Discussion on the prevention of pile driving engin

2022-08-23
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Talking about the prevention of pile driving engineering quality accidents

the importance of foundation engineering is self-evident when a ten thousand foot tall building rises from the ground. This paper briefly introduces the common quality problems of concrete precast piles and the preventive measures for quality accidents

1 from two engineering examples, high-rise buildings have developed rapidly in recent years. Many foundations use traditional precast concrete piles. In the process of pile driving, problems such as pile body breaking, pile head breaking, pile driving skew and so on occur from time to time. Two engineering examples are listed below

(1) the pile foundation of a project constructed by the enterprise in 1989 requires d4.5t pile hammer construction, and the design pile section is 400 × 40mm, 22m long pile, double section pile, 182 piles in total, pile concrete strength grade C40. According to the original plan, it can be completed in 20 days. However, the project pile was prefabricated without r525 cement according to the design requirements, and as soon as the age of the pile arrived, the contractor hurried to urge the pile driver to enter the site and began to test pile driving. When the first pile was tested, the pile broke before the number of blows reached 80. At that time, no one considered that there would be problems with the cement. The relevant units were used to questioning the pile driving process. Therefore, they tried their best to find and correct the pile driving problem, and then tried to drive 10 piles continuously. Except for two, Rao fortunately succeeded, the other eight were interrupted or the pile head was broken. The construction unit began to realize the seriousness of the problem, and convened representatives of relevant departments for discussion to comprehensively find out the cause of pile breaking, from geological exploration to the pile driving process, After several discussions and analysis, the participants eliminated all doubts, tracked the target to the problem of precast piles, and began to check, and carried out rebound and carbonation depth tests on the pile concrete. The results show that the strength of the concrete is seriously insufficient. There is a group of concrete with a strength grade of less than C20, and most of the pile bodies are not carbonated deep enough. In order to facilitate pile driving, we have to carry out the pile body concrete rebound test while driving. All the piles with a strength less than C30 are discarded. 2. Silicon Pu elastic layer and silicon Pu reinforcing layer: moderate elasticity results 68 piles in the whole batch are discarded due to insufficient strength. The insufficient number of piles had to be prefabricated again, and the construction period was delayed for more than one month, resulting in a direct loss of nearly 300000 yuan

(2) what experiments can rubber tensile testing machine be used to do? The original design of a Huayuan comprehensive office building constructed by our enterprise in 1996 used d4.5t hammer for construction. However, because the construction task of d4.5t hammer of the construction unit was relatively full at that time, it was difficult to transfer it at that time, and the construction period was tight, so it could not be delayed. After research, we decided to replace it with d6.2 hammer, and made a detailed construction organization design and conversion of control conditions. The pile type of the project is 400 × 400mm, 27.0m long, double section piles, 111 piles. Penetration control is required. When starting to drive three piles, the result is that one column is broken and one pile head is broken, and only one is successful. For this, a considerable number of people began to doubt whether the d6.2t hammer can be replaced, ignoring the inspection of the pile driving process. After several tosses, they began to check the causes of the driving process. The whole driving process was resolved. After a detailed search of the crystalline material, it was found that the thickness of the skid under the pile cap was only cm, which was obviously less than the required 25cm, which failed to play an effective buffer role. After adding the skid to the required thickness of 25cm in time, the phenomenon of breaking the pile and breaking the pile head almost no longer occurs. Results all 111 piles were completed on schedule and passed the pile test

the above examples illustrate the importance of correctly applying quality control measures to improve project quality

2 prevention of quality accidents through the practice of piling engineering for several years, this paper briefly summarizes the common quality accidents, causes and preventive measures of piling engineering

2.1 the pile top is broken, and the pile body is broken, because the concrete strength of the pile head and pile body is low or the vibration is not dense, the pile top is uneven, the protective layer is too thick, the hammer is not vertical to the pile, the drop hammer is too high, and when encountering boulders or hard soil layers, the hammer blows too long. The preventive measures should be determined according to the actual situation. While strictly controlling the quality of prefabricated piles, strengthen the management of machinery. There should be skids with a thickness of not less than 25cm between the pile hammer and the pile cap, and between the pile cap and the pile head, so as to achieve effective cushioning; In order to avoid breaking the pile, the sequence of pile driving should be strictly controlled. According to the specification requirements, the specific sequence of pile driving should follow the following principles: from the center to both sides; From the middle to the periphery; From one side to one direction; First deep then shallow, first big then small, first long then short, etc. Generally, engineering quality problems often arise from a certain detail of a certain process, so quality control should be specific to the details of each process

2.2 the reason for the torsion or displacement of the pile body is that the pile body is not correct, the pile tip is asymmetric, the soil around the pile position is disturbed, one side is hard, the other side is soft, etc. Preventive measures: strictly control the vertical deviation of the inserted pile, which is the key to avoid the displacement or inclination of the pile. The specific practice is usually controlled by two theodolites on both sides, and the deviation shall not be greater than 0.5%. The first few hammers of the hammer should be hit as low as possible, and the hammer can be lifted normally after reaching a certain depth

2.3 quality of precast piles. The following problems should be controlled during the prefabrication of piles: (1) technical management; (2) Concrete mixing; (3) Pouring and tamping of concrete; (4) Concrete curing, etc. In terms of technical management, first of all, a standard curing room should be established, and a special person should be appointed to retain and maintain the test block according to the specifications, and conduct pressure test regularly. Conduct detailed, specific and serious written technical disclosure to the team. During the preparation of mixing materials, the inspection of coarse and fine aggregates should be strict, and those who do not meet the requirements of sand and stone grading should not enter the site; Check whether the cement type is properly selected and whether its grade meets the requirements; The water cement ratio should be strictly controlled and a weighing system should be set to ensure the accurate measurement of sand, stone and ash; During pouring and tamping, the pouring sequence should be continuous pouring from the pile top to the pile tip, and it is strictly prohibited to interrupt; The position of the main reinforcement shall be accurate, and the pouring and tamping process shall be corrected in time; During vibration, the vibration points shall be evenly arranged without missing vibration. Maintenance is also a key link. Special personnel should be assigned to be responsible for regular maintenance. Maintenance should be started 12 hours after pouring. Antifreeze measures should be taken for winter construction and coverage measures should be taken for summer construction

3 conclusion the competition among construction enterprises is in the final analysis the competition in quality. To shift the economic work to the track centered on improving economic benefits, we must improve the quality of the project. The prevention and control of quality accidents is the premise to improve the project quality. The method to prevent quality accidents is to change the post inspection of quality management into pre control, change the traditional management results into the three experimental conditions of management factors, and eliminate quality accidents in the bud. Only by strengthening preventive measures can we complete the construction tasks with high quality and efficiency, so that the enterprise

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