A, the production of reinforced concrete sheet pile
1, production method
The manufacture of reinforced concrete sheet piles is not limited by the site, and can be made on site or in the factory. The production of reinforced concrete sheet piles generally adopts shaped steel formwork or wood-steel composite formwork. Maintenance methods include natural maintenance and steam maintenance kiln maintenance. Concrete test blocks with the same curing conditions should be made at the production site to determine the lifting, overturning and transportation conditions of sheet piles.
2. Production requirements in prefabrication and construction
Due to the special structure and special use of reinforced concrete sheet pile, it is required that the pile top of sheet pile wall is on the design horizontal plane, the sheet pile wall axis is in a straight line, and the tenon and groove are straight and accurate.
(1) Pile concrete shall be poured at one time without construction joints.
(2) There should be no regular cracks on the concrete surface of the reinforcement hoop.
(3) The tenon of sheet pile should not have defects such as missing angle and damage.
(4) The uplift strength of precast slab piles should be greater than 70% of the design strength.
(5) The deviation of lifting point position should not exceed 200mm, and the included angle between sling and pile axis should not be less than 45 degrees.
(6) When piling sheet piles, attention should be paid to: using multiple pads and laying them evenly; Each cushion layer stacked in multiple layers should be on the same vertical line; No more than 3 floors shall be stacked on site, and no more than 7 floors shall be stacked in the factory.
(7) During the shipment of sheet piles, attention should be paid to: draw the pile loading diagram according to the pile sinking order, and ship according to the diagram; During transportation, the cushion should be padded with wooden wedges, and appropriate reinforcement measures should be taken according to the actual situation; Shipment shall be made according to the principle of more cushions and less piles. Sheet piles are manufactured and stacked in the factory, as shown in figure 15- 12a and figure 15- 12b.
3, the allowable deviation of sheet pile production
See table 15-2 for the allowable deviation of sheet pile fabrication.
Second, the reinforced concrete sheet pile sinking construction
The influence of pile sinking on nearby buildings must be fully considered. In the process of piling, predict the influence of vibration and spoil on the surrounding environment and take corresponding measures. Measures such as static pile pressing or burying bagged manholes or plastic drainage boards in the soil beside piles, including slowing down the speed of pile pressing, have obvious effects.
1, pile sinking method
Pile sinking methods include driving method, water flushing insertion method and slot method, and driving method is the most commonly used method at present.
The driving methods are divided into single pile driving, row pile driving (or screen driving) or step driving. The construction of closed sheet pile can also be divided into open driving and closed driving. The so-called closed piling means that all sheet piles are inserted into the pile site through the guide frame, then the pile wall is closed and then driven underground. This driving method is beneficial to ensure the closed size of sheet pile wall. As shown in figure 15- 13.
2. Preparation before pile sinking
(1) pile material preparation
The sheet pile can only be driven when it reaches 100% of the design strength, otherwise it will easily break the pile head or crack the pile body. Before piling, it is necessary to strictly check whether the section size of the pile meets the design requirements and whether the error is within the allowable range. In particular, the interlocking part of the pile, whether tenon or mortise, must be inspected in detail to ensure the smooth driving and correct occlusion of the pile. Anything that does not meet the requirements must be transported, hoisted and stacked to ensure that the pile body is not damaged and cracks do not appear. See table 15-2 for the allowable deviation of sheet pile fabrication in this project.
(2) Manufacture of special-shaped piles
Special-shaped sheet pile includes corner pile for corner, inclined section pile for adjusting the inclination of pile wall axis, widened pile for adjusting the length and size of pile wall and guide pile for guiding and fixing pile position. Special-shaped sheet piles can be made of steel or other types of piles, such as H-shaped steel piles. The fabrication of corner piles is complicated, and the corners of sheet pile wall can also be constructed as T-shaped seals without corner piles (that is, the sheet pile wall at the corners are perpendicular to each other without biting each other).
3, reinforced concrete sheet pile production
Technological process: measuring and setting leveling points → detecting and removing obstacles on the longitudinal axis of sheet piles → positioning pile drivers or piling boats → driving guide purlins → manufacturing and installing guide purlins → sinking initial piles (positioning piles) → inserting piles → sending sinking piles → moving guide purlins to continue construction → clamping sinking piles.
(1) purlin making
Guide purlin devices are arranged on both sides of the sheet pile wall and driven in parallel to the sheet pile wall to ensure the correct positioning of the sheet pile, the verticality of the pile body and the straightness of the sheet pile wall.
Purlins are usually composed of guide columns and guide frames, and their types are divided into single-sided and double-sided, single-layered and double-layered and multi-layered, anchored and movable. Guide piles can be made of steel and steel pipes or special reinforced concrete sheet piles. The spacing of guide columns is 3 ~ 5m, and the depth of driving into soil is about 5m. The width of guide frame is slightly larger than the thickness of sheet pile by 3 ~ 5cm. The height from the bottom surface of the guide frame to the bottom surface is set to 50mm, and the height spacing of double-layer or multi-layer guide frames depends on the rigidity of the guide frame, but it should not be too large. Purlins should be simple, firm and easy to install. Generally, steel beams with sufficient rigidity should be selected, such as steel pipes, H-beams and double spliced large channel steels. The setting length of purlin each time depends on the specific construction situation and can be used in turn. When driving sheet piles in the guide frame, the single pile driving method can be adopted. For example, when the sheet pile is driven by shielding method, it can be driven into the ground after the sheet pile is completely inserted into the soil and the purlin guide frame is removed. The purlin type is shown in figure 15- 14.
(2) Positioning piling (i.e. starting pile or first pile)
The sheet piles behind the positioning piles will be buried along the straightness of the positioning piles, and then inserted into the future sheet pile wall. Therefore, the position and verticality of positioning piles (river bank side and upstream and downstream side) will have a great influence on the whole of sheet pile wall. Therefore, the driving of positioning piles should be more careful, especially the verticality of the pile body, and the error should be controlled to the minimum. Locate the elevation of the first purlin of the pile, but in order to prevent the next pile from carrying it down, the elevation can be appropriately increased by about1m. Guide purlin is shown in figure 15- 15.
(3) Insert sheet pile
After the positioning piles are basically inserted in place, other sheet piles can be inserted in turn.
Insert the sheet piles into place one by one in the guide purlin along the groove of the positioning pile (or the previous pile that has been inserted in place), and the depth of insertion into the soil depends on the pile length, the height of the piling frame and the geological conditions. It is required to use a pile hammer for static pressure, and leave the pile length 1/3 for piling. In the process of pile insertion, try not to open the hammer (especially the heavy hammer) to pile.
When the shield method is used for construction, the number of piles per row is 10 ~ 20. If too many piles are inserted at one time, the extrusion pressure between sheet piles is large, which makes it difficult to form piles and easy to break them.
When the geology is hard, steel pile tip can be used, and steel plate hoop or steel bar can be added to the pile top and pile top to improve the concrete grade, so as to improve the hammering resistance of sheet pile.
(4) Dismantle the guide purlin device
After the sheet pile curtain wall is formed, it is confirmed that the wall will not tilt or shake due to the removal of the guide purlin device, so that the guide purlin device can be removed and the next guide purlin can be constructed according to the construction flow. In order to make the interface with the next construction section smooth, the guide device of the last section is kept intact and connected with the next construction section in turn.
(5) Sheet piling
After the purlin device is dismantled, the sheet pile wall inserted into the curtain wall can be driven into the design elevation one by one. The order of sending piles is opposite to that of inserting piles, that is, sending piles first and then sending them. In the process of driving, if adjacent piles are found under the belt or the sheet piles are inclined (in the direction of sheet pile wall), it is necessary to consider layered driving. The order of layered stacking is generally the same as above. The last pile of each screen section wall will not be driven, and it will be connected with the next construction section.
A. Construction of inclined section pile (also called inclined cone pile)
Due to the influence of soil squeezing, it is difficult to bite the tenon of sheet pile in the whole pile range, and the pile wall will be inclined along the axis, so it is difficult to construct when the inclination is too large. At this time, it can be adjusted by driving inclined section piles, that is, wedge piles. The number and position of inclined section piles should be determined according to the construction experience and situation.
B. Corner structure
Special steel piles can be used at the corner, two H-shaped steel piles can be welded and formed, and T-shaped seal can also be used. In order to ensure the accurate size of the corner, the pile at the corner can be driven first, and then other piles can be driven. The pile tip of corner sheet pile is the same as that of square pile, and the pile length is 2m longer than that of ordinary sheet pile, so it is necessary to control the corner direction when sinking the pile.
(6) Pouring bagged concrete in the tank.
Generally, before foundation pit excavation, the relative groove between sheet piles will extend into the mud surface (excavation surface) below 1.0m, and the groove will be washed clean with a high-pressure water gun, and a sealed plastic bag with sufficient strength and circumference greater than the length in the double groove (not less than 5cm) and length greater than 0.2m will be filled in the bag, and the slump will not be less than 10cm.
4, piling construction standards
The verticality deviation of sheet pile insertion shall not exceed 0.5%; The allowable deviation of the plane position of sheet pile sinking is100 mm; ; The allowable deviation of verticality of sheet pile construction is 65438 0%; When sheet pile is used for seepage control, the clearance of sheet pile shall not be greater than 20mm；; Used for retaining soil shall not be greater than 25mm；; The allowable deviation of sheet pile axis is 20mm；; The allowable deviation of pile top elevation in sheet pile construction is100 mm.
See table 15-3 for the quality standard of pile sinking construction.
5, sheet pile tenon, anti-tilt measures
In the process of pile sinking, the prevention and treatment methods of common quality problems such as broken pile top, cracks in pile body and difficulty in pile sinking are basically the same as those of ordinary reinforced concrete square piles. This paper only expounds the special problems such as tenon and inclination in the construction of reinforced concrete sheet piles.
(1) The size and straightness of the concave-convex tenon of precast reinforced concrete sheet pile do not meet the design requirements, which is the main reason for tenon detachment. Therefore, it is necessary to check and accept them one by one before construction to avoid the above-mentioned piles being driven into the soil.
(2) When the pile tip and the pile body are not on the same axis, or when one side of the pile tip encounters hard soil or foreign objects during pile sinking, the pile body will rotate (that is, the cross section of the pile forms an angle with the axis of the sheet pile wall). If measures are not taken in time, tenoning will inevitably occur.
In this regard, precast piles should be carefully inspected and accepted first, and piles with pile tips and shafts not on the same axis should not be used. In addition, in the process of pile sinking, when the pile body rotates and the pile can't be pulled out, a small limit made of section steel with sufficient strength can be welded on the guide purlin on both sides corresponding to the sheet pile with the tendency of rotation, and the small limit is in close contact with the sheet pile body (smooth contact is required, preferably rolling contact), and then the pile is driven slowly and carefully. After the above corrective measures, it can generally be corrected, at least to prevent the development of tenon. The key to the success of this measure is to find the tenon trend early and implement the corrective measures as soon as possible.
(3) The tenon side between some sheet piles will be chamfered, as shown in figure 15- 16. The designer intends to promote the pile to penetrate the soil and drive it in. However, if the chamfer meets pebbles or other hard objects in the process of pile burial, and the pile is easy to tenon, it is suggested to cancel the chamfer.
(4) For the inclination of sheet pile wall in the front and back direction, it is only necessary to control the pile tip and the pile top on a vertical line when inserting piles (that is, the pile top and the surrounding purlin grooves are kept on the same vertical line). Especially the initial pile (positioning pile) should be controlled, because the tenon of the pile is the guide and "backing" of the sheet pile wall verticality formed later. Therefore, the positioning of the initial pile requires zero error control, and the pile insertion after confirmation is very beneficial to the future construction control.
(5) Sheet piles tend to sink one by one, and then tilt in the direction of wall formation (that is, the direction of pile tenon). The main reason is that the side friction between the driven side of the inserted pile and the previous pile is greater than that between the other side and the soil. In addition, except for positioning piles, the tip of sheet piles generally has an oblique angle on the tenon side. Because of this inclination angle, the sheet pile will be closer to the previous pile during driving. The original intention of designing this form is to make the joints of sheet pile wall overlap without tenon. But it will also greatly increase the friction resistance between the pile and the previous pile during piling, thus increasing the probability of pile inclination. Therefore, in the construction of sheet piles, there is generally a tendency to gradually tilt towards the direction of sheet piles forming walls. Therefore, the probability of pile inclination can be fundamentally reduced by using shielding method instead of driving one by one. In order to further avoid, reduce and correct the inclination of the above-mentioned piles, the following measures can be selected:
A "positioning angle iron" is arranged on the purlin, which is closely attached to the inserted pile to limit the inclination of the pile. Butter can be coated between the "positioning angle iron" and the pile insertion to facilitate the insertion of the sheet pile.
B. When inserting piles, insert a piece of bamboo (green) (about 1cm thick, slightly less than the width of tenon and mortise) into the tenon of sheet piles to reduce the friction resistance between inserted (driven) piles and driven piles.
C the inclination angle of the pile tip shown in figure 15- 16 can be corrected, which can effectively control the inclination of the pile. Sheet piles are usually prefabricated when driven, so it is impossible to make any adjustment. In order to facilitate field adjustment, several sheet piles with the same pile tip type as the initial pile can be prefabricated (that is, there are oblique angles on both sides of the pile tip, so there will be no inclination trend when lowering the pile). In the process of piling, according to the site conditions, a similar sheet pile is inserted at intervals, and the effect is very good (if there is no such sheet pile on site and the soil layer where the pile tip is located is not in hard soil, the pile tip can also be chiseled off and replaced with a "flat pile").
(6) Slotting treatment of sheet pile
It is suggested that the tenon removal of sheet piles should be strengthened by compaction grouting. That is, in addition to pouring the tenon with fine stone concrete, the tenon is reinforced by compaction grouting near the river bank. The tenon-free reinforced concrete sheet pile should be poured with fine stone concrete according to the design requirements. Before the treatment of reinforced concrete sheet piles, the sheet piles higher than the design elevation should be chiseled to the design elevation.
Sheet piles with tenons greater than 80mm are grouted by double rows of compaction, and the grouting air in the middle of sheet piles is reinforced by root piles. Rinse the soil at the tenon of the sheet pile with high-pressure water, put down the grouting pipe, then fill in the medium-coarse sand and 5-25 pieces of gravel with the weight ratio of 1: 2, and compact the surface with clay before grouting. Only double-row compaction grouting is used for the part where the tenon of sheet pile is more than 25mm and less than 80mm. When double-row grouting is carried out, the outer row is injected first, and then the inner row is injected. For sheet piles without tenon joint, drainage mud shall be injected at the tenon joint of sheet piles. Add 1: 0.3 (cement: fine sand weight ratio) and 2% water glass to the grouting slurry. The grouting quantity is controlled at about 25Kg/m, and the grouting pressure is controlled at 0.4 ~ 0.5 MP. During grouting, the grouting pressure should be strictly controlled within the specification range.
6. Corrective measures for pile sinking inclination
When sheet piles are driven, theodolite is often used to observe and keep the sheet piles vertical in two directions. If there is any inclination, it can be corrected according to the method listed in Table 15-4.
3. Selection of pile sinking equipment for reinforced concrete sheet piles
Sheet pile can be driven by diesel piling hammer, drop hammer, power hammer and other machines, and the size of pile hammer depends on sheet pile.
1, hammer requirement
For reinforced concrete sheet piles, the guide rod diesel hammer is the most suitable for construction. The energy of the double guide rod diesel hammer of 1.8t is 30 ~ 40kn.m, which is suitable for piles with construction length of 10 ~ 15m. 2.5 ~ 3.2 t double guide rod diesel hammer, its hammering energy is between 65 ~ 85 kn. M, suitable for the construction of 20m long piles; For sheet pile construction with a length of 20 ~ 30m, a cylindrical diesel hammer with an impact block of 2.5~4.6t and a hammering energy of 60 ~ 140kn.m is also used. Cylinder diesel hammer construction should adopt the method of heavy hammer percussion, or choose the drop hammer and steam hammer construction with the same hammer energy. In recent years, a batch of hammers can be put into the market for small hydraulic hammer with the capacity of 20 ~150 kn m, and can also be used for the construction of reinforced concrete sheet piles, and their construction quality is superior to other hammers.
2. Pile cap form
When hammering reinforced concrete sheet piles, pile pad (rod diesel hammer) or pile cap plus pile pad (cylinder diesel hammer) should be adopted. Due to the characteristics of sheet pile structure and the special requirements of sheet pile wall structure and its construction technology, in order to support sheet pile on a design plane, its pile cap form is different from that of building concrete square pile, and there is no pile cap baffle on one side near the pile insertion, and one side is open; When in the pile delivery stage, there are no baffles on both sides of the pile cap, and both sides are open.
When the steel sheet pile adopts a closed pile top, it can also adopt a pile cap similar to the concrete square pile with baffles on all sides.
3, hammer pad, pile pad material requirements
Because the length of reinforced concrete sheet pile is limited in use and the hammer energy used in construction is low, the pile pad and hammer pad used in construction are also different from those used in sinking reinforced concrete square piles. The pile pad is mostly cardboard or fiberboard, generally 5 ~ 10 cm thick, or 5cm thick pine. Hammer pads are mostly white brown ropes; Sometimes hardwood processing is used as a hammer pad.
Generally, the hammer pad for white palm rope processing can only be replaced by hammering 50 ~ 100 piles (generally not damaged), and the hardwood hammer pad needs to be replaced after being damaged, generally more than 500 piles.
Four. Brief introduction of precast reinforced concrete sheet piles by water jet method
Precast reinforced concrete sheet piles [3] by water injection method, also known as hydraulic plug-in reinforced concrete sheet piles, are especially suitable for construction projects in coastal areas or river waters, as shown in figure 15- 17. There are sufficient water injection sources in these places, and the use of seawater has no obvious impact on the natural environment. Hydraulic plug-in technology has been successfully applied to the construction of ports and docks, road traffic bridges, artificial islands in water, sewage treatment tanks, underground culverts, pumping stations, sluices and water conveyance channels. This technology can build long-term stable flood control dams and moisture-proof dams in flood prevention; In marine engineering, it can solve the problem of building deep-water channels by breaking sandbanks all over the world; In pile foundation engineering, various pile foundation structures can be formed, which is a new way to improve the bearing capacity. The popularization and application of this technology will have a great and far-reaching impact on water conservancy projects, pile foundation projects, port and shipping projects and the elimination of flood disasters.
The technology mainly includes the following steps:
1. Factory prefabrication: prefabricate concrete piles specially used for spraying and grouting;
2. Insert the pile on site, lift the sheet pile with crane, pontoon bridge or crane on the platform, start the water pump, and insert the pile into the soil under the action of hydraulic jet;
3. Integral connection, that is, grouting in the hole will connect the sheet pile vertically into a whole, and cast-in-place reinforced concrete at the top will connect the sheet pile horizontally and vertically into a whole, so as to strengthen the connection and improve the bearing capacity.
1, structural requirements
Besides ordinary reinforced concrete, the design of precast reinforced concrete sheet piles by water jet method also includes some technological structure requirements, as shown in figure 15- 19, and the structural diagram of precast reinforced concrete sheet piles by water jet method.
(1) central pipeline
Sheet pile has a vertical steel pipe along its central axis. The steel pipe is opened at the pile head and connected with the plastic hose to transport the pressure water from the hose to the pile tip.
(2) Pile tip nozzle
A horizontal steel pipe is embedded in the pile tip, and water is introduced from the central pipe into the nozzle of the pile tip and injected into the soil through small holes, as shown in figure 15- 18. There are a large number of holes with a diameter of about 3mm in the pile tip pipe, and the hole spacing is uniform. The central pipe is connected with the pile tip pipe.
(3) I-beam
As shown in figure 15- 19, a part of I-beam is poured on one side of the concrete sheet pile. The side of the I-beam is provided with two semicircular grooves.
(4) Rectangular pipes
A rectangular section steel pipe (rectangular pipe) is poured in the reinforced concrete sheet pile along the opposite side of the I-beam, as shown in figure 15- 19. The rectangular tube has a narrow opening, which is slightly thicker than the I-beam web, but narrower than the I-beam flange. The inner width of the rectangular tube is slightly larger than the width of the I-beam flange.
The internal length of rectangular tube is greater than the sum of the length of half web and the thickness of flange. There are two semicircular grooves prefabricated in concrete on the side of the rectangular pipeline. The lower ends of I-beam, rectangular pipeline and four semi-circular open slots are located at 1m above the tip of sheet pile.
2, the construction requirements
(1) sheet pile manufacturing
According to the manufacturing requirements of 15.5. 1 reinforced concrete sheet piles, specially designed reinforced concrete sheet piles for spraying, grouting and connection are prefabricated.
(2) Pile sinking by jet method
The method of injecting water from the pipeline in the pile is as follows:
One is to spray water from the nozzle at the pile tip with a cone;
Secondly, using many small nozzles at the tip of reinforced concrete sheet pile, water is sprayed in many downward linear high-speed ways.
When the sheet pile is erected to the correct position, the pressure water flow is pumped to the vertical center pipe through the plastic hose. The plastic hose is connected with a series of small nozzles at the pile tip, which spray water into the soil, as shown in figure 15- 18. The pumping pressure is about 1.0-2.0 MPa, the total drainage rate is 50-80l/s, and the pile sinking speed is about1m/s.
In order to ensure that the small hole at the pile tip will not be blocked by sand or gravel, the pumped and sprayed water must not contain any large solid particles. According to experience, it is suggested that the content of solid particles in water should not exceed 0. 1% of the total water mass.
The soil under the pile tip is sprayed and dispersed to liquefy, so the reinforced concrete sheet pile under the control of the crane can sink into the soil by its own weight. The crane operator keeps spraying until the pile reaches the design depth. When the pile sinks to about 0.5m above the design depth, he reduces the drainage rate and water pressure to minimize the disturbance to the soil below the permanent pile tip.
After the first pile is installed in place, the second pile should be constructed according to similar construction procedures. Before spraying, the free flange of the I-beam on the vertical side of the second sheet pile should be inserted into the rectangular tube on the vertical side of the first sheet pile, and the free flange of the I-beam on the second sheet pile should match the inside of the rectangular tube of the first sheet pile. For example, in the water sheet dam project, it is necessary to insert slideways on the side of sheet piles for positioning. This process is repeated in all subsequent piles.
(3) Sheet pile connection
Bag-shaped cement mortar is used to form two vertical cylindrical holes with four semicircular grooves corresponding to the two sheet piles, and slurry is used to replace the gap between the steel pipe and the side walls of the two concrete piles, so that the reinforced concrete sheet piles are longitudinally connected into a whole.
Finally, the reserved steel bars at the top are bound together with the newly added transverse steel bars, and the reinforced concrete capping beam is poured, so that the whole sheet pile is horizontally connected into a whole.
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