A method for correcting deviation of a prestressed concrete pipe pile

Abstract

The present application aims to provide a prestressed concrete pipe pile deviation rectification method, which relates to the technical field of building engineering. The present application comprises the following steps: A. Detecting the pile body integrity of the deviation pile by using a small strain detection method, determining the degree of pile body defects, and reinforcing the pile body which is seriously damaged (class III pile) by using a reinforcement method; B. Digging a slot-shaped ditch near the deviation pile, the slot-shaped ditch being arranged at the repositioning side of the deviation pile, the long direction of the slot-shaped ditch being perpendicular to the repositioning direction of the deviation pile, and the dug soil being placed on the other side of the deviation pile to intentionally form reverse soil sliding and drive the deviation pile to reposition. The present application has the advantages of small operation difficulty, short time consumption, low cost (compared with the usual drilling deviation rectification method, the cost is saved by more than 50%), and remarkable deviation rectification effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building engineering, in particular to a deviation rectification method of prestressed concrete pipe pile. BACKGROUND

[0002] In the large river basin and coastal areas of China, there are large areas of soft soil foundation, due to its low bearing capacity, high flow plasticity, engineering construction often leads to the deviation of the prestressed concrete pipe pile which has been driven due to various reasons.

[0003] For commonly used D300-D600 prestressed pipe pile, once the deviation exceeds the allowable value of the current design specification, the common method of deviation rectification is to drill a hole near the deviated pile (drill 1 hole or several holes on the reset line) or use a high-pressure water gun to punch a hole, and then apply a pushing force or a pulling force to force the pipe pile to slowly reset. Although this method can achieve the purpose of deviation rectification, it is difficult to operate, high in cost, and particularly has a significant lagging effect on the construction period. If the deviated pile is abandoned and a new pile is added, it not only takes a long time, but also has a very high engineering cost. Therefore, exploring a simple and reliable deviation rectification method has become the relentless pursuit of many engineering and technical personnel.

[0004] A deviation rectification method of prestressed concrete pipe pile foundation is provided in a Chinese patent document with publication number CN103243747B. The steps of this deviation rectification method are more and it is more troublesome to implement. Before deviation rectification, a stress release hole is drilled first, then a manual hoist and a steel wire rope are arranged between the pipe pile head and a large excavator, or a jack is arranged between the pipe pile head and a support seat, and an intermittent multiple force method is used to make the pipe pile gradually return to the design pile position from the actual deviated pile position. Although this method can achieve the deviation rectification of the pipe pile, it needs to drill a deep hole in advance and use a manual hoist or a jack to apply a pushing force, which is difficult to operate and has a high cost. SUMMARY

[0005] The present application provides a deviation rectification method of prestressed concrete pipe pile, which has small operation difficulty, short time consumption, low cost and significant deviation rectification effect.

[0006] The technical solution adopted by the present application is as follows: a slot-shaped trench is excavated on one side of the deviated pile (the long direction of the slot-shaped trench is perpendicular to the reset line), and appropriate load is piled on the other side of the deviated pile, so as to cause the local soil body to slowly slide and drive the deviated pile to reset. The specific steps are as follows:

[0007] A. The quality of the deviated pile body is detected by using a small strain detection method, and the deviation rectification can be performed on type I, type II and type III piles, but the type III pile should be pre-treated for local reinforcement to prevent further expansion of the pile body damage;

[0008] B. Excavate a groove near the offset pile, the groove is set on the reset side of the offset pile, the long direction of the groove is perpendicular to the reset direction of the offset pile, the depth of the groove is generally excavated to remove the hard filling layer of the surface, and the top surface of the soft soil layer is exposed, the excavated soil is placed on the other side of the offset pile, and the pressure is intentionally increased to promote the reverse sliding of the local soil body and drive the offset pile to reset;

[0009] C. If the offset values of the offset piles in the same pile cap are significantly different, the positioning support should be set in time for the pile that has been corrected (a horizontal support can be set in the groove), and the remaining piles that have not been reset should be reset by local excavation and increasing the load. If the reset direction of an individual pile in the same pile cap is not consistent with that of the other piles, specific measures should be taken to prevent the pile from being damaged by shear and torsion during reset;

[0010] D. After the pipe pile is reset, the hole behind the pile and the excavated groove are filled with sand and stone, and the concrete cushion (C20 concrete 150mm thick, with Φ10@200 mesh reinforcement) is poured and tamped to fix the pile position. Before pouring and tamping the cushion, a small strain test should be conducted on all the corrected piles to evaluate the quality of the pile body;

[0011] E. To ensure the quality and durability of the pile body, local reinforcement treatment is recommended for the piles determined as type III before correction (which may become type II after correction) and type III piles that appear after correction;

[0012] F. Whether the pipe pile that has completed the correction and reset needs to be tested should be determined by the relevant responsible units.

[0013] In the above step A, the pile body reinforcement method of the type III pile includes the following operations:

[0014] A1. A steel pipe with a length of 3.5-4.5 meters is placed in the crack section of the pipe pile (the length and wall thickness are appropriately selected according to the diameter of the pipe pile and the crack state), and the outer diameter of the steel pipe is 30-40mm smaller than the inner hole of the pipe pile;

[0015] A2. A steel plate with a thickness of 5-8mm is welded to the lower end of the steel pipe and sealed with a sealing pad, and the four sides of the steel pipe are filled with medium sand (without pressure grouting, so that the crack section of the pile body can be reinforced and have the possibility of micro-motion);

[0016] A3. After the pipe pile is reset, the center of the steel pipe is filled with C35 fine stone concrete; the outer periphery of the steel pipe is pressure grouted with high-grade cement slurry through the pre-set grouting pipe to repair the cracks and reinforce the pile body;

[0017] A4. If the pipe pile needs to be reinforced for the full length, the inner hole of the steel pipe should not be closed when the steel pipe is sealed.

[0018] In the above step B, a trench is excavated by an excavator, the width of which is the width of the excavator bucket, and the length and depth are determined to cause slow sliding of the soil body.

[0019] The prominent effect of the present application is that, compared with the traditional pipe pile deviation rectification method, the present application simplifies the deviation rectification process, greatly shortens the deviation rectification time, and does not need to punch stress release holes and use equipment to apply a pushing force or a pulling force to force the pipe pile to slowly reset, thereby reducing the deviation rectification cost and time. Due to the need to leave a large safety distance for drilling in the traditional deviation rectification method, the reset movement of the pile body is still restricted by the soil body, and a strong pushing force or pulling force must be applied, which is easy to cause new damage to the pile body quality. The present application pushes up and down by means of the reverse sliding of the soil body formed by ditching and loading, and generally does not cause new damage to the pile body, and the reliability should be higher. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a pipe pile deviation rectification plan view of the present application;

[0021] Figure 2 is a pipe pile deviation rectification sectional view of the present application;

[0022] Figure 3 is a total site plan of the actual deviation rectification example two;

[0023] Figure 4 is a B pile cap (four piles) deviation rectification schematic view in the actual deviation rectification example two;

[0024] Figure 5 is a deviation rectification site view in the actual deviation rectification example two. DETAILED DESCRIPTION

[0025] As shown in Figure 1 and Figure 2 , in the implementation process, the present application mainly includes the following steps:

[0026] A. The small strain detection method is used to detect the pile body integrity of the deviation pile, the degree of pile body defects is determined, and appropriate reinforcement measures are taken for the seriously damaged pile body (class III pile);

[0027] B. A trench is excavated near the deviation pile, the trench is arranged on the reset side of the deviation pile, the excavation length of the trench is perpendicular to the reset direction of the deviation pile, and the excavated soil is placed on the other side of the deviation pile to intentionally form reverse sliding of the soil body and drive the deviation pile to reset;

[0028] C. If the offset values of the piles in the same pile cap are significantly different, first set the support for the pile that has been corrected to the right position to prevent overcorrection, and then continue to correct the remaining piles by local excavation and increasing the load. Sometimes the offset direction of an individual pile in the same pile cap is not consistent with other piles, and the recovery line is not perpendicular to the slot-shaped trench. The sliding of the soil body in the direction of the slot-shaped trench may cause the pile to be sheared and twisted, resulting in damage to the pile body. Avoidance should be considered during correction.

[0029] D. After the pile is corrected to the right position, the slot-shaped trench should be backfilled in time, and the pile cap foundation cushion should be poured and tamped to fix the position of the pile body. The cushion label should be appropriately increased and thickened (C20 concrete 150mm thick), and a layer of mesh reinforcement should be added. Whether to use better soil excavated on site or coarse sand and gravel to make it easier to compact the material should be determined by the design party.

[0030] E. All corrected piles should be tested for small strain, whether the test range needs to be expanded, and whether the bearing capacity needs to be tested, which should be determined by the relevant responsible units.

[0031] F. For type III piles found before and after correction, it is recommended that they be reinforced. The specific reinforcement scheme should be determined by the design unit.

[0032] In the above step A, the pile body reinforcement method of the type III pile includes the following operations:

[0033] A1. A steel pipe with a length of 3.5-4.5 meters is placed in the pipe pile crack section (the length and wall thickness are appropriately selected according to the diameter of the pipe pile and the crack state), and the outer diameter of the steel pipe is 30-40mm smaller than the inner hole of the pipe pile.

[0034] A2. The lower end of the steel pipe is welded with a steel plate with a thickness of 5-8mm and sealed with a sealing pad, and the four sides of the steel pipe are filled with medium sand (without pressure grouting, so that the crack section of the pile body can be slightly moved).

[0035] A3. After the pipe pile is reset, the center of the steel pipe is filled with C35 fine stone concrete; the outer periphery of the steel pipe is pressure grouted with high-grade cement slurry through the pre-set grouting pipe to repair the cracks and reinforce the pile body.

[0036] A4. If the pipe pile needs to be reinforced for the full length, the inner hole of the steel pipe should not be closed when the steel pipe is sealed.

[0037] In the above step B, the slot-shaped trench is excavated using an excavator, and the width is the width of the excavator bucket. The length and depth are determined by the slow sliding of the soil body.

[0038] In actual deviation correction, the soil pile is arranged on the other side of the deviation pile to increase the soil pressure, thereby accelerating the resetting speed of the pipe pile. In addition, the heavy objects such as the disc steel reinforcement on the site can be placed at the soil pile to increase the ballast, thereby further accelerating the resetting speed of the pipe pile. In addition, since the pressure is uniformly and widely applied, the resetting speed of the pipe pile can not be strictly limited, and if necessary, a pushing force (the resistance is much smaller than that of the drilling deviation correction, and the excavator arm can be used to push) or a digging acceleration trench (detailed in the actual deviation correction example two) is applied to accelerate the resetting progress.

[0039] During the deviation correction, the surrounding piles should be monitored, and if necessary, the concrete cushion layer of the pile cap is poured in advance, or the positioning measures such as the steel sheet pile, support and traction are taken to prevent the adjacent piles from deviating due to the ditch digging and the load stacking. When the surface soil is a relatively hard and thick filling layer, this problem is not serious; when the silt layer is directly exposed or the filling layer is very thin, and the pile cap cushion layer (the cushion layer can be appropriately thickened and the mesh constraint steel reinforcement is arranged) pouring is not completed, sufficient attention should be paid.

[0040] Actual deviation correction example one: in August 2022, a certain industrial project located on a silt foundation (the surface soil is a plain filling soil with an average thickness of about 4 meters, and the underlying silt soil is about 10 meters thick) has 16 piles (single pile cap) of the building deviated beyond the allowable value specified in the specification, of which 5 piles deviate more than 500 mm, and the maximum deviation value reaches 674 mm. If the conventional drilling deviation correction method is used, the engineering quantity is very large. According to the requirements of the owner party for simplifying the operation and minimizing the impact on the construction period, and considering that the building is single-layer, the pile capacity is relatively large, and other factors, a very simple deviation correction method (i.e. the deviation correction method of the present application) is proposed for the construction party to try. After the construction party implements it, the deviation correction effect is very significant, and only one excavator is used for four days to successfully correct all 16 piles. This ditch deviation method avoids the concentrated force of the drilling deviation correction jacking, and instead uses the upward and downward pushing force formed by the ditching and soil stacking to push the pile, which almost does not damage the pile. After the small strain detection verification, the integrity of the pile is good, and all the piles are I and II class piles.

[0041] Actual deviation correction example two: as Figure 3 , Figure 4 and Figure 5The pile foundation and main structure of Building A have been successfully constructed. Another enterprise located near Building A is a building material company which grinds the block stone into sand. The block stone material is piled up in the factory with a length of about 40m, a width of 15m and a height of 3.5m, and is about 88.5m away from Building B. During the construction of the foundation of Building B, the partial basement was excavated with a slope (the excavation depth is about 3.6-4.2m), which caused the serious deviation and fracture of some pipe piles, with the maximum deviation value of 1140mm. Therefore, the foundation pit has to be backfilled and then the pile is supplemented (16 piles are counted). After the supplement, the construction party drives the Larsen steel sheet pile around the foundation pit for support. Due to the huge pressure from the large area of the distant load, some pipe piles are still deviated too much (the maximum value is 735mm) during the excavation, so the second pile supplement (27 piles are counted) is needed. After the further strengthening of the support system of the foundation pit, the construction of the basement is finally completed, which takes about 4 months. Before the support steel sheet pile is pulled out, the construction party measures that the displacement of four piles of four bearing platforms near the basement position exceeds the allowable value of the design specification, in which the displacement of four piles of B bearing platform is about 600mm (see Figure 4 The pile deviation correction method of the present application is again proposed in the technical consultation meeting and is recognized by the owner and the construction party. Three groups of four-pile platforms and one group of three-pile platform are excavated with four groove trenches (the deepest is 6m), which are all successfully corrected and reset, and the quality of the pile body is I and II class through small strain detection. Only two excavators are used during the correction process, which takes about 4 days.

[0042] The geological conditions of the above correction project are as follows: the surface soil is artificial fill (the thickness is 3.46m, and the local thickness is 5.50m), and the filling time is 2-3 years; the underlying silt soil layer is 11.7-16.4m thick, with an average thickness of 13.90m, a natural water content of 55.6%, a natural porosity ratio of 1.499, a cohesion of 6.0KPa, an internal friction angle of 4.7°, a standard penetration number of 0.8 hits / 30cm, and a foundation bearing capacity characteristic value of 60Kpa; and then there are a silty clay layer (the thickness is 12.28m), a completely weathered rock layer and a strongly weathered rock layer, with a pile length of about 35m.

[0043] Special instructions and suggestions

[0044] In view of the frequent pile deviation accidents on silt foundation, special care is needed, and the close cooperation between the design and construction parties is needed to prevent the occurrence of pile deviation accidents and to prevent new pile deviation accidents in the correction process. In order to help establish the prevention concept, some engineering examples and matters needing attention are listed as follows:

[0045] 1. Generally speaking, if the depth of excavation on the silt foundation exceeds 2.0m or more without slowing down the slope or supporting, it is easy to cause the foundation to be unstable. This is also the theoretical and practical basis for the aforementioned correction method. The excavation depth on the silt foundation should be reduced as much as possible, such as the pile at the fire pool can be reversed, the pile is placed under the concrete shaft wall without deep pile, etc. The less excavation is very important. The excavated soil should be transported away from the site in time, because the collapse of the foundation pit, pile displacement and other accidents caused by the pile of soil near the foundation pit or the pile of steel reinforcement are common.

[0046] A high-rise residential project, the basement is about 3.5m deep, using large diameter rotary pile foundation, lattice type cement mixing pile retaining wall support. When I visited the site, I found that the excavated soil was concentrated on the empty land about 10 meters away from the foundation pit, the soil was 2 meters high, and the area of the soil was about 500 square meters. At that time, it was required to move away as soon as possible, and effective measures should be taken to reduce the vibration caused by the operation of excavator and car, because the safety of the support was in a critical state. However, the construction management personnel did not take it seriously, and said that the monitoring did not find displacement and uplift. A few days later, the result was that the support collapsed seriously, resulting in the fracture and displacement of many long rotary piles of about 80 meters in diameter. The operation of moving soil is also very dangerous for the support in a critical state of collapse. If the conditions permit, it is better to dig a pit on the other side of the soil to unload pressure, of course, the pit depth should be significantly greater than the building foundation pit, so as to guide the pressure of the silt layer to be released to a far place.

[0047] 2. The range of influence of silt flowability often exceeds the imagination of ordinary people. In the second correction case, the load is far away from the 88m, and there are a large number of pile foundations in A building to block, but the soil pressure still transfers strongly. Two projects built for many years have been handled, and the wall cracking caused by the sliding of the pile cap is caused by the existence of a natural water channel (about 3-4m deep) about 50 meters away from the building. A large number of pile displacement occurred during the construction of the basement of a residential project (with support system), which was caused by the large area of stacking (stacking preloading or vacuum preloading after punching plastic plate) caused by the construction of the road (about 30 meters away). When there is a thick layer of filling on the surface of the deep silt, the whole area is like a big balloon under pressure, and where the pit is dug is like a balloon pierced by a needle, and the pressure will be poured out.

[0048] 3. The preloading or vacuum preloading treatment of soft ground by surcharge load on site or road has a great influence on the adjacent foundation pit construction and the building foundation in lower-lying areas, and the influence is "far-reaching" in distance and time. A two-story building constructed in 1994 has been in normal use (the silt foundation has been treated by cement mixing pile soft ground treatment), and in recent years it has been found that the frame infilled wall has been cracking obviously and increasingly, and needs to be reinforced to ensure safety. After careful investigation, it is found that a municipal road (with soft ground treatment) is constructed about 30 meters away from the building, and the soil pressure is slowly formed. Another residential area is under construction of basement foundation, and the municipal road construction is under construction nearby (30-50 meters), resulting in the deviation of dozens of pipe piles, with the maximum deviation value of more than 2 meters.

[0049] 4. The surrounding of foundation pit is often the road in the general layout of the building, and the construction road is often used as a temporary road for the sake of saving time and materials in construction. It is known that this is very unfavorable to the safety of foundation pit support. In the aforementioned actual deviation example one, in addition to the construction of the storage tank and the non-compact backfill, the close construction road is also an important reason. Therefore, the construction road should be away from the foundation pit (the foundation pit support design should be clear) and the pile position as soon as possible, and the operation route of various construction machinery should be reasonably arranged to prevent the deviation of the pile caused by extrusion and vibration.

[0050] 5. If the inclined road is used for transporting soil in the excavation of foundation pit, measures should be taken to ensure the stability of the inclined road itself and prevent the deviation of adjacent pipe piles (such accidents are common). A small pit is excavated on the silt foundation, such as elevator foundation, equipment foundation, small water tank and test pit, and the display of excavation state is often misleading due to the mutual offset of the soil pressure transmitted to the center. Remember not to use the one-sided experience of small area excavation to large area excavation, which may lead to the occurrence of sliding and uplift. The safety degree of the corner of a large foundation pit is generally high due to the mutual support of the soil body, and the accident rate of the middle of the long side of the square is high, and special attention should be paid to the reinforcement and monitoring of the support. Try not to stack heavy materials such as building materials in the middle of the support.

[0051] 6. In coastal areas and their surroundings, cement mixing pile is often used to reinforce the passive soil pressure area in foundation pit. If the soil body is reinforced in the form of single pile, it is like inserting chopsticks into tofu, and the effect is poor. If the mixing pile is formed in a lattice type layout, although the cost is higher and the time is longer, the effect is still positive. Hammer pile is used several times to fill in medium-coarse sand (which can be sea sand) to reinforce soft ground, with a spacing of about 800-1200mm. Due to the dual role of drainage and compaction of sand pile, ideal results have been achieved. If medium-coarse sand is cheap in the construction area, it can be tried.

[0052] 7. For the reinforcement of the passive zone of a small single-story basement foundation pit, a method of replacing the bottom with 1.0-1.5 meters of good soil (high-gravel content quarried soil or high-sand content plain soil) can be considered. This serves the dual purpose of supporting the lower section of the surrounding support system and preventing uplift, often with good results. For example, the support for a partial elevator shaft foundation pit in a two-story basement, originally using mixing piles, cost a total of 600,000 yuan for three pits, and was very time-consuming. After adjusting to sheet pile support and replacing the pit with graded sand and gravel, the cost was reduced to approximately 190,000 yuan. The key points for this type of sheet pile and backfill treatment are: a) When there is still more than 1 meter of space from the bottom of the design pit, excavation and backfilling should be carried out simultaneously, and the route should be planned in order to form effective support for the lower section of the sheet pile as soon as possible; b) The area excavated each time should not exceed 4 square meters, and the next section should be excavated only after the backfilling is completed; c) Due to water immersion, the backfill material must be soil and stone with high sand and gravel content, which is conducive to natural compaction and drainage; d) Close monitoring should be carried out, and countermeasures should be taken in time if any abnormalities are found.

[0053] 8. For sheet pile supported foundation pits, the completion of structural construction does not mean the job is done. Rapid pile extraction and untimely or inadequate backfilling often lead to displacement of nearby piles. Both the design and construction parties should act with caution and take appropriate measures.

[0054] 9. Closely monitor and inspect the site. If any abnormalities are found, take timely countermeasures to prevent collapse and pile deviation. Preparing sandbags for counter-pressure at the construction site is often a simple and effective way to solve problems.

[0055] China has a vast territory, and the conditions of silt foundations and other soft soil foundations formed by rivers, lakes, and seas vary greatly. The above are some experiences and observations accumulated from long-term work in Hubei and Guangdong, which can be used as a reference for colleagues. This new method of excavation for deviation correction has certain general application value as long as the layer of silt or other soft soil is relatively thick. Deviation correction is not limited to prestressed concrete pipe piles; it can also be used as a reference for deviation correction of other pile types.

Claims

1. A method for rectifying deviation of a prestressed concrete pipe pile, characterized by, The deviation correction method comprises the following steps: A. The integrity of the deviated pile is detected by using a small strain detection method, the degree of pile defects is determined, and the severely damaged type III pile is reinforced; B. A slot-shaped trench is excavated near the deviated pile, the slot-shaped trench is arranged on the repositioning side of the deviated pile, the length direction of the slot-shaped trench is perpendicular to the repositioning direction of the deviated pile, the excavated soil is placed on the other side of the deviated pile, and the soil is intentionally formed to slide in the opposite direction to drive the deviated pile to reposition; C. If the deviation values of the deviated piles in the same pile cap are greatly different, the pile that has been corrected is first positioned by setting a support, and the remaining pile that has not been repositioned is further repositioned by local excavation and increased load; D. After the pile is repositioned, the slot-shaped trench should be backfilled in time, and the pile cap foundation cushion is poured and tamped to fix the position of the pile; E. The quality of all the corrected piles is detected by using a small strain detection method to ensure that the pile quality is qualified; F. For the type III pile found before correction, the crack of the pipe pile is pressure injected with high-grade cement slurry through a pre-set grouting pipe to reinforce and repair the crack section of the pipe pile; and for the type III pile found after correction, certain reinforcement measures should be taken; In the step A, the pile reinforcement method of the type III pile comprises the following operations: A1. A steel pipe is placed in the crack section of the pipe pile, the length and wall thickness of the steel pipe are appropriately selected according to the diameter of the pipe pile and the crack state, and the outer diameter of the steel pipe is 30-40 mm smaller than the inner hole of the pipe pile; A2. The lower end of the steel pipe is welded with a steel plate with a thickness of 5-8 mm and a sealing pad is added to seal the bottom, and the surrounding of the steel pipe is filled with medium sand; A3. After the repositioning is completed, the center of the steel pipe is filled with C35 fine stone concrete, the surrounding of the steel pipe is pressure grouted with high-grade cement slurry through a pre-set grouting pipe to repair the crack and reinforce the pile; A4. If the pipe pile needs to be fully grouted and reinforced, the inner hole of the steel pipe is not closed when the bottom of the steel pipe is sealed.

2. The deviation rectifying method of the prestressed concrete pipe pile according to claim 1, characterized in that, In the step B, the slot-shaped trench is excavated by using an excavator, the width of the slot-shaped trench is the width of the bucket of the excavator, and the length and depth of the slot-shaped trench are determined according to the slow sliding of the deviated pile.

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