Construction Technology and Quality Control of Bored Pile

Transcription

1 Architecture and Design Review (2018) Original Research Article Construction Technology and Quality Control of Bored Pile Minqiang Xiao,Wenya Lu,Jun Li Civil Engineering and Architecture, Guangdong University of Technology, Guangdong, China ABSTRACT Bored pile is a kind of pile. Bored pile means mechanical drilling and steel pipe compaction to form a pile hole in the foundation of soil. The pile is filled with reinforced concrete. The pile type is defined by the classification of piles. This article is starting from the actual work practice (Cangnan County People's Court comprehensive building project). The construction technology of the bored pile is introduced, including the construction process, the construction machinery, and the method of the key introduction for this construction. According to the construction technology and the process, the factors that are influencing the bearing capacity of the borehole and clay layer involved in this project are analyzed. Followed by the construction of the project during the construction of the catheter water, reinforced cage floating and other accidents to analyze and deal with the treatment methods and describe the preventive measures taken. The summary of the construction of Bored piles equipment are simple, process is more complex, concealment and other characteristics must be strictly in accordance with the construction specifications. KEYWORDS: Bored Pile; Construction process; Quality control 1. Preface Bored piles are a pile type defined by piling method. The earliest piles is in 100 years ago. Due to the industrial development and population growth in 1893, high-rise buildings continue to increase, but because a lot of city foundation conditions are relatively poor, cannot directly bear the pressure from high-rise buildings, below the surface there is a large thickness of the soft soil or medium strength of the clay layer, the construction of high-rise buildings such as still use the common friction pile, so would inevitably produce a great settlement, bored pile from the resulting. According to the geological, hydrological and surrounding environment of the project, the paper mainly discuss about the concrete construction process of the projected bored pile, including putting pile, hull laying, mud preparation and circulation, drilling and cleaning. The main construction methods and quality control points of the hole, the construction of the reinforcement cage, the pouring of concrete and so on. Then, the bearing capacity of the cast-inplace pile is analyzed in the soil layer in this project. Combined with the construction of the project in the drilling deflection, tube, catheter water, reinforced cage floating and other causes of the accident analysis, and describes the preventive measures taken. Bored piles are underground or underwater concealed works, if the construction is operated in improper way, there may cause card, collapse, drilling skew, broken pile and other quality defects, and also will be affecting the integrity of the pile and single pile bearing capacity. Thus, posing a threat to the entire project safety. It is extremely important to take some precautionary measures in the construction before the accident to reduce the accident. Therefore, it is necessary for the specific engineering, geological and other conditions, to explore the construction of bored piles and quality control methods to ensure the quality of engineering governance. 2. The project profile Prepared by according to the project Cangnan County People s Court building project preparation. Project Location: Cangnan County New Town, east of Dupu Road, Yucang Road to the north of the block; Project size: total construction area of square meters, of which 17,111 square meters above the ground area, basement 4020 square meters. Underground layer, 12 floors above ground, frame structure; total height of the building 47.4M. Copyright This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License ( permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 36

2 Minqiang Xiao, et al Engineering geological conditions: According to the investigation of geological reports, the construction of the soil from top to bottom in order: (1) Plain fill: gray, grayish yellow, loose, mainly by the stone, gravel, sand and other components. For the artificial move back from the fill, the audience are distributed. (2) clay: grayish yellow, soft plastic ~ plastic, medium and high compression, with oxidized spots and carbon compounds, dry high strength, no shock response, smooth surface, with fine sand silt: green gray, flow plastic, high compression, with shell debris and 10 ~ 30% fine sand, containing thin layer of fine sand, the layer are distributed; 2) silt green gray, flow plastic, high compression, dry medium, no vibration response, smooth surface, with a small amount of fine sand, shell debris and semi-carbon compounds. Site hydrogeological conditions: groundwater in the site is mainly in the shallow cohesive soil in the pore water and the lower part of the gravel layer of confined water. The soils are mainly composed of clay sand and mud, and the runoff is poor and the condition of water flow is low. The main contents are as follows: the groundwater level is 0.60 ~ 1.20 m, the groundwater level is smaller, generally less than 2.0 m, porosity bearing water storage medium for the buried depth of more than 73 m of the gravel layer, water level 10.0 ~ 15.0m, smaller amplitude. 2) The bored pile construction technology and technical measures (according to the summary of Cangnan People s Court specific analysis) 2.1. Construction process Selection of XUD rotary drill: including drill, drill pipe, pipe, tube and so on. Figure 1. Titanium drill bitv Figure 2. XUD Gyroscopev 37

3 Construction Technology and Quality Control of Bored Pile 2.2. Construction methods Measurement positioning According to the red line and the level of the information provided by Party A, by the full-time surveyor with J2 theodolite in accordance with the design drawings to establish the axis control network, and the laying of permanent signs, control points as far as possible in the non-construction area, and then placed pile by according to the design drawings. With the level of its elevation Buried orifices Orifice formation become loose, soft, into the orifice after the collapse of the hole buried in the steel tube protection hole wall. Construction of protection: A. Cylinders should be solid and watertight. When the casing is deep into the soil, it is advisable to apply the method of pressing, vibrating, hammering or removing the soil. Cage joints require no protrusion inside, can be able pull, and able to resist the pressure. B. The inner diameter of the guard should be slightly larger than the pile diameter. The top of the guard should be at least above the ground. C. After the laying of the guard, surrounded by clay backfill, compaction, to prevent drilling when the slurry leakage Hole Construction A. Hole quality standards Table 1. Standard for pore quality standards NO ITEM STANDARD 1 The allowable deviation of pile diameter d D 2 The tolerance of vertical (%) 1/100 Allowable Deviation of Pile Design Requirements B. Hole operation requirements (A) After the rig is in place, the chassis is flattened and the pole is perpendicular to the frame. (B) Drilling when drilling drill pipe diameter, the depth is the first self-test, to be self-inspection after the inspection by the regulatory body acceptance Hole Acceptance After drilling to the design hole depth, use the sounding hammer to measure the correction hole depth. After the quality of self-test is correct, please on-site inspection hole, after the supervision and acceptance, transfer to the next process construction The Production of Steel Cage (A) Where according to the design of the construction drawings with a variety of steel bars should be certified by steel factory, on the quality assurance, and mechanical properties and chemical composition indicators to meet the design requirements and the relevant provisions. The provisions of each batch must do physical mechanics such as performance test, the electrode grade and steel to adapt to the performance. (B) The copy of the warranty book must be clear and should fill in the unit name of the project, the use and function of parts, the number and timing of the transfer, signed by hand, the original storage, transit unit cover and printed by stamp (C) Approach bars should be accepted by the quality of personnel, to confirm the steel without rust, grease, etc. It can be only stored once everything are done. 38

4 Minqiang Xiao, et al B Refer to the table below, about the standard of steel cage production. ITEM PERMISSIBLE DEVIATION mm MAIN REINFORCEMENT C. Steel cage production requirements Table 2. Standard table for steel cage production SPACE OF STIR UP SPACE OF STEEL CAGE DIAMETER OF STEEL CAGE PROTECTION LAYER ±10 ±20 ±10 ±100 ±20 (A) Before the production, those steel surface dirt, rust, steel cutting should be removed and control the cutting length accurately. (B) Reinforcement cage is made by ring molding, and the production site is kept flat. (C) Reinforcement cage welding E4303 electrode, weld width should not be less than 0.7d, the thickness should not less than 0.3d. (D) steel cage welding process1` should immediately slag, reinforced cage at both ends of the reinforcement hoop and the main reinforcement should be all spot welding, must be welded firmly, the rest according to the design requirements for welding. (E) Reinforcement cage reinforcement According to the design requirements, the use of single-sided welding, weld length 10D, and the same section of the number of joints 50% staggered. (F) In each steel cage, the next set of a steel positioning control pieces, each arranged along the circumference of three. The thickness of the protective layer is 50mm. (G) Formed steel cage should be stacked on a flat surface, the number of stacking should not exceed 2 layers The installation of cage reinforcement Figure 3. 9 m reinforced cage A. Reinforcement cage height, the top of the mouth of the mouth can be calculated by the elevation. for the placement, must ensure that the design of the pile top elevation, the allowable error is ± 100mm. B. Reinforcement cage should be aligned at center hole, the possible general use of and anti-rotation slowly subsided to prevent the collision, put the design elevation should be quick and immediately after the fixed. C. When lifting the catheter, it is necessary to prevent the cage from being lifted. When pouring concrete, measures must be taken to observe and measure the possible movement of the steel cage and to deal with it in a timely manner Pouring underwater concrete A. Raw material test: 39

5 Construction Technology and Quality Control of Bored Pile A) Cement (1) The use of cement must be qualified, a formal factory certificate needed, and also need the local cement record card. (2) All approach cement should be a batch number to do the physical performance of the experiment, different manufacturers of different labels should do a full set of physical tests. (3) Copies of the cement warranty should be clear and should fill in the use of unit engineering name, structural parts, indicating the use of cement number and manual signed. (4) Bagged cement site sampling, is a cyclone pit, stability will do, the intensity can be 5 batches to do 1, is a relatively stable quality of cement, stability must be done, the intensity can be done in two batches. Bag cement test to the same cement plant label, the same species, the same production time, the same date into the cement 200t for an acceptance batch, less than 200t into a number. (5) Bulk cement, suppliers according to the sea, land transport cement warehouse batch number, warranty book to the warehouse sampling, for each batch of cement must be done stability, strength test, on-site sampling, the same species, the same name of the rotary pit cement Per 100t (5 cans) for a batch. B) Sand (1) According to the fineness of the sand modulus: coarse sand (MX ), sand (MX ), fine sand MX is ). Matching is done according to the actual use of sand. (2) The amount of sand in the sand shall be within the specification. C) Stone (1) The grading of the stone is more reasonable, the size of the large size of the stone is prohibited to approach. (2) Specifications requirements of stone slag is not more than 1%, for the mud trap to be promptly washed after used. D) Water (1) The water should not contain harmful substances that affect the normal condensation and hardening of the cement. (2) Sewage, PH value must less than 4 acidic water and a large amount of sulfuric acid cannot be used as a concrete water. B. General requirements A) Construction using the laboratory to provide concrete mix construction. B) Underwater concrete for cement, aggregate, water, admixture and concrete mix design, mixing, transportation, etc. must comply with the provisions of the specification. C) When the concrete is transported to the pouring site, its uniformity and slump should be checked. If it does not meet the requirements, it would be easy to cause poor watering or blocking, then it shall not be used. D) Underwater concrete pouring should be continuous, single pile watering time should not exceed 4 hours. E) The pipe should be made of pipe with diameter that not less than 200mm. The joint should be easy to install and connect, and connect with a sealing ring to ensure that it is watertight and impermeable to avoid water from entering the pipe. The support of the conduit shall ensure that the duct can be rapidly lifted and lowered when it is necessary to slow down or stop the flow of the concrete. F) The pipe must at all times be filled with concrete until the bottom of the funnel is free of bubbles and blisters. The discharge port must be buried in the cast concrete 2m above, and should not be greater than 8m. G) The amount of concrete to be cast shall be recorded and the depth of the tunnel and the surface height of the concrete shall be measured and recorded at any time. H) During the pouring process, the mud in the hole should be drained to the mud pool to prevent the surrounding environment. I) If the concrete in the conduit is mixed with air and water, the supervising engineer must be immediately reported and a remedial request for approval from the supervising engineer. C. Casting method 40

6 Minqiang Xiao, et al A) Before the concrete is filled, the concrete funnel and the watertight plate should be quickly placed and the catheter should be lifted away from the bottom of the hole at 0.5m. The initial volume of concrete must be guaranteed to be buried in the catheter 0.8 ~ 1.3m, the initial irrigation volume selection 0.6m3. B) Each time the perfusion must be measured in accordance with the provisions of the second time, should do a good test block (three), test pieces should be marked with the station, date, and into the water conservation. C) During the infusion process, the depth of the catheter should be kept between 3m ~ 8m, the minimum embedding depth should not be less than 2m (too much buried depth can cause the accident, too little easy to make the depth of the catheter cannot be guaranteed). Watering concrete pouring with the mention, is strictly prohibited to the concrete surface or buried too deep, a promotion shall not exceed 6m, measuring the rise of concrete surface by the captain or monitor is responsible. D) If the concrete found on the site is found to be segregated and the properties do not meet the requirements, it should be mixed to prevent clogging of the pipe. E) The actual amount of concrete poured into the pile shall not be less than 1.05 times of the calculated volume of the pile and shall not exceed 1.2 times of the calculated value. F) After the completion of concrete pouring, should be cut off the hanging bar, and other concrete above the ground and then pull out the initial curing tube, remove the orifice mud and concrete residue. G) After the use of the catheter should be promptly removed inside and outside the wall adhesion of concrete residue, to prevent re-use when blocking the catheter. D. Bored Pile The quality of underwater concrete should meet the following requirements: A) Strength should meet design requirements. B) No fault or interlayer. C) Pile head chisel addition to the reserved part, no residual loose layer and weak concrete layer. Figure 4. Pile after pouring concrete 41

7 Construction Technology and Quality Control of Bored Pile Third, the factors that are influencing the bearing capacity of bored pile in specific soil layer are analyzed Pile side, pile end soil properties, pile concrete quality and so will affect the bearing capacity of bored pile. Due to the soft soil at the end of the pile, the thickness of the silt, the time and technology of the hole will have some influence on the bearing capacity of the pile. The special nature of soft soil, often there will be some quality problems, such as: collapse, drilling skew, reaming hole and so are the drilling process more prone to quality problems. In the actual construction, we must choose the appropriate construction equipment, clear hole method and hole time according to the specific situation of the site, increase the hole wall roughness, reduce the sedimentation and mud thickness, in order to increase the pile side resistance; Side of the resistance to play, the pile should be placed on the relatively hard soil layer; at the same time, but also as far as possible to extend the pile time to avoid unnecessary overload preload to improve the bearing capacity; in conditions permitting, should be used as far as possible post-grouting technology to reduce sedimentation. 3. The Causes of the Formation of Aperture and the Influence on the Bearing Capacity of Bored Piles Pore size in engineering practice should be strictly controlled. Otherwise, it would be easily lead to serious quality accidents. First of all, in the clay geological drilling, necking phenomenon occurs, especially in the soft plastic, plastic state soil drilling, such as improper construction, more likely to cause shrinkage or necking. Secondly, in some cases, due to the construction personnel to understand the norms of imperfect, that the borehole pile diameter allows negative tolerance, so in order to reduce construction costs, speed up the drilling speed, and reduce the diameter of the drill lead to less than the design of pile diameter. Due to the reasons for the speed, resulting in borehole pouring pile pore quality problems, will lead to: Due to lack of pore size, the cross-section of the pile and the surrounding area of the pile soil are reduced, resulting in a decrease in the carrying capacity of the bored pile When the shrinkage is serious, the pile cross section is seriously insufficient, the bearing capacity of the pile itself is greatly reduced, and this situation often occurs in the upper part of the pile soft soil layer, the pile in this part of the force is generally larger also become more complex, because the strength of the pile is not enough to be destroyed When the aperture is insufficient, the reinforcement cage is more difficult to install, sometimes it take the pressure or twist the steel cage to make the steel cage in place, will make the steel cage deformation. It is not only affect the normal role of steel cage, while steel cage deformation, some parts of the protective layer is not enough, it will be making the steel easy to rust and shorten the service life Effect of Mud on Quality of Bored Pile. The quality of the mud is also the main reason for the quality of the bored pile. The mud not only acts as a wall, but also has a great influence on the bearing capacity of the bored pile By using qualified mud wall, the wall thickness of the wall is thin, generally about 2mm. When the mud quality is poor, high sand content, consistency, construction time is long, easy to form a thick hole in the hole wall, the thickness of sometimes more than 4mm. This will greatly reduce the pile side friction. With the test report, a serious failure of the mud, the pile side of the friction can be reduced by more than 50% mud quality is poor, sand rate is too high, the hole wall mud to form a diaphragm effect, which is likely to cause collapse, but also because of the hole wall soak soft and reduce the pile side friction. The reason for the failure of the mud, some construction workers believe that the mud is mainly to protect the wall, does not affect the quality of bored piles. As long as not collapsed, people can ignore the control of mud quality Influence of pile bottom sediment thickness on bearing capacity of cast - in - place bored piles. The bottom of the sediment is too thick, will lead to a serious reduction in the end of the pile capacity or even loss. Especially for the bored pile (pile), the pile bottom sediment is too thick, will cause serious quality problems. So the thickness of the bottom of the pile should be strictly controlled within the standard specifications. Resulting in the bottom of the sediment is too thick reasons, mainly because: 42

8 Minqiang Xiao, et al 1) The first clear hole is not complete; 2) Did not carry out the second clear hole before concrete infusion; 3) The second clear hole and the concrete filling time interval is too long. Relationship between Pile Verticality and Bearing Capacity of Bored Pile. Drilling pile vertical tolerance of 1% tolerance. In engineering practice, if not take effective measures to control the verticality of bored piles, its quality is difficult to be guaranteed. At the point of the work, ultrasonic hole wall detection to detect the pile hole found that some pile hole vertical degree of 2.8%, seriously exceeding the standard requirements of the standard, and some holes were S-shaped bending. This will change the pile of the practice of the state of force, especially for single pile or single row of pile force structure, the actual bearing capacity greatly reduced. In addition, the quality of concrete, the quality of concrete pouring, steel cage production, installation is also the main factor that are affecting the quality of bored pile. Table I lists the causes and consequences of the main factors affecting the quality of bored piles and sets out the corresponding control measures. 4. Research on Construction Technology and Quality Accident of Bored Pile Bored pile due to the construction process links, prone to a variety of quality problems, such as the barrel of water, aperture tilt, reinforced cage floating, tube and so on. In view of some problems in the construction of the bored pile in the resettlement project of Cangnan County People s Court, according to their own practice, the author has realized the reason of the quality problems in the construction of bored piles Analysis, and put forward preventive measures Quality problems in the process of forming holes and prevention measures Protect the tube from the water Reason: 127 # works pile due to bury around the casing when the filling is not dense. Control measures: in the pit when the pit and the surrounding should use the best moisture content of the clay layer compaction; in the appropriate height of the hole in the hole, so that the protection within the maintenance of m head height; Protection tube; found that the tube should immediately stop the drilling of water, with clay around the hole in the wall to fill the reinforcement, if the casing seriously sink or shift should be re-installed protection tube Drilling skew Analysis of the reasons: the professional instrument measurement and found that 56 # engineering pile drilling drift phenomenon, the analysis may exist for the following reasons: First, the site flatness and poor density are caused by the rig installation that is not smooth or drilling process occurs uneven settlement due to drilling deflection; the second is the drill pipe bending, drill pipe joints gap caused by drilling skew; Is the drill bit worn wear different, the drill bit force caused by the deviation of the drill bit away from the direction; Fourth, drilling in the case of soft and hard soil interface or inclined rock surface when the drilling pressure is too high so that the drill force caused by uneven drill bit deviation. Prevention and control measures: the first flat and compacted the ground, the track sleepers evenly ground; installation of the rig when the turntable center and the drill on the rope on the same axis, drill pipe deviation control within 20cm; in the uneven formation of drilling should be used major. Drill rigs with high rigidity are drilled at low speed. If the oblique holes are more serious, they can be backfilled with stones and clay in the pile hole, and then are slowly hammered and repeatedly corrected The quality problems and prevention measures in the process of concrete fillingcard tube Analysis of the reasons: the project No. 4 pile driver often appears blocking phenomenon. Some factors, there are factors of the machine. The reason is due to perfusion catheter leakage, perfusion catheter bottom from the bottom of the hole depth is too small to complete the second clear hole after pouring concrete preparation time is too long, water barrier is not standardized, poor concrete and poor perfusion catheter, infiltration depth is too large and so on. Prevention and treatment measures: perfusion catheter should be checked before the installation of perfusion catheter with small holes and cracks, perfusion catheter connector is sealed, perfusion catheter thickness is qualified; catheter before use test assembly, test pressure, test water pressure MPa, To avoid the catheter into the water; the use of 43

9 Construction Technology and Quality Control of Bored Pile the diameter of the plug should be matched with the diameter of the catheter, the length should be 200 mm, while a good water barrier performance to ensure a smooth discharge; 4.3. Tendons floating on the cage Analysis of the reasons: the site often occurs in the case of steel cage floating, reinforced cage placed, the concrete when the concrete flow to promote the force to overcome the weight of the reinforced cage floating, especially the initial pouring concrete self-guided after the impact of a larger impact, reinforced cage Concrete towing up. Prevention and control measures: steel cage installation location should be accurate, fixed with a hanging bar, and with a pile driver (or heavy) connected firmly; another speed up the concrete filling speed, shorten the infusion time to prevent the top of the concrete into the reinforced cage when the initial condensate, Small and the top of the reinforced cage; when the cage floating, should immediately stop pouring concrete, and accurately calculate the depth of the catheter and the surface of the concrete has been pouring, the depth of the catheter control in the m,, The floating phenomenon can disappear. 5. Conclusion Bored pile is a hidden project, with the difficult, long duration, high cost of construction, but also related to the life of the building, so before the construction, people must be fully prepared for the work, in the continuous experience of the construction and improve the management methods, in strict accordance with the design and specification requirements of the construction process for the entire process of quality control, timely construction of the problems encountered in the construction. Only in this way can we improve the quality of the project and submit the fine works. References 1. Zhu Kui. Pile quality accident [M]. Beijing: China Construction Industry Press, Teng Yanjing, Chen Xiquan, Yang Bin. Construction Foundation Foundation Engineering Construction Technology Guide [M]. Beijing: China Construction Industry Press, Zeng Qiaoling, Cui Jiangyu, Chen Wenhua, etc. Basic Engineering [M]. Beijing: Tsinghua University Press, Jiang Zhengrong. Foundation and basic engineering construction taboo [M]. Beijing: Mechanical Industry Press, Wang Yueming, Zhu Kai. The data Pile foundation engineering quality completion [M]. Shanghai: Tongji University Press, Han Yufeng. Rotary drilling rig construction technology and quality control [J]. China Science and Technology,