I. Process equipment
1. conduit
Conduit can be made of rolled and welded steel plate with a thickness of not less than 3mm. The diameter of the conduit is determined according to the length of the pile, the pile diameter and the amount of concrete that needs to be passed every hour, generally 200～250mm. the length of the conduit section should be easy to dismantle and carry, and less than the lifting height of the conduit lifting equipment, the length of the section is generally 2m, the length of the bottom pipe can be lengthened to 4～6m. the intermediate section of the flange welded to the ends of the pipe in order to be connected to each other, the thickness of the flange is suitable for 10～12mm, the edge of the flange is bigger than the outer wall of the conduit. Flange edge than the outer wall of the conduit 40 ~ 50mm, at one end of the flange near the welding of a pair of small lugs, ready for hanging wire rope. Conduit splicing up and down the two sections of the flange should be padded with 4 ~ 5mm thick rubber gasket, the width of the outer flush flange edge, the inner side should be slightly narrower than the inner edge of the flange. In order to prevent the elevation of the conduit when hanging steel skeleton, in each section of the conduit can be set with a 1.5mm thick steel plate made of conical activity shroud, in order to elevate the conduit, cover the lower flange.
Conduit production should strive to smooth, straight, clean and no localized bump. The inner diameter of each section of the conduit should be the same size: the deviation is not more than ± 2mm.
2. Funnel
The top of the conduit should be set up with a funnel, and above it there is a chute, a hopper and a working platform. Funnel can be equipped with about 1m long upper end section conduit, in order to adjust the height of the funnel. Funnel generally made of 2 ~ 3mm thick steel plate conical or prismatic cone. About 15cm from the upper mouth of the funnel on both sides of the outside, symmetrically welded rings each one. Conical funnel diameter is generally 800mm, 900mm high. prismatic funnel is generally 1000mm × 1000mm × 800mm. inserted into the conduit of a section of the length, regardless of conical or prismatic, preferably 15cm. the capacity of the above funnel for the 0.5 ~ 0.7m3. In order to increase the rigidity of the conical funnel, can be welded along the periphery of the upper periphery of the funnel for the diameter of 14 ~ 16mm The steel bar. Prismatic conical funnel is welded along the outside of the bucket mouth 30mm × 30mm angle reinforcement.
3. Storage hopper
The role of the storage hopper is to store the filling of the first batch of concrete must be stored and will be far from the possible segregation of the concrete poured into it, and then mixed through the chute into the funnel. Hopper and hopper capacity (i.e., the first batch of concrete reserves) should make the first batch of concrete can meet the initial depth of the conduit buried needs.
4. Lifting equipment
Lifting equipment is generally used crane, can also be used rig lifting.
Second, the process method
1. catheter test splicing
Catheter in the use of a period of time, in addition to its specifications, quality and splicing structure should be carefully examined, it is also necessary to do the splicing, over the ball and hydrostatic (or wind pressure) test, hydrostatic pressure test should be not less than the filling of concrete catheter may be subjected to a pressure of 1.3 times the maximum pressure can be calculated in the following way.
PW = 1.3 (rc × hc - rw × hw)
Where PW - the maximum pressure that the conduit wall may withstand (kg/m2);
rc -concrete capacity weight, can be 2350 (kg/m3);
hc - maximum height of the concrete column in the conduit, using the full length of the conduit (m);
rw - water in the borehole or mud weight, 1.0 ~ 1.25, mud specific gravity greater than 1.25 is not suitable for filling underwater concrete (kg/m3);
hw - water or mud depth in the borehole (m).
Test method: assembled conduit first filled with 70% water, closed at both ends, one end of the welded wind pipe joint, input the calculated wind pressure. The conduit shall be rolled several times, after 15min without water leakage is qualified. The conduit should be smooth over the ball. After meeting the requirements, the outer wall of the conduit with obvious markings section by section numbering and labeling scale. The total number of catheters should be equipped with 20% to 30% of the spare casing.
2. conduit installation
Conduit can be pre-assembled in sections next to the drilling, and then assembled section by section when lifting. Segment assembly, should be carefully inspected, deformation and wear and tear serious shall not be used. The inner wall of the conduit and the flange surface if adhering to the mortar and mud sand should be wiped clean.
The conduit is appropriate to use two steel wire rope hanging in the lowest section of the conduit on the two lugs, and along the conduit every 6m or so with a lead wire to the conduit and steel wire rope bundled together.
Conduit lifting, should make the position of the hole in the center, axis straight, steady sinking, to prevent hanging steel skeleton and collision hole wall.
The scale on the conduit is marked with paint, and after the conduit is installed, it is inserted into the bottom of the hole, and then lifted away from the bottom of the hole for 30cm to check the actual length of the conduit.
3. Secondary clearing
Filling underwater concrete is an important process of bored pile construction, and special attention should be paid. The drilled hole should be qualified by the quality inspection of the hole, before starting the filling work. Before filling, the thickness of slag at the bottom of the hole should be measured again, such as the thickness of more than specified, should be processed for slag removal, qualified immediately after filling the first batch of concrete.
4. Calculation of the first batch of bottoming concrete:
The mouth of the conduit to the bottom of the hole is 0.3~0.4m, and the depth of the first batch of concrete conduit should be more than 1m, and the quantity of the first batch of concrete V will be calculated according to the following formula:
V=H1×πd 2/4+Hc×πD 2/4
In which D- - diameter of the bored pile;
D- - diameter of the bored pile;
The diameter of the bored pile -Diameter of bored pile;
d--Diameter of conduit;
Hc--Height from concrete surface to bottom of hole = depth of conduit (1m)+height from bottom of conduit to bottom of hole for the first batch;
< p>H1 - height of concrete surface to water surface.5. Bottom concrete construction
Concrete initial filling can be made of foam material cylindrical water spacer plug, the height should be about 14cm, the diameter should be smaller than the inner diameter of the conduit 1cm, with a wire hanging the plug placed in the conduit below the upper mouth of the 20 ~ 30cm. Cut the ball, pull the bolt or open the valve, the first batch of concrete into the bottom of the hole, and immediately measure the height of the concrete surface in the hole, calculate the depth of burial in the conduit, such as meeting the requirements, can be filled normally. If you find a large amount of water in the conduit, indicating that there are filling accidents, should be excluded from the accident before continuing to fill.
6. Concrete filling
Filling starts, should be compact, continuous, forbidden to stop in the middle of the work, the same pile of concrete filling time should not be greater than the concrete initial setting time. Try to shorten the time of removing the conduit, the material to master the speed, should not be too fast and too fierce, so as not to cause air blockage.
During the filling process, it is necessary to prevent the concrete mixture from overflowing from the top of the funnel or falling into the bottom of the hole from outside the funnel. So that the mud contains cement and thickened condensation, and make the depth measurement inaccurate. During the filling process, attention should be paid to observe the concrete drop in the pipe and the rise and fall of the water level in the hole, measure the height of the concrete surface in the hole in time, and correctly direct the lifting and removal of the conduit.
During the filling process, when the concrete in the conduit is not full and contains air, the subsequent concrete should be filled in slowly, not the whole bucket of funnel and conduit, so as not to form a high-pressure air pocket in the conduit, extruding the rubber cushion between the pipe joints, and make the conduit leak.
7. conduit lifting
Conduit lifting should keep the axis vertical and position in the center, gradually lifting. If the conduit franca hanging steel skeleton, you can turn the conduit, so that it is disengaged from the steel skeleton, moved to the center of the hole. When the conduit is lifted to a certain height above the exposed hole of the flange connector, 1 section and 2 sections of the conduit can be removed (depending on the length of each section of the conduit and the height of the working platform from the hole). At this time, pause the filling, first take away the funnel, re-tie the conduit at the mouth of the well, and hang up the lifting equipment, then loosen the connector bolts of the conduit or the quick connector, and at the same time hang the hook for lifting the conduit on the upper end of the conduit to be dismantled ring, until the bolts are all dismantled or the quick connector is dismantled, lifting the conduit to be dismantled, and then place it on the ground, then re-insert the funnel into the conduit at the mouth of the well, and then correct the position, and then continue to fill the hole.
Dismantling the conduit action should be fast, the time generally should not exceed 15min. to prevent bolts, rubber gaskets and tools, etc. fell into the hole, and pay attention to the safety of the removed pipe section should be immediately washed and cleaned, stacked neatly.
8. Filling of concrete depth measurement and conduit depth control
(1) depth measurement: filling of underwater concrete, should be detected below the surface of the water or mud surface of the depth of the hole and the height of the concrete surface filling, in order to control the thickness of the slag, the depth of the conduit and the height of the top of the pile.
Surveying the depth of the hammer method: at present, the rope system is used to hang a heavy hammer into the hole, so that through the mud slag and stay on the surface of the concrete (or under the surface of the 10-20cm), according to the depth of the hammer as the depth of the concrete filling. Completely in the hands of the detector proposed to measure the hammer in contact with the top surface of the concrete before and after contact with the top surface of the concrete after the different weight of the feeling and discernment.
The weight of the hammer of the depth pile is better to be heavier, in order to prevent the depth hammer from contacting the surface of the concrete into the depth of the hammer is too deep, with a flat bottom is appropriate, and the bottom area should not be too small. Generally made of conical, hammer bottom diameter of 15cm or so, high 8 ~ 12cm or so, hammer cast iron, its weight depending on the type of rope tied, probing depth and specific gravity of mud, etc. Generally 6 ~ 9kg. Generally 6 ~ 9kg. measuring rope with lightweight, strong tension, water does not stretch, labeled with the scale of the nylon tape measure is appropriate.
Detection must be careful, and with the number of filled concrete conversion proofreading, to prevent errors, timely detection of problems, timely solution.
Steel pipe sampling box: with each section of about 1 ~ 2m long steel pipe, steel pipe end of the male thread, the other end of the female thread, can be set into each other to tighten the length of the steel pipe at the bottom end of the set of an iron box, there is a live cover, with a thin rope tie cover with the steel pipe upward lead out. When the end of the filling will be nearly, slag precipitation thickening, the specific gravity of mud, viscosity and static shear force increases, only by the depth hammer is not easy to measure, can be used to insert a steel pipe sampling box into the mixture, hauling a thin rope will be open, the live cover, the mixture into the box, and then put forward the steel pipe, to identify the box of the thing is concrete or slag.
(2) catheter depth control: filling concrete, the depth of the catheter buried in the concrete, it is generally appropriate to control the better in 2 ~ 4m. In any case, shall not be less than 1m or more than 6m. less than 1m, easy to pull the conduit when pulling out the leakage (pulled out of the concrete), more than 6m above, buried pipe is not easy to pull out. Before pulling out the pipe, the depth of the concrete surface must be carefully detected. When probing with a depth hammer, at least two people must use the hammer to change hands to prevent misdiagnosis.
9. Determination of final filling height of concrete
In order to ensure the quality of the pile top, a certain height should be added above the design elevation of the pile top, so that the concrete can be removed after filling. The additional height can be determined according to the hole depth, hole formation method and hole clearing method, which should not be less than 0.5m in general, and should not be less than 1.0m for deep piles.
When the concrete is filled close to the design elevation, the duty officer of the construction site should measure the remaining quantity of concrete (the quantity inside the conduit should be estimated when calculating) and notify the mixing plant to supply the material according to the demand.
In order to reduce the workload of chiseling the pile head later, the excess section of the pile head can be dug out in advance at the end of the filling and before the concrete sets, but should be retained for 10-20cm to be subsequently trimmed to receive the filling of the bearing platform.
Near the end of the filling, the height of the concrete column in the conduit decreases, the overpressure decreases, and the mud outside the conduit and the slag contained in the consistency increases, the specific gravity increases. If there are concrete jacking difficulties, you can add water in the hole to dilute the mud, and pull out part of the precipitated soil, so that the filling work is carried out smoothly. When removing the last section of the long conduit, the pulling speed should be slow, in order to prevent the mud precipitated at the top of the pile from squeezing into the conduit, forming a mud center.
10. Precautions for pouring underwater concrete
(1) The conduit for pouring underwater concrete should not be leaky and have smooth inner wall. The assembled conduit should be checked by filling and pressurizing with water before use.
(2) Pouring shall not begin until the preparatory work has been checked and passed. Underwater concrete pouring shall be carried out in an environment not affected by water flow.
(3) When the poured base surface is not at the same level but is stepped or sloped, the pouring shall be started from the low-lying area, and then the full section shall be poured after it is roughly leveled.
(4) Underwater concrete pouring shall not be intermittent. The interval time of each conduit should be determined according to the specific situation, but should not be more than 30min.
(5) The flow distance, flow slope, depth of conduit embedded in the pouring concrete, pouring speed and elevation of the concrete surface in the pit, etc., should be inspected at any time, and adjusted in a timely manner.
(6) The conduit shall be lifted along the vertical direction, and the height of each lift shall be compatible with the speed of concrete pouring, and the conduit shall always have a sufficient height of concrete in it.
(7) The flow slope of the top surface of the underwater concrete should be below 1:5. When the flow slope is larger, should increase the bottom end of the conduit in the concrete depth of burial, at the same time should speed up the pouring speed, or switch to a larger degree of flow of concrete.
(8) when the cofferdam bottom pumping, the strength of the underwater concrete should be determined according to its thickness and the size of the water pressure, but should not be less than 10MPa.
(9) when the underwater concrete pouring area is large, should be used for several conduits pouring at the same time. The number of conduits, placement and pouring speed should be determined according to the specific conditions of the structure. The radius of action of each conduit shall depend on the diameter of the conduit pipe. The number of concrete poured per hour should be such that each conduit has appropriate depth of burial, and should not be less than 0.25m/h.
Three, common problems
1. Conduit into the water
(1) the main reasons
1) the first batch of insufficient storage of concrete, or although the storage of concrete has been enough, but the spacing of the conduit bottom from the bottom of the hole is too large, the concrete can not bury the bottom of the conduit under the concrete, and the concrete can not be buried. Falling behind can not bury the bottom of the conduit, so that mud and water from the bottom of the mouth into.
② conduit joints are not sealed, the rubber gasket between the joints is squeezed by the high-pressure airbag, or weld rupture, water from the joints or welds into.
③ conduit lifting too hard, or bathymetry error, to the bottom of the tube mouth beyond the original concrete surface, the bottom of the mouth into the mud and water.
(2) Prevention and treatment
Conduit water ingress caused by cause ①, the conduit should be raised immediately, and the concrete mixture scattered in the bottom of the hole with the drill pipe of the reverse circulation drilling rig through the mud pump sucked out, or air suction machine, hydraulic suction machine, and grabs to clear out. As a last resort, the reinforcing cage needs to be raised for removal by re-drilling. Then re-lower the skeleton, conduit and put in the first batch of concrete with sufficient storage capacity to re-fill.
Reason ②, ③ caused by the conduit into the water, depending on the circumstances, pull the original pipe under the new pipe, or the original conduit inserted into the renewal of the filling, but filling should be into the conduit before the water and slag with suction and pumping method of sucking out the mud. If re-under the tube, must use a submersible pump to pump the water inside the tube before continuing to fill the concrete. In order to prevent the pumping of water outside the conduit mud and water penetrate the original concrete pressed into the upper solidified layer of the conduit, continue to fill the concrete ratio should increase the amount of cement to improve the consistency of the conduit into the conduit, filling before the conduit for a small shake or hanging vibrator to be vibrated for a few moments, so that the original loss of concrete mobility can be made up. Later filling of the concrete can be restored to the normal ratio.
2. tube
In the filling process, the concrete in the conduit can not go down, known as the tube. There are two cases of stuck pipe.
(1) Shear ball when stuck tube. In the filling of underwater concrete, often produces the shear ball when the card tube situation, the reason for this situation, one is the shear ball production is unreasonable, plug the ball diameter and the diameter of the conduit difference is too small, shear the ball before the mortar or fine gravel infiltrated into the conduit and the ball wall caused by the clogging between the wall. If this is the case, under the premise of not wasting the amount of concrete, with a certain length (generally longer than the funnel 2m or so) diameter of 20 ~ 25mm steel bar to poke the ball, so that the concrete falls. Or the use of mechanical vibration to make the concrete fall, this method requires skillful operation to ensure that the concrete falls back to the normal position of the conduit buried pipe.
(2) due to the concrete itself, such as the collapse of too small, poor fluidity, large particles of aggregate, uneven mixing, as well as transportation segregation, leakage of conduit joints, rainy day delivery of concrete is not covered, etc., so that the concrete in the cement paste is washed away, the concentration of coarse aggregates caused by conduit clogging. Remedy can be used to long rod punching concrete in the pipe, shaking the conduit with a lanyard, or installing attached vibration tampers on the conduit to make the watertight plug fall. If still can not fall, then the conduit should be put out of the borehole together with the concrete inside, clean up and repair, and then re-lift the conduit and re-fill. Once the concrete mixture falls into the borehole, the mixture granules scattered at the bottom of the hole shall be removed. At the same time, it must be noted that: the first bucket of concrete slump is generally controlled in the underwater concrete slump specification requirements of the high limit is appropriate, in order to ensure that the shear ball is smooth, can be appropriate to control the amount of stone, such as shear ball is completed and then according to the normal ratio of mixing.
3. Collapse
In the filling process, if you find that the water (mud) level in the borehole casing suddenly rises out of the casing, and then suddenly fall and bubbles, should be suspected of collapsing hole signs, available side probe probe or side probe cone detection.
Collapse of the hole causes: leakage around the foot of the barrel, the water level in the hole is reduced: in the tidal river at high tide, the water level in the hole is reduced, can not maintain the original hydrostatic pressure: due to the barrel around the stacking of heavy objects or mechanical vibration, and so on.
After the occurrence of collapsed hole, the cause should be identified, and corresponding measures should be taken, such as maintaining or increasing the head of water, removing heavy objects or mechanical vibration. Then use the suction mud machine to suck out the mud collapsed into the hole. If the hole does not continue to collapse, normal filling can be resumed. If the collapsed hole still does not stop, the collapsed hole part is deeper, it is appropriate to pull out the conduit, the concrete will be drilled and grabbed, only to save the hole, and then backfill the hole with clay mixed with gravel, and then re-drill the pile when the time is ripe for the backfill soil to be compacted.
4. Buried pipe
There are two possibilities that the conduit can not be pulled out during the pouring process:
(1) Poor quality of steel cage production, some of the rebar is inserted into the conduit ring after detaching from the main reinforcement (in this case, it will generally float the cage). This time should be positive and negative rotation of the conduit, so that the conduit and rebar cage separation and center of the borehole, and then continue to pour.
(2) conduit buried depth is too large or the concrete initial coagulation so that the conduit inside and outside the friction increases, underwater concrete filling should be strictly control the depth of the buried pipe, shall not be greater than 6 m, and not less than 1 m. In order to prevent the concrete initial coagulation, in addition to the appropriate addition of retarder should be vibration of the conduit. Once the buried pipe occurs, should first find out what is the reason, as far as possible to increase the pulling force to pull up the conduit (but to prevent pulling the leakage of the conduit), pulling up the process should be positive and negative shaking of the conduit, so that it is easy to pull up.
5. Floating cage
Floating cage accident in the process of filling submerged concrete occurs from time to time, especially for the design of only part of the cage (i.e., the length of the cage is less than the depth of the borehole) of the drilled piles is more likely to occur. The reason for this phenomenon is related to the top thrust of the concrete, but poor prevention is a factor, so the cage should take relative fixing measures, as far as possible, weld a few more bars on the base of the drilling rig to increase the consolidation force. When the concrete approaches or enters the reinforcing cage during the filling process should be made clear. When the concrete surface is close to and enters the cage, the deeper embedded pipe within the permitted range should be maintained, and continuous filling of concrete to minimize the impact of concrete from the bottom of the conduit out of the cage; when the concrete surface enters the cage to a certain depth, the appropriate elevation of the conduit, in order to increase the depth of embedment of reinforcing steel cages, so that the concrete and reinforcing steel cage grip to ensure that the cage does not float. If there is floating cage, should be dealt with as soon as possible, to restrain continue to float, it is best to use more than one diameter 6cm or so steel pipe sleeve reinforcing steel cage and then welded in the barrel, and use steel or square wood into a net pressure residence welded steel pipe and barrel, to prevent the cage from floating when too large or exceeding the standard deviation.