six. Preliminary results of quality management of Nanjing Second Bridge Project
Nanjing Second Bridge started construction for nearly three years, and it is ideally controlled regardless of construction schedule, quality and investment. From the image progress of the project, all the bid sections have reached the requirements of the project schedule in the overall implementation plan of the project; from the aspect of project quality, from the inspection of the completed sub-projects, the project quality has also been reached. Good grade. According to the quality inspection of the completed projects by the provincial quality supervision station and the headquarters, construction and supervision units, the quality indicators of various division projects have met and exceeded the requirements of the national construction specifications and the second bridge technical specifications.
A total of 1634 drilled and bored piles have been completed in the Nanjing Second Bridge Project. After ultrasonic non-destructive testing and drilling at 5% of the sampling frequency, all the drilled piles are complete branches, without defects, and the strength of concrete specimens. The assessment exceeds the design specifications.
The sealing concrete of the steel cofferdam in the south and north main areas of the Nanxun Bridge was sampled and sampled by drilling. The indexes were in full compliance with the requirements of the specification. The plane deviation of the steel casing, the location of the rock plane and the deviation of the slope were lower than the technical specifications. The error value is promised. There are 42 3m diameter ultra-deep bored piles in the north and south main piers. The construction and supervision units have no sound damage inspection. The pile foundations are of good quality and are all complete piles. The concrete strength meets the design requirements. Two cores are randomly selected and piled. The underwater concrete is uniform and continuous, and there is no void bubble on the surface of the core column. The strength of the pile foundation sample exceeds the design requirement, indicating that the underwater concrete casting quality is good.
The flatness of the middle layer of the South Bank lead asphalt that has passed the inspection and acceptance has reached 0.76mm, which is close to the flatness of the upper layer of the Shanghai-Nanjing Expressway. It greatly exceeds the national standard of 1.8mm for the upper layer of asphalt. Of course, not only is the flatness of the asphalt pavement an indicator meets the requirements, but the other compacts, transverse slopes, widths, and thicknesses all meet the requirements of technical specifications, reaching the ministerial level of excellence, which is the first-class domestic level. The South Bank lead has been tested for more than 20,000 vehicles per day for more than one year. The quality of the roadbed is stable and the quality of the double bridgehead is very stable, with no obvious deformation and settlement.
In September 1999, the Nanjing Second Bridge Command held an expert review meeting on the steel box beam pre-spinning at the Jingjiang construction site. According to the domestic famous welding and structural experts' review of the steel box girder production, the Nanjing Second Bridge steel box girder was successfully manufactured. The new technology and new technology, such as the ultra-replacement cutting technology, the unitless assembly technology of the plate unit, and the anti-deformation welding technology of the plate unit, the overall quality of the steel box girder manufacturing is excellent, reaching a new level of domestic manufacturing.
The Nanxun Bridge cable concrete, which passed the acceptance inspection in December 1999, has been highly praised by leaders and experts for its intrinsic quality and appearance quality. It is considered to be the best cable tower for the main concrete of large span bridges in China. The vertical design requirement of the tower is 1/3000, but in fact we have reached 1/90000 and 1/13500; the strength of the concrete specimens exceeds the design specifications, and the delivery acceptance committee finally gives a high score of 97.60.
The achievements we have made in the past three years show that the measures and practices of the headquarters on quality control and control are practical and effective.
Seven, the key technology research of Nanjing Second Bridge
In conjunction with the actual situation of the project, the Nanjing Second Bridge Construction Headquarters focused on the key points and difficulties of the project construction process. In order to achieve the quality objectives we proposed in the early stage of construction, the Ministry of China increased investment in scientific research and improved the scientific and technological content of the project. The important research projects implemented in the process are summarized as follows:
l.. According to the cable-stayed anchorage zone of the South Tower Bridge. The radius of the circumferential prestressed cable is small and the design requirements for the VSL vacuum assisted grouting process are prepared. The command department has made a full-scale model structure and process test of the cable tower section at Zhejiang University and the construction site to determine the design parameters of the prestress. And construction techniques to provide practical experience for design and construction units.
2. For the design unit, the auxiliary cable was used to solve the wind-induced vibration and rain vibration problems of the cable. The headquarters commissioned Tongji University to study the wind-induced vibration and rain vibration of the cable stay, and finally adopted the hydraulic damper. Replacing the auxiliary cable not only simplifies the construction but also adds to the beauty of the bridge.
3. In view of the fact that the structural monitoring of the built bridges in China is still basically blank, the headquarters is determined to implement a comprehensive monitoring system during the construction of the two bridges in the south and north, that is, to complete the structural safety monitoring and the bridge structure during the operation period. The safety monitoring system is currently being implemented. It is believed that this research will help improve the structural safety and operational monitoring of the second bridge and provide valuable experience for the monitoring of other very large bridges.
4. Steel bridge deck pavement is a world-class engineering problem. The command department cooperates with Southeast University and Lintong International Consulting Co., Ltd. on the strength, deformation characteristics, temperature stability and fatigue durability of bridge deck pavement. In the aspect, a series of special studies and experiments were carried out. Based on the results of our current tests, the pavement design and implementation plan corresponding to the actual situation of the second bridge was proposed. The test section is planned to be carried out in August, and the main bridge in Nanxun in October. Formally paved.
5. The main beam of Nanxun Bridge is a flat streamlined steel box girder. The headquarters is responsible for the key technologies of steel box girder manufacturing, joint construction units, supervision units and universities. The steel box girder manufactured according to our research results has been obtained. The high evaluation of bridge experts at home and abroad has achieved considerable economic and social benefits.
6. Conducting research on technical difficulties in construction. For example, after the bored pile construction of Beibei Bridge was drilled into the rock formation, it was found that the hole continued to leak. It is necessary to continuously replenish the slurry to maintain the water head in the hole, and there is no collapse phenomenon in the cover layer, after careful analysis. It is judged that it is a rock fissure. After the conductor convened an expert to conduct a special discussion and study, two measures were proposed for the closed rock fissure: for the case where the mud loss rate is slow and the rock layer crack is not large, the mud performance is adjusted; the mud weight is increased and the mud is increased. Mud viscosity, and cast bricks or gravel made of clay or clay in the hole. Then increase the water head in the hole, use the scraper to drill the positive cycle and repeat the drilling slowly, and repeat the wall to achieve the purpose of closing the crack of the rock formation; for the case where the mud loss rate is fast and the rock layer is large, the positive circulation drilling is adopted, and the drill pipe is used. Press the early strength of the cement slurry. The amount of cement slurry is determined according to the rate of mud loss. After the cement slurry is pressed, the drilling hole is raised to raise the water head, so as to achieve the purpose of sealing the crack of the cement slurry. The hole is restored after the cement slurry is pressed. After practice, these application-type technical measures are properly handled, which provides a strong guarantee for the quality and progress of bored piles.
The Second Bridge Command has increased the investment in scientific research according to the different conditions in the construction. The above examples are only a part, such as the application of GPS global positioning system in high-precision measurement, high-strength concrete mix ratio test, VSL full hydraulic pressure. Crane test, 65000kN large tonnage bearing research, mass concrete temperature control test, etc. In short, in the construction of the Second Bridge, we always insist that the quality project is not only reflected in the quality of the project, but also in the scientific and technological content of the project. I hope that the construction of this project will enable the domestic construction, design and construction level to be re-appeared. New steps.
Eight, new issues we face in engineering construction governance
In the practice of the construction of the Second Bridge, we summed up the experience and felt that we are facing new problems in construction governance. In the next step, we will further strengthen and explore in the following aspects:
1. Improve the scientific and technological content of construction, increase equipment investment, and adopt new technology. New materials and new technologies are effective measures to ensure and improve the quality of the project. The quality of the project should not only be reflected in the internal and external quality of the project, but also in the scientific and technological content of the project. In the process of building the Second Bridge, we have deeply experienced that technology is the primary productive force. By introducing mature advanced construction technology and construction equipment, we not only reduce the difficulty in construction, but also ensure the construction quality, improve the construction quality and speed up the construction progress. However, special research on the weak links in the construction can not only effectively solve the construction. The problem is also conducive to improving the scientific and technological content of the project and improving the comprehensive level of building a large span bridge in China. In the later construction of the Second Bridge, we will further increase investment in science and technology to ensure the construction quality and scientific and technological content of the project, and truly reflect the technological level of modern bridge construction.
2. As the quality theme of engineering construction, the quality of the construction unit is directly related to the quality of the construction project. The quality of the construction technicians and construction workers who work directly as construction is a direct indicator for judging the quality of a unit. At present, the current situation of China's engineering construction industry is: the construction unit has a low social status, there are fewer qualified technical workers, and there are fewer senior technicians. The main body of first-line workers in civil construction units is “migrant workersâ€; The overall quality of first-line construction workers in general construction enterprises is generally low. This situation is extremely unfavorable for construction units to do a good job in project quality. Because a large number of first-line construction workers are migrant workers who learn by doing, and personnel follow the project. The construction project is constantly changing and changing, so the construction workers' operating skills and operation level are low. In the construction process, the second bridge pays attention to the propaganda education and technical training for the first-line construction technicians and construction workers. For example, in the prestressed construction of Nanxun Bridge, the command department specially invites technicians to pre-job training for the operators and take measures to issue the employment certificate. To improve the level of work and skills of workers, but for the front-line operations team with a large number of large-scale operations, it is impossible to solve the problem fundamentally by the headquarters alone.
3. Design is the soul of engineering. The quality of design is directly related to the quality of engineering and the difficulty of construction. The supervision unit is the guarantee of engineering quality. It is reflected in the review of the construction plan, the supervision of the construction process and the construction. acceptance. In the construction of modern large-scale projects, high demands have been placed on design and supervision units. However, how to ensure a reasonable design cycle, improve design level and quality, and improve the overall quality of supervision personnel remains to be done by all parties. They continue to sum up experience, dare to develop, and can't always stagnate at the level of the past.
4. Correct and comprehensive understanding of the dialectical unity of quality and duration, quality and investment, internal quality and external quality. What we need is quality progress, and we must accelerate the construction of the project under the premise of ensuring quality. When there is a contradiction between quality and progress, the quality is decisive. When there is a contradiction between quality and investment, it is better to increase the investment and meet the quality standards. The intrinsic quality of the project is as important as the quality of the appearance. In the actual construction, we must not only ensure that the intrinsic quality of the project meets the design and specification requirements, but also ensure the appearance quality of the project, so that everyone can feel from the beautiful lines of the appearance quality of large-scale infrastructure construction projects? The unique charm of the boutique project.
5. There are still some normative constraints on engineering quality control and control. At present, there are many human factors and traces in the construction quality management. Only when the quality of the construction team is high, the supervision requirements are strict, and the headquarters is in place, the quality of the project can be guaranteed. Otherwise, the quality of the project is difficult to guarantee. In the practice of work, we are familiar with the important premise of the unremitting efforts of engineering quality management. There are rules to follow and laws to follow. The intensive management of project quality can't stay in the human governance stage, and the quality control and control can't be different from person to person. Therefore, we understand that in the process of paying close attention to the quality of the project, we must combine the actual project according to the national laws, regulations and industry norms. The situation has a complete set of programmatic and normative documents on quality management, so that all builders are legally responsible for the quality of the project and bear the corresponding legal responsibilities.
6. The construction of the project is a systematic project involving many units. How to give full play to the enthusiasm and initiative of the participating units. To achieve the good connection and cooperation of the various processes of the project. Research should also be conducted in greater depth. In particular, engineers and technicians should not only study and summarize in terms of technology and governance. Modern engineering construction requires compound talents. It is difficult to adapt to a skill in modern governance. It is necessary to increase the training and education of compound talents. .
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