process, the construction units could not meet the requirements of low cost, tight construction period and high-quality construction. Among them, the single construction process of all-steel casing can ensure the quality of the pile foundation, but the required equipment is high, the cost is high, and it is not economical; the use of a single mud wall is easy to collapse holes, and the water loss is large, which affects the safety of the dam body. Hidden danger, can not meet the construction requirements.

Therefore, it is necessary to improve the existing technology.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies in the prior art, a construction method for reinforced concrete cast-in-place piles under complex geological conditions is provided.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A construction method for reinforced concrete cast-in-place piles under complex geological conditions, comprising:

S1. The site is leveled, and the pile position is laid out;

S2. Make a hole, borrow soil, and install the steel casing to a distance of X meters from the natural floor;

S3. The mud retaining wall is constructed to the rock formation;

S4. Rock entry, extubation, and hole cleaning;

S5, place the steel cage;

S6. Concrete pouring;

S7, post grouting, inspection and acceptance.

Further, in the described S2, a pipe rubbing machine is used to form a hole, the position of the pipe rubbing machine is adjusted to be in place, the rotary excavator is used to extract soil, the first section of the steel casing is hoisted and rubbed, the verticality is checked, and a punching bucket is used to remove the soil. Take soil from the steel casing, and press down the steel casing while taking the soil. When the steel casing is 12-1.5m higher than the top surface of the guide wall, install the second section of the steel casing and continue to press the soil down until the distance from the natural Floor Xm;

The value of X is determined according to the natural floor elevation and the excavated soil quality.

Further, during the borrowing process, keep the depth of the excavation surface exceeding the bottom opening of the steel casing ≥ 2.5m.

Further, the S3 includes:

S31, mud preparation, first inject 1Y m ³ tap water, after stirring for half an hour, put in 120 YKg of composite bentonite while stirring, after the bentonite is dissolved, evenly put in 0.5YKg carboxymethyl cellulose, then put in 1.5YKg caustic soda, 1Ykg water seepage in turn Alum, 2Ykg quicklime, the value of Y is determined according to the actual amount of mud;

S32. Use a rotary digging bucket to dig out the drilling slag in the hole in turn, and put chemical mud at X meters until the drilling is completed.

Further, the rock entry includes: using an ultra-deep pile to complete the hole forming operation, backfilling and compacting the surrounding of the casing, a rotary excavator punching a grab hammer into the casing, injecting mud, and using a rotary drilling bucket to excavate the drilling slag in the hole in turn. During the hole forming process, the mud is replenished at any time to ensure the mud head pressure in the casing;

The hole cleaning includes: cleaning the hole when the drilling of the rotary drilling rig reaches the design depth, the thickness of the sediment after cleaning the hole is ≤ 50mm, and using a cylindrical drill with a valve to clean the sediment when the hole is drilled to the design elevation, that is, cleaning the hole at one time and cleaning the hole. Lift the drill bit after the hole.

Further, the rebar cage is manufactured in strict accordance with the design and processing. The position of the main rebar is controlled by the rebar positioning bracket to control the equal distance, the allowable deviation of the main rebar spacing is ±10mm; the allowable deviation of the pitch of stirrups or spiral bars is ±20mm; the allowable deviation of the diameter of the rebar cage is ±10mm; The allowable deviation of length is ±50mm; a stiffening hoop is set every 2m to strengthen the strength of the reinforcement cage, and the length of the reinforcement cage is determined by the depth of the digging hole; the longitudinal reinforcement welding adopts single-sided lap welding, and the lap length is greater than or equal to 10d; the joints are not staggered. Less than 35d, the number of joints in the same section is less than or equal to 50%.

Further, the concrete is poured with conduit. When placing the conduit, control the bottom of the conduit to be 40cm from the bottom of the hole, adjust the height of the conduit chuck, and clamp the conduit. After the conduit is placed, check the thickness of the mud and sediment at the bottom of the hole. If the conditions meet the requirements at the same time, concrete can be poured directly. If one item cannot meet the requirements, secondary hole cleaning is required.

Further, the secondary hole cleaning includes: connecting and sealing the high-pressure pipe of the mud pump and the perfusion conduit, turning on the mud pump, and performing mud circulation, and when the thickness of the sediment at the bottom of the hole is less than 5cm, the mud circulation is continued to replace the mud and reduce the specific gravity of the mud. When the specific gravity of the mud is less than 1.15, the hole cleaning is stopped and the perfusion is carried out immediately;

The interval between clearing the hole and pouring concrete should not exceed 45 minutes to prevent the sediment in the hole from re-precipitating and the occurrence of borehole necking. Before pouring concrete, the specific gravity of the mud within 500mm of the bottom of the hole should be less than 1.20.

In order to ensure that there is no laitance and impurities on the top of the pile, the concrete should be poured at least 500mm above the designed pile top elevation.

Further, in the post-grouting process, 32.5MPa slag Portland cement is used for the cement slurry, the water-cement ratio is 0.6, and the grouting amount is 2000kg at the pile end. Grouting.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention adopts the construction technology of steel casing + mud wall bored cast-in-situ pile to solve the problems of super-thick fly ash layer and complex geological conditions. Serious leakage, poor wall protection and other problems, greatly reduce the cost and work intensity, and improve construction efficiency.

2. The invention exerts the comprehensive effect of the combined construction technology of the steel casing and the mud wall. The steel casing can be produced in a factory, can be installed in a stereotyped manner, can be used repeatedly, and can effectively reduce the filling coefficient; the mud wall can solve the problem of the fly ash layer and the coal The landslide problem at the junction of the ash and the original stratum has low cost, high efficiency, good hole-forming quality, and excellent pile-forming quality, which is beneficial to environmental protection.

3. The present invention adopts the self-developed ratio of mud retaining wall to ensure the quality of hole formation.

Description of drawings

The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

Fig. 1 is the process flow diagram of the present invention;

Fig. 2 is the post-grouting construction process flow chart of the present invention;

Figure 3 is a cross-sectional view of the mud retaining wall forming a hole.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example:

A construction method for reinforced concrete cast-in-place piles under complex geological conditions, comprising:

S1. The site is leveled, and the pile position is laid out;

Before construction, use an excavator for site leveling, positioning and laying out, and reserve 200 thick fly ash for manual leveling. The site must be leveled and compacted before the on-site lay-out to ensure that the mechanical driving and positioning of the pile foundation is stable and accurate. According to the coordinate control point given by the construction unit, the total station is used to carry out the stakeout and elevation measurement, and the RTK is re-measured and the error is controlled within 5mm.

S2. Make a hole, borrow soil, and install the steel casing to a distance of X meters from the natural floor;

According to the measured stake points, after the crawler crane and the pipe rubbing machine are roughly in place, repeat the test again, adjust the position of the pipe rubbing machine until it is accurately in place, use a 280 rotary excavator to extract soil, hoist and rub the first section of steel Protect the tube, check the verticality, press the depth of about 2.5m-3.5m, and then use a punching bucket to extract soil from the steel tube, while grabbing the soil, press the steel tube down, and keep the excavation surface beyond the steel tube. The depth of the bottom opening is greater than or equal to 2.5m. When the first section of the steel casing is pressed down until the steel casing is 1.5m higher than the top surface of the guide wall, check the verticality. The protective tube continues to press down to extract soil. And so on, dig to Xm from the natural floor.

The value of X is determined according to the natural floor elevation and the excavated soil quality. After analyzing the geological conditions faced by this example, it is found that the slag sandwiched by the fly ash layer with a buried depth of more than 35m to 40m has a loose structure and the strongest water permeability. ; The buried depth is below 40m and the landslide is serious at the junction of the fly ash and the original stratum, but the water permeability is weak. Therefore, choose X to be 40, and use a 280 drilling rig and a punching grab steel casing from below the ground to the buried depth of 40m. The hole-forming construction can solve the quality problems such as fly ash easy to permeate, easy to collapse, large filling coefficient, negative friction of fly ash and poor pile shape. Below 40m, 400 drilling rigs are used to drill rock combined with self-configured mud wall protection.

S3, mud wall construction;

S31. Preparation of mud: firstly inject 1*Y m ³ tap water, and after stirring for half an hour, put in 120*YKg composite bentonite while stirring, after the bentonite is dissolved, evenly put in 0.5*YKg carboxymethyl cellulose, and then put in 1.5*YKg in turn *YKg caustic soda, 1*Ykg seepage alum, 2*Ykg quicklime, the value of Y is determined according to the actual amount of mud.

S32. The drilling rig is in place: First, level the site so that the left and right crawler shoes of the main machine are on the same horizontal plane, and the construction position of the power head is arranged in the straight direction of the crawler, and the level of the front, rear, left and right of the fuselage is adjusted. Adjust the rig mast to a level perpendicular to the orifice so that the center of the drill bit is at the center of the pile inside the casing.

S33. Use a rotary drilling bucket to excavate the drilling slag in the hole in turn, and put chemical mud into the pile hole at a distance of 40m until the drilling is completed.

S4. Rock entry, extubation, and hole cleaning;

Use piles with pile length L ≥ 50m and length-diameter ratio L/D ≥ 50. Use special drill pipe 44×5×19.5 to complete the hole forming operation. Part of the surrounding of the casing is backfilled and compacted, and the 400 rotary excavator punches the hammer in the casing. Inject enough mud, and then dig out the drilling slag in the hole in turn with the rotary drilling bucket, and replenish the mud at any time during the hole forming process to ensure the head pressure of the mud in the casing. outside. If the diamond drill is replaced when encountering boulders, ladle stones or general rock mass or hard rock formation during the drilling process, check the verticality of the mast at any time, and control the verticality of the pile hole until the designed rock penetration depth.

When the drilling of the rotary drilling rig reaches the design depth, the hole should be cleaned in time, and the sediment should not be larger than 50mm after cleaning. When drilling to the design level, use a cylindrical drill with a valve to clean up the sediment, that is, clear the hole at one time. After clearing the hole, put out the drill bit, and test the hole diameter, hole depth, and verticality. After the acceptance is qualified, remove the drilling rig, cover the cover plate, and proceed to the next process construction.

S5, place the steel cage;

The reinforcement cage is manufactured in strict accordance with the design and processing, and the position of the main reinforcement is controlled by the reinforcement positioning bracket to control the equal distance. The allowable deviation of the spacing of the main bars is ±10mm; the allowable deviation of the pitch of the stirrups or spiral bars is ±20mm; the allowable deviation of the diameter of the steel cage is ±10mm; the allowable deviation of the length of the steel cage is ±50mm. Stiffening hoop is installed every 2m to strengthen the strength of the reinforcement cage. The length of the reinforcement cage is determined by the depth of the digging hole; the longitudinal reinforcement welding adopts single-sided lap welding, and the lap length is greater than or equal to 10d. The joints should be staggered by not less than 35d, and the number of joints in the same section should be less than or equal to 50%. When handling and hoisting, the steel cage should be prevented from being deformed; it is necessary to check the situation in the hole before placing it to make sure that there is no collapse and sediment in the hole; the placement should be aligned with the hole position, stabilized, slow, and straight to avoid collision with the hole wall. It is strictly forbidden to pierce the cage and twist the cage.

S6. Concrete pouring;

After the reinforcement cage is placed, the thickness of the sediment is measured and designed. If the thickness of the sediment is not greater than 5cm, the concrete conduit is installed. The concrete is poured with the conduit. The inner diameter of the conduit is 300mm and the turnbuckle connection. Check the appearance of the catheter, the inner wall of the catheter should be smooth, straight, smooth and free of local bumps. According to the elevation of the top of the casing, the elevation of the bottom of the hole, and to calculate the required length of the conduit, try to assemble the conduit and number it. The duct is installed manually by a crane. When the duct is placed, it should be stabilized manually to make the position in the center of the steel cage, and then it is steadily placed to prevent the steel frame from being stuck and colliding with the wall of the hole. When installing, the bottom of the control conduit should be 40cm away from the bottom of the hole. After the height of the conduit is determined, adjust the height of the conduit chuck with a crane, and clamp the conduit with the chuck.

After the conduit placement process is completed, the thickness of the mud at the bottom of the hole and the sediment at the bottom of the hole are detected. If the two conditions meet the requirements at the same time, concrete can be poured directly. If there is one item that cannot meet the requirements, a secondary hole cleaning is required. When cleaning the hole for the second time, connect and seal the high-pressure pipe of the mud pump and the pouring pipe, turn on the mud pump, and carry out mud circulation. When the specific gravity of the mud is less than 1.15, the hole cleaning can be stopped, and the pouring shall be carried out immediately. The interval between the completion of the hole cleaning and the pouring of concrete shall not exceed 45 minutes to prevent the sediment in the hole from re-precipitating and the occurrence of borehole necking. Before pouring concrete, the specific gravity of the mud within 500mm of the bottom of the hole should be less than 1.20.

Before pouring concrete, the hole should be cleaned, and it is required that the hole wall and hole bottom must be cleaned, there is no scum at the bottom of the hole, and the hole wall is not loose. When there is groundwater and the seepage amount is not large, the water in the hole should be removed, and then the concrete should be poured by the conduit method. The distance between the end of the pipe and the bottom of the hole should not be greater than 1.5m; the concrete should be vibrated with a plug-in vibrator, and vibrated once every 1.5m of pouring. Concrete should be continuously poured and compacted, and the filling factor should be greater than 1. Pour concrete at least 500mm above the designed pile top elevation to ensure that there is no floating slurry and impurities at the pile top.

During the piling process, since the follow-up type casing is deeply buried, it cannot be pulled out as a whole, which affects the quality of the pile, so it is extracted by sections. Connect with the power head driving sleeve of the rotary drilling rig, turn the follow-up casing until it rotates, and then continue the piling operation. The concrete surface is 6m per liter. The rotary drilling rig and the full casing are connected again. The drilling rig has a power head driving sleeve. Take out 2 sections of the follow-up protective tube, and the auxiliary worker uses a bubble level to measure and adjust the verticality of the follow-up protective tube. Repeat this until the final filling is completed, and all the casings are pulled out.

The concrete shall be C40 P6 commercial concrete, with a slump of 160-180mm, a concrete pouring slump of 180mm±20mm, an initial setting time of not less than 45 minutes and not more than 2 hours, a final setting time of not more than 6 hours, and a concrete pouring time of 10m ³ / 30 minutes, the height of the submerged casing shall not be greater than 3m when the concrete is poured, and the extubation shall be carried out after the concrete is poured to the extubation height, and the extubation time shall be controlled at 1m/6 minutes. The muck produced by the hole formation is transported to the place designated by the owner by dump truck. After the pile is formed, the mud that is no longer recycled after the hole is formed shall be transported in a sealed manner by a mud truck to the site designated by the owner.

S7, post grouting, inspection and acceptance.

Stir the cement slurry according to the designed water-cement ratio → the cement slurry is filtered to the storage slurry and ready for grouting → connect the grouting pipe joint to the pile grouting pipe → open the exhaust valve and open the pump to release air → close the exhaust valve pressure Slurry, the termination standard is comprehensively controlled by the amount of grouting, pressure and whether the ground returns to grouting: when grouting is terminated, close the stop valve and let it stand for 5-10 minutes before disassembling the pipe fittings, and plug the grouting pipe head again with a plug.

Two grouting pipes are arranged symmetrically at the bottom of Φ25mm*3mm steel pipe piles, the length is matched with the length of the steel cage, and the grouting pipe is connected with raw tape. On the steel cage, the grouting pipe should be exposed at least 30cm from the construction work surface after the concrete is poured into the hole with the steel cage, and 50cm from the bottom of the steel cage.

Determination of technical parameters of post grouting at pile side and pile end:

Cement slurry: 32.5MPa slag Portland cement, water-cement ratio 0.6, grouting amount: 2000kg at the pile end.

Pressure control: greater than or equal to 3MPa, when the grouting pressure is lower than the normal value for a long time or the ground appears grouting or the surrounding pile holes channel grouting, it should be changed to intermittent grouting, the intermittent time should be 30-60 minutes, or the slurry water should be reduced grey ratio.

Grouting time: After the concrete is poured, the grouting operation should start after 2 days, and it should not be later than 30 days after the pile is formed. The distance between the grouting operation and the hole forming operation point should not be less than 8-10m.

Grouting sequence: For pile group grouting, the outer grouting should be done first and then the interior, and two piles A and B should be alternately grouted.

Only the preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments, and within the scope of knowledge possessed by those of ordinary skill in the art, various aspects can also be made without departing from the purpose of the present invention. Various changes should be included within the protection scope of the present invention.

Claims (10)

1. A construction method of a reinforced concrete cast-in-place pile under a complex geological condition is characterized by comprising the following steps:

s1, leveling the field and setting out the pile position;

s2, forming holes, taking soil, and installing a steel casing to a position X meters away from the natural terrace;

s3, performing slurry wall protection construction;

s4, entering rock, pulling out pipes and cleaning holes;

s5, placing a reinforcement cage;

s6, pouring concrete;

and S7, post grouting, and checking and accepting.

2. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: in the step S2, a pipe rolling machine is adopted to form a hole, the position of the pipe rolling machine is adjusted to be in place, a rotary digging machine is used for taking soil, the first section of steel protective cylinder is hung and rolled in, the verticality is corrected, a punching grab bucket is used for taking soil from the steel protective cylinder, the steel protective cylinder is pressed down while taking soil, when the steel protective cylinder is 12-1.5m higher than the top surface of the guide wall, a second section of steel protective cylinder is installed, and soil is continuously pressed down until the position is Xm away from the natural terrace;

and the numerical value of the X is determined according to the elevation of the natural terrace and the excavated soil quality.

3. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition as recited in claim 2, characterized in that: and in the soil taking process, the depth of the excavation surface exceeding the bottom opening of the steel casing is kept to be more than or equal to 2.5 m.

4. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: the S3 includes:

s31, preparing slurry, firstly injecting 1 x Y m³After stirring for half an hour, adding 120 × YKg composite bentonite while stirring, after the bentonite is dissolved, uniformly adding 0.5 × YKg carboxymethyl cellulose, and then sequentially adding 1.5 × YKg caustic soda, 1 × Ykg water-seepage alum and 2 × Ykg quicklime, wherein the value of Y is determined according to the actual dosage of the slurry;

and S32, sequentially digging out drilling residues in the hole by using a rotary digging bucket, and putting chemical slurry into the position of X meters until the drilling is finished.

5. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: the rock entering comprises: using the ultra-deep pile to finish hole forming operation, locally backfilling and tamping the periphery of the sleeve, using a punching and grabbing hammer of a rotary excavator to inject slurry into the sleeve, using a rotary drilling bucket to sequentially dig out drilling slag in holes, replenishing the slurry at any time in the hole forming process, and ensuring the water head pressure of the slurry in the pile casing;

the hole cleaning comprises: and when the drill hole of the rotary drilling rig reaches the designed depth, cleaning the hole, cleaning the sediment with the thickness of less than or equal to 50mm after cleaning the hole, cleaning the sediment by using a cylindrical drill with a valve when the drill hole reaches the designed elevation, and taking out the drill bit after cleaning the hole.

6. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: the steel reinforcement cage is manufactured strictly according to the design, the position of the main reinforcement is controlled by a steel reinforcement positioning bracket to be equally spaced, and the allowable deviation of the space between the main reinforcements is +/-10 mm; the allowable deviation of the screw pitch of the stirrup or the spiral rib is +/-20 mm; the allowable deviation of the diameter of the reinforcement cage is +/-10 mm; the length of the reinforcement cage is allowed to deviate +/-50 mm; arranging a stiffening hoop every 2m to strengthen the strength of the reinforcement cage, wherein the length of the reinforcement cage is determined by the depth of the excavated hole; the longitudinal steel bar welding adopts single-side lap welding, and the lap length is more than or equal to 10 d; the joints are staggered with each other by not less than 35d, and the number of the joints on the same section is not more than 50%.

7. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: the concrete pouring adopts the conduit to pour, when the conduit is placed, the bottom of the conduit is controlled to be 40cm away from the bottom of the hole, the height of the conduit clamping disc is adjusted, the conduit is clamped and fixed, after the conduit is placed, the thickness of slurry at the bottom of the hole and the thickness of sediment at the bottom of the hole are detected, if two conditions meet the requirements at the same time, concrete can be directly poured, and if one condition cannot meet the requirements, secondary hole cleaning is needed.

8. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition as recited in claim 7, wherein: the secondary hole cleaning comprises: connecting and sealing a high-pressure pipe of a slurry pump and a pouring guide pipe, starting the slurry pump, circulating slurry, continuously circulating the slurry after the thickness of sediment at the bottom of a hole is less than 5cm so as to replace the slurry and reduce the specific gravity of the slurry, and stopping cleaning the hole when the specific gravity of the slurry is less than 1.15, and immediately pouring;

the time interval between the completion of hole cleaning and concrete pouring does not exceed 45 minutes, so that the occurrence of sediment in the hole re-precipitation and necking of the drilled hole is avoided, and the specific gravity of the slurry within 500mm of the hole bottom is less than 1.20 before the concrete is poured.

9. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: and pouring concrete at least 500mm higher than the designed pile top elevation.

10. The method for constructing the reinforced concrete cast-in-place pile under the complicated geological condition according to claim 1, which is characterized by comprising the following steps of: in the post-grouting process, the cement paste adopts 32.5MPa slag portland cement, the water cement ratio is 0.6, and the grouting amount is as follows: the pile end is 2000kg, the pile group is grouted firstly from the periphery to the inside, and A, B piles are used for alternate grouting.

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